5. DEFINITIONDEFINITION
• InIn CNCCNC ((Computer Numerical ControlComputer Numerical Control),), thethe
instructions are stored as a program in ainstructions are stored as a program in a
micro-computer attached to the machine.micro-computer attached to the machine.
The computer will also handle much of theThe computer will also handle much of the
control logic of the machine, making itcontrol logic of the machine, making it
more adaptable than earlier hard-wiredmore adaptable than earlier hard-wired
controllers.controllers.
6. Utilization of computers inUtilization of computers in
manufacturing applications hasmanufacturing applications has
proved to be one of the mostproved to be one of the most
significant developments over thesignificant developments over the
last couple of decades in helping tolast couple of decades in helping to
improve the productivity andimprove the productivity and
efficiency of manufacturingefficiency of manufacturing
systems.systems.
7. The metal cutting operationsThe metal cutting operations (also(also
called machining)called machining) is one of theis one of the
most important manufacturingmost important manufacturing
processes in industry todayprocesses in industry today (as it(as it
was yesterday)was yesterday)..
8. MACHININGMACHINING IS THEIS THE
REMOVAL OF MATERIALSREMOVAL OF MATERIALS
IN FORMS OF CHIPS FROMIN FORMS OF CHIPS FROM
THE WORKPIECE BYTHE WORKPIECE BY
SHEARING WITH A SHARPSHEARING WITH A SHARP
TOOL.TOOL.
9. The main function of a machine toolThe main function of a machine tool
is to control the workpiece-cuttingis to control the workpiece-cutting
tool positional relationship in such atool positional relationship in such a
way as to achieve a desiredway as to achieve a desired
geometric shape of the workpiecegeometric shape of the workpiece
with sufficient dimensionalwith sufficient dimensional
accuracy.accuracy.
10. Machine tool provides:
work holding
tool holding
relative motion between tool
and workpiece
primary motion
secondary motion
12. CLASSIFICATION OF THE CHIP REMOVING METHODSCLASSIFICATION OF THE CHIP REMOVING METHODS
ACCORDING TO THE RELATIVE MOTIONACCORDING TO THE RELATIVE MOTION
14. CNC SYSTEM ELEMENTSCNC SYSTEM ELEMENTS
A typical CNC system consists of thA typical CNC system consists of thee
following six elementsfollowing six elements
• Part programPart program
• Program input deviceProgram input device
• Machine control unitMachine control unit
• Drive systemDrive system
• Machine toolMachine tool
• Feedback systemFeedback system
17. CNC MACHINE TOOLCNC MACHINE TOOL
Part drawing
&
Part Programming
Input Part Programming
By Tape / MDI / Computer
18. 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..
19. Features of CNC Machinery
• The tool or material moves.
• Tools can operate in 1-5 axes.
• Larger machines have a machine control
unit (MCU) which manages operations.
• Movement is controlled by a motors
(actuators).
• Feedback is provided by sensors
(transducers)
• Tool magazines are used to change tools
20. Tools
• Most are made from
high speed steel (HSS),
tungsten carbide or ceramics.
• Tools are designed to direct waste away
from the material.
• Some tools need coolant such as oil to
protect the tool and work.
21. Tool Paths, Cutting
and Plotting Motions
• Tool paths describes the route the cutting tool takes.
• Motion can be described as point to point, straight
cutting or contouring.
• Speeds are the rate at which the tool operates e.g. rpm.
• Feeds are the rate at which the cutting tool and work
piece move in relation to each other.
• Feeds and speeds are determined by cutting depth,
material and quality of finish needed. e.g. harder
materials need slower feeds and speeds.
• Rouging cuts remove larger amounts of material than
finishing cuts.
• Rapid traversing allows the tool or work piece to move
rapidly when no machining is taking place.
22. 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.
23. Programming Key Letters
• O - Program number (Used for program identification)
• N - Sequence number (Used for line identification)
• G - Preparatory function
• X - X axis designation
• Y - Y axis designation
• Z - Z axis designation
• R - Radius designation
• F – Feed rate designation
• S - Spindle speed designation
• H - Tool length offset designation
• D - Tool radius offset designation
• T - Tool Designation
• M - Miscellaneous function
24. Explanation of commonly used
G codes
• G00 – Preparatory code to control final position of the
tool and not concerned with the path that is followed in
arriving at the final destination.
