COMPUTER AIDED PART PROGRAMMING - APT

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Methods of NC Part Programming

1. Manual part programming2. Manual data input3. Computer-Aided part programming4. Part programming using CAD/CAM

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Manual Part Programming

• Variety of CNC machine tools and equal variety of controllers

• part program for a little complex parts– Extensive calculations – Error prone

• multi-axis machining – impossible to program

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Computer Aided Part Programming

• Use of part programming language: – use an “English-like” programming language – More than 100 part programming languages

developed in the last 50 years– describe

• geometry of the part• tool motions• machining parameters, and • all other auxiliary operations

• CAD/CAM Based Part Programming:– surface and solid models using CAD software– models contain the geometric data

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APT-Automatically Programmed Tool

• A compiler for simplifying NC Programming• Developed by MIT in 1955, refined in early 1960’s• Most widely used part programming language• Other languages developed as variants

– APT (Automatically Programmed Tools)– AUTOSPOT (Automatic System for Positioning Tools)– COMPACT II– ADAPT (Adaptation of APT)– EXAPT (Extended Subset of APT)– FAPT (Fanuc APT)

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Why?

• Use of symbolic language• Programming independent of machine tool• Reduced programming time• Reduced possibility of human error• Capability of simple changeover of machining

sequence from machine to machine• Only postprocessor required to include new

machine tool

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Role of part programmer

• Define the geometry of the workpiece in terms of basic geometric elements such as point, lines, circles, planes, etc.

• Specify the tool motion and/or operations to guide the too along the geometric elements defined earlier in order to machine it

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Role of computer• Input translation

– Covert the part program into computer usable format for further processing

• Arithmetic calculations– complex arithmetic and trigonometric calculations to

generate the part surface data• Cutter offset computation

– Generate the CL data after considering the tool geometry

• Postprocessing– Prepare the part program specific for a machine tool

on the basis of CL data, and machining instructions such as speed, feed, machine tool constraints, etc.

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Engineering Drawing

Develop process plan for the part

Write a part program using APT language

Process part program -generate CL data

Diagnostics

Correct the part program

Post process the CL Data for a specific machine tool

Part program

Generation of CL Data

Flow Diagram

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Right hand Cartesian coord. system

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APT language features• Major words - left of slash, special meaning• Minor word – right of slash• Symbols - geometric elements, numerical values

L2=LINE/(POINT/100,40),PERPTO,L1

• Subscripted Symbols• Numbers• Angles – decimal degrees• Arithmetic operators: + -- * / **• Library functions

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APT Statement Types

• Postprocessor (feed, speed, coolant, … etc.)• Auxiliary (tool, tolerance, part, … etc.)• Geometry statements• Motion statements

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Postprocessor Statements

COOLNT/ : coolant to be turned on or off:

COOLNT/ MIST

COOLNT/ FLOOD

COOLNT/ OFF

UNITS

UNITS/METRIC/INCH

RAPID

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Postprocessor Statements

FEDRAT/ : feedrate for moving the tool along the part surface

FEDRAT/ 75,MMPM

SPINDL/ : spindle rotation in revolutions per minute

SPINDL/ 850,RPM

SPINDL/ON

LOADTL/ : load a specific tool from an ATC tool changer

LOADTL/ 11

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Auxiliary StatementsMACHIN: specify machine tool and call the postprocessor

MACHIN/ MILL, 3

PARTNO: part program number, inserted at the start of theprogram.

PARTNO EXAMPLE6

PRINT: Display of tool geometry on screen (ON/OFF)

PRINT/ON

CLPRNT: indicates that a cutter location printout is desired.

