9. part program

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Department of Mechatronics Engineering CHUNGNAM NATIONAL UNIVERSITY

©2008-2015 Young-Woo Park

NC Part ProgrammingNC Part Programming

Professor Young-Woo Park, Ph.D.Lecture 9

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Definition the procedure by which the sequence of processing steps to be performed on a CNC machine tool is planned & documented.

Ways manual programming tailoring to a particular controller

trigonometric computations are required.

computer-aided programming programming using English-like commands

not tailoring to a particular controller

CAD/CAM

IntroductionIntroduction

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Definition a program format for arranging information so to be suitable for input to a CNC controller

Comparison

English language CNC programming languageEnglish characters Program characters

English word Program word

English sentence Program block

Period End of block

Word Address ProgrammingWord Address Programming

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Program Language Terminology program character an alphanumeric character or punctuation mark

ex: N, G, ;

address a letter that describes the meaning of the numerical value following the address

ex: G 00

address number

X -3.75


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words are composed of two parts: an address followed by a number.

are used to describe such important information as machine motions & dimensions in programs.

ex: N0020 G90

block a complete line of information to a CNC machine tool

is composed of one word or an arrangement of words.

ex: N0020 G90 ;

program a sequence of blocks to manufacture a part

the MCU executes a program block by block.


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Syntax O: program number programs are stored in the MCU memory by program number.

O0001 to O9999

N: sequence number an optional tag that can be coded at the beginning of a block if needed

N0001 to N9999

ex: O0519 program number

N0010 G91G80G49G40G00T01

N0020 T02M01 … sequence number


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G: preparatory function G code is a command in the program specifying the mode in which a CNC machine moves along programming axes.

the # following the G address indicates the mode of movement.

two categories of G codes

Category Effectmodal the G code specification will remain effective for all subsequent blocks

unless replaced by another modal G code.

nonmodal the G code specification will only affect the block in which it appears.


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Examples

G code Mode SpecificationG00 modal Rapid positioning mode. The tool is to be moved to its

programmed XYZ location at maximum feedrate.G01 modal Linear interpolation mode. The tool is to be moved along

a straight-line path at the progammed feedrate.G21 modal Specifies metric (mm) mode for all units.

G28 nonmodal Return tool to reference point.G43 modal Specifies tool length offset (positive direction).G49 modal Cancels the tool length offset.

G98 modal Specifies a return to the initial point in a machining cycle that had been created by a modal G code.


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M: Miscellaneous machine functions Specify CNC machine functions not related to axes or dimensional movements.

Direct the controller to immediately execute the machine function indicated.

two groups of M codes

Category EffectA those executed with the start of axis movements in a block.

B those executed after the completion of axis movements in a block.


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Examples

M code Type SpecificationM00 B Cause a program stop.M02 B Cause a program end. An M02 code must be the last

command in a program. If used, do not use M30.M03 (M04) A Turns spindle on clockwise (counterclockwise).M05 B Turns spindle off. Usually used prior to a tool change &

at the end of a program. M06 B Stops the program & calls for an automatic tool change.

M07 (M08) A Turns the coolant tap oil (the external coolant) on. M08 A Turns the external coolant on.M30 B Directs the system to end program processing, reset

the memory unit. This code must be the last command in a program. If used, do not use M02.


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dimensional words are used to specify the movement of the programming axes.

X, Y, Z; linear axes

A, B, C: rotary axes

U, V, W: axes parallel to X, Y, Z axes

I, J, K: axes used as auxiliary of X, Y, Z axes

R, Q: axes used as auxiliary of Z axis

ex: N0030 G00 X.5Y.5

move tool at rapid speed/tool moves to X.5 Y.5.


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F: feedrate the rate at which the spindle moves along a programming axis

F10 = 0.001 ipm; F10. = 10 ipm

S: spindle function S codes control the speed at which the spindle rotates.

a numerical value up to 4 digits maximum

modal code replaced by a new S code or cancelled by a spindle off (M05)

spindle rotation should be specified prior to entering blocks containing cutting command.

