BHEL final report submission

1. Summer Training Report
Computer Numeric Control Machine
&
Programmable Logic Control

2. Bharat Heavy Electricals Limited Haridwar Ranipur
Under Guide Of:- Submitted By :-
Sr. Engineer Shyamveer Singh
Mr G.S Meena Reg No: 11205816
BHEL Haridwar
ACKNOWLEDGEMENT
I am highly thankful to B.H.E.L. engineers and technical staff for
providing us vital and valuable information about the different facets of
an industrial management system.We express our gratitude to Human
Resource and Development department for giving us a chance to feel
industrial environment and its working in B.H.E.L. and we are thankful
to Mr. G.S meena, Sr. Engineer for giving his precious time and help us
in understanding various theoretical and practical aspect of our project
on PLC under whose kind supervision we accomplished our project. We
are also thankful to Mr. Dhruv Bhargav H.R.D for his kind support.
Shyamveer Singh
B.Tech (ECE)

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

4. INDEX
ABSTRACT i
ACKNOWLEDGEMENT ii
CERTIFICATE iii
Sr. No. Topic Page no.
INTRODUCTION 1
1. BHEL 2-3
1.1 OVERVIEW 3
1.2 WORKING AREAS 3
1.2.1 POWER GENERATION 3
1.2.2 POWER TRANSMISSION & DISTRIBUTION 3-4
1.2.3 INDUSTRIES 4
1.2.4 TRANSPORTATION 4-5
1.2.5 TELECOMMUNICATION 5
1.2.6 RENEWABLE ENERGY 5
1.2.7 INTERNATIONAL OPERATIONS 5-6
1.3 TECHNOLOGY UPGRADATION AND RESEARCH AND 6

5. DEVELOPMENT
1.3.1 HUMAN RESOURCE DEVELOPMENT INSTITUTE 6
1.4 HEALTH SAFETY AND ENVIRONMENT MANAGEMENT 7
1.4.1 ENVIRONMENTAL POLICY 7
1.4.2 OCCUPATIONAL HEALTH AND SAFETY POLICY 7-8
1.4.3 PRINCIPLE OF THE “GLOBAL COMPACT” 8
1.5 BHEL UNITS 9
1.6 BHEL HARIDWAR 10
1.6.1 LOCATION 10
1.6.2 ADDRESS 10
1.6.3 AREA 10
1.6.4 UNITS 10
Sr. No. Topic
Page
no.
1.6.5 HEEP PRODUCT PROFILE 12-13
2. CNC Machine
2.1 INTRODUCTION 21
2.2 CNC Machine 22
2.3 History 22
2.4 CNC System Element 23
3 CNC System Units
3.1 CPU 24
3.2 Servo operator control 24
3.3 Machine Control 25
3.4 PLC 29
4 Modes Of Operation
4.1 Manual Mode Of Operation 26
4.2 Manual Data Input 26
4.3 Automatic Mode 27
4.4 Reference Mode 27
4.5 Input Mode 28
4.6 Output Mode 28
5 Interfacing 29
6 Conclusion 30
FIGURE INDEX

6. INTRODUCTION
Embarking upon the 50th Golden Year of its journey of engineering excellence,
BHEL is an integrated power plant equipment manufacturer and one of the largest
engineering and manufacturing company of its kind in India engaged in the
design, engineering, manufacture, construction, testing, commissioning and
servicing of a wide range of products and services for the core sectors of the
economy, viz. Power, Transmission, Industry, Transportation (Railway),
Renewable Energy, Oil & Gas and Defence with over 180 products offerings to
meet the needs of these sectors. Establishment of BHEL in 1964 was a
breakthrough for upsurge in India's Heavy Electrical Equipment industry.
Consistent performance in a highly competitive environment enabled BHEL attain
the coveted 'Maharatna' status in 2013.
BHEL as a part of Pt. Jawaharlal Nehru's vision was bestowed with the onus to
make the country self reliant in manufacturing of heavy electrical equipment. This
dream has been more than realised and the contribution in nation building
endeavour is going to continue likewise. Today, with 20,000 MW per annum
capacity for power plant equipment manufacturing, BHEL's mammoth size of
Sr. No. Topic Page
no.
1 CNC Victor JF 3VS 21
2 Open and Close loop System 24
TABLE INDEX
Sr. No. Topic
Page
no.
1. BHEL UNITS 9
2. BLOCKS IN HEEP 11
3. SECTIONS IN CFFP 11
4. BLADE ROOTS 15
5. LAYOUT OF BLOCK-3 18