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Auxiliary Statements

CUTTER: cutter diameter for offsetCUTTER/ 46

TOLERANCE : Nonlinear motion accomplished with straight-line segments

INTOL/ 0.015

OUTTOL/ 0.01

FINI: specifies the end of the program

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OUTTOL

Specified path

Specified path

INTOL

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Geometry statements

General format

<Symbol>=Geometry/Definition & Modifiers

Modifiers

INTOF PARLEL PERPTO TANTO

LARGE SMALL LEFT RIGHT XLARGE

XSMALL YLARGE YSMALL ZLARGE ZSMALL

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• Point POINT

• Line LINE

• Plane PLANE

• Circle CIRCLE

• Pattern (of parts) PATERN

• Cylinder CYLNDR

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Geometry statements: POINT

• Cartesian coordinatesPTA = POINT / 40,10,0

• Center of a circlePTG=POINT/CENTER,C4

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Geometry statements: POINT

• Polar coordinatePTI=POINT/XYPLAN,RTHETA,45,-30

• Intersection of two linesPTB=POINT/INTOF,LIN1, LIN2

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Geometry statements: POINT

• Intersection of a line and a circlePTC=POINT/XSMALL,INTOF,LIN1,C1

• Intersection of two circlesPTE=POINT/XSMALL,INTOF,C2,C3

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Point (POINT)

PTC = POINT/ YLARGE, INTOF, LIN3, C1PTC = POINT/ XLARGE, INTOF, LIN3, C1PTD = POINT/ YSMALL, INTOF, LIN3, C1PTD = POINT/ XSMALL, INTOF, LIN3, C1

x

PTC

PTD

LIN3 C

1

y

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Geometry statements: LINE

• Two points• One of the coordinated axes• Passing through a point and parallel to a line• Passing through a point and perpendicular to a

line• Passing through a point and at angle with a

line or axis• Passing through a point and tangent to a circle

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Line (LINE)

LIN1 = LINE/ P1, P2

P1

P2

y

x

LIN1

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Line (LINE)

LEFT or RIGHT modifiers indicates whetherthe line is to the left or right tangent point

L1A

C11

L1A = LINE/ PT51, LEFT, TANTO, C11

PT51

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Geometry statements: LINE

• LIN1 = LINE/P1,LEFT,TANTO,C1

• LIN2 = LINE/P1,RIGHT,TANTO,C1

• LIN3 = LINE/P2,RIGHT,TANTO,C1

• LIN4 = LINE/P2,LEFT,TANTO,C1

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Geometry statements: LINE

• LIN2 = LINE/P1,PARLEL,LIN1• LIN3 = LINE/P2,PERPTO,LIN1

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Line (LINE)

L8=LINE/RIGHT,TANTO,C3,LEFT,TANTO,C4

C3

L6

L9

C4

L8

L7

Right

Left

Left

Right

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Geometry statements: CIRCLE

C1 = CIRCLE/ 70, 60, 5, 40.3

C1 = CIRCLE/ CENTER, PT3, RADIUS, 4.3

PT3(70,60,5)

C1y

x

40.3

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Geometry statements: CIRCLE

C3 = CIRCLE/ CENTER, PT6, TANTO, LN4

C7 = CIRCLE/ CENTER, PT8, PT5

C3

Y

X

LN4

PT6C7

PT8

PT5

Y

X

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Geometry statements: PLANE

• PLAN1 = PLANE/P1,P2,P3• PLAN2 = PLANE/P4,PARLEL,PLAN1• PLAN2 = PLANE/PARLEL,PLAN1,ZLARGE,4.5

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Motion Statements - PTP

Rapid from current position to a specified locationFROM/ <point location>: starting point for the tool, with

the end of the tool at that point.

GOTO/ <point location>: rapid, straight- line move to thepoint specified in absolute mode.

GODLTA/ <coordinate increments>: move incrementaldistance from the current position.

