Automation in Manufacturing Systems Importance

CNC Description Automation in Manufacturing Systems Importance

1. 1
CNC TECHNOLOGY
and
CNC PROGRAMMING

2. 2
AUTOMATION IN MANUFACTURING
SYSTEMS
TRENDS IN INDUSTRY
THE OBJECTIVE:
TO BE COMPETITIVTHROUGH
INCREASING PRODUCTIVITY AND TOTAL
QUALITY ASSURANCE

3. 3
EFFICIENCY OF
MANUFACTURING
COST= COST OF
MANUFACTURING AND
COST OF MATERIAL
HANDLING
PROFIT= INCOME -COST
PRODUCTIVITY=
AVERAGE OUTPUT PER
MAN-HOUR

4. 4
PROFITincreases as COSTdecreases
and as PRODUCTIVITY increases.
PRODUCTIVITY through AUTOMATION

5. 5
AUTOMATION
any means of helping
the workers to perform
their tasks more
efficiently
transfer of the skill of
the operator to the
machine

6. 6
Transferred
skill
Results
muscle power engine driven
machine tools
First industrial
revolution
manipulating
skill
mechanizationhard automation
vision skilluse of position
transducers,
cameras
increase of
accuracy, part
recognition
brain power
cnc machines, industrial
robots, soft
automation,
computer control of
manufacturing
systems
second industrial
revolution

7. 7
Utilization of computers in
manufacturing applications has
proved to be one of the most
significant developments over the
last couple of decades in helping to
improve the productivity and
efficiency of manufacturing
systems.

8. 8
The metal cutting operations (also
called machining)is one of the
most important manufacturing
processes in industry today (as it
was yesterday).

9. 9
MACHINING IS THE REMOVAL
OF MATERIALS IN FORMS OF
CHIPS FROM THE WORKPIECE
BY SHEARING WITH A SHARP
TOOL.

10. 10
The main function of a machine
tool is to control the workpiece-
cutting tool positional relationship
in such a way as to achieve a
desired geometric shape of the
workpiece with sufficient
dimensional accuracy.

11. 11
Machine tool provides:
work holding
tool holding
relative motion between tool
and workpiece
primary motion
secondary motion

12. 12
Primary motion
Relative motion
between tool and
workpiece
Secondary motion
Cutting motion
Cutting speed
Feed motion
Feed rate

13. 13machine control unit
position transducers
work holding device
tool holding device

14. 14
CLASSIFICATION OF THE CHIP REMOVING METHODS
ACCORDING TO THE RELATIVE MOTION

15. 15
CLASSIFICATION OF MACHINE TOOLS
THOSE USING
SINGLE POINT
TOOLS
THOSE USING
MULTIPOINT
TOOLS
THOSE USING
ABRASIVE
TOOLS
lathes
shapers
planers
boring m/c’s
etc.
drilling m/c’s
milling m/c’s
broaching m/c’s
hobbing m/c’s
etc.
grinding m/c’s
honing m/c’s
etc.

16. 16
ISO MACHINE TOOL AXIS DEFINITION

17. 17
ISO MACHINE TOOL AXES DEFINITIONS
AXISMACHINE TOOL WITH SPINDLE MACHINE TOOL WITH
NO SPINDLE
Zaxis of spindle,
(+Z) as tool goes away from the work piece
perpendicular to work
holding surface, (+Z) as
tool goes away from the
workpiece
MACHINE
TOOL WITH
ROTATING
WORKPIECE
MACHINE TOOL WITH
ROTATING TOOL
HORIZONT
AL AXIS
VERTICAL
AXIS
X radial and
parallel to
cross slide,
(+X) when
tool goes away
from the axis
of spindle
horizontal
and parallel
to work
holding
surface,
(+X) to the
right when
viewed
from
spindle
towards
work piece
horizontal
and parallel
to the work
holding
surface,
(+X) to the
right when
viewed
from
spindle
towards
column
parallel to and positive in
the principal direction of
cutting (primary motion)
Y apply right hand rules

18. 18
RIGHT HAND RULE
Vertical Machine Horizontal Machine

19. 19
STANDARD LATHE COORDINATE
SYSTEM

20. 20
STANDARD MILLING MACHINE
COORDINATE SYSTEM

21. 21
NUMERICALLY CONTROLLED MACHINE
TOOLS:
An NC machine tool is functionally the same
as a conventional machine tool. The
technological capabilities NC machine tools
in terms of machining are no different from
those of conventional ones. The difference is
in the way in which the various machine
functions and slide movements are
controlled.

