Computer Aided Process Planning

Once the design of a component is over, the planning phase of

manufacturing commences.

The first task in planning is the design of the processes (process

planning).

Cost of the part depends on the process planning.

Process planning is concerned with determining the sequence of

individual manufacturing operations needed to produce a given part

or product.

Process planning is an important stage of product development since

production tooling like jigs, fixtures, special tools etc. can be

designed only after the process is finalized.

The process planning activity can be divided into the following steps:

Selection of processes and tools

Selection of machine tools/Manufacturing equipment

Sequencing the operations

Grouping of operations

Selection of work piece holding devices

Selection of inspection instruments

Determination of production tolerances

Determination of the cutting times and non-machining times

Editing the process sheets.

Group Technology

Group Technology (GT) is a manufacturing philosophy in which similar

parts are identified and grouped together to take advantage of their

similarities in manufacturing and design.

An organizational principle that can be applied to all the departments of

an enterprise concerned with production.

GT is the realization that many problems are similar, and that by

grouping similar problems, a single solution can be found to a set of

problems thus saving time and effort .

All the components combined into a group are usually subjected to

common planning and machining. This enables in achieving high

rationalization effect particularly in case of single and small batch

production.

Need of GT

To make batch manufacturing more efficient and productive.

To achieve a higher level of integration between design and

manufacturing functions.

3

Similar parts are grouped into part families.

Each part family possesses similar design and/or manufacturing

characteristics.

Processing of each member in a part family would be similar

Results in manufacturing efficiencies

Reduced setup times

Lower in-process inventories

Better scheduling

Improved tool control

The use of standardized process plan

The production equipment is arranged into machine groups, or cells

in order to facilitate work flow and part handling.

The application of GT is known as part family manufacturing or

cellular manufacturing.

Group Technology

Group Technology

6

Part Families

A part family is a collection of parts which are similar based on designattributes (such as geometric shape and size) or manufacturing attributes(the sequence of processing steps required in their manufacture)

It possible for parts in the same family to be very similar in design yetradically different in the area of production requirements. The opposite mayalso be true.

The part family concept is central to design-retrieval systems and mostcomputer-aided process planning schemes.

The parts, which are similar in their design characteristics, are grouped in afamily referred to as a design part family.

The part, which are similar in their manufacturing characteristics, aregroped in a family referred to as a manufacturing part family.

The characteristics used in classifying parts are referred to as "attributes".

Part families- Group Technology

General methods for grouping parts into families:

1. Visual inspection.

2. Route sheet analysis.

3. Parts classification and coding system.

1. Visual inspection

Simplest method.

Least sophisticated method.

Least accurate method.

Especially for grouping parts by design attributes.

Classification of parts by physical parts or photographs.

Visual Inspection Method

Put parts into

groups based on

visual inspection

method.

2. Route sheet analysis (PFA)

The route sheets used to route the parts through the various

operations to be performed, are inspected.

This method sometimes refers to as the production flow analysis

(PFA) method.

Use the information contained on production route sheet and not

on part drawing.

PFA is carried out in FOUR steps.

(i). Data Collection.

(ii). Sortation of process routings

(iii). PFA chart (Part-Machine Incidence Matrix)

(iv). Cluster Analysis

Continue..(i) Data Collection (The Route Sheet)

Part Number,

Operation Sequence - determined the machine sequence.

(ii) Sortation of process routings

Parts are arranged according to

the similarities in process

routings which make part

families.

(iii) PFA chart (Part-Machine Incidence Matrix)

(iv) Cluster Analysis

3. Parts classification and coding system.

The most widely used method for grouping parts is the parts

classification and coding method.

This is most time consuming and most difficult method.

Parts similarities

1. Design Attributes

2. Manufacturing Attributes

Part- Design Attributes

Basic External Shape

Basic Internal Shape

Rotational or Rectangular Shape

Length to diameter ratio

Aspect Ratio

Material Type

Part Function

Major Dimensions

Minor Dimensions

Tolerances

Surface Finish

Part- Manufacturing Attributes

Major Processes

Minor Processes

Operation Sequences

Major Dimensions

Surface Finish

Machine tool

Production cycle time

Batch size

Annual Production

Fixtures required

Cutting tools

Part Classification and Coding

Design retrieval:

simple change in an existing part would take much less

time than designing a whole new part from scratch.

