Research On Material Flow Control Method In Job Shop Based On Shifting Bottleneck

With the development of economy and productivity, the market and customer demand becomesdiversification and individuation gradually, which makes the production mode change fromsingle-item big-lot to multi-item small-lot. The influence of various uncertain factors in job shop onthe material flow increases as the production mode changes, which leads to severe challenges for thecontrol of material flow. Although TOC control mode can enhance the synchronism betweenmaterial flow and production pace by controlling the key bottleneck, traditional TOC mode can notadapt the uncertain production environment with bottleneck shifting. Therefore, this dissertationproposes and researches the control method of the material flow under uncertainty with thephenomenon of the shifting bottleneck.Firstly, the literature review of the related research field about material flow control issurveyed. The characteristics of production environment under modern production mode is analyzed,then the difference between the material flow control method under modern production mode andtraditional TOC control method is indicated. It shows that the identification and prediction of theshifting bottleneck is the premise of the material flow control.Then, focusing on the core problem of matrial flow control under uncertainty, the identificationand prediction of the shifting bottleneck, the matrial release, the route of matrial flow and thestability of the material flow are studied. The content is as follows:1) Based on the concept of the material flow and the definition of the shifting bottleneck in jobshop, the digitalization method of the uncertain factor which cause the bottleneck shift is proposed.Using Markov chain and neural network to analyze the coupling relationship among the uncertainfactors, then establish the integrated bottleneck measurement system including bottleneck index,bottleneck shifting index and the bottleneck sensitivity index, in order to identify and prodict theshifting bottleneck in job shop under uncertainty.2) According to the bottleneck status of each manufacturing unit, bottleneck shifting trend andthe number of the bottlenecks, a control method of material release based on the shifting bottleneckis proposed, which includes the control of the raw material input and the control of the transfer lotand lead time. Aming at the control of raw material input, WIP upbound of the bottleneck unit, theWIP upbound between bottleneck units and the WIP target value of upstream unit is presented as thecriterion of the material input. Aming at the control of the transfer lot and lead time, adopting thebottleneck index and the bottleneck shifting index to represent the pace of WIP flow, establish thesetting model of the transfer lot and lead time of which the objectives are minimizing thenon-value-added processing time and minimizing the difference of the bottleneck degree betweenthe adjacent manufacturing units, and use the particle swarm heuristic to solve this model.3) Based on considering the influence of the shifting bottleneck on the optimization of materialdistribution route, use the bottleneck index and the bottleneck shifting index to indicate the priorityof material distribution of each manufacturing unit, and provide the punishment cost if violate thepriority during the distribution route optimization. Hence, the objective of the established model oftime-varing material distribution route optimization is minimizing the total distribution costincluding the transportation cost and the punishment costdue to the violation of distribution priority.In order to guarantee that the material in the vehicle is distributed totally before the vehicle comesback to the distribution center and to avoid unnecessary distribution sub-route, suppose the condition that the vehicle haven’t to be loaded fully and material can be distributed to one manufacturing moretimes, which can enhance the distribution productivity and decrease the distribution cost further.Then, a greedy-based genetic algorithm is presented to solve the proposed optimization model.4) On the basis of differentiating the concept of the stability and roubustness of the materialflow, take a single machine shop as a special case to build the staility control model of the matrialflow under uncertain processing time and propose two heuristics to solve this NP-hade problem.Then generate the model and the result from a special case (single machine job shop) to the generalcase (multi-machine job shop) and present two control policy for multi-machine job shop—thecontrol policy of the bottleneck unit and the control policy of the upstream unit of the bottleneck.Further, according to the case study, analyze and compare the adaptation condition of two controlpolicies and the results shows that the two control policies can help to hedge the bottleneck shift andreduce the difficulty of the matrial flow control.