assignment on- kanban, increasing overall equipment effictiveness of plasma cutting machine and...
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AN INPLANT TRAINING REPORT
ATBHOR ENGINEERING PVT. LTD.
SHIVANE, PUNE
SUBMITTED BYANAND VIJAY (SEAT NO. B3217501)
UNDER THE GUIDANCE OF
Prof. V.Y. SONAWANE
DEPARTMENT OF PRODUCTION ENGINEERINGALL INDIA SHRI SHIVAJI MEMORIAL SOCIETY’S
COLLEGE OF ENGINEERING, PUNE – 01(YEAR 2008-09)
1
ALL INDIA SHRI SHIVAJI MEMORIAL SOCIETY’S COLLEGE OF ENGINEERING, PUNE – 01
DEPARTMENT OF PRODUCTION ENGINEERING
CERTIFICATE
This is to certify that the Inplant Training Report assignments on
KANBAN, INCREASING OVERALL EQUIPMENT
EFFICTIVENESS OF PLASMA CUTTING MACHINE AND STUDY
OF WELDING PROCESSES.
Submitted by
MR. ANAND VIJAY SEAT NO. B3217501
is a bonafide work carried out under the supervision and guidance of Prof. V. Y.
SONAWANE and it is approved for the partial fulfillment of the requirements of
University of Pune, Pune for the award of the Degree of Bachelor of Engineering
(Production Sandwich). The Inplant Training Work has not been earlier submitted to any
other Institute or University for the award of any Degree or Diploma.
(Prof. V. Y. SONAWANE)Guide,Production Engineering Department
(Prof. D. H. Joshi) Head, Production Engineering Department
(External Examiner)
Place: PuneDate:
2
3
ACKNOWLEDGEMENT
We are deeply indebted to our Project Guide Prof. V. Y. SONAWANE, for his
valuable Suggestions, Scholarly guidance, constructive criticism and constant
encouragement at every step of the Inplant Training.
We also, would like to express our deepest gratitude to Prof. D.H.Joshi, Head of
Production Engineering Department and Dr. J.D. Bapat, Principal, AISSMS College of
Engineering for granting the permission to choose this undertaking as our B.E. Project.
We wish to thank Mr. Vijay Nimse (Sr. Er. Q&A) and Mrs. Vrunda Zende (HR
Manager) for constant guidance, co-operation, inspiration, practical approach and
constructive criticism, which provided me the much needed impetus to work hard. I also
thank all other persons who directly and indirectly contributed in successful completion of
Inplant training.
My gratitude is also towards the management of BHOR ENGINEERING PVT
LTD, SHIVENE, PUNE. for giving me opportunity to work in their esteemed
organization.
. . MR.ANAND VIJAY
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CONTENTS
SR.NO. TITLE PAGE
TITLE PAGE I
CERTIFICATE OF COLLEGE II
CERTIFICATE OF COMPANY III
ACKNOWLEDGEMENT IV
CONTENTS V
LIST OF PHOTOS VI
LIST OF FIGURES VI
LIST OF TABLES VII
LIST OF CHARTS AND GRAPHS VII
ABSTRACT VIII
1. INTRODUCTION TO COMPANY 1
2. ASSIGNMENT NO.1
STUDY AND IMPLEMENTATION OF KANBAN
13
3. ASSIGNMENT NO. 2
INCREASING OVERALL EQUIPMENT EFFECTIVENESS (OEE) OF PLASMA CUTTING MACHINE
32
4. ASSIGNMENT NO. 3
STUDY OF WELDING PROCESSES AT BHOR ENGINEERING PVT. LTD.
74
5. CONCLUSION OF ASSIGNMENTS 101
6. REFERENCES 102
5
LIST OF PHOTOS
SR NO TITLE PAGE NO
1.1 OUTLOOK OF BEPL, SHIVANE, PUNE 1
1.2 CUSTOMERS OF BEPL 10
1.3 Level 1 11
1.4 Level 2 11
2.1 KANBAN LINE AT BEPL 29
2.2 KANBAN CARD 30
3.1 PLASMA CUTTING MACHINE 32
3.2 INSIDE A PLASMA CUTTER 41
4.1 WELDING MACHINES AT BEPL 92
LIST OF FIGURES
LIST OF TABLE
6
SR NO TITLE PAGE NO
2.1 DISTRIBUTION CANTERS 24
2.2 SUPPLIER KANBAN 24
2.3 MRP INVENTORY ASSESSMENT 25
2.4 PRODUCTION SCHEDULING 252.5 INTERNAL KANBAN PROCESS 253.1 WORKING OF PLASMA CUTTER 433.2 NESTING 68
4.1 WELDING 744.2 SECTIONAL VIEW OF GMAW 93
4.3 STRIKING THE ARC (GMAW) 94
4.4 WELDING POSITIONS 95
4.5 PULLING AND PUSHING ANGLE TECHNIQUES
96
4.6 EYE PROTECTION DEVICES 100
SR NO TITLE PAGE NO
1.1 LIST OF SPM AND EQUIPMENTS 8
2.1 LIST OF SEMI FINISHED PRODUCTS 28
2.2 LISTING OF PRODUCTS INTO GROUPS 29
3.1 MACHINE TYPE 33
3.2 SINGLE TORCH SPECIFICATION 33
3.3 M/C DIRECTION DETAIL 33
3.4 M/C TRANSVERSE DETAIL 34
3.5 PLASMA GAS SYSTEM SPECIFICATION 34
3.6 OEE FACTORS 51
3.7 SIX BIG LOSSES 52
3.8 WORLD CLASS OEE 57
3.9 OEE DATA FOR SHIFTWISE PRODUCTION 59
3.10 DETAILS OF OEE CONTENTS 60
3.11 ACTION PLAN 71
4.1 LIST OF WELDING MACHINES AT BEPL 91
LIST OF GRAPHS AND CHARTS
SR. NO. TITLE PAGE NO
GRAPH 3.1 OEE GRAPH IN FEB 62
GRAPH 3.2 OEE GRAPH IN MAY 62
CHART 3.1 PIE CHART FOR PLASMA CUTTING MACHINE
65
ABSTRACT
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Bhor Engineering Private Limited is a manufacturing industry and hence many concepts
of industrial engineering and management are used. The inplant training report focuses on
some of the techniques used in industrial engineering.
Kanban is a concept related to lean and just-in-time (JIT) production. , it proved to be an
excellent way for promoting improvements because reducing the number of kanban in
circulation highlighted problem areas. A system of continuous supply of components,
parts and supplies, such that workers have what they need, where they need it, when they
need it. Using it effectively in our system led us to achieve a systematic production and
easy target achievement.
Increasing the OEE of plasma cutting machine was a very learning assignment where we
faced the real situation of handling the problems at very close . with the successful
implementation on plasma cutting machine, it paved the way for other existing machines
in the company.
Welding division of Bhor Engineering has abundant of practical gain in store for us, we
studied the various type of welding processes being carried, and also learnt do’s and
dont’s of welding process.
1. INTRODUCTION TOBHOR ENGINEERING
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1.1 INTRODUCTIONBhor Engineering Pvt. Ltd. Started its business in the year 1998 as a manufacturer of fabricated Sheets metal parts, especially for Diesel Gensets, Automobile sectors and components for engineering industries.Address: S. No. 81, NDA Road Shivane, Pune- 411023Phone no: +91 20 25292179 +91 20 25292073Website – www.bhorengineering.comE-mail - [email protected]
Photo 1.1 Outlook of BEPL, shivane, pune.
1.2 HISTORY
Established in 1998, Bhor group emerged as Bhor Engineering Pvt. Ltd the well known
firm in the market of fabricated Sheets metal parts, especially for Diesel Gensets,
Automobile sectors and components for engineering industries. Bhor Engineering P Ltd is
an ISO 9001: 2000 certified by GLC, Accredited by GERMANISCHER LIOYD
CERTIFICATION for accreditation. Main area of production of the company is the
assembly used in the generator sets and engine parts. Cummins India Limited (high horse
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power & low horse power unit ), Cummins Power Solutions Pvt. Ltd. ,Cummins Diesels
sales & services India Ltd, Kirloskar Oil Engine Ltd, UGC Logistics, Ingersoll rand ltd.,
Bharat Earth movers ltd, Fleet guard Filters Pvt. Ltd., Filtrum Tools & components P.ltd.,
Pushalkar Mitchell Engineering Pvt. ltd., Fluid Dynamics p.ltd, are among the major
clients of the company. Company has specialists for pipe assembly of air, water and
exhaust system of diesel engine. Along with the proficiency in Sheet metal fabrication
and heavy fabrication just like Engine base rail and Engine shipments Skid; Company
also has the good hold in Painting/Metalizing, Aluminum and Powder Coating.
Bhor Engineering P Ltd is one of leading manufacturer of Fabricated & Sheet Metal
Components in Pune (India). It serves a range of industries like Automobile, General
Engineering, Diesel Engine, Generator Set, Earth moving equipments etc.
Set up in 1998, strong customer focus has leaded it to achieve cost leadership and
continuously strive to innovate and orient its processes towards maximizing customer
satisfaction.
With ISO 9001: 2000 certified quality systems, BEPL has further reengineered its
processes to serve you better. The philosophy of IS0 9001: 2000 and all its activities and
implementation of Kaizen through out the organization has resulted in processes that are
efficient and enable better servicing of customers.
In future, BEPL fabrication & sheet metal business promises to be one-stop for products
fabricated from Pipes, Plates, Channels, Angles, I beam, Sheet Metal, Wire e.t.c.
Bhor Engineering Pvt. Ltd. Pune Plant. Turnover as on 31st March 09 is Rs.12.5
Crores.
Bhor Engineering Pvt. Ltd. (Trading Div).Turnover as on 31st March 09 is Rs.15.45
Crores.
Bhor Engineering Pvt. Ltd. Hosur Plant. Turnover as on 31st March 09 is Rs.2.25
Crores.
1.3 GOALS & OBJECTIVES
Company Objectives
Operational Excellence:
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Follow continuous improvement process in all business activities.
Achieve excellence in every thing you do.
Customer Satisfaction:
Commit us to become a customer-focused organization.
Promote long – term business relationship.
Environmental Protection:
Maintain and improve workplace environment.
Become a responsible corporate citizen.
Employee Development:
Develop competence through training and skill enhancement.
Apply cross-functional team approach.
Company Goals
To become leader in Fabricated and sheet metal parts for Genset
Automobile sector.
This can be achieved through implementing ISO 9001: 2000 Standards.
Empowerment of Three ‘M’s i. Men - Continuous Training.
ii. Machine - New Technologies.
iii. Material - Better alternatives.
Recommended Strategy
To become “Preferential” Source for all types of fabrication especially in Piping & sheet
metal & heavy fabrication works to Cummins India Ltd. on the pillars of:
i. Long-term reliability.
ii. All time prompt service.
iii. Competitive price.
1.4 VISION
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The vision of Bhor Engineering Pvt.Ltd.is to be a leading player in the manufacture of
Power generation , Earth moving and Infrastructural products & a quality manufacture of
engineering products for domestic and international markets. To harness the potential
power of Human Resources across multi lingual and multi cultural backgrounds and
deploy it in the global industry, enhancing the Value of the offerings through Knowledge
management. Bhor Engineering Pvt. Ltd. is part of a vanguard of companies recognizing
that modern collaborative technologies make possible a vast expansion of "cerebral
services”. Believing in the benefits of trust learning from colleagues’ partners’ client’s
competitors. Bhor Engineering Pvt. Ltd is a structure adapting itself to the talent it unites
continuously adding room for new ideas. It is a facilitator of synergy without limits. Bhor
Engineering Pvt. Ltd. has established an effective methodology to manage a
geographically diverse development team producing a collaborative team effort that
efficiently delivers quality product implementations.
1.5 MISSION
The mission of Bhor Engineering Pvt. Ltd. is to be Rs. 150 Cores Company by 2013. The
Company's strategy has been to focus on what our customers need and respond with
creatively and competitively with solutions, services and support. They listen closely to
the customers and come up with cutting-edge solutions. Not content to just improve the
existing product, they have developed entirely new methodologies and concepts to
address the design problems encountered at the very deep level. The Company focus on
addressing real customer needs is evidenced by their growing customer base and by
the strength of those business partnerships. These strategic moves allowed them to expand
their market size and provide a wider range of engineering solutions.
The Company's goal is to achieve exceptional standards of performance and productivity,
work together effectively and learn continuously. They believe that Success requires the
highest standards of corporate behavior towards their employees, Customers and the
Society in which we live.
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1.6 QUALITY POLICY
To be the leader in the Fabricated and sheet metal parts for Genset / automobile sector, its
needed to produce the better quality of products by implementing Quality Systems. To
maintain the quality continuously the company is certified for ISO 9001: 2000 by
GERMANISCHER LIOYD CERTIFICATION of accreditation, GLC. This award is
the mark of maintaining the quality of the products. The goal can be achieved by
empowering the three m's that is “Man, Machine and Material ". Company's quality
policy is kept so strong that it can compete any other in the same field, because it’s only
possible way to stay in the market. To be the leader in the sheet metal component
assemblies, modules and aggregates, this is always needed to produce the better quality of
products. The goal can be achieved by empowering the three m's that is "Man, Machine
and Material". Company's quality policy is kept so strong that it can compete any other in
the same field, because it’s only possible way to stay in the market.
1.7 COMPANY PROFILE
Bhor Engineering Pvt. Ltd.
(ISO-9001:2000 Company)
Since 1978 the company is fabricating more than 6,000 types of Diesel Engine Parts as
Preferential vendor of:
1. Cummins India Ltd. – High Horse Power Division – Pune
2. Cummins India Ltd. – Low Horse Power Division – Daman
3. Cummins Power Solutions – Pune
4. Cummins Diesel Sales & Service - Pune
5. Volvo India Ltd. - Bangalore
6. Bharat Earth Movers Ltd. – Mysore
7. Ashok Leyland Ltd. Hosur Plant 1.
8. Ashok Leyland Ltd. Hosur Plant 2.
9. Ashok Leyland Ltd. Ennore Plant.
10. Ashok Leyland Ltd. Alwar Plant.
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11. Kirloskar Oil Engine ltd. –Pune.
12. Kirloskar Oil Engine Ltd. - Kagal
13. Cummins Power Generation – U.S.A.
14. ISMT Ltd. – Pune.
1.8 TURNOVER : 30.00 crores
1.9 EXISTING SPACE AVAILABLE AT PUNE PLANT
Plot Area – 44,000 Sq.ft.
Built up area – 18,500 Sq.ft.
Under Construction - 40,000 Sq.ft.
1.10 SERVICES
Specialist in Pipe Assembly of Air, Water & Exhaust sys. Of diesel engine.
Sheet metal fabrication, Sub base assembly & engine mounting Skids.
Aluminum Painting, Aluminum Metalizing and Powder Coating.
Stress relieving and machining for Heavy Fabrication Assemblies.
Tailor made perforation of some sheets up to 3 mm. thickness.
Specialist in heavy fabrication & machining.
1.11 FABRICATION UNIT
The fabrication unit manufactures the assemblies for the different parts of the Genset /
Radiators. These assemblies are created with the heavy machinery and engineering tools.
