CNC Seminar

Presentation
of
Vocational Training on
“COMPUTER NUMERICAL
CONTROL MACHINE”

BHARAT HEAVY
ELECTRICALS
LIMITED, JHANSI
UNDER THE GUIDENCE OF: BY:
Mr. VIJAY VERMA BHEEM SINGH
(Sr. ENGINEER, WEX) B. Tech. (E.C.E.) Final Year
BHEL, JHANSI B.I.E.T. Jhansi
1004331903

CONTENTS
1. History
2. CNC Introduction
3. how they look like?
4. Elements of CNC
5. Block diagram of CNC
6. How CNC Works?
7. Features of CNC Machines
8. CNC Programming Basics
9. Common Format of a Block
10. Programming Key Letters
11. Table of important G-codes
12. Table of important M-codes
13. Advantages
14. Challenges
15. Conclusion
16. References

*

* The first NC machines were built in the 1940s
and 1950s by Prof. John T Parson.
* CNC machine came into existence after
evolution of computer around 1980.
* Modern CNC Machine are improving further as
the technology is changing with a variety of
functions according to applications.

*
*A numerical control
system in which the
data
handling, control
sequences, and
response to input is
determined by an on-
board computer
system at the
machine tool.

CNC Machines- How do they look like?

Servo Motors

Display Console Coolant
control
Slides Automated
Tool changer

Controller
Controller

Chip collection and
removal

*

* 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

*

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

*
* 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.

*

* 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)
* Tool magazines are used to change tools automatically.

*

*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.

*
Important things to know: Programming consists of a series
of instructions in form of letter codes
* Coordinate System •Preparatory Codes:
G codes- Initial machining setup and
* Units, incremental or establishing operating conditions
absolute positioning N codes- specify program line number
to executed by the MCU
* Coordinates: X,Y,Z, RX,RY,RZ •Axis Codes: X,Y,Z
Used to specify motion of the slide along
* Feed rate and spindle speed X, Y, Z direction

•Feed and Speed Codes: F and S
* Coolant Control: Specify feed and spindle speed
On/Off, Flood, Mist
•Tool codes: T – specify tool number
* Tool Control: Tool and tool
parameters •Miscellaneous codes – M codes
For coolant control and other activities

*

Sequence Preparatory Dimension Feed Spindle Tool Misc.
# Function Words Rate Functio Functio Function
n n

N50 G90 G01 X1.40Y2.25 F10 S1500 T01 M03

Individual Words

*
* O - Program number (Used for program identification)
* N - Sequence number (Used for line identification)
* G - Preparatory function
* X - X axis designation
* Y - Y axis designation
* Z - Z axis designation
* R - Radius designation
* F – Feed rate designation
* S - Spindle speed designation
* H - Tool length offset designation
* D - Tool radius offset designation
* T - Tool Designation
* M - Miscellaneous function

*
G00 Rapid Transverse
G01 Linear Interpolation
G02 Circular Interpolation, CW
G03 Circular Interpolation, CCW
G17 XY Plane,G18 XZ Plane,G19 YZ Plane
G20/G70 Inch units
G21/G71 Metric Units
G40 Cutter compensation cancel
G41 Cutter compensation left
G42 Cutter compensation right
G43 Tool length compensation (plus)
G43 Tool length compensation (plus)
G44 Tool length compensation (minus)
G49 Tool length compensation cancel
G80 Cancel canned cycles
G81 Drilling cycle
G82 Counter boring cycle
G83 Deep hole drilling cycle
G90 Absolute positioning
G91 Incremental positioning

*
* M00 Program stop
* M01 Optional program stop
* M02 Program end
* M03 Spindle on clockwise
* M04 Spindle on counterclockwise
* M05 Spindle stop
* M06 Tool change
* M08 Coolant on
* M09 Coolant off
* M10 Clamps on
* M11 Clamps off
* M30 Program stop, reset to start

Advantages of CNC

i. - Easier to program;

ii. - Easy storage of existing programs;

iii. - Easy to change a program

iv. - Avoids human errors

v. - CNC machines are safe to operate

vi. - Complex geometry is produced as cheaply as simple ones

vii. - Usually generates closer tolerances than manual machines

*

i. Costly setup, skilled operators
ii. Computers, programming
knowledge required
iii. Maintenance is difficult

*
* 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.

*

 Manual of CNC from BHEL Jhansi

 http://en.wikipedia.org/wiki/computer_numerical
_control

 http://www.motioncontrol.com/articles/gearheads
-modular-spindle-drives

 http://www.seminarprojects.com/cnc

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