7. operations is evident from its widespread network of 17 Manufacturing Units, two
Repair Units, four Regional Offices, eight Service Centres, eight Overseas
Offices, six Joint Ventures, fifteen Regional Marketing Centres and current project
execution at more than 150 project sites across India and abroad. The total
installed capacity base of BHEL supplied equipment -138 GW in India speaks
volumes about the contribution made by BHEL to Indian power sector. BHEL's
57% share in India's total installed capacity and 65% share in the country's total
generation from thermal utility sets (coal based) as of March 31, 2014 stand
testimony to this. The company has been earning profits continuously since 1971-
72 and paying dividends since 1976-77 which is a reflection of company's
commendable performance throughout.
BHEL also has a widespread overseas footprint in 76 countries with cumulative
overseas installed capacity of BHEL manufactured power plants nearing 10,000
MW including Malaysia, Oman, Libya, Iraq, the UAE, Bhutan, Egypt and New
Zealand.
1.1 OVERVIEW
Bharat Heavy Electricals Limited (B.H.E.L.) is the largest engineering and
manufacturing enterprise in India. BHEL caters to core sectors of the Indian
Economy viz., Power Generation's & Transmission, Industry, Transportation,
Telecommunication, Renewable Energy, Defense and many more.
Established in 1960s under the Indo-Soviet Agreements of 1959 and 1960 in the
area of Scientific, Technical and Industrial Cooperation.
BHEL has its setup spread all over India namely New Delhi, Gurgaon, Haridwar,
Rudrapur, Jhansi, Bhopal, Hyderabad, Jagdishpur , Tiruchirapalli, Bangalore and
many more.
Over 65% of power generated in India comes from BHEL-supplied
equipment.Overall it has installed power equipment for over 90,000 MW.
BHEL's Investment in R&D is amongst the largest in the corporate sector in India.
Net Profit of the company in the year 2011-2012 was recorded as 6868crore

8. having a high of 21.2% in comparison to last year.
BHEL has already attained ISO 9000 certification for quality management, and
ISO 14001 certification for environment management.
It is one of India's nine largest Public Sector Undertakings or PSUs, known as the
NAVRATNAS or 'The Nine Jewels’.
The power plant equipment manufactured by BHEL is based on contemporary
technology comparable to the best in the world.
The wide network of BHEL's 14 manufacturing divisions, 4 Power Sector regional
centre, over 100 project sites, 8 Service Centre and 18 regional offices, enables the
Company to promptly serve its customers and provide them with suitable
products, systems and services efficiently.
1.2 WORKING AREAS
1.2.1 POWER GENERATION
Power generation sector comprises thermal, gas, hydro and nuclear power plant
business as of 31.03.2001, BHEL supplied sets account for nearly 64737 MW or
65% of the total installed capacity of 99,146 MW in the country, as against nil till
1969-70.
BHEL has proven turnkey capabilities for executing power projects from concept
to commissioning, it possesses the technology and capability to produce thermal
sets with super critical parameters up to 1000 MW unit rating and gas turbine
generator sets of up to 240 MW unit rating. Co-generation and combined-cycle
plants have been introduced to achieve higher plant efficiencies. to make efficient
use of the high-ash-content coal available in India, BHEL supplies circulating
fluidized bed combustion boilers to both thermal and combined cycle power
plants.
The company manufactures 235 MW nuclear turbine generator sets and has

9. commenced production of 500 MW nuclear turbine generator sets.
Custom made hydro sets of Francis, Pelton and Kaplan types for different head
discharge combination are also engineering and manufactured by BHEL.
In all, orders for more than 700 utility sets of thermal, hydro, gas and nuclear have
been placed on the Company as on date. The power plant equipment manufactured
by BHEL is based on contemporary technology comparable to the best in the
world and is also internationally competitive.
The Company has proven expertise in Plant Performance Improvement through
renovation modernization and upgrading of a variety of power plant equipment
besides specialized know how of residual life assessment, health diagnostics and
life extension of plants.
1.2.2. POWER TRANSMISSION & DISTRIBUTION (T & D)
BHEL offer wide ranging products and systems for T & D applications. Products
manufactured include power transformers, instrument transformers, dry type
transformers, series and stunt reactor, capacitor tanks, vacuum and SF circuit
breakers gas insulated switch gears and insulators. A strong engineering base
enables the Company to undertake turnkey delivery of electric substances up to
400 kV level series compensation systems (for increasing power transfer capacity
of transmission lines and improving system stability and voltage regulation), shunt
compensation systems (for power factor and voltage improvement) and HVDC
systems (for economic transfer of bulk power). BHEL has indigenously developed
the state-of-the-art controlled shunt reactor (for reactive power management on
long transmission lines). Presently a 400 kV Facts (Flexible AC Transmission
System) project under execution.
1.2.3. INDUSTRIES
BHEL is a major contributor of equipment and systems to industries. Cement,
sugar, fertilizer, refineries, petrochemicals, paper, oil and gas, metallurgical and
other process industries lines and improving system stability and voltage
regulation, shunt compensation systems (for power factor and voltage

