ABSTRACT

Practical knowledge means the visualization of the knowledge, which we read

in our books. For this, we perform experiments and get observations. Practical

knowledge is very important in every field. One must be familiar with the

problems related to that field so that he may solve them and become a

successful person. After achieving the proper goal in life, an engineer has to

enter in professional life. According to this life, he has to serve an industry,

may be public or private sector or self-own. For the efficient work in the field,

he must be well aware of the practical knowledge as well as theoretical

knowledge. To be a good engineer, one must be aware of the industrial

environment and must know about management, working in the industry, labor

problems etc. so he can tackle them successfully. Due to all the above reasons

and to bridge the gap between theory and practical

our engineering curriculum provides an industrial training of 30 days. During

this period, a student works in the industry and gets all type of experience and

knowledge about the working and maintenance of various types of machinery.

I have undergone my summer training (after 3rd yr.) at TATA GROWTH

SHOP. This report is based on the knowledge, which I acquired during my

training period at the plant.

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CHAPTER– 1

TATA STEEL

1.1 OVERVIEW OF TATA STEEL

Backed by 100 glorious years of experience in steel making, Tata Steel is the

world’s 6th largest steel making company with an existing annual crude steel

production capacity of 30 Million Tons per Annum (MTPA). Established in

1907, it is the first integrated steel plant in Asia and is now the world`s second

most geographically diversified steel producer and a Fortune 500 Company.

Tata Steel has a balanced global presence in over 50 developed European and

fast growing Asian markets, with manufacturing units in 26 countries.

Figure 1.1 Tata Steel main plant (Jamshedpur)

It was the vision of the founder; Jamsetji Nusserwanji Tata, that on 27th

February 1908, the first stake was driven into the soil of Sakchi.  His vision

helped Tata Steel overcome several periods of adversity and the Company

strove to improve against all odds.

We make the difference through:-

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1) Our people, by fostering team work, nurturing talent, enhancing leadership

capability and acting with pace, pride and passion.

2) Our offer, by becoming the supplier of choice, delivering premium products

and services, and creating value with our customers.

3) Our innovative approach, by developing leading edge solutions in

technology, processes and products.

4) Our conduct, by providing a safe working place, respecting the

environment, caring for our communities and demonstrating high ethical

standards.

Tata Steel`s Jamshedpur (India) Works has a crude steel production

capacity of 6.8 MTPA which is slated to increase to 10 MTPA by 2010. The

Company has proposed three projects in the states of Jharkhand, Orissa and

Chhattisgarh in India with additional capacity of 23 MTPA and a Greenfield

project in Vietnam. Through investments in Corus, Millennium Steel (renamed

Tata Steel Thailand) and NatSteel Holdings, Singapore, Tata Steel has created

a manufacturing and marketing network in Europe, South East Asia and the

pacific-rim countries. Corus, which manufactured over 20 MTPA of steel in

2008, has operations in the UK, the Netherlands, Germany, France, Norway

and Belgium.

Tata Steel Thailand is the largest producer of long steel products in

Thailand, with a manufacturing capacity of 1.7 MTPA. Tata Steel has

proposed a 0.5 MTPA mini blast furnace project in Thailand. NatSteel

Holdings produces about 2 MTPA of steel products across its regional

operations in seven countries.

The iron ore mines and collieries in India give the Company a distinct

advantage in raw material sourcing. Tata Steel is also striving towards raw

materials security through joint ventures in Thailand, Australia, Mozambique,

Ivory Coast (West Africa) and Oman Tata Steel’s vision is to be the global

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steel industry benchmark for Value Creation and Corporate Citizenship. Tata

Steel India is the first integrated steel company in the world, outside Japan, to

be awarded the Deming Application Prize 2008 for excellence in Total Quality

Management.

1.2 ABOUT TATA GROWTH SHOP (TGS)

1.2.1 PROFILE

Tata steel growth shop (TGS), a division of Tata steel ltd. is spread in an area

of more than 350 acres of land at Gamharia, district-Saraiekela , about 16

km from Jamshedpur, 250 km Kolkata in eastern part of India. Set against a

picturesque backdrop of lush greenery, TGS forms a part of Adityapur

Engineering Complex of Tata Steel, which spreads over a sprawling 100 acres

of land and 16 km from Jamshedpur.

Figure 1.2 Tata Growth Shop

The complex houses five gigantic, independently laid bays covering an area of

over 56,000 sq m. The main strength of the growth shop is its multi-

disciplinary engineering approach to the design and manufacture of high

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precision capital equipment. Having had access to world class technologies

through selective collaboration, with international leaders in industry, TGS has

become the first name in India in the field of heavy engineering plant and

equipment manufacture.

