ComputerAided_Design_Engineering_amp_Manufactur.pdf

5.3 Computer-Aided Process Planning
Process planning establishes the methods and means of converting the raw material to a finished part
in a manufacturing facility. Computer-aided process planning (CAPP) is the application of computers
to assist the process planners in the planning function. There are two basic approaches to CAPP: variant
and generative, which are briefly discussed below.
Variant Approach
FIGURE 5.1
The variant approach, which is also called retrieval approach, uses a group technology (GT) code to select a
generic process plan from the existing master process plans developed for each part family and then edits to
suit the requirement of the part (Figure 5.2). Variant approach is commonly implemented with GT coding
system. Here, the parts are segmented into groups based on similarity and each group has a master plan.
Several CAPP systems based on the variant approach such as DISAP, TOJICAPP (Zhang and Gao,
1984) etc., are reported in literature. However, this approach is impractical in situations where small
batches of widely varying parts are produced. Moreover, this method fails to capture the real knowledge
or expertise of process planners, and there is a danger of repeating mistakes from earlier plans that were
stored in the data base (Shah, 1991).
Generative Approach
Typical part drawing whose process plan is given.
FIGURE 5.2
Variant approach to CAPP.
In a generative approach, a process plan for each component is created from scratch without human
intervention. These systems are designed to automatically synthesize process information to develop a