Summer Training Report

Computer Numeric Control Machine

& Programmable Logic Control

Bharat Heavy Electricals Limited Haridwar Ranipur

Under Guide Of:- Submitted By :-

Sr. Engineer Shyamveer SinghMr G.S Meena Reg No: 11205816BHEL Haridwar

ACKNOWLEDGEMENT

I am highly thankful to B.H.E.L. engineers and technical staff for providing us vital and valuable information about the different facets of an industrial management system.We express our gratitude to Human Resource and Development department for giving us a chance to feel industrial environment and its working in B.H.E.L. and we are thankful to Mr. G.S meena, Sr. Engineer for giving his precious time and help us in understanding various theoretical and practical aspect of our project on PLC under whose kind supervision we accomplished our project. We are also thankful to Mr. Dhruv Bhargav H.R.D for his kind support.

Shyamveer Singh

B.Tech (ECE)

PREFACE

At very outset of the prologue it becomes imperative to insist that vocational training is an integral part of engineering curriculum. Training allows us to gain an insight into the practical aspects of the various topics, with which we come across while pursuing our vocational training gives us practical implementation of various topics we already have learned and will learn in near future. Vocational training always emphasizes on logic and commonsense instead of theoretical aspects of subject.On my part, I pursued six weeks training at B.H.E.L Haridwar. The training involved a study of various departments of the organization as per the time logically scheduled and well planned given to us. It also involved a project on PLC under the guidance of Mr.G.S meena.The rotation in various departments was necessary in order to get an overall idea about the working of the organization.

Shyamveer Singh

B.Tech (ECE)

INDEX

ABSTRACT iACKNOWLEDGEMENT iiCERTIFICATE iii

Sr. No. Topic Page no.INTRODUCTION 1

1. BHEL 2-3

1.1 OVERVIEW 3

1.2 WORKING AREAS 31.2.1 POWER GENERATION 31.2.2 POWER TRANSMISSION & DISTRIBUTION 3-41.2.3 INDUSTRIES 41.2.4 TRANSPORTATION 4-51.2.5 TELECOMMUNICATION 51.2.6 RENEWABLE ENERGY 51.2.7 INTERNATIONAL OPERATIONS 5-6

1.3 TECHNOLOGY UPGRADATION AND RESEARCH AND 6DEVELOPMENT

1.3.1 HUMAN RESOURCE DEVELOPMENT INSTITUTE 6

1.4 HEALTH SAFETY AND ENVIRONMENT MANAGEMENT 7

1.4.1 ENVIRONMENTAL POLICY 71.4.2 OCCUPATIONAL HEALTH AND SAFETY POLICY 7-81.4.3 PRINCIPLE OF THE “GLOBAL COMPACT” 8

1.5 BHEL UNITS 9

1.6 BHEL HARIDWAR 101.6.1 LOCATION 101.6.2 ADDRESS 101.6.3 AREA 101.6.4 UNITS 10

Sr. No. TopicPage no.

1.6.5 HEEP PRODUCT PROFILE 12-13

2. CNC Machine 2.1 INTRODUCTION 212.2 CNC Machine 222.3 History 222.4 CNC System Element 23

3 CNC System Units 3.1 CPU 24

3.2 Servo operator control 243.3 Machine Control 253.4 PLC 29

4 Modes Of Operation 4.1 Manual Mode Of Operation 26 4.2 Manual Data Input 26

4.3 Automatic Mode 274.4 Reference Mode 274.5 Input Mode 28

4.6 Output Mode 285 Interfacing 29

6 Conclusion 30 FIGURE INDEX

Sr. No. TopicPage no.

1 CNC Victor JF 3VS 212 Open and Close loop System 24

TABLE INDEX

Sr. No. TopicPage no.

1. BHEL UNITS 92. BLOCKS IN HEEP 113. SECTIONS IN CFFP 114. BLADE ROOTS 155. LAYOUT OF BLOCK-3 18

INTRODUCTION

Embarking upon the 50th Golden Year of its journey of engineering excellence, BHEL is an integrated power plant equipment manufacturer and one of the largest engineering and manufacturing company of its kind in India engaged in the design, engineering, manufacture, construction, testing, commissioning and servicing of a wide range of products and services for the core sectors of the economy, viz. Power, Transmission, Industry, Transportation (Railway), Renewable Energy, Oil & Gas and Defence with over 180 products offerings to meet the needs of these sectors. Establishment of BHEL in 1964 was a breakthrough for upsurge in India's Heavy Electrical Equipment industry. Consistent performance in a highly competitive environment enabled BHEL attain the coveted 'Maharatna' status in 2013.

