This paper considers the problem of selecting and sequencing operations in process planning for the objective of minimizing the sum of operation processing costs and machine, set-up and tool change costs. The main constraint is the precedence relations among operations. To represent the precedence relations and alternative operations, a tree-structured precedence graph is suggested. Based on the graph, the entire problem is decomposed into two subproblems: operation selection and operation sequencing. Then, three iterative algorithms are suggested that solve the two subproblems iteratively until optimal and nearoptimal solutions are obtained. The algorithms are illustrated using an example part, and to show the performances of the algorithms, computational experiments were done on randomly generated test problems. The results show that the algorithms suggested work well for the test problems.
IntroductionComputer-aided process planning (CAPP) is an approach that uses computers to generate a process plan that contains the route, operations, operation parameters, machines, set-ups and tools required for producing a part. Although process planning activities are different according to different industries and shops, they involve several or all of the following (Chang 1990): (1) selection of machining operations;(2) sequencing of machining operations; (3) selection of cutting tools; (4) selection of machine tools; (5) determining set-up requirements; (6) calculations of cutting parameters; (7) tool path planning and generation of NC part programs; and (8) design of jigs and fixtures. There are a number of previous research articles on the above process planning activities. For surveys on these subjects, see Ham and Lu (1988), Alting and Zhang (1989), ElMaraghy et al. (1993) and Kiritsis (1995).Among the various activities in process planning, this paper focuses on the operation selection and sequencing problems. That is, the problem considered in this paper is to select operations among alternatives as well as to determine the sequence of the selected operations so that the resulting solution satisfies the precedence constraints among operations. The objective is to minimize the sum of operation processing costs and machine, set-up and tool change costs. The operation selection and sequencing are needed to consider at the same time since better solutions can be obtained over the extended solution space. However, the two problems, especially