DEVELOPMENT OF A DECISION SUPPORT SYSTEM FOR

COMPUTER AIDED PROCESS PLANNING SYSTEM

Manish Kumar

Department of Production & Industrial Engineering, JNV University, Jodhpur - 342011, India

Keywords: Decision support system, computer aided process planning.

Abstract: A decision support system for Computer Aided Process Planning (CAPP) system has been designed,

developed and implemented. The need to introduce decision support system for CAPP system arises

specifically to solve the poorly structured stages in process planning such as determination of blank size,

setup planning, operations planning in each setup, selection of machine tools, calculation of machining time

etc. Decision Support System (DSS) is capable to support operations like turning, facing, tapering, arcing,

grooving, filleting, chamfering, knurling, threading etc. The proposed system is capable to generating

process plans for different types of rotational parts.

1 INTRODUCTION

In a manufacturing system manufacturing data are to

be transformed into work instructions by means of

process plans. Process planning is a function in a

manufacturing organization that establishes the

manufacturing processes and process parameters to

be used in order to convert a piece part from its

initial design to the final form which is

predetermined on a detailed engineering drawing

(Chang, 1990; Chang and Wysk, 1985). It has been

defined as: “The subsystem responsible for the

conversion of design data to work instructions”

(Link, 1976).

Process planning is a bridge between product

design and manufacturing. Since a large number of

factors and data need to be considered, process

planning may be a very complex and time-

consuming job. In general, several people need to

participate in developing a process plan since one

may not have the broad expertise required. On the

other hand, additional complication is introduced by

the fact that a process plan is a critical element in

making a part correctly and economically. The

activities of process planning include understanding

of the part specifications or product design data,

selection of raw material, selection of operations,

selection of machine tools, sequencing the

operations, sequencing the setups, determination of

process parameters, and generation of process

sheets.

The process of transforming component data,

process capabilities and decision rules into computer

readable format is still a major obstacle to overcome.

In the present paper, a decision support system has

been introduced in generation of process planning to

liquidate this obstacle.

2 THE PROPOSED CAPP

SYSTEM

The proposed CAPP system is designed to generate

process plans for axisymmetric components using a

decision support system. A DSS can be defined as

"an interactive system that provides the users with

easy access to decision models in order to support

semi-structured or unstructured decision making

tasks". In the present study, it performs functions

such as data interpretation, stock determination,

setup selection, sequencing of operations, selection

of process parameters etc.

Figure 1 shows a pictorial framework for

considering issues relevant to the design and

evaluation of DSS (Chitta et al., 1990). The three

types of interfaces (DSS and user, user and decision

making organization, and organization and

environment) are by no means independent.

390

Kumar M. (2007).

DEVELOPMENT OF A DECISION SUPPORT SYSTEM FOR COMPUTER AIDED PROCESS PLANNING SYSTEM.

In Proceedings of the Ninth International Conference on Enterprise Information Systems - AIDSS, pages 390-394

DOI: 10.5220/0002359003900394

 SciTePress

Figure 1: Nesting of Issues Relevant to Design and

Evaluation of DSS.

The DSS consists of rules, which are framed on

the logic based on technological considerations and

operations feasibility. The rules when fired succeed

in inferring some goals, which determine the

sequence of operations. The proposed DSS is

applicable for axisymmetric components and

operations like facing, turning, boring, taper turning,

threading etc. It performs the following tasks

(Grabowik and Knosals, 2003 and Younis and

Wahab, 1997):

1. Determination of blank size.

2. Setup planning.

3. Sequencing of operations in each setup.

4. Selection of nominal machining parameters

and calculation of power requirement.

5. Calculation of part processing time.

The architecture of the proposed CAPP system

is depicted in Figure 2.

Figure 2: The Proposed CAPP System Architecture.

Each step is controlled and executed in liaison

with DSS, which interacts with various knowledge

and databases. The DSS contains the knowledge of

process planning and technical know-how for

manufacturing axisymmetric components using

typical rule-based approach for knowledge

representation in the form of IF <antecedent> THEN

<consequence> decision tables.

For part data representation and feature

interpretation a feature-based modeling system

(FBMS) has been developed using interactive

representation of feature data in customized format

and syntax including geometric as well as technical

details of the part.

