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2. Dept. of mechanical Engineering, GIET,BBSR
Highlights
1 HISTORY OF CNC
2 ABOUT CNC
3 CNC PART PROGRAM
4 ADVANTAGE & DISADVANTAGE
5 APPLICATION AND IMPROVEMENT
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3. Dept. of mechanical Engineering, GIET,BBSR
HISTORY OF CNC
 The concept is credited to John Parson (1947). Using punched
cards he was able to control the position of a machine in an attempt
to machine helicopter blade.
 US Air Force teamed up with MIT to develop a programmable
milling machine (1949).
 In 1952, a three-axis Hydrotel milling machine was demonstrated.
The term Numerical Control (NC) originated. The machine had an
electromechanical controller and used punched cards.
 A new class of machines called machining centers and turning
centers that could perform multiple machining processes was
developed.
 Modern NC machine has a computer on board, Computer
Numerical Control (CNC). They can run unattended at over
20,000 rpm (spindlier speed) with a feed rate of over 600 rpm and
an accuracy of .0001
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4. HISTORY OF CNC
Dept. of mechanical Engineering, GIET,BBSR
 More recently, microprocessors have made CNC controls even
cheaper. The Enhanced Machine Controller project, or EMC2, was a
project to implement an Open Source CNC controller that was started
by NIST, the National Institute of Standards and Technology as a
demonstration. Some time in 2000, the project was taken into the
public domain and Open Source, and EMC2 appeared a short time
later in 2003.
(1959 CNC Machine: Milwaukee-Matic-II was first machine with a tool changer)
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5. ABOUT CNC
Dept. of mechanical Engineering, GIET,BBSR
Computer
Numerical
Control
CNC Stands for
Numerical control is a method of automatically operating a
manufacturing machine based on a code of letters, numbers, and
special characters.
The numerical data required to produce a part is provided to a
machine in the form of a program, called part program or CNC
program.
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6. ABOUT CNC
 The program is translated into the appropriate electrical signals for
input to motors that run the machine.
 A CNC machine is an NC machine with the added feature of an on-board
computer.
Dept. of mechanical Engineering, GIET,BBSR
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7. ABOUT CNC
Dept. of mechanical Engineering, GIET,BBSR
HAAS CNC Machines
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8. ABOUT CNC
Dept. of mechanical Engineering, GIET,BBSR
Basic Components
 An NC system consists of the machine tools, the part-program, and the
machine control unit (MCU).
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9. ABOUT CNC
Dept. of mechanical Engineering, GIET,BBSR
Machine Tools
The machine tools perform the useful work.
 A machine tool consists of.
 A worktable,
 One or more spindles, motors and controls,
 Cutting tools,
 Work fixtures, and.
 Other auxiliary equipment needed in the machining operation.
 The drive units are either powered by stepping motors (for open-loop
control), servomotors (for close-loop control), pneumatic drives, or
hydraulic drives.
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10. CNC PART PROGRAM
 The part-program is a collection of all data required to produce the
part. It is arranged in the form of blocks of information.
 Each block contains the numerical data required for processing a
segment of the work piece.
Dept. of mechanical Engineering, GIET,BBSR
PART PROGRAM
MANUAL PROGRAM COMPUTER ASSITED
PART PROGRAM
Part program is of two type:
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11. CNC PART PROGRAM
Dept. of mechanical Engineering, GIET,BBSR
PROCESS PLANNING
JOB & TOOL SET UP PLANNING
AXES SELECTION
MACHINING PATH PLANNING
TOOL SELECTION
PART PROGRAM WRITTING
CUTTING PROCES PARAMETER PLANNING
PART PROGRAM PROVING
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12. CNC PART PROGRAM
 MANUAL PART PROGRAM
Dept. of mechanical Engineering, GIET,BBSR
Manual part program is written in a special set of instruction
called manuscript.