22. 22
The functions and motions such as;
turning the spindle on and off
setting cutting speeds
setting feed rate
turning coolant on and off
moving tool with respect to workpiece
are performed by Machine Control Unit
(MCU) in NC machine tools.

23. 23
INTRODUCTION TO CNC

24. 24
HISTORY
US Air Force commissioned MIT (Massachusetts
institute of technology) to develop the first
"numerically controlled" machine in 1949. It was
demonstrated in 1952.
At 1970-1972 first Computer Numeric Control
machines were developed.
Today, computer numerical control (CNC)
machines are found almost everywhere, from
small job shops in rural communities to
companies in large urban areas.

25. 25
DEFINITION
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.

26. 26
CNC APPLICATIONS
Machining
2D / 3D
Turning ~ Lathes, Turning Centre
Milling ~ Machining Centres
Forming
2D
Plasma and Laser Cutting
Blanking, nibbling and punching
3D
Rapid Prototyping

27. 27
Conventional Lathe

28. 28
Turning Operation

29. 29
Threading Operation
Threading is a process of making grooves
on a metallic object

30. 30
Facing Operation
Facing is a process softening faces

31. 31
Drilling Operation
Drilling is a process making hole in a
work piece

32. 32
Knurling Operation
It is a manufacturing process,
in which visually-attractive
diamond-shaped pattern is
cut or rolled into metal.

33. 33

34. 34
Milling Operation
A milling machinerotates a multitooth
cutter into the work. A wide variety of
cutting operations can be performed on
milling machines. They are capable of
machining flat or contoured surfaces,
slots, grooves, recesses, threads, gears,
spirals, and other configurations.

35. 35

36. 36
milling Operation.

37. 37
SAMPLE
CNC MACHINES

38. 38
CNC TURNING

39. 39
CNC MILLING

40. 40
CNC LASER CUTTING

41. 41
CNC PLASMA CUTTING

42. 42
CNC PRESS

43. 43
CNC RAPID PROTOTYPING

44. 44
INDUSTRIES MOST AFFECTED
by CNC
Aerospace
Machinery
Electrical
Fabrication
Automotive
Instrumentation
Mold making

45. 45
SAMPLE PRODUCTS
OF
CNC MANUFACTURING

46. 46
AUTOMOTIVE INDUSTRY
Engine Block

47. 47
AUTOMOTIVE INDUSTRY(Cont’d)
Different Products

48. 48
AEROSPACE INDUSTRY
Aircraft Turbine Machined by
5-Axis CNC Milling Machine

49. 49
CNC MOLD MAKING

50. 50
ELECTRONIC INDUSTRY

51. 51
RAPID PROTOTYPING
PRODUCTS

52. 52
ADVANTAGES of CNC
Productivity
Machine utilisation is increased because
more time is spent cutting and less time is
taken by positioning.
Reduced setup time increases utilisation
too.

53. 53
ADVANTAGES of CNC
Quality
Parts are more accurate.
Parts are more repeatable.
Less waste due to scrap.

54. 54
ADVANTAGES of CNC
Reduced inventory
Reduced setup time permits smaller
economic batch quantities.
Lower lead time allows lower stock levels.
Lower stock levels reduce interest charges
and working capital requirements.

55. 55
ADVANTAGES of CNC
Machining Complex shapes
Slide movements under computer control.
Computer controller can calculate steps.
First NC machine built 1951 at MIT for
aircraft skin milling.

56. 56
ADVANTAGES of CNC
Management Control
CNC leads to CAD
Process planning
Production planning

57. 57
DRAWBACKS of CNC
High capital cost
Machine tools cost $30,000 -$1,500,000
Retraining and recruitment of staff
New support facilities
High maintenance requirements
Not cost-effective for low-level production on
simple parts
As geometric complexity or volume increases
CNC becomes more economical
Maintenance personnel must have both
mechanical and electronics expertise

58. 58
CNC SYSTEM ELEMENTS

59. 59
CNC SYSTEM ELEMENTS
A typical CNC system consists of the
following six elements
Part program
Program input device
Machine control unit
Drive system
Machine tool
Feedback system