The company has specialists for sheet metal fabrication and assembly. Along with these
company also provides Stress relieving and machining for heavy fabrication assemblies.
1.12 PIPING UNIT
Piping unit produces the pipes of the desired shape and size so that they can be fitted in the desired place such as Water tube assemblies in the radiator, Exhaust connection assemblies (Made with Aluminum) , Dipstick tubes etc. the company is specialist in pipe assembly of air , water and exhaust system of diesel engine. The present capacity of the company’s Pipe Bending Machine is up to 4” diameter pipes.1.13 MANUFACTURING FACILITIES
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List of available special purpose machines-
Table- 1.1 List of SPM and Equipments
List of available Special Purpose Machines/Equipments
S.N. Machines CapacityMake /
IdentificationQty. Description
1 CNC Pipe Bending M/CUp to 6” OD x 5mm thk
Naveen Hydro control
1Suitable for Tube Bending at 1.2D Bending Radius
2Planomilling M/C With Dro Attachement
2250 x 4000
Sarab Sukh1
For performing various machining operations like milling, drilling, boring etc.
3 CNC Pipe Bending M/CUpto 4inch Dia
Suhas Hydro systems P.Ltd. 1
Specially design & manufacture for different sizes of tube bending with 1.2D bending radius.
4 Shearing M/C1250 x 2500 x 8
Hindustan Hydraulics Make 1
Specially designed & manufactured for cutting the desired sizes of sheets up to 8mm
5Mechanical Press 300 Ton. Capacity
1250 x 1250Bed Size.. Ratan Power Press
1
Specially Used for Blanking & Punching, Deep Draw Operation
6 Pneu. Beading M/C7 Mm Max.
SAMRAT 1
Specially utilized to impart different bead sizes at the end of the pipe.
7 Hydraulic Bending M/CUpto 25 Mm Thk
Bepl 1
Specially used for the plate bending & deep drawing process etc
8 Plano Milling Machine 1.5 Mtr x 4 Mtr. Sarabsukh Make
1 Specially Machining Aluminium Job.
15
At High RPM.
9 Radial Drill Machine100 mm DrillCapacity.
KOLB GERMAN1
Special drill machine for drilling cap. Up to 100 mm with 2.5 Mtr. Arm Lengths.
10CNC PLAZMA PROFILE CUTTING MACHINE.10 Mtr. X 3 Mtr. Bed.
25 MM plasma cutting & 200 MM Gas Cutting.
MESSERS MAKEGERMANY
1
Cnc Profile cutting machine for cut the plates from 2 mm thick to 200 mm thick.
11 Power Press 150 Ton Rattan make 1.Specially use for blanking, punching, etc.
12 Cnc Pipe Bending M/C3.5” dia x 3mm thk.
Naveen Hydro controls.
1
Specially use for pipe bending process for large dia pipe.
13 Mechanical P Press 300 Ton Mas 1For deep drawing process.
14 CNC Press Brake 150 TonHindustan Hydraulics
1
It is used for bending the sheet metal component from 1.2 mm to 8 mm.
15 Drilling Machine80 mm Capacity
Mass Make (German)
1
1500 MM TRAVEL. With 65 mm Drill Cap.
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1.14 CUSTOMERS
Photo 1.2 customers of BEPL
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Photo 1.3 Level 1
Photo 1.4 Level 2
1.15 FUTURE PLANS Targeted Turn Over (2009-2010) – 45.00 Cr.
Targeted Turn Over (2010-2011) – 75.00 Cr.
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Targeted Turn Over (2011-2012) – 110.00 Cr.
Targeted Turn Over (2012-2013) – 150.00 Cr.
Planned Infrastructure
o New Factory Building at Pune and Hosur by June- 2010.
o Office building G+4 approx 15,000 Sq.Ft.
o ISO-TS 16949 Certification by Sept 2009 at Hosur.
o Installation of new equipments.
Enhance welding Capacity.
Turret Punching Press
Laser Cutting Machine
CNC Pipe bending machine
VMC in machining facility
Powder coating plant
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2. KANBAN- AN INTEGRATED JIT SYSTEM
2.1 INTRODUCTION
Kanban (in kanji 看板 also in katakana カンバン, where kan, 看 / カン, means "visual,"
and ban, 板 / バン, means "card" or "board") is a concept related to lean and just-in-time
(JIT) production. The Japanese word kanban (pronounce) is a common everyday term
meaning "signboard" or "billboard" and utterly lacks the specialized meaning that this
loanword has acquired in English. According to Taiichi Ohno, the man credited with
developing JIT, kanban is a means through which JIT is achieved.
The word Kan means "visual" in Japanese and the word "ban" means "card". So
Kanban refers to "visual cards".
Kanban is a signaling system to trigger action. As its name suggests, kanban historically
uses cards to signal the need for an item. However, other devices such as plastic markers
(kanban squares) or balls (often golf balls) or an empty part-transport trolley or floor
location can also be used to trigger the movement, production, or supply of a unit in a
factory.
It was out of a need to maintain the level of improvements that the kanban system was
devised by Toyota. Kanban became an effective tool to support the running of the
production system as a whole. In addition, it proved to be an excellent way for promoting
improvements because reducing the number of kanban in circulation highlighted problem
areas.
2.2 THE JAPANESE KANBAN PROCESS- MORE THAN INTERNAL 'JUST IN
TIME PRODUCTION' TECHNIQUES
Most Japanese manufacturing companies view the making of a product as continuous-
from design, manufacture, and distribution to sales and customer service. For many
Japanese companies the heart of this process is the Kanban, a Japanese term for "visual
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record", which directly or indirectly drives much of the manufacturing organization. It
was originally developed at Toyota in the 1950s as a way of managing material flow on
the assembly line. Over the past three decades the Kanban process, which Bernstein
identifies as "a highly efficient and effective factory production system", has developed
into an optimum manufacturing environment leading to global competitiveness.
The Japanese Kanban process of production is sometimes incorrectly described as a
simple just-in-time management technique, a concept which attempts to maintain
minimum inventory. The Japanese Kanban process involves more than fine tuning
production and supplier scheduling systems, where inventories are minimized by
supplying these when needed in production and work in progress in closely monitored. It
also encourages; Industrial re-engineering, such as a 'module and cellular production'
system, and, Japanese human resources management, where team members are
responsible for specific work elements and employees are encouraged to effectively
participate in continuously improving Kanban processes within the Kaizen concept.
2.3 THE KANBAN
The Japanese refer to Kanban as a simple parts-movement system that depends on cards
and boxes/containers to take parts from one work station to another on a production line.
Kanban stands for Kan- card, Ban- signal. The essence of the Kanban concept is that a
supplier or the warehouse should only deliver components to the production line as and
when they are needed, so that there is no storage in the production area. Within this
system, workstations located along production lines only produce/deliver desired
components when they receive a card and an empty container, indicating that more parts
will be needed in production. In case of line interruptions, each work-station will only
produce enough components to fill the container and then stop (Roos, 1992: 112). In
addition, Kanban limits the amount of inventory in the process by acting as an
authorization to produce more inventories. Since Kanban is a chain process in which
orders flow from one process to another, the production or delivery of components is
pulled to the production line. In contrast to the traditional forecast oriented method where
parts are pushed to the line (Roos, 1992: 113).
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The Kanban method described here appears to be very simple. However, this "visual
record" procedure is only a sub-process in the Japanese Kanban management system.
2.4 ORIGIN
The term kanban describes an embellished wooden or metal sign which has often been
reduced to become a trade mark or seal. Since the 17th century, this expression in the
Japanese mercantile system has been as important to the merchants of Japan as military
banners have been to the samurai. Visual puns, calligraphy and ingenious shapes — or
kanban — define the trade and class of a business or tradesman. Often produced within
rigid Confucian restrictions on size and color, the signs and seals are masterpieces of logo
and symbol design. For example, sumo wrestlers, a symbol of strength, may be used as
kanban on a pharmacy's sign to advertise a treatment for anemia.
In the late 1940s, Toyota was studying supermarkets with a view to applying some of
their management techniques to their work. This interest came about because in a
supermarket the customer can get what is needed at the time needed in the amount
needed. The supermarket only stocks what it believes it will sell and the customer only
takes what they need because future supply is assured. This led Toyota to view earlier
processes, to that in focus, as a kind of store. The process goes to this store to get its
needed components and the store then replenishes those components. It is the rate of this
replenishment, which is controlled by kanban that gives the permission to produce. In
1953, Toyota applied this logic in their main plant machine shop.
2.5 OPERATION
An important determinant of the success of "push" production scheduling is the quality of
the demand forecast which provides the "push". Kanban, by contrast, is part of a pull
system that determines the supply, or production, according to the actual demand of the
customers. In contexts where supply time is lengthy and demand is difficult to forecast,
the best one can do is to respond quickly to observed demand. This is exactly what a
kanban system can help: it is used as a demand signal which immediately propagates
through the supply chain. This can be used to ensure that intermediate stocks held in the
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supply chain are better managed, usually smaller. Where the supply response cannot be
quick enough to meet actual demand fluctuations, causing significant lost sales, then stock
building may be deemed as appropriate which can be achieved by issuing more kanban.
Taiichi Ohno states that in order to be effective kanban must follow strict rules of use
(Toyota, for example, has six simple rules) and that close monitoring of these rules is a
never-ending problem to ensure that kanban does what is required.
A simple example of the kanban system implementation might be a "three-bin system" for
the supplied parts (where there is no in-house manufacturing) — one bin on the factory
floor, one bin in the factory store and one bin at the suppliers' store. The bins usually have
a removable card that contains the product details and other relevant information — the
kanban card. When the bin on the factory floor is empty, the bin and kanban card are
returned to the factory store. The factory store then replaces the bin on the factory floor
with a full bin, which also contains a kanban card. The factory store then contacts the
supplier’s store and returns the now empty bin with its kanban card. The supplier's
inbound product bin with its kanban card is then delivered into the factory store
completing the final step to the system. Thus the process will never run out of product and
could be described as a loop, providing the exact amount required, with only one spare so
there will never be an issue of over-supply. This 'spare' bin allows for the uncertainty in
supply, use and transport that are inherent in the system. The secret to a good kanban
system is to calculate how many kanban cards are required for each product. Most
factories using kanban use the coloured board system (Heijunka Box). This consists of a
board created especially for holding the kanban cards.
2.6 SIMPLE VERSUS INTEGRATED KANBAN PROCESSES
The Kanban process utilizes two different kinds of cards - transport Kanban and
production Kanban. Both of the cards do not have to be used simultaneously in a
production process.
The transport Kanban contains information from where the part/component originated and
its destination. When only this card is used, it is known as a simple Kanban process. In
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this system components are ordered and produced according to a daily schedule. Roos
describes this system as "ordering a box when it is the only one left on line".
The production Kanban, on the other hand, outlines to what extent and when work has to
be accomplished by a specific station on the production line. Together with the transport
Kanban, it is known as an integrated Kanban process. This system is often used between
the corporation and its suppliers. Here, the corporation's transport Kanban is the card
which regulates the supplier's production Kanban. The same amount of components is
produced as used in production and the maximum stock level is determined by the
number of cards that are in circulation. The number of cards in circulation can be
determined by an algebraic formula.
Example-
In the case of many manufacturing plants, the supplier is the warehouse and the customer
is the assembly line. In this case, one box of components goes to the correct station at the
assembly line at a time. When the box is empty, an operator takes it back to the
warehouse, and this automatically triggers the delivery of the next box of components.
Since only the transport Kanban is used, this example represents the application of the
simple Kanban system.
Toyota of Japan has taken the example discussed above one step further. Here, certain
components are directly supplied from suppliers to the production line. Stock levels are
therefore kept low and factory overhead can be reduced. The supplier's work stations are
regulated by the production Kanban, which in turn is regulated by the transportation
Kanban from Toyota's production lines. The transport Kanban is simultaneously used
internally between the warehouse and the production lines. This is an excellent example
of the integrated Kanban system.
2.7 ADVANTAGES OF THE KANBAN PROCESS
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A simple and understandable process
Provides quick and precise information
Low costs associated with the transfer of information
Provides quick response to changes
Limit of over-capacity in processes
Avoids overproduction
Is minimizing waste
Control can be maintained
Delegates responsibility to line workers
2.8 THE KANBAN PROCESS- MORE THAN INVENTORY CONTROL
To managers outside of Japan, Kanban may look only like a pure production method
having little or nothing to do with the surrounding environment. This is a fallacy. Instead,
the concept takes form on the shop floor, in close interaction between the work force and
management, and more importantly, involves both internal and external customers.
Kupanhy identifies Kanban as a production system which draws many of its elements
from two primary sources: industrial re-engineering, and work force (Japanese) Kanban
management.
2.9 INDUSTRIAL RE-ENGINEERING AND KANBAN
Industrial re engineering which goes hand in hand with Kanban consists of elements such
as:
25
Modular/cell production. Flow-of-products-oriented layout of processes and
machines layout.
U-shaped production/processing lines
Total preventive maintenance
Mass production of mixed models
The interrelationship between the Kanban concept and industrial re-engineering is clear.
Modular/cell manufacturing, which is sometimes referred to as group technology involves
organizing machinery so that related products can be manufactured in a continuous flow.
Here, products flow smoothly from start to finish, parts do not sit waiting to be worked
on, and forklift trucks do not travel kilometres to move parts and materials from one part
of the plant to another. This can be contrasted to a typical production system, where
machines are grouped by function and products move from function to function from one
end of a facility to another and back again. This results in long waiting times between
procedures. Kanban will not work effectively without efficient logistics systems and
process-oriented plant layouts. Kanban controlled production and the Kanban itself must
be able to flow smoothly between processes. Modular/cell manufacturing can be realized
by U-shaped processing lines, which integrate the manufacturing process into a
continuous flow and increase supply accessibility to the lines. It would be impossible to
join different processes to form a U-line if processes are not integrated. In addition, Total
Preventive Maintenance, which prevents machines from breaking down or malfunctioning
during the production time, also contributes to the efficiency of Kanban.
Toyoda Gosei Co. advisor Taiichi Ohno, architect of the Toyota Kanban system believes
that the real benefits of Kanban probably will not be realized until the auto industry
moves into a mixed production mode in which modular production methods are
employed.
2.10 JAPANESE KANBAN PROCESS MANAGEMENT
26
In addition to the industrial re-engineering concept of Kanban based management, the
Kanban process indirectly focuses on the human factors of production. It involves; multi-
machine manning working structure, standard operations, quality control circles,
suggestions systems, and continuous improvement/Kaizen. All these concepts provide for
the supportive environment necessary to implement the complete Kanban process. The
secret of the Kanban's success is its requirement that each part of an organization be
totally interdependent.
Japanese-management-related elements of Kanban are methods that are either imported
directly from or highly conditioned by Japanese management. Included in that category
are the following techniques which are interlinked:
Breaking of administrative barriers (BAB) as achieved by the Kanban
Team-Work, Quality Circles and Autonomation (decision by worker to stop the
line)
Continuous improvement
Housekeeping
2.11 KANBAN FOCUSES ON THE INDIVIDUAL WITHIN THE TEAMWORK
CONCEPT
The Kanban places great emphasis on the individual within the team framework. Workers
frequently have a great deal of input about the product they manufacture, and most
companies using the Kanban provide lifetime employment. People who work in a factory
using the Kanban are very important. Management and workers believe that productivity
and quality comes from people rather than systems.
