AN OVERVIEW OF BHEL

In the past independence era when India was moving towards industrialization, the major thrust of the government was in the core sector and this sector was given to public sector. With this objective heavy electrical limited was set up in Bhopal in August, 1956 with a view to reach self-sufficiency in industrial products and power equipment. This plant was setup under technical collaboration of M/S AEI U.K.

Three more plants were subsequently set up at Tiruchy, Hyderabad and Haridwar with soviet and Czechoslovakian assistance in May 1965, December 1965 and January 1967 respectively.as there was a need for an integrated approach for the development of power equipment to be manufactured in India, heavy electrical limited, Bhopal was merged into BHEL in 1974.

MANUFACTURING UNITS OF BHEL

First generation units

• Bhopal : heavy electrical plant

• Haridwar : heavy electrical equipment plant

• Hyderabad : heavy electrical power equipment plant

Second generation units

• Tiruchy : high pressure boiler plant

• Jhansi : transformer and locomotive plant

• Haridwar : central foundry and forge plant

• Banglore : electronics division and electro porcelain division

• New manufacturing units

• Ranipet : boiler auxiliaries plant

• Jagdishpur : insulator plant

• Govindwal : industrial valve plant

• Rudrapur : component & fabrication

• Banglore : energy system division

SW0T ANALYSIS OF B.H.E.L

Strength

• Low cost producer of quality equipment due to cheap labor and fully depreciated plants.

• Flexible manufacturing setup

• Big entry barrier due to high replacement of its manufacturing facilities.

• Comprehensive turn-key experience from product design to commissioning.

Weakness

• High working capital requirement due to its exposure to cash starved SEB’s.

• Inability to provide project financing.

Opportunities

• High expected growth in power sector (7000 MW/per annum needs to be added).

• High growth forecast in India’s index of industrial production would increase demand for industrial equipment such as motors and compressors.

Threats

• Technology suppliers are becoming competitors with the opening of the Indian economy.

• Fall in global equipment prices can affect profitability.

PRODUCT PROFILE

BHEL offers a very large range of products. It has a very large product profile, which is as follows:-

Thermal sets

Gas turbine

Hydro sets

Equipment for nuclear power plants

Boiler and pressure vessels

Heat exchangers

Boiler auxiliaries

Valves

Pumps

Power station electronic equipment

Switch gear

Bus duct

Transformers

Electrical machines

Controller

Insulators and ceramic liners

Capacitors

Industrial sets

Compressors

Industrial sets

Compressors

Transportation equipment (locomotives)

Oil field equipment

Casting and forgings

Seamless steel tubes

Silicon rectifiers

Thermistor equipment

Power devices

Non-conventional energy systems

Light aircraft for aviation sector

System and services

BHARAT HEAVY ELECTRICALS LIMITED JHANSI

INTRODUCTION

This unit of Jhansi was established around 14 km from the city on the Jhansi-Lalitpur road. It is BHEL second generation plant, and was set up with an estimated cost of 16.22 crore which includes 2.1 crore for the township. The president of India, the late Mrs. Indira Gandhi, laid down its foundation and the commercial production of unit began in 1976-1977 with an output of Rs 53 lacks.

This plant of BHEL is equipped with the most modern manufacturing, processing and testing facilities for the manufacturing of power, special and instrument transformer, diesel shunting locomotives and AC/DC locomotives. The layout of the plant is well streamlined to enable smooth flow of the material from the raw material stage to the finished goods. All the feeder bays have been laid perpendicular to the main assembly bay and each feeder bay raw materials smoothly gets converted to sub-assemblies, which after inspection are sent to the main assembly bay.

The raw materials that are produced for manufacturing are used only after a through material testing in the testing lab with strict quality checks at various stages of production. This unit of BHEL is basically engaged in the production of various types of transformers and capacities with the growing competition in the transformer section. In 1985-86 the re-powering of BHEL took place, but it took a complete year for manufacturing to commence again. In 1987-88 BHEL had progressed a step further in undertaking the production of ac locomotives also. The future also is very bright for this institution for the target set is a turnover of 500 crore for the next fiscal year and with its history, BHEL will be able to make it.

THE PRODUCT PROFILE OF BHEL JHANSI

PRODUCTS RATINGS

Power transformer 250 MVA Up to 220 KV classSpecial transformer Up to 110 KVESP transformer 100KV, 1400mAFreight loco transformer 3900 to 5400 KVA & 6500 KVA (3 phase)ACEMU transformer Up to 1000 KVA, 25KV(1 phase), 1385

KVA(3 phase)Dry type transformer Up to 3150KVABus duct generating voltage Up to 15.75 KVInstrument transformer (vt &ct) Up to 220 KVDiesel and electric loco Up to 2600 HPAC/DC locomotives 5000 HPOverhead equipment cum test car.

BHEL JHANSI LAYOUT

CLASSIFICATION OF SHOPS

FABRICATION

Fabrication refers to the process of production of any job and the process is undertook in three separate areas namely bay-0, bay-1 and bay-2.