60. 60
NC SYSTEM ELEMENTS

61. 61
PART PROGRAM
A part program is a series of coded instructions required
to produce a part. It controls the movement of the
machine tool and the on/off control of auxiliary functions
such as spindle rotation and coolant. The coded
instructions are composed of letters, numbers and
symbols and are arranged in a format of functional
blocks as in the following example
N10 G01 X5.0 Y2.5 F15.0
| | | | |
| | | | Feed rate (15 in/min)
| | | Y-coordinate (2.5")
| |X-coordinate (5.0")
|Linear interpolation mode
Sequence number

62. 62
PROGRAM INPUT DEVICE
The program input device is the
mechanism for part programs to be
entered into the CNC control. The most
commonly used program input devices are
keyboards,punched tape reader, diskette
drivers, throgh RS 232 serial ports and
networks.

63. 63
MACHINE CONTROL UNIT
The machine control unit (MCU) is the heart of a CNC
system. It is used to perform the following functions:
Read coded instructions
Decode coded instructions
Implement interpolations (linear, circular, and helical) to
generate axis motion commands
Feed axis motion commands to the amplifier circuits for
driving the axis mechanisms
Receive the feedback signals of position and speed for
each drive axis
Implement auxiliary control functions such as coolant or
spindle on/off, and tool change

64. 64
TYPES of CNC CONTROL
SYSTEMS
Open-loop control
Closed-loop control

65. 65
OPEN LOOP SYSTEM

66. 66
CLOSED LOOP SYSTEM

67. 67
OPEN-LOOP CONTROL SYSTEM
In open-loop control system step motors are
used
Step motors are driven by electric pulses
Every pulse rotates the motor spindle through a
certain amount
By counting the pulses, the amount of motion
can be controlled
No feedback signal for error correction
Lower positioning accuracy

68. 68
CLOSED-LOOP CONTROL
SYSTEMS
In closed-loop control systems DC or AC
motors are used
Position transducers are used to generate
position feedback signals for error
correction
Better accuracy can be achieved
More expensive
Suitable for large size machine tools

69. 69
DRIVE SYSTEM
A drive system consists of amplifier
circuits, steppingmotorsor servomotors
and ball lead-screws. The MCU feeds
control signals (position and speed) of
each axis to the amplifier circuits. The
control signals are augmented to actuate
steppingmotors which in turn rotate the
ball lead-screws to position the machine
table.

70. 70
STEPPING MOTORS
A stepping motor provides open-loop, digital
control of the position of aworkpiece in a
numerical control machine. The drive unit
receives a directioninput (cw or ccw) and pulse
inputs. For each pulse it receives, the drive unit
manipulates the motor voltage and current,
causing the motor shaft to rotate bya fixed angle
(one step). The lead screw converts the rotary
motion of themotor shaft into linear motion of
the workpiece.

71. 71
STEPPING MOTORS

72. 72
RECIRCULATING BALL SCREWS
Transform rotational motion of the motor
intotranslationalmotion of the nut attached to
the machine table.

73. 73
RECIRCULATING BALL SCREWS
Accuracy of CNC
machines depends on
their rigid
construction,care in
manufacturing,and
the use of ballscrews
to almosteliminate
slop in thescrews
used to moveportions
of themachine.

74. 74

75. 75
POSITIONING
The positioning resolution of a ball screwdrive
mechanism is directly proportional tothe
smallest angle that the motor can turn.
The smallest angle is controlled by the motor
step size.
Microsteps can be used to decrease the motor
step size.
CNC machines typically have resolutions of
0.0025mmor better.

76. 76
MACHINE TOOL
CNC controls are used to control various
types of machine tools. Regardless of
which type of machine tool is controlled, it
always has a slide table and a spindle to
control of position and speed. The
machine table is controlled in the X and Y
axes, while the spindle runs along the Z
axis.

77. 77
FEEDBACK SYSTEM
The feedback system is also referred to as
the measuring system. It uses position
and speed transducers to continuously
monitor the position at which the cutting
tool is located at any particular time. The
MCU uses the difference between
reference signals and feedback signals to
generate the control signals for correcting
position and speed errors.

78. 78
CNC MACHINES FEEDBACK
DEVICES

79. 79
POTENTIOMETERS

80. 80
POTENTIOMETERS

81. 81
ENCODERS
A device used to convert linear or
rotationalposition information into an
electrical outputsignal.

