| This study examines the relationships between manufacturing lead time, planned lead time (PLT), and manufacturing performance in a multi-stage manufacturing using the Material Requirements Planning (MRP) system as a basis for planning and control. Three issues pertaining to these relationships are examined. First, the impact of PLTs on the manufacturing performance is examined. Second, the factors affecting an item's manufacturing lead time are identified. Two independent approaches are used to identify these factors, and to estimate an item's manufacturing lead time. Finally, these predictive models are used to prescribe PLTs.;Computer simulations are conducted to generate data. These data are analyzed in two phases. The first phase examines, using analysis of variance, the impact of PLTs on manufacturing performance. The second phase analyzes an item's manufacturing lead time through two independent approaches, and develops models to estimate its manufacturing lead time parameters. In the first approach, the entire manufacturing process is modelled as a queuing network. An approximation method for translating the factor settings in the simulation to job arrival and processing parameters is developed. The queuing network is analyzed, using the decomposition method, to estimate queuing time parameters. The application of queuing models is extended to multi-stage manufacturing by using the queuing time parameters to estimate component delay parameters. In the second approach, a regression analysis is performed using the data from the simulation. Four methods of prescribing PLTs are compared using a second set of computer simulations. Two of these methods are based on the two approaches to estimating manufacturing lead time, and the remaining two methods are based on the literature.;The major findings in this study are: (a) PLT is an important factor affecting customer service, but has a small effect on inventory levels, (b) lot size, capacity utilization, number of operations, and processing time variability affect queuing time significantly, (c) lot size an an item's level in the bill of material affect component delay significantly, (d) the fixed order quantity rule results in a lower inventory level, a better customer service, and a lower manufacturing lead time than the periodic order quantity rule, and (e) queuing-based prescriptions of PLTs reduce inventory levels without sacrificing customer service. |