The complex houses 9 covered sheds covering an area of above 72000

sq meters. The main strength of the Growth Shop is its multidisciplinary

engineering approach for the design, Manufacturing and Supply of high

precision equipment for various industrial sectors such as Steel, Aluminum

Energy & Power, Railways, Cement plant and Ports etc.

TGS has large-scale fabrication facilities with CNC profile cutting

machines, heavy plate bending machines, press brakes and host of other plate

forming machines. Its crane lifting capacity of up to 100 tones enable the Shop

to handle heavy assemblies. Facilities for shot blasting and cleaning of plates

ensure smooth surface finish.

A combination of meticulous training and experience enables TGS Shop

floor team to utilize these excellent facilities for maintaining sustained high

quality of production.

1.2.2 PRODUCT OFFERINGS

The product range offered by TGS includes:

1) Blast furnace

2) Transfer cars

3) Rolling mills equipment

4) EOT cranes up to 500 T capacity

5) Floor frame assembly of Diesel locomotive parts

6) Stator frames and fabricated structures etc. in Power plants

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CHAPTER – 2

COMPUTER NUMERICAL CONTROL

2.1 INTRODUCTION TO CNC

NC system came into existence in 1952 & it opened a new era in automation.

NC stands for NUMERICAL CONTROL. It means controlling a machine tool

by means of a prepared programme, which consists of blocks or series of

numbers.

An important advancement in the philosophy of NC M/C tools, which

took place during early 1970s, was this shift towards the use of computers

instead of controller units in NC system. This produced “COMPUTER

NUMERICAL CONTROL (CNC)”. CNC is a self contained NC system for a

single machine tool including a dedicated computer controlled by stored

instructions to perform some/all of the basic NC-functions. CNC has become

much more widely used for manufacturing systems (e.g., Machine Tools,

Welders, and Laser Beams Cutters, Water Jet Cutting) mainly because of its

flexibility & due to the availability & declining costs of computers.

2.2 Basic differences between conventional and CNC machine

In conventional machines when a job comes, the operator has to start it

manually at his own skill and experience. It varies from man to man as well as

the cutting parameters and the tools used by them. There is a chance of human

error always in calculation as well as in operation of the machine tools.

On conventional machine tool the time taken for a job is much more in

comparison to CNC machine because of the manual operation and the

checking of job dimensions after each pass by the operator and also time taken

in calculating over for the next pass. On conventional machines the tool

changing also consumes more time because of manual setting and changing.

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On CNC machine tools when the job comes, the preplanning is very necessary

because all the passes to prepare a job will be determined earlier and according

to these passes programmer, tools and other fixtures are prepared. For these

items there should be sufficient time to take care of above said items. On these

machines the skill of the operator do not effect on the job accuracy because

everything is controlled by a computer itself. There is a no chance of human

error during operation if it ones approved. On CNC machine tools, tools

changing, speeds, feeds and other cutting parameter controlled automatically

by computer. Hence the time consumed for above said operation is negligible

in comparison to conventional machine tools.

2.3 WORKING OF CNC

Everything that an operator would be required to do with conventional

machine tools is programmable with CNC machines. Once the machine is

setup and running, a CNC machine is quite simple to keep running. In fact

CNC operators tend to get quite bored during lengthy production runs because

there is so little to do. With some CNC machines, even the work piece loading

process has been automated. (We don't mean to over-simplify here. CNC

operators are commonly required to do other things related to the CNC

operation like measuring work pieces and making adjustments to keep the

CNC machine running good work pieces)

Let's look at some of the specific programmable functions.

2.3.1 MOTION CONTROL

All CNC machine types share this commonality: They all have two or more

programmable directions of motion called axes. An axis of motion can be

linear (along a straight line) or rotary (along a circular path). One of the first

specifications that implies a CNC machine's complexity is how many axes it

has. Generally speaking, the more axes, the more complex the machine.

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The axes of any CNC machine are required for the purpose of causing

the motions needed for the manufacturing process. In the drilling example,

these (3) axis would position the tool over the hole to be machined (in two

axes) and machine the hole (with the third axis). Axes are named with letters.

Common linear axis names are X, Y, and Z. Common rotary axis names are A,

B, and C.

