Research On Order Release And Scheduling Methods Of Make-to-order SMEs Based On Work Load Control

After more than 30 years'reform and opening-up to the outside world, China's small and medium-sized manufacturing enterprises developed rapidly and become one of the key factors of national economic and social employment. However, in recent years the rapidly changing global competition background and financial storm brought a sharp change of Chinese SMEs to make all the existing problems becoming obvious. Increased demand for customized products has led to a large growth in the number of MTO companies, leading to greater competition amongst these companies and the increasing environmental risks of uncertainty and dynamic. The traditional production plan and control strategy, including MRP, TOC, JIT/Kanban are not adapt to the Chinese SMEs faced the uncertainty of the MTO's dynamic environment characteristics. Workload control(WLC), one of the production planning and scheduling methods put forward by western scholars, by controlling and balancing machines' workload, can effectively reduce the work-in-process inventory, improve the performance of the delivery order, and well satisfy the non-repetitive and highly customized products during the dynamic and uncertain production environment.The framework Based on WLC control provides theoretical basis and practical application results for the order release and scheduling problem of small and medium enterprises, but still has several disadvantages such as follows:â‘ Most researches are based on such assumptions that the production routing with a MTO context acts as pure job shop characteristics, however this is unlikely to be the case in reality.â‘¡Existing research did not pay much attention of rush orders, but the release and scheduling strategy of rush orders is one of the key problems under MTO production situation.â‘¢Most researches assume that each station has a single capacity, but in the actual production scene, the processing center tends to have multiple devices or cross-function machines, constitute the optional flexible production capacity.â‘£Most order release and scheduling strategy based on WLC architecture using only local dispatching rules to assign the priority of orders in order pool and work floor, which can't reach global optimal, also can't guarantee high priority order must be completed on time.In this dissertation, practice problems which are urgently need to be analyzed and solved related to order release and scheduling are extracted from china's MTO SMEs, then heuristic rules and optimization algorithms are put forward to give solutions to such problems, simulation experiments were carried out to test the feasibility and validity of the proposed methods, and this will provide theory method guidance for the implementation of production planning and control logic architectures of small and medium-sized enterprises in China based on work load control.The main content of the dissertation is as follows:(1) two new order release methods were proposed to better implement order's accurate release into shop floor under directed-products-routing environment, and the overall performance of the proposed two methods have different environment applicability, MTO enterprises can select appropriate order release method according to their own circumstance, so as to realize reasonable WIP control and on-time delivery.(2) Recognition coefficient of rush orders includes of due-date emergency degree factor, tardiness punish factor and important degree factor of customers are analyzed and defined, then two new release methods of rush orders and one dispatching rule is proposed, simulation experiments were carried out to test the effectiveness applicability of the proposed methods.(3) Flexible capacity distribution problems of different processing time are studied and discussed, The result shows that under the uncertain dynamic production situation, the history of the system state is not a key factor for decision-making, but the current state of the system and the feature of new orders will bring significant influence on the performance of the system. Threshold adjustment strategies of flexible capacities combining with the existing of products' mainstream routing are discussed, and the performance of two dispatching rules includes of FIFO and SPT are compared.(4) A genetic algorithm combined with local search is proposed to solve the FJSP with Makespan criterion. During the local search process, Logistic chaotic sequence is adopted to explore better neighborhood solutions around the best individual of the current generation. Then bi-objective dynamic flexible job-shop scheduling problem is constructed, two rescheduling strategies include of stable rescheduling and rolling rescheduling are proposed to minimize the makespan and tardiness objectives. Representative flexible job shop scheduling benchmark problems are solved in order to test the feasibility and validity of the proposed algorithm, the experiment result shows that in stochastic dynamic production environment, decision makers should not have to be limited to the original plan, scheduling should be quickly adjusted and optimized with the dynamic environment.(5) Order release & scheduling experimental architecture is designed and realized based on work load control, two new heuristic scheduling methods, include of FRFA(First ready first arrange) and APS&PT(average process slack & processing time) are proposed to compared with the rescheduling algorithm presented in above, the experiment result shows that the global optimization scheduling algorithm presents obvious advantages when the system tends to be crowded than the heuristic methods, especially when tardiness performance is involved, enterprise should consider whether to invest in the development of optimal scheduling module in light of its own environment characteristics.