GT

1. COMPUTER INTEGRATED
MANUFACTURING SYSTEMS (CIMS)
Kripa Shanker
Kripa Shanker Ph.D. (Cornell)
Professor
Industrial and Management Engineering Department
Indian Institute of Technology Kanpur
GROUP TECHNOLOGY
1

2. Kripa Shanker IIT Kanpur 2
GROUP TECHNOLOGY
Group Technology is a philosophy that implies the notion of
recognizing and exploiting similarities in the following
ways :
1. By performing the like activities together
2. By standardizing the similar tasks
3. By efficiently storing and retrieving information about recurring
problems
Design Attributes :
part configuration (round or prismatic), dimensional envelope
(length/diameter ratios), surface integrity (e.g. surface
roughness, dimensional tolerance), material type, raw material
state (e.g. casting, forging, bar stock), etc.
Manufacturing Attributes :
operations (such as turning, drilling, milling, etc.) and their
sequences, batch sizes, machine tools and cutting tools needed to
perform operations, processing times, etc.

3. Kripa Shanker IIT Kanpur 3
GROUP TECHNOLOGY
Group Technology allows batch production to gain economic advantages
similar to those of mass production while retaining the flexibility of job shop.
Job shop
Batch
Mass
Product Variety
Volume
per
Variety

4. Kripa Shanker IIT Kanpur 4
GROUP TECHNOLOGY
CLASSIFICATION APPROACHES
CLASSIFICATION APPROACHES
 Visual Inspection Method
 Coding Method
Design Attributes
•part configuration (round or prismatic),
•dimensional envelope (length/diameter ratios),
•surface integrity (e.g. surface roughness, dimensional tolerance),
•material type and raw material state (e.g. casting, forging, bar stock),
etc.
Manufacturing Attributes
•operations (such as turning, drilling, milling, etc.) and their
sequences,
•batch sizes,
•machine tools and cutting tools needed to perform operations,
processing times, etc.

5. Kripa Shanker IIT Kanpur 5
GROUP TECHNOLOGY
CLASSIFICATION APPROACHES
VISUAL INSPECTION METHOD
Creating part families by visually inspecting the physical characteristics of
the parts or their photographs
 The method is inexpensive, least sophisticated, and dependent on personal
preferences.
 Its utilities are limited to situations having smaller numbers of parts.
CODING METHODS
Process of assigning codes (symbols) to parts based on design attributes of parts,
manufacturing attributes of parts, or both. Parts are then categorized into part
families based on the codes.
Types of Codes :
 Monocode or hierarchical code
 Polycode
 Mixed-mode code

6. Kripa Shanker IIT Kanpur 6
GROUP TECHNOLOGY
CLASSIFICATION APPROACHES
MONOCODE or HIERARCHICAL CODE
Total part
population
Raw
materials
9
Purchased
Components
2
All
machined parts
1
Sheet
metal parts
0
......
Non rotational
machined parts
1
Rotational
machined parts
0
0 < L/D < 0.5
0
0.5 < L/D < 1
1
L/D > 10
9
L/W > 8
9
0 < L/W < 1
0
1 < L/W < 3
1
...... ......

7. Kripa Shanker IIT Kanpur 7
The structure of a monocode is like a tree in which each symbol magnifies the information
provided in the previous digit
The applicability of these codes in manufacturing is rather limited, as it is difficult to
capture information on manufacturing sequences in hierarchical manner.
The major advantage of hierarchical code is that it captures a great deal of information in
a relatively short code. The hierarchical nature of the code makes it useful for storage of
design related information such as part geometry, material, and sizes.
GROUP TECHNOLOGY
CLASSIFICATION APPROACHES
MONOCODE or HIERARCHICAL CODE
The disadvantage of this type of code is that it requires expertise to conceive such a
coding system.

8. Kripa Shanker IIT Kanpur 8
 In polycode, each code symbol is independent of each other. Each digit in a
specific location describes a unique property of the part.
 It is easy to learn and is useful in manufacturing situations in which the part
functions or manufacturing processes have to be described.
 The length of a polycode may become excessive because of its unlimited
combinational features.
POLYCODE
(Chain Code, Discrete Code, Fixed-Digit Code)
Material
Position
Material chemistry
Material shape
Machine element
orientation
Tolerance
Production quantity
Surface finish
1 2 3 4 5 6 7
GROUP TECHNOLOGY
CLASSIFICATION APPROACHES

9. Kripa Shanker IIT Kanpur 9
In polycode, as compared to monocode, the information storage capacity is
much less.
For example, suppose there are five symbols and each of the five contains
10 digits ( 0 to 9). Then,
Number of characteristics stored in monocode =
101 + 102 + 103 + 104 + 105 =1,11,110
Number of characteristics stored in polycode =
10 +10 +10 +10 +10 = 50
The information storage capacity of monocodes grows exponentially, compared
with the linear growth in the polycodes.
Coding Method - POLYCODE
(Chain Code, Discrete Code, Fixed-Digit Code)

