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Research paper : Toward the integrated optimization of steel plate production process (K. Nishioka et al.)−99−Synthesiology - English edition Vol.5 No.2 (2012) As a result, actions to deal with the problems of increasing in-process stock and of smaller order lot sizes resulting from the highly sophisticated product mix tended to wane. Under the circumstances where operation under chronically excessive in-process stock was accepted as the norm, the bottlenecks in the finishing processes surfaced when demand increased and delivery delay due to substantial prolongation of the manufacturing lead time occurred. Situations arose where adjustment of the amount of orders to be received was required, which used to be dealt with symptomatically by, for example, increasing the number of workers in the bottleneck process.4.2 Management innovations that enabled integrated optimizationIn order to realize production control that enables optimization at the level of each individual plant, there has to be a series of management innovations that makes it possible. During the many years when Japanese crude steel production stagnated, Nippon Steel continued its long-term efforts to streamline its management. During the 1990s, under the strong leadership of top management, it made innovations in terms of its organization/ management structure, aiming to fortify its competitiveness. The core innovations made were the individual product-type-wise management that contains the integration of production and sales,[10] and the drastic integration/ restructuring of organizations was realized by streamlining head office functions and compressing hierarchies.[11] The organizational reform at the corporate level effectuated in 1997 authorized middle management such as plant superintendents to make independent and centralized decisions on shop floor operations, giving them the opportunity to work as entrepreneurs. Kimitsu Works used to have an organizational structure where one department oversaw production scheduling etc. of the whole company and supported each division that manufactured individual products. However, as a result of the organizational restructuring, all the categories concerning the production of steel plates, of production scheduling, quality control and equipment maintenance that used to be overseen overall at headquarters were placed under the management of the Plate Mill. Under this new structure, the Plate Mill superintendent initiated the innovation of the control structure for plate production. Based on the understanding that it is integrated optimization at the level of individual plants that creates the power to maintain the product competitiveness for a long period of time, the management paradigm of the production control shifted substantially from the conventional system that aimed at enhancing productivity at the level of each facility to one that aims at shortening the manufacturing lead time through the curtailment of in-process stock. This was the start of the challenge to apply the lean production system developed in a pull-type industry to the plate manufacturing that is intrinsically compliant with the push-type industry.4.3 Actions taken by middle management on the shop floorThe rolling process greatly affects the quality and cost of a plate mill. Therefore, the superintendent, aiming first to enhance the rolling efficiency, worked on the development and application of a support model of production control. Then, to solve the predicted problem of insufficient capacity of the finishing processes that would occur once the rolling efficiency was enhanced, he worked on enhancement of the efficiency of each one of the finishing processes in addition to the bottleneck processes (flattening process, etc.). The finishing processes used to be positioned as subordinate processes to rolling and their equipment was maintained mainly based on the breakdown maintenance (BDM). However, the superintendent changed it to the total productive maintenance (TPM), under which the functions of equipment maintenance and manufacturing work together in unison, aiming to keep the equipment/ devices functioning properly whenever required.Furthermore, the optimization of plant management as a whole required a series of supporting activities by the staff related to the integrated optimization. Among all the problems, the reduction of in-process stock in the finishing processes works in opposition to the enlargement of production lot sizes in the preceding processes, and may become a short-term cost-push factor. This means that the reduction of in-process-stock in the finishing processes gives rise to problems that the efficiency enhancement of individual equipment alone will not solve, thereby requiring “Heijunka” leveling for allocating even process loads at the planning level. The designing of production lot sizes (material procurement design) is the responsibility of scheduling staff, but at the time, there was no system capable of conducting material design that took into consideration the even distribution of loads in the finishing processes. In order to solve this problem, engineers who were familiar with the shop floor operation and knowledgeable also in system development were deployed to the production scheduling group and a support system was developed for leveling the loads of finishing processes evenly from the perspectives of cost, efficiency and manufacturing lead time. Technical details describing the way in which the above was achieved in a time series are mentioned in the following chapter.5 Innovation in the production control system of the Plate Mill5.1 History of support system developmentProduction control schedule and schedule types are classified into the primary schedule (overall production), secondary schedule (reference production) and detailed schedule (order of manufacturing), and for each type, the planning elements are organized by the time scale of plan, units of scheduling and frequency of modifying the plan, product categories, and

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