The Quality Circle (QC) concept is a crucial component of the Kanban system. QCs
provide for dynamic canters where employees are able to discuss and find solutions to
various problems within the team's boundaries of production. Within this framework, the
Kanban process is run by workers who make a large percentage of the decisions
27
traditionally made by supervisors and quality control inspectors. Morris notes that it is
often the people who are producing the product or supplying the service who are in the
best position to make positive changes. In addition, modular and cellular production
concepts increase the scope of the team's work. Such industrial re-engineering concepts
encourage modular organization of work, where members of a team are responsible for
the completion of any one stage in the production process. This further encourages multi-
skilling which is achieved via job-rotation and on the job training procedures.
Traditional companies believe quality is costly, defects are caused by workers, and the
minimum level of quality that can satisfy the customer is enough. Companies practicing
the Kanban believe quality leads to lower costs, that systems cause most defects, and that
quality can be improved within the Kaizen framework
The simplicity of the Kanban system supports Stoddard's argument that "It's organization,
not hardware that needs to be changed. People want a high-tech solution, some wonderful
magic bullet." Kanban is not a magic bullet; it is rather an organizational shift towards
decentralization of responsibility.
2.12 KANBAN AND KAIZEN
Kaizen is the Japanese term for continuous improvement. "It is both a rigorous, scientific
method using statistical quality control (SQC) and an adaptive framework of
organizational values and beliefs that keep workers and management alike focused on
zero defects. It is a philosophy of never being satisfied with what was accomplished last
week or last year.
The Kaizen cycle has four steps:
Establish a plan to change whatever needs to be improved.
Carrying out changes on a small scale
Observe the results,
Evaluate both the results and the process and determine what has been learned.
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The link between Kaizen and the Kanban process is clear. Quality Circles within the team
framework decentralize responsibility for improving processes. It is the team’s
responsibility to improve current systems and procedures, including the Kanban. Kanban,
like any other management theory will improve with time, and it is the primary
responsibility of the individual worker within the team to continuously improve it within
the Kaizen model.
2.13 HOUSEKEEPING AND KANBAN
In order to facilitate the logistic process of quickly moving material to numerous work
stations on the production line, a clean and well organized environment is required. Roos
notes that such a workplace increases safety, employee well-being, and productivity. In
addition to the duties directly related to working on the line, team members should be
responsible for keeping their stations neat and clean and keeping tools in good condition.
Production down time is often dedicated to housekeeping activities.
More importantly, the factory layout should encourage and ease the housekeeping
process, which Toyota refers to as Siiton. All movable items, such as material boxes
should have dedicated positions on line indicated by symbols or lines on the ground.
Kanban cards should be kept on in-going and outgoing racks.
2.14 GETTING STARTED WITH KANBAN-
Introducing Kanban in BHOR Engineering Pvt. Ltd.
Kanban is usually introduced gradually and typically may involve some trial and error.
The first step is to become familiar with Kanban and the options it offers. Some parts
of Kanban may be suitable for your company, others may not.
This tutorial is just a brief overview of Kanban. Becoming familiar with Kanban will
requiring in-depth reading, possibly attending a seminar or hiring a consultant.
29
Select the components of Kanban that will work in your facility. Not all parts of Kanban
may be appropriate for the types of products you produce. Kanban may be appropriate for
one product, and not for another. In some cases a simple manual Kanban will work well.
In other cases computer automation of Kanbans may be the best option.
You will need to evaluate both your in-house production and your suppliers in order to
determine which Kanban options will benefit your facility.
Plan your Kanban system. Kanban involves more than just manufacturing. Other
functions such as purchasing, warehousing, shipping/receiving, quality control,
transportation, accounts payable and engineering will be involved. Include all of those
who will be affected in your Kanban planning and design process.
In planning, keep in kind that your object to have what is needed (supplies, parts,
manpower, information, energy, equipment, etc.), where it is needed when it is needed.
Set goals for Kanban. Based on your plan, set a schedule with measurable goals. What do
you want Kanban to accomplish and when should that goal be reached? Determine what
will be measured, and how it will be measured. Be sure to get baseline measurements of
your current manufacturing system and inventory levels, before Kanban is implemented.
Begin implementation of Kanban. A common approach to implementing Kanban is to
start with a generous number of Kanbans - containers, pallets, boxes, etc. Then
systematically reduce the number of containers until the point at which the supply of
materials is just in balance with the rate of use is reached. As containers are removed
from the process, it will eventually reach the point at which production is delayed because
the next container has not yet arrived. At this point add one container to the system to
bring it back into balance.
In using this trial and error approach, be sure a safety stock is available so that production
is not interrupted. You identify the point at which there is one too few containers as the
point at which material from the safety stock is used.
30
This trial and error approach should be spread over a significant period of time to allow
for normal fluctuations in production. In other words, don't remove a container every
thirty minutes. Instead, remove a container once a day, or even once a week.
2.15 CONTAINER IDENTIFICATION
It is important that containers are clearly identified. Workers should be able to
immediately identify the contents of a container just by looking at it. Color coding and
labeling containers are an effective approach. For example, paint pallets or containers
different colours so that each colour is associated with one component or part. Use large
labels that are easy to read from a distance, making it easy for anyone to identify the
contents of a pallet or container. In addition to colour coding your containers, use the
same colour code for your labels. Label materials are available in a wide variety of
colours, giving you flexibility in colour coding Kanban containers.
Figure- 2.1 Distribution canters
31
Figure- 2.2 Supplier Kanban
Figure- 2.3 MRP Inventory Assessment
Figure- 2.4 Production Scheduling
32
Figure- 2.5 Internal Kanban Process
2.16 BENEFITS OF KANBAN SYSTEM
Kanban provides a number of benefits, they are as follows:-
1. Reduce inventory and product obsolescence.
Since component parts are not delivered until just before they are needed, there is a
reduced need for storage space. Should a product or component design be upgraded, that
upgrade can be included in the final product ASAP. There is no inventory of products or
components that become obsolete.
This fits well with the Kaizen system on continual improvement. Product designs can be
upgraded in small increments on a continual basis, and those upgrades are immediately
incorporated into the product with no waste from obsolete components or parts.
2. Reduces waste and scrap.
With Kanban, products and components are only manufactured when they are needed.
This eliminates overproduction. Raw materials are not delivered until they are needed,
reducing waste and cutting storage costs.
3. Provides flexibility in production.
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If there is a sudden drop in demand for a product, Kanban ensures you are not stuck with
excess inventory. This gives you the flexibility to rapidly respond to a changing demand.
Kanban also provides flexibility in how your production lines are used. Production areas
are not locked in by their supply chain. They can quickly be switched to different
products as demand for various products changes. Yes, there are still limits imposed by
the types of machines and equipment, and employee skills; however the supply of raw
materials and components is eliminated as a bottleneck.
4. Increases Output.
The flow of Kanban (cards, bins, pallets, etc.) will stop if there is a production problem.
This makes problems visible quickly, allowing them to be corrected ASAP. Kanban
reduces wait times by making supplies more accessible and breaking down administrative
barriers. This results in an increase in production using the same resources.
5. Reduces Total Cost.
The Kanban system reduces your total costs by:
Preventing Over Production
Developing Flexible Work Stations
Reducing Waste and Scrap
Minimizing Wait Times and Logistics Costs
Reducing Stock Levels and Overhead Costs
Saving Resources by Streamlining Production
Reducing Inventory Costs
Apart from the above stated benefits there are some more advantages of Kanban system
like:-
34
A simple and understandable process
Provides quick and precise information
Low costs associated with the transfer of information
Provides quick response to changes
Limit of over-capacity in processes
Avoids overproduction
Delegates responsibility to line workers
2.17 IMPLEMENTATION OF KANBAN IN BEPL
The major client of BEPL is Cummins India Limited, which has 234 products under
Kanban system as their requirement is daily. For the effective working of the Kanban
system we enlisted the semi finished products which needed 2-3 operations to form
finished products. So this list could be used for smooth and fast supply of Kanban
products. The list of such semi finished products is:-
Table- 2.1 List of semi finished products
Sr
.
no
.
Product no Quantity
1. 4072915 15
2. 4072485 20
3. 4055805 31
4. 3413586 20
5. 3414333 26
6. 3167812 53
7. 4072242 33
35
8. 3413268 53
9. 3413899 41
10
.
3413256 20
11
.
4056425 94
12
.
4072505 10
13
.
4979918 3
14
.
4957901 10
15
.
4927002 5
16
.
4104988 200
17
.
3815978 50
18
.
4925790 100
19
.
3167912 5
20
.
3413331 40
21
.
4056428 50
22
.
4056432 12
23
.
3232601 10
24 4957952 10
36
.
25
.
3018653 6
Then we distinguished these products into six different groups as:-
Table- 2.2 Listing of products into groups
Sr.
no.
Product Group Quantity
1. Brazing products 4
2. Pipe assembly 9
3. Brackets 6
4. Flanges 3
5. Powder coating 2
6. Fan guard assembly 1
The above details were used during scheduling of operations as per requirement.
Photo- 2.1 Kanban line at BEPL
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2.18 KANBAN CARD:-
To maintain the details of the Kanban product the Kanban card is used.
Photo 2.2 Kanban Card
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2.19 SPECIFICATIONS OF KANBAN CARD:-
1. Part name
This indicates the name of the product.
2. Part number
The product is represented by a number.
3. Kanban Quantity
This number represents the no of product in a tray.
4. Ship lot
This indicates the no of products transported to the customer.
5. Lead time
This indicates the no of days in which a tray of products has to manufactured
and stored.
6. Card no. (2/2)
The denominator represents the total no of trays in the store. Each tray is represented
by a card. The numerator represents the individual tray card.
7. Storage location
It represents the exact location of the product in the store.
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3. INCREASING OVERALL EQUIPMENT EFFECTIVENESS
(OEE) OF PLASMA CUTTING MACHINE
3.1 AIM OF THE PROJECT-
Increasing overall equipment effectiveness of Plasma Cutting Machine from 60% to 83%.
Photo 3.1 Plasma Cutting Machine
3.2 MAIN TECHNICAL DATA AND SPECIFICATIONS:-
1. Type
Track length Determined by order
40
Working width Track gauge-600(for one
carriage)
Working length Length of track-2000
Temperature of the
workshop
0-45 degree
Fuel gas Acetylene, propane etc
Table- 3.1 machine type
2. Single Torch
Height of lifting 170 mm
Speed of lifting 15-30 mm/ sec
Automatic height regulating Capacity type
Automatic ignition Fuel gas: acetylene, propane
etc
Ignition voltage 7000 V
Thickness of cutting 6-200mm(for one torch)
Table- 3.2 single torch specification
3. Longitudinal direction
Driving type Driving on one side
Moving speed 0-6000mm/min
Table- 3.3 m/c direction detail
4. Transverse direction
One of the transverse carriages is the driving carriage, the other carriages can move in the
same direction by the driving of the steel rope.
Range of moving speed 0-6000mm/min
Rapid moving speed 6000mm/min
Table- 3.4 m/c transverse detail
5. Gas system
Longitudinal transportation
of gas
Cutting oxygen, heating
oxygen, acetylene, propane
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etc
Maximum consumption of
the oxygen
Depends on the torch
quantity
Pressure of the oxygen 1.2MPa
Purity of the oxygen >=99.6%
Maximum consumption of
the fuel gas
Depends on the torch
quantity
Pressure of the fuel gas 0.08MPa
Table- 3.5 plasma gas system specification
6. Total weight of the machine
About 1 Tonne (basic type)
3.3 FUNCTIONS OF THE MACHINE:-
This Omnicut machine is composed of electrical, mechanical and gas system components.
It is new automatic equipment for cutting steel plates.
1. The main use of this machine
It can cut straight lines and any kind of curves. When a single torch is used, it can cut
straight beveling.
2. High accuracy
Omnicut cutting machine is driven on one side. The gantry carriage is light weighted and
with high rigidity. The AC servomotors, big gears and racks enable a precision moving in
transversal and longitudinal direction. It also has the function of position inspection also,
so the running accuracy is very high.
3. High cutting quality
It has the function of constant speed and kerf offset, so the cutting accuracy is high and
the cutting quality is very good.
4. High automatic level
Use the tracing head, we can control the whole cutting process, includes the automatic
dropping to the workpiece---automatic ignition---automatic turning on the heating
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oxygen---automatic turning on the cutting oxygen---automatic piercing---automatic
cutting---flame extinguish when the cutting is finished---automatic rising---automatic
returning.
5. With complete functions of CNC
This machine is equipped with EASYCUT system, it can receive signals from the traffic
head, and we can manually input from the keyboard. It has also the function of kerf offset
and reducing the speed at corners.
6. Safety and reliability
The longitudinal carriage rolls on the tracks and moves briskly. Use link arm and cup
spring shaft to eliminate the clearance between the guiding wheels of the carriage and the
track. The main wheel housing is equipped with chip cleaners on its two ends. At the end
of the tracks, there are two buffers.
The transverse carriage rolls on the transverse track and moves briskly too. The lifting
shaft of the single torch is mounted in a box; guiding wheels guide the movement of the
shaft. Two limit switches are mounted in the single torch suspension.
The control valves in the gas system are all made of copper or stainless steel or other
corrosion-resistant materials. To prevent the backfire, the pipe systems of oxygen and fuel
gas are equipped with backfire preventers.
3.4 PLASMA CUTTING TECHNOLOGY
Plasma cutting is a process that is used to cut steel and other metals of different
thicknesses (or sometimes other materials) using a plasma torch. In this process, an inert
gas (in some units, compressed air) is blown at high speed out of a nozzle; at the same
time an electrical arc is formed through that gas from the nozzle to the surface being cut,
turning some of that gas to plasma. The plasma is sufficiently hot to melt the metal being
cut and moves sufficiently fast to blow molten metal away from the cut. Plasma can also
be used for plasma arc welding and other applications.
Modern industry depends on the manipulation of heavy metal and alloys: We need metals
to build the tools and transportation necessary for day-to-day business. For example, we
build cranes, cars, skyscrapers, robots, and suspension bridges out of precisely formed
43
metal components. The reason is simple: Metals are extremely strong and durable, so
they're the logical choice for most things that need to be especially big, especially sturdy,
or both.
The funny thing is that metal's strength is also a weakness: Because metal is so good at
resisting damage, it's very difficult to manipulate and form into specialized pieces. So
how do people precisely cut and manipulate the metals needed to build something as large
and as strong as an airplane wing? In most cases, the answer is the plasma cutter. It may
sound like something out of a sci-fi novel, but the plasma cutter is actually a common tool
that has been around since World War II.
Conceptually, a plasma cutter is extremely simple. It gets the job done by harnessing one
of the most prevalent states of matter in the visible universe. In this article, we'll cut
through the mystery surrounding the plasma cutter and see how one of the most
fascinating tools has shaped the world around us.
3.5 HISTORY
44
Where Saws Failed
The plasma-arc process had its origin almost 50 years ago, during the height of
World War II. In an effort to improve the joining of aircraft materials, a method of
welding was developed that used a protective barrier of inert gas around an electric
arc to protect the weld from oxidation.
