CNC PROGRAMMING & MACHININGCNC PROGRAMMING & MACHINING

PREPARED BYPREPARED BY

At Ashoka Institution

At Ashoka Institution

DEFINITIONDEFINITION

• In In CNC CNC ((Computer Numerical ControlComputer Numerical Control),), the the instructions are stored as a program in a instructions 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 the The computer will also handle much of the control logic of the machine, making it control logic of the machine, making it more adaptable than earlier hard-wired more adaptable than earlier hard-wired controllers.controllers.

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

CNC SYSTEM CNC SYSTEM ELEMENTSELEMENTS

CNC SYSTEM ELEMENTSCNC SYSTEM ELEMENTS A typical CNC system consists of thA typical CNC system consists of the e

following six elements following six elements • Part program Part program • Program input device Program input device • Machine control unit Machine control unit • Drive system Drive system • Machine tool Machine tool • Feedback system Feedback system

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NC SYSTEM ELEMENTSNC SYSTEM ELEMENTS

OPERATIONAL FEATURES of OPERATIONAL FEATURES of CNC MACHINESCNC MACHINES

CNC MACHINE TOOLCNC MACHINE TOOL

Part drawing &

Part Programming

Input Part ProgrammingBy Tape / MDI / Computer

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..

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

automatically.

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.

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.

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.

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

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)

Table of Important G codesG00 Rapid TransverseG01 Linear InterpolationG02 Circular Interpolation, CWG03 Circular Interpolation, CCWG17 XY Plane,G18 XZ Plane,G19 YZ PlaneG20/G70 Inch unitsG21/G71 Metric UnitsG40 Cutter compensation cancelG41 Cutter compensation leftG42 Cutter compensation rightG43 Tool length compensation (plus)G43 Tool length compensation (plus)G44 Tool length compensation (minus)G49 Tool length compensation cancelG80 Cancel canned cyclesG81 Drilling cycleG82 Counter boring cycleG83 Deep hole drilling cycleG90 Absolute positioningG91 Incremental positioning

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

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

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.

• 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

• Miscellaneous codes – M codes For coolant control and other activities

CNC programming

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

Rules for programmingRules for programmingBlock 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 beindependent of all other commands (on separate lines)• The data within a block should follow the sequence shownin the above sample block

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HardwareHardware Configuration of NC Configuration 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.

Point to Point and Tool Paths

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Point-to-Point Tool MovementsPoint-to-Point Tool MovementsPoint-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.

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Continuous-Path Tool Continuous-Path Tool MovementsMovements

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.

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Loop Systems for Controlling Tool Loop Systems for Controlling Tool MovementMovementOpen Loop

SystemUses 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.

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Loop Systems for Controlling Tool Loop Systems for Controlling Tool MovementMovementClosed Loop SystemAC, 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.

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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.

Horizontal milling machine

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CNC Machine Axes of MotionCNC Machine Axes of Motion

Coordinate system for a Lathe

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CNC Machine Axes of MotionCNC Machine Axes of MotionMore complex CNC machines have the capability of executing additional rotary motions (4th and 5th axes).

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CNC Machine Axes of MotionCNC Machine Axes of Motion

Five-axis machine configurations

X +

X -

Y +

Y -

Z +

Z -

DEFINING THE AXIS OF CNC MACHINING CENTREDEFINING THE AXIS OF CNC MACHINING CENTRE

X0.Y0.Z0

X0,Z0

X+

X -Z+Z -

AXIS DEFINITION OF CNC LATHEAXIS DEFINITION OF CNC LATHE

Machine TableWork piece

Machine X

YZ

Coordinate SystemCoordinate SystemMachine Vs Work pieceMachine Vs Work piece

Reference PointX0,Y0,Z0

Work pieceReference Point

X0,Y0,Z0

MACHINESPINDLE

STANDARDTOOL BAR

LENGTH 200 mm

MACHINE TABLESLIP GAUGE(25 mm)

Z 25 mm

Z 200+25 mm

ZZ AXIS MACHINE REFERENCE POINT SETTING AXIS MACHINE REFERENCE POINT SETTING

X1

Z1

MEASURED VALUE

X0,Z0

MACHINE REFERENCE

POINT

SHIFTING MACHINE REFERENCE POINTSHIFTING MACHINE REFERENCE POINT TOTO

WORK PIECE REFERENCE POINT IN CNC LATHEWORK PIECE REFERENCE POINT IN CNC LATHE

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,G60 ZERO 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

R1

R2

End mill

Work Piece

Manual Part Programming Vs Computer ProgrammingManual Part Programming Vs Computer Programming

R1>R2

Coordinate Values in Absolute / IncrementalCoordinate Values in Absolute / Incremental

Absolute IncrementalY Y

XX

20

4020 20

30

3030

60

A

B

A

B

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

orI.J

X1.Y1

X1.Y1

I.J

G00 OR G01

X2,y2

CIRCULAR MOTION

COUNTERCLOCKWISE

DIRECTION

CIRCULAR MOTION

CLOCKWISE

DIRECTION

GO3

GO2

Start point

End point

Start point

End point

CIRCULAR MOTIONCIRCULAR MOTION

Z

X

Y

G02 G03G18

G19

G03

G02

G02G03

G17

Circular Interpolation With Respect to plane selectionCircular Interpolation With Respect to plane selection

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Basic Concept of Part Basic 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 functionBlock numberG-code Tool number

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Basic Concept of Part Basic 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 positioningG01 linear interpolation (generating a sloped or straight cut)G06 parabolic interpolation (produces a segment of a parabola)G17 XY plane selectionG20 circular interpolationG28 automatic return to reference pointG33 thread cutting

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Basic Concept of Part Basic Concept of Part ProgrammingProgrammingMiscellaneous commands (M code)

M00 program stopM03 start spindle rotation (cw)M06 tool changeM07 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.

