SPC-based Optimal Analysis And Control For Lead Time

The assumptions of traditional lead time optimal control models are very strict, which didn't consider the variety of product types and batch of orders, the maintenance process, and the control problem of lead time. New methods are explored and investigated for the above problems.First, this dissertation introduces the research background, the review of time between events control chart and lead time estimation, and then introduces the design principle of Shewhart control charts and time between events control chart and the basic theory of lead time modeling.Thereafter, the time between events control chart is used to monitor lead time, and method of designing lead time control chart is proposed. The method of designing lead time control chart is developed individually based on the single stage manufacturing and assembly systems, multistage manufacturing and assembly systems and the complex manufacturing and assembly systems in which the distribution function of lead time is unknown. Moreover, two special queueing systems based on the failure rate of products and the batch arrivals of multi-type of orders are investigated. The two types of manufacturing and assembly systems are optimized by using the total probability decomposition and Markov process method, and the mean service time, the mean delaying time, the mean waiting time for different types of orders or products are obtained. Then, two multi-objective optimal control problems are developed, and the most optimal lead time is obtained by using Goal Attainment Method to solve the two multi-objective optimal control problems. The distribution function of service time, waiting time and lead time are obtained using some approximate estimation methods, and the lead time control chart for multi-type of orders which considered the failure rate of products and the batch arrivals are estabilished.Numerical examples show that the parameters which affect the lead time can be well optimized and the most optimal lead time which is obtained using the above lead time optimal control models is accurate and can be well monitored by the lead time control charts. It will be a good instruction to the real production.