10. Kripa Shanker IIT Kanpur 10
OPITZ Coding and Classification System
 Most widely used.
 Provides a basic framework for understanding the classification and coding process
 Can be applied to machined, non-machined parts (both formed and cast), and
purchased parts.
 Considers both design and manufacturing information.
 Developed at the Technical University of Aachen, Germany.
 Nonproprietary (Opitz, 1970).
Coding Method – MIXED CODE
OPITZ Classification System
1 2 3 4 5 6 7 8 9 A B C D
Form Code
Mixed-mode
Part geometry
dimensions and
features
Supplementary
Code
Polycode
Manufacturing
information
Secondary
Code
Production
processes &
sequences

11. Kripa Shanker IIT Kanpur 11
OPITZ Coding System
0 L/D ≤ 0.5
1 0.5<L/D<3
2 L/D≥3
3 with deviation
L/D ≤2
4 with deviation
L/D> 2
5 Special
6 A/B ≤3
A/C ≥4
7 A/B> 3
8 A/B ≤3
A/C <4
9 Special
Rotational
Nonrotational
External
shape
element
Main
shape
Main
shape
Main
shape
Main
shape
External shape
element
Machining of
plane surfaces
Other holes
and teeth
Rotational
machining
Main bore and
rotational
machining
Machining of
plane surfaces
Machining of
plane surfaces
Other holes
teeth and
forming
Other holes
teeth and
forming
Dimensions
Material
Original
shape
of
raw
material
Accuracy
Digit 1
Part class
Digit 2
Main shape
Digit 3
Rotational
machining
Digit 4
Plane surface
machining
Digit 5
Additional holes
teeth and forming
Digits
6 7 8 9

12. Kripa Shanker IIT Kanpur 12
OPITZ Classification System
Part class : Rotational part, L/D = 9.9/4.8 = 2.0 (approx.) based on pitch dia of gear. Digit 1 = 1
External shape : The part is stepped on one side with functional groove. Digit 2 = 3
Internal shape : The part has through hole. Digit 3 = 1
Plain surface machining : There is no plain surface machining. Digit 4 = 0
Auxiliary holes and gear teeth : There are spur gear teeth on the part. Digit 5 = 6
FORM CODE : 1 3 1 0 6

13. Kripa Shanker IIT Kanpur 13
GROUP TECHNOLOGY
CLASSIFICATION AND CODING SYSTEMS – SELECTION
CRITERIA
 Flexibility
part family formation, process planning, costing, and purchasing
 Accuracy
to provide accuracy
 Expandability
to accommodate information on more part attributes deemed
important later on
 Ease of learning
 Ease of retrieval
 Reliability and availability of software
 Suitability for specific applications

14. Kripa Shanker IIT Kanpur 14
BENEFITS OF
GROUP TECHNOLOGY
 Engineering Design
Reduction in new part design
Reduction in the number of drawings through standardization
Reduction in drafting effort in new shop drawings
Reduction of number of similar parts, easy retrieval of similar
functional parts, and identification of substitute parts
 Layout Planning
Reduction in production floor space required
Reduced material-handling effort
 Specification of Equipment Tools, Jigs, and Fixtures
Standardization of equipment
Implementation of cellular manufacturing systems
Reduced number of tools, jigs, and fixtures
Significant reduction in up-front costs incurred in the release of new parts
for manufacture

15. Kripa Shanker IIT Kanpur 15
BENEFITS OF
GROUP TECHNOLOGY
 Manufacturing : Process Planning
Reduction in setup time and production time
Alternative routing leading to improved part routing
Improved machine loading and shortened production cycles
Reduction in number of machining operations and numerical control (NC)
programming time
 Manufacturing : Production Control
Reduced work-in-process inventory
Easy identification of bottlenecks
Improved machine loading and shortened production cycles
Faster response to schedule changes
Improved usage of jigs, fixtures, pallets, tools, material handling, and
manufacturing equipment
 Manufacturing : Quality Control
Reduction in number of defects leading to reduced inspection effort
Reduced scrap generation
Better output quality
Increased accountability of operators and supervisors responsible for
quality production, making it easier to implement total quality control
concepts.

16. Kripa Shanker IIT Kanpur 16
BENEFITS OF
GROUP TECHNOLOGY
 Purchasing
Coding of purchased parts leading to standardized rules for
purchasing
Economies in purchasing possible because of accurate knowledge
of raw material requirements
Reduced number of parts and raw materials
 Customer Service
Accurate and faster cost estimates
Efficient spare parts management, leading to better customer
service