prerequisites - fit staffwebstaff.fit.ac.cy/eng.os/unit1_1.pdf · mike lynch the cnc parametric...
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Advanced CAD/CAM Systems - MDME502
THE
CNC PARAMETRIC PROGRAMMING
TECHNIQUE
THE CNC PARAMETRIC PROGRAMMING TECHNIQUE
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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.
THE CNC PARAMETRIC PROGRAMMING TECHNIQUE
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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
THE CNC PARAMETRIC PROGRAMMING TECHNIQUE
CONTENTS
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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.
THE CNC PARAMETRIC PROGRAMMING TECHNIQUE
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.
THE CNC PARAMETRIC PROGRAMMING TECHNIQUE
1. INTRODUCTION
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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.
THE CNC PARAMETRIC PROGRAMMING TECHNIQUE
1. INTRODUCTION
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“ The best-kept secret of CNC”MIKE LYNCH
THE CNC PARAMETRIC PROGRAMMING TECHNIQUE
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.
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Where to apply PPT
Machining of families of parts
New machining cycles
Motion along complex curves
THE CNC PARAMETRIC PROGRAMMING TECHNIQUE
1. INTRODUCTION
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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
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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.
THE CNC PARAMETRIC PROGRAMMING TECHNIQUE
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.
THE CNC PARAMETRIC PROGRAMMING TECHNIQUE
3. DESCRIPTION OF PPT
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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.
THE CNC PARAMETRIC PROGRAMMING TECHNIQUE
3. DESCRIPTION OF PPT
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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
3. DESCRIPTION OF PPT
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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.
THE CNC PARAMETRIC PROGRAMMING TECHNIQUE
3. DESCRIPTION OF PPT
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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.
THE CNC PARAMETRIC PROGRAMMING TECHNIQUE
3. DESCRIPTION OF PPT
Heidenhain Control
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This approach eliminates theredundant codes in the partprogram and substantiallyreduces the size of theprogram and programmingtime.
THE CNC PARAMETRIC PROGRAMMING TECHNIQUE
3. DESCRIPTION OF PPT
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
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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
THE CNC PARAMETRIC PROGRAMMING TECHNIQUE
3. DESCRIPTION OF PPT
Heidenhain Control
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A trapezoid dimensioned with parameters
THE CNC PARAMETRIC PROGRAMMING TECHNIQUE
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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4. APPLICATIONS A. FAMILIES OF PARTS
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4. APPLICATIONS A. FAMILIES OF PARTS
Program List
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4. APPLICATIONS A. FAMILIES OF PARTS
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:
THE CNC PARAMETRIC PROGRAMMING TECHNIQUE
4. APPLICATIONS
a = b = 1
B. MOTION GENERATION FOR COMPLEX CURVES
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4. APPLICATIONS A. MOTION GENERATION FOR COMPLEX CURVESB. MOTION GENERATION FOR COMPLEX CURVES
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4. APPLICATIONS A. MOTION GENERATION FOR COMPLEX CURVESB. MOTION GENERATION FOR COMPLEX CURVES
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4. APPLICATIONS A. MOTION GENERATION FOR COMPLEX CURVESB. MOTION GENERATION FOR COMPLEX CURVES
a = 10b = 30
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4. APPLICATIONS A. MOTION GENERATION FOR COMPLEX CURVESB. MOTION GENERATION FOR COMPLEX CURVES
a = 20b = 40
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4. APPLICATIONS A. MOTION GENERATION FOR COMPLEX CURVESB. MOTION GENERATION FOR COMPLEX CURVES
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
B. MOTION GENERATION FOR COMPLEX CURVES
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4. APPLICATIONS A. MOTION GENERATION FOR COMPLEX CURVES
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
B. MOTION GENERATION FOR COMPLEX CURVES
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4. APPLICATIONS A. MOTION GENERATION FOR COMPLEX CURVESB. MOTION GENERATION FOR COMPLEX CURVES
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4. APPLICATIONS A. MOTION GENERATION FOR COMPLEX CURVESB. MOTION GENERATION FOR COMPLEX CURVES
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4. APPLICATIONS A. MOTION GENERATION FOR COMPLEX CURVES
R = 100r = 50d = 25
B. MOTION GENERATION FOR COMPLEX CURVES
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4. APPLICATIONS A. MOTION GENERATION FOR COMPLEX CURVES
R = 50r = 25d = 12
B. MOTION GENERATION FOR COMPLEX CURVES
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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.
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4. APPLICATIONS C. NEW MACHINING CYCLES
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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4. APPLICATIONS C. NEW MACHINING CYCLES
The usually existing machining cycles
Rectangular pocket
Array of holes
Circular pocket
Linear slot
Circular slots
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4. APPLICATIONS
CNC machining of axisymmetric molds
Generation of an axisymmetric cavity
C. NEW MACHINING CYCLES
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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
C. NEW MACHINING CYCLES
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4. APPLICATIONS
Roughing
C. NEW MACHINING CYCLES
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4. APPLICATIONS A. MOTION GENERATION FOR COMPLEX CURVESB. MOTION GENERATION FOR COMPLEX CURVES
Finishing
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4. APPLICATIONS
Longitudinal-section view Cross-section view
C. NEW MACHINING CYCLES
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4. APPLICATIONS C. NEW MACHINING CYCLES
Spherical pocket
Torus
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4. APPLICATIONS C. NEW MACHINING CYCLES
Spherical pocket
D, R: variables to be expressed as parameters
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4. APPLICATIONS C. NEW MACHINING CYCLES
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4. APPLICATIONS C. NEW MACHINING CYCLES
Roughing – step angle 50
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4. APPLICATIONS C. NEW MACHINING CYCLES
Finishing– step angle 10
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4. APPLICATIONS C. NEW MACHINING CYCLES
Torus
D, R, r: variables to be expressed as parameters
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4. APPLICATIONS C. NEW MACHINING CYCLES
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4. APPLICATIONS C. NEW MACHINING CYCLES
Roughing – step angle 150
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4. APPLICATIONS C. NEW MACHINING CYCLES
Finishing– step angle 10
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4. APPLICATIONS C. NEW MACHINING CYCLES
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.
THE CNC PARAMETRIC PROGRAMMING TECHNIQUE
5. CONCLUSIONS