T: tool function


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Three planes in the Cartesian coordinate system XY planeconventional standard

YZ plane

XZ plane

reference points MRZ a point on the actual machine

PRZ = part reference zeroa point on the actual part

lower left-hand top corner

CNC Milling FundamentalsCNC Milling Fundamentals

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three major phases of a CNC program program setupalways start with the program start flag (% sign)

line two: a program number

line three: the first that is actually numbered

increments of 1, 5 or 10

absolute units, inch programming, etc.

material removal: actual cutting

system shutdownspindle off, coolant off, end of program


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preparing to program develop an order of operations

before writing your program, plan it from start to finish considering all operations that must be performed.

do all the necessary math and complete a coordinate sheet.

choose your tooling and calculate the speeds and feeds.

decide on which tools are going to use & ensure the tools available that will perform the required tasks.

calculate the required speeds and feeds.


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safety rules for G00 If the Z value represents a negative move, the X- and Y-axes should be executed first.

If the Z value represents a positive move, the X- and Y-axes should be executed last.

If the basic rules are not followed, an accident can result.


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1. The computer interprets the instructions in the program into computer-usable form.

2. The computer performs the necessary geometry and trigonometry calculations required to generate the part surface.

3. The part-programmer specifies the part outline as the tool path. Since the tool path is at the periphery of the cutter that machining actually takes place, it must be offset by the radius of the cutter.

4. The cutter offset computations in contour part-programming are performed by the computer.

5. Part-programming languages are general-purpose languages. Since NC machine tool systems have different features and capabilities, the computer must take the general instructions and make them specific to a particular machine tool system. This function is called post processing


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6. After converting all instructions into a detailed set of machine tool motion commands, they are downloaded to the specific NC machine.

7. Graphic proofing techniques provide a visual representation of the cutting tool path.

8. This representation may be a simple two-dimensional plot of the cutter path or a dynamic display of tool motion using computer generated animation.

9. If necessary, part-programs are also verified on the NC station using substitute materials such as light metals, plastics, foams, wood, laminates, and other castable low cost materials used for NC proofing.


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Syntax: G01 Zn Fn

X1 Y1

X2 Y2

…

ExampleG01 Z-0.125 F5

X3 Y2

Linear Interpolation, G01Linear Interpolation, G01

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coordinate sheet

Position X Y

②③④⑤⑥⑦⑧


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coordinate sheet

Position X Y

② -0.35 4.25

③ 2.25 4.25

④ 2.25 1.25

⑤ 5.25 1.25

⑥ 5.25 -0.25

⑦ -0.25 -0.25

⑧ -0.25 4.25


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Direction

Circular Interpolation, G02, G03Circular Interpolation, G02, G03

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Plane Specification

Circular Interpolation, G02, G03Circular Interpolation, G02, G03

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I, J, K

the DISTANCE from the ARC START POINT to the CENTER POINT of the arc

G17 – Use I and J

G18 – Use I and K

G19 – Use J and K

Circular Interpolation : I, J, K MethodCircular Interpolation : I, J, K Method

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Syntax: G02 Xn Yn In Jn (XY plane) (G17 G90 G02)

XY planeabsolute coordinate

G03 Xn Yn In Jn (XY plane) (G17 G90 G03)


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Syntax: G02 Xn Yn In Jn (XY plane) (G17 G91 G02)

XY plane incremental coordinate

G03 Xn Yn In Jn (XY plane) (G17 G91 G03)


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Exercise


Ref: http://www.manufacturinget.org/2011/12/cnc-g-code-g02-and-g03/

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Exercise

G01Y1.0 F8.0;

G02 X1.2803 Y1.5303 I.750;


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Syntax: G02(G03) Xn Yn Rn (XY plane)

Circular Interpolation : R MethhodCircular Interpolation : R Methhod

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Exercise


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Exercise

G01Y1.0 F8.0;

G02 X1.2803 Y1.5303 R-.750;


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Linear & Circular InterpolationLinear & Circular Interpolation

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coordinate sheet

Linear & Circular InterpolationLinear & Circular Interpolation

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All of CNC MTs require some form(s) of compensation.

Examples of Compensation in Daily Life airplane pilot

for wind velocity & direction as a heading is set.

race car driver for weather & track conditions as a turn is negotiated.

bowler for spin of the bowling ball as the ball rolls down the valley.

marksman firing a rifle for the distance to the target.

CompensationCompensation

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Way of Compensation initial compensation fine tuning

example: marksman

adjust the sight on the rifle to allow for a distance.

fine tune to adjust for minor imperfections within the initial adjustment after the first firing.


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Offsets All forms of compensation work with offsets.

