26938916 computer aided process planning capp

8/2/2019 26938916 Computer Aided Process Planning CAPP

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Computer Aided ProcessPlanning(CAPP)

By:Dhiman Johns

M.E.(PIE),Thapar University, Patiala


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To understand CAPP, We must briefly

discussabout ProcessPlanning

Products and their components are designed to perform certainspecific functions.

Every product has some design specifications which ensure itsfunctionality aspects.

The task of manufacturing is to produce components such that they

meet design specifications.


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Process planning acts as a bridge between design andmanufacturing by translating design specifications intomanufacturingprocessdetails.

Process planning answers the questions regarding requiredinformation and activities involved in transforming raw materialsinto a finished product. The process starts with the selection of rawmaterial and endswith thecompletion of part.


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The development of process plans involvesmainly a set of followingactivities:

Analysis of part requirements

Selection of raw work piece

Selection of manufacturing operations and their sequences

Selection of machine tools

Selection of tools, tool holding devices, work holding devices andinspection equipments

Selection of manufacturing condit ions i.e. cutting speed, feed anddepth of cut

Determination of manufacturing times


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Process Planning In Different Environments

} In tool-room type manufacturing makepart asper drawing issufficient

} In metal formingtypeoperations

The process planning requirements are embedded directly intothe die.

Processplanning is fairly trivial

} Job shop type manufacturing requires most detailed processplanning Design of tools, jigs, fixtures and manufacturing sequence are

dictated directly by theprocessplan.


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Two Methods of Process Planning are:

a) The manual experience based planning method

b) Computer Aided Process Planning


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The manual experience based planning method:

Themanual experience based processplanningis most widely used.

It is mainly based on a manufacturing engineer's experience andknowledge of production facilit ies, equipment, their capabilities,

processesand tooling.

The major problem with this approach is that it is time consumingand developed plansmay not beconsistent and optimum.


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The feasibility of developed process plan is dependant on manyfactors such as availability of machine tools, scheduling andmachineallocation etc.

Modern industry is currently lacking skilled labor force to producemachined partsaswasdone in thepast.

Computer Aided Process Planning is developed to overcome theseproblemsto some extent.


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Computer Aided Process Planning

As we have already discussed, the primary purpose of processplanning is to translate the design requirements into manufacturingprocessdetails.

Thus a system was developed in which design information isprocessed by the process planning system to generate

manufacturingprocessdetails.

CAPP is usually considered to be part of CAM, however this resultsCAM asastand alone system.

Synergy of CAM can be achieved by integrating it with CADsystem andCAPPactsasaconnection between the two.


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Computer AidedDesign

Computer AidedManufacturing

CAPP

Synergy results in when CAM is integrated with CAD to formCAD/CAM systems than a stand alone CAD or CAM systems. In

such a system CAPP becomes a direct connection between designand manufacturing.


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Readymade CAPP systems are available today to prepare routesheets.

CAPP integrates and optimizes system performance into the interorganizational flow.

For example, when one changes the design, it must be able to fallback on CAPP module to generate manufacturing process and costestimatesfor these design changes.

Similarly, in case of machine breakdown on the shop floor, CAPPmust generate the alternative actions so that most economicalsolutioncan beadopted in thegiven situation.


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When compared with manual experience basedprocess planning, CAPP offers followingadvantages: Systematic development of accurateand consistent processplans.

Reduction of cost and lead time of processplanning.

Reduced skill requirements and Increased productivity of processplanners.

Higher level application programs such as cost and manufacturing

lead time estimationand work standardscan be interfaced.


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Approaches to CAPP

Retrieval or Variant CAPP System

Generative CAPP System


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Retrieval or Variant Process Planning

It is based on the principles of Group Technology (GT) and PartsClassification & Coding.

In this a standard process plan is stored in the computer files foreach part code number.

These standard route sheets are based on current part routings oron an ideal process plan that has been prepared for each partfamily.

Development of the data base of these process plans requiressubstantial effort.


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New Part Design

Derive GT Code No. for

Part

Search Part Family File

For GT Code No.

Retrieve StandardProcess Plan

Edit existing or write anew plan

Process Plan Formatter

Process Plan (RouteSheet)

Part Family File

Standard Process PlanFile

Other Application

Program

Select coding system &Form Part Families

Prepare Standard

Process Plans for PartFamilies

GeneralGeneral procedureprocedure forfor usingusing oneone ofof thetheRetrievalRetrieval CAPPCAPP SystemsSystems

Preparatory Stage


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Before the system can be used for process planning a significant

amount of information must be compiled and entered into theCAPPdata files. Thisis referred to asthe PreparatoryStage.

PreparatoryStage consistsof followingsteps:

a) Selecting appropriate classification and coding scheme for company.

b) Formingpart families for the partsproduced by the company.c) Preparing standard processplansfor the part families.