BHEL as a part of Pt. Jawaharlal Nehru's vision was bestowed with the onus to make the country self reliant in manufacturing of heavy electrical equipment. This dream has been more than realised and the contribution in nation building endeavour is going to continue likewise. Today, with 20,000 MW per annum capacity for power plant equipment manufacturing, BHEL's mammoth size of operations is evident from its widespread network of 17 Manufacturing Units, two Repair Units, four Regional Offices, eight Service Centres, eight Overseas Offices, six Joint Ventures, fifteen Regional Marketing Centres and current project execution at more than 150 project sites across India and abroad. The total installed capacity base of BHEL supplied equipment -138 GW in India speaks volumes about the contribution made by BHEL to Indian power sector. BHEL's 57% share

in India's total installed capacity and 65% share in the country's total generation from thermal utility sets (coal based) as of March 31, 2014 stand testimony to this. The company has been earning profits continuously since 1971-72 and paying dividends since 1976-77 which is a reflection of company's commendable performance throughout.

BHEL also has a widespread overseas footprint in 76 countries with cumulative overseas installed capacity of BHEL manufactured power plants nearing 10,000 MW including Malaysia, Oman, Libya, Iraq, the UAE, Bhutan, Egypt and New Zealand.

1.1 OVERVIEW

Bharat Heavy Electricals Limited (B.H.E.L.) is the largest engineering and manufacturing enterprise in India. BHEL caters to core sectors of the Indian Economy viz., Power Generation's & Transmission, Industry, Transportation, Telecommunication, Renewable Energy, Defense and many more.

Established in 1960s under the Indo-Soviet Agreements of 1959 and 1960 in the area of Scientific, Technical and Industrial Cooperation.

BHEL has its setup spread all over India namely New Delhi, Gurgaon, Haridwar, Rudrapur, Jhansi, Bhopal, Hyderabad, Jagdishpur , Tiruchirapalli, Bangalore and many more.

Over 65% of power generated in India comes from BHEL-supplied equipment.Overall it has installed power equipment for over 90,000 MW.

BHEL's Investment in R&D is amongst the largest in the corporate sector in India. Net Profit of the company in the year 2011-2012 was recorded as 6868crore having a high of 21.2% in comparison to last year.

BHEL has already attained ISO 9000 certification for quality management, and ISO 14001 certification for environment management.

It is one of India's nine largest Public Sector Undertakings or PSUs, known as the

NAVRATNAS or 'The Nine Jewels’.

The power plant equipment manufactured by BHEL is based on contemporary technology comparable to the best in the world.

The wide network of BHEL's 14 manufacturing divisions, 4 Power Sector regional centre, over 100 project sites, 8 Service Centre and 18 regional offices, enables the Company to promptly serve its customers and provide them with suitable products, systems and services efficiently.

1.2 WORKING AREAS1.2.1 POWER GENERATION

Power generation sector comprises thermal, gas, hydro and nuclear power plant business as of 31.03.2001, BHEL supplied sets account for nearly 64737 MW or 65% of the total installed capacity of 99,146 MW in the country, as against nil till 1969-70.

BHEL has proven turnkey capabilities for executing power projects from concept to commissioning, it possesses the technology and capability to produce thermal sets with super critical parameters up to 1000 MW unit rating and gas turbine generator sets of up to 240 MW unit rating. Co-generation and combined-cycle plants have been introduced to achieve higher plant efficiencies. to make efficient use of the high-ash-content coal available in India, BHEL supplies circulating fluidized bed combustion boilers to both thermal and combined cycle power plants.

The company manufactures 235 MW nuclear turbine generator sets and has commenced production of 500 MW nuclear turbine generator sets.

Custom made hydro sets of Francis, Pelton and Kaplan types for different head discharge combination are also engineering and manufactured by BHEL.

In all, orders for more than 700 utility sets of thermal, hydro, gas and nuclear have been placed on the Company as on date. The power plant equipment manufactured

by BHEL is based on contemporary technology comparable to the best in the world and is also internationally competitive.

The Company has proven expertise in Plant Performance Improvement through renovation modernization and upgrading of a variety of power plant equipment besides specialized know how of residual life assessment, health diagnostics and life extension of plants.1.2.2. POWER TRANSMISSION & DISTRIBUTION (T & D)

BHEL offer wide ranging products and systems for T & D applications. Products manufactured include power transformers, instrument transformers, dry type transformers, series and stunt reactor, capacitor tanks, vacuum and SF circuit breakers gas insulated switch gears and insulators. A strong engineering base enables the Company to undertake turnkey delivery of electric substances up to 400 kV level series compensation systems (for increasing power transfer capacity of transmission lines and improving system stability and voltage regulation), shunt compensation systems (for power factor and voltage improvement) and HVDC systems (for economic transfer of bulk power). BHEL has indigenously developed the state-of-the-art controlled shunt reactor (for reactive power management on long transmission lines). Presently a 400 kV Facts (Flexible AC Transmission System) project under execution.

