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CNC Machining and otherCNC Applications
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Lesson Outcomes
By the end of this lesson, students should be able to:• Understand the concept of Computer NumericalControl System and its applications
• Understand the fundamental components of anCNC system
• Understand aspects of CNC motion control
• Understand aspects of CNC codes• Understand the advantages and disadvantages of
CNC control systems
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What is Computer Numerical
Control (CNC)?
– (Definition:) A form of programmableautomation in which the mechanical actions ofa machine tool or other equipment are
controlled by a program. – Program of instructions (numbers, letters
symbols) used to control a process
– Main advantage: Flexibility (easy to change program of instructions for different parts)
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1. Machine tool applications to control the
relative motion between cutting tool andworkpiece.
Examples: – CNC Lathe
– CNC Milling
– CNC Machining Ctr – CNC Turning Center
– CNC Wire-cut
– CNC EDM
– CNC Grinder
– CNC Laser-cut – CNC Water-jet
– CNC Punch & Blanking
– CNC Drilling & Boring
Applications of CNC Control
Technology
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Applications of CNC Control
2. Non-Machine Tool Applications
Examples:-Assembly
(CNC used to control assembly machines)
-Drafting
(Once a CAD drawing is completed, CNC is used tocontrol a plotter to generate an engineering drawing)
-Robotics(CNC is used to control the motors that move robotic arms)
-Quality Control and Inspection
(eg CNC CMM)
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Components of an CNC System
1. Program of instructions or part program2. Machine control unit
3. Processing equipment
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Components of an CNC System
1. Program of instructions:The detailed step by step commands that
direct the actions or movements of the
machine
Program – written manually & key-in or viaCAD/CAM
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Components of an CNC System
2. Machine Control Unit (MCU):Microcomputer and control hardware thatread and interprets the program of instructions
and converts it into signals to the processingequipment.
Diskette / RS232C/ CPU/CRT/HDD/RAM buffer/CPU – convert CNC program intoelectronic pulses to drive various motors
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Components of an CNC System
3. Processing equipment:The part of the CNC System that performs theuseful work
Examples are:
• Worktable, spindle and motors in a machine tool
• Motors and linkages in a robotic system
• This machine tool/ production process designed togive high level of repeatability and precision
CNC M ti C t l
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CNC Motion Control
Systems
Three aspects of CNC Motion ControlSystems:
1. Point-to-point
2. Interpolation methods (Continuous Path
Control)
3. Absolute vs. Incremental positioning
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NC Motion Control Systems1. Point to point system:
• Tool movement is arbitrary as long as the finaldestination is reached
• A tool may move through a number of different points before reaching the final destination.
• Examples: drilling and spot welding operations
• Processing action is performed after location isreached
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NC Motion Control Systems
2. Interpolation methods (Continuous path controlsystem)
• Some shapes such as circles and ellipses arecontinuous.
• NC control system, however, is digital.
• Therefore, a circle or ellipse must be divided
into straight segments to approximate the curve.• This leads to a very large number of points
• Interpolation methods calculate the intermediate
points and generate a smooth continuous points
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NC Motion Control Systems2. Interpolation methods (Continuous path control
system:• The path followed by the tool is continuouslycontrolled to get the desired geometrical feature
• Movement of worktable by continuously andsimultaneously controlling two or more axes.
• Provides control of the tool path.
• Processing action is performed duringmovement.
• Allow for generation of 2D and 3D contours
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CNC Motion Control Systems2. Absolute vs. Incremental Positioning
Absolute positioning:
Positions are defined with respect to the origin
of coordinate system
Incremental positioning:
Positions are defined relative to the previouslocation
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CNC Co-ordinate System
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Floating zero point system
• This feature allows the user to place asecondary coordinate system anywhere on
the machine table.
• This makes it easy to develop the part
program & machine the workpiece
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CNC Codes• CNC Code (forms the
program of instructions)
• Types of CNC Code:
– Sequence/block number (NCode)
– Preparatory Codes (GCodes)
– Miscellaneous Codes (M
Codes) – Feed and Speed Codes
– Tools Codes
Source: MTAB
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CNC Codes
Sequence/Blocknumber (N
Codes)
– Describes the
block of codes in
a program
Source: MTAB
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CNC Codes
Preparatory Codes (G Codes)
Relevant G Codes:G00G00
G01G01G02G02
G03G03
G20G20
G21G21
G28G28
G90G90G91G91
G92G92G94G94
Source: MTAB
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CNC CodesPreparatory Codes (G Codes)
G00 Rapid Traverse of fast Traverse
• A G00 causes the tool to move to the specified position at maximum speed.