2.3.2 PROGRAMMABLE ACCESSORIES

A CNC machine wouldn't be very helpful if all it could only move the work

piece in two or more axes. Almost all CNC machines are programmable in

several other ways. The specific CNC machine type has a lot to do with its

appropriate programmable accessories. Again, any required function will be

programmable on full-blown CNC machine tools.

2.3.3 AUTOMATIC TOOL CHANGER

Most machining centers can hold many tools in a tool magazine. When required, the required tool can be automatically placed in the spindle for machining.

2.3.4 SPINDLE SPEED AND ACTIVATION

The spindle speed (in revolutions per minute) can be easily specified and the

spindle can be turned on in a forward or reverse direction. It can also, of

course, be turned off.

2.3.5 COOLANT

Many machining operations require coolant for lubrication and cooling

purposes. Coolant can be turned on and off from within the machine cycle.

2.4 THE CNC CONTROL

The CNC control will interpret a CNC program and activate the series of

commands in sequential order. As it reads the program, the CNC control will

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activate the appropriate machine functions, cause axis motion, and in general,

follow the instructions given in the program.

Along with interpreting the CNC program, the CNC control has several other

purposes. All current model CNC controls allow programs to be modified

(edited) if mistakes are found. The CNC control allows special verification

functions (like dry run) to confirm the correctness of the CNC program. The

CNC control allows certain important operator inputs to be specified separate

from the program, like tool length values. In general, the CNC control allows

all functions of the machine to be manipulated.

2.5 CONFIGURATION OF CNC SYSTEM

A CNC system basically consists of the following:

1) Central Processing Unit

2) Panel Processing Unit

3) Machine Control Panel

4) I/O modules

5) Servo drives and control

Figure 2.1 CNC System

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2.5.1 CENTRAL PROCESSING UNIT

Central Processing Unit, the CPU, is the heart and brain of a CNC system.

This translates the part program stored in memory to position signals. It also

oversees the movement of the control axis or spindle and whenever this does

not match with the program signal, a corrective action is taken.

All the compensations required for machine accuracies (Lead screw,

pitch error, tool wear out etc.) are calculated by the CPU and provided in the

data for axis movement. This unit also checks whether all the safety conditions

on the machine have been fulfilled, and whenever this does not happen, it

provides the necessary corrective action. If the situation becomes beyond the

control of CPU, it takes the final action of shutting down the machine.

2.5.2 PANEL PROCESSING UNIT

Figure 2.2 Panel Processing Unit

Panel processing unit provides the user interface to facilitate two way

communications between the user and the CNC system/machine tool. This

consists of two parts:-

1. Video display unit

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2. Keyboard

1. VIDEO DISPLAY UNIT

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

machine tool. It displays all current information such as:-

1. Complete information on the block currently being executed.

2. Actual position value, set/actual difference, current feed rate, spindle speed.

3. Active G functions.

4. Main program number, subroutine number.

5. Display of all entered data, user programs, user data, machine data etc.

6. Alarm messages in plain text.

7. Soft key designations.

In addition to CRT, few LED’s are generally provided to indicate important

operating modes and status.

Video display units may be of two types:-

1. Monochrome or black and white displays

2. Color display

2. KEY BOARD

Key board is provided for the following purposes:

1. Editing of part programs, tool data, and machine parameters.

2. Selection of different pages for viewing.

3. Execution of part programs.

4. Execution of other tool functions.

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2.5.3 MACHINE CONTROL PANEL

Figure 2.3 Machine Control Panel

It is direct interface between the operator and the NC system, enabling the

operation of the machine through the CNC system.

2.5.4 MODES OF OPERATION

Generally the CNC systems can be operated in the following modes:-

1. Manual mode

2. Manual data input mode

3. Automatic mode

4. Input/output mode

1. Manual mode

In this mode, movement of a machine slide can be done manually by pressing.

The particular buttons (+ve or-ve). Selection of the slide (axis) is done through

an axis selector switch or through individual switches (e.g., X+, X-, Y+, Y-,

Z+, Z-etc). Feed rate of the slide movement is prefixed. Some CNC systems

allow axis to be jogged at high feed rate (rapid) also.

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2. Manual data input mode

In this mode the following operations can be performed:-

1. Editing of part programs stored in system memory

2. Building a new part program

3. Entering tool offsets in the system memory

3. Automatic mode (auto and single block)

In this mode the system allows the execution of 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 blocks 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. Selection of part programs block by block (auto), or one

block at a time (single block) is done through machine control panel.