10. improvement) and HVDC systems(for economic transfer of bulk power) BHEL
has indigenously developed the state-of-the-art controlled shunt reactor (for
reactive power management on long transmission lines).Presently a 400 kV
FACTS (Flexible AC Transmission System) projects is under execution. The range
of system & equipment supplied includes: captive power plants, co-generation
plants DG power plants, industrial steam turbines, industrial boilers and
auxiliaries. Water heat recovery boilers, gas turbines, heat exchangers and pressure
vessels, centrifugal compressors, electrical machines, pumps, valves, seamless
steel tubes, electrostatic precipitators, fabric filters, reactors, fluidized bed
combustion boilers, chemical recovery boilers and process controls.
The Company is a major producer of large-size thruster devices. It also supplies
digital distributed control systems for process industries, and control &
instrumentation systems for power plant and industrial applications. BHEL is the
only company in India with the capability to make simulators for power plants,
defense and other applications. The Company has commenced manufacture of
large desalination plants to help augment the supply of drinking water to people.
1.2.4. TRANSPORTATION
BHEL is involved in the development design, engineering, marketing, production,
installation, and maintenance and after-sales service of Rolling Stock and traction
propulsion systems. In the area of rolling stock, BHEL manufactures electric
locomotives up to 5000HP, diesel-electric locomotives from 350 HP to 3100 HP,
both for mainline and shunting duly applications. BHEL is also producing rolling
stock for special applications viz., overhead equipment cars, Special well wagons,
Rail-cum-road vehicle etc., Besides traction propulsion systems for in-house use,
BHEL manufactures traction propulsion systems for other rolling stock producers
of electric locomotives, diesel-electric locomotives, electrical multiple units and
metro cars. The electric and diesel traction equipment on India Railways are
largely powered by electrical propulsion systems produced by BHEL. The
company also undertakes retooling and overhauling of rolling stock in the area of
urban transportation systems. BHEL is geared up to turnkey execution of electric
trolley bus systems, light rail systems etc. BHEL is also diversifying in the area of

11. port handing equipment and pipelines transportation system.
1.2.5. TELECOMMUNICATION
BHEL also caters to Telecommunication sector by way of small, medium and
large switching system.
1.2.6. RENEWABLE ENERGY
Technologies that can be offered by BHEL for exploiting non-conventional and
renewable sources of energy include: wind electric generators, solar photo voltaic
systems, solar lanterns and battery-powered road vehicles. The Company has
taken up R&D efforts for development of multi-junction amorphous silicon solar
cells and fuel based systems.
1.2.7. INTERNATIONAL OPERATIONS
BHEL has, over the years, established its references in around 60 countries of the
world, ranging for the United States in the west to New Zealand in the far east.
These references encompass almost the entire product range of BHEL, covering
turnkey power projects of thermal, hydro and gas-based types, substation projects,
rehabilitation projects, besides a wide variety of products, like transformers,
insulators, switch gears, heat exchangers, castings and forgings, valves, well-head
equipment, centrifugal compressors, photo-voltaic equipment etc. apart from over
1110mw of boiler capacity contributed in Malaysia, and execution of four
prestigious power projects in Oman, some of the other major successes achieved
by the company have been in Australia, Saudi Arabia, Libya, Greece, Cyprus,
Malta, Egypt, Bangladesh, Azerbaijan, Sri Lanka, Iraq etc.
The company has been successful in meeting demanding customer's requirements
in terms of complexity of the works as well as technological, quality and other
requirements viz. extended warrantees, associated O&M, financing packages etc.
BHEL has proved its capability to undertake projects on fast-track basis. The

