2. CONTENTS
•About BHEL
•CNC Introduction
•History of CNC Machines
•CNC Machines-How do they look like?
•Elements of CNC Machines
•Block Diagram of CNC Machines
•How CNC works
•Control: Open loop and Closed loop
•Modes of Operation
•Features of CNC machinery
•CNC Programming Basics
•Advantages of CNC
•Challenges
•Conclusion
3. About BHEL
•Bharat Heavy Electrical Limited is power plant
equipment manufacturer based in New Delhi,
India
•It was established in 1964
•It has 17 manufacturing units
•It manufactures gas turbines, steam turbines,
generators and boilers
•It is 7th largest power plant equipment
manufacturer in the world
4. A computer
numerical control
system is a system in
which actions are
controlled by direct
insertion of
numerical data at
some point
Definition:
5. ●The CNC machines were first introduced in
the 1950s by Prof. John T Parson
●First CNC machine was built at
Massachusetts Institute of Technology in
1953
●Modern CNC Machine are improving further
as the technology is changing with a variety
of functions according to applications.
6. CNC Machines- How do they look
like?
Slides
Controller
Display
Automated
Tool changer
Chip collection and
removal
7. A CNC machine consist of following 6
major elements:
i. Input Device
ii. Machine Control Unit
iii.Machine Tool
iv.Driving System
v. Feedback Devices
vi.Display Unit
8. Input Device
•Floppy Disk
•USB Flash Drive
•Serial Communication etc.
Machine Control Unit
i. Data Processing Unit
(DPU)
ii. Control Loop Unit
9. Driving system
•DC Motor
•Stepper Motor
Feedback Devices
i. Positional Feedback Devices
• Linear Transducer
• Rotary Encoder
ii. Velocity Feedback Device
10. Display Unit
• Shows position of machine slide, part
programmes etc.
• Can also show graphics simulation of tool path
so that part programmes may be verified
12. *Controlled by G and M codes.
*These are number values and co-ordinates.
*Each number or code is assigned to a particular operation.
*Typed in manually to CAD by machine operators.
*G & M codes are automatically generated by the computer
software.
13. In open loop systems the slide may overshoot or may not
reach desired position because of inertia, wear and tear
and friction, hence inaccurate machining.
In closed loop systems the position sensors are used to
correct slide movements and achieve higher accuracy and
repeatability
15. Manual Mode
Movement of machine slide carried out
manually by pressing particular jog
button(+ or -)
Axis is selected through axis selector
switch
Machine slide movement may also be
achieved by using a hand wheel
Manual Data Input (MDI) Mode
part programs are fed manually for each
movement of machine tool by the operator
16. Automatic Mode
The part program is executed continuously
While one block is being executed, next block is
read by the system and kept ready for execution
Input and Output Mode
The part programs and machine information like
machine setup data can be loaded into and unloaded
from memory of the system or floppy disks, USB flash
derives etc.
17. •The tool or material moves automatically.
•Tools can operate in 1-5 axes.
•Larger machines have a machine control unit (MCU) which
manages operations.
•Movement is controlled by motors (actuators).
•Feedback is provided by sensors (transducers)
•Tools can be changed automatically.
18. *CNC instructions are called part program commands.
*When running, a part program is interpreted one
command line at a time until all lines are completed.
*Commands, which are also referred to as blocks, are
made up of words which each begin with a letter
address and end with a numerical value.
20. M02 : Program end
M06 : Tool change
M08 : Coolant on
M09 : Coolant off
M30 : Program stop, reset to start
21. Advantages of CNC
Increased productivity
Consistent quality
Automatic material handling
High accuracy
Reliable operation
Reduced manpower
Increased operation safety
22. i. Costly setup, skilled operators
required
ii. Programming knowledge required
iii.Maintenance is difficult
23. The advantage of a CNC system are that the
operation of a conventional machine is removed and
the part production is made automatic.
It reduces the labor work and hence highly efficient
in the manufacturing process.
BHEL generally uses CNC machines to achieve its
manufacturing targets. For manufacturing works of
large scale it is very difficult to work with manual
machines as they are time consuming. CNC machines
have their wide scope because they are easy to
handle, the work becomes easier and jobs are done
with perfection.