Over the course of the next couple of decades, it was discovered that by restricting
the opening through which the inert gas passed, the heat produced by the process
was greatly increased. At the same time, the smaller opening caused the flow of gas
to speed up dramatically, ultimately blowing out a channel in the work.
The plasma-arc cutting process started seeing commercial use in the first few years
of the sixties. It was an extremely expensive process to undertake, and most cutting
was performed by large burning services that used their systems continuously to
help amortize the equipment.
In the ensuing years, various manufacturers have realized the enormous benefit even
small shop owners could derive from being able to burn both ferous and non-ferrous
metals. Today, dozens of manufacturers offer portable plasma cutters -- some so
light they can be carried with little effort. Units are starting to appear with built-in
air compressors that make the whole operation fully mobile.
Most, if not all, of the light portable plasma cutters are 110 volt machines that are
suited primarily for cutting sheet metal and other light work. The next level up is
the 220 volt machines with 50 to 80 amp output current. These are portable from
the standpoint that one person can put it on a truck and take it to the job.
3.6 PROCESS
45
The HF Contact type typically found in budget machines uses a high-frequency, high-
voltage spark to ionize the air through the torch head and initiate an arc. These require the
torch to be in contact with the job material when starting, and so are not suitable for
applications involving CNC cutting.
The Pilot Arc type uses a two cycle approach to producing plasma, avoiding the need for
initial contact. First, a high-voltage, low current circuit is used to initialize a very small
high-intensity spark within the torch body, thereby generating a small pocket of plasma
gas. This is referred to as the pilot arc. The pilot arc has a return electrical path built into
the torch head. The pilot arc will maintain itself until it is brought into proximity of the
workpiece where it ignites the main plasma cutting arc. Plasma arcs are extremely hot and
are in the range of 15,000 degrees Celsius.
Plasma is an effective means of cutting thin and thick materials alike. Hand-held torches
can usually cut up to 2 in (48 mm) thick steel plate, and stronger computer-controlled
torches can pierce and cut steel up to 12 inches (300 mm) thick. Formerly, plasma cutters
could only work on conductive materials; however, new technologies allow the plasma
ignition arc to be enclosed within the nozzle, thus allowing the cutter to be used for non-
conductive workpieces such as glass and plastics.
Since plasma cutters produce a very hot and very localized "cone" to cut with, they are
extremely useful for cutting sheet metal in curved or angled shapes.
3.7 STARTING METHODS
Plasma cutters use a number of methods to start the pilot arc, depending on the
environment the unit is to be used in and its age. Older cutters use a high voltage, high
frequency circuit to start the arc. This method has a number of disadvantages, including
risk of electrocution, difficulty of repair, spark gap maintenance, and the large amount of
radio frequency emissions. Plasma cutters working near sensitive electronics, such as
CNC hardware or computers, use the contact start method. The nozzle and electrode are
in contact. The nozzle is the cathode, and the electrode is the anode. When the plasma gas
46
begins to flow, the nozzle is blown forward. A third, less common method is capacitive
discharge into the primary circuit via a Silicon Controlled Rectifier.
3.8 INVERTER PLASMA CUTTERS
Analog plasma cutters, typically requiring more than 2 kilowatts, use a heavy mains-
frequency transformer. Inverter plasma cutters rectify the mains supply to DC, which is
fed into a high-frequency transistor inverter between 10 kHz to about 200 kHz. Higher
switching frequencies give greater efficiencies in the transformer, allowing its size and
weight to be reduced.
The transistors used were initially MOSFETs, but are now increasingly using IGBTs.
With paralleled MOSFETs, if one of the transistors activates prematurely it can lead to a
cascading failure of one quarter of the inverter. A later invention, IGBTs, is not as subject
to this failure mode. IGBTs can be generally found in high current machines where it is
not possible to parallel sufficient MOSFET transistors.
The switch mode topology is referred to as a dual transistor off-line forward converter.
Although lighter and more powerful, some inverter plasma cutters, especially those
without power factor correction, cannot be run from a generator (that means manufacturer
of the inverter unit forbids doing so; it is only valid for small, light portable generators).
However newer models have internal circuitry that allows units without power factor
correction to run on light power generators.
3.9 WHAT IS PLASMA?
If you boost a gas to extremely high temperatures, you get plasma. The energy begins to
break apart the gas molecules, and the atoms begin to split. Normal atoms are made up of
protons and neutrons in the nucleus (see How Atoms Work), surrounded by a cloud of
electrons. In plasma, the electrons separate from the nucleus. Once the energy of heat
releases the electrons from the atom, the electrons begin to move around quickly. The
electrons are negatively charged, and they leave behind their positively charged nuclei.
These positively charged nuclei are known as ions.
47
When the fast-moving electrons collide with other electrons and ions, they release vast
amounts of energy. This energy is what gives plasma its unique status and unbelievable
cutting power.
3.10 INSIDE A PLASMA CUTTER-S
Plasma cutters come in all shapes and sizes. There are monstrous plasma cutters that use
robotic arms to make precise incisions. There are also compact, handheld units that you
might find in a handyman's shop. Regardless of size, all plasma cutters function on the
same principle and are constructed around roughly the same design.
Plasma cutters work by sending a pressurized gas, such as nitrogen, argon, or oxygen,
through a small channel. In the center of this channel, you'll find a negatively charged
electrode. When you apply power to the negative electrode, and you touch the tip of the
nozzle to the metal, the connection creates a circuit. A powerful spark is generated
between the electrode and the metal. As the inert gas passes through the channel, the
spark heats the gas until it reaches the fourth state of matter. This reaction creates a
stream of directed plasma, approximately 30,000 F (16,649 C) and moving at 20,000 feet
per second (6,096 m/sec) that reduces metal to molten slag.
The plasma itself conducts electrical current. The cycle of creating the arc is continuous
as long as power is supplied to the electrode and the plasma stays in contact with the
metal that is being cut. In order to ensure this contact, protect the cut from oxidation and
regulate the unpredictable nature of plasma, the cutter nozzle has a second set of channels.
These channels release a constant flow of shielding gas around the cutting area. The
pressure of this gas flow effectively controls the radius of the plasma beam.
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Photo- 3.2 Inside a plasma cutter
The electrode is at the center, and the nozzle is just below it. The orange piece is the swirl
ring, which causes the plasma to turn rapidly as it passes.
Plasma on the Job
Plasma cutters are now a staple of industry. They are used largely in custom auto shops as
well as by car manufacturers to customize and create chassis and frames. Construction
companies use plasma cutters in large-scale projects to cut and fabricate huge beams or
metal-sheet goods. Locksmiths use plasma cutters to bore into safes and vaults when
customers have been locked out.
3.11 CNC CUTTING METHODS-
Plasma cutters have also been used in CNC (computer numerically controlled) machinery.
Manufacturers build CNC cutting tables, some with the cutter built in to the table. The
idea behind CNC tables is to allow a computer to control the torch head making clean
sharp cuts. Modern CNC plasma equipment is capable of multi-axis cutting of thick
material, allowing opportunities for complex welding seams on CNC welding equipment
that is not possible otherwise. For thinner material cutting, plasma cutting is being
progressively replaced by laser cutting, due mainly to the laser cutter's superior hole-
cutting abilities.
49
A specialized use of CNC Plasma Cutters has been in the HVAC industry. Software will
process information on ductwork and create flat patterns to be cut on the cutting table by
the plasma torch. This technology has enormously increased productivity within the
industry since its introduction in the early 1980s.
In recent years there has been even more development in the area of CNC Plasma Cutting
Machinery. Traditionally the machines' cutting tables was horizontal but now due to
further research and development Vertical CNC Plasma Cutting Machines are available.
This advancement provides a machine with a small footprint, increased flexibility,
optimum safety, faster operation, energy efficiency, ergonomic and more environmentally
friendly.
3.12 COSTS-
Plasma torches were once quite expensive. For this reason they were usually only found
in professional welding shops and very well-stocked private garages and shops. However,
modern plasma torches are becoming cheaper, and now are within the price range of
many hobbyists. Older units may be very heavy, but still portable, while some newer ones
with inverter technology weigh only a little, yet equal or exceed the capacities of older
ones.
3.13 HOW A PLASMA CUTTER WORKS -
Plasma cutters work by sending an electric arc through a gas that is passing through a
constricted opening. The gas can be shop air, nitrogen, argon, oxygen. Etc.
This elevates the temperature of the gas to the point that it enters a 4th state of matter.
We all are familiar with the first three: i.e., solid, liquid, and gas. Scientists call this
additional state plasma. As the metal being cut is part of the circuit, the electrical
conductivity of the plasma causes the arc to transfer to the work.
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The restricted opening (nozzle) the gas passes through causes it to squeeze by at a high
speed, like air passing through a venturi in a carburetor. This high speed gas cuts through
the molten metal. The gas is also directed around the perimeter of the cutting area to
shield the cut.
Figure 3.1 Working of plasma cutter
In many of today's better plasma cutters, a pilot arc between the electrode and nozzle is used
to ionize the gas and initially generate the plasma prior to the arc transfer.
Other methods that have been used are touching the torch tip to the work to create a spark,
and the use of a high-frequency starting circuit (like a spark plug). Neither of these latter two
methods is compatible with CNC (automated) cutting.
The photo at right shows consumables from a Hypertherm Powermax 900 plasma cutter. The
electrode is at the center, and the nozzle just below it. The orange piece above the electrode is
the swirl ring, which causes the plasma to turn rapidly as it passes.
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While these parts are all referred to as consumables, it is the electrode and nozzle that wear
and require periodic replacement.
3.14 SELECTING A PLASMA CUTTER -
To start with, there are a number of questions that we must answer for ourself, before we
can go any further:
How many hours a day do we plan to use our plasma cutter?
In other words, what kind of duty cycle must it have?
What kind of electrical service do we have where we intend to use the machine? Is it 50
amp 220 volt single phase, or perhaps 30 amp 110 volt single phase? What other
equipment will be running simultaneously on the same circuit?
What kind of portability must our plasma cutter have?
Will we be using it exclusively in our shop, or will we need to take it to the job? Do we
have a means of supplying the machine with compressed air in remote locations?
How we will do that, with a portable compressor or an air bottle?
How will we supply electric current at the site?
What kind of material do we plan to cut, and how thick is it likely to be?
Will we be doing manual cutting exclusively, or is there a possibility that we may want to
use our plasma cutter with a CNC cutting machine?
3.15 WHAT ARE OUR BUDGET LIMITATIONS?
Generally speaking, the higher the amperage output of the plasma cutter, the greater the
duty cycle is at lesser amperages. In other words, if we plan to use the machine around
the clock, we should consider a larger unit than we would need to cut the material we will
be working.
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If we will be using your machine frequently, but not continuously, consider a unit that is
capable of cutting the thickest material we are likely to work. Most manufacturers
provide duty cycle information in their literature.
Many people make the mistake of thinking that the greater the capacity of the machine,
the better it is. In general, fabricators consider oxy-fuel to be superior to plasma for
cutting steel when thicknesses exceed about 1/2 inch. This is because of the slight bevel
(4 to 6 degrees) in the cut face that plasma produces. It is not noticeable in thinner
materials, but becomes more so as thicknesses increase. Also, at thicknesses above 1/2
inch, plasma has no cutting speed advantage over oxy-fuel.
There is little point in buying a plasma cutter that will cut 1 1/2" plate, if you are going to
use acetylene for such work anyway. If we are planning to cut non-ferrous metals such as
stainless or aluminum, which cannot be cut by oxy-fuel, consider a 50 to 80 amp. 220 volt
plasma cutter.
If we plan to use your plasma cutter outside the shop occasionally, we should consider
one of the new breed of semi-portable machines. These units are little powerhouses that
weigh less than 100 lbs., yet are capable of cutting 3/4" to 1" in a pinch. We will need a
bottle of air or a compressor, and a hefty portable generator.
If we believe that we may automate our plasma cutting at some point, we must select a
unit that does not use a high-frequency starting circuit. A high-frequency start acts like a
spark plug in a car. Rather than using a relatively lower voltage pilot arc to initiate the
plasma process, it uses a high voltage spark. This causes electrical interference such as
locking up the computer, destroying files, etc. None of Hypertherm's Powermax units use
a high frequency starting circuit.
Like most other things in life, we get what we pay for. Imported plasma cutters can be
found on the market for $800 or less. However, that is money that could be put toward a
modern inverter type unit costing more initially, but less over time when the cost of
replacement parts and consumables is factored in. On that note, it should be pointed out
53
that Hypertherm's Powermax line uses a new, patented air flow system and torch design
that actually delivers up to 4 times the consumables life of their other models and
competing brands.
Make selection intelligently, based on the above considerations and our plasma cutter will
give us years of reliable performance.
3.16 CNC PLASMA CUTTER-
CNC (computer numerical control) plasma cutting has been around for 30 years, but only
in the past decade has it become affordable enough for the small shop.
The plasma cutting process, itself, is capable of almost surgical precision. It is the human
hand that guides a manual plasma cutting torch that is responsible for the roughness
sometimes seen in plasma cut pieces.
Today's CNC plasma cutting systems typically use the operator's personal computer to
create the shapes to be cut and control the cutting machine. The resulting shapes are
smoother than would be possible with a band saw, and can include intricate curves, inside
cuts, and sharp corners.
The computer also controls the actuation of the torch, turning it on slightly before
beginning the cut, to permit it to burn through the material first.
3.17 COMPARISON OF PLASMA CUTTING WITH OXYFUEL CUTTING:-
Plasma cutting can be performed on any type of conductive metal - mild steel, aluminum
and stainless are some examples. With mild steel, operators will experience faster, thicker
cuts than with alloys.
Oxyfuel cuts by burning, or oxidizing, the metal it is severing. It is therefore limited to
steel and other ferrous metals which support the oxidizing process. Metals like aluminum
and stainless steel form an oxide that inhibits further oxidization, making conventional
54
oxyfuel cutting impossible. Plasma cutting, however, does not rely on oxidation to work,
and thus it can cut aluminum, stainless and any other conductive material.
While different gasses can be used for plasma cutting, most people today use compressed
air for the plasma gas. In most shops, compressed air is readily available, and thus plasma
does not require fuel gas and compressed oxygen for operation.
Plasma cutting is typically easier for the novice to master, and on thinner materials,
plasma cutting is much faster than oxyfuel cutting. However, for heavy sections of steel
(1 inch and greater), oxyfuel is still preferred since oxyfuel is typically faster and, for
heavier plate applications, very high capacity power supplies are required for plasma
cutting applications.
The plasma cutting machines are typically more expensive than oxyacetylene, and also,
oxyacetylene does not require access to electrical power or compressed air which may
make it a more convenient method for some users. Oxyfuel can cut thicker sections (>1
inch) of steel more quickly than plasma
3.18 USE OF PLASMA CUTTER
Plasma cutting is ideal for cutting steel and non-ferrous material less than 1 inch thick.
Oxyfuel cutting requires that the operator carefully control the cutting speed so as to
maintain the oxidizing process. Plasma is more forgiving in this regard. Plasma cutting
really shines in some niche applications, such as cutting expanded metal, something that
is nearly impossible with oxyfuel. And, compared to mechanical mean of cutting, plasma
cutting is typically much faster, and can easily make non-linear cuts.