Bay-0

This is the preparation shop where the raw materials are sent after examination and testing for the necessary pre-processing. The following machines are used here in –

Planner machine – to reduce thickness

Shearing machine – for desired cutting

CNC/ANC flame-cutting machine – for cutting complicated shafts using oxy-acetylene shafts using oxy-acetylene flames

Bending machine

Rolling machine

Flattening machine

Nibbling machine

Bay-1

This is the assembly shop where different parts of tank come from bay-0. Here welding processes are used for assembly after which a rough surface is obtained. A grinder running at a constant 1200 rpm is used to remove this roughness.

Bay-2

This assembly shop deals with making the following:

Tank assembly

Tank cover assembly

End frame assembly

Foot assembly

Cross assembly

Core feed assembly

Pin and pad assembly

Before assembly short blasting (firing of small materials i.e. acid picketing) is done on different parts of job to clean the surface before painting. After assembly some tests are carried out known as non-destructive tests.

Ultrasonic test: to detect the welding faults. The CRO shows high amplitude waves at the fault place.

Die penetration test: red solution is put at the welding and then cleaned. After sometime a white solution is applied and appearance of red spots indicate fault.

Magnetic crack detection: magnetic field is created and then iron powder is put at the welded area. If the powder sticks it indicate a fault.

X-ray test: it is the same as human x-ray testing and fault is seen on an X-ray film.

Bay-3

Bay-3 basically comprises of the following three sections:

1. Machine section

2. Copper section

3. Tooling section

1. Machine section

The operations to form small components of power and traction transformers are done in this section. The shop consists of the following:

• Central lathe : on this machine facing and threading is done.

• Turret lathe : its function is same as central lathe.

• Capstan lathe : it is a belt driven lathe machine.

• Radial arm drilling machine : used for drilling & boring.

• Horizontal boring machine : is computerized and is used to make bores, facing etc.

• Milling machine : horizontal milling machine is used for making gears and cutting operations. Vertical milling machine is used for facing and t-slot cutting.

2. Copper section

All processing related to copper is done here. The various machines used in this section are:

• Tube slitting machine : this machine is develop here and is used for cutting the tube along its diameter.

• Shearing machine : it is operated hydraulically and it has a V-shaped blade of 15mm thickness

• Die and punching machine : it is also hydraulically operated and has a die and punch for making holes

• Hydraulic machine : it is used for bending the job up to 90 degree.

• Shearing machine : it is used to cut the job along the width.

• Fly press machine : it is used to press the job.

• Bend saw machine : is used for cutting jobs having a small thickness.

3. Tooling section

Tools are repaired in this section and the machines operating in this section are:

• Blade sharpening machine : it sharpens the blade(of cnc cropping machine) using a circular diamond cutter.

• Mini surface grinder : is used for grinding and has a grinding wheel made of “Aluminium oxide”

• Drill grinding machine : to grind the drills.

• Tool and surface grinding machine : this is especially used to grind the tools used in bay-7.

BAY -4

This is the winding section, and the following types of windings are made here:

• Reverse section winding

• Helical winding

• Spiral winding

• Interleaved winding

• Half section winding

There are four types of coil fixed in a transformer:

• Low voltage coil(LV)

• High voltage coil(HV)

• Tertiary coil

• Tap coil

The type of winding depends upon job requirement. Also, the width and thickness of conductor are designed by design department. Conductors used for winding are in the form of long stripes of copper wire wound on a spool, covered with cellulose paper for insulation.

For winding, first the mould of diameter equal the inner diameter of the required coil is made. The diameter of the mould is adjustable as its body is made up of interlocking wooden sections. The moulds are of belly type, link type and cone type.

BAY-5

It is core punching section. The lamination used for making the core of Power, Dry type and ESP transformers are cut here.

CRGOS (cold rolled grain oriented silicon steel) is used for lamination which is imported from japan, U.K. and Germany. It is available in 0.27 and 9.28mm thick sheets, 1m wide and measured in kgs. The sheets are coated with a very thin layer of insulating material called “caritas”.

For the purpose of cutting and punching the core, three types of machines are installed in the shop.

• Slitting machine : it is used to cut CRGOS sheets in different width. It has circular cutter whose position can be changed as per requirement.

• CNC cropping line pneumatic : It contains only one blade that can rotate 90 degree above the sheet. It is operated pneumatically.

• CNC cropping line hydraulic : it is also used to cut CRGOS. It has two blades, one is fixed and other can rotate 90 degrees above the sheet.

BAY-6

Single phase traction transformers for AC locomotives are assembled in this section. These freight locomotives transformers are used where there is frequency in speed. In this bay core winding and all the assembly and testing of traction transformer is done.

Three phase transformer for ACEMU are also manufactured here. The supply lines for this transformer are of 25 KV and power of the transformer is 6500KVA.

The tap changer of rectifier transformer is also assembled in this bay. Rectifier transformer is used in big furnace like the thermal power stations.

BAY-7

This is insulation shop. The insulation materials are used in various types of transformer. These materials are:

Press paper: 0.2 to 0.5 mm thick.