1.2.3. INDUSTRIES

BHEL is a major contributor of equipment and systems to industries. Cement, sugar, fertilizer, refineries, petrochemicals, paper, oil and gas, metallurgical and other process industries lines and improving system stability and voltage regulation, shunt compensation systems (for power factor and voltage improvement) and HVDC systems(for economic transfer of bulk power) BHEL has indigenously developed the state-of-the-art controlled shunt reactor (for reactive power management on long transmission lines).Presently a 400 kV FACTS (Flexible AC Transmission System) projects is under execution. The range of system & equipment supplied includes: captive power plants, co-generation plants

DG power plants, industrial steam turbines, industrial boilers and auxiliaries. Water heat recovery boilers, gas turbines, heat exchangers and pressure vessels, centrifugal compressors, electrical machines, pumps, valves, seamless steel tubes, electrostatic precipitators, fabric filters, reactors, fluidized bed combustion boilers, chemical recovery boilers and process controls.

The Company is a major producer of large-size thruster devices. It also supplies digital distributed control systems for process industries, and control & instrumentation systems for power plant and industrial applications. BHEL is the only company in India with the capability to make simulators for power plants, defense and other applications. The Company has commenced manufacture of large desalination plants to help augment the supply of drinking water to people.

1.2.4. TRANSPORTATION

BHEL is involved in the development design, engineering, marketing, production, installation, and maintenance and after-sales service of Rolling Stock and traction propulsion systems. In the area of rolling stock, BHEL manufactures electric locomotives up to 5000HP, diesel-electric locomotives from 350 HP to 3100 HP, both for mainline and shunting duly applications. BHEL is also producing rolling stock for special applications viz., overhead equipment cars, Special well wagons, Rail-cum-road vehicle etc., Besides traction propulsion systems for in-house use, BHEL manufactures traction propulsion systems for other rolling stock producers of electric locomotives, diesel-electric locomotives, electrical multiple units and metro cars. The electric and diesel traction equipment on India Railways are largely powered by electrical propulsion systems produced by BHEL. The company also undertakes retooling and overhauling of rolling stock in the area of urban transportation systems. BHEL is geared up to turnkey execution of electric trolley bus systems, light rail systems etc. BHEL is also diversifying in the area of port handing equipment and pipelines transportation system.

1.2.5. TELECOMMUNICATION

BHEL also caters to Telecommunication sector by way of small, medium and large

switching system.

1.2.6. RENEWABLE ENERGY

Technologies that can be offered by BHEL for exploiting non-conventional and renewable sources of energy include: wind electric generators, solar photo voltaic systems, solar lanterns and battery-powered road vehicles. The Company has taken up R&D efforts for development of multi-junction amorphous silicon solar cells and fuel based systems.

1.2.7. INTERNATIONAL OPERATIONS

BHEL has, over the years, established its references in around 60 countries of the world, ranging for the United States in the west to New Zealand in the far east. These references encompass almost the entire product range of BHEL, covering turnkey power projects of thermal, hydro and gas-based types, substation projects, rehabilitation projects, besides a wide variety of products, like transformers, insulators, switch gears, heat exchangers, castings and forgings, valves, well-head equipment, centrifugal compressors, photo-voltaic equipment etc. apart from over 1110mw of boiler capacity contributed in Malaysia, and execution of four prestigious power projects in Oman, some of the other major successes achieved by the company have been in Australia, Saudi Arabia, Libya, Greece, Cyprus, Malta, Egypt, Bangladesh, Azerbaijan, Sri Lanka, Iraq etc.

The company has been successful in meeting demanding customer's requirements in terms of complexity of the works as well as technological, quality and other requirements viz. extended warrantees, associated O&M, financing packages etc. BHEL has proved its capability to undertake projects on fast-track basis. The company has been successful in meeting varying needs of the industry, be it captive power plants, utility power generation or for the oil sector requirements. Executing of overseas projects has also provided BHEL the experience of working with world renowned consulting organizations and inspection agencies.

In addition to demonstrated capability to undertake turnkey projects on its own, BHEL possesses the requisite flexibility to interface and complement with international companies for large projects by supplying complementary equipment and meeting their production needs for intermediate as well as finished products.

The success in the area of rehabilitation and life extension of power projects has established BHEL as a comparable alternative to the original equipment manufacturers (OEM’S) for such plants.

1.3. TECHNOLOGY UPGRADATION AND RESEARCH & DEVELOPMENT

To remain competitive and meet customers' expectations, BHEL lays great emphasis on the continuous up gradation of products and related technologies, and development of new products. The Company has upgraded its products to contemporary levels through continuous in house efforts as well as through acquisition of new technologies from leading engineering organizations of the world.