12. company has been successful in meeting varying needs of the industry, be it
captive power plants, utility power generation or for the oil sector requirements.
Executing of overseas projects has also provided BHEL the experience of working
with world renowned consulting organizations and inspection agencies.
In addition to demonstrated capability to undertake turnkey projects on its own,
BHEL possesses the requisite flexibility to interface and complement with
international companies for large projects by supplying complementary equipment
and meeting their production needs for intermediate as well as finished products.
The success in the area of rehabilitation and life extension of power projects has
established BHEL as a comparable alternative to the original equipment
manufacturers (OEM’S) for such plants.
1.3. TECHNOLOGY UPGRADATION AND RESEARCH &
DEVELOPMENT
To remain competitive and meet customers' expectations, BHEL lays great
emphasis on the continuous up gradation of products and related technologies, and
development of new products. The Company has upgraded its products to
contemporary levels through continuous in house efforts as well as through
acquisition of new technologies from leading engineering organizations of the
world.
The Corporate R&D Division at Hyderabad, spread over a 140 acre complex,
leads BHEL's research efforts in a number of areas of importance to BHEL's
product range. Research and product development centers at each of the
manufacturing divisions play a complementary role.
BHEL's Investment in R&D is amongst the largest in the corporate sector in India.
Products developed in-house during the last five years contributed about 8.6% to
the revenues in 2000-2001.
BHEL has introduced, in the recent past, several state-of-the-art products
developed in-house: low-NOx oil / gas burners, circulating fluidized bed
combustion boilers, high-efficiency Pelton hydro turbines, petroleum depot

13. automation systems, 36kV gas-insulated sub-stations, etc. The Company has also
transferred a few technologies developed in-house to other Indian companies for
commercialization.
Some of the on-going development & demonstration projects include: Smart wall
blowing system for cleaning boiler soot deposits, and micro-controller based
governor for diesel-electric locomotives. The company is also engaged in research
in futuristic areas, such as application of super conducting materials in power
generations and industry, and fuel cells for distributed, environment-friendly
power generation.
1.3.1 HUMAN RESOURCE DEVELOPMENT INSTITUTE
The most prized asset of BHEL is its employees. The Human Resource
Development Institute and other HRD centers of the Company help in not only
keeping their skills updated and finely honed but also in adding new skills,
whenever required .Continuous training and retraining, positive, a positive work
culture and participative style of management, have engendered development of a
committed and motivated workforce leading to enhanced productivity and higher
levels of quality.
1.4. HEALTH, SAFETY AND ENVIRONMENT MANAGEMENT
BHEL, as an integral part of business performance and in its endeavor of
becoming a world-class organization and sharing the growing global concern on
issues related to Environment. Occupational Health and Safety, is committed to
protecting Environment in and around its own establishment, and to providing safe
and healthy working environment to all its employees. For fulfilling these
obligations, Corporate Policies have been formulated as.
1.4.1. ENVIRONMENTAL POLICY
Compliance with applicable Environmental Legislation/Regulation.Continual
Improvement in Environment Management Systems to protect our natural
environment and Control Pollution. Promotion of activities for conservation of
resources by Environmental Management.
Enhancement of Environmental awareness amongst employees, customers and
suppliers. BHEL will also assist and co-operate with the concerned Government

14. Agencies and Regulatory Bodies engaged in environmental activities, offering the
Company's capabilities is this field.
1.4.2. OCCUPATIONAL HEALTH AND SAFETY POLICY
Compliance with applicable Legislation and Regulations.
Setting objectives and targets to eliminate/control/minimize risks due to
Occupational and Safety Hazards.
Appropriate structured training of employees on Occupational Health and Safety
(OH&S) aspects.
Formulation and maintenance of OH&S Management programs for continual
improvement.
Periodic review of OH&S Management System to ensure its continuing
suitability, adequacy and effectiveness.
Communication of OH&S Policy to all employees and interested parties.
The major units of BHEL have already acquired ISO 14001 Environmental
Management System Certification, and other units are in advanced stages of
acquiring the same. Action plan has been prepared to acquire OHSAS 18001
Occupational Health and Safety Management System certification for all BHEL
units.
In pursuit of these Policy requirements, BHEL will continuously strive to improve
work particles in the light of advances made in technology and new
understandings in Occupational Health, Safety and Environmental Science
Participation in the "Global Compact" of the United Nations.
The "Global Compact" is a partnership between the United Nations, the business
community, international labor and NGOs. It provides a forum for them to work
together and improve corporate practices through co-operation rather than
confrontation.
BHEL has joined the "Global Compact" of United Nations and has committed to
support it and the set of core values enshrined in its nine principles.
1.4.3. PRINCIPLES OF THE "GLOBAL COMPACT"
HUMAN RIGHTS

