1. CNC TECHNOLOGY

2. INTRODUCTION TO CNC AND METAL CUTTING

3. HISTORY
US Air Force commissioned MIT to develop the first "numerically controlled" machine in It was demonstrated in 1952.
At 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.

4. 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.

5. CNC APPLICATIONS Machining 2.5D / 3D Turning ~ Lathes, Turning Centre
Milling ~ Machining Centres
Forming 2D
Plasma and Laser Cutting
Blanking, nibbling and punching 3D
Rapid Prototyping

6. SAMPLE CNC MACHINES

7. CNC TURNING

8. CNC MILLING

9. CNC LASER CUTTING

10. CNC PLASMA CUTTING

11. CNC PRESS

12. CNC RAPID PROTOTYPING

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

14. SAMPLE PRODUCTS OF CNC MANUFACTURING

15. AUTOMOTIVE INDUSTRY Engine Block

16. AUTOMOTIVE INDUSTRY(Cont’d) Different Products

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

18. CNC MOLD MAKING

19. ELECTRONIC INDUSTRY

20. RAPID PROTOTYPING PRODUCTS

21. ADVANTAGES OF CNC

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

23. 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.

24. PROFIT increases as COST decreases and as PRODUCTIVITY increases
PROFIT increases as COST decreases and as PRODUCTIVITY increases. PRODUCTIVITY through AUTOMATION

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

26. Transferred skill Results
muscle power
engine driven machine tools
First industrial revolution
manipulating skill
mechanization
hard automation
vision skill
use 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

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

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

29. 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.

30. 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.

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

32. 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

33. FUNDAMENTAL OF METAL CUTTING

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

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

36. 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.

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

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

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

40. 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
grinding m/c’s
honing m/c’s

41. BASIC COMPONENTS OF CNC SYSTEMS

43. ISO MACHINE TOOL AXIS DEFINITION

44. ISO MACHINE TOOL AXES DEFINITIONS
AXIS
MACHINE TOOL WITH SPINDLE
MACHINE TOOL WITH NO SPINDLE Z
axis 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
HORIZONTAL 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

45. RIGHT HAND RULE Vertical Machine Horizontal Machine

46. STANDARD LATHE COORDINATE SYSTEM

47. STANDARD MILLING MACHINE COORDINATE SYSTEM

48. 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.

49. 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.

50. MACHINE TOOL AUTOMATION

51. 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

52. NC SYSTEM ELEMENTS

53. OPERATIONAL FEATURES of CNC MACHINES

54. 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

55. 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.

56. 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

57. TYPES of CNC CONTROL SYSTEMS
Open-loop control
Closed-loop control

58. 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

59. 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

60. CONTROL Desired path (p, v, a) Path generator
3-axis position control (encoder feedback)
Velocity control (tachometer feedback)
Torque control (current feedback)
Path generator
Linear interpolation
Circular interpolation
Complex path interpolation (contouring)

61. DRIVE SYSTEM
A drive system consists of amplifier circuits, stepping motors or 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 stepping motors which in turn rotate the ball lead-screws to position the machine table.

62. STEPPING MOTORS
A stepping motor provides open-loop, digital control of the position of a workpiece in a numerical control machine. The drive unit receives a direction input (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 the motor shaft into linear motion of the workpiece .

63. STEPPING MOTORS

64. RECIRCULATING BALL SCREWS
Transform rotational motion of the motor into translational motion of the nut attached to the machine table.

65. RECIRCULATING BALL SCREWS
Accuracy of CNC machines depends on their rigid construction, care in manufacturing, and the use of ball screws to almost eliminate slop in the screws used to move portions of the machine.

66. COMPONENTS OF RECIRCULATING BALL SCREWS
Ball nut (anti-backlash)
Ways
Linear bearings

68. POSITIONING
The positioning resolution of a ball screw drive mechanism is directly proportional to the 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 mm or better.

69. 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.

70. 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.

71. CNC MACHINES FEEDBACK DEVICES

72. ENCODERS
A device used to convert linear or rotational position information into an electrical output signal.

73. ENCODERS

74. INDUSTRIAL APPLICATIONS of ENCODERS

75. RESOLVERS
A resolver is a rotary transformer that produces an output signal that is a function of the rotor position.

