Kalite maliyetleri optimizasyonuna çok amaçlı karar verme yaklaşımı

Cesur, Cenk
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Fen Bilimleri Enstitüsü
Bu çalışmada kalite maliyetleri ele alınarak incelenmiştir. Birinci bölümde kalite sistemi ve kalite planlama üzerinde durulmuştur. Kalite planlama kalite yöntem sistem elemanlarının organize edilmesidir. Müşteri isteklerinin karşılanabilmesi ve şikayetlerin azaltılabilmesi için kalite, güvenilirlik, emniyet konulannda sistematik faaliyetlerin sonucu olarak sorular sorulur. Böyle bir yaklaşımın adı kalite sistemidir. Kalite maliyetlerinin düşürülmesi ve kalite hedeflerine ulaşılabilmesi için kalite sisteminin firmaya adapte edilmesi gerekir. İkinci bölümde kalite maliyetleri incelenmiştir. Kalite maliyetleri en geniş anlamda dörde ayrılır : 1)önleme maliyetleri, 2) ölçme ve değerlendirme maliyetleri, 3) İç hata maliyetleri, 4) Dış hata maliyetleri Kalite maliyet sisteminin amacı, istenen kalite düzeyinde toplam kalite maliyetini minimize etmektir. Kalite maliyet programının esası; "önlemeye yapılan bir birim harcama, ölçme ve değerlendirmeye yapılan bir birim harcamaya göre çok daha faydalı ve önemlidir." Üçüncü bölümde kalite maliyet programı incelenmiştir. Bu bölümde adım adım kalite maliyetlerini minimize eden kalite maliyet programının oluşturulması ve çalıştırılması konusunda farklı yaklaşımlar yer almaktadır yer almaktadır. Dördüncü bölümde çok amaçlı karar verme modelleri konusunda verilmiş, beşinci bölümde ise kalite maliyetlerinin optimizasyonuna yönelik bir çok amaçlı karar verme modeli kurulmuştur. Bu modelin amacı karar vericiye katlandığı hata oranı ve hedeflediği kusursuz oranı doğrultusunda maliyetleri minimize eden kusursuz üretim oranlarını vermektir. Kurulan model lineer hedef programlaması yöntemiyle çözülmüş ve elde edilen değerler grafik olarak ifade edilmiştir.
In this study quality costs are examined. Discussions made in the first section about quality system and quality planning. Quality planning is a function which organize quality system elements. When systems become more complexity the role of the coordination and information flow will be more important. To satisfy the customers and decrease the customers complaints questions asked about quality, reliability and safety as a result of systematic activities. The system like this is called as a quality system. The reason of the system approach to the quality is that all other approaches were unsuccessful. Reducing quality costs and fulfilling the quality objectives are possible when a quality system is adopted to the company. Quality is measured in two ways : 1) adherence to standards ; and 2) optimizing quality costs. The basic philosophy of establishing quality standards and then using them as a determinant of quality is the same for a manufacturing concern as for a service industry; however the application differs. The quality of manufacturing concern's output is evaluated by more tangible criteria than is a service industry. Whereas a manufacturing concern initially inspects tangible items based on physical and functional conformance, and then accepts or rejects the product, a service industry establishes standards for a product or service which are much less tangible. A manufacturing concern sets internal standards which are often based on external requirements, and then tests the production process to ensure functional uniformity, product reliability and product safety. The cost of producing or offering a product or service are evaluated to determine the efficiency of the operation. If the cost of an operation is high due to rework or scrap, then two assumptions can be made. First, the operation is not as efficient as it could be, and second, the employees are not working as productively as possible. Either of these assumptions, or both, may apply and can be tested. Development of quality costs can help to quantify specific quality levels and ultimately improve productivity. If the quality costs reflect high failure costs and, in turn, increase productivity. However, before developing quality costs, the definition of each cost category should be clearly understood. Quality costs are examined in the second section. In times of economic stress when management must look around for places to cut manufacturing costs, it is inevitable that their collective eyes come to rest on the quality organization. The quality organization produces no hardware to sell, has no direct profit responsibility, and cannot state with any degree of certainty the impact of contemplated changes on profits. A continuing cost effectiveness study of quality organization will give answers on the impact of decisions affecting quality as well as initiating profit consciousness among quality people. Quality costs can be divided broadly to four categories as follows : - Prevention costs are costs incurred to reduce, eliminate, and prevent defects. Such costs typically include the costs of job training, quality report preparation, quality planning and analysis, computer/manual system design, developing and presenting quality related seminars, and user-testing of quality control system. - Appraisal costs are costs incurred to detect errors, and to evaluate the quality of the work done. Such costs typically include the costs for proofing, verifying, inspecting, checking, signing, balancing, and recapping. - Internal Failure costs are costs incurred in correcting the errors before delivery of the product to the customer. In other words, internal quality costs are the cost of re-doing work a second time. Such costs typically include the labor cost of reworking items that were incorrectly processed, the cost of scrapped forms, and the cost of wasted computer and other equipment time. - External Failure costs are costs incurred in correcting errors after delivery of the product to the customer. Such costs typically include the cost of compensation paid, penalties, difference write-offs, interest payment on late deliveries, as well as the cost of investigations. Quality costs have effects on many areas. Some these areas are : - Customer - Inflation - Competition - Technology Quality costs can be used in many areas. They act as an indicator. They give the opportunity to the formation and development of a quality program and the evaluation of the values obtained from the outcome of the activities of the program. Quality costs also help to analyze the process quality, as how to give the priority to which manufacturing facility. VI With