Step b & c are repeated asnew partsare designed and added tothecompanysdesign database.


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After the preparatory phase is completed, the system is ready for

use.

Now assume a new component for which the process plan is to bedetermined, the first step is to derive the GT Code number for thepart.

With this code no., a search is made in the part family file todetermine if a standard route sheet exists for the given part code, ifa standard route sheet exists for the part, it is retrieved from thedatabase. Hence theword Retrieval for this CAPPSystem.


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The standard process plan is examined to determine whether anymodifications are necessary. Modifications to be made may be

minor or major. Theuser edits thestandard plan accordingly.

This ability to edit the standard plan is what gives the retrievalsystem itsalternativename: Variant CAPPSystem.

If the file does not contain a standard process plan for the givencode number, the user may search the computer file for a similar orrelated code number for which a standard route sheet does existand edit that processplan accordingto hisrequirements.


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Even if the user does not find any related file than he may startfrom scratch, thus the user prepares the route sheet for the new

part and this route sheet becomes the standard for the new partcodenumber.

The process planning session concludes with the Process PlanFormatter, which prints out thesheet in theproper format.

Theformatter may call other application programsinto use.

for example: to determine machining conditions for the various

machine tool operations in the sequence, to calculate standard times forthe operations, etc.


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Advantagesand limitations of Variant CAPP

Investment in hardware and software isnot much.

The system offers a shorter development time and lowermanpower consumption to develop processplan.

The system is very reliable and reasonable in real production

environmentsfor small and medium size companies. Quality of process plan depends on knowledge and background of

processplanner

Example of Retrieval CAPP system is MultiCAPP, from

OIR, the Organization for Industrial Research.


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Generative Process Planning

It isan alternativeapproach to automated processplanning.

Instead of retrieving and editing an existing plan contained in

a computer database, a generative system creates the process

plan by means of decision logics, formulas, algorithms andgeometry based data that are built or fed as input to the

system.


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Format of input may be:a) Text input (interactive)

b) Graphical input (from CADmodels)

A fully Generative CAPPSystem would produce a route sheet

without any human assistance and without a set ofpredefined standard plans.


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Ingredients Required In A FullyIngredients Required In A FullyGenerative CAPP SystemGenerative CAPP System

First ingredient is technical knowledge of manufacturing.

This CAPP system requires an expert system which can

convert the logic used by successful process planners into acomputer program by using certain codes. Such an expert

system generatesa knowledge base.

This knowledge base is used by Generative CAPP System to

solve processplanningproblems(i.e.- to create route sheets)


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Second Ingredient is a computer compatible description ofthe part to be produced. This description contains all of the

dataand information needed to plan theprocesssequence.

Two waysof providingthisdescription are:

a) Geometric model of the part that is developed on a CAD system

during product design.

b) A GT code number of the part that defines the part features insignificant detail.


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The third ingredient is the capability to apply

the process knowledge and planning logiccontained in the knowledge base to a givenpart description.

In brief we can say that, Generative CAPPsystem uses its knowledge base to solve aspecific problem, i.e.- planning the process.This system synthesizes a new process planfrom scratch for each new part that has beenpresented to it.


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Advantages and limitations of Generative

CAPP System

The generative CAPP has all the advantages of Variant CAPPhowever it has an additional advantage that it is fullyautomatic and a up-to-date process plan is generated at each

time.

It requires major revisions if a new equipment or processingcapabilit iesbecame available.


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Some FactsAbout CAPPTechnology:

Many CAPP systems have so far been developed andcommercialized. New systems adopt many advanced techniquesand approaches such as feature-based modelling, object orientedprogramming, utilizes advanced computing methods includingexpert system and art ificial intelligence.

The implementation of CAPP systems in industry lags behind therate of development of new systemsand introduction of new ideasin the field. Though tremendous effort has been made indeveloping CAPPsystems, the effectiveness of these systems is notfully satisfactory.


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In spite of the benefits promised by the various developed CAPPsystems, their adaptation by industry ispainfully slow.

Today, when companies use CAPP systems, it is mostly done inisolation from the product design as well as the productionplanningand control activities.

It is also becoming increasingly essential to feedback theinformation from process planning to assist the designer at anearly stage in assigning various design features not only fromfunctional point of view but also regarding manufacturability andeconomicpoint of view.


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References:1. Automation, Production Systems and Computer Integrated

ManufacturingBy Mikell P. Groover

2. Proceedings of the 7th Annual Paper Meet and 2nd

InternationalConference, The Institution of Engineers, Bangladesh (MechanicalEngineeringDivision) 25-27 October, 2001(Paper No. 10 pages81-92)


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THANK YOU!!

26938916 computer aided process planning capp

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