بررسی اثر اندازه کانبان در سیستم های ساخت فقط از نظر زمان

Setting kanban sizes is one of the first decisions that users of kanban system must address, yet researchers have largely assumed kanban sizes to be given. This paper investigates the effect of varying kanban size on the performance of just-in-time (JIT) manufacturing systems. Two types of JIT production systems, the Pull-type and the Hybrid-type are analysed using computer simulation models. The performance measures considered simultaneously are the fill rate, in-process inventory, and manufacturing lead time. Parameters such as demand rate, processing time, and kanban size are taken into consideration, thereby finding the possible solutions of the kanban size that can be employed to achieve the most favourable conditions for production. A favourable condition usually refers to the ability of the system to produce finished goods at a shortest possible lead time, which the customers are always demanding for. Both the single product and multi-products manufacturing environments are investigated. With reference to the analysis, for a single product, as the kanban size increased, the fill rate decreased, whilst with both the in-process inventory and the manufacturing lead time increased. Generally, for multi-products manufacture, it was observed that as the kanban size increased, the fill rate increased with a decrease in the manufacturing lead time. However, for multi-products the interaction between the manufacturing lead time and the fill rate is discussed in depth in this paper.

In many high-tech manufacturing enterprises, the just-in-time (JIT) philosophy has been adopted widely in their production system to minimize the level of inventory. Prior to making any comments on the pros and cons of the application of JIT theory in manufacturing situations, it should be defined clearly. The American Production and Inventory Control Society (APICS) defines JIT as “In broad sense, an approach to achieving excellence in a manufacturing company based on the continuing elimination of waste (waste being considered as those things which do not add value to the product). In the narrow sense, JIT refers to the movement of material at the necessary place at the necessary time. The implication is that each operation is closely synchronized with the subsequent ones to make that possible”. From the narrow sense, the underlying principle of JIT manufacturing philosophy is to produce the right quantity at the right time with the right quality level. To produce the desired quantity that both internal and external customers demand, at the time that they demand it, the kanban manufacturing system would be the most appropriate. “Kanban” is the Japanese word meaning for a card. In JIT, production is triggered by a kanban signal, which usually comes from the customer order or the master production schedule, the signal then flowing backwards via each work centre. Each work-in-progress (WIP) container is attached with a kanban, specifying the details of that particular WIP such as product name, part code, card number, batch number, lot size, due date, etc. By implementing JIT concepts in manufacturing, many of the practitioners experience advantages such as shorter lead times, fewer inventories, and higher quality. To achieve this specific goal, numerous parameters in optimizing the conditions for the production system should be determined carefully. Amongst those, the size of the kanban is a very obvious one to be concerned. Generally, a large kanban size implies a higher inventory level but a shorter lead time benefited by less frequent machine set-up time. The specific aims of this research paper on JIT systems are as follows: 1. An investigation of the influence of kanban size on the performance of JIT production systems, including both Pull and Hybrid systems. 2. An examination of the effect of kanban size on the interaction of the fill rate and the manufacturing lead time in a JIT production system. 3. With reference to the above findings, to determine a feasible kanban size to optimize the performance of production in terms of fill rate and manufacturing lead time.

Manufacturers are pursued to provide better customer service in today’s competitive industry. However, the constituents of better customer service are implicit. This paper defined the fill rate in a simpler way for the ease of investigation. Through simulation, production planners can improve their understanding of the system performance of JIT manufacturing systems. This paper describes a practical approach to determine the optimal kanban size via simulation, with one of the objectives of being to achieve 100% fill rate. In a single product manufacturing systems, although the trends of the performance measures for these two systems (i.e., Pull and Hybrid) are similar, the values of the performance measures differ significantly (see Fig. 6, Fig. 7, Fig. 8, Fig. 9, Fig. 10 and Fig. 11). The impact of increasing the kanban size on various performance measures are summarized as follows: In a multi-products manufacturing system, the results of increasing the kanban size on various performance measures are summarized as follows: With reference to the research findings in the multi-products Hybrid system, a larger kanban size often leads to the result of higher average fill rate, and lower average manufacturing lead time. Contrarily, a smaller kanban size needs more frequent machine set-up, thus the non-productive time is increased significantly. In other words, for a larger kanban size situation, the productive time in normal working hours can be maximized, and the factory may probably benefit from savings such as the reduction of labour hours in overtime production, and energy. However, a fill rate of over 100% is not desired. Therefore, the kanban size needs to be controlled within limits. The main advantage of a smaller kanban size is the lower level of in-process inventory. From the viewpoint of a manufacturer, inventory means money. Smaller kanban size facilitates a faster movement of materials between stations. Therefore, the manufacturing resources are easily free from production, which may help in other manufacturing activities such as Research and Development projects. However, a 100% fill rate is not easily achievable when a smaller kanban size is implemented. In fact, reducing the kanban size to achieve lower inventory level, and simultaneously retaining the full customer satisfaction (i.e., 100% fill rate), may not be easily implemented in some real situations. This paper examined two suggestions to reduce the size of the kanban without damaging the customer satisfaction, namely, reduction of the machine set-up time, and breakdown of customer order size. The former may require capital investment in equipment, therefore, breakeven analysis should be carried out for detailed investigations of the possibility in terms of sales revenue. However, the latter requires agreement between the manufacturer and the customer, which may not be an advantage, since it may cause the loss of sales, and disturbance of the business schedules of values dear customers. Hence, the decision of the size of the kanban should be made based on the trade-off between inventory level and better customer service.