AN INTEGRATED SETUP PLANNING AND FIXTURE DESIGN SYSTEM FOR PRISMATIC PARTS

Abstract

Fixtures are indispensable tools in a manufacturing environment. They are used in machining, assembly and inspection of workpieces. The basic requirements of fixtures are to locate and secure the workpiece in the correct orientation and relationship, so the manufacturing processes can be carried out to design specifications. Fixture design has traditionally been regarded as an activity which is difficult to automate due to extensive requirements of heuristic knowledge and skilled craftsmanship. The progress in the field of CAD, in artificial intelligence (AI) techniques and knowledge representation schemes, and the availability of modular tooling have opened up scopes to automate this activity. The objective of the work presented in this thesis is to develop an automated fixture design system which aims at integrating the fixture planning and setup planning functions. The developed fixture design system consists of three functional modules viz., pre-setup conceptual fixture design, post-setup conceptual fixture design and fixture layout design. In the pre-setup conceptual design stage, possible machining orientations are identified based on the approach directions of the machining features. For each possible machining orientation, the system analyses the machining features in both geometric and technological contexts and identifies all the fixturing features using a knowledge-based approach. Suggestions on machining orientation sequence and feasibility due to fixturing constraints are generated. This set of information is then input to the setup planner for setup selection and sequencing. After the setup plan is generated, the intermediate state of the workpiece of each setup is determined. The post-setup conceptual fixture design is carried out in which the surface candidates for each fixturing datum of a setup are identified and ranked according to the various geometrical and technological criteria. The best candidate for each fixturing datum category is selected. The fixture layout design module generates a set of fixturing points for each setup based on a simplified geometrical interference checking algorithm and static stability analysis. The fixture design rules and modular element database are embedded into a knowlegde-based system based on IDL (ICAD Design Language) and Common Lisp programs. The present system can generate fixturing solutions to prismatic workpieces machined in 3-axis vertical machining centres.