PREREQUISITES - FIT Staffwebstaff.fit.ac.cy/eng.os/UNIT1_1.pdf · MIKE LYNCH THE CNC PARAMETRIC...

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DR. SOTIRIS OMIROU - 1 -

Advanced CAD/CAM Systems - MDME502

THE

CNC PARAMETRIC PROGRAMMING

TECHNIQUE

THE CNC PARAMETRIC PROGRAMMING TECHNIQUE


PREREQUISITES

It is assumed that students have not any knowledge of parametric programming but they possess a firm understanding of G-code level manual programming.

In almost all applications, merging parametric programming techniques with manual programming is required.


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1. INTRODUCTION

2. BENEFITS OF PARAMETRIC PROGRAMMING TECHNIQUE (PPT)

3. DESCRIPTION OF THE TECHNIQUE

4. APPLICATIONS:

A. FAMILIES OF PARTS

B. MOTION GENERATION FOR COMPLEX CURVES

C. NEW MACHINING CYCLES

5. CONCLUSIONS


CONTENTS


Parametric programming constitutes an innovativeprogramming technique of G/M-code programminglanguage. This innovation is not well known, which isunusual because of the fact that it simplifies the CNCprocedures dramatically, lessens the user'sdependence on CAD/CAM and minimizes the cycletime.


1. INTRODUCTION

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As production quantities grow, every second ofprogram execution time becomes more critical. Animportant factor that minimizes the cycle time is howthe program is formatted. While CAM systems havecome a long way, it can be difficult, if not impossible,to cause some CAM systems to output CNC programsas efficiently as can be done with parametricprogramming technique.


1. INTRODUCTION


PPT is another one option for the CNC user

• Parametric program is never a replacement for other methods - it only enhances them.

• There could be a significant investment in time spent on parametric program development. The resulting benefits must be tangible and measurable, in order to be economically efficient.


1. INTRODUCTION

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“ The best-kept secret of CNC”MIKE LYNCH


1. INTRODUCTION

Keeping PPT a secret was not intentional.

The reason why most machine tool builders and control manufacturers do not heavily publicize this feature is that PPT was not originally developed for use by CNC users.

It was developed by CNC control manufacturers to allow machine tool builders to integrate higher level programming capabilities at G-code level.


Where to apply PPT

Machining of families of parts

New machining cycles

Motion along complex curves


1. INTRODUCTION

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DR. SOTIRIS OMIROU - 9 -THE CNC PARAMETRIC PROGRAMMING TECHNIQUE

2. BENEFITS OF PPTBENEFITS IN THE PROGRAMMING AREA

Drastic reduction in programming time

Reduced time for program checking

Easier workload transition

OVERALL BENEFITS

Increased productivity of the CNC machine

Decrease of overall production costs


What it is…

Parametric programming can be compared to any computer programming language like BASIC, C Language, and PASCAL.

However, this programming language resides right in the CNC control and all parametric expressions are used to represent the machine axis position (x, y, z), feedrate (F), and spindle speed (S) functions.

Computer-related features like variables, arithmetic, logic statements, and looping are available.


3. DESCRIPTION OF PPT

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What it is…

Parametric programming has been developed to overcome the need for discrete programs for each independent task that a machine performs.

Parametric programming is a technique that allows a CNC programmer to vary the parameters within one program, instead of writing an entirely new program each time the parameters are varied.




What it is…

For example, if a parametric program is stored in a machine'smemory to drill a bolt hole, the program can be used withany corresponding data file to drill any size hole in anylocation.

Parametric programming also includes structures for:

- conditional and unconditional program branching,- repetitive looping - mathematical equations.



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Versions of Parametric Programming (Most popular)

Heidenhain Parametric Programming

Custom Macro B (used by Fanuc controls)

User Task (from Okuma)

Q Routine (from Sodick)

Advanced Programming Language [APL] (from G& L)

Knowledge of a specific version can be adapted in any versionTHE CNC PARAMETRIC PROGRAMMING TECHNIQUE



The PPT in Heidenhain Control Systems

In the Heidenhain control, parameters are designated by theletter Q and a number between 0 and 99. Using Qparameters, an entire family of parts can be accommodatedby a single part program. In such a case, Q parameters areentered in the part program instead of fixed numericalvalues.