(for non-cutting movements)
• Example: G00 X20 Y30 Z1
Here the tool is moved to X 20mm, Y 30mm, and
Z 1mm (for metric system)
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CNC Codes
Preparatory Codes (G Codes)
G01 Linear Interpolation• A G01 causes linear motion to the given
position.
• Example: G01 X20 Y30 F45
Here the tool is moved to X 20mm, Y 30mm
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CNC CodesPreparatory Codes (G Codes)
G02 Clockwise Circular Interpolation
• Arcs can be specified by either radius or by centre.
• Example: G02 X30 Y20 R15
In this example the tool is moved to X 30mm and Y20mm. The arc has a radius of 15mm.
• “I” and “J” specifies the arc centre relative to the arcstart. If the value-+ is 0 then it need not be specified.
Example: G02 X30 Y20 I15 J0
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CNC CodesPreparatory Codes (G Codes)
G03 Counter-Clockwise Circular Interpolation
• G03 causes counter-clockwise circular motion• Similar to G02
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CNC CodesPreparatory Codes (G Codes)
G20 Imperial Units
• All future instruction parameters will be takenas imperial values.
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CNC CodesPreparatory Codes (G Codes)
G21 Metric Units
• All Future instruction parameters will be takenas metric values.
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CNC CodesPreparatory Codes (G Codes)
G28 Automatic Zero Return
• Send spindle to home position• Usually used for tool change or setting up for a
new programMilling: Lathe:
N020 G91 G28 Z0N020 G91 G28 Z0
N030 G28 X0 Y0N030 G28 X0 Y0N020 G28 U0 W0N020 G28 U0 W0
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CNC CodesPreparatory Codes (G Codes)
G40 Cancel cutter compensation
• G41 and G42 are used to locate the tool oneither left or right side of the profile
• G40 is used to cancel this tool compensation
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CNC CodesPreparatory Codes (G Codes)
G90 Absolute Movement
• All future movements will be absolute untiloverridden by a G91 instruction
Example: G90G01 X30 Y0
The new position becomes X30 Y0
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CNC CodesPreparatory Codes (G Codes)
G91 Incremental Movement
• All future movements will be incremental until
overridden by a G90 instruction.
• Example: G90
G01 X15G91
G01 X2The position becomes X17
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CNC CodesPreparatory Codes (G Codes)
G92 Programming of the coordinate system
• Defines a coordinate system
• Example: G00 X30.0 Y40.0
G92 X0.0 Y0.0Converts the position that was X30 Y40 to X0
Y0
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CNC Codes
Miscellaneous Codes (M Codes)
Relevant M Codes:
M03M03
M05M05M06M06
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CNC CodesMiscellaneous Codes (M Codes)
Relevant M Codes:
M03 Start Spindle
• An M03 instruction starts forward spindle motion.• Example: M03 S2200
• The spindle should be switched on before anymovement below the component surface.
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CNC CodesMiscellaneous Codes (M Codes)
Relevant M Codes:
M05 Stop Spindle• An M05 instruction stops spindle rotation.
• M05 is issued before a tool change, and at theend of a program.
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CNC CodesMiscellaneous Codes (M Codes)
Relevant M Codes:
• M06 Change Tool
• The M06 instruction causes the a change to adifferent tool. The tool changing operation should bedone in the home position only.
• Example: M06 T1Changes to the tool in turret 1
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CNC CodesMiscellaneous Codes (M Codes)
Relevant M Codes:
M30 End of Program• Rewind program and reset memory
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CNC CodesFeed and Speed Codes
• Feed code (F code) – Specifies the tool motion feed rate
– Unit can be in mm/min, in/min, mm/rev or in/rev
Example: F50
• Speed code (S code)
– Specifies the rate of tool revolution – Unit is in RPM
Example: S1200
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CNC CodesTool code (T code)
• Refers to a location on tool turretExample: M06 T1
CNC Machine tools:
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Program of Instructions example (Milling)
G00 Rapid Traverse of fast TraverseG00 Rapid Traverse of fast Traverse
G01 Linear InterpolationG01 Linear Interpolation
G02 Clockwise Circular InterpolationG02 Clockwise Circular InterpolationG03 Counter G03 Counter --Clockwise CircularClockwise Circular
InterpolationInterpolation
G20 Imperial UnitsG20 Imperial Units
G21 Metric UnitsG21 Metric Units
G28 Automatic Zero ReturnG28 Automatic Zero Return
