Abstract-Overhaul and repair services are important segments of the remanufacturing industry, and are characterized by complicated disassembly, repair and assembly process plans, stochastic operations, and the usage of rotable inventory. In view of today's time-based competition, effectively scheduling such services and managing rotable inventory and uncertainties are becoming imperative to achieve on-time deliveries and low overall costs. In this paper, a novel formulation for overhaul and repair services is presented where key characteristics, such as uncertain asset arrivals and operation processing times, and rotable parts are abstracted to model an overhaul center and multiple repair shops in a distributed framework to reflect organizational structures. Interactions between the overhaul center and repair shops are described by sets of coupling constraints across the organizations. Rotable inventory dynamics is formulated in terms of repair operation completion times and asset assembly beginning times to facilitate minimization of inventory holding costs through scheduling. A solution methodology combining Lagrangian relaxation, stochastic dynamic programming, and heuristics is developed to schedule operations in a coordinated manner to minimize total tardiness, earliness, and inventory holding costs. Additionally, penalty terms associated with coupling constraint violations are introduced to the objective function to improve algorithm convergence and schedule quality, and a surrogate optimization framework is used to overcome the inseparability difficulty caused by the penalty terms. Numerical testing results show that the new approach is computationally effective to handle rotable inventory and uncertainties, and provides high quality schedules with low overall costs for stochastic remanufacturing systems.Note to Practitioners-Overhaul and repair services for jet engines, helicopters, airplanes, are important segments of the remanufacturing industry, and are characterized by complicated disassembly, repair and assembly process plans, stochastic operations, and the usage of rotable inventory. In view of today's highly competitive business climate, effectively scheduling such services and managing rotable inventory and uncertainties are becoming critical to achieve on-time deliveries and low overall costs. In this paper, a novel formulation for overhaul and repair services is presented where key characteristics, such as uncertain asset

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Time-based competition and market globalization make it imperative for supply chains to have short and reliable order deliveries. This is difficult to achieve in view that activities of individual manufacturers are subject to various uncertainties such as unknown order arrivals and stochastic operations. Furthermore, delays of one manufacturer may propagate to it downstream manufacturers through precedence relationships. To stay competitive, it is critical to control variability and order lead-times across a chain, and to achieve delivering final products within specified target time windows with high probability. This is the key idea of achieving x-sigma delivery performance. In this paper, make-to-order supply chains with sequential workflows are considered. An effective solution methodology is developed to minimize overall order tardiness, earliness costs and delivery variability through effective scheduling and coordination. To accommodate new arrivals while fulfilling commitments of existing orders, a rescheduling approach is presented to generate high-quality schedules in a timely fashion. Numerical testing results demonstrate that the new approach is effective to schedule manufacturers across a chain to achieve the required three-sigma deliveries.

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Time-based competition and market globalization make it imperative for supply chains to have reliable product deliveries within customer required lead times. This may not be easy to achieve in view that manufacturing activities are subject to various uncertainties. Furthermore, a delay of one manufacturer may propagate to othen through precedence relationship. To improve delively performance, it is critical to reduce the variance of product lead times. Motivated by the six sigma quality movement, a variance COntroI technique is developed where lead time variances are accurately calculated and significantly reduced through effective scheduling individual manufacturers as well as coordinating across a chain with limited communication requirements. Numerical testing results demonstrate that the new approach is effective to schedule manufacturers on a supply chain to achieve on-time and reliable deliveries.