Offsets are storage locations into which numerical values can be placed in the CNC control.

Reasons for Offsets To specify each tool's length

At the time of setup, the setup person measures the length of each tool & inputs the length value into the corresponding offset.

To specify the radius of the cutting tool The cutter radius compensation allows the programmer to ignore the cutter size as the program is written. So, the setup person inputs the cutter size into its corresponding tool offset.


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Types of Compensation tool length compensation

cutter diameter compensation

dimensional tool (wear) offsets for turning center

tool nose radius compensation for turning center


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Definition a process in which the machine controller automatically moves the cutter so that the edge cuts the programmed movement, rather than the center of the cutter following the programmed movement.

Reasons for CDC Program coordinates are easier to calculate

Range of cutter sizes

Easy sizing

Roughing and finishing

Cutter Diameter CompensationCutter Diameter Compensation (CDC)(CDC)

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Comparison

Cutter Diameter CompensationCutter Diameter Compensation

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Understanding

With a little imagination, you can see all the possibilities for tweaking your part, or getting your part made with any size endmill.


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How to turn CDC on to zero your part & program a move away from the part in the X & Y direction equal to the tool radius.

Then move back to 0,0, and then continue cutting your profile.


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How to turn CDC “ON” A CDC G code must be followed by an X, Y linear motion code.

It signals the controller to initiate (ramp on) or cancel (ramp off) CDC.

G02 & G03 blocks must be programmed after the initial linear motion blocks.

The 1st X, Y linear tool movement following a CDC block must be equal to or greater than the radius of the cutter being used.


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How to turn CDC “ON” The MCU will apply compensation by offsetting the cutter in the direction perpendicular to the next X, Y axis tool movement.

The offset will be equal to the cutter radius previously entered at setup.


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How to turn CDC “ON” The 1st move for an inside cut should be to a location away from an inside corner.

This will prevent the cutter from notching the part.


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How to turn CDC “OFF” send the tool off in the X & Y direction a distance equal to the tool radius.

after reaching 0,0 turn off cutter compensation and ramp off to A.


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Syntax: G41 Xn Yn Dn

G41 directs the controller to offset (ramp on) the tool to the left side of upward tool motion.

Dn specifies the address in memory where the cutter radius offset value is stored.

n = register number


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Syntax: G42 Xn Yn Dn

G41 directs the controller to offset (ramp on) the tool to the right side of upward tool motion.

G40 cancels G41 or G42.


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G01 X1.0 Y-1.0 G41 X1.0 Y0.0 D1 Y1.0 X0.0 Y0.0 G01 G40 X1.0 Y-1.0


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Example


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Solution

G90 G00 X-11.0 Y6.0 S800 Rapid to position .②G01 Z-.5 M03 G41 X-10.5 D21 Ramp on to left of upward tool

motion on next move to .③ G01 X10.0 F10.0 Cut to ④ at feedrate 10.Y-6.0 Cut to .⑤X-10.0 Cut to .⑥Y6.5 Cut to .⑦G00 G40 Y7.0 Ramp off on the next move to

.⑧


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Definition a canned cycle is a single line of code which, in effect, says "Start cutting here, finish cutting there, remove the material with cuts that are so deep and use this cutting feed rate".

Hole operation

Modal command

These cycles are used when NC code is created manually.

Canned CycleCanned Cycle

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Five operations in a canned cycle Positioning of the X and Y axes

Rapid traverse to the R plane

Drilling, boring and tapping

Operation at the bottom of hole

Retract to the R plane


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Codes G80, G81, G82, G83, G84, G98, G99

G80: Cancel canned cycle

G81: Drill F, L, P, R, X, Y & Z

L; # of repeats

R; Reference plane

G82: Center Drill F, L, P, R, X, Y & Z

P; Dwell operation time in seconds


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G83: Peck drill F, L, Q, R, X, Y & X

Q; Peck Depth

If the depth of hole is 1”, Q.25 will peck 4 times.

G84: Tapping Same as G81 but be careful with F.

G98: Initial point return

G99: Reference plane return


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G83: Pack drill F, L, Q, R, X, Y & X

Q; Peck Depth

If the depth of hole is 1”, Q.25 will peck 4 times.

G84: Tapping Same as G81 but be careful with F.

G98: Initial point return

G99: Reference plane return


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G98 and G99


9. part program

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