GROUP TECHNOLOGY AND COMPUTER AIDED PROCESS PLANNING
1. Group technology (GT)
Group technology (GT) is a manufacturing philosophy to increase production efficiency by grouping a variety of parts having similarities of shape, dimension, and/or process route.
2. Part family
A part family is a collection of parts which are similar either because of geometric shape and size or because similar processing steps are required in their manufacture. Design attributes:
· Part configuration (round or prismatic)
· Dimensional envelope (length to diameter ratio)
· Surface integrity (surface roughness, dimensional tolerances)
· Material type & Raw material state (casting, forging, bar stock, etc.)
Part manufacturing features:
Operations and operation sequences (turning, milling, etc.)
· Batch sizes
· Machine tools
· Cutting tools
· Work holding devices
· Processing times
3. General methods used for part families.
4. Visual inspection,
5. Parts classification and coding system, and
6. Production flow analysis.
4. Production Flow analysis
Production Flow analysis (PFA) is a method for identifying part families and associated machine groupings that uses the information contained on production route sheets rather on part drawings.
5. Code structures used in GT application
· Attribute codes (or polycodes or chain type structure).
· Hierarchical codes (or monocodes or tree structure).
· Decision-tree codes (or hybrid codes or mixed codes).
6. Coding systems.
1. Opitz classification system, 2. MICLASS system,
3. DCLASS system, 4. CODE system,
5. KK-3 system,and 6. CUTPLAN system.
7. Benefits of Group Technology
Group technology is a management strategy to help eliminate waste caused by duplication of effort.
It affects all areas of a company, including:
· Equipment specification
· Facilities planning
· Process planning
· Production control
· Quality control
· Tool design
7. Cellular manufacturing
Cellular manufacturing (CM) is an application of group technology in which dissimilar machines have been aggregated into cells, each of which is dedicated to the production of a part family.
8. Design considerations guiding the cell-formation.
· Parts/products to be fully completed in the cell.
· Higher operator utilization.
· Fewer operations than equipment.
· Balanced equipment utilization in the cell.
9. Process planning
Process Planning is the systematic determination of the methods by which a product is to be manufactured, economically and competitively.
10. Computer/Aided Process Planning
§ CAPP refers to computer/aided process planning.
§ CAPP is used to overcome the drawbacks of manual process planning.
§ With the use of computers on the process planning one can reduce the routine clerical work of manufacturing engineers.
§ Also it provides the opportunity to generate rational, consistent and optimal
11. Process planning techniques used in the modern manufacturing technologies
§ Manual approach
§ Computer aided process planning techniques
§ Retrieval type CAPP system (Variant type CAPP system)
§ Generative type CAPP system
Computer aided process planning system offers the potential for reducing the routine clerical work of manufacturing engineers. It provides the opportunity to generate routings which are rational, consistent and perhaps even optimal.
13. Retrieval type CAPP (Variant type) systems
For each part family a standard process plan is established and stored in computer files and then it is retrieved for new work parts which belong to that family. Because of the alterations that are made in the retrieved process plan, the CAPP system is known as variant system.
14. Generative CAPP system
Generative process planning involves the use of computer to create an individual process plan automatically without human assistance. The computer would employ a set of algorithms to progress through the various technical and logical decisions toward a final plan.
15. Role of process planning
1. Interpretation of product design data
2. Selection of machining processes.
3. Selection of machine tools.
4. Determination of fixtures and datum surfaces.
5. Sequencing the operations.
6. Selection of inspection devices.