This document discusses group technology and computer-aided process planning. It defines group technology as a manufacturing technique that groups similar parts together to take advantage of their common design and production needs. It describes methods for forming part families and coding systems. It also discusses two types of computer-aided process planning systems: retrieval systems that store and retrieve standard process plans, and generative systems that create process plans using logical procedures similar to human planners.

1. GROUP TECHNOLOGY
FACULTY
MD SHADAB REZA
UNIT – 4
DEPARTMENT OF SCIENCE & TECHNOLOGY
GOVERNMENT POLYTECHNIC PURNEA
DEPARTMENT OF MECHANICAL ENGINEERING

2. GROUP TECHNOLOGY
 Group Technology is a manufacturing technique in
which similar parts are identified and grouped
together to take the advantage of their similarities
in design and production.
 In group technology parts with similar geometry,
manufacturing process, and/or functions are
manufactured in a single location using a small
number of machines or processes.
 It is based on the general principle that many
problems are similar, and that by grouping similar
problems, a single solution to a set of problems can
be found, which saves time, cost and effort.

3. • The Objectives of Group Technology are to
Reduce average lot size, Increase part variety,
Increase variety of materials, Achieve close
tolerance, Improve scheduling, Reduce tooling,
Increase equipment utilization etc.
 The benefits of group technology are :
• Reduction in setting up times cost and lot size.
• Reduction in material handling costs.
• Reduction in production planning cost.
• Output is improved due to improved resource
utilization.
• Improved product quality and less scrap.
• Smaller variety of tools, jigs and fixtures.
• Robots can be easily used for material handling.

4. PART FAMILIES
 A part family is a group of parts having similar
geometry and/or requiring a similar production
process or the processing steps used in their
manufacturing.
 Part families are the most important feature of
group technology.
 Similarities among parts allow them to be
classified into part families and In each part family,
the processing steps are similar.
 The group of machineries used to process an
individual part family is known as a machine cell
that specialize in production of certain part
families.

5.  Methods to form Part Families
• There are three methods that can be used to
form part families:
I. Manual visual inspection
II. Production flow analysis (PFA)
III.Part Classification and coding system
I. Manual visual inspection- It involves
arranging a set of parts into groups by
visually inspecting the physical
characteristics of the parts by using best
judgment to group parts into appropriate
part families.

6. II. Production Flow Analysis - PFA is a method
of identifying part families and associated
machine tool grouping by analyzing the route
sheets for parts produced in a given shop.
• It group together the parts that have similar
operation sequences and machine routings.
III. Parts Classification And Coding-
Identifying Similarities And Differences Among
Parts And classifying Them By Means Of A Coding
method.
• Large manufacturing system can be decomposed
into smaller subsystems of part families based on
similarities in part.

7. PARTS CLASSIFICATION AND CODING
 In parts classification and coding, similarities
among parts are identified, and these
similarities are related in a coding system.
 Coding: assignment of a symbol (or a set of
symbols) to represent information.
 Classification: a procedure that is used to
separate a large group of objects into separate
sub-groups.
 Parts classification and coding requires
examination and analysis of the design and/or
manufacturing attributes of each part.

8. Part classification as per Attributes
1. Part design attributes
2. Part manufacturing attributes
3. Both design and manufacturing attributes
 Part design attributes – Major dimensions,
Minor dimensions, Basic external shape, Basic
internal shape, Length/diameter ratio, Material
type, Part function , Tolerances , Surface finish
etc
 Part manufacturing attributes - Major
process , Minor process, Operation sequence,
Batch size, Annual production, Machine tools,
Cutting tools, Material type etc.

9.  Coding methods- Coding methods
are used to classify the parts into part families.
Coding refers to the process of assigning
symbols to the parts.
 The symbols represent design attributes of
parts or manufacturing features of part families.
 Three structures used in classification
and coding schemes are as follows;
I. Monocode or hierarchical code
II.Polycode or chain type
III.Hybrid or mixed code

10. MONOCODE OR HIERARCHICAL CODE
 In this type of code, the meaning of each code symbol
is dependent on the meaning of the previous code;
that is, each character amplifies the information of the
previous code.
 Such a coding system can be depicted using a tree
structure.
Consider all parts to be classified in terms of a
feature: rotational symmetry.
 1 == Non-rotational (prismatic) parts
 2 == Rotational parts.
Within these groups, we can further classify by
feature: presence of hole(s).
 0 == No holes
 1 == Has holes

12. POLYCODE OR CHAIN TYPE
 In this method the code symbols are independent
of each symbol in the sequence which is fixed and
not depend on the preceding digit
 Each digit in specific location of the code describes
a unique property of the work piece.
 It is easy to learn and useful in manufacturing
situations where the manufacturing process have
to be described.
 The length of a Polycode may become excessive
because of its unlimited combinational features.

14. HYBRID OR MIXED CODE
 It is the mixture of both monocode and
polycode systems.
 Mixed code having the advantages of both
systems.
 Most coding systems use this code structure,
A code created by this manner would be
relatively more compact than a pure
polycode while retaining the ability to easily
identify parts with specific characteristics.