The Corporate R&D Division at Hyderabad, spread over a 140 acre complex, leads BHEL's research efforts in a number of areas of importance to BHEL's product range. Research and product development centers at each of the manufacturing divisions play a complementary role.

BHEL's Investment in R&D is amongst the largest in the corporate sector in India. Products developed in-house during the last five years contributed about 8.6% to the revenues in 2000-2001.

BHEL has introduced, in the recent past, several state-of-the-art products developed in-house: low-NOx oil / gas burners, circulating fluidized bed combustion boilers, high-efficiency Pelton hydro turbines, petroleum depot automation systems, 36kV gas-insulated sub-stations, etc. The Company has also transferred a few technologies developed in-house to other Indian companies for commercialization.

Some of the on-going development & demonstration projects include: Smart wall blowing system for cleaning boiler soot deposits, and micro-controller based

governor for diesel-electric locomotives. The company is also engaged in research in futuristic areas, such as application of super conducting materials in power generations and industry, and fuel cells for distributed, environment-friendly power generation.

1.3.1 HUMAN RESOURCE DEVELOPMENT INSTITUTE

The most prized asset of BHEL is its employees. The Human Resource Development Institute and other HRD centers of the Company help in not only keeping their skills updated and finely honed but also in adding new skills, whenever required .Continuous training and retraining, positive, a positive work culture and participative style of management, have engendered development of a committed and motivated workforce leading to enhanced productivity and higher levels of quality.1.4. HEALTH, SAFETY AND ENVIRONMENT MANAGEMENT

BHEL, as an integral part of business performance and in its endeavor of becoming a world-class organization and sharing the growing global concern on issues related to Environment. Occupational Health and Safety, is committed to protecting Environment in and around its own establishment, and to providing safe and healthy working environment to all its employees. For fulfilling these obligations, Corporate Policies have been formulated as.

1.4.1. ENVIRONMENTAL POLICY

Compliance with applicable Environmental Legislation/Regulation.Continual Improvement in Environment Management Systems to protect our natural environment and Control Pollution. Promotion of activities for conservation of resources by Environmental Management. Enhancement of Environmental awareness amongst employees, customers and suppliers. BHEL will also assist and co-operate with the concerned Government Agencies and Regulatory Bodies engaged in environmental activities, offering the Company's capabilities is this field.

1.4.2. OCCUPATIONAL HEALTH AND SAFETY POLICY

Compliance with applicable Legislation and Regulations.

Setting objectives and targets to eliminate/control/minimize risks due to Occupational and Safety Hazards. Appropriate structured training of employees on Occupational Health and Safety (OH&S) aspects. Formulation and maintenance of OH&S Management programs for continual improvement. Periodic review of OH&S Management System to ensure its continuing suitability, adequacy and effectiveness. Communication of OH&S Policy to all employees and interested parties.

The major units of BHEL have already acquired ISO 14001 Environmental Management System Certification, and other units are in advanced stages of acquiring the same. Action plan has been prepared to acquire OHSAS 18001 Occupational Health and Safety Management System certification for all BHEL units.In pursuit of these Policy requirements, BHEL will continuously strive to improve work particles in the light of advances made in technology and new understandings in Occupational Health, Safety and Environmental Science Participation in the "Global Compact" of the United Nations.

The "Global Compact" is a partnership between the United Nations, the business community, international labor and NGOs. It provides a forum for them to work together and improve corporate practices through co-operation rather than confrontation.

BHEL has joined the "Global Compact" of United Nations and has committed to support it and the set of core values enshrined in its nine principles.1.4.3. PRINCIPLES OF THE "GLOBAL COMPACT"

HUMAN RIGHTS 1. Business should support and respect the protection of internationally proclaimed human

rights and.2. Make sure they are not complicit in human rights abuses.

LABOUR STANDARDS 1.Business should uphold the freedom of association and the effective recognition of the right to collective bargaining.

2.Eliminate discrimination. 3.The elimination of all form of forces and compulsory labour. 4.The effective abolition of child labour. 5.Eliminate discrimination.

ENVIRONMENT Businesses should support a precautionary approach to environmental challenges . Undertake initiatives to promote greater environmental responsibility and Encourage the development and diffusion of environmentally friendly technologies. By joining the "Global Compact", BHEL would get a unique opportunity of networking with corporate and sharing experience relating to social responsibility on global basis.

1.5 BHEL UNITS

UNIT TYPE PRODUCT

1. Bhopal Heavy Electrical PartSteam Turbines, Turbo Generators, HydroSets,Switch Gear Controllers

2. HaridwarHydro Turbines, Steam Turbines, GasTurbines, Turbo Generators, Heavy Castings

HEEPHeavy Electrical

Equipement

and Forging, Control Panels, Light Aircrafts,

Plant Electrical Machines.