15. LABOUR STANDARDS
1.Business should uphold the freedom of association and the effective recognition
of the right to collective bargaining.
2.Eliminate discrimination.
3.The elimination of all form of forces and compulsory labour.
4.The effective abolition of child labour.
5.Eliminate discrimination.
ENVIRONMENT
Businesses should support a precautionary approach to environmental challenges .
Undertake initiatives to promote greater environmental responsibility and
Encourage the development and diffusion of environmentally friendly
technologies.
By joining the "Global Compact", BHEL would get a unique opportunity of
networking with corporate and sharing experience relating to social responsibility
on global basis.
1.5 BHEL UNITS
UNIT TYPE PRODUCT
1. Bhopal Heavy Electrical Part
Steam Turbines, Turbo Generators,
Hydro
Sets,
Switch Gear Controllers
2. Haridwar
Hydro Turbines, Steam Turbines,
Gas
Turbines, Turbo Generators, Heavy
Castings
HEEP
Heavy
Electrical
Equipemen
t
and Forging, Control Panels, Light
Aircrafts,
Plant Electrical Machines.
CFFP
Central Foundry Forge
Plant
1. Business should support and respect the protection of internationally proclaimed human
rights and.
2. Make sure they are not complicit in human rights abuses.

16. 3. Hyderabad
Industrial Turbo-Sets, Compressor
Pumps
and Heaters, Bow Mills, Heat
Exchangers
HPEP
Heavy Power Equipement
Plant
Oil Rings, Gas Turbines, Switch
Gears,
Power Generating Sets.
4. Trichy Seamless Steel Tubes, Spiral Fin
Welded
HPBP High Pressure Boiling Plant Tubes.
5. Jhansi Transformers, Diesel Shunt Less AC
locos
TP
Transformer
Plant and EC EMU.
6. Banglore
Energy Meters, Watt Meters,
Control
Equipement, Capacitors, Photo Voltic
Panels,
EDN Electronics Division
Simulator, Telecommunication System,
Other
Advanced Microprocessor based
Control
EPD Electro Porcelains Devision
System, Insulator and Bushing,
Ceramic
Liners
7. Ranipet
Electrostatic Precipitator, Air Pre-
Heater,
Fans, Wind Electric Generators,
Desalination
BAP Boiler Auxilary Plant Plants.
8. Goindwal Industrial Valves Plant Industrial Valves & Fabrication
9. Jagdishpur
High tension ceramic, Insulation
Plates and
IP Insulator Plant
Bushings
10. Rudrapur
Component Fabrication
Plant
Windmill, Solar Water Heating
system

17. 11. Gurgaon
Amorphous
Silicon Solar Cell
Solar Photovoltaic Cells, Solar
Lanterns,
Plant. Chargers ,Solar clock
1.6. BHEL HARIDWAR
1.6.1. LOCATION
It is situated in the foot hills of Shivalik range in Haridwar. The main
administrative building is at a distance of about 8 km from Haridwar.
1.6.2. ADDRESS
Bharat Heavy Electrical Limited (BHEL)
Ranipur, Haridwar PIN- 249403
1.6.3. AREA
BHEL Haridwar consists of two manufacturing units, namely Heavy Electrical
Equipment Plant (HEEP) and Central Foundry Forge Plant (CFFP), having area
HEEP area:- 8.45 sq km
CFFP area:- 1.0 sq km
The Heavy Electricals Equipment Plant (HEEP) located in Haridwar, is one of the
major manufacturing plants of BHEL. The core business of HEEP includes design
and manufacture of large steam and gas turbines, turbo generators, hydro turbines
and generators, large AC/DC motors and so on.
Central Foundry Forge Plant (CFFP) is engaged in manufacture of Steel
Castings:Up to 50 Tons per Piece Wt & Steel Forgings: Up to 55 Tons per Piece
Wt.
1.6.4. UNITS
There are two units in BHEL Haridwar as followed:
1)Heavy Electrical Equipment Plant (HEEP)
2)Central Foundry Forge Plant (CFFP)

18. There are 8 Blocks in HEEP:
There are 3 Sections in CFFP:
1.6.5. HEEP PRODUCT PROFILE
THERMAL SETS:
Blocks Work Performed In Block
I) Electrical Machine Turbo Generator, Generator Exciter , Motor (AC and DC)
II) Fabrication Large Size Fabricated Assemblies or Components
III) Turbines & Steam , Hydro Turbines, Gas turbines, Turbine Blade, Special Tooling.
Auxilary
IV) Feeder Winding of Turbo ,Hydro Generators, Insulation for AC & DC Motors
V) Fabrication Fabricated Parts of Steam Turbine, Water Boxes, Storage Tank, Hydro
Turbine Parts
VI) Fabrication Fabricated Oil Tanks, Hollow Guide Blades, Rings, Stator Frames and
Stamping & Die Rotor Spindle, All Dies, Stamping for Generators and Motor
Manufacturing
VII) Wood Working Wooden Packing, Spacers
VIII) Heaters & LP heaters, Ejectors, Glands, Steam and Oil Coolers, Oil Tank, Bearing
Coolers Covers
Blocks Work Performed In Block
1.Foundry Casting of Turbine Rotor, Casing and Francis Runner
2.Forging Forging of Small Rotor Parts
3.Machine Shop Turning, Boring, Parting off, Drilling etc.

