ComputerAided_Design_Engineering_amp_Manufactur.pdf

process plan for a part (Figure 5.3). These systems contain the logic to use manufacturing data bases and
suitable part description schemes to generate a process plan for a particular part. Most of the contemporary
CAPP systems being developed are generative in nature. Generative approach eliminates disadvantages
of variant approach and bridges the gap between the CAD and CAM.
5.4 CAPP: Implementation Techniques
Logical decision is a traditional implementation technique used in CAPP. The simplest approach is to
code the process capability in a computer program. A tree-structured classification can be used in the
system and each process can be coded as a branch of a decision tree (Chang and Wysk, 1984).
The decision logic should be present in a format that is easy to visualize and check for completeness,
contradictions, and redundancy. Generally, each manufacturing process is defined as a separate entity
based on the capabilities to generate or modify geometric features or properties. Only values of decision
variables change over time or between companies. The techniques for structuring the decision logic are
numerous and varied.
The objective of decision logic in a CAPP system is to match the process capabilities with design
specifications in an optimal way. Generally, most common decision logic can be classified as one of the
three methods: decision tables, decision trees and AI.
Decision Tables
A decision table is partitioned into conditions and actions and is represented in a tabular form. It is a
program-structuring tool which provides readable documentation as an automatic by-product. Also,
decision tables can be used with preprocessors to eliminate some program coding, and to provide
automatic checks for completeness, contradiction, and redundancy.
Decision Trees
FIGURE 5.3
Generative approach to CAPP.
A decision tree is a graph with a single root and branches emanating from the root. Decision trees
are easier to customize, update, maintain, visualize and develop than decision tables. Decision trees
can be represented as computer codes or data. The tree as computer code is converted to a flow chart;
the starting node is the root and every branch represents a decision statement which is either false or
true.