GROUP TECHNOLOGY
Sunith H Guraddi
Mtech (CIM)
RVCE,Bangalore

Contents
• Introduction
• Part families
• Part classification and coding

Introduction
• Batch manufacturing is estimated to be the most common
form of production in the United States, constituting more
than 50% of total manufacturing activity.
• It is important to make batch manufacturing as efficient and
productive as possible. Also there has been a trend to
integrate the design and manufacturing functions in a firm.
• An approach directed at both of these objectives is Group
technology(GT)

GROUP TECHNOLOGY
• The term group technology was first used by Prof. Mitrofanov in early
1950s.
• Group technology is manufacturing philosophy in which similar parts are
identified and grouped together to take advantage of their similarities in
design and production. Similar parts are arranged into part families, where
each part family possesses similar design and / or manufacturing
characteristics.
.

For e.g:
• A plant producing 10000 different part numbers may be able
to group the vast majority of these parts into 30-40 distinct
families. It is reasonable to believe that the processing of each
member of a given family is similar and this should result in
manufacturing efficiencies.
The efficiencies are generally achieved by arranging the
production equipment into machine groups or cells to
facilitate work flow. Grouping the production equipment into
machine cells where each cell specializes in the production of
a part family is called cellular manufacturing

Objectives of Group technology
• Reduce MLT
• Reduce WIP
• Improve scheduling
• Reduce tooling
• Increase equipment utilization

Group technology is most appropriate under the
following conditions:
• The plant currently uses traditional batch production
and a process type layout.
• The parts can be grouped into part families.

There are two major tasks that a company must undertake
when it implements group technology. These two tasks
represent significant obstacles to the application of GT
1. Identifying the part families:
If the plant makes 10000 different parts reviewing all of the
part drawings and grouping the parts into families is a
substantial task that consumes a significant amount of time.
2. Rearranging production machines into machine cells:
It is the time consuming and costly to plan and accomplish
this rearrangement and the machines are not producing
during the changeover.

Group technology offers substantial benefits
to companies they are
• GT promotes standardization of tooling, fixturing and
setups.
• Material handling is reduced because the distances within
a machine cell are much shorter than within the entire
factory.
• Process planning and production scheduling are simplified.
• Setup times are reduced, resulting in lower manufacturing
lead times.
• Work in process is reduced.
• Worker satisfaction usually improves when workers
collaborate in a GT cell.
• Higher quality work is accomplished using group
technology.

PART FAMILIES
• Part family is a collection of parts that are similar
either because of geometric shape and size or
because similar processing steps are required in their
manufacture.
• The parts within a family are different, but their
similarities are close enough to merit their inclusion
as members of the part family.

figures 1 and 2 show to different part families.
Fig 1. Two parts of identical shape and size but different
manufacturing requirements
(a) 1,00,000 pc/yr, material = 1015 CR steel,nickel plate
(b) 100 pc/yr, material = 18-8 stainless steel

Fig.2 A family of parts with similar manufacturing process
requirements but different design attributes.
All parts are machined from cylindrical stock by turning: some parts require
drilling and /or milling

• One of the important manufacturing advantages of grouping
work parts into families can be explained with reference to
figures 3 and 4 .
• figure 3 shows a process type plant layout for batch
production in a machine shop.
• The various machine tools are arranged by function.
• There is a lathe department, milling machine department,
drill press department and so on.
• To machine a given part , the work piece must be transported
between departments.
• This results in work piece to visit the same department in
several times.

Fig.3 Process type and plant layout

1. Significant amount of material handling
2. Work in process inventory
3. More machine setups
4. More lead time
5. High cost
PROCESS TYPE LAYOUT
Results in

• In the group technology layout machines are
arranged into cells.
• Each cell is organized to specialize in the production
of a particular part family.

Fig.4 Group technology layout

GROUP TECHNOLOGY LAYOUT
Results in:
1. Reduced material handling
2. Lower setup time
3. Less in process inventory
4. Shorter lead time
5. Low cost

PART FAMILY FORMATION
• The biggest single obstacle in changing over to GT from
conventional production shop is the problem of grouping the parts
into families. There are three general methods for solving this
problem.
1. Visual inspection
2. Parts classification and coding
3. Production flow analysis
• All the three methods are time consuming and involve the analyze
of much data by properly trained personal.