76. SERVOMOTOR with RESOLVER

77. DRIVE MOTORS DC servo motors AC servo motors Stepper motors
Hydraulic motors

78. POSITION FEEDBACK Incremental encoder Quadrature Absolute encoder
Resolver
Tachometer
No feedback (open loop)

79. POTENTIOMETERS

80. POTENTIOMETERS

81. CNC Programming Manual Computer-assisted CAD/CAM Write code directly
Draw cutter path
CAD/CAM
Draw the part
Cutter path is generated

82. VELOCITY FEEDBACK Tachometers:
Electrical output is proportional to rate of angular rotation.
Encoders, Resolvers, Potentiometers:
Number of pulses per time is proportional to rate change of position.

83. CNC MACHINES CUTTING TOOLS (CUTTERS)

84. CNC CUTTERS
Turning center cutters
Machining center cutters

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

86. STANDART INSERT SHAPES
V – used for profiling, weakest insert, 2 edges per side.
D – somewhat stronger, used for profiling when the angle allows it, 2 edges per side.
T – commonly used for turning because it has 3 edges per side.
C – popular insert because the same holder can be used for turning and facing. 2 edges per side.
W – newest shape. Can turn and face like the C, but 3 edges per side.
S – Very strong, but mostly used for chamfering because it won’t cut a square shoulder. 4 edges per side.
R – strongest insert but least commonly used.

87. TYPICAL TURNING, THREADING and PARTING TOOLS

88. MACHINING CENTER CUTTING TOOLS
Most machining centers use some form of HSS or carbide insert endmill as the basic cutting tool.
Insert endmills cut many times faster than HSS, but the
HSS endmills leave a better finish when side cutting.

89. MACHINING CENTER CUTTING TOOLS (cont’d)
Facemills flatten large surfaces quickly and with an excellent finish. Notice the engine block being finished in one pass with a large cutter.

90. MACHINING CENTER CUTTING TOOLS (cont’d)
Ball endmills (both HSS and insert) are used for a variety of profiling operations such as the mold shown in the picture.
Slitting and side cutters are used when deep, narrow slots must be cut.

91. MACHINING CENTER CUTTING TOOLS (cont’d)
Drills, Taps, and Reamers
Common HSS tools such as drills, taps, and reamers are commonly used on CNC machining centers. Note that a spot drill is used instead of a centerdrill. Also, spiral point or gun taps are used for through holes and spiral flute for blind holes. Rarely are hand taps used on a machining center.

92. 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 mill adapters, 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 in the flange. The machine pulls on the pull stud to hold the holder in the spindle, and the groove in the flange gives the automatic tool changer something to hold onto. HSK tool holders were designed a number of years ago as an improvement to CAT tapers, but they are gaining acceptance slowly.

93. CNC PROGRAMMING

94. CNC PROGRAMMING Offline programming linked to CAD programs.
Conversational programming by the operator.
MDI ~ Manual Data Input.
Manual Control using jog buttons or `electronic handwheel'.
Word-Address Coding using standard G-codes and M-codes.

95. Basics of NC Part Programming:
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.

96. 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.

97. In defining the motion of the tool from one point to another, either absolute positioning mode or incremental positioning mode can be used.

98. 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.

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

100. 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.

101. 1. Fixed sequential format
2. Tab sequential format
0050 TAB 00 TAB TAB TAB TAB TAB
0060 TAB 01 TAB TAB TAB TAB 0500 TAB 08
0070 TAB 00 TAB TAB TAB TAB 0000 TAB 09
3. Word address format
N50 G00 X25400 Y125 Z0 F0
N60 G01 Z F500 M08
N70 G00 Z0 M09

102. 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.

103. CNC PROGRAMMING

104. INFORMATION NEEDED by a CNC
1. Preparatory Information: units, incremental or absolute positioning
2. Coordinates: X,Y,Z, RX,RY,RZ
3. Machining Parameters: Feed rate and spindle speed
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, direction of rotation, stops for part movement
This information is conveyed to the machine through a set
of instructions arranged in a desired sequence – Program.

105. 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 be independent of all other commands (on separate lines)
The data within a block should follow the sequence shown in the above sample block

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

107. G & M Codes G-codes: Preparatory Functions involve actual tool moves.
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).
N5 G90 G20
N10 M06 T3
N15 M03 S1250
N20 G00 X1 Y1
N25 Z0.1
N30 G01 Z F5
N35 X3 Y2 F10
N40 G00 Z1
N45 X0 Y0
N50 M05
N55 M30

108. G Codes G40 Cutter compensation – cancel
G00 Rapid traverse
G01 Linear interpolation
G02 Circular 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-circle programming off
G75 Full-circle programming on
G80 Fixed-cycle cancel
G81-G89 Fixed cycles
G90 Absolute dimensions
G91 Incremental dimensions

109. Modal G-Codes
Most G-codes set the machine in a “mode” which stays in effect until it is changed or cancelled by another G-code. These commands are called “modal”.