19. Steam turbines and generators up to 500 MW capacity for utility and combined
cycle applications Capability to manufacture up to 1000 MW unit cycle.
GAS TURBINES:
Gas turbines for industry and utility application range 3 to 200 MW
(ISO). Gas turbines based co-generation and combined cycle system.
HYDRO SETS:
Custom– built conventional hydro turbine of Kaplan, Francis and Pelton with
matching generators up to 250 MW unit size. Pump turbines with matching motor-
generators. Mini micro hydro sets. Spherical butterfly and rotary valves and
auxiliaries for hydro station.
EQUIPMENT FOR NUCLEAR POWER PLANTS:
Turbines and generators up to 500MW unit
size. Steam generator up to 500MW unit size.
Re-heaters / Separators.
Heat exchangers and pressure vessels.
ELECTRICAL MACHINES:
DC general purpose and rolling mill machines from 100 to 19000KW suitable for
operation on voltage up to 1200V. These are provided with STDP, totally enclosed
and duct ventilated enclosures.
DC auxiliary mill motors.
CONTROL PANEL:
Control panel for voltage up to 400KW and control desks for generating stations
and EMV sub–stations.
CASTING AND FORGINGS:
Sophisticated heavy casting and forging of creep resistant alloy steels, stainless
steel and other grades of alloy meeting stringent international specifications.

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

21. CNC
Machine:
Numerical
control (NC) is
a method of
automatically,
operating a
manufacturing
machine based
on a code,
letters,
numbers and
special
characters.The
numerical data
required to
produce a part
is provided to
a machine in
the form of
program,
called part
program or
CNC
(computer
numerical
control).
In CNC
(Computer Numerical Control), the instructions are stored as a program in a
micro-computer attached to the machine. The computer will also handle much of
the control logic of the machine, making it more adaptable than earlier hard-wired
controllers.
NC & CNC:
The program is translated into the appropriate electrical signals for input to motors
that run the machine. A CNC machine is an numerical control machine with the
added feature of an on board computer. The computer is referred to as the machine
control unit (MCU).
HISTORY

22. 1. In 1775, John Wilkinson- cannon boring machine (lathe).
2. In 1881, Eli Whitney- milling machine.
3. In 1947, Mr. John Parsons began experimenting for
using 3-axis curvature data to control the machine tool
motion for the production for aircraft components.
4. In 1949, parsons- first NC machine.
5. In 1951, MIT was involved in the project.
6. In 1955, after refinements NC became available in
industry
7. Today, modern machinery are CNC milling machines
and lathes.
CNC SYSTEM ELEMENTS
A typical CNC system consists of the following six
1.Elements
2.Part program
3.Program input device
4.Machine control unit
5.Drive system
6.Machine tool
7.Feedback system
CNC system basically consists of the following units:
1.Central processing unit (CPU)
2.Servo-control unit
3.Operator control panel
4.Machine control panel
5.Other peripheral device
6.Programmable logic controller (PLC)
Central Processing Unit (CPU)
The CPU is the heart and brain of a CNC system. It accepts the
information stored in the memory as part program. This data is decoded and
transformed into specific position control and velocity control signals. It also
oversees the movement of the control axis or spindle whenever this does
not match the programmed values, a corrective action is taken.All the
compensations required for machine accuracy (like lead screw pitch error, tool
wear out, backlash, etc.) are calculated by the CPU depending upon

23. 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 unit
and the CPU unit will provide continuous necessary corrective actions. Whenever
the situation goes beyond control of the CPU, it takes the final
action of shutting down the system in turn the machine.
Speed Control Unit
This unit acts in unison with the CPU for the movement of the machine axes. The
CPU sends the control signals generated for the movement of the axis to the servo
control unit and the servo control unit convert these signals into the
suitable digital or analog signal to be fed to the machine tool axis
movement. This also checks whether machine tool axis movement is at
the same speed as directed by the CPU. In case any safety conditions related to
the axis are over ruled during movement or otherwise they are reported to the CPU
for corrective action.
Servo-Control Unit
The decoded 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 servo-drive
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 passed on
to the CPU for further processing. Thus the servo-control unit
performs the data communication between the machine tool and the CPU.
As explained earlier, the actual movements of the slides on the machine
tool is achieved through servo drives. The amount of movement and the
rate of movement are controlled by the CNC system depending upon the
type of feedback system used, closed-loop or open-loop system.
Closed-loop System
The closed-loop system is characterized by the presence of feedback. In this
system, the CNC system send out commands for movement and the result is
continuously monitored by the system through various feedback devices.

