Process planning for machining centre operations

The paper presents part of the work carried out within a research project on 'Flexible Manufacturing Automation in Small Batches' at VTT. The project focused on the process planning of prismatic workpieces. These workpieces are usually manufactured in a machining centre. The main interest has been in automatic tool selection based on the information of tools used previously in similar manufacturing operations. A 'Computer Aided Process Planning System for Machining Centre Operations' has been developed. Even the most sophisticated conventional CAPP-system used in manufacturing industry today seldom produces more than a limited workstation routing and bill of materials. This has been taken into account during the planning period of this project. The CAPP-system developed within this project is capable of · creating machining phases (work elements), · selecting cutting tools and machining parameters, · sequencing the machining operations, and · generating the NC-program for the machine tool. The prototype CAPP-system created uses a combination of the variant and generic process planning principles. An explanation of these two approaches is included and examples are given. The system contains the most favourable characteristics of both approaches. One of the central ideas in this project was to gather knowledge and expertise in a knowledge base. The tool selection is based on this knowledge. This information can be expanded and updated by each user as he/she acquires more experience. Thus forthcoming manufacturing operations can be carried out in a 'standardized' way at the manufacturing cell level. When skilled personnel leave the company their knowledge can be retained in the system and the enterprise is able to carry-on its production without a time-consuming and costly teaching period. The major advantage of this kind of CAPP-system appears to lie in the production of one-of-a-kind and small batches where the share of process planning is large compared with mass production. Thus the design and manufacturing operations are integrated more closely and the dialogue between these activities increases. The result is shorter lead times and therefore lower production costs. The paper suggests extended research into more complicated feature handling covering all machining operations in machining centre environments