3 MODULES OF DECISION

SUPPORT SYSTEM

3.1 Determination of Blank Size

Ferrous material rods are available in the following

standard diameters (Mahadevan and Reddy, 1983).

Stock dia. (in mm) = {6, 8, 10, 12, 14, 16, 18, 20,

22, 25, 28, 32, 36, 40, 45, 50, 56, 63, 71, 80, 90, 100,

110, 125, 140, 160, 180, 200, 220, 240, 260, 280,

300, 320, 340, 360, 380, 400, 420, 440, 450, 480,

500, 530, 560, 600}.

A stock bar diameter equal to or just greater than

the maximum coordinate of the part is selected as

the raw stock for the part. Length of the required

stock is taken as 10 mm more than the maximum X

coordinate of the part in order to consider facing

operation on both ends of the part and for clamping

purpose. It is assumed that the part is to be machined

from a cylindrical stock bar. A semi-finished

component is not considered as the starting stock for

the generation of CAPP.

3.2 Setup Planning

Once the part description and feature representation

is complete, the next step is to determine a method

of holding the part. Various methods of holding

axisymmetric components include: chuck only,

between centers and using face plate and dog as

driver, chuck and center and using chuck as driver,

and special fixtures and collets (Jasthi et al., 1995).

The decision about holding method is based on a set

of rules using length-to-diameter ratio. Parts are

classified as either short or shaft on the basis of

Environment

USER

DSS

Organization

Part data representation and

feature inter

retation

Setu

lannin

Sequencing of operations in

each setu

Selection of nominal machining

parameters and calculation of

power requirements

Calculation of part processing

Decision

Support

System

Determination of blank size

Tool &

work

material

database

Machining

parameters

database

Generation of process plan

DEVELOPMENT OF A DECISION SUPPORT SYSTEM FOR COMPUTER AIDED PROCESS PLANNING SYSTEM

391

these rules. Only short parts that can be held using

chuck only holding method have been considered in

the present work.

In this module a demarcation line concept has

been used which helps primarily to identify the

clamping span of the part. Its secondary purpose is

to help grouping features under different setups such

that all features belonging to one setup can be

machined in one clamping of the part. A setup is

defined as a group of features that can be machined

during a single clamping of the part being processed

(Kovan, 1959). Reversing the part on the same

machine or shifting the part from one machine to

another can be treated as different setups. A setup is

planned such that maximum number of features can

be synchronously machined with minimum number

of setups (Huang et al., 1997). Majority of

axisymmetric components can be machined in two

setups. At this stage, a setup is considered as a basic

element of a process plan.

Tool approach direction is an important factor in

planning setups. The tool approach direction of a

feature is an unobstructed path that a tool can take to

access the feature (Chang, 1990). Features with the

same tool approach direction can be grouped into

one setup. In case of a single setup condition, all

features can be machined from a blank to finished

part stage in a single setting. However, if a part

needs to be machined in two setups, it is necessary

to establish the accessibility limits of various

features in each setup. To locate clamping span and

to associate various features to different setups, a DL

is to be identified which divides the length of the

part into clamping span and machining span as

shown in Figure 3. It is assumed that a plain

cylindrical surface is present in the clamping span.

The DL is determined for parts with external and

internal features based on the rules provided by

Hinduja and Huang, 1989.

The next task is to associate various features of the

part to different setups, so that all features belonging

to a setup can be machined in a single clamping of

the part.

3.2.1 Setup Planning for External Features

The DL can be used to group all the external

features of a part in two setups as per the following

rule (Figure 3):

• For i

external feature {

If (X

& X

<= DL)

Then associate the feature with setup 1

Else associate the feature with setup 2

}

Setup 1: Features 1, 2, 3

Setup 2: Features 4, 5, 6, 7

Figure 3: Setups for Part with external features.

3.2.2 Setup Planning for Internal Features

The DL is located on the basis of external features

only, and as such cannot be used for grouping

internal features in different setups. A separate

demarcation line, called Segregating Line (SL), is

thus required. The procedure to locate SL and use it

to group internal features in different setups depends

on the part type.