The instruction are prepared in précised manner because the
typist prepare the NC tape directly from the manuscript
Manuscript includes instructions and also other data such as
other preparatory commands, miscellaneous instructions and
speed/feed specifications all of which need to operate the machine
under tape control .
MANUAL PART PROGRAM
PTP JOBS
COUNTOURING JOBS
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13. CNC PART PROGRAM
Dept. of mechanical Engineering, GIET,BBSR
COMPUTER ASSISTED PART PROGRAMMING
Programmers Activities:
 Geometry workspace entry
 Entry of sequence of operation
Computer Activities:
 Input Translation
 Advance computation
 Cutting tool offset calculation
 Post processing
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14. CNC PART PROGRAM
Dept. of mechanical Engineering, GIET,BBSR
Preparatory command (G code)
The G codes prepare the MCU for a given operation, typically involving a
cutter motion.
G00 rapid motion, point-to-point positioning
G01 linear interpolation (generating a sloped or straight cut)
G06 parabolic interpolation (produces a segment of a parabola)
G17 XY plane selection
G20 circular interpolation
G28 automatic return to reference point
G33 thread cutting
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15. CNC PART PROGRAM
Dept. of mechanical Engineering, GIET,BBSR
Miscellaneous commands (M code)
M00 program stop
M03 start spindle rotation (cw)
M06 tool change
M07 turn coolant on
Feed commands (F code)
Used to specify the cutter feed rates in inch per minute.
Speed commands (S code)
Used to specify the spindle speed in rpm.
Tool commands (T code)
Specifies which tool to be used, machines with automatic tool
changer.
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16. CNC PART PROGRAM
Dept. of mechanical Engineering, GIET,BBSR
CNC Machine Axes of Motion
The coordinate system used for the tool path must be identical to the
coordinate system used by the CNC machine. The standards for machine
axes are established according to the industry standard report EIA RS-267A.
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17. CNC PART PROGRAM
Dept. of mechanical Engineering, GIET,BBSR
CNC Machine Axes of Motion
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18. CNC PART PROGRAM
 CNC MOTION CONTROL
 POINT TO POINT MOTION
 STRAIGHT CUT MOTION
 COUNTORING MOTION
Dept. of mechanical Engineering, GIET,BBSR
1. Point-to-point (PTP) MOTION
 The cutting tool is moved relative to the work piece (i.e. Either the cutting
tool moves, or the work piece moves) until the cutting tool is at a
numerically defined position and then the motion is paused.
 The cutting tool then performs an operation.
 When the operation is completed, the cutting tool moves relative to the
work piece until the next point is reached, and the cycle is repeated.
 The simplest example of a PTP NC machine tool is the NC drilling
machine.
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19. CNC PART PROGRAM
Dept. of mechanical Engineering, GIET,BBSR
Straight-cut MOTION
 Straight-cut system are capable of moving the cutting tool parallel to one of
the major axes (X-Y-Z) at a controlled rate suitable for machining.
 It is appropriate for performing milling operations to fabricate work pieces
of rectangular configurations.
 Straight-cut NC systems can also perform PTP operations.
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20. CNC PART PROGRAM
Dept. of mechanical Engineering, GIET,BBSR
Contouring NC
 In contouring (continuous path) operations, the tool is cutting while the
axes of motion are moving.
 The axes can be moved simultaneously, at different velocity.
 The path of the cutter is continuously controlled to generate the desired
geometry of the work piece.
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21. CNC PART PROGRAM
Dept. of mechanical Engineering, GIET,BBSR
Example of a part program
N1 G00 X-35 Z-5
N2 G01 X10 Z0 F100
N3 G01 X0 Z-30 F100
N4 G01 X10 Z0 F100
N5 G01 X0 Z-30 F100
N6 G01 X10 Z-0 F100
N7 G01 X0 Z-40 F100
N8 G00 X-35 Z-5
M30
(This is a manual part program for lathe machining)
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P1
P2
P3 P4
+X
+Z
-X
-Z

22. Dept. of mechanical Engineering, GIET,BBSR
ADVANTAGE & DISADVANTAGE
 ADVANTAGE
 CNC machines can be used continuously 24 hours a day, 365 days a
year and only need to be switched off for occasional maintenance.