• G01 – Tool is required to move in a straight line
connecting current position and final position. Used for
tool movement without any machining- point to point
control. (linear interpolation)
• G02 – Tool path followed is along an arc specified by I, J
and K codes.( circular interpolation)
25. Table of Important G codes
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
26. Table of Important 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
27. Optimum machine programming requires consideration of certain machine
operating parameters including:
• Positioning control
• Compensations
• Special machine features
Positioning control is the ability to program tool and machine slide movement
simultaneously along two or more axes. Positioning may be for point-to-point
movement or for contouring movement along a continuous path. Contouring
requires tool movement along multiple axes simultaneously. This movement is
referred to as “Interpolation” which is the process of calculating intermediate
values between specific points along a programmed path and outputting those
values as a precise motion. Interpolation may be linear having just a start and end
point along a straight line, or circular which requires an end point, a center and a
direction around the arc.
Program Command Parameters
28. CNC Programming Basics
• Each letter address relates to a specific machine
function. “G” and “M” letter addresses are two of the
most common. A “G” letter specifies certain machine
preparations such as inch or metric modes, or absolutes
versus incremental modes.
• A “M” letter specifies miscellaneous machine functions
and work like on/off switches for coolant flow, tool
changing, or spindle rotation. Other letter addresses are
used to direct a wide variety of other machine
commands.
29. • 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
CNC programming
30. 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 parameters
31. Rules for programmingRules for programming
Block Format
N135 G01 X1.0 Y1.0 Z0.125 F5
Sample Block
• 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 feed rate
• 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
32. Two computer-based systems which impact the use of CNC technology are
computer aided design and computer aided manufacturing.
A computer aided design, or CAD, system uses computers to graphically create
product designs and models. These designs can be reviewed, revised, and
refined for optimum end use and application. Once finalized, the CAD design is
then exported to a computer aided manufacturing, or CAM, system.
CAM systems assist in all phases of manufacturing a product, including process
planning, production planning, machining, scheduling, management and quality
control.
CAD/CAM
35. O0013
N0005 G53
N0010 T0404
N0020 G57 G00 X26.0 Z0.0 S500 M04
G57 To set the working zero point as saved
G00 Rapid movement (no cutting)
X26.0 X location (as a diameter; 13 form zero)
Z0.0 Z location
S500 Spindle speed is 500 rpm
M04 Rotate spindle counterclockwise
APT Program Interpretation
x
z
(0,0) +ve
+ve
36. O0013
N0005 G53
N0010 T0404
N0020 G57 G00 X26.00 Z0.0 S500 M04
N0030 G01 X-0.20 F100
G01 Linear interpolation (cutting)
X-0.20 Move only in x direction until
you pass
the center by 0.1 mm (facing)
F100 Set feed rate to 100 mm/min.
APT Program Interpretation
37. O0013
N0005 G53
N0010 T0404
N0020 G57 G00 X26.00 Z0.0 S500 M04
N0030 G01 X-0.20 F100
N0040 G00 Z2.0
G00 Move rapidly away from work piece (no
cutting)
Z2.0 the movement is 2 mm away from the
face.
APT Program Interpretation
38. O0013
N0005 G53
N0010 T0404
N0020 G57 G00 X26.00 Z0.0 S500 M04
N0030 G01 X-0.20 F100
N0040 G00 Z2.0
N0050 X50.0 Z50.0
Go to a safe location away from the
workpiece [x = 50 (25 from zero), z
= 50] to change the tool.
APT Program Interpretation
46. 4646
HardwareHardware Configuration of NCConfiguration of NC
MachineMachine
Machine Control Unit (MCU)
the brain of the NC machine.
The Data Processing Unit (DPU)
reads the part program.
The Control Loop Unit (CLU)
controls the machine tool operation.
48. 4848
Point-to-Point Tool MovementsPoint-to-Point Tool Movements
Point-to-point control systems cause the tool to move to a point on
the part and execute an operation at that point only. The tool is not in
continuous contact with the part while it is moving.
Drilling, reaming, punching, boring and tapping are examples of point-to-
point operations.