82. 82
ENCODERS

83. 83
INDUSTRIAL APPLICATIONS of
ENCODERS

84. 84
RESOLVERS
A resolver is a rotary
transformer that produces
anoutput signal that is a
function of the rotor
position.

85. 85
SERVOMOTOR with RESOLVER

86. 86
VELOCITY FEEDBACK
Tachometers:
Electrical output is proportionalto rate of
angular rotation.
Encoders,Resolvers,Potentiometers:
Number of pulses per time isproportional
torate change ofposition.

87. 87
CNC CUTTERS
Turning center cutters
Machining center cutters

88. 88
TURNING CENTER CUTTERS
Types of cutters used on CNC turning
centers
Carbides(and other hard materials) insert
turningand boring tools
Ceramics
High Speed Steel (HSS) drills and taps

89. 89
STANDART INSERT SHAPES
V –used for profiling, weakest
insert, 2edges per side.
D –somewhat stronger, used for
profilingwhen the angle allows it,
2 edges per side.
T –commonly used for turning
because ithas 3 edges per side.
C –popular insert because the
same holdercan be used for
turning and facing. 2 edgesper
side.
W –newest shape. Can turn and
face likethe C, but 3 edges per
side.
S –Very strong, but mostly used
forchamfering because it won’t
cut a squareshoulder. 4 edges per
side.
R –strongest insert but least
commonlyused.

90. 90
TYPICALTURNING,
THREADINGand PARTINGTOOLS

91. 91
MACHINING CENTER CUTTING
TOOLS
Most machiningcenters
use someform of HSS or
carbide insert endmillas
the basic cuttingtool.
Insert endmills cutmany
times fasterthan HSS,
but the
HSS endmills leave a
better finish whenside
cutting.

92. 92
MACHINING CENTER CUTTING
TOOLS (cont’d)
Facemills flatten large
surfaces quickly and
withan excellent
finish. Noticethe
engine block being
finished in one pass
with alarge cutter.

93. 93
MACHINING CENTER CUTTING
TOOLS (cont’d)
Ball endmills (both
HSS and insert)are
used for a variety of
profilingoperations
such as the mold
shownin the picture.
Slitting and side
cutters are usedwhen
deep, narrow slots
must becut.

94. 94
MACHINING CENTER CUTTING
TOOLS (cont’d)
Drills, Taps, and Reamers
Common HSS tools such as
drills,taps, and reamers are
commonlyused on CNC
machining centers.Note that a
spot drill is used insteadof a
centerdrill. Also, spiral point or
gun taps are used for through
holesand spiral flute for blind
holes. Rarelyare hand taps
used on a machiningcenter.

95. 95
TOOL HOLDERS
All cutting tools must be held in a holder
that fits in the spindle.These include end
mill holders (shown), collet holders, face
milladapters, etc.Most machines in the
USA use a CAT taper which is a modified
NST 30, 40, or 50 taper that uses a pull
stud and a groove inthe flange. The
machine pulls on the pull stud to hold the
holderin the spindle, and the groove in
the flange gives the automatictool
changer something to hold onto.HSK tool
holders were designed a number of years
ago as animprovement to CAT tapers,
but they are gaining acceptanceslowly.

96. 96
CNC PROGRAMMING

97. 97
CNC PROGRAMMING
Offline programminglinked to CAD programs.
Conversational programmingby the
operator.
MDI~ Manual Data Input.
Manual Controlusing jog buttons or
`electronic handwheel'.
Word-Address Codingusing standard G-codes
and M-codes.

98. 98
During secondary motion, either the tool
moves relative to the workpiece or the
workpiece moves relative to the tool. In NC
programming, it is always assumed that the
tool moves relative to the workpiece no
matter what the real situation is.
Basics of NC Part Programming:

99. 99
The position of the tool is described
by using a Cartesian coordinate
system. If (0,0,0) position can be
described by the operator, then it is
called floating zero.

100. 100
In defining the motion of the tool
from one point to another,
either
absolutepositioningmode or
incrementalpositioningmode
can be used.

101. 101
1. Absolute positioning. In this mode, the
desired target position of the tool for a
particular move is given relative to the origin
point of the program.
2. Incremental positioning. In this mode, the
next target position for the tool is given
relative to the current tool position.