3.19 LIMITATIONS OF PLASMA CUTTING
The plasma cutting machines are typically more expensive than oxyacetylene, and also,
oxyacetylene does not require access to electrical power or compressed air which may
make it a more convenient method for some users. Oxyfuel can cut thicker sections (>1
inch) of steel more quickly than plasma.
55
3.20 INTRODUCTION TO OVERALL EQUIPMENT EFFECTIVENESS
OEE is a "best practices" way to monitor and improve the effectiveness of your
manufacturing processes (i.e. machines, manufacturing cells, assembly lines).
OEE is simple and practical. It takes the most common and important sources of
manufacturing productivity loss, places them into three primary categories and distills
them into metrics that provide an excellent gauge for measuring where you are - and how
you can improve!
OEE is frequently used as a key metric in TPM (Total Productive Maintenance) and
Lean Manufacturing programs and gives you a consistent way to measure the
effectiveness of TPM and other initiatives by providing an overall framework for
measuring production efficiency.
3.21 OEE FACTORS-
Where Do We Start?
OEE analysis starts with Plant Operating Time; the amount of time your facility is open
and available for equipment operation.
From Plant Operating Time, you subtract a category of time called Planned Shut Down,
which includes all events that should be excluded from efficiency analysis because there
was no intention of running production (e.g. breaks, lunch, scheduled maintenance, or
periods where there is nothing to produce). The remaining available time is your Planned
Production Time.
OEE begins with Planned Production Time and scrutinizes efficiency and productivity
losses that occur, with the goal of reducing or eliminating these losses. There are three
general categories of loss to consider - Down Time Loss, Speed Loss and Quality Loss.
56
Availability
Availability takes into account Down Time Loss, which includes any Events that stop
planned production for an appreciable length of time (usually several minutes – long
enough to log as a trackable Event). Examples include equipment failures, material
shortages, and changeover time. Changeover time is included in OEE analysis, since it is
a form of down time. While it may not be possible to eliminate changeover time, in most
cases it can be reduced. The remaining available time is called Operating Time.
Performance
Performance takes into account Speed Loss, which includes any factors that cause the
process to operate at less than the maximum possible speed, when running. Examples
include machine wear, substandard materials, misfeeds, and operator inefficiency. The
remaining available time is called Net Operating Time.
Quality
Quality takes into account Quality Loss, which accounts for produced pieces that do not
meet quality standards, including pieces that require rework. The remaining time is called
Fully Productive Time. Our goal is to maximize Fully Productive Time.
57
Table- 3.6 OEE Factors
OEE LOSS OEE
FACTOR
PLANNED
SHUTDOWN
Not part of the OEE calculation
DOWN
TIME LOSS
Availability is the ratio of Operating
time to Planned production time
(operating time is Planned production
time less down time loss)
Calculated as ratio of Operating time
to planned production time.
100% availability means the process
has been running without any recorded
stops.
SPEED
LOSS
Performance is the ratio of net
operating time to operating time.
Calculated as the ratio of Ideal cycle
time to Actual time.
100% performance means that the
process has been consistently running
at its theoretical maximum speed.
QUALITY
LOSS
Quality is the ratio of fully productive
time to net operating time.
Calculated as the ratio of good pieces
to total pieces.
100% quality means there has been no
reject or rework pieces.
58
3.22 SIX BIG LOSSES-
Defining the Six Big Losses
One of the major goals of TPM and OEE programs is to reduce and/or eliminate what are
called the Six Big Losses – the most common causes of efficiency loss in manufacturing.
The following table lists the Six Big Losses, and shows how they relate to the OEE Loss
categories.
Table- 3.7Six Big Losses
Six Big
Loss
Catego
ry
OEE
Loss
Category
Event
Examples
Comment
Breakd
owns
Down
Time
Loss
• Tooling Failures
• Unplanned Maintenance
• General Breakdowns
• Equipment Failure
There is
flexibility
on where to
set the
threshold
between a
Breakdown
(Down
Time Loss)
and a Small
Stop (Speed
Loss).
Setup
and
Adjust
Down
Time
Loss
• Setup/Changeover
This loss is
often
addressed
59
ments • Material Shortages
• Operator Shortages
• Major Adjustments
• Warm-Up Time
through
setup time
reduction
programs.
Small
Stops
Speed
Loss
• Obstructed Product Flow
• Component Jams
• Misfeeds
• Sensor Blocked
• Delivery Blocked
• Cleaning/Checking
Typically
only
includes
stops that
are under
five
minutes and
that do not
require
maintenanc
e personnel.
Reduce
d Speed
Speed
Loss
• Rough Running
• Under Nameplate Capacity
• Under Design Capacity
• Equipment Wear
• Operator Inefficiency
Anything
that keeps
the process
from
running at
its
theoretical
maximum
speed
(a.k.a. Ideal
Run Rate or
60
Nameplate
Capacity).
Startup
Rejects
Quality
Loss
• Scrap
• Rework
• In-Process Damage
• In-Process Expiration
• Incorrect Assembly
Rejects
during
warm-up,
startup or
other early
production.
May be due
to improper
setup,
warm-up
period, etc.
Produc
tion
Rejects
Quality
Loss
• Scrap
• Rework
• In-Process Damage
• In-Process Expiration
• Incorrect Assembly
Rejects
during
steady-state
production.
3.23 ADDRESSING THE SIX BIG LOSSES-
Now that we know what the Six Big Losses are and some of the Events that contribute to
these losses, we can focus on ways to monitor and correct them. Categorizing data makes
loss analysis much easier, and a key goal should be fast and efficient data collection, with
data put it to use throughout the day and in real-time.
61
Breakdowns
Eliminating unplanned Down Time is critical to improving OEE. Other OEE Factors
cannot be addressed if the process is down. It is not only important to know how much
Down Time your process is experiencing (and when) but also to be able to attribute the
lost time to the specific source or reason for the loss (tabulated through Reason Codes).
With Down Time and Reason Code data tabulated, Root Cause Analysis is applied
starting with the most severe loss categories.
Setup and Adjustments
Setup and Adjustment time is generally measured as the time between the last good part
produced before Setup to the first consistent good parts produced after Setup. This often
includes substantial adjustment and/or warm-up time in order to consistently produce
parts that meet quality standards.
Tracking Setup Time is critical to reducing this loss, together with an active program to
reduce this time (such as an SMED – Single Minute Exchange of Dies program).
Many companies use creative methods of reducing Setup Time including assembling
changeover carts with all tools and supplies necessary for the changeover in one place,
pinned or marked settings so that coarse adjustments are no longer necessary, and use of
prefabricated setup gauges.
Small Stops and Reduced Speed
Small Stops and Reduced Speed are the most difficult of the Six Big Losses to monitor
and record. Cycle Time Analysis should be utilized to pinpoint these loss types. In most
processes recording data for Cycle Time Analysis needs to be automated since cycles are
quick and repetitive events that do not leave adequate time for manual data-logging.
By comparing all completed cycles to the Ideal Cycle Time and filtering the data through
a Small Stop Threshold and Reduced Speed Threshold the errant cycles can be
62
automatically categorized for analysis. The reason for analyzing Small Stops separately
from Reduced Speed is that the root causes are typically very different, as can be seen
from the Event Examples in the previous table.
Startup Rejects and Production Rejects
Startup Rejects and Production Rejects are differentiated, since often the root causes are
different between startup and steady-state production. Parts that require rework of any
kind should be considered rejects. Tracking when rejects occur during a shift and/or job
run can help pinpoint potential causes, and in many cases patterns will be discovered.
Often a Six Sigma program, where a common metric is achieving a defect rate of less
than 3.4 defects per million “opportunities”, is used to focus attention on a goal of
achieving ”near perfect” quality.
3.24 WORLD CLASS OEE
OEE is essentially the ratio of Fully Productive Time to Planned Production Time (refer
to the OEE Factors section for a graphic representation). In practice, however, OEE is
calculated as the product of its three contributing factors:
OEE = Availability x Performance x Quality
This type of calculation makes OEE a severe test. For example, if all three contributing
factors are 90.0%, the OEE would be 72.9%. In practice, the generally accepted World-
Class goals for each factor are quite different from each other, as is shown in the table
below.
Table- 3.8 World Class OEE
OEE Factor World
63
Class
Availability 90.0%
Performance 95.0%
Quality 99.9%
OEE 85.0%
3.25 HOW TO USE OEE?
Implementing the Overall Equipment Effectiveness formula in your facility can take on
many different forms. It can be used as an analysis and benchmarking tool for either
reliability, equipment utilization, or both. Don't let indecision on how to best use OEE
become a barrier that prevents you from using it at all. Start out small if necessary,
picking your bottleneck to collect the OEE metrics on.
Once you see first hand what a valuable tool it is, you can gradually take OEE
measurements on other equipment in your facility. If you work in manufacturing, there is
no substitute for going out to the shop floor and taking some rough measurements of
OEE. You will be surprised by what you find. While monitoring OEE per equipment
brings focus on the equipment itself, it may not provide true cause of major costs, unless
the cause is obvious. For example OEE can appear improved by actions such as
purchasing oversize equipment, providing redundant supporting systems, and increasing
the frequency of overhauls.
3.26 CALCULATING OEE-
64
The Formulas
As described in World Class OEE, the OEE calculation is based on the three OEE
Factors, Availability, Performance, and Quality. Here's how each of these factors is
calculated.
Availability
Availability takes into account Down Time Loss, and is calculated as:
Availability = Operating Time / Planned Production
Time
Performance
Performance takes into account Speed Loss, and is calculated as:
Performance = Ideal Cycle Time / (Operating Time /
Total Pieces)
Ideal Cycle Time is the minimum cycle time that your process can be expected to achieve
in optimal circumstances. It is sometimes called Design Cycle Time, Theoretical Cycle
Time or Nameplate Capacity.
Since Run Rate is the reciprocal of Cycle Time, Performance can also be calculated as:
Performance = (Total Pieces / Operating Time) / Ideal
Run Rate
65
Quality
Quality takes into account Quality Loss, and is calculated as:
Quality = Good Pieces / Total Pieces
OEE
OEE takes into account all three OEE Factors, and is calculated as:
OEE = Availability x Performance x Quality
It is very important to recognize that improving OEE is not the only objective. Take a
look at the following data for two production shifts.
Table 3.9 Oee Data For Shiftwise Production
OEE Factor Shift 1 Shift 2
Availability 90.0% 95.0%
Performance 95.0% 95.0%
Quality 99.5% 96.0%
OEE 85.1% 86.6%
Superficially, it may appear that the second shift is performing better than the first, since
its OEE is higher. Very few companies, however, would want to trade a 5.0% increase in
Availability for a 3.5% decline in Quality!
66
The beauty of OEE is not that it gives you one magic number; it's that it gives you three
numbers, which are all useful individually as your situation changes from day to day. And
it helps you visualize performance in simple terms – a very practical simplification.
Example OEE Calculation
The table below contains hypothetical shift data, to be used for a complete OEE
calculation, starting with the calculation of the OEE Factors of Availability, Performance,
and Quality. Note that the same units of measurement (in this case minutes and pieces)
are consistently used throughout the calculations.
Table 3.10 details
of OEE contents
Planned Production Time = [Shift Length - Breaks] = [480 - 60] = 420 minutes
Operating Time = [Planned Production Time - Down Time] = [420 - 47] = 373 minutes
Good Pieces = [Total Pieces - Reject Pieces] = [19,271 - 423] = 18,848 pieces
Availability = Operating Time / Planned Production Time
= 373 minutes/420minutes
= 0.8881 (88.81%)
Performance = (Total Pieces / Operating Time) / Ideal Run Rate
= (19,271 pieces / 373 minutes) / 60 pieces per minute
67
Item Data
Shift Length 8 hours = 480 min.
Short Breaks 2 @ 15 min. = 30 min.
Meal Break 1 @ 30 min. = 30 min.
Down Time 47 minutes
Ideal Run Rate 60 pieces per minute
Total Pieces 19,271 pieces
Reject Pieces 423 pieces
= 8611 (86.11%)
Quality = Good Pieces / Total Pieces
= 18,848 / 19,271 pieces
= 0.9780 (97.80%)
OEE = Availability x Performance x Quality
= 0.8881 x 0.8611 x 0.9780
= 0.7479 (74.79%)
WHY OEE?
Apart from increasing the availability of the m/c , OEE has got other added
advantages such as improving quality and performance.
After the Breakdown analysis of the machines, the Plasma Cutting Machine was
a part of the list of critical machines.
In Breakdown analysis, machines were ranked, based on the breakdowns of last
one year.
As OEE being a tool of TPM it effectively aims at reducing all type of wastes
related in the plant.
3.27 COMPARATIVE STUDY
68
OEE IN THE MONTH OF FEBRUARY
OEE IN THE MONTH OF FEB
01020304050607080
2-5FEB
8-11FEB
14-16FEB
19-21FEB
24-26FEB
1-3MAR
5-7MAR
10-12MAR
DAYS
OE
E OEE
AVG OEE=60%
Graph 3.1 OEE Graph in FEB
OEE IN THE MONTH OF MAY
OEE IN THE MONTH OF MAY
6668707274767880828486
1-5 MAY 7-12MAY
14-19MAY
21-26MAY
28MAY-2 JUNE
DAYS
OE
E OEE
AVG OEE=78%
Graph 3.2 OEE Graph in MAY
3.28 NEED OF THE PROJECT
69
Due to sudden increase in demand the supply needs to be matched with the market
demands.
In our case, the different types of flanges are welded to about a 1000 varieties of
pipes, needed greater productivity rates; the demand for brackets had also increased.
Automatically the production group faces a lot of problems because of sudden
increment in the demand to be met with their limited resources.
As many companies have different policies towards their capital utilization viz.
capital investment.
So the only option that remains with the group is to optimize their available resources
For that we need to improve OEE of Plasma Cutting Machine from 60% to 78%.
Improve quality and performance of the machine.
3.29 OVERVIEW OF THE PROJECT
PROCESS STUDY.
GAP ANALYSIS.
PROJECT IDENTIFICATION.
IDEA GENERATION.
IMPLEMENTATION
MONITORING OF THE RESULTS.
3.29.1 PROCESS STUDY
70
It is a scientific methodology that was developed in the 18th century in England to
counter their problems in cotton industries.
The basic principles that are associated with the process study are:-
It aims at identifying each and every aspect of a method by constantly
observing the operator and the process.
With the help of templates, flow process charts ,therbligs and diagrams this
processes are recorded.
These recorded data’s are then analyzed till a new format or method is
developed.
3.29.2 GAP ANALYSIS
In business and economics, gap analysis is a business resource assessment tool enabling a
company to compare its actual performance with its potential performance.
If a company or organization is under-utilizing resources it currently owns or is forgoing
investment in capital or technology then it may be producing or performing at a level
below its potential. This concept is similar to the base case of being below one’s
production possibilities frontier.
This goal of the gap analysis is to identify the gap between the optimized allocation
and integration of the inputs and the current level of allocation. This helps to provide the
company with insight into areas that have room for improvement. The gap analysis
process involves determining, documenting and approving the variance between business
requirements and current capabilities. Gap analysis naturally flows from benchmarking
and other assessments. Once the general expectation of performance in the industry is
understood it is possible to compare that expectation of performance in the industry is
understood it is possible to compare that expectation with the level of performance at
which the company currently functions. This comparison becomes the gap analysis. Such
analysis can be performed at the strategic or operational level of organization. Gap
analysis has also been used for classification of how well a machine is running or meets a
target set.