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Z

X

Y

Motion Statements - Continuous

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Continuous Path Motion Commands

GOLFT/ : Move left along the drive surface

GORGT/ : Move right along the drive surface

GOFWD/ : Move forward from a tangent position

GOBACK/ : Move backward from a tangent position

GOUP/ : Move up along the drive surface

GODOWN/ : Move down along the drive surface

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Exercise

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PARTNO EXAMPLE5$$POSTPROCESSOR STATEMENTSCLPRNTMACHIN/MILL,3INTOL/0OUTTOL/0.01PRINT/ON$$ GEOMETRY STATEMENTSSP=POINT/0,0,10P0=POINT/-70,-140ZSURF/-10$$ ALL GEOMTERY DEFINITIONS HAVE Z=-10

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$$ CIRCLE DEFINITIONS

C1=CIRCLE/0,0,30

C2=CIRCLE/-100,80,25

C3=CIRCLE/-100,-80,25

C4=CIRCLE/100,0,30

$$ LINE DEFINITIONS

L1=LINE/RIGHT,TANTO,C1,LEFT,TANTO,C2

L2=LINE/LEFT,TANTO,C1,RIGHT,TANTO,C3

L3=LINE/LEFT,TANTO,C2,LEFT,TANTO,C4

L4=LINE/RIGHT,TANTO,C3,RIGHT,TANTO,C4

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$$ TOOL PATH DEFINITION CUTTER/20 LOADTL/1 SPINDL/1200,RPM,CLWCOOLNT/ ON $$ MOTION STATEMENTSFROM/SP RAPID TLLFT GOTO/P0GODLTA/-20 AUTOPS GO/TO,L4FEDRAT/50

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$$ CONTINUOUS PATH MOTION STATEMENTSGOLFT/L4,TANTO,C3 GOFWD/C3,TANTO,L2 GOFWD/L2,TANTO,C1 GOFWD/C1,TANTO,L1 GOFWD/L1,TANTO,C2 GOFWD/C2,TANTO,L3GOFWD/L3,TANTO,C4GOFWD/C4,TANTO,L4GOFWD/L4,TANTO,C3

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GODLTA/20

GOTO/P0

COOLNT/OFF

SPINDL/OFF

RAPID

GOTO/SP

END $$ End of this program

FINI $$ End of APT processing

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CL File

$$ GEOMETRY STATEMENTSSP=POINT/0,0,10*SP .0000 .0000 10.0000

P0=POINT/-70,-140*P0 -70.0000 -140.0000 .0000

ZSURF/-10$$ ALL GEOMTERY DEFINITIONS HAVE Z=-10$$ CIRCLE DEFINITIONSC1=CIRCLE/0,0,30*C1 .0000 .0000 30.0000

C2=CIRCLE/-100,80,25*C2 -100.0000 80.0000 25.0000

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CL File

$$ LINE DEFINITIONSL1=LINE/RIGHT,TANTO,C1,LEFT,TANTO,C2*L1 .2288 .9735 .0000 30.0000

L2=LINE/LEFT,TANTO,C1,RIGHT,TANTO,C3*L2 -.2288 .9735 .0000 -30.0000

L3=LINE/LEFT,TANTO,C2,LEFT,TANTO,C4*L3 .3497 .9368 .0000 64.9739

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CL File

$$ CONTINUOUS PATH MOTION STATEMENTSGOLFT/L4,TANTO,C3*FEED -87.7591 -112.7897 -20.0000

GOFWD/C3,TANTO,L2 *CIR -100.0000 -80.0000 35.0000 CLW

-108.0074 -45.9283 -20.0000GOFWD/L2,TANTO,C1*FEED 4.5756 -19.4695 -20.0000

GOFWD/C1,TANTO,L1*CIR .0000 .0000 20.0000 CCLW

4.5756 19.4696 -20.0000

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Postprocessing - Part Prgram

N5 G20N10 T01 M06N15 S1200 M21N20 M03N25 M08N30 G00 X-70.00 Y-140.00 Z.00N35 G01 Z-20.00 F50.N40 X-81.09 Y-110.30N45 X-87.76 Y-112.79N50 G02 X-100.00 Y-115.00 I35.N55 X-135.00 Y-80.00 I35.N60 X-108.01 Y-45.93 I35.