110. Modal G-Code List G43 Tool length compensation (plus)
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

111. 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

112. N Codes Gives an identifying number for each block of information.
It is generally good practice to increment each block number by 5 or 10 to allow additional blocks to be inserted if future changes are required.

113. X,Y, and Z Codes
X, Y, and Z codes are used to specify the coordinate axis.
Number following the code defines the coordinate at the end of the move relative to an incremental or absolute reference point.

114. I,J, and K Codes
I, J, and K codes are used to specify the coordinate axis when defining the center of a circle.
Number following the code defines the respective coordinate for the center of the circle.

115. F,S, and T Codes F-code: used to specify the feed rate
S-code: used to specify the spindle speed
T-code: used to specify the tool identification number associated with the tool to be used in subsequent operations.

116. Application of Some Codes G01 Linear Interpolation
Format: N_ G01 X_ Y_ Z_ F_
Linear Interpolation results in a straight line feed move.
Unless tool compensation is used, the coordinates are associated with the centerline of the tool.

117. 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.

118. Application of Some Codes G01 Linear Interpolation

119. 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.

120. Application of Some Codes G01 Linear Interpolation

121. G01 Linear Interpolation
N10 G00 X1 Z1 N15 Z0.1 N20 G01 Z F5 N25 X2 Z2 F10 X Z

122. 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.

123. G02 Circular Interpolation (CW)
The G02 command requires an endpoint and a radius in order to cut the arc.
I,J, and K are relative to the start point.
N_ G02 X2 Y1 I0 J-1 F10 or
N_ G02 X2 Y1 R1

124. G02 Circular Interpolation (CW)

125. Canned Cycles
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

126. Some Commonly Used Canned Cycle
Code
Function
Down feed
At bottom
Retraction
G81
Drilling
Continuous feed
No action
Rapid
G82
Spot face, counterbore
Dwell
G83
Deep hole drilling
Peck
G84
Tapping
Reverse spindle
Feed rate
G85
Through boring(in & out)
G86
Through boring(in only)
Stop spindle

127. G81 ILLUSTRATION

128. Three Main parts of a CNC program
Part 1- Program Petup
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 rpm)

129. Three Main parts of a CNC program
Part 2- Chip Removal
N20 G00 X1 Y1 (Rapid to X1,Y1 from origin point)
N25 Z (Rapid down to Z0.125)
N30 G01 Z F100 (Feed down to Z at 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)

130. Three Main parts of a CNC program
Part 3- System Shutdown
N50 M05 (Turn the spindle off)
N55 M00 (Program stop)

131. EXAMPLE OPERATION on CNC MILLING MACHINE

132. G-CODE PROGRAM
First pass : conventional mill to a depth of around edge profile. Tool 1 is a ½ inch dia. end mill. %
:1002
N5 G90 G20
N10 M06 T1
N15 M03 S1200
N20 G00 X0.125 Y0.125
N30 Z0.125
N35 G01 Z F5
N40 X3.875
N45 Y4.125
N50 X0.125
N55 Y0.125

133. Second pass: conventional mill to a depth of 0.25 around edge profile.
N35 Z-0.250
N40 X3.875
N45 Y4.125
N50 X0.125
N55 Y0.125
N60 Z0.125

134. Third pass: conventional mill to a depth of 0
Third pass: conventional mill to a depth of around pocket profile.
N65 G00 X1.25 Y1.0
N70 G01 Z F5
N75 X1.75
N80 Y2.5
N85 X1.25
N90 Y1.0
N95 Z0.125

135. Fourth pass: climb mill to a depth of 0.125 across remaining material.
N100 Y2.125
N105 X2.625
N110 Z0.125
N115 G00 X-5 Y-5 Z5
N120 M05
N125 M30

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

138. Direct Numerical Control (DNC):
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.

139. Direct Numerical Control (DNC):
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.

140. Distributed Numerical Control (DNC):
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.

141. Distributed Numerical Control (DNC):
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.

142. Computer Aided Part Programming:
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.

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. 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. CAD/CAM Based Part Programming:
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).