71
In this case we have done the gap analysis to find out where time is being lost
so that we can improve it, in short we found out the unproductive time during a day of 12
hours.
1
0.40.40.5
0.5
0.4
0.5
No operator
Overhead crane notavailableSheet Loading
Dispatching
Consumables Changing
Individual plate loading
Reduced speed
After analyzing the problems in the gap analysis and time study which we did we rated
them according to their time lost. We prioritize them and prepared an action plan to
counter these losses which are as follows
1) Problem:- No operator
After preparing the analysis chart it is observed that almost 1 hours /day is lost due
to the no operator problem.
72
Chart 3.1 Pie Chart for Plasma Cutting Machine
Cause:-“No operator” problem was a combination of various factors such as voluntary
retirement and absence of skilled laborers. Absentees also sometimes led to this problem.
Solution:- We identified list of laborers so that training could be imparted to them. 3
workers were trained. Barring the problem of absentees, almost problem due to unskilled
workers was solved.
2. Problem:- Overhead crane not available for dispatching of scrap sheet
Cause:-The overhead was sometime not available for dispatching due reasons like
breakdown.
Solution:-Cut the scrap plate into 3 parts using plasma cutting machine so that the plates
can be easily handles by the workers and can be dispatched easily.
3..Problem:-Improper storage of raw and scrap sheet.
Cause:-Improper placement of raw sheet and scrap sheet. Storage area was also being
used for keeping engine base rails.Thus time lost in loading of sheets.
Solution:-All the raw materials and scrap sheet to be kept in proper allotted positions
separately. New place assigned for engine base rails at the side of the plate storage area.
4.Problem:- Time lost in dispatching of product
Cause:-The product which has been cut by the m/c is to be dispatched to the power press
for punching of hole. The m/c remains idle while the product is being dispatched
manually to the power press.
Solution:-A makeshift trolley was provided to dispatch the product to the power press.
73
5.Problem:- Time lost in changing of consumables(tip ,nozzle)
Cause:-Due to improper or angular cutting and frequent piercing of plate by plasma
flame wear and tear of the costly consumables(tip, nozzle) takes place which needs
replacement leading to production time loss.
Solution:-
Proper training imparted to the operators, proper distance needs to be maintained
between the tip and plate, avoid angular cut.
NESTING:-
The major reason for consumable wear and tear is due to frequent piercing of plate by the
plasma flame. To avoid this, the method of nesting was used. This process involves
cutting of a group of products in a single pierce.
Fig 3.2 Nesting
74
6.Problem:- Time lost for loading plate for individual product
Cause:-There is a certain group of products under the Kanban system which have daily
requirement but they are cut in limited quantity.Each product needs individual plate and
drawing which takes a lot of time.
Solution:- To counter this the drawing was modified to fit more than one product in a
single sheet.This lead to elimination of time loss for individual plate loading.
Figure 3.3
75
Figure 3.4
7. Problem:- Loss due to dropping of pressures of compressor and dryer.
Cause:-The pressure that needs to be maintained at compressor is 8-10 bars and at dryer
is 6-8 bars which was not available .To account for the loss in pressure the velocity of
torch was altered for optimum quality of cut which led to time loss.
Solution:-A separate line from the compressor was taken to provide a continous supply of
8-10 bar pressure gas.
8. Problem:-Rework due to warpage of sheet.
Cause:-As the temperature of the plasma flame is very high, warpage of sheet occurs
leading to rejection of a considerable no of product.
Solution:-Modification in the sequence of cutting of product was made. Alternate parts of
the plate were cut sequentially rather than cutting the plate serially along a straight path.
3.29.3 ACTION PLAN TO IMPROVE OEE OF PLASMA CUTTING MACHINE
76
SR
NO
CAUSES ACTION TAKEN STATUS HRS
RECOVERY
1. No operator 3 additional workers
trained
completed 1
2. Overhead crane
not available
Cut scrap plate for manual
handling
pending 0
3. Consumables
changing
Proper cutting
method ,Nesting
completed 0.5
4. Dispatching Makeshift trolley provided pending 0
5. Sheet Loading Proper management of
sheet storage area
pending 0
6. Individual plate
loading
Drawing modified to fit
more than one product
completed 0.2
7. Reduced speed Separate line from
compressor given
completed 0.2
Table 3.11 Action Plan
3.30 OVERALL BENEFITS
OEE of the Plasma Cutting m/c has increased by 18 % after completion of the projects. (Jan-May)
Due to improvement of OEE of this m/c the feed given to other m/c through plasma cutting like Power Press, Welding m/c has increased leading to increased productivity of the whole plant.
77
OEE of the m/c can be further improved if the pending action is implemented. Thus this project gives a scope for further improvement.
Quality and performance of the m/c has improved.
Safety aspects have improved.
Ease of operation has been achieved.
3.31 LEARNINGS
Understanding of OEE, TPM and other world class manufacturing methods such as KANBAN.
Stock Management for tubes, co-ordination in NDT tests.
All processes carried out in winding shop.
Correlating the designing aspects that we have studied to the practical problems in the industry.
Supervision skills
3.32 CONCLUSION
As per the requirements, the OEE of the Plasma Cutting machine is increased from 60%
to 78% because of which the productivity of the plant has increased. These are the
tangible benefits after implementation of Project. Other benefits include safety at work
place, systematic functioning of the plant.
The projects and assignment helped us to apply our technical fundamentals and
gave us a practical insight into the factory activities. They developed our ability to think
innovative which brought variety and depth in our knowledge. They put forward the truth
that every manufacturing activity needs a thorough blend of right inputs and capabilities.
78
The project OEE improvement of Plasma Cutting m/c not only improved the
effectiveness of the machine, it also improved the quality of the process carried on it. The
important tangible and intangible benefits can be concluded as follows:-
OEE of the m/c is increased to 78% from 60%.
Project was conducted taking all six wastes of production in mind. These were also
considered for improving the process that is done on the machine and the majority of
these were minimized.
All the NVA activities were eliminated and time recovered from was utilized in
improving OEE.
Design, manufacturing and installation of the inputs provided to us was all done in
the company itself.
79
4. STUDY OF WELDING PROCESSES AT BHOR ENGINEERING PVT. LTD.
4.1 INTRODUCTION
Welding is a fabrication or sculptural process that joins materials, usually metals or
thermoplastics, by causing coalescence. This is often done by melting the workpieces and
adding a filler material to form a pool of molten material (the weld pool) that cools to
become a strong joint, with pressure sometimes used in conjunction with heat, or by itself,
to produce the weld. This is in contrast with soldering and brazing, which involve melting
a lower-melting-point material between the workpieces to form a bond between them,
without melting the workpieces.
Many different energy sources can be used for welding, including a gas flame, an electric
arc, a laser, an electron beam, friction, and ultrasound. While often an industrial process,
welding can be done in many different environments, including open air, under water and
in outer space. Regardless of location, however, welding remains dangerous, and
precautions must be taken to avoid burns, electric shock, eye damage, poisonous fumes,
and overexposure to ultraviolet light.
Figure 4.1 of welding 4.2 HISTORY-
The history of joining metals goes back several millennia, with the earliest examples of
welding from the Bronze Age and the Iron Age in Europe and the Middle East. Welding
was used in the construction of the iron pillar in Delhi, India, erected about 310 AD and
weighing 5.4 metric tons.
80
The Middle Ages brought advances in forge welding, in which blacksmiths pounded
heated metal repeatedly until bonding occurred. In 1540, Vannoccio Biringuccio
published De la pirotechnia, which includes descriptions of the forging operation.
Renaissance craftsmen were skilled in the process, and the industry continued to grow
during the following centuries.[2] Welding, however, was transformed during the 19th
century—in 1800, Sir Humphry Davy discovered the electric arc, and advances in arc
welding continued with the invention of metal electrodes in the late 1800s by a Russian,
Nikolai Slavyanov, and an American, C. L. Coffin, even as carbon arc welding, which
used a carbon electrode, gained popularity. Around 1900, A. P. Strohmenger released a
coated metal electrode in Britain, which gave a more stable arc, and in 1919, alternating
current welding was invented by C. J. Holslag but did not become popular for another
decade.
Resistance welding was also developed during the final decades of the 19th century, with
the first patents going to Elihu Thomson in 1885, who produced further advances over the
next 15 years. Thermite welding was invented in 1893, and around that time another
process, oxyfuel welding, became well established. Acetylene was discovered in 1836 by
Edmund Davy, but its use was not practical in welding until about 1900, when a suitable
blowtorch was developed. At first, oxyfuel welding was one of the more popular welding
methods due to its portability and relatively low cost. As the 20th century progressed,
however, it fell out of favor for industrial applications. It was largely replaced with arc
welding, as metal coverings (known as flux) for the electrode that stabilize the arc and
shield the base material from impurities continued to be developed.
World War I caused a major surge in the use of welding processes, with the various
military powers attempting to determine which of the several new welding processes
would be best. The British primarily used arc welding, even constructing a ship, the
Fulagar, with an entirely welded hull. Arc welding was first applied to aircraft during the
war as well, as some German airplane fuselages were constructed using the process. Also
noteworthy is the first welded road bridge in the world, designed by Stefan Bryła of the
Warsaw University of Technology in 1927, and built across the river Słudwia Maurzyce
near Łowicz, Poland in 1929.
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During the 1920s, major advances were made in welding technology, including the
introduction of automatic welding in 1920, in which electrode wire was fed continuously.
Shielding gas became a subject receiving much attention, as scientists attempted to
protect welds from the effects of oxygen and nitrogen in the atmosphere. Porosity and
brittleness were the primary problems, and the solutions that developed included the use
of hydrogen, argon, and helium as welding atmospheres. During the following decade,
further advances allowed for the welding of reactive metals like aluminum and
magnesium. This in conjunction with developments in automatic welding, alternating
current, and fluxes fed a major expansion of arc welding during the 1930s and then during
World War II.
During the middle of the century, many new welding methods were invented. 1930 saw
the release of stud welding, which soon became popular in shipbuilding and construction.
Submerged arc welding was invented the same year and continues to be popular today.
Gas tungsten arc welding, after decades of development, was finally perfected in 1941,
and gas metal arc welding followed in 1948, allowing for fast welding of non-ferrous
materials but requiring expensive shielding gases. Shielded metal arc welding was
developed during the 1950s, using a flux coated consumable electrode, and it quickly
became the most popular metal arc welding process. In 1957, the flux-cored arc welding
process debuted, in which the self-shielded wire electrode could be used with automatic
equipment, resulting in greatly increased welding speeds, and that same year, plasma arc
welding was invented. Electro slag welding was introduced in 1958, and it was followed
by its cousin, electro gas welding, in 1961.
Other recent developments in welding include the 1958 breakthrough of electron beam
welding, making deep and narrow welding possible through the concentrated heat source.
Following the invention of the laser in 1960, laser beam welding debuted several decades
later, and has proved to be especially useful in high-speed, automated welding. Both of
these processes, however, continue to be quite expensive due the high cost of the
necessary equipment, and this has limited their applications
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Until the end of the 19th century, the only welding process was forge welding, which
blacksmiths had used for centuries to join metals by heating and pounding them. Arc
welding and oxyfuel welding were among the first processes to develop late in the
century, and resistance welding followed soon after. Welding technology advanced
quickly during the early 20th century as World War I and World War II drove the demand
for reliable and inexpensive joining methods. Following the wars, several modern
welding techniques were developed, including manual methods like shielded metal arc
welding, now one of the most popular welding methods, as well as semi-automatic and
automatic processes such as gas metal arc welding, submerged arc welding, flux-cored arc
welding and electro slag welding. Developments continued with the invention of laser
beam welding and electron beam welding in the latter half of the century. Today, the
science continues to advance. Robot welding is becoming more commonplace in
industrial settings, and researchers continue to develop new welding methods and gain
greater understanding of weld quality and properties.
4.3 ARCThese processes use a welding power supply to create and maintain an electric arc between an electrode and the base material to melt metals at the welding point. They can use either direct (DC) or alternating (AC) current, and consumable or non-consumable electrodes. The welding region is sometimes protected by some type of inert or semi-inert gas, known as a shielding gas, and filler material is sometimes used as well.4.4 POWER SUPPLIESTo supply the electrical energy necessary for arc welding processes, a number of different power supplies can be used. The most common welding power supplies are constant current power supplies and constant voltage power supplies. In arc welding, the length of the arc is directly related to the voltage, and the amount of heat input is related to the current. Constant current power supplies are most often used for manual welding processes such as gas tungsten arc welding and shielded metal arc welding, because they maintain a relatively constant current even as the voltage varies. This is important because in manual welding, it can be difficult to hold the electrode perfectly steady, and as a result, the arc length and thus voltage tend to fluctuate. Constant voltage power supplies hold the voltage constant and vary the current, and as a result, are most often used for automated welding processes such as gas metal arc welding, flux cored arc welding, and submerged arc welding. In these processes, arc length is kept constant, since any fluctuation in the distance between the wire and the base material is quickly rectified by a large change in current. For example, if the wire and the base material get too close, the current will rapidly increase, which in turn causes the heat to increase and the tip of the wire to melt, returning it to its original separation distance.
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The type of current used in arc welding also plays an important role in welding. Consumable electrode processes such as shielded metal arc welding and gas metal arc welding generally use direct current, but the electrode can be charged either positively or negatively. In welding, the positively charged anode will have a greater heat concentration, and as a result, changing the polarity of the electrode has an impact on weld properties. If the electrode is positively charged, the base metal will be hotter, increasing weld penetration and welding speed. Alternatively, a negatively charged electrode results in more shallow welds. Non consumable electrode processes, such as gas tungsten arc welding, can use either type of direct current, as well as alternating current. However, with direct current, because the electrode only creates the arc and does not provide filler material, a positively charged electrode causes shallow welds, while a negatively charged electrode makes deeper welds. Alternating current rapidly moves between these two, resulting in medium-penetration welds. One disadvantage of AC, the fact that the arc must be re-ignited after every zero crossing, has been addressed with the invention of special power units that produce a square wave pattern instead of the normal sine wave, making rapid zero crossings possible and minimizing the effects of the problem. 4.5 PROCESSES
One of the most common types of arc welding is shielded metal arc welding (SMAW),
which is also known as manual metal arc welding (MMA) or stick welding. Electric
current is used to strike an arc between the base material and consumable electrode rod,
which is made of steel and is covered with a flux that protects the weld area from
oxidation and contamination by producing CO2 gas during the welding process. The
electrode core itself acts as filler material, making separate filler unnecessary.
The process is versatile and can be performed with relatively inexpensive equipment,
making it well suited to shop jobs and field work. An operator can become reasonably
proficient with a modest amount of training and can achieve mastery with experience.
Weld times are rather slow, since the consumable electrodes must be frequently replaced
and because slag, the residue from the flux, must be chipped away after welding.
Furthermore, the process is generally limited to welding ferrous materials, though special
electrodes have made possible the welding of cast iron, nickel, aluminum, copper, and
other metals. Inexperienced operators may find it difficult to make good out-of-position
welds with this process.