CFFPCentral Foundry Forge Plant

3. HyderabadIndustrial Turbo-Sets, Compressor Pumpsand Heaters, Bow Mills, Heat Exchangers

HPEPHeavy Power Equipement Plant

Oil Rings, Gas Turbines, Switch Gears,Power Generating Sets.

4. Trichy Seamless Steel Tubes, Spiral Fin

Welded

HPBP High Pressure Boiling Plant Tubes.5. Jhansi Transformers, Diesel Shunt Less AC

locos

TPTransformer Plant and EC EMU.

6. BangloreEnergy Meters, Watt Meters, ControlEquipement, Capacitors, Photo Voltic Panels,

EDN Electronics DivisionSimulator, Telecommunication System, OtherAdvanced Microprocessor based Control

EPD Electro Porcelains DevisionSystem, Insulator and Bushing, CeramicLiners

7. RanipetElectrostatic Precipitator, Air Pre-Heater,Fans, Wind Electric Generators, Desalination

BAP Boiler Auxilary Plant Plants.

8. Goindwal Industrial Valves Plant Industrial Valves & Fabrication

9. JagdishpurHigh tension ceramic, Insulation Plates and

IP Insulator PlantBushings

10. RudrapurComponent Fabrication Plant

Windmill, Solar Water Heating system

11. GurgaonAmorphous Silicon Solar Cell

Solar Photovoltaic Cells, Solar Lanterns,

Plant. Chargers ,Solar clock

1.6. BHEL HARIDWAR

1.6.1. LOCATION

It is situated in the foot hills of Shivalik range in Haridwar. The main administrative building is at a distance of about 8 km from Haridwar.1.6.2. ADDRESS

Bharat Heavy Electrical Limited (BHEL)

Ranipur, Haridwar PIN- 249403

1.6.3. AREA

BHEL Haridwar consists of two manufacturing units, namely Heavy Electrical Equipment Plant (HEEP) and Central Foundry Forge Plant (CFFP), having area

HEEP area:- 8.45 sq km

CFFP area:- 1.0 sq km

The Heavy Electricals Equipment Plant (HEEP) located in Haridwar, is one of the major manufacturing plants of BHEL. The core business of HEEP includes design and manufacture of large steam and gas turbines, turbo generators, hydro turbines and generators, large AC/DC motors and so on.

Central Foundry Forge Plant (CFFP) is engaged in manufacture of Steel Castings:Up to 50 Tons per Piece Wt & Steel Forgings: Up to 55 Tons per Piece Wt.1.6.4. UNITSThere are two units in BHEL Haridwar as followed:

1)Heavy Electrical Equipment Plant (HEEP)

2)Central Foundry Forge Plant (CFFP)

There are 8 Blocks in HEEP:

Blocks Work Performed In BlockI) Electrical Machine Turbo Generator, Generator Exciter , Motor (AC and DC)

II) Fabrication Large Size Fabricated Assemblies or Components

III) Turbines & Steam , Hydro Turbines, Gas turbines, Turbine Blade, Special Tooling.

Auxilary

IV) Feeder Winding of Turbo ,Hydro Generators, Insulation for AC & DC Motors

V) Fabrication Fabricated Parts of Steam Turbine, Water Boxes, Storage Tank, HydroTurbine Parts

VI) Fabrication Fabricated Oil Tanks, Hollow Guide Blades, Rings, Stator Frames andStamping & Die Rotor Spindle, All Dies, Stamping for Generators and MotorManufacturing

VII) Wood Working Wooden Packing, Spacers

VIII) Heaters & LP heaters, Ejectors, Glands, Steam and Oil Coolers, Oil Tank, BearingCoolers Covers

There are 3 Sections in CFFP:

Blocks Work Performed In Block1.Foundry Casting of Turbine Rotor, Casing and Francis Runner

2.Forging Forging of Small Rotor Parts

3.Machine Shop Turning, Boring, Parting off, Drilling etc.

1.6.5. HEEP PRODUCT PROFILE

THERMAL SETS:

Steam turbines and generators up to 500 MW capacity for utility and combined cycle applications Capability to manufacture up to 1000 MW unit cycle.

GAS TURBINES:

Gas turbines for industry and utility application range 3 to 200 MW (ISO). Gas turbines based co-generation and combined cycle system.

HYDRO SETS:

Custom– built conventional hydro turbine of Kaplan, Francis and Pelton with matching generators up to 250 MW unit size. Pump turbines with matching motor-generators. Mini micro hydro sets. Spherical butterfly and rotary valves and auxiliaries for hydro station.