Press board: 1.0 to 38 mm thick.

Pre compressed board: 1.0 to 30 mm thick

Bakelite: 10 to25 mm thick

Grey press board: 1.5 mm thick

Fiber glass: 1 to 3 mm thick

Epoxy glass: 10 to 35 mm thick

NBC (naporenion bonded cork sheet) : 3,6,10,12 mm thick

Silicon rubber: 1,3,6 mm thick

Nitric rubber: 3 to 12 mm thick- PVA (poly vinyl alcohol) is used as additive.

Machines used in this shop are:

• Rolling machine

• Circle cutting machine

• Bending machine

• Press machine

• Dimension saw

• Drilling machine

• Bend saw machine

• Shearing machine or gullatins machine

BAY-8

It can be called as purely assembly shop. The two types of transformers are assembled here are Electrostatic precipitator (ESP) and Instrument transformer

1. Electrostatic precipitator (ESP): Used in thermal power plant to remove precipitate carbon from smoke coming out of chimneys.

ESP is of two types-

• Silicon oil type

• Transformer oil type

Manufacturing of ESP started in 1986-87, with present manufacturing capacity of nearly 220 transformers a year. Each costing 4 to 5 lacs.

2. Instrument transformer: they are used for measurement. Actual measurement is done by the measuring instrument but these transformers are used for the purpose of stepping down the voltage to protect the measuring instrument. They are of two types:

• Current transformers: Basically a step down transformer. Since current cannot be measured at high rating so it is stepped down to measured value and then measured through an ammeter connected across secondary winding corresponding to line value.

• Voltage transformer: Same concept as above. Apart it has a top chamber, bushing and a bottom chamber as well.

Steps taken for the manufacturing of transformer in this shop are as follows:

Core making and coil winding assembly is done initially.

Assembly is then kept in and over at 100 degree C.

Other accessories are fitted in transformer to form Atg.

Whole unit is then kept in a tank.

Then it is kept in vaccume type vessel twice.

Oil is then poured in the transformer in vaccume and tested for required temperature and pressure.

Then sent for final testing after that painting is done. Temp. indicator, rollers etc. are attached.

BAY-9

Three types of transformers are fabricated in the bay:

• Power transformers

• Dry type transformers

• Rectifier type transformers

Manufacturing stages involved:

Core building

Job unlacing

Bottom coil support given

Coil assembly

Top insulation

Replacing

Terminal gear mounting

Trial tanking

Vapour phase processing

Final servicing

Testing

Ratio test resistance test

Magnetizing current test

2kva test

Tanking

Case fitting

Vapour phase processing and oil filling

Case fitting

Transformer commercial (TRC)

The objective of this department is interaction with the customers. It brings out tenders and notices and also responds to them. It is this department that bags contract of building transformers. After delivery, regarding faults this department does failures and maintenance.

One of the major tasks of this department is to decide profits over negotiations. Transformer industry has become very competitive, and the company offering the lowest price gets the contract but this process may continue leading to very low profits. To avoid this situation, a body by the name of the Indian Electrical Manufacturers Association (IEMA) was set up. This association helps maintain a healthy competitive atmosphere in the manufacturing of electrical appliances.

The main work of the TRC can be classified as:

Tenders and notices

Intraction with the design department

Place of work

Approximate cost of work

Earnest money

Place and time of viewing contrast documents

Place and time of obtaining tender documents

Deciding time upto which tender documents will be sold

The amount, if any, to be paid for such documents

The place, date and time of submission of tenders and opening of tenders.

Transformer engineering (TRE)

The transformers manufactured in BHEL Jhansi range from 10 MVA to 240 MVA and upto 220 KVA. The various transformers manufactured in this unit are:

1. Power transformers

o Generator transformers

o System transformers

o auto transformers

2. Special transformer

o Freight loco transformers

o ESP transformers

o Instrument transformers

o Dry type transformers

All the above transformers are oil cooled except for dry type which is air cooled.

Technology

This department analyses the changed taking place in the world and suggests changes and upgrades accordingly. This is very important department because the products must not get obsolete in the market or else they will be rejected by the customer.

The function of technology department can be classified as:

• Processing sequence : the sequence of processes of manufacturing is decided for timely and economic completion of the job.

• Operation time estimate : it includes incentive scheme management.

• Allowed operation time : it includes incentive amount and time.

• Facilities identification : it includes looking for new equipment or plant or tools to increase productivity.

• Special process certification : special processes are the ones requiring expertise, for example identifying errors, cracks, air bubbles in wielding.

• Special tools requirement : special tools allotted, if possible, else the design has to be reconsidered.

• Productivity projects compilations : it includes the initial analysis of the problem and their appropriate solutions to enhance productivity.

Locomotive production (LMP)

The products mainly produced here are:

• Alternating current locomotive (AC loco)

• Wag-5H

• AC/DC loco

• WCAM-2P

• WCAM-3

Where the abbreviations stand for:

W-broad gauge

AC- Running in AC mode

DC- running in DC mode

G-hauling goods train

P-hauling passenger train

M-hauling passenger and goods

• Diesel electric locomotive shunting (DESL):350HP and 700 HP

• Single power pack (SSP): one 700 HP m/c is made as a single unit. It is a meter gauge locomotive.

