Tam zamanında üretim sistemlerinin maliyet analizi
Başlık çevirisi mevcut değil.
- Tez No: 75166
- Danışmanlar: PROF. DR. ETHEM TOLGA
- Tez Türü: Yüksek Lisans
- Konular: Endüstri ve Endüstri Mühendisliği, Industrial and Industrial Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1998
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Endüstri Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 155
Özet
ÖZET Klasik yönetim tarzlarının günümüzün ağır rekabet koşullarında yetersiz kalması, organizasyonları yeni yönetim sistemlerini uygulamaya teşvik etmektedir. Tam zamanında (JIT) sistemi bu koşullarda en çok tercih edilen sistemlerden biridir. JIT, hem üretim hem de servis sektöründe başarıyla uygulanabilen bir sistemdir. JIT için literartürde birçok tanımlama yapılmıştır. Hepsinin ortak yönü JIT'in organizasyondaki israfları elimine etmeye yönlendiren, kaliteye, çalışana önem veren ve müşteri odaklı bir yönetim sistemi olmasıdır. JIT üretim yönetim prensiplerine göre sadece istenen miktarda, istenilen kalitede ve istenilen zamanda üretim yapmak ve envanter, gereksiz taşıma, bekleme vb. ürüne müşteri açısından değer katmayan tüm aktivitelerin yok edilmesi gereklidir. Günümüzde müşterilerin sadece fiyata değil kaliteye ve zamanında teslimata da önem vermesi bu sistemin kullanımım zorunlu kılmaktadır. Bu sistemin kullanılmadığı ortamda müşterinin beklentilerini tam olarak karşılayabilmek ancak yüksek maliyetlerle mümkün olacaktır. JIT kavramı ilk olarak Toyota Motor şirketinin başkanı Taiichi OHNO tarafından geliştirilmiştir. A.B.D.'de büyük sanayi devlerinin Japon şirketleri ile girdikleri yarışta büyük pazar kayıplarına uğramaları bu sistemin gündeme gelmesini sağlamıştır. JIT sisteminin en önemli unsuru zamandır. Tüm aktiviteler zamanında, bir uyum içinde ve su gibi akan bir sistemde gerçekleştirilmelidir. Bunu sağlamak için organizasyondaki problemlerin bulunup kökten çözümlerin üretilmesi ve uygulanması gerekir. Envanter organizasyonlarda problemleri gizler. Dolayısıyla envanterin düşürülmesi ile problemler birer birer ortaya çıkacaktır. JIT sistemini uygulamayı düşünen organizasyonlar kısa dönemli değil uzun dönemli yatırımlar yapmalı ve çalışanlarında katılımın sağlanması gereklidir. Envantere yatırılan para JIT'e göre israftır. Bitmiş ürünün stokta bekletilmesi fırsat maliyetlerine ve fiyatların artışına sebep olacaktır. Bu da firmanın rekabet gücünü azaltacaktır. Tezin birinci bölümünde JIT sistemi ile ilgili genel bilgi verilecektir. İkinci bölümde JIT sisteminin tanımı, gelişimi, yararları ve uygulamaya geçirilebilmesi için gerekli çalışmalardan genel olarak bahsedilecektir. Üçüncü bölümde JIT envanter yönetimi prensipleri ile ilgili açıklamalar yapılmış ve geleneksel ekonomik sipariş miktarı hesabının JIT ortamında sipariş maliyeti, elde bulundurma maliyeti kısıtı altında ve enflasyonlu ortamlarda kullanılabilecek şekilde geliştirdiğimiz ekonomik sipariş miktarı modelleri ve örnekleri gösterilmiştir. xi
Özet (Çeviri)
SUMMARY Just In Time is an approach which covers a wide range of techniques and considerations. The subject of JIT means many things to many people. Some feel it is an approach to production planning and control; to others it is a methodology to achieve manufacturing excellence; to still others it is a philosophy to guide everyday work activities; some businesses even view JIT as a winning strategy in the highly competitive marketplace of the 1990s. All businesses know that when a winning strategy comes along, out of competition, it must be used to win, or have it used against you and lose. JIT is well organized and respected by all as a winning strategy, methodology or approach. The lack of willingness (mostly because of lack of information on the subject) in the 1970s to use JIT has forced the US to play catch-up in the 1980s. Much of the JIT implementation in the 1980s has only moved US industries closer to a state of parity with the Japanese and other foreign competitors who use JIT. Much of this work centered on imitating what the Japanese do in Japan in hopes of making it work in the US Obvious differences between Japanese and US production philosophies, such as the US orientation toward the use of computer technologies, have offered some challenges to those US managers who have been trying to integrate JIT. Combining the 1980s experience with JIT in the US and recent research on how to go about integrating JIT has now poised US operations to extend JIT philosophy by making it a unique America philosophy. JIT, TQC and TPM are replacing the over complex methods of the past in which a high level of waste is permissible. The accent now is on flexibility and process layouts are being replaced by cells and flow lines manufacturing production families. Shorter production runs and fast changeovers are also required, with maintenance now being more important than ever before. Workstations are moved closer together in distance and time to cut down flow distance and to involve operators in problem solving. In a new approach, manufacturability and quality are designed into the product. Expensive buffers stocks are replaced by frequent, small deliveries of supplier-certified quality parts. Kanban or better still visual signal systems are used to pull parts only as required. Contrary to popular belief, cost, quality, time and flexibility are not in opposition. In JIT production, the causes of stoppages and slowdowns are recorded and the data so generated should be put to use in order to get the best from the system. By using JIT, a few companies have achieved a five-to ten fold reduction in lead times. In the JIT environment, computer