Job shop scheduling with alternative process plans

Article Abstract:

Successful implementation of automated manufacturing systems highly depends on effective utilization of resources. Efficient scheduling algorithms for alternative process plans may increase the throughput rate and guarantee a reasonable return on investment. This paper investigates an optimization methodology for scheduling jobs in a just-in-time environment. We consider the non-preemptive case where each job consists of a distinct number of operations to be processed in a specified order. Each operation has to be processed on one of a set of resources (e.g. machines) with possibly different efficiency and hence processing time. The objective is to minimize the sum of the weighted quadratic tardiness of the jobs. We obtain a fast near-optimal algorithm with guaranteed bounds for the distance to the optimum by using Lagrangian relaxation and show that just one relaxation suffices. Keywords: Job shop scheduling; Alternative process plans; Lagrangian relaxation

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Manufacturing cells design with flexible routing capability in presence of unreliable machines

Article Abstract:

Flexible manufacturing systems generally provide the possibility to use different process plans to manufacture a part owing to versatile machines. In this context, the design of manufacturing cells includes two problems, the constitution of the cells of machines and the assignment of the process plans to be used by the parts. Flexible routings allow the machines usage factor and the throughput time to be improved. The manager of such a system can also change the process plans to bypass unusable machines. The design of robust cell configurations which can accommodate different process plans assignment is an important issue. This paper proposes a new approach for designing manufacturing cells when the process plans can be changed because of machine breakdowns. The impact of our method is illustrated through a small example. Keywords: Manufacturing cells; Alternative routings; Machine breakdowns; Markov chain; Mathematical programming

Manufacturing cells

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Spare provisioning strategy for preventively replaced systems subjected to random failure

Article Abstract:

jointly optimal periodic replacement and spare parts provisioning strategy is discussed. This strategy is completely defined once the replacement period T, the replenishment cycle R = kT (k = 1, 2, ...), and the ordering point s are determined. The optimal strategy ([T.sup.*], [R.sup.*], [s.sup.*]), if it exists, is one which minimizes the total expected cost (replenishment cost + spare parts inventory management cost) per time unit over an infinite span. A numerical algorithm is proposed to find the optimal strategy. The system lifetime distribution, the probability distribution of the demand during the lead-time and the costs associated to the replenishment and the spare parts inventory management are supposed to be known. Some numerical results are presented. Keywords: Optimal replacement strategy; Spare provisioning; Block replacement

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