4. Input/output mode

Under input mode, the part programs, machine setup data, tool offsets etc. can

be loaded into the memory of the system from external sources like

programming units, magnetic cassettes or floppy drives. Transfer of data is

though RS232C or RS422C port.

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2.5.5 PLC I/O MODULES

Figure 2.4 PLC I/O Module

PLC I/O (72/48) module consists of following:

1) 72 digital inputs (24V)

2) 48 digital outputs (24V, 0.25A)

3) 50pin standard connectors for inputs and outputs

4) 24 I/P / 16 O/P per connector

5) Connectable to distribution boards or to terminal adapters

6) Up to 2 boards possible (144 I / 96 O)

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2.5.6 SERVO DRIVES AND CONTROL

Figure 2.5 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

depends upon the command signal from the 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 electronic for

driving the motor.

Feed motors Spindle motor

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Encoder

Figure 2.6 Motors and Encoder

CNC system gives the command for axis movement, and other machine tool

functions depending upon the part program or manual data inputs or manual

operation (JOG mode). Serve control unit also receives the feedback signals of

the actual movement of the machine tool slides from feedback devices e.g.,

digital encoders etc. and pass this information to the CPU for processing. In

actual sense, the servo control unit performs the data communication between

the machine tool and CPU .Actual movement of the slides on the machine tool

is achieved through servo drives. The amount of movement and rate of

movement and of movement may be controlled by the CNC system depending

on the type of feedback system used i.e. closed loop or open loop system.

1. CLOSED LOOP SYSTEM

In the closed loop system, the CNC System sends out command for movement

and the result is continuously monitored by the system through various

feedback devices. There are generally two types of feedback requirements to a

CNC system namely velocity feedback and position feedback. Normally a

tacho generator is employed for velocity feedback and an encoder or a linear

scale is used for position feedback.

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Figure 2.7 Closed Loop System

2. VELOCITY FEEDBACK

Tachogenerator 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 the motor. This 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.

3. POSITIONAL FEEDBACK

As the slide of the machine tool moves, its movement is feedback 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 possible, the system declares a fault and initiates action

for disabling the drives and if necessary, switches off the machine.

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Figure 2.8 velocity and position feedback

4. OPEN LOOP SYSTEM

In the open loop system, the CNC system sends out signals for movement but

does not check whether actual movement is taking place or not. Stepper

motors are used for actual movement and the electronics of these stepper

motor is run on digital pulses from the CNC system. As the system controllers

have no access to any real-time information about the system performance,

they can be utilized in point-to-point system, where loading torque on the axial

motors is low and almost constant.

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Figure 2.9 Open Loop System

2.6 DNC

Once the program is developed (either manually or with a CAM system), it

must be loaded into the CNC control. Though the setup person could type the

program right into the control, this would be like using the CNC machine as a

very expensive typewriter. If the CNC program is developed with the help of a

CAM system, then it is already in the form of a text file. If the program is

written manually, it can be typed into any computer using a common word

processor (though most companies use a special CNC text editor for this

purpose). Either way, the program is in the form of a text file that can be

transferred right into the CNC machine. A distributive numerical control

(DNC) system is used for this purpose.

A DNC system is nothing more than a computer that is networked with one or

more CNC machines. Until only recently, rather crude serial communications

protocol (RS-232c) had to be used for transferring programs. Newer controls

have more current communications capabilities and can be networked in more

conventional ways (Ethernet, etc.). Regardless of methods, the CNC program

must of course be loaded into the CNC machine before it can be run.

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CHAPTER – 3

CNC PART PROGRAMMING

3.1 INTRODUCTION

PART PROGRAMME is the sequence of operation of the part (job) to be

produced like the operation layout, compiled in a language such that the CNC

system can understand to execute it to produce a job (part) on the machine. It

is a set of instructions in coded form written in a special form called part

programming format.

The control cabinet contains a MICRO-PROCESSOR that interprets this

set of coded instructions to produce a component or PART – hence the term

“PART PROGRAMME”. The programmes are written in ALPHA –

NUMERIC code, (ALPHA as in ALPHABET i.e. letter; NUMERIC i.e.

numbers). The program contains all the information’s to make a part, i.e. slide

movement, speed & feed, tool changes, coolant on/off etc.

3.1.1 WHAT IS PROGRAMMING?

The numerical control machine tool receives information through a punched

paper tape or floppy disc. The tape is prepared as per program manuscript

written for the job/operations to be carried out on the CNC machine. The

program is prepared by listing the coordinate values (X, Y, Z) of the entire tool

paths as suited to machine to indicate the type of movement required (point-to-

point, straight or circular) from one coordinate to another. Also, t he

coordinates are suffixed with miscellaneous codes for initiating machine tool

functions like start, stop, spindle CW or CCW, coolant ON/OFF, optional stop,

etc. All these elements in a line of information form one meaningful command

for the machine to execute and are called a block of information.

