Computer Aided Process Planning Capp Computer Science Essay

Introduction

Procedure planning is common undertaking in distinct fabrication. It is performs the undertaking of finding the sequence of single fabrication operations needed to treat a given portion or merchandise. The resulting operation sequence is documented on a signifier typically referred to as a route sheet. The route sheet is a listing of the production operations and associated machine tools for a workpart or assembly. In traditional procedure planning, there arises a job of variableness among contrivers. In add-on to this, there are frequently troubles in the conventional procedure planning process.

New machine tools in the mill render old routings less than optimum. Machine breakdowns force store forces to utilize impermanent routings and these go the documented routings even after the machine is repaired. For these grounds and others, a important proportion of the entire Numberss of procedure programs used in fabrication are non optimum. Because of the jobs encountered with manual procedure planning, efforts have been made in recent old ages to capture the logic, judgement, and experiences required for this of import map and integrate them into computing machine plans.

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Based on the features of a given portion, the plan automatically generates the fabrication operation sequence. A computing machine aided procedure planning ( CAPP ) system offers the potency for cut downing the everyday clerical work of fabricating applied scientists. At the clip, it provides the chance to bring forth production routing which is rational, consistent, and possibly even optimum. ( Groover )

CAPP

Modern fabrication is characterized by low volume, high assortment production and close tolerance high quality merchandises.

Computer Integrated Manufacturing ( CIM ) is recognized as an effectual platform for increasing fabrication fight. Computer Aided Process Planning is an indispensable key for accomplishing CIM. The integrating of design, computing machine aided procedure planning ( CAPP ) and production planning and control ( PPC ) is going indispensable particularly in a concurrent technology environment where many merchandise life rhythm factors are of concern. An overview of the major development push in CAPP is presented along with some of the germinating tendencies and challenges such as rapid, generic, dynamic and/or distributed procedure planning. Related issued of quality and evolving criterions are besides discussed.

CAPP works at the interface between CAD and Cam. It takes Cad informations, converts it to production informations, and feeds the later to a production system. Fig shows a CAPP theoretical account based on this interface construct. The CAPP theoretical account utilizes the flow shown in the fig. to change over Cad informations into production informations.

After the CAD theoretical account is created, it is prepared for transportation into CAPP theoretical account. This preparation measure is performed by a preprocessor, and it could affect bring forthing an IGES or STEP file that the CAPP theoretical account can read. This measure is necessary because both the theoretical accounts are independent of each other. CAD informations besides needs to be prepared to obtain the proper merchandise definition as required by the CAPP theoretical account.

The CAPP theoretical account applies its cognition and regulations to the prepared CAD informations to bring forth its end product, the procedure program.

The CAPP theoretical account performs necessary station processing operations on its end product to bring forth end product that production and scheduling systems can read and use in their ain activities.

Fig. shows that the constituents of the CAPP theoretical account are independent of both the CAD and production system. Thus the theoretical account requires two transition stairss: one to change over Cad informations, and the other to change over the CAPP end product itself. ( Mastering CAD/CAM, Ibrahim Zeid )

CAD system

Pre-processor

Production planning and programming

Postprocessor

Planning regulations

Input signal

End product

CAPP

Cognition

CAPP theoretical account

CAPP Approachs:

( 1 ) Variant CAPP ( besides called as Retrieval-type attack )

Retrieval type CAPP systems usage parts categorization and cryptography and group engineering as a foundation. In this attack, the parts produced in the works are grouped into portion households, distinguished harmonizing to their fabrication features. For each portion household, a standard procedure program is established. The standard procedure program is stored in the computing machine files and the retrieved for new workpart which belong to that household. Some signifier of parts categorization and cryptography system is required to form the computing machine files and to allow efficient retrieval of the appropriate procedure program for a new workpart. For some new work portion, redacting of the bing procedure program may be required. This is done when the fabrication demands of the new portion are somewhat different from the criterion. The machine routing may be the same for the new portion, but the specific operations required at each machine may be different. The complete procedure program must document the operations every bit good as the sequence of machines through which the portion must be routed. Because of the changes that are made in the retrieved procedure program, these CAPP systems are sometimes besides called by the name `` variant systems. ''

Part household matrix file

Part household hunt

User enters portion codification figure.

