Geleneksel üretim sistemlerinden tam zamanında üretim sistemine dönüşümünün tasarlanmasında simülasyon yaklaşımı
Başlık çevirisi mevcut değil.
- Tez No: 46297
- Danışmanlar: PROF.DR. ATAÇ SOYSAL
- Tez Türü: Doktora
- Konular: Endüstri ve Endüstri Mühendisliği, Industrial and Industrial Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1995
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 209
Özet
ÖZET Tam Zamanında Üretim felsefesi ile ilgili yapılan yayınlar incelendiğinde çalışmaların daha ziyade hipotetik (düşünsel) sistemler üzerinde yoğunlaştığı ve gerçek bir üretim sistemine bu felsefenin operasyonel seviyede uyarlanabilmesi için belli bir sistematiğe dayandırılan çalışmaların oldukça sınırlı bir düzeyde olduğu belirlendi. İşte bu nedenle daha ziyade bir ekip çalışmasını gerektiren böyle bir projenin, bir tez çalışması bünyesinde değerlendirilmesi ve değerlendirme sırasında oluşturu¬ lan modelleme sistematiğinin içerisinde simülasyon, mühendislik ekonomisi teknik¬ leri, karar verme tekniklerinden analitik hiyerarşik proses yönteminin kullanılması konuya getirilen yaklaşım açısından önemlidir. TZÜ1 e geçiş ile ilgili gerçekleştirilen faaliyetlerin tümü atölye düzeyindeki şartlara bağlı kalınarak gerçekleştirilmiş olup, belirlenen işletim şartlarının, firma yöneticilerine genel bir bilgi vermesi açısından önemli ipuçlarını içerdiği söylene¬ bilir.
Özet (Çeviri)
SUSVSIVSARY Simulation Approach in Designing a Conversion from a Conventiona! Manufacturing System to a (JIT) Just-în- Time Manufacturing System. Öne of the most significant characteristic of the second half of 20 th. century is the increasing competitiveness of market place as a result of rising trend on the amount of world class manufacturers. in this situation, industrial companies have to act vvisely and develop proper strategies to survive. The companies in automotive industry, which has a great share in the world of industry, should manufacture cheaper, high quah'ty products in short delivery times with flexible production systems in order to be able to meet the customers' changing needs. Obviously this is not possible with traditional production systems. in recent years, the renovvned successes of Japanese production ör inventory management approaches have created an interest in non-Japanese manufacturing environments. Öne of these approaches that has attracted more attention both from researchers and practitioners is the approach of just-in-time manufacturing systems with the ultimate goal of eliminating waste of sources that mainly comprises the inventory held at various stages of manufacturing. For this approach, companies should reorganize their traditional production systems according to principles of JIT. First of ali, with this type of production systems, it is possible to reduce the information flow between production areas and production control systems. Due to this fact, in a production area, workstations are so close to each other and necessity of completing the whole process in the production area before a feed back to production control center improves the eflectiveness of production control. The designing independent production areas from each other is the objective ceflular production system, and also majör steps in accessing JIT. Due to this subject, companies must change their layout from process oriented type to product oriented type. This implementation covers most aspects of the manufacturing function and necessitates majör changes in production control, quality control, process planning and manpower assignment. Potential benefits from an actual implementation of JIT, if done properly, include improved product quality, reduced inventory and higher productivity levels. Due to its effectiveness, several majör manufacturing.companies such as General Motors, Ford, Chrysler, General Electric, Hewlett Packard have adapted some parts of UT to their systems, but actually and originaüy, the JTT philosophies have flourished at Toyota Motor Company in Japan. Just-in-Time (JTT) production is a disciplined approach, ör philosophy, for improving productivity and eliminating waste. it is based on the cost-effective production and deHvery of only the required quantity of parts at an acceptable quality level and at the right time and place, whüe using mmunum facilities, equipment and human resources. Although JTT has proven to be an efficient production approach in Japan, the reported success is also attributable to a number of other factors including cooperation from the Japanese government, the Japanese management style and the cultural and social aspects of the Japanese work force, as well as the manufacturing system being utilized. The primary conditions \vhich are mentioned as being important for a JTT system are fallow..The Master Production Schedule needs to be stable for a period of at least several weeks into the future (i.e., four to six weeks for Toyota). This allows for the basic requirements of capacity and long lead time raw materials to be predicted; a necessity since there exists virtually no buffer stocks to allow for short-term changes in customer orders in quantity ör product mix..The use of