• Twin power pack (TPP): two 350 HP m/c are combined in one engine and can be operated individually or in combination depending on the load.

• 450HP, 1400HP, 1150HP,1350 HP, 2600HP.

Also the following non-conventional products are designed and developed for the Indian railways based on their requirements:

• OHE(overload electrical) recording and testing cars

• UTV(Utility vehicles)

• RRV(Rail cum road vehicle)

• DETV(Diesel electric tower car)

• PRV(Battery powered road vehicle)

• BCM(Blast cleaning machine)

• 200 ton well wagon for BHEL haridwar

Locomotive manufacturing (LMM)

This section deals with the manufacturing of locomotives parts which includes parts like:

• Under frame on which the locomotive is build.

• Super structure : the shell made up of mild steel

• Dc motor

• Alternator

• Compressor

• Flower

• Static rectifier – MSR

• Static converter – SC

• Exchanger

• Bogie : the wheel arrangement of loco is called bogie. It contains wheel axel arrangement, suspension and brake rigging.

• Traction transformer : is fixed on the under frame and gets supply from an overhead line by an equipment called pantograph. The transformer steps down voltage and is fitted with a tap changer.

Railways have two types of supplies 25KV single phase 50 Hz AC and 1500 V DC. An AC/DC loco is able to work on both these supplies for e.g.WCAM-3.

The machines used in this shop are:

• Copper machine

• Asquith cnc machine (bogie machine center)

• Hydraulic press

• Radial arm drilling machine

• Turret lathe

• Axel drilling machine

• Centre drilling and facing machine

• Axel turning machine

• Churchill machine tool

Bus duct

Bus ducts are used as connections between generators and transformers. They are used in power connections over 1500MV. It is an assembly of bus bars with associated joints connections and supporting insulation within a grounded metal enclosure.

Types:

1. Isolated phase bus duct – high current rating

2. Segregated phase bus duct – low current rating

Main parts of bus duct:

1. Enclosure – aluminium sheets 6 – 7 m is used

2. Conductor – aluminium made circular, square, rectangular or octagonal.

3. Insulator – for conductor mounting purpose. Made of either epoxy or porcelain material.

4. Heater and thermostat – only required in segregated once due to low current rating.

Other accessories of bus duct manufactured here are:

• Rubber bellows

• Seal of bushings

• Air pressurization equipment

• Hot air blower

Central quality service

This is where all the finished products are inspected, checked, sent back for rectification or sent to the testing area.

Central testing consists of the following areas of interest:

1. Quality : inspection and evaluation of the finished goods for self-assurance and customer satisfaction.

2. Quality assurance : checking procedures and inspection of the goods and customer supervision for providing complete satisfaction to the customer.

3. Quality control : assuming stringent methods of job processing to enhance quality and ensure that all defects are noted and then product is sent for rectification.

4. Quality inspection : activities such as measuring, testing, gauging one or more characteristics of a product or service and comparing these with the specified requirements to determine conformity, are termed as quality inspection.

INTRODUCTION

CNC machine tools have been widely accepted as time proven standard manufacturing techniques all over the world. In India too CNC machine have picked up momentum and Indian industries are going for more and more CNC machines.

Numerical control turns machine tools into a flexible production unit with a multitude of possible applications. Although at first they were mainly used for the manufacturing of geometrically complex parts. Numerical control was latter used for added efficiency in the medium batch production of turned and milled parts. Now the next step is being taken with the introduction of numerical control in all sector of production. The aim in all the cases is to combine high productivity with flexible possibilities of NC technology.

Other machine processes are being added to turning and milling which may be described as the classical NC applications. Conventional methods are being replaced by NC for sheet metal working processes of punching, nibbling and cutting. Productivity increases multifold using numerical control with grinders, gear hobblers and spark erosion

Numerical control is the most sophisticated form of automatic control of a machine tool. The data necessary for producing the part is called “part program”. It is inserted into the control system through a suitable input medium and the control system operates the machine to produce the part with a higher degree of precision, accuracy and reliability and generally have high precision, accuracy, high rigidity, high rate of material removal capability and high productivity. The part program consists of set instruction comprising of:

1. Dimensional data, which defines the size and shape of the component.

2. Technological data, which defines the sequence of operations, speeds, feeds etc.

3. Auxiliary data such as coolant on/off, spindle on/off, tool clamp/unclamp etc.

The instruction is at some stage or the other in the form of set of coded numbers and hence the term “numerical control”.

Numerical control was applied to machine tools in 1950s by Prof. John T. Parson. The first NC machines was produced by converting a three- axis hydraulic servo controlled copy milling machine by joint efforts of Prof. John of Massachusetts University and air force. The control system was quite crude and cumbersome consisting a large array of cabinets and was based on vaccum tube technology.