Machine routing file

Standard machine routing retrieve

Operation sequence file

Standard operation retrieve/edit

Other application plans

Procedure program

Procedure program formatter

Figure will assist to explicate the process used in a retrieval procedure planning system. The user would originate the process by come ining the portion codification figure at a computing machine terminus. The CAPP plan so searches the portion household matrix file to find if a lucifer exists. If the file contains an indistinguishable codification figure, the standard machine routing and operation sequence are retrieved from the several computing machine files for show to the user. The standard procedure program is examined by the user to allow any necessary redaction of the program to do it compatible with the new portion design. After redacting, the procedure program formatter prepares the paper papers in the proper signifier.

If an exact lucifer can non be found between the codification Numberss in the computing machine file and the codification figure for the new portion, the user may seek the machine routing file and the operation sequence file for similar parts that could be used to develop the program for the new portion. Once the procedure program for a new portion codification figure has been entered, it becomes the standard procedure for future parts of the same categorization.

In figure the machine routing file is distinguished from the operation sequence file to stress that the machine routing may use to a scope of different portion households and codification Numberss. It would be easier to happen a lucifer in the machine routing file than in the operation sequence file. Some CAPP retrieval systems would utilize merely one such file which would be a combination of operation sequence file and machine routing file.

The procedure program formatter may utilize other application plans. These could include plans to calculate machining conditions, work criterions, and standard costs. Standard cost plans can be used to find entire merchandise costs for pricing intent.

A figure of variant type CAPP systems have been developed. These include MIPLAN, one of the MICLASS faculties, the CAPP system developed by Computer Aided Manufacturing-International, COMCAPP V by MDSI, and systems by single companies.

( 2 ) Generative procedure be aftering systems

Generative procedure planning involves the usage of the computing machine to make an single procedure program from abrasion, automatically and without human aid. The computing machine would use a set of algorithms to come on through the assorted proficient and logical determinations toward a concluding program for fabrication. Inputs to the system would include a comprehensive description of the workpart. This may affect the retrieval of portion codification figure to sum up the workpart informations, but it does non affect the retrieval of bing standard programs. Alternatively, the productive CAPP system synthesizes the design of the optimal procedure sequence, based on an analysis of portion geometry, stuff, and other factors which would act upon fabrication determinations.

In the ideal productive procedure planning bundle, any portion design could be presented to the system for creative activity of the optimum program. In pattern, current generative-type systems are far from cosmopolitan in their pertinence. They tend to fall short of genuinely productive capableness, and they are developed for a slightly limited scope of fabrication procedures.

Need for the integrating of procedure planning and programming.

Existing CAPP systems fail to integrate scheduling while bring forthing a procedure program. Scheduling is done individually after the procedure program has been generated, and hence, it is possible that procedure programs so generated may non be optimum from the scheduling point of position. If process programs are generated without consideration of occupation store position information, many jobs arise within the fabrication environment. Some of the troubles encountered are

as follows:

( Journal of Materials Processing Technology 138 ( 2003 ) 297-300

* Corresponding writer.

E-mail reference: mkumargupta @ rediffmail.com ( M. Kumar ) .

0924-0136/03/ $ - see front matter # 2003 Elsevier Science B.V. All rights reserved.

doi:10.1016/S0924-0136 ( 03 ) 00088-8 )

( I ) Procedure contrivers assume an ideal mill with limitless resources on the store floor. They plan for the most recommended alternate procedure. Therefore, desirable machines are selected repeatedly by assorted procedure contrivers. As programming follows the procedure planning, existent procedure programs when carried out consequence into waiting lines at assorted workstations and therefore these optimum procedure plans become impracticable.

( two ) Often procedure planning and scheduling have conflicting aims. Process planning emphasizes the technological demands of a undertaking, while scheduling involves the timing facets of it.

( three ) The throughput mark of orders in a workshop frequently suffers from breaks caused by constriction machines, non-availability of tools and forces, or dislocation of machines and equipment. A readily generated agenda becomes invalid and has to be regenerated.

( four ) In most of the instances for both procedure planning and programming, a individual standard optimisation technique is used for finding the best solution. However, the existent production environment is best represented by sing at the same time more than one standard.

