Computer Aided Process Computer Aided Process Planning

8/4/2019 Computer Aided Process Computer Aided Process Planning

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Computer Aided ProcessComputer Aided ProcessPlanningPlanning

Dr. Pulak M. PandeyDr. Pulak M. Pandeyhttp://paniit.iitd.ac.in/~pmpandeyhttp://paniit.iitd.ac.in/~pmpandey


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Computer Aided Process Planning (CAPP)Computer Aided Process Planning (CAPP)

..Process planning with the aid of computer..Process planning with the aid of computer Process planning is concerned with the preparation of route sheeProcess planning is concerned with the preparation of route sheets thatts that

list the sequence of operations and work centers require to prodlist the sequence of operations and work centers require to produce theuce theproduct and its components.product and its components.

Manufacturing firms try to automate the task of process planningManufacturing firms try to automate the task of process planning usingusingCAPP systems due to many limitations of manual process planning.CAPP systems due to many limitations of manual process planning.These includes:These includes:

Tied to personal experienceTied to personal experience

and knowledge of planner of production facilities, equipment, thand knowledge of planner of production facilities, equipment, theireircapabilities, process and tooling. This results in inconsistentcapabilities, process and tooling. This results in inconsistent plans.plans.

Manual process planning is time consuming and slow.Manual process planning is time consuming and slow. Slow in responding to changes in product design and production.Slow in responding to changes in product design and production.

The experience of manufacturing of different engineers, who areThe experience of manufacturing of different engineers, who are likelylikelyto retire, can be made available in future by CAPP.to retire, can be made available in future by CAPP.

CAPP is usually considered to be part of CAM, however this resulCAPP is usually considered to be part of CAM, however this results CAMts CAMas stand alone system.as stand alone system. Synergy of CAM can be achieved by integrating it with CAD systemSynergy of CAM can be achieved by integrating it with CAD system andand

CAPP acts as a connection between the two.CAPP acts as a connection between the two.

Readymade CAPP systems are available today to prepare route sheReadymade CAPP systems are available today to prepare route sheets.ets.


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Computer Aided Design(CAD)

Computer Aided Manufacturing(CAM)

CAPP

Synergy results in when CAM is integrated with CAD

to form CAD/CAM systems than a stand alone CAD orCAM systems. In such a system CAPP becomes adirect connection between design and manufacturing


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Benefits derived from CAPPBenefits derived from CAPP

Process rationalization and standardizationProcess rationalization and standardization Increased productivity of process plannersIncreased productivity of process planners

Reduced lead time for process planningReduced lead time for process planning

Improved legibilityImproved legibility

Incorporation of other application programsIncorporation of other application programs


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PreprocessorCAD system

CAPP

Knowledge

Input Output

Planning rules

Postprocessor

Production planning andScheduling

CAPP ModelCAPP Model

CAPP Model


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CAPP System ArchitectureCAPP System Architecture

CAD System Preprocessor

MachiningKnowledge base

Machining selectionmodule

Constraint applicationmodule

Process plangeneration module

ConstraintCreation module

Manufacturingknowledge base


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Design approaches of CAPP systemsDesign approaches of CAPP systems

Retrieval CAPP systems/ Variant CAPPRetrieval CAPP systems/ Variant CAPP This has evolved out of the traditional manual process planningThis has evolved out of the traditional manual process planning

method. A process plan for a new part is created by identifyingmethod. A process plan for a new part is created by identifying andandretrieving an existing plan for a similar part, followed by theretrieving an existing plan for a similar part, followed by thenecessary modifications to adapt it to the new part.necessary modifications to adapt it to the new part.

It is based on GT principles, i.e., part classification and codiIt is based on GT principles, i.e., part classification and coding. Theseng. Thesecoding allow the CAPP system to select a baseline process plan fcoding allow the CAPP system to select a baseline process plan fororthe part family and accomplish about 90% of the planning work. Tthe part family and accomplish about 90% of the planning work. Theheplanner adds the remaining 10% of the planning by modifying theplanner adds the remaining 10% of the planning by modifying thebaseline plan.baseline plan.

If the code of the part does not match with the codes stored inIf the code of the part does not match with the codes stored in thethedatabase, a new process plan must be generated manually and thendatabase, a new process plan must be generated manually and thenentered into database to create a new baseline process plan forentered into database to create a new baseline process plan forfuture use.future use.

Advantages and limitations of Variant CAPPAdvantages and limitations of Variant CAPP

Investment in hardware and software is not much.Investment in hardware and software is not much.

The system offers a shorter development time and lower manpowerThe system offers a shorter development time and lower manpowerconsumption to develop process plan.consumption to develop process plan.

The system is very reliable and reasonable in real productionThe system is very reliable and reasonable in real productionenvironments for small and medium size companies.environments for small and medium size companies.

Quality of process plan depends on knowledge and background ofQuality of process plan depends on knowledge and background ofprocess planner.process planner.


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Generative CAPPGenerative CAPP

Process plans are generated by means of decision logics,Process plans are generated by means of decision logics,formulas, algorithms, and geometry based data that areformulas, algorithms, and geometry based data that arebuilt or fed as input to the system.built or fed as input to the system.

Format of inputFormat of input Text input (interactive)Text input (interactive)

Graphical input (from CAD models)Graphical input (from CAD models)

First key: to develop decision rules appropriate for theFirst key: to develop decision rules appropriate for the

part to be processed. These rules are specified usingpart to be processed. These rules are specified usingdecision trees, logical statements, such as ifdecision trees, logical statements, such as if--thenthen--else,else,or artificial intelligence approaches with object orientedor artificial intelligence approaches with object orientedprogramming.programming.

Second key: Finding out the data related to part to driveSecond key: Finding out the data related to part to drivethe planning. Simple forms of generative CAPP systemsthe planning. Simple forms of generative CAPP systemsmay be driven by GT codes.may be driven by GT codes.


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A pure generative system can produce a complete process planA pure generative system can produce a complete process planfrom part classification and other design data which does notfrom part classification and other design data which does not

require any further modification or manual interaction.require any further modification or manual interaction. In generating such plans, initial state of the part (stock) mustIn generating such plans, initial state of the part (stock) must

be defined in order to reach the final state i.e., finished partbe defined in order to reach the final state i.e., finished part..

Forward or backward planning can be done.Forward or backward planning can be done.

Forward and backward planning apparently appear to be similarForward and backward planning apparently appear to be similarbut they effect programming significantly. The requirement andbut they effect programming significantly. The requirement andthe results in of a setup in forward planning are the results anthe results in of a setup in forward planning are the results anddrequirements , respectively, of the set up in backward planning.requirements , respectively, of the set up in backward planning.

Forward planning suffers from conditioning problems; theForward planning suffers from conditioning problems; theresults of a setup affects the next set up.results of a setup affects the next set up. In backward planning, conditioning problems are eliminatedIn backward planning, conditioning problems are eliminated

because setups are selected to satisfy the initial requirementsbecause setups are selected to satisfy the initial requirementsonly.only.

The generative CAPP has all the advantages of variant CAPPThe generative CAPP has all the advantages of variant CAPPhowever it has an additional advantage that it is fully automatihowever it has an additional advantage that it is fully automaticcand a upand a up--toto--date process plan is generated at each time.date process plan is generated at each time.

It requires major revisions if a new equipment or processingIt requires major revisions if a new equipment or processingcapabilities became available.capabilities became available.

he develo ment of the s stem in the be innin is a difficult

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Computer Aided Process Computer Aided Process Planning