The control system has since then undergone several stages of development such as semiconductors transistor, small to medium scale integrated circuit technology etc. these were hard wired systems. The required logic was obtained by physically wiring the necessary hardware elements by dedicated integrated circuits. Computer Numerical Control (CNC) was introduced in 1980s. In this case control system was built around a

mini or a microcomputer and all the logic functions are achieved by a set of software instruction the logic function are achieved by a set of software instruction.

The present generation of CMS system is a microprocessors oasis systems with single or multi-microprocessors having large control and data processing power. With the advent of CNC the earlier hard wire NC systems have become absolute through the words.NC and CNC are synonymously used in present’s context they invariably referred to CNC systems.

PRINCIPLES OF CNC MACHINE

Electronic industries association defines numerical control as a system in which actions are controlled by direct insertion of numeric data. The system must automatically interpret at least some portion of data. It means control by numbers. The main function is to control the displacement and positioning of slides, spindles, speed feed rates, selection of tools and many other auxiliary functions. CNC directs the machine tool to achieve all these function in a very controlled and synchronized manner. The main element that comprise CNC machine tools are:

Control system CNC

The machine tool

Feedback devices

Operator’s control

Electrical cabinet

A CNC production facility needs three pieces of equipment:

A computer:

The computer is used to draw the design. However, the design is only picture and the CNC machine cannot use this to manufacture the product. The computer software must also convert the drawing into numbers (coordinates) that the CNC machine can use when it starts to cut and shape the material.

An interface:

A computer cannot be directly connected to a CNC machine. The computer is connected to an interface. This converts the signal from the computer to a form that CNC machine understands. The signal are in the form of digital signals when they are sent to the CNC machine.

CNC machine:

The signal from the interface controls the motors on CNC machine. The signals determine the way the vice moves. The vice moves in three directions X, Y and Z. The signals also control the speed of the cutting tool.

FEATURES OF CNC MACHINES

1. Structure:

CNC machine are built to have a very rigid structure to meet the requirements of high productivity and high accuracy. Welded steel structure has the advantage of high stiffness to weight ratio. The necessary damping is achieved through friction in the welded joints. Fine-grained cast structure has the advantage of internal damping due to granular structure of the material.

2. Slide ways

CNC machine tools use anti-friction slide-way elements such as recirculating ball bushings. Some of the manufacturers (THK Co. Japan) of slide way element offer ball bushing. These types of guide-ways are called “LM” guides and are used in low cost machines like FANUC Tape center model. Some manufactures use nonmetallic liners such as Poly Tetra Fluoro Ethylene (PTFE), Epoxy liners, and thermosetting resin liners. The most popular of these liners are “Trucite” and the “rulon”. The liners have negligible difference co-efficient of static or dynamic friction and hence eliminate the phenomenon of stick slip.

3. Spindle drive:

High power and high speed are common features of CNC machines spindle drives of high productivity. DC motor with SCR control is commonly used to provide step less variation of wide range spindle speeds in two or three ranges of late AC motor spindle drive with frequency and voltage regulation is becoming popular. Some machines offer spindle speeds upto 6000 and 1000 rpm.

Regenerative spindle drive is used in some machines to save energy one of the horizontal spindle machining centers with 25 HP and 45000rpm.

4. Feed drive:

Majority of CNC machine tools use permanent type DC motors with SCR control or width modulated drives. The motor drives the slides through precision preloaded ball screw and nut. Preloaded rack and pinion drivers are used where long transfers are involved. AC servo motors with variable frequency regulation have been in some machines. Rapid transverse rates of 10m/min are common. Some machines have rapid rates of up to 15m/min.in some positioning applications like turret-punch presses, rapid transverse up to 50m/min have been used.

5. Measuring system:

Measuring system facilitates continuous monitoring of the position of the slides and provides position feed-back to the servo drive. Both direct and indirect measuring systems use linear scales mounted directly on slides with a corresponding pick-up head.

Indirect measuring systems use brushless synchronic resolvers or optical encoders or rotary inductosyus mounted on the motors or at the free end of the screw. A resolution of 0.001 mm at the slides can be easily achieved.

6. Accuracy:

Positioning accuracy of 0.001/300mm and 0.025 over the entire transverse repeatability of 0.005mm is generally available. Indexing accuracy of 10 sec of arc and repeatability of 5 sec of arc is commonly provided. Higher accuracies are available on precision machines. Positioning of 0.005mm/1000mm and repeatability of 0.002mm indexing accuracy of 3 sec of arc and repeatability of 1 sec of arc has been achieved. Positioning accuracy of CNC machine can be provided by axis calibration features.

THE ELEMENT OF CNC SYSTEM

The basic elements of CNC system are:

Control panel

Control circuit

Tape reader

Programmable machine interface

Power supply unit

CONTROL WITH A MINI COMPUTER/MICROPROCESSOR

CNC machines employ a microcomputer and semiconductor memories as the central processing unit. This offers the manufacturer t produce hardware at a reasoning cheaper price independently of the machine technology.

