Toward Hybrid Variant/generative Process Planning

INTRODUCTION In process planning practice, variant techniques are the tools of choice: they currently support almost all practical implementations of computer-aided process planning. Several variant process planning systems are commercially available and have provided significant benefits—but despite the relative popularity of this approach, variant process planning has some well known drawbacks. A generative process planner that provides realistic process plans for a reasonably wide spectrum of products would make a great impact on industrial practice. Thus, a great deal of research has been done on generative approaches, and a number of experimental systems have been developed for various aspects of process planning. However, generative process planning has proved quite difficult. Most existing systems work only in restricted domains, and have not really achieved significant industrial use. This paper describes a hybrid process planning approach that we are developing. This approach attempts to combine the best characteristics of both variant and generative process planning while avoiding the worst limitations of each. As shown in Figure 1, our approach involves the following steps: • Create a database of designs and process plans similar to a variant database—but instead of using GT codes to index and classify the entries in the database, use detailed product design attributes that are more meaningful and accurate than GT codes and can be computed automatically from the designs stored in the database. • Given a new design for which a process plan is needed, retrieve relevant process planning information from the database—but unlike traditional variant process planning, this information is not a single plan but includes instead portions or “slices” of several plans, each of which is relevant for a different portion of the design. • Use generative plan-merging techniques to combine and modify the retrieved plan slices in order to synthesize a process plan for the new design. This paper describes the basic approach we are developing for each of these steps. Some of the steps are implemented and working, and some of them are still work in progress.