Petri net techniques for process planning cost estimation

The problem under consideration is the cost estimation of operation sequencing for nonlinear process planning, i.e. taking into consideration processing alternatives. In order to determine overall costs for feasible process plans, we take into account in our Petri net model of manufacturing process planning the costs caused by machine, setup and tool changing in addition to the pure operation cost. We present two modelling and cost estimation techniques based on Petri nets. Both are based on a new Petri net model: the PP-net (Process Planning net) which represents manufacturing knowledge in the form of precedence constraints and incorporates the cost of machining operation in each operation transition. The first method is based on building a complex Petri net called PPC-system (Process Planning Cost system) by integrating the PP-net and separate Petri nets describing the costs of machine, setup and tool changing. The second method proceeds in the cost calculation by attaching a specific data structure to each PP-net transition which describes the associated machine, setup and tool for the operation modelled by that transition. We apply the developed methods and calculate the optimum process plan to an industrial case study of a mechanical workpiece of moderate complexity. (C) 1999 Elsevier Science Ltd. All rights reserved.