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Part programming can be classified into two categories:

1) Manual part programming

2) Computer-Aided part programming

1) Manual part programming:- In manual part programming the programmer

writes the machining instructions on a special form called Part Programming

Format. The instructions must be prepared in a very precise manner because

the NC tape is prepared directly from the manuscript.

2) Computer-aided/assisted part programming:- Manual part programming

becomes an extremely tedious task and subject to error if the job has

complicated shape. In this case we take help from the computer to make the

part program.

3.2 KNOWLEDGE TO DO PART-PROGRAMMING

The programmer should have a very sound knowledge about the following

aspects:-

1. Machine tool specification

The programmer must be well aware about the specification/capacity of the

CNC machine tool and the control system on which the required porkpies is to

be machined. The programmer must also understand the “Axis configuration”

of the machine.

2. Geometry of the workpiece

The programmer should understand mechanical drawings very clearly so that

he/she can understand the geometry of the work piece.

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3. NC–Tooling for tool selection

The programmer should be well conversant with the NC – Tooling system so

that he /she can select correct types of cutting tools (inserts and tool holders)

for different operations.

4. Method of loading and clamping a workpiece on the machine tool

Considering the shape of the workpiece and the operations to be carried out the

programmer has to decide the way the work is to be loaded and champed on

the table of the machine tool. So the programmer must have clear concept

about this.

5. Machining sequence

The programmer has to decide the sequence of operation through which the

operations will be performed to finish the job. So he / she must have sound

knowledge about the sequence of operations.

6. Cutting parameters

The programmer must be well aware of the Cutting Parameters i.e. cutting

speed, Feed and Depth of cut as the programmer has to decide these before

writing a part programme.

3.3 TERMINOLOGIES USED IN PART PROGRAMMING

3.3.1 ABSOLUTE PROGRAMMING

In this system the co-ordinates are mentioned in the programme with respect to

one reference point called Datum.

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Figure 3.1 Absolute programming co-ordinates

3.3.2 INCREMENTAL PROGRAMMING

In incremental system the co-ordinates of a point are mentioned in the

programme with respect to the previous point.

Figure 3.2 Incremental programming co-ordinates

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3.4 BLOCKS

Block is the smallest part of the programme. It contains the commands used to

execute operations on CNC machine. The block is composed of words and

always ends with the characters “END OF BLOCK” for every single

movement of the machine an independent block is need.

A block contains the following WORDS:

1) Sequence / Block number __________________________N

2) Preparatory Functions _____________________________G

3) Dimensions _____________________________________X, Y, Z

4) Arc Center Offset ________________________________ I, J, K

5) Feed Function ___________________________________F

5) Speed Function __________________________________S

6) Tool Function ___________________________________T

7) Miscellaneous Function ___________________________M

Example: N001 GO1 S7 MO3 TO1 X05000 Y08000 EOB

3.5 FUNCTIONAL CODES

3.5.1 PREPATATORY FUNCTIONS (G-CODES)

These are the commands which prepare the machine for different modes of

movements like Positioning, Contouring, Thread cutting etc. There are 100 G-

Codes.

Example:-

1) G00 ------------------ Rapid Traverse

2) G01 ------------------ Linear Movement

3) G02 ------------------ Circular Interpolation (CW)

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3.5.2 DIMENSIONAL DATA(X, Y, Z & I, J, K)

Movement of machine tool slides in one or more axes is determined by the

dimensional data entered in the programme.

Example: X04000 Y08000 etc.

3.5.3 MISCELLANEOUS FUNCTIONS (M-CODES)

These are the functions pertaining to the other functions like Coolant ON/OFF

spindle CW/CCW programmer STOP etc. There are 100 M-Codes.

Example:

1) M02 ------------------------- Programme stop

2) M03 ------------------------- Spindle rotation ( “CW” ).

3) M07 ------------------------- Coolant “ON”

4) M13 ------------------------- Spindle “ON” (CW) + coolant “ON” etc.

3.5.4 SPEED FUNCTIONS (S-CODES)

This function pertains to the speed of the spindle. It is denoted by “S” word

followed by some digit.