For parts with through internal features, a SL

can be located as follows:

• Find Y

min

coordinate among all internal

features

• For i

internal feature {

If (Y

or Y

= Y

min

)

Then SL = X

}

Once the SL is located for such parts, the

internal features can be grouped according to the

following rule (Figure 4):

• For i

internal feature {

If (X

& X

<= SL)

Then associate the feature with setup 1

Else associate the feature with setup 2

}

It is assumed that a hole of diameter less than

min

is drilled throughout the length of the part in the

first setup itself.

ICEIS 2007 - International Conference on Enterprise Information Systems

392

(a) Part with external as well as Internal features

Setup 1: Features 1, 2, 3

Setup 2: Features 4, 5, 6, 7, 8

(b) Part with only internal features

Setup 1: Features 2, 3, 4, 5

Setup 2: Feature 1

Figure 4: Parts with Internal Features.

3.3 Sequence of Operations in Each

Setup

Sequence of operations to be followed to generate

all features associated with one setup is based on the

general practice followed in the industry. A

sequential order of operations within one setup is

recommended as shown in Table 1

Table 1: Recommended Sequential Order of Operations.

S.No. Operations Associated feature

1 External facing EFAC

2 External turning ETRN

3 External tapering ETPR

4 External arcing EARC

5 External grooving EGRV

6 External filleting EFIL

7 External chamfering ECHF

8 External knurling EKNR

9 External threading ETHD

10 Boring IBOR

11 Internal tapering ITPR

12 Internal arcing IARC

13 Internal grooving IGRV

14 Internal filleting IFIL

15 Internal chamfering ICHF

16 Internal threading ITHD

If more than one similar type of features are to

be processed in a single setup, then machining is

done in decreasing order of Y

Coordinate for

external features and increasing order of Y

coordinate for internal features.

3.4 Selection of Nominal Machining

Parameters

Various job materials considered in this study

include: carbon steels (wrought with low or medium

carbon), alloy steels (wrought with low or medium

carbon), high strength steels (wrought), stainless

steels (wrought), and gray cast irons. Different

compositions and hardness grades of each of these

materials are possible. High-speed steel tools and

carbide tipped tools have been considered for

machining these job materials.

Recommended values of nominal machining

parameters (speed, feed) for various combinations of

job material and tool material, type of machining

(turning, forming, drilling etc.), and type of cut

(rough or finish) and depth of cut are extracted from

available standard data handbooks (ASM Metals

Handbook, 1997, and Metcut Machining data

handbook, 1980).

3.5 Calculation of Part Processing

Time

Machining time for each pass of an operation is

calculated on the basis of the selected machining

parameters. These times are cumulated for various

passes to obtain machining time for each feature,

and subsequently for each setup. Processing time of

each setup includes its machining time, as well as

allowances to be provided for tool changes and job

setup time. These allowances are assumed to be 50%

of the machining time. Thus, the processing time of

a job can be determined.

The material removal rate for each pass of an

operation is calculated as a product of the machining

parameters. Power required at the spindle is

calculated by multiplying this material removal rate

with unit power extracted from database. Assuming

80% efficiency of the mechanical power

transmission system, the power required at the motor

can be calculated for each pass of an operation. The

maximum power required at the motor can thus be

calculated for the whole setup of the job. This helps

in identifying the machine tool on which the job can

be processed.

In this manner, the final process plan of the part

is generated that outlines the operations, their

DEVELOPMENT OF A DECISION SUPPORT SYSTEM FOR COMPUTER AIDED PROCESS PLANNING SYSTEM

393

sequential machining order, process parameters,

processing time and maximum power requirements

on the machine tool.

4 CONCLUSION

This paper discusses development of a Decision

Support system required for a generative computer

aided process planning system for axisymmetric

components. A decision support system performs

tasks of input data interpretation, stock

determination, setup planning, sequencing of

operations in each setup, selection of process

parameters, determination of part processing time

and power requirements. Some of the tasks, such as

setup planning and establishing operations sequence,

are semi-structured in nature and can be performed

using rule-based approach of the decision support

system. The proposed system generates and reports

decision support system required for process plan

outlining machining sequence, machining

parameters, machining time, and power required.

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