Non-Machining CAPP Applications
Manufacturing is not limited to only machining. It includes other processes like, casting, forming, shearing, heat treatment, joining, assembly, sheet metal working, inspection, etc. Some researchers have made effort to build CAPP system for such non-machining applications.
Akira (5) focused on computer aided assembly planning. Firstly a sequence of assembly operations is determined according to a configuration of parts for assembly and assemblability. Then some successive operations are grouped together. Considering resources like robots, machines or human operators, a planner assigns assembling machines or operators to each group. On the basis of production volume and cost, assembly process in which operation time for each group of operations is less than the cycle time is prepared and resources are selected for maximum economy by effective utilisation of the plant's existing resources. A relational model is used to describe the process. In resource assignment, the order of precedence, correspondence between operations and resources, and the number of resources are considered. Resources are allocated to operations by using an assumption based truth maintenance system with generated logic expressions (ATMS). The process plans generated by ATMS are evaluated by a production line simulator and a good plan is selected on the basis of simulation results.
De vin et. al (6) reported a system (PART-S) for sheet metal components, with considerations on bending sequence. The generation of bending sequences involves the selection of positioning features (or sequence of setups). It is necessary for accuracy aspects and handling rules while generating a collision free bending sequence. The reverse bending sequence approach (from part to initial flat stock) is used. The search space is reduced by eliminating non-feasible solutions. The dimensions and tolerance scheme are also reduced to avoid redundant work. All those dimensions that are not affected by bending operation are eliminated and the rest are grouped in such a way that each group contains relationships between two faces or features belonging to those faces. At each state of the product alternative preceding states are considered by unfolding one bend and searching for candidate positioning feature (CPF). If no CPFs are found, then the state of the product is not feasible. Whenever several CPFs exist, their number is reduced by rational elimination and combination. The alternative solutions are evaluated considering accuracy, handling and tooling, and the most promising solution is selected. Finally an interference check is made if tool data is available. The main operations considered are punching, nibbling, laser welding, laser cutting, and air bending.
Lauwers and Kruth (7) concentrated on EDM operations. Their feature based CAPP system generates process plans using an optimisation algorithm to determine the plan with minimum variable cost. The system first reads the feature based workpiece description from a file, and for each instanced feature, the generic plan is evaluated. During this evaluation machining and electrode costs are evaluated. The system checks the feasibility of combining operations and a global process plan for the whole workpiece is generated based on the evaluated generic plan of all manufacturing features. A branch and bound method is used to define the optimal path. The process planning system is written in LISP and is provided with object oriented programming facilities.