Gas metal arc welding (GMAW), also known as metal inert gas or MIG welding, is a
semi-automatic or automatic process that uses a continuous wire feed as an electrode and
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an inert or semi-inert gas mixture to protect the weld from contamination. As with
SMAW, reasonable operator proficiency can be achieved with modest training. Since the
electrode is continuous, welding speeds are greater for GMAW than for SMAW. Also, the
smaller arc size compared to the shielded metal arc welding process makes it easier to
make out-of-position welds (e.g., overhead joints, as would be welded underneath a
structure).
The equipment required to perform the GMAW process is more complex and expensive
than that required for SMAW, and requires a more complex setup procedure. Therefore,
GMAW is less portable and versatile, and due to the use of a separate shielding gas, is not
particularly suitable for outdoor work. However, owing to the higher average rate at
which welds can be completed, GMAW is well suited to production welding. The process
can be applied to a wide variety of metals, both ferrous and non-ferrous.
A related process, flux-cored arc welding (FCAW), uses similar equipment but uses wire
consisting of a steel electrode surrounding a powder fill material. This cored wire is more
expensive than the standard solid wire and can generate fumes and/or slag, but it permits
even higher welding speed and greater metal penetration.
Gas tungsten arc welding (GTAW), or tungsten inert gas (TIG) welding (also sometimes
erroneously referred to as heliarc welding), is a manual welding process that uses a
nonconsumable tungsten electrode, an inert or semi-inert gas mixture, and a separate filler
material. Especially useful for welding thin materials, this method is characterized by a
stable arc and high quality welds, but it requires significant operator skill and can only be
accomplished at relatively low speeds.
GTAW can be used on nearly all weldable metals, though it is most often applied to
stainless steel and light metals. It is often used when quality welds are extremely
important, such as in bicycle, aircraft and naval applications. A related process, plasma
arc welding, also uses a tungsten electrode but uses plasma gas to make the arc. The arc is
more concentrated than the GTAW arc, making transverse control more critical and thus
generally restricting the technique to a mechanized process. Because of its stable current,
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the method can be used on a wider range of material thicknesses than can the GTAW
process, and furthermore, it is much faster. It can be applied to all of the same materials as
GTAW except magnesium, and automated welding of stainless steel is one important
application of the process. A variation of the process is plasma cutting, an efficient steel
cutting process.
Submerged arc welding (SAW) is a high-productivity welding method in which the arc is
struck beneath a covering layer of flux. This increases arc quality, since contaminants in
the atmosphere are blocked by the flux. The slag that forms on the weld generally comes
off by itself, and combined with the use of a continuous wire feed, the weld deposition
rate is high. Working conditions are much improved over other arc welding processes,
since the flux hides the arc and almost no smoke is produced. The process is commonly
used in industry, especially for large products and in the manufacture of welded pressure
vessels. Other arc welding processes include atomic hydrogen welding, carbon arc
welding, electroslag welding, electrogas welding, and stud arc welding.
4.6 GAS
The most common gas welding process is oxyfuel welding, also known as oxyacetylene
welding. It is one of the oldest and most versatile welding processes, but in recent years it
has become less popular in industrial applications. It is still widely used for welding pipes
and tubes, as well as repair work. It is also frequently well-suited, and favored, for
fabricating some types of metal-based artwork. Oxyfuel equipment is versatile, lending
itself not only to some sorts of iron or steel welding but also to brazing, braze-welding,
metal heating (for bending and forming), and also oxyfuel cutting.
The equipment is relatively inexpensive and simple, generally employing the combustion
of acetylene in oxygen to produce a welding flame temperature of about 3100 °C. The
flame, since it is less concentrated than an electric arc, causes slower weld cooling, which
can lead to greater residual stresses and weld distortion, though it eases the welding of
high alloy steels. A similar process, generally called oxyfuel cutting, is used to cut metals.
Other gas welding methods, such as air acetylene welding, oxygen hydrogen welding, and
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pressure gas welding are quite similar, generally differing only in the type of gases used.
A water torch is sometimes used for precision welding of small items such as jewelry.
Gas welding is also used in plastic welding, though the heated substance is air, and the
temperatures are much lower.
4.7 RESISTANCE
Resistance welding involves the generation of heat by passing current through the
resistance caused by the contact between two or more metal surfaces. Small pools of
molten metal are formed at the weld area as high current (1000–100,000 A) is passed
through the metal. In general, resistance welding methods are efficient and cause little
pollution, but their applications are somewhat limited and the equipment cost can be high
Spot welding is a popular resistance welding method used to join overlapping metal
sheets of up to 3 mm thick. Two electrodes are simultaneously used to clamp the metal
sheets together and to pass current through the sheets. The advantages of the method
include efficient energy use, limited workpiece deformation, high production rates, easy
automation, and no required filler materials. Weld strength is significantly lower than
with other welding methods, making the process suitable for only certain applications. It
is used extensively in the automotive industry—ordinary cars can have several thousand
spot welds made by industrial robots. A specialized process, called shot welding, can be
used to spot weld stainless steel.
Like spot welding, seam welding relies on two electrodes to apply pressure and current to
join metal sheets. However, instead of pointed electrodes, wheel-shaped electrodes roll
along and often feed the workpiece, making it possible to make long continuous welds. In
the past, this process was used in the manufacture of beverage cans, but now its uses are
more limited. Other resistance welding methods include flash welding, projection
welding, and upset welding.
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4.8 ENERGY BEAM
Energy beam welding methods, namely laser beam welding and electron beam welding,
are relatively new processes that have become quite popular in high production
applications. The two processes are quite similar, differing most notably in their source of
power. Laser beam welding employs a highly focused laser beam, while electron beam
welding is done in a vacuum and uses an electron beam. Both have a very high energy
density, making deep weld penetration possible and minimizing the size of the weld area.
Both processes are extremely fast, and are easily automated, making them highly
productive. The primary disadvantages are their very high equipment costs (though these
are decreasing) and a susceptibility to thermal cracking. Developments in this area
include laser-hybrid welding, which uses principles from both laser beam welding and arc
welding for even better weld properties, and X-ray welding.
4.9 SOLID-STATE
Like the first welding process, forge welding, some modern welding methods do not
involve the melting of the materials being joined. One of the most popular, ultrasonic
welding, is used to connect thin sheets or wires made of metal or thermoplastic by
vibrating them at high frequency and under high pressure. The equipment and methods
involved are similar to that of resistance welding, but instead of electric current, vibration
provides energy input. Welding metals with this process does not involve melting the
materials; instead, the weld is formed by introducing mechanical vibrations horizontally
under pressure. When welding plastics, the materials should have similar melting
temperatures, and the vibrations are introduced vertically. Ultrasonic welding is
commonly used for making electrical connections out of aluminum or copper, and it is
also a very common polymer welding process.
Another common process, explosion welding, involves the joining of materials by
pushing them together under extremely high pressure. The energy from the impact
plasticizes the materials, forming a weld, even though only a limited amount of heat is
generated. The process is commonly used for welding dissimilar materials, such as the
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welding of aluminum with steel in ship hulls or compound plates. Other solid-state
welding processes include co-extrusion welding, cold welding, diffusion welding,
exothermic welding, friction welding (including friction stir welding), high frequency
welding, hot pressure welding, induction welding, and roll welding.
4.10 GEOMETRY
Welds can be geometrically prepared in many different ways. The five basic types of
weld joints are the butt joint, lap joint, corner joint, edge joint, and T-joint (a variant of
this last is the cruciform joint). Other variations exist as well—for example, double-V
preparation joints are characterized by the two pieces of material each tapering to a single
center point at one-half their height. Single-U and double-U preparation joints are also
fairly common—instead of having straight edges like the single-V and double-V
preparation joints, they are curved, forming the shape of a U. Lap joints are also
commonly more than two pieces thick—depending on the process used and the thickness
of the material, many pieces can be welded together in a lap joint geometry.
Often, particular joint designs are used exclusively or almost exclusively by certain
welding processes. For example, resistance spot welding, laser beam welding, and
electron beam welding are most frequently performed on lap joints. However, some
welding methods, like shielded metal arc welding, are extremely versatile and can weld
virtually any type of joint. Additionally, some processes can be used to make multipass
welds, in which one weld is allowed to cool, and then another weld is performed on top of
it. This allows for the welding of thick sections arranged in a single-V preparation joint,
for example.
After welding, a number of distinct regions can be identified in the weld area. The weld
itself is called the fusion zone—more specifically, it is where the filler metal was laid
during the welding process. The properties of the fusion zone depend primarily on the
filler metal used, and its compatibility with the base materials. It is surrounded by the
heat-affected zone, the area that had its microstructure and properties altered by the weld.
These properties depend on the base material's behavior when subjected to heat. The
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metal in this area is often weaker than both the base material and the fusion zone, and is
also where residual stresses are found.
4.11 QUALITY
Most often, the major metric used for judging the quality of a weld is its strength and the
strength of the material around it. Many distinct factors influence this, including the
welding method, the amount and concentration of energy input, the base material, the
filler material, the flux material, the design of the joint, and the interactions between all
these factors. To test the quality of a weld, either destructive or nondestructive testing
methods are commonly used to verify that welds are defect-free, have acceptable levels of
residual stresses and distortion, and have acceptable heat-affected zone (HAZ) properties.
Welding codes and specifications exist to guide welders in proper welding technique and
in how to judge the quality of welds.
4.12 HEAT AFFECTED ZONEThe effects of welding on the material surrounding the weld can be detrimental—depending on the materials used and the heat input of the welding process used, the HAZ can be of varying size and strength. The thermal diffusivity of the base material plays a large role—if the diffusivity is high, the material cooling rate is high and the HAZ is relatively small. Conversely, a low diffusivity leads to slower cooling and a larger HAZ. The amount of heat injected by the welding process plays an important role as well, as processes like oxyacetylene welding have an unconcentrated heat input and increase the size of the HAZ. Processes like laser beam welding give a highly concentrated, limited amount of heat, resulting in a small HAZ. Arc welding falls between these two extremes, with the individual processes varying somewhat in heat input. To calculate the heat input for arc welding procedures, the following formula can be used:
where Q = heat input (kJ/mm), V = voltage (V), I = current (A), and S = welding speed (mm/min). The efficiency is dependent on the welding process used, with shielded metal arc welding having a value of 0.75, gas metal arc welding and submerged arc welding, 0.9, and gas tungsten arc welding, 0.8.[31]
4.13 DISTORTION AND CRACKINGWelding methods that involve the melting of metal at the site of the joint necessarily are prone to shrinkage as the heated metal cools. Shrinkage, in turn, can introduce residual stresses and both longitudinal and rotational distortion. Distortion can pose a major problem, since the final product is not the desired shape. To alleviate rotational distortion,
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the workpieces can be offset, so that the welding results in a correctly shaped piece. Other methods of limiting distortion, such as clamping the workpieces in place, cause the buildup of residual stress in the heat-affected zone of the base material. These stresses can reduce the strength of the base material, and can lead to catastrophic failure through cold cracking, as in the case of several of the Liberty ships. Cold cracking is limited to steels, and is associated with the formation of martensite as the weld cools. The cracking occurs in the heat-affected zone of the base material. To reduce the amount of distortion and residual stresses, the amount of heat input should be limited, and the welding sequence used should not be from one end directly to the other, but rather in segments. The other type of cracking, hot cracking or solidification cracking, can occur with all metals, and happens in the fusion zone of a weld. To diminish the probability of this type of cracking, excess material restraint should be avoided, and a proper filler material should be utilized.
4.14 WELDABILITYThe quality of a weld is also dependent on the combination of materials used for the base material and the filler material. Not all metals are suitable for welding, and not all filler metals work well with acceptable base materials.4.14.1 STEELSThe weldability of steels is inversely proportional to a property known as the hardenability of the steel, which measures the probability of forming martensite during welding or heat treatment. The hardenability of steel depends on its chemical composition, with greater quantities of carbon and other alloying elements resulting in a higher hardenability and thus a lower weldability. In order to be able to judge alloys made up of many distinct materials, a measure known as the equivalent carbon content is used to compare the relative weldabilities of different alloys by comparing their properties to a plain carbon steel. The effect on weldability of elements like chromium and vanadium, while not as great as carbon, is more significant than that of copper and nickel, for example. As the equivalent carbon content rises, the weldability of the alloy decreases. The disadvantage to using plain carbon and low-alloy steels is their lower strength—there is a trade-off between material strength and weldability. High strength, low-alloy steels were developed especially for welding applications during the 1970s, and these generally easy to weld materials have good strength, making them ideal for many welding applications. Stainless steels, because of their high chromium content, tend to behave differently with respect to weldability than other steels. Austenitic grades of stainless steels tend to be the most weldable, but they are especially susceptible to distortion due to their high coefficient of thermal expansion. Some alloys of this type are prone to cracking and reduced corrosion resistance as well. Hot cracking is possible if the amount of ferrite in the weld is not controlled—to alleviate the problem, an electrode is used that deposits a weld metal containing a small amount of ferrite. Other types of stainless steels, such as ferritic and martensitic stainless steels, are not as easily welded, and must often be preheated and welded with special electrodes. 4.14.2 ALUMINUMThe weldability of aluminum alloys varies significantly, depending on the chemical composition of the alloy used. Aluminum alloys are susceptible to hot cracking, and to combat the problem, welders increase the welding speed to lower the heat input.
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Preheating reduces the temperature gradient across the weld zone and thus helps reduce hot cracking, but it can reduce the mechanical properties of the base material and should not be used when the base material is restrained. The design of the joint can be changed as well, and a more compatible filler alloy can be selected to decrease the likelihood of hot cracking. Aluminum alloys should also be cleaned prior to welding, with the goal of removing all oxides, oils, and loose particles from the surface to be welded. This is especially important because of an aluminum weld's susceptibility to porosity due to hydrogen and dross due to oxygen.
4.15 SAFETY ISSUES
Welding, without the proper precautions, can be a dangerous and unhealthy practice.
However, with the use of new technology and proper protection, risks of injury and death
associated with welding can be greatly reduced. Because many common welding
procedures involve an open electric arc or flame, the risk of burns is significant. To
prevent them, welders wear personal protective equipment in the form of heavy leather
gloves and protective long sleeve jackets to avoid exposure to extreme heat and flames.
Additionally, the brightness of the weld area leads to a condition called arc eye in which
ultraviolet light causes inflammation of the cornea and can burn the retinas of the eyes.
Goggles and welding helmets with dark face plates are worn to prevent this exposure, and
in recent years, new helmet models have been produced that feature a face plate that self-
darkens upon exposure to high amounts of UV light. To protect bystanders, translucent
welding curtains often surround the welding area. These curtains, made of a polyvinyl
chloride plastic film, shield nearby workers from exposure to the UV light from the
electric arc, but should not be used to replace the filter glass used in helmets.
Welders are also often exposed to dangerous gases and particulate matter. Processes like
flux-cored arc welding and shielded metal arc welding produce smoke containing
particles of various types of oxides, which in some cases can lead to medical conditions
like metal fume fever. The size of the particles in question tends to influence the toxicity
of the fumes, with smaller particles presenting a greater danger. Additionally, many
processes produce fumes and various gases, most commonly carbon dioxide, ozone and
heavy metals, that can prove dangerous without proper ventilation and training.