Example: S7 (means Spindle Speed = 2000 R.P.M. in case of Terco mill

Trainer)

Similarly,

1) S1 --------------- 500 R.P.M.

2) S2 --------------- 750

3) S3 --------------- 900

4) S4 --------------- 1250

5) S5 --------------- 1500

In some of the production machine direct value of R.P.M. is accepted i.e. for

indicating RPM 1250. We can write in the program S 1250.

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3.5.5 FEED FUNCTION (F-CODE)

This function pertains to the feed rates of the slides. It is denoted by letter F

followed by some digits.

Example: G94 F080 (means Feed rate per minute of slide = 80mm / minute).

3.5.6 TOOL FUNCTION (T-CODE)

This function pertains to the selection of required tool for the particular

operation. It is donated by the letter “T” accompanied by a digit (tool number)

Example: T2 (means Tool number 2)

3.6 WHAT THE PROGRAMMER HAS TO DO?

1. Study the drawing thoroughly.

2. Identify the type of the material to be machined.

3. Know the specifications and functions of machine to be used.

4. Decide the dimension and mode –metric or inch.

5. Decide the coordinate system –absolute or incremental.

6. Identify the plane of cutting.

7. Know the cutting parameters for the job combination.

8. Decide the federate programming – mm/min or mm/revs.

9. Check the tooling required.

10.Establish the sequence of machining operations.

11.Identify whether use of special features like subroutines is required or not.

12.Decide the mode of storing the part program once completed

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CHAPTER–4

ELECTRICAL ASSEMBLY

4.1 MPCB’S

Figure 4.1 MPCB’S

4.1.1 INTRODUCTION

MPCB (Motor protection circuit breakers) offers wide range up to 100A &

high breaking capacity up to 100Ka. MPCBs are most suitable for switching &

protection three phase induction motors up to 45KW at 415VAC and for loads

up to 100A.Its compact design saves size of a panel by having both functions

of MCCB and Thermal Overload Relay.

MPCB delivers more efficiency through various functions & compact

design such as:

1. Protection of group installation.

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2. Protection of circuits

3. Wide range of ambient temperature compensation.

4. Phase failure protection.

MPCB offers excellent features for ease of both end users & panel

makers such as:

1. Compact width in three sizes: 32AF : 45mm , 63AF : 55mm & 100AF :

70mm

2. Distinct three position: ON-TRIP-OFF

3. Complete range of common accessories like Aux. Switch, Alarm Switch,

Fault alarm Switch, Shunt trip & under voltage trip. Accessories remain

common for entire range.

4. Locking of handle in OFF position.

5. Class 10 over load trip characteristics.

6. Trip test facility.

4.2 CONTACTORS

Figure 4.2 Contactor

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4.2.1 INTRODUCTION

A contactor is an electrically controlled switch used for switching a power

circuit, similar to relay except with higher amperage ratings. A contactor is

controlled by a circuit which has a much lower power level than the switched

circuit. Contactors come in many forms with varying capacities and features.

Unlike a circuit breaker, a contactor is not intended to interrupt a short

circuit current.

Contactors range from those having a breaking current of several amps

and 24 V DC to thousands of amps and many kilovolts. The physical size of

contactors ranges from a device small enough to pick up with one hand, to

large devices approximately a meter (yard) on a side.

Contactors control electric motors, lighting, heating, capacitor banks and other

electrical loads.

4.2.2 CONSTRUCTION

A contactor is composed of three different items. The contacts are the current

carrying part of the contactor. This includes power contacts, auxiliary contacts,

and contact springs. The electromagnet provides the driving force to close the

contacts. The enclosure is a frame housing the contact and the electromagnet.

Enclosures are made of insulating materials like Bakelite, Nylon 6

and thermosetting plastics to protect and insulate the contacts and to provide

some measure of protection against personnel touching the contacts. Open-

frame contactors may have a further enclosure to protect against dust, oil,

explosion hazards and weather.

A basic contactor will have a coil input (which may be driven by either

an AC or DC supply depending on the contactor design). The coil may be

energized at the same voltage as the motor, or may be separately controlled

with a lower coil voltage better suited to control by programmable

29

controllers and lower-voltage pilot devices. Certain contactors have series coils

connected in the motor circuit; these are used, for example, for automatic

acceleration control, where the next stage of resistance is not cut out until the

motor current has dropped.

4.2.3 OPERATING PRINCIPLE

When current passes through the electromagnet, a magnetic field is produced,

which attracts the moving core of the contactor? The electromagnet coil draws

more current initially, until its inductance increases when the metal core enters

the coil. The moving contact is propelled by the moving core; the force

developed by the electromagnet holds the moving and fixed contacts together.

