2011 Summer Training Report On COMPUTER NUMERIC CONTROL(CNC) Machines
Submitted To:-
Compiled & Submitted By-
Mr. Vijay Verma Sr. Engineer WE & S Deptt.
Ankit Awasthi Univ. Roll No. 08020G B. Tech (ECE), VII Sem. JUET, Guna
[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011
ACKNOWLEDGEMENT
We are highly thankful to B.H.E.L. engineers and technical staff or providing us vital and valuable information
about the different facets of an industrial management system.
We express our gratitude to Human Resource and Development department for giving us a chance to
feel the industrial environment and its working in B.H.E.L. and we are thankful to Mr. Vijay Verma, Sr.
Engineer for giving his precious time and help us in understanding various theoretical and practical aspect of
our project on CNC under whose kind supervision we accomplished our project. We are also thankful to Mr.
M.K. Nagayach for his kind support.
Ankit Awasthi (B.Tech (ECE), JUET, GUNA)
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011
PREFACE At very outset of the prologue it becomes imperative to insist that vocational training is an integral part of
engineering curriculum. Training allows us to gain an insight into the practical aspects of the various topics,
with which we come across while pursuing our B.Tech i.e. vocational training gives us practical implementation
of various topics we already have learned and will learn in near future. Vocational training always emphasizes
on logic and commonsense instead of theoretical aspects of subject.
On my part, I pursued four weeks training at B.H.E.L. Jhansi. The training involved a study of various
departments of the organization as per the time logically scheduled and well planned given to us. It also
involved a project on CNC machines under the able guidance of Mr. Vijay Verma (Sr. Engineer in WE & S
Department).
The rotation in various departments was necessary in order to get an overall idea about the working of the
organization.
Ankit Awasthi (B.Tech (ECE), JUET, GUNA)
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011
CERTIFICATE It is hereby certified that Ankit Awasthi student of Jaypee University of Engineering & Technology (JUET), Guna has successfully carried out his summer training project on Computer Numeric Control (CNC) Machines in BHEL Jhansi.
To the best of my knowledge, this project is truly original & has not been produced whatsoever.
He sincerely completed his project with dedication & I wish him success in future.
Mr. Vijay Verma Sr. Engineer Work Engineering & service B.H.E.L. Jhansi
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011
CORPORATE PROFILE
.
B.H.E.L is the largest engineering and manufacturing enterprise of its kind in India is one of the leading international companies in the field of power equipment manufacture. The first plant of BHEL was setup at Bhopal in 1956, which signaled the dawn of the heavy electrical industry in India. In the early sixties, three more major plants were set up at Haridwar, Hyderabad and Tiruchnapalli. That forms the core of the diversified product range system services that BHEL offer today. BHEL ranges of services extend from product feasibility studies to after sale services, successfully meeting diverse needs through turnkey capability. The company now has 14 manufacturing unit, 9 services centers and 4 power sectors regional centers besides project sites all over India and abroad. BHEL today is the largest engineering and manufacturing enterprise of its kind, with a well recognized track record of performance, making profit continuously since 1971-72 and paying dividends since 1976-77. BHEL manufactures over 180 products under 30major product group and cares to core sectors of Indian economy viz, power generation and transmission industry, transportation, telecommunication, defense etc. the quality and reliability of its products is due to the emphasis on design ,engineering and manufacturing to international standards by acquiring and adopting some of the best technologies from leading companies in the world, together with technology developed in its own R&D centers i.e. BHEL Hyderabad. BHEL has acquired ISO 9000 certification for its operation and has also adopted the concepts of total quality management (TQM) and environment management (EMS).
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011
BHARAT HEAVY ELECTRICALS LIMITED, JHANSI
“A BRIEF INTRODUCTION “ By the end of the fifth year plan, it was envisaged by the planning commission that the demand for the power transformer would raise in the coming years. Anticipating the country’s requirement BHEL decided to set up a new plant, which would manufacture power and other type of transformer in addition to the capacity available at BHEL in Bhopal. The Bhopal plant was engaged in the manufacture transformers of large rating and Jhansi unit would concentrate on power transformer, traction transformer for railway etc. The unit at Jhansi was established in 9 Jan, 1974 and it is situated around in 15 kms from the city on the national highway number 26 i.e. Jhansi-lalitpur road. It is called second generation plant of BHEL it was setup in 1974 and estimated cost of Rs 16.22crores inclusive of Rs 2.1crores for township. Late Mrs. Indira Gandhi, the prime minister laid the foundation on 9thjan 1974. The commercial production of the unit began on 1976-77 with an output of Rs 53 lakh, than there has been no looking back for Jhansi. Unit of BHEL is basically engaged in the production and manufacturing of transformers of various types and capacities with growing competition in the transformer section in 1985-88 it undertook the re-powering of diesel but it took a complete year for the manufacturing to begin. In 1987-89, BHEL has taken a step further in undertaking it is also, manufacturing AC/DC locomotives.
VISION, MISSION AND VALUES OF B.H.E.L. VISION: A world class engineering enterprise committed to enhancing stakeholder value. Mission: To be an Indian Multinational Engineering Enterprise providing total business solution through quality products, system and services in the fields of energy, industry, transportation, infrastructure and other potential areas. VALUES: 
Zeal to Excel Zest for change.

Integrity and fairness in all matters.

Respect for dignity and potential of every individual.

Strict adherence to commitments.

Ensure speed of response.

Faster learning, teamwork and creativity.

Loyalty and Pride in the Company.
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 BHEL OBJECTIVE
A dynamic is one its aim high adopts itself quickly to changing environment. So here we are in BHEL. Business mission To be a leading engineering enterprises providing quality product, systems and services in the field of energy, transportation, industry, infrastructure, and their potential areas Growth To ensure steady growth by enhancing the competitive edge of BHEL in existing, new areas and international operations so as to fulfill national expectation for BHEL. Profitability To provide a reasonable and adequate return on capital employed, primarily through improvement in operational efficiency, capacity utilization and productivity and generate adequate internal resources to finance the company’s growth. Customer Focus To build a high degree of customer confidence by providing increased value for his money through international standards of product performance superior customer service. People Orientation To enable each employee to achieve his potential, improve his capabilities, perceive his role and responsibilities and participate and contribute to the growth and success of the company, to invest in human resources continuously and be alive to their needs. Technology To achieve technological excellence in operations by development of indigenous technologies and efficient absorption and provide competitive advantage to the company. Image To fulfil the expectations which stakeholders like government as owner, employees, customers and the country at large have from B.H.E.L.
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 THE MANUFACTURING UNITS OF B.H.E.L. First Generation Units BHOPAL
(Heavy Electrical Plant)
HARDWAR
(Heavy Electrical Equipment Plant)
HYDERABAD
(Heavy Electrical Power Equipment Plant)
TIRUCHY
(High Pressure Boiler Plant)
Second Generation Units JHANSI
(Transformer and Locomotive Plant)
HARDWAR
(Central Foundry and Forge Plant)
TIRUCHY
(Seamless Steel Tube Plant)
Unit Through Acquisition and Merger BANGALORE
(Electronic Porcelain Division)
New Manufacturing Units RANIPAT
(Boiler Auxiliaries Plant)
JAGDISHPUR
(Insulator Plant)
RUDRAPUR
(Component and Fabrication Plant)
BANGALORE
(Industrial System Group)
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 PRODUCT PROFILE OF B.H.E.L., JHANSI
1.
Power Transformer
Up to 220 KV Class 250 MVA
2.
Special Transformer
Up to 110 KVA
3.
ESP Transformer
1000 KVA
4.
Freight Loco Transformer
3900-5400
5.
ACEMU Transformer
Up to 1000 KVA 25 KV(1Phase)
6.
Dry Type Transformer
Up to 3150 KVA
7.
Bus duct
Up to 15.75 KVA(Generating Voltage)
8.
Instrument Transformer
VT and CT Up to 220 KV
9.
Diesel Electric Locomotive
Up to 2600 HP
KVA&6500KVA (3 Phase)
10. AC/DC Locomotive
Up to 5000 HP(25 KV AC/1500V DC)
11. Well Wagon
200 Tonne
12. Over Head Equipment Cum Test Car 13. Dynamic Track Stabilizer 14. Ballast Cleaning Machine
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 GROWTH OF PRODUCTION AND MILESTONES OF BHEL JHANSI UNIT YEAR
MILESTONES
1976-77
Start of Instrument Transformer Production
1977-78
Start of Traction Transformer and Power Transformer (Up To132 KV)
1978-79
Start of HFTT type freight Locomotive
1979-80
Commissioning of 2,500 KV DG Set (due to server power cuts)
1980-81
Start of ESP Transformer
1981-82
Start of 220 KV Power Transformers
1982-83
Achieve Break Even
1983-84
Start of Bus duct
1984-85
Start of Dry Type Transformer
1985-86
Re powering of Diesel Locomotive Started
1986-87
Start of Diesel Locomotive Started
1987-88
Manufacturing Facilities for AC Locomotive
1988-89
Crossed Core Target
1990-91
Successful Design and Manufacturing of 400 HP 3 Axel Diesel CCI
1991-92
Manufacture of First 2600 HP Diesel for NTPC
1992-93
Successful Design and Development of 5000 HP Thyristor Control Locomotive
1993-94
Unit has been Awarded ISO-19001 Certificate for Quality Systems
1994-95
240 MVA Power Transformers Produced First Time
1995-96
AC/DC Locomotives first time in India
1996-97
Hundredth Locomotive Manufactured
1997-98
250 MVA Transformer Produced First
1998-99
Developed Over Head Equipment cum Test Car
1999-00
Diesel Hydraulic Shunting
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011
ROTATION REPORT
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 JHANSI UNIT Organizational unit Our summer training consist of two parts, 1st is the rotation of various departments of BHEL Jhansi and second is the preparation of this project. MAIN AIM OF THE ROTATION Main aim behind the rotation of various departments is that one can understand the working of each and every department and to see that how people (workers, middle level executive, top officials) work in corporate environment. Main departments of BHEL Jhansi 
Administration