16. PART CLASSIFICATION AND CODING
SYSTEMS
 Part classification and coding systems which
are widely used in manufacturing field for
GT are as follow:
1. OPTIZ system
2. MICLASS system
3. KK-3 system
3. CODE system
4. The DCLASS System

17. OPTIZ SYSTEM
 This system was developed by H. Opitz of the
University of Aachen in Germany.
 It the most frequently used, of the parts
classification and coding systems.
 It provides a basic framework for understanding
the classification and coding process .
 It can be applied to machined parts, non-
machined parts and purchased parts.
 It considers both design and manufacturing
information.

18. • The Opitz coding scheme uses the following digit
sequence:
Form Supplementary Secondary
code code code
12345 6789 ABCD
•features relevant to part geometry and part design
•part class (rotational/non-rotational), external
shape, internal shape, plane surface features and
machining, auxiliary features (off-axis holes, gear
teeth etc.).
• information relevant to manufacturing -
Dimensions, Material, Original shape of raw stock,
and Accuracy
•Production processes and production sequences

19. COMPUTER-AIDED PROCESS PLANNING (CAPP)
 Process planning is defined as an act of preparing
processing documents for the manufacturing of a
piece, part or an assembly, etc.
 If process planning is done by using a computer it is
called Computer-Aided Process Planning(CAPP).
 CAPP is a technique to produce a design that needed
for manufacturing and to give a complete information
to manufacture a product.
 This is widely used due to the quick response and
more flexibility in manufacturing plants.
 This used to set standard timings in operation and
helps in improving the process planning.

20.  There are two types of CAPP systems:
1. Retrieval type of CAPP system.
2. Generative CAPP system.
1. Retrieval type of CAPP system - A retrieval
CAPP system, also called a variant
CAPP system, is based on the principles of
group technology (GT) and parts classification
and coding.
• One of the commercially available retrieval
CAPP systems is MultiCapp.
• In this type of CAPP, a standard process plan
(route sheet) is stored in computer files for each
part code number.

21. • The standard route sheets are based on current
part routings in use in the factory or on an
ideal process plan that has been prepared for
each family.
• Before the system can be used for process
planning, a significant amount of information
must be compiled and entered into the CAPP
data files.
• This is called the "preparatory phase:‘ and It
consists of the following steps:
(1) selecting an appropriate classification and
coding scheme for the company.
(2) forming part families for the parts produced by
the company.

22. (3) preparing standard process plans for the part
families.
• steps (2) and (3) continue as new parts are
designed and added to the company's design data
base.
• After the preparatory phase has been completed,
the system is ready for use, For a new component for
which the process plan is to be determined. the first
step is to derive the GT code number for the part.
• With this code number, a search is made of the
part family file to determine if a standard route
sheet exists for the given part code.
• If the file contains a process plan for the part it is
retrieved from the database.

23. (hence the word "retrieval" for this CAPP system)
and displayed for the user.
• The standard process plan is examined to
determine whether any modifications are necessary.
• If the file does not contain a standard process plan
for the given code number, the user may search the
computer file for a similar or related code number
for which a standard route sheer does exist.
• Either by editing an existing process plan, or by
starting from scratch, the user prepares the route
sheet for the new part.
• This route sheet becomes the standard process
plan for the new part code number.

24. 2. Generative CAPP system - Generative CAPP
systems represent an alternative approach to
automated process planning.
• Instead of retrieving and editing an existing plan
stored in a computer data base, a generative system
creates the process plan based on logical
procedures similar to the procedures a human
planner would use.
• In a fully generative CAPP system, the process
sequence is planned without human assistance and
without a set of predefined standard plans.
•Designing a generative CAPP system is usually
considered as a part of the field of expert systems, a
branch of artificial intelligence.

25. • An expert system is a computer program that is
capable of solving complex problems that normally
require a human with years of education and
experience.
• There are several things required in a fully
generative process planning system.
• First, the technical knowledge of manufacturing
and the logic used by successful process planners
must be captured and coded into a computer
program.
• In an expert system applied to process planning,
the knowledge and logic of the human process
planners is integrated into a "knowledge base’’.

26. • The generative CAPP system then uses that
knowledge base to solve process planning
problems i.e., create route sheets.
• The second requirement is a computer-
compatible description of the part to be produced.
• This description contains all of the relevant data
and information needed to plan the process
sequence, Two possible ways of providing this
description are:
(l) the geometric model of the part that is
developed on a CAD system during product design
(2) a GT code number of the part that defines the
part features in significant detail.

27. • Third requirement is the capability to apply the
process knowledge and planning logic stored in the
knowledge base to a given part description.
• The CAPP system uses its knowledge base to solve
a specific problem i:e planning the process for a
new part.
• This problem-solving procedure is referred to as
the "inference engine’ in the terminology of expert
systems.
• By using its knowledge base and inference engine,
the CAPP system creates a new process plan for
each new part.