G40 Cancel cutterG40 Cancel cutter
compensationcompensation
G71 Rough out profile byG71 Rough out profile by
turningturning
G70 Finishing CycleG70 Finishing Cycle
G90 Absolute MovementG90 Absolute Movement
G91 Incremental MovementG91 Incremental Movement
G92 Programming of theG92 Programming of the
coordinate s stemcoordinate s stem
G94 Feed rate in mm/minG94 Feed rate in mm/min
in/min (G98 performs thein/min (G98 performs the
function in the CNC lathefunction in the CNC lathe
G95 Feed rate in mm/revG95 Feed rate in mm/revin/revin/rev
M03 Start SpindleM03 Start Spindle
M05 Stop SpindleM05 Stop Spindle
M06 Change ToolM06 Change Tool
M30 End of ProgramM30 End of Program
F Feed code (FF Feed code (F
code)code)
S Speed codeS Speed code
(S code)(S code)
T Tool code (TT Tool code (T
code)code)
Program of Instructions example (Milling)
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Program of Instructions example (Milling)
Source: MTAB
G00 Rapid Traverse of fast TraverseG00 Rapid Traverse of fast Traverse
G01 Linear InterpolationG01 Linear Interpolation
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Source: MTAB
AC
DEF
B
G01 Linear InterpolationG01 Linear Interpolation
G02 Clockwise Circular InterpolationG02 Clockwise Circular Interpolation
G03 Counter G03 Counter --Clockwise CircularClockwise Circular
InterpolationInterpolation
G20 Imperial UnitsG20 Imperial Units
G21 Metric UnitsG21 Metric Units
G28 Automatic Zero ReturnG28 Automatic Zero Return
G40 Cancel cutter compensationG40 Cancel cutter compensation
G71 Rough out profile by turningG71 Rough out profile by turning
G70 Finishing CycleG70 Finishing Cycle
G90 Absolute MovementG90 Absolute Movement
G91 Incremental MovementG91 Incremental MovementG92 Programming of the coordinate systemG92 Programming of the coordinate system
G94 Feed rate in mm/min or in/min (G98G94 Feed rate in mm/min or in/min (G98
performs the same function in the CNCperforms the same function in the CNC
lathe)lathe)
G95 Feed rate in mm/rev or in/revG95 Feed rate in mm/rev or in/rev
M03 Start SpindleM03 Start Spindle
M05 Stop SpindleM05 Stop Spindle
M06 Change ToolM06 Change Tool
M30 End of ProgramM30 End of Program
F Feed code (F code)F Feed code (F code)
S Speed code (S code)S Speed code (S code)
T Tool code (T code)T Tool code (T code)
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CNC Program of Instructions example (Lathe)
Z1
Source: MTAB
CNC Codes:
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Summary of relevant codes
G00 Rapid Traverse of fast TraverseG00 Rapid Traverse of fast TraverseG01 Linear InterpolationG01 Linear Interpolation
G02 Clockwise Circular InterpolationG02 Clockwise Circular Interpolation
G03 Counter G03 Counter
--Clockwise CircularClockwise Circular
InterpolationInterpolation
G20 Imperial UnitsG20 Imperial Units
G21 Metric UnitsG21 Metric Units
G28 Automatic Zero ReturnG28 Automatic Zero Return
G40 Cancel cutter compensationG40 Cancel cutter compensation
G71 Rough out profile by turningG71 Rough out profile by turning
G70 Finishing CycleG70 Finishing Cycle
G90 Absolute MovementG90 Absolute Movement
G91 Incremental MovementG91 Incremental Movement
G92 Programming of the coordinate systemG92 Programming of the coordinate system
G94 Feed rate in mm/min orG94 Feed rate in mm/min orin/min (G98 performs the samein/min (G98 performs the same
function in the CNC lathe)function in the CNC lathe)
G95 Feed rate in mm/rev orG95 Feed rate in mm/rev or
in/revin/rev
M03 Start SpindleM03 Start Spindle
M05 Stop SpindleM05 Stop Spindle
M06 Change ToolM06 Change Tool
M30 End of ProgramM30 End of Program
F Feed code (F code)F Feed code (F code)
S Speed code (S code)S Speed code (S code)
T Tool code (T code)T Tool code (T code)
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Advantages of CNC Control systems
1. Reduce nonproductive time
2. Greater accuracy and repeatability
3. More complex part geometeries are
possible4. Lesser operator skill-level is required
5. Easy to make engineering changes(flexible).
6. Less floor space requirement
Disadvantages of CNC
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Control Systems
1. Higher cost of initial investment
2. Higher maintenance cost
3. Requires part programming (conventional
machining does not require any
programming)
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Summary• CNC is a form of programmable automation
• The three components of an CNC system are the program of instructions, MCU, and the processing equipment
• Three aspects of CNC motion control are Point-to-point vs. Continuous Path Control,Interpolation methods and Absolute vs.Incremental positioning
• Alphanumeric CNC codes (G&M) codes areused for tool motion control and miscellaneous
parts