Malzeme ihtiyaç planlama sistemi

Esen, Ş. Engin
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Sosyal Bilimler Enstitüsü
Günümüzde» değişen teknoloji ve tüketici istekleri, eko nomik şartlar beraberinde yoğun ve ezici bir rekabet ortamı doğurmuştur, Bu rekabet ortamında, maliyetlere önemli bir etkisi bulunan envanter maliyetleri dikkate alınmalıdır. En vanter maliyetlerini azaltan ve üretim planlamanın ait fonk siyonu olan malzeme ihtiyaç planlama sistemi, ana üretim pla nını, zaman boyutunda net ihtiyaçlara dönüştüren bir sistem dir ve planın gerçekleşmesi için gereken tüm envanter birim leri bazında bu ihtiyaçların karşılanmasını planlayan karar kuralı setlerini ve yöntemlerini içerir. Malzeme ihtiyaç planlaması, 1960* 1 ardan sonra gelişmiş, bugün ülkemizde de kullanımı yaygın hale gelmiş üretim plan lama ye kontrol cizelgeleme tekniğidir. Bu çalışma beş bölümden oluşmaktadır. Birinci bölüm gi riş niteliğindedir ve envanter yönetimi hakkında kısaca bilgi ve r mek t ed ir. îkinci bölümde malzeme ihtiyaç planlama sistemi ayrıntı lı bir şekilde ele alınmıştır. üçüncü ve dördüncü bölümlerde, sipariş miktarlarının bu lunması yöntemleri ve malzeme ihtiyaç planlama sisteminde bilgisayar sistemi incelenmiştir. Son bölümde ise, imalat sanayinde faaliyet gösteren orta büyüklükte ve atelye tipi üretim yapan bir fabrikada ya pılan uygulama yer almaktadır. Fabrika değişik tiplerde tes tere tezgahı üretmektedir ve stoka üretim yapmaktadır. Yapı lan uygulamada atelye tipi üretim yapan işletmelerde etkili sonuçlar veren Gozinto Yöntemi kullanılmış ve yöntemin esası nı oluşturan matris hesaplatmaları Lotus paket programında yapılmıştır.
Many of the inventory problems look for an answer for two basic questions? - How much? - When? There are two approches which look for an answer for two basic questions» These ares 1 »Statistical Inventory Control (Order Point) 2»Materiai Requirement Planning The order point is constructed by estimating demand over lead time and adding safety stock to it. This is a classic approch and it is not sufficient to solve inventory problems- There is one other fundamental technique for determining when to order, and this is called material requirement plan ning (MRP), The clear need is for a material -management information system that takes into account the specific timing of demands for materials at all levels of manufacture- MRP is such a computerized inventory planning and control system. It is also known as "time- phased requirements planning". MRP begins with a master schedule of demand for finished goods. For fu ture planning periods, the gross demand for each finished product is listed. An MRP system is a collection of logical procedures for managing, at the most detailed level, inventories of compo nent assemblies, subassemblies, parts, and raw materials in a manufacturing environment. In the context of multistage production, we distinguish between independent demand and dependent demand. The inde pendent demand originates in market demand for an item. The demand by a parent item for its components is dependent de mand. If an item is needed both as a component and as a VII spare part, we say that it experiences both dependent and independent demand. An MRP system is designed to deal with dependent demand items. In the case of component items also having independent demand, the forecast quantity is added to the gross require ments in the same period. Several requirements have to be met, in order to give an MRP implementation project a chance of success. - Availability of a computer is a must. Although it is possible to obtain a material requirements plan manually, it would be impossible to keep it up to date because of the hig hly dynamic nature of manufacturing environments. - A feasible master production schedule must be drawn up, or else the accumaleted planned orders of components might "bump" into the resource restrictions and become in fe asible. - The bills of material should be accurate. It is es- santial to update them promptly to reflect any engineering changes brought to the product. - Inventory records should be a precise representation of reality. - Lead times for all inventory items should be known and given by MRP system. - Shop floor discipline is necessary to ensure that orders are processed in conformity with the established priorities. The major objectives of an MRP system are simultaneously to; - Ensure the availability of materials, components, and products for planned production and for customer delivery, - Maintain the lowest possible level of inventory, - Plan manufacturing activities, delivery schedules, and purchasing activities. There are three major inputs for MRP system. These are the master production schedule, the inventory status records and the bill of materials-product structure records. VIII MRP