The microprocessor in an electronic LSI device, which consist of an arithmetic logic unit, General registers, instruction registers, program conductor address lines, data lines and control lines. The microprocessors have their own instruction sets.

FUNCTIONS OF CNC

1. Machine tools control: it is prime function of the CNC system to control the machine tool. This involves conversion of the part program instruction into machine tool motion through the computer interface and servo system.

2. in process compensation: it is closely related function to machine tool control. This evolves the dynamic correction of the machine tool motions for changes of errors, which occurs during the processing. The main operations are as follows:

• Adjustment for errors sensed by in-process inspection probes and gauges

• Computation of an axis position when an inspection probe is used to locate a datum reference on a work part.

• Offset adjustment for tool radius and length.

• Adaptive control adjustment to speed and feed.

• Computation of predicted tool life and selection of alternative tooling when indicated.

3. improved programming and operating features: the soft wired control has permitted the introduction of many continent programming and operating features. The main features are as follows:

• Editing of part programs at the machine.

• Graphic display of the tool path to verify the shape.

• Provision of various types of interpolation, circular, parabolic, exponential etc.

• Support of old customary units and new metric units.

• Use specially written subroutines.

• Manual data input.

• Local storage of more than single part program.

4. Diagnostics: presently CNC machine are equipped with a diagnostics capabilities to assist in maintaining and repairing the system.

CLASSIFICATION OF CNC SYSTEM

1. Based on feedback control.

2. Based on motion control system

1. Based on feedback control: in the CNC machines, it is feasible from the control point of view to relate the behavior of a particular variable (velocity/position of tool or job) to one corresponding variable.

To control the position/velocity of a machine slide, a group of electro-mechanical, pneumatic or hydraulic components are used which are collectively known as servomechanisms. The output from the data handling equipment (one data for each axis of machine motion) is passed through separate channels to servo system, based on feedback control, can be approached in three ways:

a) open loop control system: a control system, in which the final output value is not directly measured and checked against the desired value, is known as open loop control system. The final value may, however, be implicitly known providing there has been no malfunction.

In open loop control system, there is no feedback device to measure the actual position of tool slide on the work table. Hence, it cannot be compared and verified with the positional value given in the command.

So, the system appears to be an ‘open’ in the sense that it does not respond depending upon the position value of tool/work. The indication, that the desired location has reached, is the end of input command signal to the servo meter.

Applications of O.L.C.S.

• Open loop closed system are best suited for following applications:

• Light duty machinery upto 5KW and with torque of 200 Nm.

• Less memory can be spent.

• Not much accuracy required.

• Less maintenance is required due to absence of monitoring devices.

b) Closed Loop Control System: a control system in which the displacement of the machine slide is balanced with respect to input signals mainly by the signal received from feedback devices, is known as closed loop system. In this system there are two input signals to drive a motor. One command signal due to which servo motor is driven, as soon as the displacement takes place the position sensor known as transducer, gives the reading whether the position sensor has been achieved generates another signal or not. This actual position is fed to the comparator device, which compares it with the command signal and produces an electrical signal proportional to the difference between the two. This signal is fed to the servo motor through an amplifier to move the machine slide in a direction to reduce the difference. This loop is followed again and again till the difference between the two signals (input and feedback) becomes zero and the machine slides comes to rest in the correct position. This mechanism takes care of the inertia effects of the machine slide.

In addition to above, another feedback transducer is used to control the velocity of motor in the case of continuous path system. It is essential to ensure that the cutter follows the path as required by the profile.

Application of C.L.C.S.

• It is used for getting higher degree of accuracy during the machining operations.

• Most of the contouring controls are closed loop systems.

c) semi closed loop control system: in these systems a transducer is not used for measuring the exact position of the machine slide, but is derived from the rotary motion of the lead screw by a pinion and gear arrangement. Thus the linear displacement of the machine slide is directly proportional to the rotary displacement. This system is ‘closed’ in the sense that it gives a feedback for displacement but ‘not closed’ in the scene that it largely depends on the accuracy of the lead screw or the gear arrangement. These systems reduce the bulkiness by removing one part i.e. positional transducer.

2. Based on motion control system: some machine tools like drilling, boring and milling require that the cutting tool and the work piece be placed at certain positions and

also be moved relative to each other. Based on the relative motion NC machine can be classified as:

a) point to point motion control system: Point-to-point (PTP) motion control systems are those in which importance is given to position the cutting tool at a predefined location relative to the work piece. The machining operation is done only after the tool has taken particular position w.r.t. position of work or vice versa, i.e. movement of slide ceases. Hence, it is required that the tool reaches the particular fixed point in shortest time span and shortest path. Due to this reason, PTPs are also called positioning type (P-type) systems. As the machine is not utilized as it moves from one position to another, the movement takes place very rapidly.