support is not as vital as in job-lot manufacturing, where production and inventory control is crucial to high xiiperformance. Indeed, one can envisage computers being used for major event planning only every few weeks. The waste is found in conventional approaches to quality, design, purchasing, job assignments, plant configuration, equipment selection, maintenance, scheduling, accounting, product-line development, material handling, material control and shop- floor control. The waste is found and the interested in JIT is appearing in nearly all manufacturing industries throughout the world. There are still misunderstandings of JIT's objectives. For one thing, there is too much spending on equipment without regard for the flexibility of the plant. There also are some fundamental questions and issues to be resolved, such as whether to throw out or patch up state of the computer-based systems of inventory and shop-floor control (such as MRP). JIT is a manufacturing philosophy, a philosophy of eliminating waste in the total manufacturing process, from purchasing through distribution. If this philosophy is properly implemented, JIT enables a company to develop manufacturing into a strategic weapon. Too often since JIT came to America to America's shores, companies have used ht philosophy only to cut costs and attain greater profits. This is a short term view of JIT's potential and will like all other short-term solutions, eventually falter. The long term result of eliminating waste is a manufacturing process that is so streamlined, cost efficient, quality oriented and responsive to the customer that it becomes a strategic weapon. By having a more efficient, less wasteful manufacturing system, companies will no longer be forced to depend on marketing and advertising as the only ways to differentiate products and capture market share. JIT not only affords companies great increases in quality of their manufactured goods. It allows a company to cut response time to market by as much as 90 percent. New products or product changes requested by customer can be brought to market in half the time it currently takes. At the same time, the capital equipment necessary to do this can be reduced and inventories can be drastically cut, if not eliminated. With successful implementation of JIT, companies that in the past have been forced to market themselves as service and quality oriented, because they were unable to compete on price, can begin to see themselves as low cost producers. This could open up completely new markets for the companies, and help differentiate the company from all other service and quality oriented companies. Because JIT offers these opportunities, it is imperative for a company to plan for and implement JIT in conjunction with a total business or marketing plan. Often, because of a company's strategic goals, certain elements of JIT will be important to carry out early xiiiwhile other elements will not be as important. On the other hand, given the opportunities provided by JIT, some companies will want to modify or even rewrite their business or marketing plans to fit better with JIT opportunities. In JIT systems, because in-process inventories have been drastically reduced, production stops until the production problem is solved. Only when the machine is fixed, the quality control problem solved, or the reason for running out of material found and corrected only then can production begin again. JIT is already a system of enforced problem solving. With in-process inventories stripped away, every material must meet quality standards, every part must arrive exactly at the time promised and precisely at the place it is supposed to be, and every machine must function as intended without breakdowns. If they do not, the interruptions to production would be intolerable. In JIT systems, enormous effort is there put into permanently eliminating each problem as it arises so that production is not interrupted again for that problem. Prerequested for JIT systems are as follows: 1. Stable and level production schedules. 2. Smaller and more focused factories. 3. Smaller batch or lot sizes and reduced changeover times. 4. Repetitive manufacturing. JIT projects are being launched in cost of the better known industrial firms in the world. The projects turn into JIT campaigns and the campaigns link with total quality control to become as many are saying, the new way of life in manufacturing. In a few companies, result are in the order of five to ten fold reductions in lead time. For example, several of Hewlett-Packard's and Omark Industries' plants achieved this levels of improvement. JIT is usually most successful when the focus is on moving workstations close together. This act reduces several forms of waste and cost. These include: JIT/TQC is designed to continuously improve ability to economically respond to change. Constraints occur as our attempts to increase velocity threatens to negativekly affect quality, delivery or cost. These constraints appear in the form of waste In JIT environment, waste is defined as any activity that does not add value for the customer. It is the use of resources in the excess of the theoretical minimum required (manpower, equipment, time, space, energy). Waste can be excess inventory, setup times, inspection, material movement, transactions or rejects, essentially, any resource that is not actively involved in a process that adds value is in a waste state. Shigeo Shingo, one of the Japanese founding fathers of improved manufacturing methods, detailed what are now known as his Famous Seven Wastes. They are the following: xiv1. Waste of