Production
PRODUCTION UNIT DEPARTMENTS
STORE There are separate stores for different type of material in the BHEL There are three sections in store; 
Control Receiving Section

Custody Section

Scrap Disposal Section Functions: - A list of material coming in store is prepared and Quality Control people are called for inspection. If material is found as par standard SRV (Store Receipt Voucher) is issued for each material. A total of 08 SVR’s are prepared. Some materials such as Silicon oil, Transformer oil, insulating material etc are directly stored in the Bays. Scraps are also sold through unit by a MATERIAL SCRAP TRADING –DELHI FABRICATION (BAY-0, 1, 2) Fabrication shop is the shop which deals with the manufacturing of transformer and locomotive components such as Tanks, Plates, and Nuts and Bolts. Fabrication shop is divided into three parts-
BAY-0 These are the fabrication shops established in 1978 and mainly deal with fabrication with fabrication work of transformers and locomotive. Different processing machines in this BAY are as follows:
CNC FLAME CUTTING MACHINE (2 nos.) By the use of this machine, we can cut different shapes in our products via Oxy-Acetylene Flame through a copper nozzle. This machine can cut upto 300mm thick sheet. One of the machines has 4 burners while the other has 2 burners, which can work simultaneously. Maker
-
ESAB Germany made
Flame
-
Oxy-Acetylene Flame
Axes
-
Two axis x & y. In X-axis, tool can move upto 7m & in Y-axis it can move upto
-
D.C. Drive
3.5m. Drive
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 Feedback 
-
Rotary Encoders
BENDING MACHINE Principle – Hydraulically operated Pistons Used-
2
Pressure Gauge is used to read out the pressure applied. The pressure applied may vary upto 250 Tonnes. It bends the sheets in the required
way. It is up/down switch operated & has 3 cast iron
solid cylinders. Stopping mechanism used is nut & screw mechanism to prevent the ram blade from collapsing with bending grooves. 
ROLLING MACHINE This machine is used for decreasing the roll thickness. The roller material used is High Carbon Steel. It has two rollers and one bending roller. In this machine, gears are used for speed reduction of the rollers to give uniform and better thickness and good surface finish.

FLATTENING MACHINE Principle –
Hydraulically operated
This machine is used to straighten the job. The flattening load is applied by hydraulic method where the hydraulic oil of suitable grade is used. The capacity of this machine is 100 tonnes. 
RADIAL DRILLING MACHINE (2 nos.) In this machine, tool can move radially. In it the drill tool is cooled using cutting oil mixed with water. Different drill tools are used from 2mm to 100mm diameter.

SHEARING MACHINE Principle –
Knife cutting via hydraulic pressure
This machine is used for simple cutting in the metal sheets. Cutting range is 2mm to 6mm. Suitable materials for use are Al, Standard Steel & Cu. This is also hydraulically operated.
BAY- 1, 2 These bays are known as assembly bays. In these bays, different operations to be performed are:Fitting – In this section, as the name suggests, we fit different components as per the drawing requirements. Welding – In this section, we weld the different components of different drawing by permanent joints. The different types of welding done here
are metal inert gas (MIG), Submerge Arc Welding
(SAW) & manual arc welding. Testing – When our tank for the transformer is completed, then we check the leakage tests on the tank, which are of two types:1. AT (Air leakage test) In this test, first we fill the tank by compressed air and dip the tank in the soap solution for bubble test. 2. VT (Vacuum test) Shot Blasting PlantWhen we check the leakage by satisfying result then we use SHOTBLASTING for removing the carbon layer from the surface of the tank. In the SHOT BLASTING, we use the small rings with the high pressure of 7kg. 
Overhead Cranes (2 nos.)
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 They are used for moving different heavy jobs from 1 place to another within the bay. A new electromagnet system is also available which can be used to lift heavy items if needed. Painting – After shot blasting, we paint the tank for corrosion resistant. FABRICATION MAIN PRODUCTS 1.
Transformers tank (Auto & Dry type freight loco)
2.
CCP (Core Clamp Plate)
3.
End frames & foot parts ETP (End Tie Plate)
4.
350, 700, 1400 HP diesel Underframe/bogies
5.
Aluminium Bus Duct
BAY-3 It is split in two parts, half is consist of machine shop and the other half is consist of winding of dry type transformer. There is different type machines used in section. These are listed below. 1. Tool Cutter grinder – Used for cutting tool also grinding them. 2. Hydraulic surface grinder – It is consist of magnetic platform. Cooling oils is used as coolant. 3. Drill sharp machine – It is used for sharping the drill bits by means of grinding wheel. 4. Vertical grinder machine – It is used for grinding purpose. 5. Hydraulic power press – Used for straightening the material, capacity of this machine is 25 tones. 6. Resistance brazing machine – Used for overlap connections. 7. Bend saw machine– It is used for cutting circular object. In this machine blade thickness is ¾ inch. 8. Electric furnace – Used for heating the object. 9. Hydraulic punching machine – Used for making small pieces of material for desire purpose. Range of this machine is 12mm to 250mm. 10. Hydraulic shearing machine – Used for cutting the material in range between 12mm to 25mm. 11. Lathe machine– There are mainly three types of lathes are there these are listed as below. 
Turret lathe – Used for heavy duty. Range of this machine is 250mm to 300mm.

Capstone lathe – Used for light work, range of this machine is 20mm to 150mm.