When the contactor coil is de-energized, gravity or a spring returns the

electromagnet core to its initial position and opens the contacts.

4.3 TIMERS

Timers used are of two types i.e.

1. Pneumatic timers

2. Electronic timers

4.3.1 PNEUMATIC TIMERS

1. How Pneumatic Timers Works?

Pneumatic timers are used in areas where the use of an electrical current is

undesirable or dangerous. (Many oil refineries use pneumatic timers instead of

electric clocks. An electric spark in such a manufacturing establishment can

easily start a fire.)The operation of these devices can be a little confusing, but

the most basic pneumatic timer involves a piston and a control valve. It is

necessary to hook all pneumatic equipment up to an air supply for proper

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operation. An air supply slowly pushes the piston towards the end of the

chamber. A small valve on the other end controls the flow of air. The piston

will eventually reach its intended destination. It will take the piston some time

before it accomplishes this task, however. Other types of air timers use a

different controlling mechanism, but the piston chamber is used most often.

(Creating or filling a vacuum is another common timer control technique.)

Figure 4.3 Pneumatic Timer

2. How the Piston Gets Slowed?

Some doors contain a mechanism that prevents a door from being slammed.

When too much air builds up behind the door, the door will slow down until

and close at a more manageable pace. The piston works in a similar fashion.

The valve at the end of the piston chamber prevents the air from escaping too

quickly, and thus allows a precise time to be set by the user of a pneumatic

timer.

3. What Pneumatic Timer Controls Allow?

The controls for a pneumatic timer allow the user to set up how much time will

pass before the piston opens the chamber. The dial, essentially, controls how

far the valve opens when the timer is in operation. Thus, industries can get

precise timing without relying on electrical timing devices.

4.3.2 ELECTRONIC TIMERS

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Electronic timers are essentially quartz clocks with special electronics, and can

achieve higher precision than mechanical timers. Electronic timers have digital

electronics, but may have an analog or digital display. Integrated circuits have

made digital logic so inexpensive that an electronic timer is now less

expensive than many mechanical and electromechanical timers.

Figur 4.4 Electronic Timer

4.4 MCB’S

A circuit breaker is an automatically-operated electrical switch designed to

protect an electrical circuit from damage caused by overload or short circuit.

Its basic function is to detect a fault condition and, by interrupting continuity,

to immediately discontinue electrical flow. Unlike a fuse, which operates once

and then has to be replaced, a circuit breaker can be reset (either manually or

automatically) to resume normal operation. Circuit breakers are made in

varying sizes, from small devices that protect an individual household

appliance up to large switchgear designed to protect high voltage circuits

feeding an entire city.

All circuit breakers have common features in their operation, although details

vary substantially depending on the voltage class, current rating and type of

the circuit breaker.

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The circuit breaker must detect a fault condition; in low-voltage circuit

breakers this is usually done within the breaker enclosure. Once a fault is

detected, contacts within the circuit breaker must open to interrupt the circuit.

Some mechanically-stored energy (using something such as springs or

compressed air) contained within the breaker is used to separate the contacts,

although some of the energy required may be obtained from the fault current

itself. Small circuit breakers may be manually operated; larger units

have solenoids to trip the mechanism, and electric motors to restore energy to

the spring.

.

Figure 4.5 MCB’S

4.4.1 TYPES OF CIRCUIT BREAKER

1. LOW VOLTAGE CIRCUIT BREAKER

Low voltage (less than 1000 VAC) types are common in domestic, commercial

and industrial application, include:

MCB (Miniature Circuit Breaker)—rated current not more than 100 A.

2. MAGNETIC CIRCUIT BREAKER

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Magnetic circuit breakers use a solenoid (electromagnet) whose pulling force

increases with the current. Certain designs utilize electromagnetic forces in

addition to those of the solenoid. The circuit breaker contacts are held closed

by a latch. As the current in the solenoid increases beyond the rating of the

circuit breaker, the solenoid's pull releases the latch which then allows the

contacts to open by spring action.

Figure 4.6 Magnetic Circuit Breaker

3. HIGH VOLTAGE BREAKERS

Electrical power transmission networks are protected and controlled by high-

voltage breakers. The definition of high voltage varies but in power

transmission work is usually thought to be 72.5 kV or higher, according to a

recent definition by the International Electrotechnical Commission (IEC).

High-voltage breakers are nearly always solenoid-operated.