the help of quality costs, the budgeting of quality control activities can also be obtained. Quality costs are very useful to predict the costs of a new product or service and to predict the competitive power of the company. In a broad view, the interrelations between quality costs can be seen in the following chart. Total Quality 100% Defective Quality Level FIGURE 1. QUALITY COST RELATIONSHIP 100% Good As product quality tends toward the 100% defective level, failure costs tend toward infinity while appraisal plus prevention costs tend toward zero. As product quality tends toward the 100% good level, failure costs tend toward zero while appraisal plus prevention costs tend toward infinity. Total quality costs are algebraic sum of appraisal, prevention and failure costs at each point along the axis. The total quality cost curve is seen to have a minimum point; the point at which the other two curves intersect. It is desirable to have the organization operate at this point of minimum total quality costs. With the economic rationale, it is possible to construct a self-correcting quality cost system which will seek the optimum cost for any given business situation. It is self-correcting in that if failure cost increase, prevention and detection (appraisal) costs must be increased to maintain the equality, and if failure costs decline, prevention and detection costs should be reduced. Very little experience should be necessary to eliminate over-correcting. The aim of the quality cost system is to minimize the total quality cost at an indicated quality level. The principal is that, an increase in the prevention cost helps to decrease the failure cost and as a result the total quality cost decreases. Quality costs are interrelated, and the objective in allocating resources for quality activities is that dollars spent on prevention and appraisal should prevent or reduce failure costs. In general, optimum quality cost mix is the point at which an additional dollar allocated to prevention and/or appraisal will not reduce failure costs. Ml Therefore each area or unit must determine its actual quality cost mix and its optimal cost mix, and consciously adjust quality activities to reduce and erase any difference that may exist. The fundamental of the quality cost program is "a unit cost for preventing failure is more useful and important compared to a unit cost for measuring and evaluating". Reports on quality cost systems are very important for management to give decisions and to act. Quality cost program is discussed in the third section. Formation and study of the quality cost program that help minimize quality costs step by step is the main topic of this section. Quality costs are incurred by all major functions in an organization so problem areas can exist anywhere. Careful analysis must be developed to attack them. When these needs exists, a strategic program should be developed using input from all functions. The object of any quality cost program is to improve quality and reduce quality cost. When the highest cost areas are analyzed, many improvement projects become apparent. For example, high warranty costs are a trigger to rank customer failure problems for detail investigation, with the aim of looking into product design, process control or inspection planning for the cures to the highest cost problems. A natural temptation due to high external failure costs might be to put more emphasis on appraisal efforts; but this approach may simply convert some external failure to internal failure (scrap, rework) and bear an increased inspection burden to this. Regardless of what the category may be, by identifying it, it can be reduced. The entire process of quality improvement and quality cost reduction necessarily is pursued on a problem- by-problem basis. Any quality cost improvement depends on understanding cause and relationships, and the study of total quality costs is the most effective tool available to management. While eventually total costs should come down with the use of an effective program, short term changes in these costs are not good measures of progress. Most measure success and each individual 's contribution by measuring and totaling the effect of each individual improvement. In some situations total costs go up because of increases in wage and material costs, but the cost improvement program is a success because it prevents a larger rise. In review, there are five steps in effective quality cost reduction : - Finding the problems - Setting targets - Planning action - Organizing to take action - Measuring results. Vlll A practical quality improvement program that will guarantee improved productivity through quality management took us from the selling to management leading to the commitment and policy to the establishment of the quality organization, the setting of quality standards, the measuring of implementation and managing of the quality program through communications and recognition. It also introduced some concepts associated with service/administrative quality costs. General information about multiple criteria decision making models together with the goal programming method is the main subject of the fourth section. In the fifth section, a multiple criteria decision making model is constructed and solved as an application keeping in mind the interrelations between quality costs. Linear goal programming method is used to solve above mentioned model. For this, the major reasons of failure are put in order as major and minor according to Pareto analysis. The goals set by the decision maker are satisfied after this application using the constructed model. The multiple criteria decision making model is as follows : Objectives : (1) Min f-j = C-) (n - x-|) + C2 (n - X2) + +C7 (n - X7) Cj : failure costs i = 1, 2 n xj : number of conforming products on operation i. n : total production quantity (2) Min f2 = S<|Xi + S2X2 + +87x7 Sj : prevention cost per unit Constraints : (3) x^p^n (4) x2rj*n Pi : The ratio of conforming products to total production rj : Acceptable quality level of decision maker This model is solved nine times by using different values of decision maker. The results of this model can be seen at section 5. Most of these graphs are seem same as the theoretical graphs.
Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 1993
Anahtar kelimeler
Endüstri ve Endüstri Mühendisliği, Kalite maliyeti, Çok amaçlı karar verme, Industrial and Industrial Engineering, Quality cost, Multiobjective decision making