Essays on lot scheduling in production and disassembly

Abstract: This Licentiate Thesis is concerned with the lot scheduling of multiple items on a single facility, both in production and disassembly. The thesis contains an introductory overview and four research papers, entitled: I. Lot Sizes in a Capacity Constrained Facility – A simulation Study of Stationary Stochastic Demand II. Determination of Safety Stocks for Cyclic Schedules III. Lot Scheduling in a Disassembly Factory IV. Cyclic Lot Scheduling with Sequence-dependent Setups: A Heuristic for Disassembly Processes In paper I, the applicability of two deterministic lot sizing-procedures is tested in a simulation study when demands are stochastic. The paper shows that a deterministic model can be used in a practical situation where the demand rate is stationary stochastic, but the models must be complemented by a decision rule; which item to produce and when to produce it. Paper II develops a planning and control model for determination of safety stocks for cyclic schedules, both with and without idle time. The paper shows how the variance in demand during lead time can be estimated, which is used for determination of safety stocks and order-up-to levels. For systems with idle time, a control model for the decision to produce next item or idle the facility is presented. Paper III is an introduction to lot scheduling in disassembly processes. The performance of two different lot scheduling policies for the disassembly of multiple items is tested in a simulation study when setup times are sequence-dependent. It is concluded that cyclic schedules are preferable in disassembly processes with sequence-dependent setup times. In paper IV, a lot scheduling heuristic for disassembly processes with sequence-dependent setups is developed. The heuristic determines disassembly frequencies and the profitable use of the facility and results in a cyclic schedule.