 CNC machines are programmed with a design which can then be
manufactured hundreds or even thousands of times. Each
manufactured product will be exactly the same.
 Less skilled/trained people can operate CNCs unlike manual lathes /
milling machines etc.. which need skilled engineers.
 CNC machines can be updated by improving the software used to
drive the machines
 Training in the use of CNCs is available through the use of ‘virtual
software’. This is software that allows the operator to practice using
the CNC machine on the screen of a computer. The software is similar
to a computer game.
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23. Dept. of mechanical Engineering, GIET,BBSR
ADVANTAGE & DISADVANTAGE
 CNC machines can be programmed by advanced design software
such as Pro/DESKTOP®, enabling the manufacture of products that
cannot be made by manual machines, even those used by skilled
designers / engineers.
 Modern design software allows the designer to simulate the
manufacture of his/her idea. There is no need to make a prototype or a
model. This saves time and money.
 One person can supervise many CNC machines as once they are
programmed they can usually be left to work by themselves.
Sometimes only the cutting tools need replacing occasionally.
 A skilled engineer can make the same component many times.
However, if each component is carefully studied, each one will vary
slightly. A CNC machine will manufacture each component as an
exact match.
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24. Dept. of mechanical Engineering, GIET,BBSR
ADVANTAGE & DISADVANTAGE
 DISADVANTAGES
 CNC machines are more expensive than manually operated machines,
although costs are slowly coming down.
 The CNC machine operator only needs basic training and skills,
enough to supervise several machines. In years gone by, engineers
needed years of training to operate centre lathes, milling machines and
other manually operated machines. This means many of the old skills
are been lost.
 Less workers are required to operate CNC machines compared to
manually operated machines. Investment in CNC machines can lead
to unemployment.
 Many countries no longer teach pupils / students how to use manually
operated lathes / milling machines etc... Pupils / students no longer
develop the detailed skills required by engineers of the past. These
include mathematical and engineering skills
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25. Dept. of mechanical Engineering, GIET,BBSR
ADVANTAGE & DISADVANTAGE
COMPUTER NUMERICAL CONTROL - MACHINE MANUALLY OPERATED CENTRE LATHE
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26. APPLICATION AND ADVANCEMENT
 APPLICATION
CNC machine is used
 In the metal removal industry
 In the metal fabrication industry
 In the electrical discharge machining industry
 In the woodworking industry
 Laser welding in automobile industry
 Laser machining and Cutting
Dept. of mechanical Engineering, GIET,BBSR
Small parts made using
EDM
Laser welding in automobile industry LASER MACHINING
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27. Dept. of mechanical Engineering, GIET,BBSR
APPLICATION AND ADVANCEMENT
 Other Industries where CNC machines are used:
Many forms of lettering and engraving systems use CNC
technology. Water jet machining uses a high pressure water jet
stream to cut through plates of material. CNC is even used in the
manufacturing of many electrical components. For example, there
are CNC coil winders, and CNC terminal location and soldering
machines.
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28. APPLICATION AND ADVANCENENT
 ADVANCES OF CNC:
 CNC are operated using DNCs
 Reverse engineering is possible only because of CNC
 Robotics technology is introduced in CNC technology
 3D printing is done using CNC. Advance machining process such
as EDM,LBM, Stereolithography (SLA), Fused Deposition
Modeling (FDM)
 Rapid prototyping, Rapid manufacturing concepts are developed
after CNC .
Dept. of mechanical Engineering, GIET,BBSR
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A rapid prototyping machine
using selective laser sintering

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Dept. of mechanical Engineering, 29
GIET,BBSR

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