Center lathe – It is used for light work and range of this machine is 20mm to 200mm.
Tanning Spot- Here Pb, Sn are used for tanning the connections in the job. Sulphuric Acid (H2SO4) – It is used for remove the blackening of the job. Marking Table- This table is used for marking on the job for processing in different machines.
COPPER SECTION This part is only concern with copper cutting, bending, tinning etc. Machine used are as listed below. a) Shearing machine: Range 4mm to 6mm and length of the blade is 830mm. b) Hydraulic power press: Used for straightening the product. c) Tube slitting machine: This machine is developed here and is used for cutting the tube along its length and across its diameter. Its blade thickness is
3 mm.
d) Fly press machine: It is fully mechanical and is used to press the job. It is operated mechanically by a wheel, which is top on the machine.
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 e) Lincing belt machine: It creates a smooth surface.
BAY–4 Here winding work of the power transformer& dry type transformer is carried out. The coil of transformer is of four types. a) Low voltage coil b) High voltage coil c) Tap coil d) Tertiary coil All the winding performed by the paper insulation copper conductor (PICC) or by continuously transposed conductor (CTC) is also made of copper. They can be arranged in different ways. a)
Reverse section winding
b)
Helical winding
c)
Interlinked winding
d)
Half section winding
Arrangement & type of coil depends on job requirements. Also the width & thickness of the conductors are designed & decided by design department. Conductors used for winding is in the form of very long spiral wound on a spool, conductor is covered by cellulose paper insulation. For winding, first the winding mould of diameter equal to inner diameter of required coil is made. The specification of coil is given in the drawing section that interlocks with each other. This interlocking can be increased and decreased to adjust the inner diameter of coil. The moulds are of following types. a) Belly types b) Link types c) Cone types
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 Figure Showing Cast Resin Dry Type Transformer
BAY–5 It is core and punch section but in a part of it cast resin coil encapsulation plant is situated. The coils of dry type transformer are casted, cut and finally prepared. In this bay various type of lamination of core is made, they are – a) Side leg: This lamination is at the extreme ends of the core which stand vertical. They are isosceles trapezium in shape with angle of 45. b) Central leg: This as the name suggests is central vertical portion of the core. It is diamond shaped with vertical edges longer. At the narrower edge
one side is kept longer than the other for making a
well fixed joint, the angles are kept 45. c) Yoke: The horizontal lamination of the core is called yoke. They are also isosceles trapezium in shape with angles of 45.
Slitting machine: It is used to cut CRGO sheets in different width. It has a circular cutter whose position can be changed as per the requirement.  CNC cropping line pneumatic: It contains only one blade which can rotate 90º about the sheet. It is operated pneumatically. 
CNC cropping line hydraulic: It is also used to cut the CRGO sheet it contains two blades, one is fixed and other rotates 90º above the sheet. It is operated hydraulically. M4 quality sheet 0.230.27 mm thickness is used. CNC per hour Consumption: 75 kWh CNC per hour Expenditure: 375 Rs.
Figure showing cut CRGO’s & stacked to form core
BAY-6 This shop is divided into two parts one is traction transformer winding and other one consist of assembly of traction transformer. These transformers are used in locomotive used in the AC locomotive called freight locomotive transformer. These are mainly of two types: Single phase (5400 KVA) and three phase (6500 KVA). For local train EMU (Electrical multiple unit transformers) is to be used. These are also two types: Single phase (1000 KVA) and three phase (1500 KVA). The major difference is that it has various output terminals. The various outputs are required to supply the machine of different rating mounted on the loco. A tap changer (0-32 taps) is also provided and is used to obtain supply of different rating power.
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 BAY–7 In this bay various types of insulation are prepared which is to be used in transformers. MATERIALS USED: a) Permawood: Size 10mm to 50mm. b) Precompressed: Size 1.5mm to 25mm. c) Grey press board: Size 1.5mm. d) Bakelite: Size 4mm to 25mm. e) Fibreglass: Size 1mm to 3mm. f) Epoxy glass: Size 10mm to 25mm. g) N.B.C. sheets (Naporeniom bonded cork sheet): Size 3mm, 6mm, 10mm, and 12mm. h) Silicon rubber: Size 1mm, 3mm, 6mm. i) Nitric rubber: Size 3mm to 12mm. j) Gas Cut: Size 1.5mm to 16mm. It is used to prevent oil leak in transformers. PVA (poly vinyl alcohol) is used as additive. MACHINE USED: 1. Rolling machine: It is used to roll the press board. 2. Hard press machine: It is used to build up any thickness plate by heating plates and then hardly pressing on this machine. 3. Circle cutting machine: It is used for cutting the circular objects and also used for machining 4. Scarfing machine: It is used for taper cutting. 5. Finishing machine: It is used to maintain the cuts in the job & hence provide finishing.
BAY–8 This bay was established in the year 1974. It is one of the earliest bays to setup. It involved in the manufacturing of instruments transformer like 132KV and 220KV voltage/ current transformer. ESP transformer is also manufactured here. INSTRUMENT TRANSFORMER: These are of two types a) Current transformer (C.T.) b) Voltage transformer (V.T.)
 CURRENT TRANSFORMER It is a step down transformer. Higher current is not directly measured rather it is stepped down to lower measurable values by the current transformer, which is generally low. Body •
The main body is a bushing, it also acts as insulator in which winding is placed.
•
The CT has a bottom and top chamber.
•
The top chamber is the cylindrical tank of mild steel. It has terminals for connection of HV coils. It has
a glass window to indicate the oil level. •
Below the top chamber there is bushing made of porcelain.
It has several folds and “rain sheds” to provide a specific electrical field distribution and long leakage path. Some bushings are of cylindrical while modern one is conical as amount of oil porcelain used is reduced without any undesirable effect. •
Bottom chamber house is the secondary winding. There is also connection box to which the
connection low voltage (LV) is made.
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011
Windings The primary winding consists of hollow copper/aluminium pipe bent form of ‘U’, where aluminium is used for low rating. For higher rating a set of wire is passed through the pipe. For still higher rating, copper pipe is used and for highest rating copper pipe with copper wire passing through it is used. This arrangement depends on the current carrying capacity. The bent portion of primary is in the bottom chamber where as the free end is the top chamber. The straight portion lies inside the bushing. The primary is wound with crepe paper insulation goes in increasing as we go downwards in the bottom chamber. The free ends are provided with ‘ferrules’, which are small hollow cylinder through which wires can pass connection to the primary, are made through these ferrules. The secondary is divided in a number of coils for different set of tapings. Connections are different taping are made in connection box. Each coil has an annular core of CRGO (silicon steel).
 VOLTAGE TRANSFORMER This is also step-down transformer the out of construction is the same as that of C.T. It has also a top chamber, bushing and a bottom chamber. The difference is only in windings. Windings The primary winding is of thick wire having a few turns. The winding is heavily insulated with paper insulation. It has a hollow cylinder passing centrally through it, which houses the secondary winding. It is cleaned and painted with either enamel or epoxy paint. The customer gives the choice of paint. Epoxy paint is generally used in chemical plant and seashore installation. Terminals are then marked and rating and diagram plate is fixed. The job is sent to shipping department which takes care of its dispatch by packing in the wooden boxes. DIFFERENCE: In current transformer, primary has less turns then secondary and vice versa. 
ESP TRANSFORMER (High Voltage Rectifier)
The Electro static precipitator rectifier transformer is used for environmental application. It is used to filter the suspended charge in the waste uses of an industry. They are of particular use in thermal power station and cement industry. The ESP is a single Φ phase transformer. It has primary and secondary windings. The core is laminated and is made up of CRGO sheet. It is a step up transformer. An AC reactor is connected in series with primary coil. The output of the transformer must be DC which is obtained by rectifying AC using a bridge rectifier (bridge rectifier is a combination of several hundred diodes). A radio frequency choke (RF choke) is connected in series with the DC output for the protection of secondary circuit and filter circuit. The output is chosen as negative terminal because the particles of carbon (impurity) are positively charged. The dc output from the secondary is given to a set of plate arrange one after the other. Impurity particles being positively charged stick to these plates, which can be jerked off by hammer. For this, a network of plant has to be set up all across the plants .This is very costly process in comparison with the transformer cost. A relevant is also provided to prevent the transformer from bursting, as higher pressure develops inside it. It is the weakest point in the transformer body. An oil temperature indicator and the secondary supply spark detector are also provided. One side of the transformer output is taken and the other side has a “marshalling box” which is the control box of the transformer.
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 BAY–9 This is one of the largest bays in the unit engaged in the assembly of power and rectifier transformer. The time taken for assembly ranges from 4-12 weeks. It is built all along the rest of the bays. A transformer in a process of assembly is called a job. The design of the transformer is done by the design department & is unique of each job & it depends on the requirements of the customers. The design department provides drawing to the assembly shop which assembles the job. The main processes involved in this shop are:1.
Core building – with the help of drawing provided
2.
Core lifting – lifted by a crane & placed vertical
3.
Unlacing, in which yoke of the transformer is removed – to place bottom insulation in the form of 50mm thick UDEL sheet.
4.
Relacing & end frame mounting – the connections are re-made as per the drawing
5.
H.V. terminal gear & L.V.T.G. mounting
6.
Final servicing & tanking – job is inserted in a mild steel tank after passing some pre-tests & oil filling
7.
Case fitting – tank cover, fixing bushing, fixing valves etc are done
TRANSFORMER COMMERCIAL (TRC) The objective of this department is to interact with the customers. It is infact the commercial window between BHEL & its customers. It brings out tenders and notices and also responds to them. It also deals with the pre-bid discussions. It is this department that places contracts of building the transformer and after delivery further interacts with the customer regarding faults, failure and maintenance. All such snags are reported to them and they forward the information to the concerning department. It is mainly divided into two cells: 1.
Tender Cell: It deals with the marketing of the product. It includes cost of material, transportation, machinery, labour etc.
2.
Contract Execution Cell: It deals with the co-ordination of drawings, documents, testing, past supply, payment, commissioning, sales & services.
Tendering 1. Tender requirements of the customer comprises of the following specifications: A. Technical specifications/requirements.
2.
3.
4.
B.
Estimated Cost of the project/requirements.
C.
Estimated Time of completion of the project.
D.
Other information.
Types of tender: A.
Open Tender – published in news, dailies – open for all.
B.
Limited Tender – issued to limited parties.
C.
Single Party Tender – issued to parties on property basis.
Enquiry: On the receipt of tender forms, enquiries are issued to A.
Engineering department for technical acceptance.
B.
Production planning & control for delivery period.
C.
Central dispatch cell for mode of transportation & transportation charge.
Offer: If tender is feasible as obtained from reports of other departments, offer is submitted to the
customer. 5.
Contract Agreement: On the opening of the technical bid, the commercial bid of technically qualified tenders is opened & order is placed on the lowest value tender, which is followed by negotiations if required.
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 CONTRACT EXECUTION CELL 1. Issue of work orders. 2. Type of work orders. 3. Monitoring. 4. Payment collection. 5. Contract closing.
After Sales Services 1. Within warranty period – free of cost service & replacement of material if required. 2. Beyond warranty period – on chargeable basis.
TESTING TRANSFORMER TESTING In this shop testing on the transformer is carried out in one section and for loco in other section. In transformer testing section there are for MG. sets. The electrical specification of the entire test is already given. These tests are done on demand of customer on transformer manufactured, in this unit there are basically of these tests For power transformer – routine test 
Ratio test: Special equipment transformer from routine meter.