overproduction 2. Waste of waiting 3. Waste of transportation 4. Waste of stocks 5. Waste of motion 6. Waste of making defects 7. Waste of processing itself (when the product should not be made or the process should not be used). As part of the JIT philosophy, there are three basic and equally important components for eliminating waste. The first basic component of waste elimination is establishing balance and synchronization and flow in the manufacturing process, either where it does not exist or where it can be enchanced. The second component is the company's attitude toward quality, the idea of doing it right the first time. The third component of the Just In Time philosophy is employee involvement. It is a prerequisite for waste elimination. Every member of the organization from the shop-floor to senior management has a part to play in the elimination of waste and solving the manufacturing problems that cause waste. The only way a company can solve the hundreds or even thousands of problems that occur in a manufacturing system from small problems to large is total employee involvement. Some of the benefits claimed for JIT systems are: 1. Inventory levels are drastically reduced. 2. The time it takes for products to get through the factory is greatly reduced, thus enabling factories to be more flexible to be more flexible and more responsive to changing customer demands. 3. Product quality is improved and the cost of scrap is reduced. One reason that scrap cost is reduced is that with smaller product batches, defective parts are discovered earlier. 4. With smaller product batches, less space is taken up with inventory and materials handling equipment. Workers are closer together so that they can see each other, communicate more easily, work out problems more efficiently, learn each other's jobs and switch jobs as needed. All of this promotes teamwork among workers and flexibility in work assignments. 5. Because the focus in manufacturing is on solving production problems, manufacturing operations are streamlined and problem-free. Reduced production costs, increased worker productivity and improved product quality are the bottom line of these benefits. JIT programs require investing heavily in engineering studies and equipment modifications to achieve drastically reduced setup times, establishing training programs that train workers for several jobs and developing different business strategies with narrower product lines that allow stable and level production schedules. Unless manufacturers are willing to commit new price instead of the old price of high inventory levels and low flexibility, they cannot expect to reap the benefits of JIT. xvJIT is a Japanese innovation and key features were perfected by Toyota. But there is nothing uniquely Japanese about JIT production. It is usable anywhere. JIT production means producing and buying in very small quantities just in time for use. It is a simple hand to mouth mode of industrial operations that directly cuts inventories and also reduces the need for storage space, racks, conveyors, forklifts, computer terminals for inventory control and material support personnel. More important, the absence of extra inventories creates an imperative to run an error free operation because there is no cushion of excess parts to keep production going when problems crop up. Causes of errors are rooted out, never to occur again. The JIT transformation begins with inventory removal. Fewer materials are bought and parts are made in smaller quantities: so called lot-size inventories thereby shrink. The immediate result is work stoppages. Production comes to a standstill because feeder processes break down or produce too many defectives and now there is no buffer to keep things going. This is exactly what is supposed to happen. For now the analysts and engineers pour out of their offices and miggle with foremen and workers trying to get production going again. When round of problems is solved, inventories are cut again so that more problems crop up and get solved. Each round of problem exposure and solution increases productivity and quality too. A widely used measure of the efficiency of a JIT system is the manufacturing efficiency ratio. This measure expresses the time spent in value adding activities (such as processing) as a percentage of total cycle time. The lenght of time required for a product to pass completely through a manufacturing process is called cycle time. Cycle time often is viewed as containing four separate elements: These are: processing time, storage and waiting time, movement time and inpection time. Only during processing time, however, is value added to the product. Ideally, the other elements of cycle time should be reduced as much as possible. The manufacturing efficiency ratio may be applied to specific production processes or to the manufacturing process is viewed as whole, cycle time begins with the arrival of direct materials and ends with the shipment of the finished goods.) The basic purpose of the manufacturing efficiency ratio is to highlight the percentage of time spent in non value adding activities. The optimal efficiency ratio is 100%, which indicates that no time is being spent on non value adding activities. In practice, however, this ratio is always less than 100%. If a manufacturing company has not made a concerted effort to reduce its non value adding activities, its manufacturing efficiency ratio often is less than 10%. JIT opportunities can be summarized as follows: Lead-time reduction 83-92% Productivity increase Direct labor 5-50% XVIxvii
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