CNC machining processes for all branches 1st students. And also important for those who want to have a basic knowledge of different type of machining processes. This topic is basically depend upon computer assisted machining.

1. Abhishek Rao
B.Tech (CSE) 1st Year
Central University of Haryana

2. CNC
Machining
Computer Numerical Controlled
Machining

3. CONTENTS
1. History
2. CNC introduction
3. Elements of CNC
4. Block diagram of CNC
5. Types of CNC machine
6. How CNC works?
7. Features of CNC machines
8. CNC programming basics
9. Common format of a block
10. Advantages
11. Disadvantages

4. History of CNC machines
 Numerical control for machines tools were
introduced in 1950’s by Prof.John T Parsons.
 The first NC machine was built at the
Massachusetts institute of Technology in 1953
by joint efforts of US Air Force, the MIT and
parson’s cooperation

5. Introduction
A CNC machine is 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.
The machine follows a predetermined sequence of machining operations at the
predetermined speeds necessary to produce a workpiece of the right shape
and size and thus according to completely predictable results. A different
product can be produced through reprogramming and a low-quantity
production run of different products is justified. flash drive, or RAM card etc.
“ A system in which actions are controlled by the direct insertion of numerical
data at some point.The system must automatically interpret at least some
portion of this data.”
In a simple word, a CNC system receives numerical data, interpret the data
and then control the action accordingly.

7. ELEMENTS OF CNC MACHINE
• 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. <-Control Panel

9. Block Diagram of CNC

10. TYPES OF CNC MACHINE
• Plasma.
• Spring forming.
• Laser Cutting machine.
• Flame cutting machine.
• Electric Discharge Machine.
• Water Jet.
• Welding.
• CNC Punch Press.

11. Open loop and closed loop controls
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

12. HOW CNC WORKS ?
• 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. FEATURES OF CNC MACHINERY
• 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

14. CNC PROGRAMMING BASICS
• 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.

15. CNC PROGRAMMING
Important things to
know:
• Coordinate System
• Units, incremental
or absolute positioning
• Coordinates: X,Y,Z,
RX,RY,RZ
• Feed rate and spindle
speed
• Coolant Control:
On/Off, Flood, Mist
• Tool Control: Tool and
tool
Programming consists of a series
of instructions in form of letter
codes
•Preparatory Codes:
G codes- Initial machining setup
and
establishing operating conditions
N codes- specify program line
number
to executed by the MCU
•Axis Codes: X,Y,Z
Used to specify motion of the slide
along
X, Y, Z direction
•Feed and Speed Codes: F and S
Specify feed and spindle speed
•Tool codes: T – specify tool
number
•Miscellaneous codes – M codes
For coolant control and other
activities

16. COMMON FORMAT OF A BLOCK

17. 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
viii. -The advantage of a CNC system are that the operation of a
conventional machine is removed and the part production is
made automatic.
ix. -It reduces the labor work and hence highly efficient in the
manufacturing process.

18. Disadvantages
i. COSTLY SETUP, SKILLED OPERATORS.
ii. COMPUTERS, PROGRAMMING
KNOWLEDGE REQUIRED.
iii. MAINTENANCE IS DIFFICULT.

19. Thank
You…