standardized parts and processes must be emphasized. Product redesign, use of special options, and special orders must be kept to a mmin-mm. The products must be as standard as possible since the stability of the system is important..The manufacturing process should be modified to be as close to a repetitive manufacturing environment as it is possible. This may be accomplished through the use of more specialized machinery \vith minimal setup times, which, in turn, contributes to the stabüity of the day-to-day operations, an important requirements of a JTT system. Such a process modification is often accomplished by the implementation of Group Technology ör Fleable Manufacturing Systems (FMS)..The worker in a JIT environment is considered an essential element who contributes to the success of the system. Without buffer stocks, the worker should be capable of performing several types of jobs, \vith quality control responsibility and must be committed to the success of the system..Preventive maintenance programs must be thorough and cover ali critical machinery. Since parts are produced in small xquantities and only when immediately needed, the machinery used to produce them must be operable as soon as product demand is recognized. « Suppliers of raw materials must be brought into the production ör inventory system. in Japan, suppliers often physicaHy locate their operations very close to the plants that they suppty and are expected to make deliveries in small quantities several times a day. The purchasers make long- range commitments for particular supphers to serve as single sources. The purchasing company also provides a stable Master Production Schedule so that the supplying company can better predict its own production and capacity requirements. Production control system in the JTT phüosophy can be classified as a pull system. in a pull system, the production planning and control departments produce a production schedule only for the final production üne ör final assembly line. The other processes get information via an information system such as Kanban system.“Kanban”is a simple, visual control technique which is implemented as a part of a JIT production system. This manual system is used to authorize the production of required components and“pull”the units through the system just in time to meet the demand at each production stage. inventory level between stages is controlled by the number of Kanbans allocated. A Kanban card is used as a communication tool between two production stages. A Kanban is sent firom a workstation to the preceding workstation to initiate production of a unit ör a specified number of units. in an ideal pull production system, öne unit of inventory at each production stage is enough; but, this goal is not achievable in real manufacturing environments due to variations in demand and processing times. The pull system works backwards to not only include every production operation in the plant, but also incorporates the suppliers in order to:.Mmimize work-in-process inventory;.Minimize fhıctuations of work-in-process inventory in order to simplify inventory control;.Prevent ampüfied transmission of demand fluctuations from stage to stage;.Raise the level of shop control through decentralization; and.Reduce defects. The Just-in-Time production system is designed as a pull system in order to achieve these objectives. The JTT approach is especially attractive because cutting lot sizes triggers a chain of benefits including productivity, quality and plant improvements. Among the JIT productivity enhancements achieved by Japanese manufacturers are less lot-size inventory, less buffer inventory, less serap, less direct labor wasted on revvork, fewer indirect cost for interest on idle inventories, less space needed to xistore inventories, less equipment to handle inventory, less inventory accounting, and less physical inventory control, ali of which lower the input component of the productivity equation. At the same time, the output component will be improved, since sources of dekys and serap are removed. There has been considerable research in the area of JIT system management Although technical research on how to adapt JIT to Turkish models of manufacturing operations has not been reported in JIT related literatüre, a review of the relevant management literatüre reveals that certain conditions are commonly mentioned as being important for a feasible JIT system. Much of the published research has been devoted to theoretical investigations and studies with assumed data. Clearly, there is a need for real-life studies to better understand system behavior. A case study to apply JIT philosophy to a company that is a sub-contractor of the automotive industry will be presented here. The company vvhere the study is performed is öne of the suppliers to Renault, Ford, Tofaş and Toyota, ete. The company's majör field of apph'cation is to produce engine valves. Total number of valve types that have been manufactured is around 1300 and the company produces from 350 to 400 different valves each year. When the percentages of valves are taken into consideration, it can easily be said that