4.5 PUSH BUTTONS

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A push-button (also spelled pushbutton) or simply button is a simple switch

mechanism for controlling some aspect of a machine or a process. Buttons are

typically made out of hard material, usually plastic or metal. The surface is

usually flat or shaped to accommodate the human finger or hand, so as to be

easily depressed or pushed. Buttons are most often biased switches, though

even many un-biased buttons (due to their physical nature) require a spring to

return to their un-pushed state. Different people use different terms for the

"pushing" of the button, such as press, depress, mash, and punch.

Figure 4.7 Push Buttons

Push buttons are often color-coded to associate them with their function so that

the operator will not push the wrong button in error. Commonly used colors

are red for stopping the machine or process and green for starting the machine

or process.

Red push buttons can also have large heads (called mushroom heads) for

easy operation and to facilitate the stopping of a machine. These push buttons

are called emergency stop buttons and are mandated by the electrical code in

many jurisdictions for increased safety. This large mushroom shape can also

be found in buttons for use with operators who need to wear gloves for their

work and could not actuate a regular flush-mounted push button. As an aid for

operators and users in industrial or commercial applications, a pilot light is

commonly added to draw the attention of the user and to provide feedback if

the button is pushed. Typically this light is included into the center of the

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pushbutton and a lens replaces the pushbutton hard center disk. The source of

the energy to illuminate the light is not directly tied to the contacts on the back

of the pushbutton but to the action the pushbutton controls. In this way a start

button when pushed will cause the process or machine operation to be started

and a secondary contact designed into the operation or process will close to

turn on the pilot light and signify the action of pushing the button caused the

resultant process or action to start.

In industrial and commercial applications, push buttons can be linked

together by a mechanical linkage so that the act of pushing one button causes

the other button to be released. In this way, a stop button can "force" a start

button to be released. This method of linkage is used in simple manual

operations in which the machine or process have no electrical circuits for

control.

4.6 TERMINAL BOX (T.B)

Figure 4.8 Terminal box

The Terminal Box provides easy, reliable connections for splicing wires and

cables. All connections are housed in a weather-resistant enclosure. The

terminal box can simplify and speed up the task of wiring the weather station

sensors, sensor interface module (SIM), and communication lines.

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4.7 LIMIT SWITCHES

Figure 4.9 Limit switches

A mechanical limit switch interlocks a mechanical motion or position with an

electrical circuit. A good starting point for limit-switch selection is contact

arrangement. The most common limit switch is the single-pole contact block

with one NO and one NC set of contacts; however, limit switches are available

with up to four poles.

Limit switches also are available with time-delayed contact transfer.

This type is useful in detecting jams that cause the limit switch to remain

actuated beyond a predetermined time interval.

Other limit switch contact arrangements include neutral-position and

two-step. Limit switches feature a neutral-position or center-off type transfers

one set of contacts with movement of the lever in one direction. Lever

movement in the opposite direction transfers the other set of contacts. Limit

switches with a two-step arrangement, a small movement of the lever transfers

one set of contacts, and further lever movement in the same direction transfers

the other set of contacts.

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Maintained-contact limit switches require a second definite reset motion.

These limit switches are primarily used with reciprocating actuators, or where

position memory or manual reset is required. Spring-return limit switches

automatically reset when actuating force is removed.

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CONCLUSION

I fell highly overwhelmed as I got such opportunity of being a part of TGS as a

trainee. It was a great experience and i learnt a lot from it. I find no suitable

words to express my profound, sincere and heart full thanks to TGS for their

prestigious guidance, support and supervision. Their occasional words of

advice would surely act as a beacon of light. It was due to their cheerful and

sincere co-operation which made my training a fruitful, pleasant and life time

experience.

Last but not the least, I would like to thank the TGS Engineers, my

colleagues and teachers who helped me in preparing this seminar report. I hope

this report comes out to be useful in understanding the technology

implemented in the industry. This valuable training let me understand the

world of instrumentation applied and used in industries.

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BIBLIOGRAPHY

[1] Debashish Chatterjee, “CNC part-programming”, Tata Steel, SNTI,

Jamshedpur, Aug 2008, page no.1-28.

[2] John Parsons, “CNC”, http://www.invent.org/hall_of_fame/118.html

[3] Kenneth Youssefi, “Product design and manufacturing”, print 2005, page

no. 56-154

[4] Mr. K.N. Choubey, “CNC Machine”, Tata Steel, SNTI, Jamshedpur,

March 2009, page no. 1-35

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