EQUIPMENT FOR NUCLEAR POWER PLANTS:

Turbines and generators up to 500MW unit size. Steam generator up to 500MW unit size. Re-heaters / Separators. Heat exchangers and pressure vessels.

ELECTRICAL MACHINES:

DC general purpose and rolling mill machines from 100 to 19000KW suitable for operation on voltage up to 1200V. These are provided with STDP, totally enclosed and duct ventilated enclosures. DC auxiliary mill motors.

CONTROL PANEL:

Control panel for voltage up to 400KW and control desks for generating stations and EMV sub–stations.

CASTING AND FORGINGS:

Sophisticated heavy casting and forging of creep resistant alloy steels, stainless steel and other grades of alloy meeting stringent international specifications.

DEFENCE:

Naval guns with collaboration of Italy.

INTRODUCTION:

Numerical control (NC) is a method employed for controlling the motions of a machine tool slide and its auxiliary functions with input in the form of numerical data. A computer numerical control (CNC) is a microprocessor-based

system to store and process the data for the control of slide motions and auxiliary functions of the machine tools. The CNC system is the heart and brain of a CNC machine which enables the operation of various machine members such as slides,spindles, etc. as per the sequence programmed into it, depending on the machining operations.The main advantage of a CNC system lies in the fact that the skills of the operator hither to required in the operation of a conventional machine is removed and the part production is made automatic.The CNC systems are constructed with a NC unit integrated with a programmable logic controller (PLC) and some times with an additional external PLC (non-integrated). The NC controls the spindle movement and the speeds and feeds in machining. It calculates the traversing path of the axes as defined by the inputs. The PLC controls the peripheral actuating elements of the machine such as solenoids, relay coils, etc. Working together, the NC and PLC enable the machine tool to operate automatically. Positioning and part accuracy depend on the CNC system's computer control algorithms, the system resolution and the basic mechanical machine accuracy. Control algorithm may cause errors while computing, which will reflect during contouring, but they are very negligible. Though this does not cause point to point positioning error, but when mechanical machine inaccuracies are present, it will result in poorer part accuracy.This chapter gives an overview of the configuration of the CNC system, interfacing and introduction to PLC programming.

CNC Machine:

Numerical control (NC) is a method of automatically, operating a manufacturing machine based on a code, letters, numbers and special characters.The numerical data required to produce a part is provided to a machine in the form of program, called part program or CNC (computer numerical control).

In CNC (Computer Numerical Control), the instructions are stored as a program in a micro-computer attached to the machine. The computer will also handle much of the control logic of the machine, making it more adaptable than earlier hard-wired controllers.

NC & CNC:

The program is translated into the appropriate electrical signals for input to motors that run the machine. A CNC machine is an numerical control machine with the added feature of an on board computer. The computer is referred to as the machine control unit (MCU).

HISTORY

1. In 1775, John Wilkinson- cannon boring machine (lathe). 2. In 1881, Eli Whitney- milling machine. 3. In 1947, Mr. John Parsons began experimenting for using 3-axis curvature data to control the machine tool motion for the production for aircraft components. 4. In 1949, parsons- first NC machine. 5. In 1951, MIT was involved in the project. 6. In 1955, after refinements NC became available in industry 7. Today, modern machinery are CNC milling machines and lathes.

CNC SYSTEM ELEMENTS

A typical CNC system consists of the following six

1.Elements 2.Part program 3.Program input device 4.Machine control unit 5.Drive system 6.Machine tool 7.Feedback system

CNC system basically consists of the following units:

1.Central processing unit (CPU)2.Servo-control unit3.Operator control panel4.Machine control panel5.Other peripheral device6.Programmable logic controller (PLC)

Central Processing Unit (CPU)

The CPU is the heart and brain of a CNC system. It accepts the

information stored in the memory as part program. This data is decoded and transformed into specific position control and velocity control signals. It also oversees the movement of the control axis or spindle whenever  this does not match the programmed values, a corrective action is taken.All the compensations required for machine accuracy (like lead screw pitch error, tool wear out, backlash , e tc . ) a re ca lcula ted by the CPU depending upon the corresponding inputs mad e available to the system. The same will be taken care of during the generation of control signals for the axis movement. Also, some safety checks are built into the system through this unit and the CPU unit will provide continuous necessary corrective actions. Whenever the situation goes beyond cont ro l of the CPU, i t t akes the f ina l ac t ion of shut t ing down the system in turn the machine.

Speed Control Unit

This unit acts in unison with the CPU for the movement of the machine axes. The CPU sends the control signals generated for the movement of the axis to the servo control unit and the servo cont ro l uni t conver t these s ignals in to the sui table d ig i ta l or ana log s igna l to be fed to the machine tool axis movement. This also checks whether machine tool axis movement is at the same speed as directed by the CPU. In case any safety conditions related to the axis are over ruled during movement or otherwise they are reported to the CPU for corrective action.

