Inter-Cell Part Scheduling Strategy For Hybird Manufacturing Systems With Multi-level Of Machining And Assembly

To meet variety of customer’s demand and production of complex products, production mode gradually changes from single procedure and mass production to multiple processing, hybrid manufacturing of machining, furnace-heat treatment and assembling, and variable batching. Due to the capacity limitation and scarce configuration of machining equipment in single workshop, the cooperative production among different workshops becomes more frequent in an enterprise. It is a fairly new challenge for production scheduling methods because of the difficulty of cooperative scheduling among different workshops. Based on the background of the management practice arising from manufacture workshop, this work was financially supported by National Natural Science Foundation of China. On the basis of analyzing the research state-of-the-art on workshop scheduling, especially on inter-cell scheduling problem for hybrid manufacturing systems with multi-level of machining and assembly, this dissertation focuses on the study of modeling and optimization algorithms for workshop scheduling problem. The major research results of this dissertation fall on three aspects as follows:(1) Part scheduling strategy for the scenario of single-level machining and assembly of products is studied. For the scenario of an independent workshop with a universal machining device and assembly equipment, two basic structural units of products and their formulation method are presented. One the basis of this, we propose a computing method of theoretical minimum completion time based on the ideal production unit. Mathematical formulation is proposed for product structure graph and branch-priority based scheduling strategy. Comparative analysis of three scheduling strategies for the scenarios that two branches’ production structure with multiple operations and one assembly device under single machining and parallel machining respectively, is presented.(2) Part scheduling strategies for the scenarios of multi-level machining and assembly of products is investigated. The minimum impact value based scheduling strategy is proposed for scheduling product with basic structure units. Considering the situations that multi-level assembling with two or three assembly devices, and one or parallel machining are equipped in a workshop, to producing products with two or three of branches, by introducing the idea of synchronizing assembly and concepts of maximum/minimum tolerance of processing time, and real tolerance of processing time, two different scheduling strategies basing on the idea of synchronizing assembly are developed for scenarios with production structure with two or three branches, one or multiple machining device and two or three assembling devices.(3) Two heuristic algorithms are developed for inter-cell moving part scheduling problems between two workshops. For the scenario of cooperative production among two workshops, we introduce the concepts of logical joint-workshop and joint scheduling mode, referenced beginning processing time, referenced end processing time, penalty costs for delay processing and value-added benefit for earlier processing. From the cooperative scheduling perspective, a mathematical programming model is proposed to formulate inter-cell part scheduling problems that both of the two workshops use its opponent machines to process one or several operations that could not be implemented in its own machines. It aims to minimize the total cost of production in order to balance the overall production time, delay time and earlier time for each workshop. According to the characteristics of the problem, two heuristic algorithms are developed. The former is based on joint scheduling idea and genetic search, the latter is based on system coordination towards minimizing costs. The original problem is divided into three stages by these two algorithms. The first two stages solve the parts batching and dispatching problem based on two levels of structure graph of genetic operators. At the third stage, the heuristic scheduling strategy is applied to complete the last parallel machine scheduling. The performance of these two heuristic algorithms is analyzed with different examples and algorithm parameters.