102. 102
Structure of an NC Part Program:
Commands are input into the controller in
units called blocksor statements.
Block Format:
1. Fixed sequential format
2. Tab sequential format
3. Word address format

103. 103
EXAMPLE:
Assume that a drilling operation is to be
programmed as:
1. The tool is positioned at (25.4,12.5,0) by a
rapid movement.
2. The tool is then advanced -10 mm in the z
direction at a feed rate of 500 mm/min., with the
flood coolant on.
3.The is then retracted back 10 mm at the rapid
feed rate, and the coolant is turned off.

104. 104
1. Fixed sequential format
0050 00 +0025400 +0012500 +0000000 0000 00
0060 01 +0025400 +0012500 -0010000 0500 08
0070 00 +0025400 +0012500 +0000000 0000 09
2. Tab sequential format
0050 TAB 00 TAB +0025400 TAB +0012500 TAB +0000000 TAB TAB
0060 TAB 01 TAB TAB TAB -0010000 TAB 0500 TAB 08
0070 TAB 00 TAB TAB TAB -0000000 TAB 0000 TAB 09
3. Word address format
N50 G00 X25400 Y125 Z0 F0
N60 G01 Z-10000 F500 M08
N70 G00 Z0 M09

105. 105
Modal commands: Commands issued in the
NC program that will stay in effect until it is
changed by some other command, like, feed
rate selection, coolant selection, etc.
Nonmodal commands: Commands that are
effective only when issued and whose
effects are lost for subsequent commands,
like, a dwell command which instructs the
tool to remain in a given configuration for a
given amount of time.

106. 106
CNC PROGRAMMING

107. 107
INFORMATION NEEDED by a CNC
1. Preparatory Information: units, incremental orabsolute
positioning
2. Coordinates: X,Y,Z, RX,RY,RZ
3. Machining Parameters: Feed rate and spindlespeed
4. Coolant Control: On/Off, Flood, Mist
5. Tool Control: Tool and tool parameters
6. Cycle Functions: Type of action required
7. Miscellaneous Control: Spindle on/off, directionof
rotation, stops forpart movement
This information is conveyed to the machine through a set
of instructions arranged in a desired sequence –Program.

108. 108
BLOCK FORMAT
Sample Block
N135 G01 X1.0 Y1.0 Z0.125 F5
Restrictions on CNC blocks
Each may contain only one tool move
Each may contain any number of non-tool move G-codes
Each may contain only one feedrate
Each may contain only one specified tool or spindle
speed
The block numbers should be sequential
Both the program start flag and the program number
must beindependent of all other commands (on
separate lines)
The data within a block should follow the sequence
shownin the above sample block

109. 109
WORD-ADDRESS CODING
N5 G90 G20
N10 M06 T3
N15 M03 S1250
N20 G00 X1 Y1
N25 Z0.1
N30 G01 Z-0.125 F5
N35 X3 Y2 F10
N40 G00 Z1
N45 X0 Y0
N50 M05
N55 M30
Example CNC Program
Each instruction to the machine
consistsof a letter followed bya
number.
Each letter is associated with a
specifictype of action or pieceof
informationneeded by themachine.
Letters used in Codes
N,G,X,Y,Z,A,B,C,I,J,K,F,S,T,R,M

110. 110
G & M Codes
N5 G90 G20
N10 M06 T3
N15 M03 S1250
N20 G00 X1 Y1
N25 Z0.1
N30 G01 Z-0.125 F5
N35 X3 Y2 F10
N40 G00 Z1
N45 X0 Y0
N50 M05
N55 M30
Example CNC Program
•G-codes: Preparatory Functions
involve actual tool moves.
•M-codes: Miscellaneous
Functions –involve actions
necessary for machining (i.e.
spindle on/off, coolant on/off).

111. 111
G Codes
G00Rapid traverse
G01 Linear interpolation
G02Circular interpolation,
CW
G03 Circular interpolation,
CCW
G04 Dwell
G08 Acceleration
G09 Deceleration
G17 X-Y Plane
G18 Z-X Plane
G19 Y-Z Plane
G20 Inch Units (G70)
G21 Metric Units (G71)
G40 Cutter compensation –
cancel
G41 Cutter compensation –
left
G42 Cutter compensation-
right
G70 Inch format
G71 Metric format
G74 Full-circleprogramming
off
G75 Full-circle programming
on
G80 Fixed-cycle cancel
G81-G89 Fixed cycles
G90 Absolute dimensions
G91 Incremental dimensions

112. 112
Modal G-Codes
Most G-codes set themachine in a “mode”
which stays in effectuntil it is changed or
cancelled by another G-code.These
commandsare called “modal”.