Servo-Control Unit

The decoded posi t ion and ve loc i ty cont ro l s igna ls , genera ted by the CPU for the axis movement forms the input to the servo-control unit. This unit in turn generates suitable signals as command values. The servo-drive unit converts the command values, which are interfaced with the axis and the spindle motors.The servo-cont ro l uni t rece ives the pos i t ion feedback s ignals for ac tual movement of the machine tool axes from the feedback devices (like linear scales, rotary encoders, resolves, etc.).The velocity feedback is generally obtained through tacho generators. The feedback signals are passed on to the CPU for fur ther process ing. Thus the servo-contro l uni t per forms the data communication between the machine tool and the CPU.As explained earlier, the actual movements of the slides on the machine tool is achieved through servo drives. The amount of movement and the rate of movement are controlled by the CNC system depending upon the type of feedback system used, closed-loop or open-loop system.

Closed-loop System

The closed-loop system is characterized by the presence of feedback. In this system, the CNC system send out commands for movement and the result is continuously monitored by the system through various feedback devices.

Position Feedback 

A closed-loop system, regardless of the type of feedback device, will constantly try to achieve and maintain a given position by self-correcting. As the slide of the machine tool moves, its movement is fed back to the CNC system for determining the position of the slide to decide how much is yet to be traveled and also to decide whether the movement is as per the commanded rate. If the actual rate is not as per the required rate, the system tries to correct it. In case this is not poss ib le , the sys tem declares faul t and in i t ia tes ac t ion for d isabl ing the dr ives and i f  necessary, switches off the machine. Velocity feedback 

In case no time constraint is put on the system to reach the final

programmed position,then the sys tem may not produce the requi red path or the sur face f in ish accuracy. Hence , velocity feedback must be present along with the position feedback whenever CNC system are used for contouring, in order to produce correct interpolation and also specified acceleration and deceleration velocities. The tacho generator used for velocity feedback is normally connected to the motor and it rotates whenever the motor rotates, thus giving an analog output proportional to the speed of motor. The analog voltage is taken as speed feedback by the servo-controller and swift action is taken by the controller to maintain the speed of the motor within the required limits.

Open-loop system

The open loop system lacks feedback. In this system, the CNC system send out signals for movement but does not check whether ac tual movement i s taking p lace or not . S tepper  motors are used for actual movement and the electronics of these stepper motors is run on digital  p u l s e s f r o m t h e C N C s y s t e m . S i n c e s y s t e m c o n t r o l l e r s h a v e n o a c c e s s t o a n y r e a l t i m e information about the system performance, they cannot counteract disturbances appearing during the operation. They can be utilized in point to point system, where loading torque on the axial motor is low and almost constant.

Servo-drive

The servo-drive receives signals from the CNC system and transforms it into actual movement on the machine. The actual rate of movement and direction depend upon the command signal from CNC system. There are various types of servo-drives, viz., dc drives,ac drives and stepper motor drives. A servo-drive consists of two parts, namely, the motor and the electronics for driving the motor.

Operator Control Panel

The opera tor  control panel provides the user interface to facilitate a two-way communication between the user,CNC system and the machine tool.

Video Display Unit (VDU)

The VDU displays the status of the various parameters of the CNC system and the

machine tool. It displays all current information such as:

1.Complete information of the block currently being executed2.Actual position value, set or actual difference, current feed rate, spindle speed3.Active G functions4.Main program number, subroutine number 5.Display of all entered data, user programs, user data, machine data, etc.6.Alarm messages in plain text7.Soft key designation In addition to a CRT, a few LEDs are generally provided to indicate important operating modes and status.

Keyboard

A keyboard is provided for the following purposes:1.Editing of part programs, tool data, and machine parameters.2.Selection of different pages for viewing.3.Selection of operating modes, e.g. manual data input.4.Selection of feed rate override and spindles speed override.5.Execution of part programs.6.Execution of other toll functions.

Machine Control Panel (MCP)

It is the direct interface between operator and the NC system, enabling the operation of the machine through the CNC system.1.Establishing a correct reference point2.Loading the system memory with the required part program3.Loading and checking of tool offsets, zero offsets, etc.For these tasks, the system must be operated in specific.

Modes of operation

1.Manual mode2.Manual data input (MDI) mode3.Automatic mode4.Reference mode5.Input mode6.Output mode

Manual Mode:

I n t h i s m o d e , m o v e m e n t o f a m a c h i n e s l i d e c a n c a r r i e d o u t m a n u a l l y b y p r e s s i n g t h e  particular jog button (+ or -). The slide (axis) is selected through an axis selector switch or  through individual swi tches (e .g . , X+, X- , Y+, Y- , Z+, Z- , e tc . ) . The feed ra te of the s l ide movement is prefixed. CNC system allows the axis to be jogged at high feed rate also. The axis movement can also be achieved manually using a hand wheel interface instead of jog buttons. In this mode slides can be moved in two ways:1.Continuous2.Incremental

Continuous mode

In This mode, the slide will move as long as the jog button is pressed.

