Research On Time Buffer Control Method Based On DBR For Remanufacturing

At present, with economic development resource shortages, environmental pollution problem is being gradually revealed and consciousness of people's environmental protection and conservation is enhancing. The substantial eliminated End-of-Life products each year is an important reason for resource waste and environmental pollution aggravation. Therefore, many countries are beginning to require manufacturers responsible for product life cycle, especially the recycling of End-of-Life products. And because of its great significance in economy, society and environmental protection, remanufacturing is beginning to emerge, and accepted by more and more enterprises.Different from traditional manufacturing, there are a series of uncertainties in the whole process of remanufacturing and uncertainties of routing and processing time a major problem that manufacturers are facing. The theory research and practice exploration at domestic and abroad has proved that time buffer is an effective measurements that Drum-Buffer-Rope (DBR) method applies to achieve production planning and process control. Under the circumstance of many uncertainty factors existing, DBR time buffer method is more superior than MRP and JIT in improving production performance. But due to the research on DBR time buffer mainly focus on manufacturing system, so there are limitations existing in traditional DBR in solving remanufacturing uncertainty problems in buffer location determination, buffer size determination and buffer control mechanism.To develop the method that is suit for solving remanufacturing uncertainty problems, a time buffer model based on DBR was established by analyzing DBR method in consideration of the effect of three stochastic factors including routing and processing time uncertainties, machine failures rate and maintenance rate. Furthermore taking engine remanufacturing system for example and applying simulation methods to verify the model. Simulation results show that appliance of the control method enables resource utilization of bottleneck increased, average WIP in front of bottleneck and total WIP decreased and system productivity increased, therefore the aim of time buffer control to weaken the negative effect by uncertainties is attained.Dissertation includes five chapters and two key problems to be solved: developing a time buffer control method based on DBR and applying example to verify the validation of the method. The specific contents are as follows:Chapter 1, the introduction. The background, purpose and significance of this research are introduced in brief. The current research status in domestic and foreign countries, research contents and idea are introduced in this chapter, too.Chapter 2, the summarization of theory of constraints and DBR control method. The chapter is theoretical foundation of the research. The control thought, content and steps about TOC and DBR technique are introduced systemically.Chapter 3, time buffer control method based on DBR. Based on current research on DBR and in consideration of the effect of three stochastic factors, time buffer control method based on DBR is developed. There are three steps including time buffer location determination, buffer size determination and control mechanism development. The aim of this research is to lessen the negative effect on remanufacturing system by applying the control method. Firstly, it determines systematic bottleneck, therein the buffer control location using simulation method and queue length as evaluation index. Then in consideration of the effect of three main stochastic factors including routing and processing time uncertainties, machine failures rate and maintenance rate in front of bottleneck resources, time buffer size determination model is developed. Lastly, it can monitor on real time systematic bottleneck and operation situation under the above uncertainties and control speed of putting material by changing controllable input variable BT using simulation method to obtain different systematic performance. Optimal BT value is obtained by comparing the simulation results.Chapter 4, case study. The main content of this chapter is through end-of-life engine remanufacturing case to apply the buffer control method put forward above in engine remanufacturing system to verify the effect.Chapter 5, the conclusion which summarizes the main research and also analyses the problem requires further research.Innovation of this dissertation is as follows:1. On buffer site determination, system simulation method is used to identify bottleneck in order to determine buffer location accurately. Due to considering the effect of three main stochastic factors including routing and processing time uncertainties, machine failures rate and maintenance rate in front of bottleneck resources, the limitations that stochastic factors can not be considered fully and quantified, which simulates actual system characteristics and determines bottleneck.2. On buffer size determination, time buffer determination method fit to remanufacturing system is put forward by introducing modified coefficientα.3. By developing buffer control mechanism, the aim of alleviating the negative effect of stochastic factors on system at correct site, with proper buffer size and through effective control mechanism. The research status that buffer site, size and control mechanism is isolated is improved. A suit of complete time buffer method based on DBR is developed to solve the uncertainty problems in remanufacturing system.