Resistance test: Special equipments – Kelvin and Wheatstone bridge.

Insulation resistance test: Special equipment megger.

Separate source voltage withstand test: Special equipments – HV transformers with associated control and measuring desk, standard capacitance potential divider.

Iron loss measurement test: Special equipment : •
Electro dynamometer
•
RMS voltmeter
•
Average voltmeter
•
Precision class measuring VT
•
Variable frequency sine wave generator
TEST OF CURRENT TRANSFORMER 1. POLARITY TEST: INSTRUMENT USED: Polarity meter analog multimeter One of the winding is supplied with 1.5V D.C supply and other is connected to ammeter. If the direction of the deflection is correct implies the connections are correct else it is wrongly connected. 2. ACCURACY TEST: It is the test for rechecking various parameters like turn ratio, phase angle etc. 3. INTER TURN INSULATION TEST: 
First current is given to the primary while the secondary is kept open circuited

Either of the rated primary current or the 4.5kV peak secondary voltage, whichever occurs first is allowed to withstand for 1 min.

Then if the insulation can withstand it, it is said to be okay.
20
[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 TRANSFORMER ENGINEERING (TRE) The transformer manufactured in BHEL Jhansi range from the 10MVA to 240MVA and up to 200 KV.
TECHNOLOGY This department analyses the changes taking place in the world and suggest changes accordingly. This is very important because the product must not get obsolete in the market otherwise they will be rejected by customer. Function: Technology function can be classified as: 
Processing sequence: The sequence of process 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.

Facilities identification: It includes looking for new equipment, plant or tools to increase productivity.

Special process certification: Special processes are the once required expertise for example identifying errors, cracks, air bubble in winding.
 
Special tool requirement: Special tools are allotted if possible. When required else the design has to be reconsider. Productivity projects compilation: It includes the initial analysis of the problem and their appropriate solution to enhance productivity. The principle of working is that “IF YOU DON’T MAKE CHANGES IN YOUR COMPANY, THE COUSTMER WILL CHANGE YOU”.
BUS DUCT Bus duct is used as connection between generators and transformer. Bus duct are used in power connection over 150 M V. The question now arise that why are bus duct preferred over normal conductors. In high power application, insulations are the major problems and frequent insulation breakdown occurs. If this does happens then possibility of shorting of conductor’s and hence serious damage may occur to both transformer and generators. Bus duct are hollow pipes made of aluminum the cross section of these ducts depends on requirements of the customer and is done by the design department. It has also the separate department BUS DUCT COMMERCIAL.
LOCOMOTIVE A locomotive is a rail vehicle that provides the motive power for a train. “Loco” means from a place “Motive” means causing motion. A locomotive has no payload capacity of its own. It is used to move a train.
21
[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 Locomotives manufactured at BHEL Electric Locomotives
 
WAG-5

WCAM-2 AC/DC

WCAM-3 AC/DC

WCAG-1 Main customer: INDIAN RAILWAYS

Diesel Shunting Locomotive

Diesel Electric Loco
 
350HP DESL

450HP DESL

700HP SPP/TPP DESL

1150 DESL

1350 DESL

1400 DESL

2600 DESL Diesel Hydraulic Loco

WAG 7 LOCOMOTIVE
800 HP DHSL

Customer: IFFCO, Kandala Battery Loco
 
450 HP Customer: DMRC, New Delhi
Main Parts of Diesel Locomotives  Underframe: The one on which loco is built.  Super Structure: The body of loco is called super structure & is made of sheet of mild steel.  Bogie: The wheel arrangement of loco is called bogie. A bogie is essentially contains: 
Bogie Frame

Wheel & Axle

Traction motor

Gear & pinion

Brake shoe

Pull rod

Sand box

Springs

Brake cylinder
 Main Equipment of DESL 
Traction Alternator/Generator.

Traction Motor.

Blower.

Compressor or Expresser.

Switchgear Equipments

Drive Desk.

Fuel Tank.

Batteries

Radiator
22
[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011  Brake System 
Simple Air Brake System.

Air Brake System with MU operation

Air Brake System with MU Operation and air break on trailing stock.

Dual Break System-Air and Vacuum.
Traction Transformer: It is fixed on under frame and gets supply from an overhead line by equipment called pantograph. The type of pantograph depends on supply. This transformer steps down voltage and is fitted with a tap changer. Different taps are taken from it for operating different equipment. One tap is taken rectified into DC using MSR and is fed to the DC motor.
CENTRAL QUALITY SERVICE First we get acquainted with a few terms concerning this department. Quality: It is the extent to which product and service satisfy the customer needs. Quality assurance: All those plants and systematic action necessary to provide adequate confidence that the product or the service will satisfy the given requirement is called quality assurance. Quality control: Activity such as measuring testing, gauging one or more characteristics of product or service and comparing these with specified requirement to determine conformity are termed quality section.
Work Engineering & Services (WE & S) As the name suggests, this section deals with the services & maintenance. It has the following sections:  Plant Equipment: This has electronics & electrical/mechanical maintenance.    
Services: This section deals with air, steam and power equipments. Telephone Exchange: Township Electrical Maintenance: WE & S Planning
23
[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011
PROJECT REPORT
24
[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011
Numerical control Siemens CNC panel Numerical
control (NC) refers to the automation of machine
tools that are operated by abstractly programmed commands encoded on a storage medium, as opposed to manually controlled via hand wheels or levers, or mechanically automated via cams alone. The first NC machines were built in the 1940s and 1950s, based on existing tools that were modified with motors that moved the controls to follow points fed into the system on punched tape. These early servomechanisms were rapidly augmented with analog and digital computers, creating the modern computer numerical control (CNC) machine tools that have revolutionized the machining processes. In modern CNC systems, end-to-end component design is highly automated using computer-aided design (CAD) and computer-aided manufacturing (CAM) programs. The programs produce a computer file that is interpreted to extract the commands needed to operate a particular machine via a postprocessor, and then loaded into the CNC machines for production. Since any particular component might require the use of a number of different tools-drills, saws, etc., modern machines often combine multiple tools into a single 'cell'. In other cases, a number of different machines are used with an external controller and human or robotic operators that move the component from machine to machine. In either case, the complex series of steps needed to produce any part is highly automated and produces a part that closely matches the original CAD design.
25
[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011
Description Modern CNC mills differ little in concept from the original model built at MIT in 1952. Mills typically consist of a table that moves in the X and Y axes, and a tool spindle that moves in the Z (depth). The position of the tool is driven by motors through a series of step-down gears in order to provide highly accurate movements, or in modern designs, direct-drive stepper motors. Closed-loop control is not mandatory today, as open-loop control works as long as the forces are kept small enough. As the controller hardware evolved, the mills themselves also evolved. One change has been to enclose the entire mechanism in a large box as a safety measure, often with additional safety interlocks to ensure the operator is far enough from the working piece for safe operation. Most new CNC systems built today are completely electronically controlled. CNC-like systems are now used for any process that can be described as a series of movements and operations. These include laser cutting, welding, friction stir welding, ultrasonic welding, flame and plasma cutting, bending, spinning, pinning, gluing, fabric cutting, sewing, tape and fibre placement, routing, picking and placing (PnP), and sawing.
Tools with CNC variants 
Drills

EDMs

Lathes

Milling machines

Wood routers

Sheet metal works (Turret Punch)