Mechanical Engineering Mechanical Engineering DepartmentDepartment 5050

CNC Machine Tool Positioning CNC 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.

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Manual Part Manual Part Programming Example:Programming Example:

Mechanical Engineering Mechanical Engineering DepartmentDepartment 5252

Example of a part programExample of a part program

Loading toolN003 G00 X0.0 Y0.0 Z40.0 T01 M06

Tool change

Rapid motion

Positioning tool at P1

N004 G01 X75.0 Y0.0 Z-40.0 F350 M03 M08

Start spindleStart coolant

Linear interpolation

N001 G91 (incremental) N002 G71 (metric)

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Manual Part Programming Manual Part Programming Answer:Answer:N001 G91 N001 G91 N002 G71 N002 G71 N003 G00 X0.0 Y0.0 Z40.0 T0.1 M06 N003 G00 X0.0 Y0.0 Z40.0 T0.1 M06 N004 G01 X65.0 Y0.0 Z-40.0 F950 S717 M03 N004 G01 X65.0 Y0.0 Z-40.0 F950 S717 M03 N005 G01 X10.0 F350 M08 N005 G01 X10.0 F350 M08 N006 G01 X110.0 N006 G01 X110.0 N007 G01 Y70.0 N007 G01 Y70.0 N008 G01 X-40.86 N008 G01 X-40.86 N009 G02 X-28.28 Y0.0 I14.14 J5.0 N009 G02 X-28.28 Y0.0 I14.14 J5.0 N010 G01 X-40.86 N010 G01 X-40.86 N011 G01 Y-70.0 N011 G01 Y-70.0 N012 G01 X-75.0 Y0.0 Z40.0 F950 M30N012 G01 X-75.0 Y0.0 Z40.0 F950 M30

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Computer-Assisted Part Computer-Assisted Part ProgrammingProgramming

• Identify the part geometry, cutter motions, Identify the part geometry, cutter motions, speeds, feeds, and cutter parameter.speeds, feeds, and cutter parameter.

• Code the above information using ATP.Code the above information using ATP.• Compile to produce the list of cutter Compile to produce the list of cutter

movements and machine control information movements and machine control information (Cutter Location data file, CL).(Cutter Location data file, CL).

• Use post-processor to generate machine Use post-processor to generate machine control data for a particular machine. This is control data for a particular machine. This is the same as NC blocks.the same as 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

NomenclatuNomenclaturere

Tool Tool NoNo

RadiusRadius XX

LengtLengthh ZZ

ENDMILLENDMILL T01T01 20.0020.00 150.0150.000

DRILLDRILL T02T02 00 100.0100.000

BORING ToolBORING Tool T03T03 125.0125.000

Starting point Ending point

G41

Starting point

G42Required tool path

Actual tool path

CRC CUTTER RADIUS COMPENSATION CRC CUTTER RADIUS COMPENSATION G41& G42G41& G42

Tool Starting point

Arc ending point

I, J LEAD

X1,(Y1+LEAD)

X2,Y2

Arc starting point X1,Y1 Cutter compensation executed

Programmed path

Cutter moving path

Centre of arc

Radius Compensation ExecutionRadius Compensation Execution

G42

R1

R2

Point1

Point2

N20 G54 X (point1 value) Y(point1 value) Z500 N30 T0101 M06

N60 G02X-(R1value) Y-(R1value) I0 J-(R1value)

N90 G53 G00 G40 X(point1 value) Y(point1 value)

N55 G01 Z-500 F500

%N9001N10 G00 G90

N40 G01 G42 X (point2 value) Y(point2 value)N50 G91

N70 G03 X0 Y0 I0J-(R2value) N80 G02X-(R1value) Y+(R1value) I0 J+(R1value)

Greater than Cutter Radius

N35 M03

N95 M05

CIRCULAR INTERPOLATION PROGREMMECIRCULAR INTERPOLATION PROGREMME

R1

R2

Point1

Point2

N20 G54 X (point1 value) Y(point1 value) Z500 N30 T0101 M06

N90 G53 G00 G40 X(point1 value) Y(point1 value)

N55 G01 Z-500 F500

%N9001N10 G00 G90

N40 G01 G42 X (point2 value) Y(point2 value)

N50 G91

N70 G03 X0 Y0 I0J-(R2value)

N80 G02X-(R1value) Y+(R1value) I0 J+(R1value)