Automated process planning:

part code for a new part can be used to search for process

plan for existing part with identical or similar codes.

Machine cell design:

part codes can be used to design machine cell capable of

producing all parts from a part family.

Part Classification and Coding

Parts classification and coding is a method in which the

various design and/or manufacturing attributes of a part

are identified, listed and assigned a code number.

Parts classification and coding systems can be grouped into

three general types:

i Systems based on design attributes

ii Systems based on part manufacturing attributes

iii Systems based on both design and manufacturing

attributes

Ex: Machine tool manufacturing industry

Large part families can be grouped as :

i Heavy parts - beds, columns etc

ii Shafts, characterized by large L/D ratios

iii Spindles (long shafts, screw rods included)

iv Non-rounds (small prismatic parts)

v Gears, disc type parts

(whose L/D ratios are small)

Coding system structure

Begins with data input, usually through a classification and

coding system.

A classification and coding system is a means of describing

the attributes of parts and grouping them according to those

descriptions, as shown in Figure.

Cont..

A parts-coding scheme consists of symbols that identify the

design and/or manufacturing attributes.

The symbols in the code can be all numeric, all-alphabetic,

or a combination of both types.

There are three basic code structures used in group technology

applications:

i Hierarchical structure (Mono code)

ii Chain type structure (Poly code)

iii Hybrid structure which is a combination of the above two

(Hybrid code, Decision Tree coding)

1. Mono code

A hierarchical code is set up as a tree structure.

Each element, or digit, amplifies the information given in the

previous digit.

Difficult to construct.

Provide a very deep analysis of the items classified and can

pack an enormous amount of information into a coding

system.

The resulting code is very compact and yet contains a wealth

of information in a rather limited number of digits.

321X

32XX 32XX32XX

32XX

322X

323X

32323231 3233

32223221 3223

Hydr

aulic

Mechanical

Electrical

No thre

ad

UN

C th

readUNF thread

Pow

er

Rece

iving

Transmission

Hierarchical Structure Scheme (Mono Code)

Mono code

2. Poly code (Chain type structure)

Based on the total population of different attributes.

The interpretation of each character in a given digit position isindependent of any other digit.

Presents information not dependent on previous ones.

Tend to be relatively long.

Easier to accommodate change

One advantage of a poly code over a mono code is that parts witha specific characteristics can be readily identified.

This makes the poly codes structures attractive.

Poly code

3. Hybrid Codes or mixed codes

Most industrial coding system

uses a hybrid construction.

Combine the best features of

mono codes and poly codes.

To reduce the length of a strict

poly code, the first digit of

such System may split the

population into appropriate

subgroups, as in mono code

structure.

Optiz Classification System (German-1970)

Coding system uses the following digital sequence(13 digits)

12345 6789 ABCD - Basic code

12345: Form Code

Describe the primary design attributes of the parts like externalshapes, machined features.

6789: Supplementary Code

Manufacturing attributes

dimensions,

work material,

starting shape and

accuracy

ABCD: Secondary Code,

Identify the production operation type

Operation sequences

Basic Structure of the Optiz System

Example 1: A part coded 20801

2 - Parts has L/D ratio >= 3

0 - No shape element (external shape elements)

8 - Operating thread

0 - No surface machining

1 - Part is axial

Example

Determine the form code as per the Optiz part classification

and coding system

Length to Diameter ratio L/D=1.5 Digit 1=1

External Shape: Stepped on both ends with

screw threads on one end Digit 2=5

Internal Shape: Part contains a through hole Digit 3=1

Plane surface machining: none Digit 4=0

Auxiliary holes, gear teeth etc: none Digit 5=0

The form code in Optiz system is 15100

MICLASS Coding System-1974

Stands for Metal Institute Classification System

Developed by Netherlands Organization for

Applied Scientific Research.

MICLASS is an hybrid code system.

The MICLASS classification number range

from 12 to 30 digits.

First 12 digits Universal code, remaining 18

digits specific to the particular company (lot

size , piece time, cost data and operation

sequence).

The work attributes code in the first 12 digits of

the MICLASS system are:

42

MICLASS system was developed to help automate and standardize a

number of design, production and management functions:

Standardization of engineering drawings

Retrieval of drawing according to classification number

Standardization of process planning

Automated process planning

Selection of parts for processing on particular groups of machine tools

Machine tool investment analysis

DCLASS Coding System

KK-3 System(1998)