öne type of valve have more than öne property. Table l Valve Properties Valve PropertyProduction (%) Bi-metallic29 Chromium plated80 Aluminized21 Fillet raachined49 Stem-blend machined2 Head-face machined19 Solution treated8 Seat hardened45 Tip-end relief2 Cut to length twice7 The steps in this study are separated into two stages:. in the fîrst stage, it is pointed out the usage of group technology for selecting the pilot production area to apply JTT principles instead of traditional production system in the work shop of the company. xii. In the second stage, to increase the benefit of production cells on the selected pilot production area, a series of simulation experiments using SIMAN simulation language is made. The reason of constructing a pilot production area in this study is to establish the product oriented production system with independent cells. However, the conversion from an existing job shop system to a cellular manufacturing system is a huge job. This system is a product oriented manufacturing type, that workers and especially machine groups are brought together to produce some kind of parts (part family) which have similar characteristics. Major advantage of cellular production systems, is the decrease in manufacturing lead time as a result of parallel processing. In other words, it means overlapped production with smaller lot sizes. However, in the case of, smaller lot size, manufacturing requires reduced setup time. Therefore modelling of the conversion from the job shop system to cellular manufacturing system is concentrated on setup reduction and hence lot sizes. However, cell interactions by means of exceptional elements can deteriorate the effectiveness of overlapping operations. This can be eliminated by machine duplication or by existing machines in the shop.. Generation of the machine-parts incidence matrix regarding the first 50 parts, constituting the 75 percent of the total production according to ABC analysis is the first step of the study. There are in total 42 different machine types in the system. Moreover, 216 different types of processes are eliminated to construct the final 5 1 types to simplify the system. Most of the processes eliminated, are the ones like heat-treatment, clearing, marking, etc. After analyzing the different group technology clustering method regarding the machine part incidence matrix, a technique that gives the least exceptional elements, best filled cell, minimum transporting intercell for the valve production system is selected. By using the clustering method, the system is divided into major production cells. One of them, which produces the majority of 75 percent of annual production is selected as a pilot cell for JIT implementation. In the second stage, a simulation model is developed using SIMAN for cellular manufacturing systems that assume a multi level, multi product and unconstrained labor production environment. The model that is developed has the following properties.. The model is concerned with the pull of parts from workstations according to the continuous review system.. Modelling of the machine breakdown is done by preempt block function in SIMAN.. The developed model is concerned with the investigated system. For this reason, the model is not generic applicability. xniThe problem-specific and the general results obtained from the experiments which have been designed in Section 5.7 are as follows:. When production transfer lot size (bin capacity) is decreased, lead time and lead time variance reduction are possible due to parallel processing within cells.. The elimination of imbalance between me machine operation times has crucial importance in reducing the lead time variance.. lh transformation to cellular manufacturing, the calculation economic lot sizes gets less importance as the cycle time decreases.. The increase in the number kanbans in bottleneck resources does seen to have not any effect on smoothing the production flow.. The reduction in heat treatment operation times, if technology permits, have impact on lead time reduction. It is observed that, if the furnace capacity can be doubled, the targeted three day cycle period, can be easily achieved.. Since automatic machines in cells 2 and 3 have high processing rates, in those cells and especially at those machines which follows the automatic machines there occurs bottlenecks due to bulking queues thus decreasing the effectiveness of automatic machine tools. In the JIT environment, the sensrvity of Pull system, as a production control technique, to the machine breakdowns can be summarized as follows: Along the production line, the negative effect of machine breakdowns at the downstream stations of the line is more than the ones in the upstream stations. The negative effect of breakdowns in the downstream stations may be reduced by the use of small bin capacities, hence lead to a more stabilized system. On the other hand, the negative effect of breakdowns in the downstream stations may be eliminated by the use of larger bin capacities. This positive effect depicts itself in lead time variance decrease. xiv
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