Wire bending machines

Hot-wire foam cutters

Plasma cuttings

Water jet cutters

Laser cutting

Oxy-fuel

Surface grinders

Cylindrical grinders

3D Printing

Induction hardening machines
Tool / machine crashing In CNC, a 'crash' occurs when the machine moves in such a way that is harmful to the machine, tools, or parts being machined, sometimes resulting in bending or breakage of cutting tools, accessory clamps, vises, and fixtures, or causing damage to the machine itself by bending guide rails, breaking drive screws, or causing structural components to crack or deform under strain. A mild crash may not damage the machine or tools, but may damage the part being machined so that it must be scrapped. Many CNC tools have no inherent sense of the absolute position of the table or tools when turned on. They must be manually 'homed' or 'zeroed' to have any reference to work from, and these limits are just for figuring out the location of the part to work with it, and aren't really any sort of hard motion limit on the
26
[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 mechanism. It is often possible to drive the machine outside the physical bounds of its drive mechanism, resulting in a collision with itself or damage to the drive mechanism. Many CNC tools also don't know anything about their working environment. They often lack any form of sensory capability to detect problems with the machining process, and will not abort if something goes wrong. They blindly follow the machining code provided and it is up to an operator to detect if a crash is either occurring or about to occur, and for the operator to manually abort the cutting process. If the drive system is weaker than the machine structural integrity, then the drive system simply pushes against the obstruction and the drive motors 'slip in place'. The machine tool may not detect the collision or the slipping, so for example the tool should now be at 210mm on the X axis but is in fact at 32mm where it hit the obstruction and kept slipping. All of the next tool motions will be off by -178mm on the X axis, and all future motions are now invalid, which may result in further collisions with clamps, vises, or the machine itself. Collision detection and avoidance is possible, through the use of absolute position sensors (optical encoder strips or disks) to verify that motion occurred, or torque sensors or power-draw sensors on the drive system to detect abnormal strain when the machine should just be moving and not cutting, but these are not a common component of most CNC tools. Instead, most CNC tools simply rely on the assumed accuracy of stepper motors that rotate a specific number of degrees in response to magnetic field changes. It is often assumed the stepper is perfectly accurate and never miss-steps, so tool position monitoring simply involves counting the number of pulses sent to the stepper over time. An alternate means of stepper position monitoring is usually not available, so crash or slip detection is not possible.
CONTROL SYSTEMS OF A CNC Point-to-Point System CNC controls can be either a point-to-point or continuous path system. The point –to-point (PTP) control moves the tool to the programmed point, normally in rapid traverse, without engaging the work piece. The PTP system is also called the positioning system because its exact tool path normally cannot be controlled. PTP tool path follow one of the three modes: axial path, 450 line and
linear
path.
Figure presents
these
three
modes.
(a)Axial path
(b) Line path (c) Linear path
27
[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011
An application of a PTP control system The PTP systems are typically used in drilling machines, punch presses, and spot welders, which require positioning in the XY plane in rapid traverse mode and executing machining in Z-axis direction. PTP systems are easy to maintain and less expensive.
Straight Line Motion Control System The NC system in which the tool works along a straight line in the direction of a major co-ordinate axis, such as along the direction of feed during turning, boring or milling operation at a controlled rate, are known as straight line control systems. These are best suited for plain turning, face milling, vertical milling & horizontal milling.
Continuous Path Control Systems This is also known as contouring system. It is capable of synchronizing two or more axial drives to produce a desired path. Here the cutting takes place while the position of work piece & tool are changing. Contour systems are of five types, depending upon type of control. These are: 2-D contouring
It synchronizes feed only in two axes simultaneously
2 ½-D contouring 3-D contouring
Any two of three can be controlled simultaneously Capable of synchronizing three axes simultaneously
4-axis machining
Apart from 3 regular axis, 4th axis is rotary axis
5-axis machining
It incorporates 3 regular and 2 rotary axis
These are the most complex, costly & versatile systems & usually require the assistance of a computer because of large data regarding positional values to be processed.
FUNCTIONS OF A CONTROL SYSTEM Some important functions controlled by control system are:•Displacement of machine slides •Angular rotation of circular table •Start / Stop of the main spindle •Changing of spindle speed •Reverse spindle direction •Changing the feed rate of machine slides •Rotate tool turret •Change tool •Coolant ON / OFF •Lock table in position
28
[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011
CNC Drive Systems The structure of CNC control can be either an open loop or closed loop system. The main difference between the two systems depends on whether or not the system has a feedback loop to insure the accuracy of the system performance.
Open Loop Open loop is characterized by no feedback system in the drive system. MCU provides control to the drive motors. It is being assumed by the system that the machine table will reach the target position. There is no way from the MCU to know the actual performance of the system. Figure shows a block diagram of an open loop CNC drive system.
Open loop CNC drive systems PTP system usually uses open loop drive systems, where cutting tool doesn’t engage with work piece during positioning. They can also be used in light-loaded cutting machines. Although they are economical but are vulnerable to load resistances during positioning.
Closed Loop With closed loop drive systems, feedback sub systems are used to monitor the actual output and correct any discrepancy between the desired and the actual system performance. Feedback subsystems are of two types: 1. Analog feedback system: Variations in physical systems such as position and velocity are being measured as voltage levels in analog feedback system. Tachometers are typically used to measure the velocity, whereas the resolvers are used to measure position. There are two feedback loops in CNC drive systems; position loop and velocity loop as shown in figure, the position loop is the outer loop, which consists of comparator, an amplifier circuit, a velocity loop, a resolver, and a resolver interface.
29
[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 2. Digital feedback system: A digital feedback system uses a digital position transducer to measure the position. Encoders are popular digital position transducers. Comparator and amplifier are replaced by updown counter and digital-to-analog converter.
Construction A CNC system basically consists of the following: •Central processing unit (CPU) •Servo-control unit •Operator control panel •Machine control panel •Other peripheral device •Programmable logic controller (PLC)
Central Processing Unit (CPU) T h e C P U is t h e he art an d b rai n o f a C NC s y s t em . I t acc e pts t h e i n fo rm at i o n s t o re d i n t h e memory as part program. This data is decoded and transformed into specific position control and velocity control signals. It also oversees the movement of the control axis or spindle whenever this does not match the programmed values, a corrective action is taken. All the compensations required for machine accuracy (like lead screw pitch error, tool wear out, backlash, etc.) are calculated by the CPU depending upon the corresponding inputs made available to the system. The same will be taken care of during the generation of control signals for the axis movement. Also, some safety checks are built into the system through this u ni t an d t h e CP U u n i t w i ll pro vi de c o n t i nu o us ne ces s ary c o rre c t i ve ac t i o ns . Wh e ne ve r t h e situation goes beyond control of the CPU, it takes the final action of shutting down the system in turn the machine.
30
[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 Speed Control Unit This unit acts in unison with the CPU for the movement of the machine axes. The CPU sends the control signals generated for the movement of the axis to the servo control unit and the servo c o n t ro l u n i t c o n ve rt t h es e s i gn als in t o th e s u it ab le di gi t al o r an a lo g s i gn al t o be fe d t o t h e machine tool axis movement. This also checks whether machine tool axis movement is at the same speed as directed by the CPU. In case any safety conditions related to the axis are overruled during movement or otherwise they are reported to the CPU for corrective action
Servo-Control Unit The decoded position and velocity control signals, generated by the CPU for the axis movement forms the input to the servo-control unit. This unit in turn generates suitable signals as command values. The servodrive unit converts the command values, which are interfaced with the axis and the spindle motors .The servo-control unit receives the position feedback signals for actual movement of the machine tool axes from the feedback devices (like linear scales, rotary encoders, resolves, etc.).The velocity feedback is generally obtained through tacho generators. The feedback signals are pas s e d o n t o t h e C P U fo r fu rt h e r p ro c e s s in g. Th u s t h e se rvo -c o n t ro l u n i t pe rfo rm s t h e dat a communication between the machine tool and the CPU.As explained earlier, the actual movement of the slides on the machine tool is achieved through servo drives. The amount of movement and the rate of movement are controlled by the CNC system depending upon the type of feedback system used, i.e. closed-loop or open-loop system.
PROGRAMMABLE LOGIC CONTROL (PLC) Throughout the ages people have been working in research institutes and industries in machine automation so as to have less involvement of operator in machine operations. In the development of automation controllers the trend has been to move towards soft controllers so as to provide better control, more flexibility
and
more
reliability
with
intelligent diagnostics of machine faults. So industries have gradually moved from conventional
relay
logic
control
to
programmable logic control and then to computerised numeric control. Also Since there were problems related to large electrical panels with a number of electrical
components
and
extensive
wiring, people felt the need for software logic controllers. So they gave birth to Programmable
Logic
Controller
(P.L.C)
wherein the control logic is developed in ladder diagram, a software logic control, with a number of inputs taken from the environment and generating the outputs, depending on the logic programmed, to the environment. This helped to control any
31
[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 machine sequence with small electrical panels, less number of electrical components and less wiring with more flexibility to change machine sequence and providing ease to reusability of the components. These fulfilled some of their needs but the desire to obtain software controlled automation with accuracy necessitated the development of Computer Numeric Control (C.N.C). Here the controller acts as a master over the P.L.C. and connected with encoders to provide positional feedback .In order to have better control for positioning, controlled speed and quick reversal of direction of slide movement, servo motors having less inertia, along with servo drives are interfaced with the C.N.C . The user based part program decoded by the C.N.C. provides the desired profile with the control being transferred to P.L.C. and drives as and when required. Special measuring devices as locators, gauges being interfaced with the C.N.C. through independent controllers provide more accuracy. Programmable Logic Controller: The diagram here shows the functional units of a typical P.L.C. Program Memory (EPROM/EEPROM): The Program Memory shown in the functional block is a specified area of the CPU RAM. This memory has the following characteristics: 
Memory contents can be changed quickly