Incremental mode

The slide will move through a fixed distance, which is select able. Normally, system allows jogging of axes in 1, 10, 100, 1000, 10000, increments. Axis movement is at a prefixed feed rate. It is initiated by pressing the proper jog+ or jog- key and will be limited to the no of increments selected even if the jog button is continuously pressed. For subsequent movement the jog button has to be released and once again pressed.

Manual Data Input (MDI) Mode

In this mode the following operation can be performed:Building a new part program editing or deleting of part program stored in the system memory entering or editing or deleting of Tool offsets (TO), Zero offsets (ZO), Test data, etc.

Automatic Mode

In this mode the system allows the execution of a part program continuously. The part program is executed block by block. While one block is being executed, the next block is read by the system, analyzed and kept ready for execution. Execution of the program can be one block  after another automatically or the system will execute a block, stop the execution of the next block till it is initiated to do so (by pressing the start button). Selection of part program execution continuously (Auto) or one block at a time (Single

Block ) is done through the machine control  panel.Many systems allow blocks (single or multiple) to be retraced in the opposite direction. Block retrace is allowed only when a cycle stop state is established. Part program execution can resume and its execution begins with the retraced block. This is useful for tool inspection or in case of tool breakage. Program start can be effected at any block in the program, through the BLOCK SEARCH facility.

Reference Mode

Under th is mode the machine can be referenced to i t s home posi t ion so tha t a l l the compensat ions (e . g p i tch er ror compensat ion) can be proper ly appl ied . Par t programs are generally prepared in absolute mode with respect to machine zero. Many CNC systems make it compulsory to reference the slides of the machine to their home positions before a program is executed while others make it optional.

Input Mode and Output Mode

In this mode, the part programs, machine setup data, tool offsets, etc. can be loaded unloaded into from the memory of the system from external devices like programming units, magnetic cassettes or floppy discs, etc. During data input, some systems check for simple errors (like parity, tape format,block length, unknown characters, program already present in the memory,etc.). Transfer of data is done through a RS232C or RS422C port.

Programmable Logic Controller (PLC)

A PLC matches the NC to the machine. PLCs were basically introduced as replacement for hard wired relay control panels. They were developed to be reprogrammed without hardware changes when requirements were altered and thus are reusable. PLCs are now available within creased functions, more memory and large input/output capabilities.gives the generalized PLC block diagram.In the CPU, all the decisions are made relative to controlling a machine or a process. The CPU receives input data, performs logical decisions based upon stored programs and drives the outputs. Connections to a computer for hierarchical control are done via the CPU.The I/O structure of the PLCs is one of their major strengths. The inputs can be push buttons,limit switches, relay contacts, analog sensor, selector switches, proximity switches, float switches, etc. The outputs can be motor starters, solenoid valves, position valves, relay coils,indicator lights, LED displays, etc.The

field devices are typically selected, supplied and installed by the machine tool builder or the end user. The voltage level of the field devices thus normally determines the type of I/O. So, power to actuate these devices must also be supplied external to the PLC. The PLC power supply is designated and rated only to operate the internal portions of the I/O structures, and not the field devices. A wide variety of voltages, current capacities and types of I/O modules are available.

INTERFACING

Interconnecting the individual elements of both the machine and the CNC system using cables and connectors is called interfacing.Extreme care should be taken during interfacing. Proper grounding in electrical installation is most essential. This reduces the effects of interference and guards against electronic shock to personnel. It is also essential to properly protect the electronic equipment.Cable wires of suff ic ient ly la rge cross-sec t ional area must be used. Even though proper  grounding reduces the effect of electrical interference, signal cable requires additional protection.This is generally achieved by using shielded cables. All the cable shields must be grounded at control only, leaving other end free. Other noise reduction techniques include using suppression devices, proper cable separation, ferrous metal wire ways, etc. Electrical enclosures should be designed to provide proper ambient conditions for the controller.

CONCLUSION

This training has proved to be quite faithful. This gave me, a chance to have an encounter with such heavy CNC machines. The architecture of B.H.E.L. ,the way the various units are linked and the way the working of the whole plant is controlled, makes the student realize that engineering is not just the structural description but more of planning and management. It has provided an opportunity to learn that optimization of technology used at proper place and time can save a lot of labour.The training has proved to be immensely helpful as it has helped me to have an exposure of the practical implementation of the theoretical knowledge that I have gained till date.