Furthermore, because the use of compressed gases and flames in many welding processes
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poses an explosion and fire risk, some common precautions include limiting the amount
of oxygen in the air, keeping combustible materials away from the workplace, or making
use of a positive pressure enclosure. Welding fume extractors are often used to remove
the fume from the source and filter the fumes through a HEPA filter
4.16 COSTS AND TRENDS
As an industrial process, the cost of welding plays a crucial role in manufacturing
decisions. Many different variables affect the total cost, including equipment cost, labor
cost, material cost, and energy cost. Depending on the process, equipment cost can vary,
from inexpensive for methods like shielded metal arc welding and oxyfuel welding, to
extremely expensive for methods like laser beam welding and electron beam welding.
Because of their high cost, they are only used in high production operations. Similarly,
because automation and robots increase equipment costs, they are only implemented
when high production is necessary. Labor cost depends on the deposition rate (the rate of
welding), the hourly wage, and the total operation time, including both time welding and
handling the part. The cost of materials includes the cost of the base and filler material,
and the cost of shielding gases. Finally, energy cost depends on arc time and welding
power demand.
For manual welding methods, labor costs generally make up the vast majority of the total
cost. As a result, many cost-savings measures are focused on minimizing the operation
time. To do this, welding procedures with high deposition rates can be selected, and weld
parameters can be fine-tuned to increase welding speed. Also, removal of welding spatters
generated during welding process is highly labor intensive and time consuming.
Implementation of Welding Anti Spatter & Flux which is safe and non-polluting is
considered as a welcome change in cost cutting and weld joint quality improvement
measures. Mechanization and automation are often implemented to reduce labor costs, but
this frequently increases the cost of equipment and creates additional setup time. Material
costs tend to increase when special properties are necessary, and energy costs normally do
not amount to more than several percent of the total welding cost.
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In recent years, in order to minimize labor costs in high production manufacturing,
industrial welding has become increasingly more automated, most notably with the use of
robots in resistance spot welding (especially in the automotive industry) and in arc
welding. In robot welding, mechanized devices both hold the material and perform the
weld, and at first, spot welding was its most common application. But robotic arc welding
has been increasing in popularity as technology has advanced. Other key areas of research
and development include the welding of dissimilar materials (such as steel and aluminum,
for example) and new welding processes, such as friction stir, magnetic pulse, conductive
heat seam, and laser-hybrid welding. Furthermore, progress is desired in making more
specialized methods like laser beam welding practical for more applications, such as in
the aerospace and automotive industries. Researchers also hope to better understand the
often unpredictable properties of welds, especially microstructure, residual stresses, and a
weld's tendency to crack or deform
4.17 WELDING FACILITY AT BHOR ENGINEERING PVT. LTD.These Welding Machines A Installed At Our CompanyWelding Machines
CO2 MIG ESAB MAKE; MODEL NO. – POWER COMPACT – PC- 255
1
CO2 –MIG Esab Make Model No – Origo Arc –150 3CO2 –MIG Esab Make Model No Auto K400 1CO2 –MIG Migatronic Make Model No – Auto MIG 250 E
5
CO2 –MIG Migatronic Make Model No – Auto MIG 300 XE
3
TIG Welding Powell Make Model No –DG- 160 DPR
1
Table- 4.1 List of welding machines at BEPL
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Photo- 4.1 Welding machines at BEPL4.18 GAS METAL ARC WELDING
Gas metal arc welding (GMAW), sometimes referred to by its subtypes metal inert gas
(MIG) welding or metal active gas (MAG) welding, is a semi-automatic or automatic arc
welding process in which a continuous and consumable wire electrode and a shielding gas
are fed through a welding gun. A constant voltage, direct current power source is most
commonly used with GMAW, but constant current systems, as well as alternating current,
can be used. There are four primary methods of metal transfer in GMAW, called globular,
short-circuiting, spray, and pulsed-spray, each of which has distinct properties and
corresponding advantages and limitations.
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Figure- 4.2 Sectional view of GMAW
Originally developed for welding aluminium and other non-ferrous materials in the 1940s,
GMAW was soon applied to steels because it allowed for lower welding time compared
to other welding processes. The cost of inert gas limited its use in steels until several
years later, when the use of semi-inert gases such as carbon dioxide became common.
Further developments during the 1950s and 1960s gave the process more versatility and
as a result, it became a highly used industrial process. Today, GMAW is the most
common industrial welding process, preferred for its versatility, speed and the relative
ease of adapting the process to robotic automation. The automobile industry in particular
uses GMAW welding almost exclusively. Unlike welding processes that do not employ a
shielding gas, such as shielded metal arc welding, it is rarely used outdoors or in other
areas of air volatility. A related process, flux cored arc welding, often does not utilize a
shielding gas, instead employing a hollow electrode wire that is filled with flux on the
inside.
4.19 GMAW PROCEDURESAs with any other type of welding, the GMA weld-ing procedure consists of certain variables that you must understand and follow. Many of the variables have already been discussed. This section applies some of these variables to the actual welding procedure.4.19.1 STARTING THE ARCFor a good arc start, the electrode must make good electrical contact with the work For the best results, you should clean the metal of all impurities. The wire stick-out must be set correctly because as the wire stick-out increases, the arc initiation becomes increasingly diffi-culte When preparing to start the arc, hold the torch at an angle between 5 and 20 degrees. Support the weight of the welding cable and gas hose across your shoulder to ensure free movement of the welding torch. Hold the torch close to, but not touching, the workpiece. Lower your helmet and squeeze the torch trigger. Squeezing the trigger starts the flow of shielding gas and energizes the welding circuit. The wire-feed motor does not energize until the wire electrode comes in contact with the workpiece.
Figure- 4.3 Striking the arc (GMAW)
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Move the torch toward the work, touching the wire electrode to the work with a sideways scratching motion, as shown in figure 8-29. To prevent sticking, you should pull the torch back quickly, about 1/2 of an inch—the instant contact is made between the wire electrode and the workpiece. The arc strikes as soon as contact is made and the wire-feed motor feeds the wire automatically as long as the trigger is held.A properly established arc has a soft, sizzling sound. Adjustment of the wire-feed control dial or the welding machine itself is necessary when the arc does not sound right. For example, a loud, crackling sound indicates that the arc is too short and that the wire-feed speed is too fast. You may correct this problem by moving the wire-feed dial slightly counterclockwise. This decreases the wire-feed speed and increases the arc length. A clockwise movement of the dial has the opposite effect. With experience, you can recognize the sound of the proper length of arc to use.To break the arc, you simply release the trigger. This breaks the welding circuit and de-energizes the wire-feed motor. Should the wire electrode stick to the work when striking the arc or during welding, release the trigger and clip the wire with a pair of side cutters.4.20 WELDING POSITIONS
Figure- 4.4 Welding positionsIn gas metal-arc welding, the proper position of the welding torch and weldment are important. The position of the torch in relation to the plate is called the work and travel angle. Work and travel angles are shown in figure 8-30. If the parts are equal in thickness, the work angle should normally be on the center line of the joint; however, if the pieces are unequal in thickness, the torch should angle toward the thicker piece.The travel angle refers to the angle in which welding takes place. This angle should be between 5 and 25 degrees. The travel angle may be either a push angle or a drag angle, depending on the position of the torch. When the torch is ahead of the weld, it is known as pulling (or dragging) the weld. When the torch is behind the weld, it is referred to as pushing the metal (fig. 8-31).
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Figure- 4.5 Pulling and pushing angle techniquesThe pulling or drag technique is for heavy-gauge metals. Usually the drag technique produces greater penetration than the pushing technique. Also, since the welder can see the weld crater more easily, better quality welds can consistently be made. The pushing technique is normally used for light-gauge metals. Welds made with this technique are less penetrating and wider be-cause the welding speed is faster.For the best results, you should position the weldment in the flat position. ‘This position improves the molten metal flow, bead contour, and gives better shielding gas protection.After you have learned to weld in the flat position, you should be able to use your acquired skill and knowledge to weld out of position. These positions include horizontal, vertical-up, vertical-down, and overhead welds. The only difference in welding out of position from the fiat position is a 10-percent reduction in amperage.When welding heavier thicknesses of metal with the GMA welding process, you should use the multipass technique (discussed in chapter 3). This is accomplished by overlapping single small beads or making larger beads, using the weaving technique. Various multipass welding sequences are shown in figure 8-32. The numbers refer to the sequences in which you make the passes.4.21 COMMON WELD DEFECTSOnce you get the feel of welding with GMA equipment, you will probably find that the techniques are less difficult to master than many of the other welding processes; however, as with any other welding process, GMA welding does have some pitfalls. To produce good quality welds, you must learn to recognize and correct possible welding defects. The following are a few of the more common defects you may encounter along with corrective actions that you can take.SURFACE POROSITY— Surface porosity usually results from atmospheric contamination. It can be caused by a clogged nozzle, shielding gas set too low or too high, or welding in a windy area. To avoid surface porosity, you should keep the nozzle clean of spatter, use the correct gas pressure, and use a protective wind shield when welding in a windy area.CRATER POROSITY— Crater porosity usually results from pulling the torch and gas shield away before the crater has solidified. To correct this problem, you should reduce
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the travel speed at the end of the joint. You also may try reducing the tip-to-work distance.COLD LAP— Cold laps often result when the arc does not melt the base metal sufficiently. When cold lap occurs, the molten puddle flows into an unwelded base metal. Often this results when the puddle is allowed to become too large. To correct this problem, you should keep the arc at the leading edge of the puddle. Also, reduce the size of the puddle by increasing the travel speed or reducing the wire-feed speed. You also may use a slight whip motion.LACK OF PENETRATION— Lack of penetration usually results from too little heat input in the weld zone. If the heat input is too low, increase the wire-feed speed to get higher amperage. Also, you may try reducing the wire stick out.BURN-THROUGH — Burn-through (too much penetration) is caused by having too much heat input in the weld zone. You can correct this problem by reducing the wire-feed speed, which, in turn lowers the welding amperage. Also you can increase the travel speed. Burn-through can also result from having an excessive amount of root opening. To correct this problem, you increase the wire stick-out and oscillate the torch slightly.WHISKERS — Whiskers are short pieces of electrode wire sticking through the root side of the weld joint. This is caused by pushing the wire past the leading edge of the weld puddle. To prevent this problem, you should cut off the ball on the end of the wire with side cutters before pulling the trigger. Also, reduce the travel speed and, if necessary, use a whipping motion.4.22 DIFFERENCE BETWEEN MIG & TIG WELD-A MIG welder and a TIG welder can be used during welding, which is the process involving the fusing together of metals by melting the metal where they meet and will be joined. In many cases, pressure and / or filler material is used to aid in the fusion process.Both MIG and TIG welds are types of arc welding, which utilizes the concentrated heat of an electric arc to join together metals by fusion of the parent metal by a consumable electrode. Depending on the material to be welded and the electrode used, the process utilizes either direct or alternating current for the welding arc.The MIG weld process, or Metal Inert Gas weld, fuses the metal by heating with an arc. With this type of weld, the arc is placed between the filler metal electrode and the work piece. Shielding is provided by outwardly supplied gas or gas mixtures. A TIG weld or Tungsten Inert Gas, on the other hand, functions by joining metals through the process of heating with tungsten electrodes that do not become part of the completed weld. The process utilizes argon or other inert gas mixtures as shielding and filler metals are rarely used.Some of the basic differences between the two types of welds are that MIG welding is faster than using TIG welding, as utilizing TIG welding requires more skill that MIG welding. A solid wire is used in the MIG Flux Cored Arc Welding-Gas Shield (FCAW-G) while TIG uses a flux cored electrode.Another obvious difference is that TIG uses Tungsten to carry the arc, and a user of a TIG welder needs to have sufficient experience in the craft of welding. A MIG weld user, meanwhile, can carry on working despite being a novice welder.Overall, while both MIG and TIG are gas shielded arc welding processes, the primary difference lies in the way the filler metal is added to produce the weld. With the TIG process, the arc is created between a tungsten electrode mounted in a hand-held torch and
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the work piece to be welded. The welder initiates the arc by means of a switch. The filler metal, in the form of a hand held rod, is then added to the weld puddle by the welder as the torch is manipulated along the joint which is to be welded. The MIG process uses a filler metal which is the electrode and the arc is created when the filler metal comes into contact with the work surface.
Figure- 4.6 Eye protection devices
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CONCLUSION
Undergoing an inplant training in well established and one of the best professionally
managed company like BHOR ENGINEERING PVT. LTD. during these six months of
training was a career. The training offered me the exposure to industrial environment
which cannot be stimulated in any of the engineering colleges. I understood the scope,
functions and job responsibilities of various departments of an industrial organization. It
enabled me to get familiarized with the various processes, products and their applications
along with relevant aspects of shop management. I gained knowledge of various
machines, welding procedures and lot more. I also realized the need for cooperative
efforts of various persons at different levels in achieving set goals and targets. I also
realized the importance of effective communications. The training thus proved to be an
enriching experience which is bound to help me in years to come.
As our training revolves around implementing our technical know how into industrial
environments. I executed various assignments through which I benefited a lot. They are as
follows:-
Study and implementation of KANBAN was a sort of revision, but in heavy engineering
company, KANBAN is a key process in fabrication.
Increasing OEE of Plasma cutting machine taught me the technical fundamentals needed
in the process ,the way it is carried out and the points to taken care of while cutting,
handling and inspecting.
Study of Welding processes at BEPL, deals with technical know how of the process,
specifications and safety precautions taken while operation.
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REFERENCES
BOOKS-[1] Cary, Howard B. and Scott C. Helzer (2005). Modern Welding Technology. Upper Saddle River, New Jersey: Pearson Education ISBN 0-13-113029-3[2] Kalpakjian, Serope and Steven R. Schmid (2001). Manufacturing Engineering and
Technology. Prentice Hall ISBN 0-201-36131-0.
[3] Lincoln Electric (1994). The Procedure Handbook of Arc Welding. Cleveland:
Lincoln Electric ISBN 99949-25-82-2.
[4] Lincoln Electric (1997). MIG/MAG Welding Guide. Accessed July 20, 2005
Accessed July 20, 2005
[5] Weman, Klas (2003). Welding processes handbook. New York: CRC Press LLC ISBN 0-8493-1773-8[6] Miller’s guideline for Gas Metal Arc Welding.
[7] Vorne Industries, The Fast Guide to OEE, 2005.[8] Khanna O P, Industrial Engineering and Management, Dhanpat Rai Publication.[9] Ohno, Taiichi (June 1988). Toyota Production System - beyond large-scale production. Productivity Press. pp. 29. ISBN 0915299143[10] Hansen, Robert C (2005), Overall Equipment Effectiveness (OEE), Industrial Press, ISBN (978-0-8311-)3237-8
LINKS-[1] http://www.graphicproducts.com/tutorials/kanban/index.php[2] http://www.kanban.com/[3] http://en.wikipedia.org/wiki/Kanban[4] http://www.oee.com/[5] http://www.oee.com/calculating_oee.html[6] http://en.wikipedia.org/wiki/Overall_equipment_effectiveness[7] http://en.wikipedia.org/wiki/Welding[8] http://www.aws.org/w/a/[9] http://www.thefabricator.com/ArcWelding/ArcWelding_Article.cfm?ID=9 29
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