treats items as if their priorities are dependent and it calculates future demands. This calculation is based on a master schedule that may itself be based on a forecast, ît has been said, however, that when using MRP, uncertainty exists only at the master schedule level. The inventory status records contain the- on-hand and on- order status of inventory items. In MRP system, net requ irements are determined by netting the gross requirements against any amount on hand or already on order. A key element to the determination of component require ments is the bill of materials, which is an engineering docu ment and can be represented as a symbolic exploded view of the end item structure. There are levels in the bill of ma terials. Each level involves some action that requires a lead time to accomplish: purchasingof materials, fabrication, assembly, and so on. Bills of materials when put on a computer file are often called product structure records. MRP system has various output reports. The most impor - tant of these are purchase orders and reschedule notices. MRP outputs can be changed according to the managers. Some of these are forecasts of inventory, reports of performance, etc. Today, MRP is considered an important but single module in a total closed- looped system of production, sometimes re ferred to as manufacturing resource planning. MRP system is usually superior to other inventory systems, when the follo wing conditions hold. - The final product is complex and contains several other items. - The specific demand for the product in any time period is known. - The forces creating the demand in one time period are distinguishable from in other time periods. - The final product is expensive. - The demand for an item is tied in a predictable fash ion to the demand for other items- In MRP system, 8 techniques are used for order quanti ties are listed below» 1. Fixed order quantity IX 2 -Economic order quantity 3.Lot-for- lot ordering 4 »Fixed period requirements 5. Period order quantity 6, Least unit cost 7 »Least total cost S.Part-period balancing. Effectiveness of these techniques is dependent on cer tain factors. These arei Change of demand 5 length of plan ning time (the number of periods), length of planning period, preparing cost to unit cost rate. On the benefit side of using an MRP system, one can count the following: - Reduced inventories resulting from a better match bet ween order quantities and requirements, and from better ti ming of inventory replenishments - Improved customer service (fewer stockouts and less late orders) by early warning of possible trouble spots such as insufficient capacity, late deliveries of components, and so on - Lower manufacturing costs coming from the previous two benefits as well as from reductions in such personnel as clerks, expediters, and storekeepers. In the last part of this study, there is an application for a factory. Factory produces various type of saw counters and have approximately 60 workers. In the factory organiza tion, there is a general manager, an accounting and a product manager. Factory has not got an effective organization beca use of family company. Factory has got two computers which have been used in accounting department. But company will set up a planning department in the future. In this application, Bozinto technique was applied for this particular factory. This technique is suitable for the workshop type production system. Vazsonyi (1958) developed a systematic procedure based upon matrix albegra that provides a good framework for per- forming the planning function when large numbers of products and parts are involved» In this application, all of matrix computations have been carried out by a computer. 602in to Decisions ? the procedure for determining parts requirements outlined in the previous section is most useful for processing customer orders for a single time period. If we want to determine requirements for forecasted demand over several time periods, an extended procedure is needed. Such a procedure, developed in this section, will also generate a great deal more information needed in making several other planning decisions. The decisions to be rendered ares 1. Time-phased parts requirements (gross) 2. T i me- phased parts requirements (netted against stock on hand and outstanding production and purchase orders) 3. From decision 2S we can obtain following decisions: - Whether to order raw materials; how much to order - Whether the requirements can be met with present capacity, considering machine time and roan- hours available. Possibility of extra shifts and overtime is considered.
Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Sosyal Bilimler Enstitüsü, 1992
Anahtar kelimeler
Gozinto yöntemi, Malzeme ihtiyaç planlaması, Gozinto method, Material requirement planning