Group technology (GT).pdf

1. GROUP TECHNOLOGY
Group technology is a manufacturing
philosophy in which similar parts are
identified and grouped together to take the
advantage of their similarities in both design
and manufacturing.
Similar parts are arranged into Part families.
Part family: It is a collection of parts which are
similar either because of geometric shape and
size or because of similar processing steps in
their manufacture. 1

2. Example 1: Two parts of identical shape and size but different
manufacturing requirements is shown below
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3. Example 2: Parts with similar manufacturing process
requirements but different design attributes.
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4. Methods used to group the parts into part family:
1)Visual inspection:
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5. Methods used to group the parts into part family:
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2) Production flow analysis:
- by analysing the route sheets for parts produced in a machine
shop.
- it groups together the parts that have similar operation
sequences and machine routings.
- it accepts the validity of existing route sheets with no
consideration given to whether these process plans are logical
or consistent.
3) Part classification and coding system:
- involves an examination of the design and/or manufacturing
attributes of each part.
- the attributes of the part are uniquely identified by means of a
code number.
- the part classification and coding system is custom engineered
for a given company.

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Classification of part coding systems:
1) Coding systems based on part design attributes
2) Coding systems based on part manufacturing attributes
3) Coding systems based on both design and manufacturing attributes
Part design attributes:
Basic external shape Major dimensions
Basic internal shape Minor dimensions
Length/ diameter ratio Tolerances
Material type Surface finish
Part function
Part manufacturing attributes:
Major process Operation sequence
Minor operations Production time
Major dimensions Batch size
Length/diameter ratio Annual production
Surface finish Fixtures needed

7. CODING SYSTEM STRUCTURE:
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8. CODING SYSTEM STRUCTURE:
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9. CODING SYSTEM STRUCTURE:
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10. CODING SYSTEM STRUCTURE:
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18. Example 1:
The form code for the part design shown in the figure is as follows:
- the overall length/diameter ratio, L/D = 1.5, first digit code = 1
-the part is stepped on both ends with a screw thread on one end, second digit code =5
- the part has a through hole, third digit code = 1
- there is no surface machining, fourth digit code = 0
- there are no auxiliary holes or gear teeth on the part, fifth digit code = 0
Hence the complete form code = 15100 18

19. Example 2:
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20. Example 3:
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21. 2) MICLASS SYSTEM:
- Metal Institute Classification System
- Developed to help automate and standardize a number of design, production and
management functions.
These include:
- Standardization of engineering drawings
- Retrieval of drawings according to classification number
- Standardization of process routing
- Automated process planning
- Selection of parts for processing on particular groups of machine tools
- Machine tool investment analysis
The MICLASS classification number can range from 12 to 30 digits
- the first 12 digits are a universal code that can be applied to any part
- upto 18 additional digits can be used to code data that are specific to the particular
company or industry (ex: lot size, piece time, cost data and operation
sequence)
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22. -The workpart attributes coded in the first 12 digits of the MICLASS number are as
follows.
1st digit - Main shape
2nd and 3rd digit - Shape elements
4th digit - Position of shape elements
5th and 6th digit - Main dimensions
7th digit - Dimension ratio
8th digit - Auxiliary dimension
9th and 10th digit - Tolerance codes
11th and 12th digit - Material codes
- parts can be coded using a computer interactively
- the user responds to a series of questions asked by the computer
- the number questions depends on the complexity of the part
-on the basis of responses to its questions, the computer assigns a code number to the
part.
Example:
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25. 3) CODE SYSTEM:
- developed and marketed by Manufacturing Data Systems, Inc (MDSI)
- its most universal application is in design engineering for retrieval of part design data,
manufacturing process planning, purchasing, tool design and inventory control
- has 8 digits
- for each digit there are 16 possible values ( 0 through 9 and A through F) which are
used to describe the part’s design and manufacturing charecteristics.
1st digit - indicates the basic geometry of the part (cylinder/block)
- the remaining digits interpretation depends on the value of first digit, but
these remaining digits form a chain-type structure, hence the CODE
system possesses a hybrid structure.
2nd and 3rd digits – additional information concerning the basic geometry and principal
manufacturing process for the part.
4th,5th and 6th digits – specify secondary manufacturing processes such as threads,
grooves, slots and so forth.
7th and 8th digit – indicate the overall size of the part
Ex:
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27. GROUP TECHNOLOGY MACHINE CELLS:
- in a GT machine cell, groups of machines arranged to produce similar part families.
- a machine cell can be defined by defining a composite part concept.
COMPOSITE PART CONCEPT:
- It conceives of a hypothetical part that represents all of the design and manufacturing
attributes possessed by the various individuals in the family.
- to produce one of the members of the part family, operations are added and deleted
corresponding to the attributes of the particulat part design.
- for example, the composite part in figure is a rotational part made up of seven
separate design and manufacturing features.
- a machine cell would be designed to provide all seven machining capabilities
- a part with all seven attributes, such as the composite part of figure would go through
all seven processing steps.
- for part designs without all seven features, unneeded operations would be canceled.
- the composite part concept is useful for visualizing the machine cell design problem.
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28. Design and manufacturing attributes of the composite part:
Number Design and manufacturing attribute
1 Turning operation for external cylindrical shape
2 Facing operation for ends
3 Turning operation to produce step
4 External cylindrical grinding to achieve specified surface finish
5 Drilling operation to create through hole
6 Counterbore
7 Tapping operation to produce internal threads
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29. TYPES OF GT MACHINE CELLS:
The organisation of machines into cells can follow one of three general patterns.
1. Single machine cell:
- can be used for workparts whose attributes allow them to be made on one type of
machine such as turning or milling.
- for example, the composite part could be produced on a conventional turret lathe with
the exception of the cylindrical grinding operation.
2. Group machine cell:
- several machines are used together with no provision for conveyorized parts
movement between the machines.
- cell contains the machines needed to produce a certain family of parts and the
machines are organized with the proper fixtures, tools, and operators to efficiently
produce the parts family.
3. Flow line design:
- group of machines connected by a conveyor system.
- Certain of the processing steps can be omitted, but the flow of work through the
system must be in one direction.
- Reversal of work flow is accommodated in the more flexible group machine layout.
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