In this study, we consider the General Lot Sizing and Scheduling Problem in single level capacitated environments with sequence dependent item changeovers. Process industries may be regarded as suitable application areas of the problem. The focus on capacity utilization and intensively time consuming changeovers necessitate the integration of lot sizing and sequencing decisions in the production plan. We present a mathematical model which captures the essence of cases in the most generic and realistic setting of the problem. We discuss the impact and validity of some of the assumptions commonly encountered in the related literature. We also represent the problem using an alternative formulation and attempt to enhance the formulations with the use of some additional inequalities. Finally, we develop a heuristic by restricting the number of possible changeovers. Computational results are discussed.

In today's competitive manufacturing environment, companies are constantly looking for ways to improve. Because of this, many companies are striving to become "lean" by implementing lean manufacturing, which is a difficult process. To aid in the implementation of lean manufacturing, simulation was used to reduce the trial-and-error period of lean manufacturing and find to optimum approach to implement the lean manufacturing principle. In this research, a case study of implementing level loading of the production schedule for BullFrog International, L.C. will be examined. To make it possible to implement level loading, the thermo-former machine at the beginning of the operations was improved to allow quick changeovers. The changeover time was reduced by 60% and with a few additional changes changeovers could be completely external. In order to be able to conduct simulation experiments to find the optimum production schedule, cycle times were gathered for each operation and a simulation model was developed of BullFrog International, L.C. current manufacturing operations. Historical data was gathered of previous month's sales orders and orders were divided into three different groups. Group 1 the spa orders are roughly 50% single-pump and 50% double-pump, group 2 the spa orders are roughly 60% or more single-pump spas and group 3 the spa orders are roughly 60% or more double-pump spas. Using historical data, level loading production schedules were developed using lean manufacturing principles by reducing lot sizes to the smallest possible and still preserving the correct ratios. All of these suggested production schedules were tested with the simulation model and through various experiments, the optimum production schedule were determined. The optimum production schedules were implemented and the results were recorded. The results were an average throughput increase of 49.1% in group 1, an average throughput increase of 58.7% in group 2 and an average throughput increase of 58.7% in group 3. These results support the hypothesis that level loading will increase throughput in a complex manufacturing system where there is a high mix and low volume production schedule. The results also support the hypothesis that the trial-and-error period was reduced by the use of simulation.

Volvo GTO is one of the strongest brands in the truck industry, with a long and proud history of world-leading innovations. The factory in Skövde produces diesel engines of various sizes to Volvo GTO. The project has been carried out on the processing part of grovdel crankshaft. Where the objective was to construct a simulation model that reflects flows 0, 1 and 2 on the crankshaft grovdel order to produce the best driving style for the size of the batches and sequences, focusing on PIA, between the stock and conversion-up times. A theoretical study intervention gave knowledge to the methodology to ensure that the data is collected and processed correctly. The data were collected in an Excel document, which was integrated with the simulation model for an overview and adjustments would be possible. The simulation program, Siemens Plant Simulation 12 used in the construction of the complex model of the three flows, which where verified and validated against the real flows. Optimization on the simulation model was made with a high and a low demand for crankshafts. Several objects were taken into consideration as: minimal waiting processing Findel, minimal setup time and minimal total-PIA from a truly viable perspective. The optimization showed a possible production planning in order to best be able to run such large batches as possible with reduced readjustment time and for delays of production in processing rawflows to not occur in the refined flow. For maximum capacity in the company there are two different optimal solutions one solution focused on reducing setup time and the second solution to minimize the number of additional production hours per week. Discrete simulation of production flows are being used to support production planning and simulation model is created for the continued use of the Volvo GTO, either in simulation group or future researches and theses in collaboration with the University of Skövde. The project objectives were achieved with good results and resulted as a standing basis for future planning of batches and sequences of processing crankshaft Volvo GTO.