Greater than Cutter Radius

N65 E0205

N60 G02X-(R1value) Y-(R1value) I0 J-(R1value)

N85 G01 G90 Z500

CIRCULAR INTERPOLATION PROGREMMECIRCULAR INTERPOLATION PROGREMME

THREAD CUTTING PROGRAMMETHREAD CUTTING PROGRAMME

Greater than Cutter RadiusR1

R2

R1 Greater than Cutter Radius

R2 Circular InterpolationG90G00 X (Point1 value) Y (Point1 value) Z0D01

G41 G01 X (Point 2value) Y (Point2 value)

G91 G03 X-(R1value) Y+(R1value) I-(R1value) J 0 G03 X0 Y0 I0 J-(R2value) Z -(Pitch value)G03 X-(R1value) Y-(R1value) I0 J-(R1value)G90 G00 Z500G40

Threading tool

Point 1Point2

10 20

3060

M10, 4Nos 10mm depth Tapped as shown

PointsPoints XX YY

11 10.010.000

30.030.000

22 20.020.000

30.030.000

33 10.010.000

60.060.000

44 20.020.000

60.060.000

N40 G81 M03 X10.00 Y30.00 R200S500 F300 Z-300N50 G22 X9008

N60 G22 X9005

N30 T0101 M06

N30 T0102 M06 N40 G81 M03 X10.00 Y30.00 R200 S500 F300 Z-1500N50 G22 X9008N60 G22 X9005N40 G84 M03 X10.00 Y30.00 R200 S40 F100 Z-1500

N50 G22 X9008

N60 G22 X9005N10 X2000 Y3000N20 X1000 Y6000N30 X2000 Y6000

% N9008 Sub Programme

% N9005 Sub ProgrammeN10 G80 G00 X50000 Y50000

DRILLING PROGRAMMEDRILLING PROGRAMME

Centre drilling

Core drilling

M10 Tapping

%N9001N10 G54N20 G22 X9005

N70 G53 M05

#102 = 12

#103 = 90#110 = 1#104 = #103 + #102N10 #105= 270 *COS(#104)#106=270*SIN(#104)IF( #110 EQ 8) GOTO30IF (#110 EQ 15) GOTO30IF (#110 EQ 22) GOTO30G81 x#105 Y#106 Z-8 R10 F150

#110=#110+1#104 = #104 +#102GOTO10N20 G80

N30 IF(#110GT30) GOTO20

Programme using Mathematical FunctionProgramme using Mathematical Function

X0.Z0

X1.Z1

X4.Z4

G71 P10 Q60 U200 W200 D300 e100G00 X4+500 Z+200

N10 G00 X0 G42 G01 Z0

X1 Z1G03 X2 Z2 R400G01X3Z3N60 X4 Z4G40

ROUGH TURNING CYCLE AT CNC LATHEROUGH TURNING CYCLE AT CNC LATHE

X3.Z3X2.Z2

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Direct numerical controlDirect numerical control

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

CNC Lathe•Automated version of a manual

lathe.•Programmed to change tools

automatically.•Used for turning and boring wood,

metal and plastic.

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.

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ADVANTAGES of CNCADVANTAGES of CNC

• ProductivityProductivity Machine utilisation is increased Machine utilisation is increased

because more time is spent cutting because more time is spent cutting and less time is taken by positioning. and less time is taken by positioning.

Reduced setup time increases Reduced setup time increases utilisation too. utilisation too.

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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.

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ADVANTAGES of CNCADVANTAGES of CNC

• Reduced inventoryReduced inventory Reduced setup time permits smaller Reduced 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 Lower stock levels reduce interest

charges and working capital charges and working capital requirements. requirements.

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ADVANTAGES of CNCADVANTAGES of CNC

• Machining Complex shapesMachining Complex shapes Slide movements under computer Slide movements under computer

control. control. Computer controller can calculate Computer controller can calculate

steps. steps. First NC machine built 1951 at MIT First NC machine built 1951 at MIT

for aircraft skin milling. for aircraft skin milling.

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ADVANTAGES of CNCADVANTAGES of CNC

• Management ControlManagement Control CNC leads to CAD CNC leads to CAD Process planning Process planning Production planning Production planning

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DRAWBACKS of CNCDRAWBACKS of CNC• High capital cost High capital cost Machine tools cost $30,000 - $1,500,000 Machine tools cost $30,000 - $1,500,000 • Retraining and recruitment of staff Retraining and recruitment of staff • New support facilities New support facilities • High maintenance requirementsHigh maintenance requirements• Not cost-effective for low-level production on Not cost-effective for low-level production on

simple partssimple parts• As geometric complexity or volume increases As geometric complexity or volume increases

CNC becomes more economicalCNC becomes more economical• Maintenance personnel must have both Maintenance personnel must have both

mechanical and electronics expertise mechanical and electronics expertise

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INDUSTRIES MOST AFFECTED INDUSTRIES MOST AFFECTED by CNCby CNC

• Aerospace Aerospace • Machinery Machinery • Electrical Electrical • Fabrication Fabrication • Automotive Automotive • Instrumentation Instrumentation • Mold making Mold making