VISUAL INSPECTION
• This method is the least sophisticated and least expensive
method.
• It involves the classification of parts into families by looking at
either the physical parts or their photographs and arranging
them into groups having similar features.
• This method is generally considered to be the least accurate
of the three, one of the first major success stories of GT in the
United States made the change over using the visual
inspection.
• This method is fast and simple and is useful when the part mix
is not complex.

Fig.5 Visual inspection method

PARTS CLASSIFICATION AND CODING
• This method is the most time consuming of the three
methods.
• In parts classification and coding, similarities among parts are
identified and these similarities are related in a coding
system.

Reasons for using a coding scheme include
1. Design retrieval: A designer faced with the task of
developing a new part can use a design retrieval system to
determine if a similar part already exists. Simply changing an
existing part would take much less time than designing a
whole new part from scratch.
2. Automated process planning: The part code for a new part
can be used to search for process plans for existing parts
with identical or similar codes.
3. Machine cell design: The part codes can be used to design
machine cells capable of producing all members of a
particular part family

Two categories of part similarities can be distinguished
1. Design attributes
2. Manufacturing attributes
• Design attributes are concerned with part
characteristics such as geometry, size, and material.
• Manufacturing attributes are concerned with the
processing steps required to make a part.

Part design attributes
• Basic external shape
• Basic internal shape
• Rotational or rectangular shape
• Length–to–diameter ratio
(rotational parts)
• Aspect ratio (rectangular parts)
• Material type
• Part function
• Major dimensions
• Minor dimensions
• Tolerances
• Surface finish

Part manufacturing attributes
• Major processes
• Minor operations
• Operation sequence
• Major dimension
• Surface finish
• Machine tool
• Production cycle time
• Batch size
• Annual production
• Fixtures required
• Cutting tools used in manufacture

Parts classification and coding cont…
• To accomplish parts classification and coding requires
examination and analysis of the design and/or manufacturing
attributes of each part. The examination is sometimes done
by looking in tables.
• An alternative and more productive approach involves
interaction with a computerized classification and coding
system, in which the user responds to questions asked by the
computer.
• On the basis of the responses, the computer assigns the code
number to part. Whichever method is used, the classification
results in a code number that uniquely identifies the part’s
attributes.

Parts classification and coding cont…
• A number of classification and coding systems are available
and there are a number of commercially available coding
packages. However, none of the systems has been universally
adopted. One of the reasons for this is that a classification and
coding system should be customized for a given company or
industry. A system that is best for one company may not be
best for another company.

FEATURES OF PARTS CLASSIFICATION
AND CODING
Parts classification system fall into one of three categories
1. Systems based on part design attributes
2. System based on part manufacturing attributes
3. Systems based on both design and manufacturing attributes

In terms of the meaning of the symbols in the code, there are three
structures used in classification and coding schemes.
1. Hierarchical structure, or monocode
2. Chain type structure or polycode
3. Hybrid, or mixed
• Hierarchical structure also known as a monocode, in which the
interpretation of each successive symbol depends on the value of
the preceding symbols.
 In this type of code, the meaning of each character is dependent
on the meaning of the previous character.
 This type of code is particularly preferred in design departments for
part retrieval because this type of system is very effective for
capturing shape, material, and size information.

The following figure illustrates the structure of
a monocode:

• Chain type structure also known as polycode, in which the
interpretation of each symbol in the sequence is always the
same; it does not depend on the value of preceding symbols.
 The meaning of each character in a polycode is independent
of all other digits.
 Each digit is used to completely to classify some feature of the
item.
 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

• Mixed-mode structure which is a hybrid of the two previous coding
schemes.
• The mixed mode structure uses a combination of hierarchical and
chain type structures.
• It is the most common structure found in GT parts classification and
coding systems.
• Coding schemes that contain only design data require fewer digits,
perhaps 12 or fewer.
• Most modern classification and coding system include both design
and manufacturing data, and this usually requires 20 to 30 digits.
• This might seem like too many digits for a human reader to easily
comprehend, but most of the data processing of codes is
accomplished by computer.

Some general classification and coding systems developed.

