Research On Pull Control Strategy Of Job Shop

To cater to consumers personalized requirements and meet the rapid change of market,enterprise mode of production gradually shift from mass production to flexible multi-product and small batch production.The Pull control strategy takes obvious advantage to reduce the production cost,shorten production cycle,reduce the wip inventory,and suits for high repeatability,steady production environment.However,in the environment of multi-product,due to the complexity of the problem between manufacturing technique and every production process connect often cause congestion on the manufacturing process production line,then the bottleneck accrued.Making the advantages of pull strategy is difficult to fully play.So this thesis decided to study the pull control strategy considering the effect of bottleneck in the manufacturing system.In order to identify the bottleneck resources in the production process,firstly this thesis analyzes and compares the existing main bottleneck identification methods,and establishes the bottleneck identification model of multi-product processing by integrating the machine utilization rate and the average waiting time of the products.On the based of analyzing and summarizing the existing Push and Pull production control strategy(PCS),and then put forward a "double closed loop" control strategy on the strength of Push and Pull control strategy combination(CK-DBR control strategy),integrating pull control strategy and constraint theory together and applied them to the workshop production control process.Oriented multi-product production process,proposed a kind of push and pull control strategy which combined with CONWIP(Constant Work in Process)control strategy and DBR(Drum-Buffer-Rope)technology.The inner ring is a DBR control structure triggered by the internal bottleneck of the system.The outer ring is a CONWIP control structure triggered by the actual demand.By using the internal and external structure of the "double closed loop" in order to reduce the work-in-process inventory and shorten the average production cycle-time while maintaining the flexibility of the capacity,high productivity and utilization of the equipment.In order to verify the validity of the bottleneck model and control strategy,this thesis uses discrete event simulation technology to complete the system simulation.Applying queuingnetwork model established Push,Kanban,CONWIP and CK-DBR control strategy mode respectively and described the running mechanism of the four kinds of control strategies.For further,this thesis against with multi-product job scheduling problem,simulation research based on ExtendSim platform,selecting single path and mixed flow path as the object respectively,comparison and analysis of the different control effects in four modes of push,Kanban,CONWIP and CK-DBR control strategies and discussing the order fluctuations,rework fluctuations,fluctuations in the position of rework and the change of the Bottleneck for the impact of the scheduling results.The simulation results show that the effectiveness of the pull control is higher than the push control,and then the CK-DBR control strategy which this thesis proposed work better than the other three control strategy in term of reducing work in process inventory,shorting the average production cycle-time,improving machine utilization and so on.In addition,the CK-DBR control strategy in reducing the impact of fluctuations in the production process also has a satisfactory performance,and have a beneficial to smooth operation of the system.