24. Position Feedback
A closed-loop system, regardless of the type of feedback device, will
constantly try to achieve and maintain a given position by self-
correcting. As the slide of the machine tool moves, its movement is fed
back to the CNC system for determining the position of the slide to decide how
much is yet to be traveled and also to decide whether the movement is as
per the commanded rate. If the actual rate is not as per the required rate, the
system tries to correct it. In case this is not possible, the system declares
fault and initiates action for disabling the drives and if necessary,
switches off the machine.
Velocity feedback
In case no time constraint is put on the system to reach the final
programmed position,then the system may not produce the required
path or the surface finish accuracy. Hence, velocity feedback must
be present along with the position feedback whenever CNC system are
used for contouring, in order to produce correct interpolation and also specified
acceleration and deceleration velocities. The tacho generator used for velocity

25. feedback is normally connected to the motor and it rotates whenever the motor
rotates, thus giving an analog output proportional to the speed of motor. The
analog voltage is taken as speed feedback by the servo-controller and
swift action is taken by the controller to maintain the speed of the motor
within the required limits.
Open-loop system
The open loop system lacks feedback. In this system, the CNC system
send out signals for movement but does not check whether actual
movement is taking place or not. Stepper motors are used for actual
movement and the electronics of these stepper motors is run on digital p u l s e s
f r o m t h e C N C s y s t e m . S i n c e s y s t e m c o n t r o l l e r s h a v e n o
a c c e s s t o a n y r e a l t i m e information about the system performance, they
cannot counteract disturbances appearing during the operation. They can be
utilized in point to point system, where loading torque on the axial motor
is low and almost constant.
Servo-drive
The servo-drive receives signals from the CNC system and transforms it into
actual movement on the machine. The actual rate of movement and
direction depend upon the command signal from CNC system. There are
various types of servo-drives, viz., dc drives,ac drives and stepper motor
drives. A servo-drive consists of two parts, namely, the motor and the
electronics for driving the motor.
OperatorControl Panel
The operator control panel provides the user interface to facilitate a two-way
communication between the user,CNC system and the machine tool.
Video Display Unit (VDU)
The VDU displays the status of the various parameters of the CNC system and the
machine tool. It displays all current information such as:
1.Complete information of the block currently being executed
2.Actual position value, set or actual difference, current feed rate, spindle speed
3.Active G functions

26. 4.Main program number, subroutine number
5.Display of all entered data, user programs, user data, machine data, etc.
6.Alarm messages in plain text
7.Soft key designation In addition to a CRT, a few LEDs are generally provided to
indicate important operating modes and status.
Keyboard
A keyboard is provided for the following purposes:
1.Editing of part programs, tool data, and machine parameters.
2.Selection of different pages for viewing.
3.Selection of operating modes, e.g. manual data input.
4.Selection of feed rate override and spindles speed override.
5.Execution of part programs.
6.Execution of other toll functions.
Machine Control Panel (MCP)
It is the direct interface between operator and the NC system, enabling
the operation of the machine through the CNC system.
1.Establishing a correct reference point
2.Loading the system memory with the required part program
3.Loading and checking of tool offsets, zero offsets, etc.For these tasks, the system
must be operated in specific.
Modes of operation
1.Manual mode
2.Manual data input (MDI) mode
3.Automatic mode
4.Reference mode
5.Input mode
6.Output mode
Manual Mode:
I n t h i s m o d e , m o v e m e n t o f a m a c h i n e s l i d e c a n c a r r i e d o u t
m a n u a l l y b y p r e s s i n g t h e particular jog button (+ or -). The slide
(axis) is selected through an axis selector switch or through individual
switches (e.g., X+, X-, Y+, Y-, Z+, Z-, etc.). The feed rate of the