( V ) The clip hold between be aftering stage and executing stage may do problem. Due to the dynamic nature of a production environment, it is really likely that when a design is ready to be manufactured, the restraints that were used in bring forthing the program have already changed greatly, therefore rendering, that plan sub-optimal or wholly invalid.

Many research workers have attempted parts to incorporate procedure be aftering with programming. Some of the work done in this way are by Torri et Al. [ 11 ] , Halevi and Weill [ 13 ] , Chryssolouris and Chan [ 6 ] , Sundaram and Fu [ 10 ] , Tonshoff et Al. [ 14 ] , Khoshnevis [ 15 ] , Khoshnevis and Chen [ 16 ] , Liao et Al. [ 5 ] , Usher and Fernandes [ 17 ] , Gu et Al. [ 18 ] and Yang et Al. [ 19 ] .

Probes have shown that 20-30 % of the sum store

burden in a given period has to be redirected to alternative

machines to achieve the coveted end product mark [ 5 ] . Merely a little

portion of the occupation store orders really comply with the production

program. This implies that 20-30 % of all procedure programs are

non valid and have to be altered when production starts.

There is therefore a major demand for an incorporate procedure planning

and scheduling system. A procedure planning system should

interface with a programming system for bring forthing more

realistic procedure programs and agendas. In making so, the

efficiency of the fabrication system as a whole is

expected to better. Without the integrating of procedure

planning and programming, a true CIM system, which strives to

incorporate the assorted stages of fabrication in a individual

comprehensive system will non efficaciously happen

[ 11,12 ] .

Many research workers have attempted parts to incorporate

procedure planning with programming. Some of the work

done in this way are by Torri et Al. [ 11 ] , Halevi and

Weill [ 13 ] , Chryssolouris and Chan [ 6 ] , Sundaram and Fu

[ 10 ] , Tonshoff et Al. [ 14 ] , Khoshnevis [ 15 ] , Khoshnevis and

Chen [ 16 ] , Liao et Al. [ 5 ] , Usher and Fernandes [ 17 ] , Gu et Al.

[ 18 ] and Yang et Al. [ 19 ] .

However really few of these attacks reported above consider machine capacity and

the current position of the store while bring forthing a procedure program. Scheduling is done individually after the procedure program is generated and, hence, it is possible that procedure programs so generated are either non executable or sub-optimal from the scheduling point of position. In some of the instances where alternate procedure programs are generated in concurrence with

satisfaction of scheduling standards, the solution hunt infinite additions. This increases the clip required to bring forth an optimum program and agenda and renders it impractical for existent

clip applications. This work tries to look into the above highlighted points.

3. Methodology

This paper suggests a method for incorporating scheduling with CAPP by sing the store floor conditions of the machines, i.e. , handiness, initial cost, cost of operation,

rhythm clip and breakdown status while delegating machines to assorted procedures to develop procedure program This helps in bring forthing procedure programs that are executable with

regard to the current handiness of the production installations. In this method existent clip position of store floor is important and dynamic feedback is required for scheduling. This method

may be called online procedure planning [ 7,20 ] .

4. On-line machine programming

This measure involves alteration of the procedure determination regulation to guarantee that the machine that is assigned to execute an operation is the best possible machine from among all the

options in the store, after the programming standards have been taken into history. The machines that are capable of accomplishing the same tolerance or surface finish demands

without go againsting the procedure planning standards are the options for a peculiar operation.

The programming standards considered here are the average flow clip and the figure of belated occupations. The integrating of CAPP and programming is expected to cut down both the mean

flow clip and the figure of belated occupations. This consequences in rapid response to demand and closer attachment to deadlines.

In this system a programming factor, m, is developed as:

m A?

X1C

X2CoX3TX4N

where C is the cost of the machine, Co the operating cost of machine per unit clip, T the mean rhythm clip for executing the operation on a machine, and N the figure of

alternate machines that can fix the occupation. X1-X4 are the of import evaluations given to respective variable on a graduated table of 1-10 ( 1-least of import and 10-most

of import ) . The machine with the highest value of scheduling factor is

selected for a peculiar operation. This factor is straight