The PTP machine are the cheapest and simplest in construction and are best suitable for drilling, punch pressed, boring, spot welding and zig boring machines.

b) Straight line motion control system: the NC system in which the tool works along a straight line in the direction of a major co-ordinates axis, such as along the direction of feed during turning, boring or milling operation at a controlled rate, are known as straight-line control system. As most of the straight line cutting NCs can work as PTP system also so they are an extension of the PTP systems. Usually P-type NC machine are not capable of taking shortest path straight line be used to machine along diagonal line, by calculating and displacing the slides continuously to reach the desired point. Here the tool dimensions are very important, as grinding it will reduce their size and hence, the size of component can be changed. These are best suited for plain turning and face milling,vertical and horizontal milling.

c) Contouring/continuous path motion control system: the NC system in which the position of the table along with the speed (velocity) and feed of tool each under continuous i.e. the cutting takes place while the position of work piece and tool are changing, are known as continuous motion control systems. Each axis of motion moves simultaneously and motion and all with different speeds, which can also change. For example a parabolic curve has speed change in sine on one axis and with cosine rate on other axis. These are mostly used for making contouring profiles.

These are the most complex, costly and versatile control systems and usually require the assistance of a computer, because of large data regarding positional values to be processed continuous path control are popular for fusion welding flame cutting etc.

d) Combined motion control system: All the above mentioned PTP, straight lined and contouring motion control systems have individual specially I operations for taking advantages of these specialties, the control system are combined in C-I and P-L groups.

For example PTP systems are faster as comparing to contouring mode systems, so both of these can be combined if a profile is having some portion as contour and other requires only positioning. Thus, implementing PTP in later stages of operation increases the speed. In C-L type motion control system, contour milling is carried out by using any two axes out of three continuously for the work and depth of cut with variable feed rate along the third axis of the tool. Most of the milling machine uses this type of combination.

In P-L type motion control systems, the point-to-point control is done along X and Y axis, and line control is done in the axis cutting i.e. Z-axis. Due to these systems are sometimes also called as 2PL systems. In most of the jig boring, horizontal boring and drilling machines these types of control systems are used.

P-L-C type motion control systems are having 3 or 4 linear axis to be controlled continuously and 2 or 3 rotary movements along with the positioning facility. This combination is used for complex contouring operations to be carried out on machining centers.

CNC CO-ORDINATE SYSTEM:

“The distance or angle which specifies the position of a point, line, circle or any other geometrical figure with reference to a series of intersecting planes or planes and cylinders (usually three) defines a co-ordinate system”. For calculating the position of the tool and the work piece relatively to each other and also direction of motion giving the value of displacement, we need to know the co-ordinates. Any controlled movement, whether it is translation or rotational, it is known as axis and co-ordinate system of axes is established with respect to machine table. Most of CNC machines have two axes X and Y for controlling the table movement. Third Z axis is responsible for the tool as in case of drilling machine. For turning, there are only two axes, X for location of cutting tool radially and Z for the axis of rotation of work piece.

The guiding principles, which best describe the relative movement of the cutting tool to the work piece, is right hand co-ordinate system, for finding the positive and negative directions of motion. There are two methods of listing the co-ordinates of points in NC system, which can be used independently or in combination:

1. Absolute co-ordinate system

2. Incremental co-ordinate system

CNC MACHINES IN BHEL JHANSI UNIT:

The different CNC machines which serve some special purpose in this unit are:

CNC Oxyacetylene flame cutting machines

This machine is used for cutting M.S. sheets. This machine can cut up to 300mm thick sheet. It has four burners, which can work simultaneously.

• Control system: ESAB German (NCE-510)

• Axes: there are two axes in the machine, in the x axis tool can move up to 7m and 3.5m in y axis.

• Drive: DC

• Feedback rotary encoders

CNC cropping line

The cropping line CNC machines are used to cut CORGO sheets for construction of core transformer. First machine has been manufactured by George German with the control system from Siemens 810D. This machine consists of mainly two tools: punch and swing shear for cutting laminations as required by the program. The other machine has been manufactured Soener Company. It has two punches, one fixed shear and one movable shear, which can shear straight as well as 45 degree. It consists of 1 tip cut and 1-v cut also.

• Control system: Siemens 810d

• Axes: one axis.

• Driveway

• Feedback linear scale.

Asquith CNC bogie machining center

This machine is in the bogie shop. It is used for all operations in bogie manufacturing like milling, drilling and boring. All the operation can be done on single machine.

• Control system: GE FANUC 15M

• Axes it works three axes x, y and z axis. It can travel up to 8000m in x-axis, 4000mm in y-axis and 800mm in z-axis.

• Feedback linear scale.

It has auto tool changer, which can change tools automatically according to the program. Its spindle diameter is 180mm and and 40KW power is required to operate the spindle.

HMT SB CNC lathe

This is used for turning the job.

• Control system: Sinumeric 3T

• Axes: it works in 2 axes x and z. Tool can travel up to 1000mm in x and 300mm in z axes respectively.

• Drive DC

• Feedback: rotary encoder

HMT CNC Vertical milling machine

This machine is used for milling purpose.

• Control system: sinumeric 800m

• Axes: it works in three axes x, y and z-axis. Tool travels 1200mm in x, 600mm in y and 400mm in z axes respectively.