Memory contents are lost in case of power failures if there is no battery backup.
It is always advisable to store the program in a memory sub-module (EPROM/EEPROM) from where the program can be copied to CPU RAM in case the program is lost or corrupted. Operating System (ROM): It determines how the user program is executed, how inputs and outputs are managed, how the memory is divided, and how data are managed. The operating system is fixed and cannot be changed. Process Image Tables (PII, PIQ): The signal status of input and output modules is stored in a specified area of CPU RAM which is known as the “process image table”. Input and Output modules have the following separate image tables: 
Process image input table (PII)

Process image output table (PIQ)
Serial Interface: Through the serial port programmers, operator panels and monitors are connected through cables and the CPU can be connected as a slave to a local area network. Timers, Counters, Flags: There are Timers, Counters and Flags available internally in the CPU memory that is used by the control program. The program can set, delete, start and stop the timers and counters and the values are stored in reserved area of RAM memory. A separate area in the RAM memory stores some intermediate results as flags. Input/output Modules: These modules transfer information between CPU and process peripherals as sensors, transducers and actuators. These are of the following type: 
Digital Input and Output Module

Analog Input and Output Module
  
These involve signal states “0” and “1” only These record and generate variable quantities as voltage and current
High-speed Counter and Position detection Module 
These are used to record counters pulses of 25/500 kHz (typical value for Siemens S5100U PLC). It can be used for position detection tasks.
Processor: Depending on the control program the processor calls the statements from the program memory in sequence, executes them, processes information from PII and sets PIQ.
32
[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011
Computer Numeric Control (CNC) with PLC The major components associated with a CNC system are power supply, PLC, servo drives, CRT monitor and keyboard and some special controllers might be interfaced for specific accuracy requirements such as precise positioning of job, accurate sizing of any machining operations. The power unit supplies constant 24V D.C. to the system. PLC interfaced with the CNC is programmed for the machine sequence. The part program of the CNC determines the operational sequence of the machine. To clarify the machine sequence and operational sequence CNC-PLC interface has been dealt later in this paper. Servo drives are used in conjunction with servo motors for better variable speed control with less response time as the inertia of the rotor is less. The diagram shown below shows the CNC block diagram with the necessary interfaces for a single axis machine. There are two types of servo drives: (1) Constant torque-speed drives used for axis motors (2) Constant power drives used for spindle motors The external inputs and outputs from the machine are connected to the PLC through the I/O interface of PLC. The system program of the CNC executes the part program, reads the machine data, perform the calculations. CNC reads in the signal from the axis encoder from the measuring card which is placed in one of the slots of the controller. Thus having the machine data as pitch of the ball-screw, number of
encoder
pulses
generated
and
resolution of the encoder mounted on the slide the distance moved by the slide can be calculated as Distance
=
(p/r)*ep
(here
backlash
compensation is not taken into account) Where p = pitch of ball-screw (mm) r = resolution of encoder in (PPR) ep = number of encoder pulses generated
CNC block diagram This provides the positional feedback to the system. The velocity feedback is directly fed to the drive from the encoder or tacho-generator of the servo motor. The next diagram shows the interface of the CNC with the servo drives. CNC sends a drive enable signal to a drive and the drive tends to retain its position unless some command for movement is send from the CNC. To give feed command CNC along with the drive enable signal sends a reference voltage to the drive in the range of +/-10V proportional to the desired speed. The +/- sign denotes the direction of movement. The reference voltage is calculated as: Reference voltage = (10/n)*S Where n = maximum speed i.e. rated speed of motor (r.p.m) S = desired speed (r.p.m)
33
[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 The drive calculates the commanded speed from the reference voltage and calculates the actual motor speed from the motor encoder feedback to the drive. Thus the error is known and by changing the frequency and phase voltage drive tries to minimise the error to maintain the desired speed. If the drives and motors are in healthy condition then a drive ready signal is send to the PLC. If this signal is missing then fault appears and axes movements or spindle operations are not possible. The next diagram shows a CNC-PLC interface of a CNC system. The part program determines the operational sequence of the machine. It executes the part program as follows: N10............. N20............. N30 CNC sets a predetermined flag in PLC for M-code M24 (signal 1) PLC resets “read in enable” (signal 2) in CNC to stop further execution of part Program. PLC sends an output (signal 3) to clamp solenoid from the ladder
Drive-CNC interface diagram
PLC-CNC interface diagram
logic. Pressure switch signal comes as input to PLC (signal 4) once clamping operation is completed. PLC sets the “read in enable” (signal 5) in CNC and execution of part program is resumed. N40.......... N50 Similarly M08 sets a PLC flag (signal 6).PLC resets “read in enable “in CNC (signal 7).PLC sends output to coolant solenoid (signal 8).Once coolant flow starts flow switch sends input to PLC (signal 9). PLC sets “read in enable” (signal 10) in CNC and part program execution is resumed till M02. Intelligent Fault Diagnostics: A CNC system is capable of diagnosing some of the machine faults and prompts the operator or maintenance personnel. It is mainly monitored by the PLC logic. There are preset flags for operator messages, fault messages and M-codes. When PLC generates an output and the corresponding feedback signal is not fed back as input to the PLC within a certain time the corresponding fault flag is set. During the time duration the corresponding operator flag is set which will help to prompt the operator that a certain function is going on. To make the system user friendly certain portion of the CNC system memory is reserved which contain the operator and fault messages in text format. So when a particular flag is set the system displays the corresponding text.
34
[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011
TYPES OF CNC MACHINES In every aspects of manufacturing CNC machines are used. It can be mainly classified in eight classes. 1. Mills and Machining centres 2. Lathes and Turning centres 3. EDM Machines 4. Grinding machines 5. Cutting Machines 6. Fabrication Machines 7. Welding Machines 8. Coordinate Measuring Machines
FEATURES OF CNC MACHINES 
Slideways