49. 4949
Continuous-Path Tool MovementsContinuous-Path Tool Movements
Continuous-path controllers cause the tool to maintain continuous contact
with the part as the tool cuts a contour shape. These operations include milling
along any lines at any angle, milling arcs and lathe turning.
50. 5050
Loop Systems for Controlling ToolLoop Systems for Controlling Tool
MovementMovement
Open Loop
System
Uses stepping motor to create movement. Motors rotate a fixed
amount for each pulse received from the MCU. The motor
sends a signal back indicating that the movement is
completed. No feedback to check how close the actual
machine movement comes to the exact movement
programmed.
51. 5151
Loop Systems for Controlling ToolLoop Systems for Controlling Tool
MovementMovement
Closed Loop System
AC, DC, and hydraulic servo-motors are used. The speed of
these motors are variable and controlled by the amount of
current or fluid. The motors are connect to the spindle and the
table. A position sensor continuously monitors the movement
and sends back a single to Comparator to make adjustments.
52. 5252
CNC Machine Axes of MotionCNC 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.
Right hand rule
CNC machines milling machines can
perform simultaneous linear motion along
the three axis and are called three-axes
machines.
Horizonta
l milling
machine
53. 5353
CNC Machine Axes of MotionCNC Machine Axes of Motion
Coordinate system for a Lathe
54. 5454
CNC Machine Axes of MotionCNC Machine Axes of Motion
More complex CNC machines have the capability of executing additional
rotary motions (4th
and 5th
axes).
55. 5555
CNC Machine Axes of MotionCNC Machine Axes of Motion
Five-axis
machine
configurations
56. MACHINING PLANMACHINING PLAN
* Determination of work pieces machining range
* Method of mounting workpieces on the machine
* Machining sequence in every cutting process
* Cutting tools and cutting conditions
57. X +
X -
Y +
Y -
Z +
Z -
DEFINING THE AXIS OF CNC MACHINING CENTREDEFINING THE AXIS OF CNC MACHINING CENTRE
X0.Y0.Z0
62. CODE FOR SHIFTING MACHINE REFERENCE POINTCODE FOR SHIFTING MACHINE REFERENCE POINT
TO WORK PIECE REFERENCE POINTTO WORK PIECE REFERENCE POINT
OROR ZERO OFFSETZERO OFFSET
G54,G55, G56,G57,G59,G60ZERO OFFSET are
CANCELLATION OF ZERO OFFSET IS G53
G54 X,Y,Z
Note:
The Values of X,Y,Z are
difference between machine reference point
to work piece reference point
EXAMPLE
64. Coordinate Values in Absolute / IncrementalCoordinate Values in Absolute / Incremental
Absolute Incremental
Y Y
X
X
20
40
20 20
30
3030
60
A
B
A
B
65. Circle
Part of Circle
Straight Line
Starting point
&
Ending point are same
Starting point
Ending point
Starting point Ending point
Ending point
Start point
or or
Commonly used GeometryCommonly used Geometry
Centre of
circle
Ending point
Starting point
or
or
I.J
X1.Y1
X1.Y1
I.J
G00 OR G01
X2,y2
68. 6868
Basic Concept of PartBasic Concept of Part
ProgrammingProgramming
Part programming contains geometric data about the part and motion
information to move the cutting tool with respect to the work piece.
Basically, the machine receives instructions as a sequence of blocks
containing commands to set machine parameters; speed, feed and
other relevant information.
A block is equivalent to a line of codes in a part program.
N135 G01 X1.0 Y1.0 Z0.125 T01 F5.0
Coordinates Special function
Block number
G-code Tool number
69. 6969
Basic Concept of PartBasic Concept of Part
ProgrammingProgramming
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
70. 7070
Basic Concept of PartBasic Concept of Part
ProgrammingProgrammingMiscellaneous 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.
71. Mechanical EngineeringMechanical Engineering
DepartmentDepartment 7171
CNC Machine Tool PositioningCNC Machine Tool Positioning
ModesModesWithin a given machine axes coordinate system, CNC can be
programmed to locate tool positions in the following modes; incremental,
absolute, or mixed.
75. 7575
Computer-Assisted PartComputer-Assisted Part
ProgrammingProgramming
• Identify the part geometry, cutter motions, speeds,Identify the part geometry, cutter motions, speeds,
feeds, and cutter parameter.feeds, and cutter parameter.