• Drive DC

• Feedback rotary encoder.

Copper CNC Vertical Boring Machine

This machine is used for boring purpose.

• Control system: cruceder.

• Axes: tool can move in two axes x and z. It can move 600mm an x-axis and 400mm in z-axis.

• Drive: DC

• Feedback: linear scale.

ADVANTAGES OF CNC MACHINES

Some of the most significant advantages of CNC machine are:

1. High accuracy.

2. High repeatability.

3. Reduced inspection.

4. Ease of assembly and interchange ability.

5. Less scrap and rework.

6. Reduced floor space.

7. Reduced work handling.

8. Reduced lead-time.

9. Flexibility for design changes.

10. Reduced tooling.

11. Design freedom.

12. Ownership of skill.

13. Better machine utilization.

14.Reduced paper work.

CODES USED IN CNC PROGRAMS:

G-code is a common name for the programming language driving NC and CNC machine tool. It was developed by EIA in the early 1960s a final revision was approved in February 1980 as RS274D.

G-code is also the name of any word in a CNC program that begins with the letter G and generally is a code telling the machine tool what action to perform, such as

1. Rapid move

2. Controlled feed move in straight line or arc

3. Series of controlled feed moves that would result in a hole being bored, a work piece cut to a specific dimension, or a decorative profile shape added to the edge of a workpiece.

4. Change a pallet

5. Set tool information such as offset.

There are other codes such as:

• X –absolute position

• Y –absolute position

• Z –absolute position

• M code

• F - Feed rate

• S- spindle speed

• N- line number

• R – radius

• %-start of program

• P- program number

• B-Binary code division

M codes control the overall machine causing it to stop, start, turn an, coolant, etc. whereas other codes pertain to the path traversed by cutting tools.

Different machine tools however may use the same code to perform different functions.

Some common G-codes

G00 Fast positioning

G01 Linear interpolation

G02 CW Circular interpolation

G03 CCWCircular interpolation

G17 X-Y Plan selection

G18 X-Z Plan selection

G19 Y-Z Plan selection

G20 Programming in inches

G21 Programming in mm

G33 Constant pitch threading

G34 Variable pitch threading

G40 Tool radius compensation off

G41 Tool radius compensation left

G42 Tool radius compensation right

G90 Absolute programming

G91 Incremental programming

G94/G95 Feed

G96 Constant cutting speed

G97 Constant rotation speed

Common M codes

M00 program stop

M02 program end

M03 cut off

M04 cut 0n

M30 program end wrt window

M86 rotary C home and hold

M210 X sign toggle

M211 Y sign toggle

Basic function and their names:

Function name descriptionChain bottom and increment Used in conjunction with chain top to

perform a program repeat function. When the chain bottom is reached the internal part count is incremented automatically.

Cut off/cut on These are cutting process, after performing any sequencing. Machine moves at high transverse speed to the next piece location.

KERF Modal change. Used by the dial-in-KERF routine to compensate cutting path for the amount material removed by the cutting process.

Marker 1 off/on Turns off/on marker 1 operation. Machine moves at high transverse speed to the next piece location.

Offset 1 off/on Cancels the marker 1 offset and moves the cutting torch back to programmed position. Moves the distance set up as the X/Y dimension.

Absolute program dimension Modal change. Signals that all subsequent dimensions are in absolute programming format. The moves designated by the X, Y,

I and J values are offset from a reference end point i.e. fixed for the entire part.

Incremental program dimension Modal change signals that all subsequent dimensions are in incremental programming format.

LEAD-IN DIM. Moves Non modal function which may be included along with the arc or line performing the lead into the part.

PROGRAMS OF FLAME CUTTING CNC MACHINE:

1. Cutting of rectangular block with semicircular arc:

%

G91

G21

G01X10

G01Y-20

G02XOY-10I0J-10

G01Y-20

G01Y-10

G01Y+50

M30

M31

2. Cutting of rectangular block having different dimensions:

%

G91

G21

G01X10

G01Y-10

G01X10

G01Y-10

G01X-15

G01Y-10

G01X-5

G01Y30

M30

M31

3. Cutting of designer block having different arcs:

%

G91

G21

MO4Y10

Y100

X200

X-200Y-100

M03

M30

M31

4. Cutting of wedge shape two similar blocks:

%

G91

G21

M04X-20

X15Y-20

Y-190

X-94

X-40Y150

Y55

X119

X15Y15

Y190

X-94

X-40Y-150

Y-55

M30

M31

CONCLUSION:

To conclude numeric control is the most sophisticated form of automatic control of machine tool. It has high degree of precision, accuracy and reliability. The control system has undergone several stages of development. With the above qualities of CNC machines there are numerous advantages like:

High accuracy.

High repeatability.

Less scrap and network.

Better machine utilization.

Some of the special features offered by CNC machine manufacture are:

Thermal stabilization.

Axis calibration.

Lost motion compensation.

The program written to CNC machine is easy to write and understand. This program use code (G codes and M codes) that runs the program. The codes are simple to understand.