Spindle Drive

Feed Drive

Position measuring transducers

Tool magazines and automatic tool changers

Lubrication system

Coolant system
Slideways: In the conventional machine tools, there is a direct metal to metal contact between the
•
slideway and the slides. Since the slide movement are very slow, & machine utilization is also low, this arrangement is adequate for conventional machine tools. However, the demand on slideways is much more in CNC machines because of rapid movements & higher machine utilisation. The design of slideway in a CNC machine should:
Siemens offers a range of SINUMERIK
a)
Reduce friction
CNC models such as the 810D, 840Di, 840D,
b)
Reduce wear
and the compact FM357-2 positioning and
c)
Satisfy the requirements of movement of slides
d)
Improve smoothness of a drives
To meet these requirements in CNC machine tool slideways, the techniques used include hydrostatic slideways, linear bearings with balls, rollers or needles & surface coatings.
path control module. These products provide the coordinated multi-axis control needed for milling, drilling, turning, and grinding applications.
SINUMERIK
interconnect
operator
CNCs
also
panels
and
SIMODRIVE servo and spindle drives and associated motors to form a complete control
system
for
the
machine
tool.
Linear bearings with balls & rollers The sliding friction, due to direct metal-to-metal contact, between the slide & slideways is replaced with rolling friction by the use of anti-friction ball or roller bearings. For movement along a flat plane, recirculating linear roller bearings are used. The main characteristic of the linear roller bearing is that there is a continuous roller circulation which allows unlimited linear movement. In case of roller bearings,
35
[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 the rollers are guided between shoulders of the supporting elements with very close tolerances. The guiding element prevents the rollers from falling out & sliding against each other.
Linear Roller Bearings
Surface Coatings The guiding surfaces of the machines are sometimes coated with low friction material such as polytetrafluoroethylene (PTFE) or replaceable strips of low friction material are used. When the strips wear to such an extent that the alignment is in error, these can be replaced.
Spindle drive: At the high cutting speeds and high material removal rates, the spindle carrying
•
the work piece or the tool are subjected to deflection & thrust forces. To ensure increased stability & minimise torsional strain, the machine spindle is designed to be short & stiff & the final drive to the spindle is located as near to the front bearing as possible. To meet common features of CNC machines i.e., High power & High speeds, DC motor with SCR control is commonly used to provide step-less variations of wide range of productivity.
Feed drives: The conventional CNC machines use recirculating ball screw and nut arrangement. In
•
case of light duty machines, stepper motors can also be used. Rack & pinion drivers are used where long transfers are involved. The connection between the screw & the nut is through an
endless stream of recirculating balls. Majority of machine tools used permanent type DC motor with SCR control or width modulation drives for
axis
drives.
•
Ball screw and nut arrangement GENERAL INTRODUCTION TO ELECTRICAL AND ELECTRONICS ITEMS 1. Proximity Switches Proximity switches are solid state switching device which required no physical contact to actuate them. These are use for control and positioning signals because of long life, high switching speed, no touch, zero operation force, wear and maintenance free operation, bounce free signal and reliable switching under extreme conditions. It comprises of three principle parts.
36
[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 i) Oscillator ii) Trigger stage and iii) Amplifier stage To obtain a switching signal at given voltage and temperature, sensing distance (Sn) is the main factor. Sensing distance is the maximum distance between the target and the sensing face. Sensing face is the surface from which the electromagnetic field radiates. Sn depends upon material, thickness and area of target. Target diameter = Oscillator Unit Diameter
2. Limit Switch Limit switches are used to make or break control circuit when mechanically actuated by a moving member. Moving member might be a dog mounted on the moving component, as in the case of traveller over travel limit switches, or may be of plunger actuated type as in case of filter clogged limit switch. The limit switch type may be of normally open type (NO) which will close when switch is actuated or normally close type (NC) which will actuated.
3. Circuit Breaker A device designed to open and close by non automatic means and to open the circuit automatically on the predetermined overload of current, when properly, applied within its rating. Two types are there: 1) Thermal 2) Hydraulic Thermal circuit breakers respond only to temperature change in the bimetallic element. Heat is generated in the element because of i2rlosses. The element bends or deformed to open the contacts and unlatch the mechanism. Mainly used is MCB (Miniature Circuit Breaker) which offer dual protection i.e., protection against overload and short circuit. MCBs are preferred over fuses as it disconnects supply instantaneously, and requires seldom replacement. Some of the technical features of Circuit Breakers are: 
Long mechanical and electrical operational life
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High breaking capacity
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Overload tripping through accurately calibrated bimetal strip.
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Short circuit tripping through magnetic coil.
Circuit breakers give protection to the equipments such as motors, transformers, air conditioners, refrigerators, geysers, mixers etc. and cables/wires in electrical distribution system.
4. Overload Relays It can be defined as the device which is operative by variation in the conditions of one electrical circuit to affect another device in same or another electric circuit. Relays provides overload protection over control circuits when used in conjugation with contactors and other motor control equipments, they provide accurate and reliable control and protection under overload condition.
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 5. Contactors Device used for repeatedly establishing and interrupting an electric power circuit. The contactors are suitable for controlling electrical circuit of all kinds e.g. capacitor, lighting, heating, switching A.C. circuit as well D.C. circuits Also suitable for use in control panel for machine tools, motor control centres and other applications where high frequency requirement is must. Contactors should have following design features: 
Long Life: Bounce free contact system contributes to long contact life.
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Modern techniques of arc quenching: In case of A.C. contactor, double breaking contact divide the arc into two. For contactors of higher size, deionization chamber split the arcs into numerous short arcs.
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Contactors are designs for very high frequency operation
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Compact Size
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Installation: Some contactors can be mount in any position and some with maximum inclination, from vertical surface, of 22 ½ degrees.
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Auxiliary Contact: For control a interlocking purposes, contactors can be provided with a number of auxiliary contacts.
6. Fuses A device used for protection of equipments. A wide range of fuses is available for protection of transformer, cables, capacitors and motors for application in Air or Oil. HRC fuses are used for the interruption of fault current in indoor and outdoor high voltage system and also protection of distribution power equipment.
7. Pressure Switch The function of pressure switch is to break or make the control circuit whenever the pressure actuates the switch contacts. The switch contacts may be normally open type which closes on increasing pressure or of normally close type which open on increasing pressure. Pressure switches use single pole double throw (SPDT) micro switches as switching element. These switches are use with water, oil, air, nitrogen, inert gases, steam, mineral oil and natural gas etc.
8. Introduction to NC Automation has been associated with advancement in technology. The problem of automation of small lot production has been overcome by numerical control (NC) machine tools have great extent. NUMERICAL CONTROL (NC) is defines as “A system in which actions are controlled by direct insertion of numerical data at some point. The system must automatically interpret at least some portion of this data.”
CNC In CNC system, a dedicated computer is used to perform all the basis NC functions as per the control program also called executive program stored in the memory of the computer. It is this executive program, which makes it flexible/soft wired. Unlike NC systems, machine control data comes directly from the computer memory. Because of the memory availability user can store part programs also in computer. The capability to edit this part program is a real advantage to the part programmer right at the machine station. Additional features such as tape punching option, user oriented subroutine programs etc are also possible on CNC.
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 9. Feedback device CNC system requires a measuring device and measurement can be done with feedback system. Basically feedback allows the control system to compare the machine’s actual position with command valve. The result of this comparison provides the ability of velocity and position control. Encoders, resolver or inducto-syn are used as feedback devices.
ENCODERS Incremental rotary encoder is most commonly used feedback device. The rotary encoder is a shaft-driven device delivering electrical pulses at its output terminal. The pulse frequency is directly proportional to shaft speed. Encoder consists of glass disc marked with a precise circular pattern of alternate clear and opaque segments on its periphery. The disc is mounted on the shaft. A fixed source of light is on one side and a photo cell is placed on other side of the disc. As disc rotates, light is permitted to fall on photo cell, to produce the output signal which is approximately sinusoidal. Internal or external amplifier is used to amplify the photocell output to a level suitable for feeding logic circuits. Amplified signal is fed to a circuit which converts the signal to a proper square wave with suitable rise and fall times. To sense direction of rotation a two photocell system is used. Photocell is arranged so that output signals have 900 shifts to each other. External logic circuitry is used to determine the direction of rotation.
10. D.C Motor A D.C. motor can be thought of made up of two parts: 1) A stationary field either of permanent magnet or electromagnet 2) An armature which is allowed to rotate. The armature consists of series of coils which are connected to motor’s commutator and brushes. The commutator serves to switch the power to successive coils as the armature rotates so that magnetic armature poles remain in the same position relative to the field poles. As the armature rotates in the magnetic fields the motion of its conductor generates a voltage. This is true whether motor is delivering the power or driven by some external means.
11. D.C. Drives D.C. drive controls motor speed through control of armature current by varying DC voltage applied to the motor. This is accompanied by controlling the point on AC input sine wave at which an SCR begins to conduct. For motors up to a few kilowatts the armature converter can be supplied from either single-phase or three-phase mains, but for larger motors three-phase is always used. A separate thyristor or diode