Selection of classification and coding systems
Some of the important classification and coding system attributes include:
1. Flexibility for various applications such as part family formation, process planning,
costing, and purchasing.
2. Accuracy, to provide correct information on parts
3. Expandability, to accommodate information on more part attributes.
4. Ease of learning
5. Ease of retrieval
6. Reliability and availability of software
7. Suitability for specific applications

OPTIZ PARTS CLASSIFICATION AND CODING
SYSTEM
• This is the most common and widely used coding system .
• This system was developed by H.Optiz of the University of Aachen in Germany
• It is generally a 9 digit code with 5 forming the primary code while the last 4
are secondary code.
• It represents one of the pioneering efforts in GT and is probably the best
known, if not the most frequently used, of the parts classification and coding
systems.
• It is intended for machine parts.
• The Optiz coding scheme uses the following digit sequences.
12345 6789 ABCD

• The basic code consists of nine digits, which can be extended by adding
four more digits.
• The first nine are intended to convey both design and manufacturing data.
• The interpretation of the first nine digits is defined in figure 5.
• The first five digits, 12345 are called the form code. This describes the
primary design attributes of the part. Such as external shape (For example,
rotational vs rectangular) and machined features (for example, holes,
threads, gear teeth, and so forth)
• The next four digits ,6789, constitute the supplementary code , which
indicates some of the attributes that would be useful in manufacturing.
(for example, dimensions, work material, starting shape, and accuracy.)
• The extra four digits ,ABCD, are referred to as secondary code and are
intended to identify the production operation type and sequence.
• The secondary code can be designed by the user firm to serve its own
particular needs.

The Opitz coding system consists of three groups of digits:

Fig.5 Basic structure of the Opitz system of parts classification and coding

Fig.6 Form code for rotational parts in the Opitz coding system

• let us examine the from code consisting of the first five
digits, defined generally in fig 6.
• The first digit identifies whether the part is rotational or
non rotational. It also describes the general shape and
proportions of the part.
• We limit our survey here to rotational parts possessing no
unusual features, those with first digit values of 0,1,or 2. for
this class of work parts, the coding of the first five digits is
defined in fig 6.
• Consider the following examples to determine the coding of
a given parts.

EXAMPLE 1
Figure 7

Given the rotational part design in figure 7. determine the form code in the Optiz
parts classification and coding system.
With reference to figure 6 ,the five digit code is developed as follows:
Length-to-diameter ratio, L/D = 1.5 digit 1 = 1
External shape: stepped on both ends with screw thread on 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
Hence the form code for the given part is 15100

EXAMPLE 2
Figure 8
Develop the opitz form code (first fiive digits) for component given in figure 8

Solution
1 2 1 3 2
Part class:
Rotational part,
L/D =2
External shape:
Stepped to one
end ,thread
Internal shape:
Stepped to one
end, no shape
element
Surface
machining:
External groove
Auxiliary holes:
Axial on pitch
circle diameter

EXAMPLE 3
Figure 9
Develop the opitz form code (first fiive digits) for component given in figure 9

Solution
1 3 0 3 3
Part class:
Rotational part,
L/D =1.52
External shape:
Stepped to one
end ,smooth ,
no shape
elements
Internal shape:
no hole
Surface
machining:
External groove
Auxiliary holes:
Radial , not on
pitch circle
diameter

MICLASS coding system
• The MICLASS ( Metal Institute Classification)was developed
by organisation for Applied Scientific Research in
Netherlands in 1960s and 1970s to develop a system for
both design and manufacture needs for OIR (Organisation
for Industrial Research).
• The various functions MICLASS was developed for are
 Standardise engineering drawings
 Retrieve drawings based on classification
 Standardise process routing
 Automate process planning
• MICLASS is an expandable hybrid code system of up to 30
digits, while the first 12 digits have been standardised.

• The system can be enlarged to thirty digits to cover any
classification attribute desired by the user
• Computer software is provided by OIR for deriving the
part code ,after the user goes through series of questions
and answers them interactively.
•The built in logic is in the form of decision tree

KK-3 Coding System
• This is a code developed by the Japan Society for the promotion of the Machine
industry(JSPMI) and was presented first in 1976

CODE MDSI System
• Manufacturing Data Systems, Incorporated(MDSI) has developed this
classification and coding system called CODE.
• It is an 8 digit hybrid code used primarily to classify and code mechanical
piece parts.
• The typical code structure is shown below.