• Code the above information using ATP.Code the above information using ATP.
• Compile to produce the list of cutter movements andCompile to produce the list of cutter movements and
machine control information (Cutter Location datamachine control information (Cutter Location data
file, CL).file, CL).
• Use post-processor to generate machine controlUse post-processor to generate machine control
data for a particular machine. This is the same asdata for a particular machine. This is the same as
NC blocks.NC blocks.
Automatically Programmed Tools (ATP) language is the most comprehensive
and widely used program. The language is based on common words and easy
to use mathematical notations
85. CNC Machines-
Advantages/Disadvantages
Advantages:
• High Repeatability and Precision e.g. Aircraft parts
• Volume of production is very high
• Complex contours/surfaces need to be machined. E.g. Turbines
• Flexibility in job change, automatic tool settings, less scrap
• More safe, higher productivity, better quality
• Less paper work, faster prototype production, reduction in lead
times
Disadvantages:
• Costly setup, skilled operators
• Computers, programming knowledge required
• Maintenance is difficult
86. CNC Lathe
• Automated version of a manual lathe.
• Programmed to change tools
automatically.
• Used for turning and boring wood, metal
and plastic.
87. CNC Milling Machine
• Has 3 to 5 axes.
• Used for wood, metal and plastic.
• Used to make 3D prototypes, moulds,
cutting dies, printing plates and signs.
90. 20042004 9090
ADVANTAGES of CNCADVANTAGES of CNC
• ProductivityProductivity
Machine utilisation is increased becauseMachine utilisation is increased because
more time is spent cutting and less time ismore time is spent cutting and less time is
taken by positioning.taken by positioning.
Reduced setup time increases utilisationReduced setup time increases utilisation
too.too.
91. 20042004 9191
ADVANTAGES of CNCADVANTAGES of CNC
• QualityQuality
Parts are more accurate.Parts are more accurate.
Parts are more repeatable.Parts are more repeatable.
Less waste due to scrap.Less waste due to scrap.
92. 20042004 9292
ADVANTAGES of CNCADVANTAGES of CNC
• Reduced inventoryReduced inventory
Reduced setup time permits smallerReduced setup time permits smaller
economic batch quantities.economic batch quantities.
Lower lead time allows lower stock levels.Lower lead time allows lower stock levels.
Lower stock levels reduce interest chargesLower stock levels reduce interest charges
and working capital requirements.and working capital requirements.
93. 20042004 9393
ADVANTAGES of CNCADVANTAGES of CNC
• Machining Complex shapesMachining Complex shapes
Slide movements under computer control.Slide movements under computer control.
Computer controller can calculate steps.Computer controller can calculate steps.
First NC machine built 1951 at MIT forFirst NC machine built 1951 at MIT for
aircraft skin milling.aircraft skin milling.
94. 20042004 9494
ADVANTAGES of CNCADVANTAGES of CNC
• Management ControlManagement Control
CNC leads to CADCNC leads to CAD
Process planningProcess planning
Production planningProduction planning
95. 20042004 9595
DRAWBACKS of CNCDRAWBACKS of CNC
• High capital costHigh capital cost
Machine tools cost $30,000 - $1,500,000Machine tools cost $30,000 - $1,500,000
• Retraining and recruitment of staffRetraining and recruitment of staff
• New support facilitiesNew support facilities
• High maintenance requirementsHigh maintenance requirements
• Not cost-effective for low-level production onNot cost-effective for low-level production on
simple partssimple parts
• As geometric complexity or volume increasesAs geometric complexity or volume increases
CNC becomes more economicalCNC becomes more economical
• Maintenance personnel must have bothMaintenance personnel must have both
mechanical and electronics expertisemechanical and electronics expertise
96. 20042004 9696
CNC APPLICATIONSCNC APPLICATIONS
• MachiningMachining
2.5D / 3D2.5D / 3D
Turning ~ Lathes, Turning CentreTurning ~ Lathes, Turning Centre
Milling ~ Machining CentresMilling ~ Machining Centres
• FormingForming
2D2D
Plasma and Laser CuttingPlasma and Laser Cutting
Blanking, nibbling and punchingBlanking, nibbling and punching
3D3D
Rapid PrototypingRapid Prototyping
