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Title: Scheduling of production and maintenance operations with mold maintenance consideration
Authors: Wong, Chun Sing
Degree: Ph.D.
Issue Date: 2015
Abstract: In general, studies of production scheduling focus on figuring out the optimal work sequence to achieve specified business goals. The reliability issue is usually not included in the scope of the studies. However, in real-life situations, resource breakdown or failure often occurs and seriously interrupts the planned production schedule. Maintenance of the machinery is an effective way to improve plant reliability. Typically, however, the production and maintenance activities are executed independently. The mismatch of both production and maintenance schedules mostly induces high cost during production. To harmonize both activities, recent studies have attempted to integrate machine maintenance planning with production scheduling; the so-called Production-Maintenance Scheduling (PMS) problem. Although some studies on PMS problems have been comprehensive, with encouraging results, most of the PMS studies only included machine maintenance, which may not improve the production system reliability as a whole. Other critical resources, such as injection molds, are usually assumed to be available. In fact, the proportion of mold-related downtime is even higher than the machine-related one. Nowadays, due to a highly competitive business environment, many manufacturers are facing a tradeoff between the mold quality and its cost. They tend to reduce mold costs, which may lead to lower mold quality and reliability. The scheduling of mold maintenance becomes an acute issue for maintaining high plant reliability in the overall production process. Injection molds are actually the major components in the operation of injection molding machines and represent a significant amount of capital investment for plastics manufacturers. Thus, the condition and availability of injection molds are very crucial. Basically, the condition of the mold is subject to deterioration relative to the usage and age of the mold, and thus requires maintenance or reconditioning which will the interrupt the planned production activities. In this connection, this study considers mold usage, mold age, and mold maintenance in PMS problems, and a new PMS model, named the Production Scheduling with Mold Scheduling (PSMS) model, is therefore developed. This integrated problem is much more complicated and challenging. To deal with this new problem, a genetic algorithm approach named Genetic Algorithms with Dominant Gene (GADG) is developed to minimize the makespan of all jobs. This approach has been shown to outperform existing algorithms. A Joint Scheduling (JS) approach is proposed to integrate production and maintenance scheduling. As a result, production jobs, maintenance tasks of both machine and mold are jointly (but not sequentially) scheduled. To our best knowledge, there is no such integration in production scheduling research, especially in the area of injection mold maintenance.
Two case studies have been carried out to investigate two scenarios during the adoption phase of the PSMS model in a studied company. In the first case study, the scheduling policy for various types of maintenance tasks is probed. In the real-life situation, machines and molds require different sets of maintenance tasks. All of those tasks have their own frequency and duration. The maintenance scheduling methodology should therefore consider the requirements of different sets of maintenance tasks and, hence, a new scheduling methodology has been developed to consider multiple maintenance tasks. In the second case study, the scheduling policy for multiple mold series is investigated. As the PSMS model is developed based on the requirements of the operation of injection molding, each job only considers a single operation with a single mold. The PSMS model is not workable in other manufacturing systems, such as die stamping, which may contain multiple operations with multiple molds in each job. In this connection, the PSMS model has been modified to make it suitable for the requirement of multiple mold series. This research is pioneering in the area of production and mold maintenance scheduling, and can provide a vital reference for future research on PMS problems. Overall, five deliverables are generated in this thesis. First, a novel PSMS problem integrating the scheduling of production, machine maintenance and mold maintenance is identified and modeled. Second, a GADG optimization methodology is developed and shown to be able to obtain better solutions compared with the existing algorithms. Third, the proposed JS approach is proven to outperform other traditional approaches with shorter makespan. Fourth, a new methodology for scheduling multiple maintenance tasks is developed and demonstrated. Fifth, a modified PSMS model is developed to consider the maintenance of multiple mold series.
Subjects: Plant maintenance -- Planning.
Plant maintenance -- Management.
Production management.
Hong Kong Polytechnic University -- Dissertations
Pages: xv, 220 pages : illustrations (chiefly color) ; 30 cm
Appears in Collections:Thesis

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