27. slide movement is prefixed. CNC system allows the axis to be jogged at high
feed rate also. The axis movement can also be achieved manually using a hand
wheel interface instead of jog buttons. In this mode slides can be moved in two
ways:
1.Continuous
2.Incremental
Continuous mode
In This mode, the slide will move as long as the jog button is pressed.
Incremental mode
The slide will move through a fixed distance, which is select
able. Normally, system allows jogging of axes in 1, 10, 100, 1000, 10000,
increments. Axis movement is at a prefixed feed rate. It is initiated by pressing the
proper jog+ or jog- key and will be limited to the no of increments selected
even if the jog button is continuously pressed. For subsequent movement
the jog button has to be released and once again pressed.
Manual Data Input (MDI) Mode
In this mode the following operation can be performed:
Building a new part program editing or deleting of part program stored in the
system memory entering or editing or deleting of Tool offsets (TO), Zero offsets
(ZO), Test data, etc.
Automatic Mode
In this mode the system allows the execution of a part program
continuously. The part program is executed block by block. While one block is
being executed, the next block is read by the system, analyzed and kept ready
for execution. Execution of the program can be one block after another
automatically or the system will execute a block, stop the execution of
the next block till it is initiated to do so (by pressing the start button). Selection
of part program execution continuously (Auto) or one block at a time (Single
Block ) is done through the machine control panel.Many systems allow
blocks (single or multiple) to be retraced in the opposite direction.
Block retrace is allowed only when a cycle stop state is established. Part program
execution can resume and its execution begins with the retraced block. This

28. is useful for tool inspection or in case of tool breakage. Program start
can be effected at any block in the program, through the
BLOCK SEARCH facility.
Reference Mode
Under this mode the machine can be referenced to its home
position so that all the compensations (e.g pitch error
compensation) can be properly applied. Part programs are
generally prepared in absolute mode with respect to machine zero. Many CNC
systems make it compulsory to reference the slides of the machine to their
home positions before a program is executed while others make it optional.
InputModeandOutputMode
In this mode, the part programs, machine setup data, tool offsets, etc. can be
loaded unloaded into from the memory of the system from external devices
like programming units, magnetic cassettes or floppy discs, etc. During
data input, some systems check for simple errors (like parity, tape
format,
block length, unknown characters, program already present in the
memory,etc.). Transfer of data is done through a RS232C or RS422C port.
Programmable Logic Controller(PLC)
A PLC matches the NC to the machine. PLCs were basically introduced as
replacement for hard wired relay control panels. They were developed to be
reprogrammed without hardware changes when requirements were altered and
thus are reusable. PLCs are now available within creased functions, more memory
and large input/output capabilities.gives the generalized PLC block diagram.In the
CPU, all the decisions are made relative to controlling a machine or a process. The
CPU receives input data, performs logical decisions based upon stored programs
and drives the outputs. Connections to a computer for hierarchical control are
done via the CPU.The I/O structure of the PLCs is one of their major strengths.
The inputs can be push buttons,limit switches, relay contacts, analog sensor,
selector switches, proximity switches, float switches, etc. The outputs can be
motor starters, solenoid valves, position valves, relay coils,indicator lights, LED
displays, etc.The field devices are typically selected, supplied and installed by the
machine tool builder or the end user. The voltage level of the field devices thus

29. normally determines the type of I/O. So, power to actuate these devices must also
be supplied external to the PLC. The PLC power supply is designated and rated
only to operate the internal portions of the I/O structures, and not the field devices.
A wide variety of voltages, current capacities and types of I/O modules are
available.
INTERFACING
Interconnecting the individual elements of both the machine and the
CNC system using cables and connectors is called interfacing.Extreme care
should be taken during interfacing. Proper grounding in electrical
installation is most essential. This reduces the effects of interference and
guards against electronic shock to personnel. It is also essential to properly
protect the electronic equipment.Cable wires of sufficiently large cross-
sectional area must be used. Even though proper grounding reduces
the effect of electrical interference, signal cable requires additional
protection.This is generally achieved by using shielded cables. All the
cable shields must be grounded at control only, leaving other end free. Other
noise reduction techniques include using suppression devices, proper cable
separation, ferrous metal wire ways, etc. Electrical enclosures should be
designed to provide proper ambient conditions for the controller.
CONCLUSION
This training has proved to be quite faithful. This gave me, a chance to have an
encounter with such heavy CNC machines. The architecture of B.H.E.L. ,the way
the various units are linked and the way the working of the whole plant is
controlled, makes the student realize that engineering is not just the structural
description but more of planning and management. It has provided an opportunity
to learn that optimization of technology used at proper place and time can save a
lot of labour.
The training has proved to be immensely helpful as it has helped me to have an
exposure of the practical implementation of the theoretical knowledge that I have
gained till date.