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 rectifier is used to supply the field of the motor: the power is much less than the armature power, so the supply is often single-phase, as shown. The arrangement shown in next figure is typical of the majority of D.C. drives and provides for closed-loop speed control. The main power circuit consists of a six-thyristor bridge circuit, which rectifies the incoming a.c. supply to produce a D.C. supply to the motor armature. The assembly of thyristors, mounted on a heatsink, is usually referred to as the 'stack'. By altering the firing angle of the thyristors the mean value of the rectified voltage can be varied, thereby allowing the motor speed to be controlled.
The controlled rectifier produces a crude form of D.C. with a pronounced ripple in the output voltage. This ripple component gives rise to pulsating currents and fluxes in the motor, and in order to avoid excessive eddy-current losses and commutation problems, the poles and frame should be of laminated construction. It is accepted practice for motors supplied for use with thyristor drives to have laminated construction, but older motors often have solid poles and/or frames, and these will not always work satisfactorily with a rectifier supply. It is also the norm for drive motors to be supplied with an attached 'blower' motor as standard. This provides continuous through ventilation and allows the motor to operate continuously at full torque even down to the lowest speeds without overheating. Low power control circuits are used to monitor the principal variables of interest (usually motor current and speed), and to generate appropriate firing pulses so that the motor maintains constant speed despite variations in the load. The 'speed reference' is typically an analogue voltage varying from 0 to 10 V, and obtained from a manual speed-setting potentiometer or from elsewhere in the plant. The combination of power, control, and protective circuits constitutes the converter. Standard modular converters are available as off-the-shelf items in sizes from 0.5 kW up to several hundred kW, while larger drives will be tailored to individual requirements. Individual converters may be mounted in enclosures with isolators, fuses etc., or groups of converters may be mounted together to form a multimotor drive.
CNC MACHINES There are different CNC machines in Jhansi unit, which serve some special purposes.
CNC OXY-ACETYLENE FLAME CUTTING This machine is in bay-0 & is used for M.S sheet. This machine can cut up to 300mm thick sheet. It has four burners, which can work simultaneously. • Control system: ESAB German (NCE-510)
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 • Axes: There are two axes in machine X and Y axis. In X axis tool can move up to 7 meters and in Y axis tool can move up to 3.5 meters • Drive: D.C. • Feedback rotary encoders
CNC CROPPING LINE There are two cropping line CNC machine in bay-5. These are used to cut CRGO sheets for construction of core of transformer. First machine has been made by George German with control system from Siemens 810D. This machine mainly consists of two tools: punch and swing shear for cutting lamination as required by program. The other machine has been manufactured by Sooner Company. It has two punches. One fixed shear and one movable shear, which can shear straight as well as 45 degree. It consists of one tip cut and one V cut also. 
Control System 810D
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Axis: One axis
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Drive Way
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Feedback linear Scale
ASQUITH CNC BOGIE MACHINE CENTRE
This machine is in boogie shop. It is used for all operation in boogie manufacturing like milling, drilling and boring. All the operation can be done in the single machine. 
CONTROL SYSTEM : GE FANUC 15M
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Axis: It works three axis X, Y and Z axis. It can travel up to 8000 mm in X-axis. 4000 mm in Yaxis and 800 mm in Z-axis.
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Feedback linear scale.
It has auto tool changer, which can change tools automatically. According to program its spindle diameter is 180 mm and 40 KW power is required to operate the spindle.
(A)HMT SB CNC LATHE This is used for turning the job. 
Control system: Sinumeric 3T
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 
Axis: It works in two axis X and Z axis. Tool can traverse up to 1000 mm in X-axis and 300mm in Z-axis.
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Drive D.C.
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Feedback: Rotary Encoder.
(B) HMT CNC VERTICLE MILLING MACHINE This machine is used for milling purpose. 
Control system : Sinumeric 800 M
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Axis: it works in three axes X, Y and Z axis. Tool can travel 1200 mm in X-axis, 600 mm in Y-axis, 400 mm in Z-axis.
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Drive D.C.
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Feedback rotary encoder.
(C) COOPER CNC VERTICLE BORING MACHINE This machine is used for boring purpose. 
Control System: Viking kirloskar
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Axis: Tool can move in two axes: X and Z- axis. It can move 600 mm in X- axis and 400 mm in Zaxis.
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Drive D.C.
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Feedback : Linear Sale
CODES USED IN CNC PROGRAMS G-code is the name of any word in a CNC program that begins with the letter G and generally is a code telling machine tool what type of action to perform. Such as: Rapid Move etc. Controlled feed move in straight line or are series of controlled feed moves that would result in hole being bored, a work piece cut(routed) to a specific dimension, or a decorative profile shape added to edge of work piece. There are other codes; the type codes can be thought of registers in the computer X absolute position Y absolute position Z absolute position A position (rotary around X) B position (rotary around Y) C position (rotary around Z)
Common Fanuc M & G- Codes G02
CW circular interpolation
G03
CCW circular interpolation
G04
Dwell
G10/G11 Data writing/Data write cancel G17
X-Y plane selection
G18
X-Z plane selection
G19
Y-Z plane selection
G20
Programming in inches
G21
Programming in mm
G28
Return to home position
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 G31
Skip function
M00
Program stop
M01
Optional stop
M02
Program stop
M03
Spindle CW
M04
Spindle CCW
M05
Spindle stop
M08
Coolant/Lubricant on
M09
Coolant/Lubricant off
M30
Program end
ADVANTAGES OF CNC MACHINES 1. Productivity Since cutting tool is brought to its machining position much more efficiently than it was done manually by the machine operator, NC machine is spending much more time per shift cutting than in past. Conventional machines very seldom remove metal for more than 15% of total available time under normal batch production conditions. Whereas CNC machine tools should be capable of removing metal for between 50% and 75% of available time. When working on medium batch production, CNC machining has around 4 to 1 productivity advantage over conventional machine. The actual advantage may vary from batch to batch depending upon the complexity of components to be produced and is normally proportional to the number of conventional operation required to produce the components.
2. Flexibility in design and production Machine can switch over to different job as set up times are low and sudden changes in sales requirement are much more easily catered for. This enables the formulation of more aggressive marketing plans. The use of CNC machines also give designers freedom to design component switch, by conventional means, are often impossible to produce. Change of design can also be easily incorporated as it means change of tape.
3. Inspection High position accuracies and repeatability are inherent features of CNC machines and reduce inspection time considerably. Normally a 100% inspection of the first component produced by a new tape is all that is necessary to prove the tape and tooling. Subsequently it is required to have only sample inspection. In process gauging and inspection is also provided on modern CNC machines.
4. Floor space One CNC machine can replace five to six conventional machines. Thus manufacturing activities of a company can be expanded without increasing the floor area proportionately.
5. Inventory By using CNC machine, procurement sizes and batch sizes can be reduced because of shorter lead time’s .This results in substantial saving. Lead time is time taken to progress a batch of component through a
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011 batch of production shop and is proportional to number of operation required by conventional methods. For example a component which requires 112 set ups by conventional methods may requires only 1 or 2 set ups in CNC machining center reducing total product flow times.
6. Material Handling Handling of component from machine to machine which is necessary on conventional machine is significantly reduced on CNC machine, as all the operations are performed on one machine. This obviously reduces labour cost.
7. Tooling This ability to complete machine part in a single setup means that fewer and simpler fixtures are required, which in turns requires less storage space and maintenance. The simpler a fixture is, the less expensive is to manufacture it.
8. Operator’s Skill Dependence on skilled labour can be dispensed with. The accuracy of part produced with CNC machines machine depend upon accuracy and ability of machine and tape – and not on individual operator.
9. Scrap and Rework Drastic reduction in scrap is achieved because of the inherent accuracy and repeatability of CNC machine.
10. Costing Time required to produce a component is a function of machining cycle of CNC machines and is not influenced by operator’s efficiency or variation in labour’s rate, a great stability of prices can often be achieved throughout the life cycle of the respective product. Also cost accounting becomes very precise.
11. Better Management Information and Control With various advantages of CNC machines, decisions effecting unit cost, delivery and quality are firmly placed in the hands of management and not of the machine operator.
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CONCLUSION
It is true that CNC machine costs more to install initially. But higher initial cost is set off by the direct & indirect gains resulting from various advantages of CNC machines. In most cases, careful techno-economic evaluation of a given manufacturing situation will clearly bring out that unit cost of production is definitely less tools with that of so called conventional machine. To conclude numeric control is the most sophisticated form of automatic control of machine tool. It has high degree of precision and reliability. The control system has undergone several stage of development. Some of the special features offered by CNC machine manufacture are:  Thermal stabilization  Axis calibration  Lost machine compensation With the various above qualities of CNC machine there are numerous advantages. They are 
High accuracy
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High reliability
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Less scrap and network
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Better machine utilization
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Computer control of manufacture capability of integration into distribution numeric control (DNC) etc.
The programs written for CNC are easy to write and understand. These programs use either G-cod or M-code that runs the program. The codes are simple to understand. No wonder CNC machines tools are becoming more and more popular day by day in modern industries. In longer run CNC machine pays for itself with such outstanding qualities.
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[COMPUTER NUMERIC CONTROL(CNC) MACHINES] June 25, 2011
Bibliography 1. Wikipedia
www.wikipedia.org/wiki/Main
2. B.H.E.L official website
www.bhel.com/home.php
3. www.cnccncmachines.com/
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