113. 113
Modal G-Code List
G00Rapid Transverse
G01Linear Interpolation
G02Circular Interpolation, CW
G03Circular Interpolation,
CCW
G17XY Plane
G18XZ Plane
G19YZ 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)
G43Tool length compensation
(plus)
G44Tool length compensation
(minus)
G49Tool length compensation
cancel
G80Cancel canned cycles
G81Drilling cycle
G82Counter boring cycle
G83Deep hole drilling cycle
G90Absolute positioning
G91Incremental positioning

114. 114
M Codes
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

115. 115
N Codes
Gives anidentifying number for eachblock
of information.
It is generally good practice toincrement
each block number by5 or 10 to allow
additionalblocks to be inserted if future
changes are required.

116. 116
X,Y, and Z Codes
X, Y, and Z codes are used tospecify the
coordinate axis.
Number following the codedefines the
coordinate at the endof the move relative
to anincremental or absolutereference
point.

117. 117
I,J, and K Codes
I, J, and K codes are used tospecify the
coordinate axiswhen defining the center
of acircle.
Number following the codedefines the
respective coordinatefor the center of the
circle.

118. 118
F,S, and TCodes
F-code: used to specify the feedrate
S-code: used to specify thespindle speed
T-code: used to specify the tool
identification number associatedwith the
tool to be used insubsequent operations.

119. 119
Three Basic Categories of Motion
Systems
Point to Point -No contouring capability
Straight cut control -one axis motion at a
time is controlled for machining
Contouring -multiple axis’s controlled
simultaneously

120. 120
Three Basic Categories of Motion
Systems

121. 121
Application of Some Codes
G01 Linear Interpolation
Format: N_ G01 X_ Y_ Z_ F_
Linear Interpolation results in a straight
line feedmove.
Unless tool compensation is used, the
coordinates areassociated with the
centerline of the tool.

122. 122
Application of Some Codes
G01 Linear Interpolation
. As an example, for the motion that occurs in
x-y plane with the same maximum speed for the
x-and y-axis, initial motion is at an angle of 45o
to the axes until motion in one of
the axes is completed and then the balance of
the motion occurs in the other axis. This is called
point-to-point motion.

123. 123
Application of Some Codes
G01 Linear Interpolation5
10
15
20
25
5 10 15 20 25 30
A
B C
Positioning motion from A to C
N10 G00 X30000 Y20000 F0

124. 124
Application of Some Codes
G01 Linear Interpolation
G01 is another preparatory function to specify
that the tool should be moved to a specified
location along a straight line path. It is referred
to as linear interpolation.
This function is typically used to specify
machining of straight features such as turning
a cylindrical surface in turning, cutting a slot in
milling, etc.

125. 125
Application of Some Codes
G01 Linear Interpolation5
10
15
20
25
5 10 15 20 25 30
A
C
Linear interpolation from A to C
N10 G01 X30000 Y20000 F2500

126. 126
N10 G00 X1 Z1
N15 Z0.1
N20G01 Z-0.125 F5
N25 X2 Z2 F10
G01 Linear Interpolation
X
Z

127. 127
G02 Circular Interpolation
G02 is also a preparatory function to specify that
the tool should be moved to a specified location
along a circular path in a clockwise direction. In
order to specify the path to the MCU, the end
point of the arc and the location of the center of
the arc should be specified. Within the block in
which the G02 code is programmed, the center
of the arc is given by specifying its location
relative to the start of the arc.

128. 128
G02 Circular Interpolation (CW)
The G02 commandrequiresan
endpoint and a radiusinorder
to cut the arc.
I,J, and K are relativeto the
start point.
N_ G02 X2 Y1 I0 J-1 F10
or
N_ G02 X2 Y1 R1

129. 129
G02 Circular Interpolation (CW)5
10
15
20
25
5 10 15 20 25 30
C
C
Circular interpolation from A to B
about a circle centered at C
N10 G02 X20000 Y10000
I5000 J15000 F2500
A
B
I=5
J=15

130. 130
The sequence of some machining operations is may be
the same for any part and for any machine. For example,
drilling a hole involves the following steps:
Position the tool above the point where the hole will be
drilled
Set the correct spindle speed
Feed the tool into the workpiece at a controlled feed rate
to a predetermined depth
Retract the tool at a rapid rate to just above the point
where the hole started
Canned Cycles

