Group technology is a 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 example, a plant producing 10,000 different part numbers may be able 10 groups 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.
2. Part families
A 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 show two different part families. The two parts in Figure 1 are very similar in terms of geometric design, but quite different in terms of manufacturing because of differences in tolerances, production quantities, and material. The ten parts shown in Figure 2 constitute part family in manufacturing, but their different geometries make them appear quite different from a design viewpoint.
3. Coding-technology -
This 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. Two categories of part similarities can be distinguished:
(1) Design attributes, which are concerned with part characteristics such as geometry, size, and material; and
(2) Manufacturing attributes, which consider the sequence of processing steps required to make a part.
The parts coding scheme consists of a sequence of numerical digits to identify the parts design and manufacturing attributes. Coding scheme for part classification can be of two basic structures.
1. Hierarchical structure – In this code structure, the interpretation of each succeeding symbol depends on the value of the preceding symbols.
2. Chain type structures – In this type of code, the interpretation of each symbol in the sequence is fixed. It does not depend on the value of the preceding symbol
3. mixed-mode structure which is a hybrid of the two previous codes
4. Obstacles to GT.
1) Identifying the part families (the biggest problem) If the plant makes 10,000 different parts, reviewing all of the part drawings and grouping the parts into families is a substantial task
2) Rearranging production machines in the plant into the appropriate machine cells It takes time to plan and accomplish this rearrangement, and the machines are not Producing during the changeover
5. Methods of classification.
i) Visual inspection.
ii) Classification and coding system.
iii) Production flow analysis
i) Visual inspection involves arranging a set of parts into groups by visually inspecting the physical characteristics of the parts.
ii) Parts classification and coding - identifying similarities and differences among parts and relating them by means of a coding scheme
iii) Production flow analysis - using information contained on route sheets to classify parts
6. Types of classification and coding system
Some of the coding system of Process Planning are:
a) OPITZ System
b) The CODE System
c) The KK-3 System
d) The MICLASS System
e) The DCLASS System
f) COFORM (Coding For Matching)
a) THE OPITZ CLASSIFICATION SYSTEM:
The opitz system is of historical interest because it was one of the first published classification & coding schemes for mechanical parts. This parts classification & coding system was developed by it opitz of the university of Aachess in West Germany. It represents one of the pioneering efforts in the group technology areas and is probably the best known of the classification & coding schemes. The Opitz coding system uses the following digit, sequence:
12345 6789 ABCD
The basic code consists of nine digits, which can be extended by adding four more digits. The first nine digits are intended to convey both Design & manufacturing data. The first five digits 1 2 3 4 5, are called the ―form code‖ and describe the primary design attributes of the part of the part. The next four digits 6 7 8 9, constitute the ―supplementary code‖ which indicates some of the attributes that would be of use to manufacturing. The extra four digits, A B C D are referred to as the ―secondary code‖ and are intended to identify the production operation type & sequence. The secondary code can be designed by the firm to serve its own particular needs
7. Benefits of well designed classification and coding system.
I. Engineering
Reduction of number of similar parts
Elimination of duplication parts
Identification of expensive parts
Reduction of drafting efforts
Easy retrieval of similar functional parts
Identification of substitute parts
II. Equipment Specification and Facility Planning
Flow line layout of production equipment
Location of bottlenecks
Location underutilized machine tools
Reduction of part transportation times
Improvement of facility planning
III. Process Planning
Reduction of number of machining operations
Shortening of production cycles
Improvement of machine loading operation
Easier prediction of tool wears and tool changes
8. Benefits of Group Technology
a) Standardization of tooling, fixtures, and setups is encouraged
b) Material handling is reduced
c) Parts are moved within a machine cell rather than entire factory
e) Process planning and production scheduling are simplified
e) Work-in-process and manufacturing lead time are reduced
f) Improved worker satisfaction in a GT cell
g) Higher quality work
Great breakdown of group technology and its impact on manufacturing efficiency. The biggest hurdle, like you mentioned, is the time-consuming task of identifying part families. Companies like onshore technology group help simplify complex production processes like these.
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