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For example, several parts mayrequire machining a pocketwith different sizes.A single parametric programcan be called up to machinethe specific feature. Prior tothe execution of theparametric program, thenumerical values for eachpocket are transferred to therespective parameters.



Heidenhain Control


This approach eliminates theredundant codes in the partprogram and substantiallyreduces the size of theprogram and programmingtime.



Heidenhain Control

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3. DESCRIPTION OF PPT Heidenhain Control

Function group Operation Code

Basic arithmetic assignadditionsubtractionmultiplicationdivisionsquare root

D00D01D02D03D04D05

Trigonometric functions

sinecosineroot sum of squaresangle

D06D07D08D13

If/then conditions, jumps

if equal jumpif not equal jumpif greater than jumpif less than jump

D09D10D11D12


Examples:

1. ADDITION: D01 Q1 P01 Q2 P02 5

2. SINE: D06 Q3 P01 Q4

3. IF LESS THAN JUMP: D12 P01 Q2 P02 360 P03 1



Heidenhain Control

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A trapezoid dimensioned with parameters


4. APPLICATIONS A. FAMILIES OF PARTS

Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8

X0 Y0 a b C Depth of cut

Feedrate Spindlespeed



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Program List



Start X = 25Start Y = 25Side a = 50Side b = 20Height = 40Depth = -4

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Serpentine curve The curve is given by the cartesian equation:


4. APPLICATIONS

a = b = 1



4. APPLICATIONS A. MOTION GENERATION FOR COMPLEX CURVESB. MOTION GENERATION FOR COMPLEX CURVES

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a = 10b = 30

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a = 20b = 40



a = 20b = 15

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4. APPLICATIONS A. MOTION GENERATION FOR COMPLEX CURVES

An epitrochoid is a plane curve generated by a point P attached to a circle of radius r rolling around the outside of a fixed circle of radius R.

EPITROCHOID




Epitrochoid curve has important industrial applications such as the trochoidal-shaped housing for rotary internal combustion engines and rotary piston pumps.

The machining of the inner surface of the housing can be accommodated by a parametric program adapted in this case to generate a smooth motion along the epitrochoidal profile

Epitrochoidal shaped housing


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R = 100r = 50d = 25




R = 50r = 25d = 12


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4. APPLICATIONS C. NEW MACHINING CYCLES

What is a machining cycle?

A powerful and common option available on most CNC machines is the ability to perform machining cycles. Machining cycles give the programmer the option to do some routine functions with a simpleG-code instead of writing many lines of information.



What is a machining cycle?

For example, if the programmer wanted to drill a hole 60 mm deep and clear the chip every 5mm. Without using a machining cycle for drilling , there would be more than 30 lines of program information per hole. With a machining cycle, the programmer need only specify the correct G-code for the operation to be performed, define the values for a series of variables, then call out coordinate points for the holes. The machine will drill the desired hole at every program point.

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The usually existing machining cycles

Rectangular pocket

Array of holes

Circular pocket

Linear slot

Circular slots


4. APPLICATIONS

CNC machining of axisymmetric molds

Generation of an axisymmetric cavity


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4. APPLICATIONS

CNC machining of axisymmetric molds

Tool path planning

A convenient tool centre path consists of a series of small arcs of prescribed length along the generatrix’s offset, followed by semicircular motion perpendicular to the axis of symmetry, followed by arcs of equal length along the mirror image of the generatrix’s offset, until the end of the generatrix’soffset is reached



4. APPLICATIONS

Roughing


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Finishing


4. APPLICATIONS

Longitudinal-section view Cross-section view


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Spherical pocket

Torus



Spherical pocket

D, R: variables to be expressed as parameters

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Roughing – step angle 50

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Finishing– step angle 10



Torus

D, R, r: variables to be expressed as parameters

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Roughing – step angle 150

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Finishing– step angle 10



Cross-section view

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• Parametric programming technique extends the feature generating capabilities of CNC machines

• Many applications based on parametric programming can save time, reduce effort, and minimize the potential for costly mistakes.

• These benefits, of course, result in a direct cost savings.In many cases, the cost to have parametric programming added to machine’s control (if it is not a standard feature) can be easily justified in light of the benefits it can provide.


5. CONCLUSIONS

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PREREQUISITES - FIT Staffwebstaff.fit.ac.cy/eng.os/UNIT1_1.pdf · MIKE LYNCH THE CNC PARAMETRIC...

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