131. 131
Some Commonly Used Canned Cycle
CodeFunction Down feedAt bottomRetracti
on
G81Drilling Continuous
feed
No actionRapid
G82Spot face,
counterbore
Continuous
feed
Dwell Rapid
G83Deep hole drillingPeck No actionRapid
G84 Tapping Continuous
feed
Reverse
spindle
Feed
rate
G85Through boring(in
& out)
Continuous
feed
No actionFeed
rate
G86Through boring(in
only)
Continuous
feed
Stop
spindle
Rapid

132. 132
G81 ILLUSTRATION

133. 133
Three Main parts of a CNC program
N5 G90 G21 (Absolute units, metric)
N10 M06 T2 (Stop for tool change, use
tool # 2)
N15 M03 S1200 (Turn the spindle on CW to
1200 rpm)
Part 1-Program setup

134. 134
Three Main parts of a CNC program
N20 G00 X1 Y1 (Rapid to X1,Y1 from origin
point)
N25 Z0.125 (Rapid down to Z0.125)
N30 G01 Z-0.125 F100(Feed down to Z-0.125 at
100 mm/min)
N35 G01 X2 Y2 (Feed diagonally to X2,Y2)
N40 G00 Z1 (Rapid up to Z1)
N45 X0 Y0 (Rapid to X0,Y0)
Part 2-Chip Removal

135. 135
ThreeMain parts of a CNC program
N50 M05 (Turn the spindle off)
N55 M00 (Programstop)
Part 3-System Shutdown

136. 136
Advanced features:
Execution of the part of the program in a
rotated or mirrored position.
Ability to scale the program and produce
larger or smaller programs.
Three dimensional circular interpolation
which produces a helical shape.
Parabolic and cubic interpolation.

137. 137
Program Loading:
Through keyboard
Through punched tape reader
Through diskette drive
Through RS 232 serial port
Through network interface card

138. 138
A system in which a central computer
downloads the NC programs block by block
to many NC machine tools simultaneously is
called Direct Numerical Control(DNC)
system.
Direct Numerical Control (DNC):

139. 139
This system used to work with the early NC
machine tools which can not read more than a
block of information at a time. The central
computer feed the program information one
block at a time. When the machine execute the
information, the next block of information
would be fed.
Direct Numerical Control (DNC):

140. 140
Distributed NC is known by the same acronym
as Direct Numerical Control (DNC). After the
introduction of CNC, the machine tools have
had the capability of storing large amount of
information. Therefore, there have been no
need to have drip feed information system,
like, Direct Numerical Control. Instead,
Distributed Numerical Control is introduced. In
such a system, a host computer communicate
with many CNC machine tools via networks
and download or upload programs.
Distributed Numerical Control (DNC):

141. 141
With Distributed Numerical Control systems, it
is possible to monitor the activities in individual
CNC machine tools on host computer.
Therefore, better shop floor control can be
achieved.
Distributed Numerical Control (DNC):

142. 142
NC program preparation may be tedious and
difficult if the part to be machined has a
complex geometry. The main difficulty is to find
out the cutter locations during the machining.
Computers may be used to assist the
programmers in preparing the NC codes.
Computer Aided Part Programming:

143. 143
Advantages of applying computer-aided part
programming include the following:
 1. It reduces the manual calculations
involves in determining the geometric
characteristics of the part.
It provides the cutter path simulation.
It provides tool collision checking.
It shortens the program preparation time.
It makes the program preparation easier.

144. 144
The Aerospace Industries Association
sponsored the work that led to the first part
programming language, developed in MIT in
1955.
This was called:Automatically Programmed
Tools(APT).
APT is an English like simple programming
language which basically produce the Cutter
Location(CL) data.
Using the cutter location data, the program can
generate the actual NC codes by using a
postprocessor .

145. 145
The output of any CAD package include the
geometric data of the part to be machined.
Therefore, many CAD/CAM package can
produce cutter location (CL) data to be used
for NC code generation.
There is still to be a process planning module
for a workable NC code generation.
Some of the CAD/CAM packages that have the
NC code generation capabilities are
Computervision, CATIA, CADAM, ProEngineer,
MechanicalDesktop (Auto Desk).
CAD/CAM Based Part Programming: