Tedarik Zinciri Yönetiminde Dağıtım Ağı Optimizasyonu : Gıda Sektöründe Bir Uygulama

Abstract

Teknolojinin hızla ilerlemesi müşteri beklentilerini de aynı oranda arttırmakta ve ürünlerin daha kaliteli, daha kullanışlı, uygun fiyatla ve hızlı olarak pazara ulaşması gerekli olmaktadır. Hız faktörü hem ürünün hem de hizmetin bütünleştirilmesi ile sağlanabilmektedir. Bu bütünleşmenin sağlanmasında ise etkili çözüm yöntemlerinden biri olarak Tedarik Zinciri Yönetimi ve buna bağlı çözümler kullanılmaktadır. Tedarikçiler, üreticiler, dağıtıcılar, toptancılar ve perakendeciler gibi çeşitli iş paydaşlarının oluşturduğu tedarik zinciri, hammadde temininden başlayıp ürünlerin son tüketiciye dağıtım ve pazarlanması gibi tüm iş süreçlerindeki uyumun sağlanmasında etkili olmaktadır. Zincir boyunca aynı zamanda malların ve bilginin akışı da yönetilmektedir. Tedarik zinciri yönetiminde son ürünlerin müşteriye dağıtımı önemli bir rol oynamaktadır. Küresel pazardaki gelişmelerle beraber tedarik zincirinin önemi gün geçtikçe artmaktadır. Tedarik zinciri yönetiminin amacı üretimden teslimata kadar olan süreçlerin iyileştirilmesini sağlayarak müşteri memnuniyetini arttırmaktır. Tedarik zinciri yönetiminin bir alt başlığı olan soğuk zincir yönetimi ise bir başka özen gösterilmesi gereken konudur. Hammaddenin tedarik edilmesiyle başlayan süreçte tüketiciye ulaşana kadar olan soğuk zincirin korunması, gıdaların çabuk bozulabilir olması açısından büyük önem taşımaktadır. Bu çalışmanın amacı gıda sektöründe tedarik zinciri dağıtım ağı optimizasyonu için bir model önerisinde bulunmaktır. Genel bir giriş yapıldıktan sonra tez çalışmasının ikinci bölümünde tedarik zinciri ve tedarik zinciri yönetimi kavramları üzerinde durulmuş ve tarihsel gelişimi anlatıldıktan sonra, tedarik zinciri yönetiminde karşılaşılan süreçlere yer verilmiştir. Daha sonra, gıda sektöründe tedarik zinciri konusu ele alınmış ve çalışmanın uygulama alanı olan gıda sektöründe soğuk zincir konusu detaylı incelenmiştir. Tez çalışmasının üçüncü bölümünde tedarik zinciri modelinin oluşturulması, kısıtları ve karar değişkenleri anlatılmıştır. Daha sonra optimizasyon modelleri konusu ayrıntılı bir şekilde incelenmiş ve literatür araştırması kapsamında incelenen makalelerden bu bölümde bahsedilmiştir. Tez çalışmasının uygulama bölümü olan dördüncü bölümünde Türkiye’de faaliyet gösteren bir işletmenin soğuk zincir ürünlerinin dağıtımına ilişkin bir doğrusal programlama modeli geliştirilmiştir. Geliştirilen model iki planlama dönemine ilişkin olarak bir fabrikada üretilecek ürün miktarının, fabrikadan depolara gönderilecek ürün miktarının ve depolardan müşterilere gönderilecek ürün miktarının belirlenmesine yöneliktir. Üretim, taşıma, depolama, soğutma maliyetlerini kapsayan toplam maliyetin minimizasyonunun amaçlandığı modelde taşıma sırasında meydana gelebilecek kusurlu ürün yüzdeleri dikkate alınmış ve bir kısıt olarak modele eklenmiştir. Kusurlu ürün yüzdelerinin belirsiz olmasından dolayı kısıtlar stokastik olarak ele alınmış ve daha sonra deterministik yapıya dönüştürülmüştür. Modelin sonuçları Lindo 6.1 software programı kullanılarak elde edilmiştir. Ayrıca deterministik ve stokastik model sonuçları karşılaştırılmış ve bazı analizler yapılarak belirsizliğin amaç fonksiyonu değerini ne kadar etkilediğine bakılmıştır. Elde edilen verilere göre stokastik modelin çözümü sonucunda toplam maliyetin daha fazla olduğu görülmüştür. Ayrıca belirsizliğin artmasıyla maliyetin de arttığı sonucuna varılmıştır. Tez çalışmasının beşinci bölümünde ise uygulamanın sonuçları yorumlanmış ve geleceğe yönelik genel değerlendirmelere yer verilmiştir.

Technological developments increase customer expectations and as a result, today’s customers demand lower priced, high quality products that are conveniently located in the market place. As well as being avaible in the markets, its also important for the products to be served to the end users very fast.At this point, supply chain management offers various solutions to the companies. Supply chain is a set of activities among suppliers, manufacturers, wholesalers, and retailers which plays a major role in the process of acquiring raw materials, turning this to finished products, delivering the products to sellers, and marketing them to their end users. Supply chain management also entails information system technologies as well as logistical organization. The most important goal of the supply chain management is to deliver finished products to their end users in the most efficient manner. The importance of supply chain management has increased as a result of the developments in the global market. The objective of the supply chain management is to improve the ways in which products meet end users while increasing customer satisfaction. Cold chain management is a subcategory under supply chain management which is an important subject that needs attention. Cold chain management is especially important in the process of sourcing raw materials and delivering the finished products that need refrigeration in order to avoid waste. Among the factors in the cold chain, the deviations in temperature, shelf life and the possible defect during the distrubution can be considered. In addition to these factors, warehouses should be designed as suitable as possible for food products. In food sector, it is very important that the structure of supply chain is modelled according to the needs of firms and presented for today’s conditions properly. If the supply chain is managed fast, productively and profitably, the total cost would be decreased. By the way, the firms can extent their market share by increasing their competitiveness. The increase of quality, just in time production, storage, transportation and distrubution can be advantage to the firms. As a result of these improvements, new models and methods are developed both theoreticaly and practicaly in supply chain management. This project aims to offer an ideal optimization of the supply chain management in the food sector. After general introduction, components of supply chain and supply chain management are analyzed with a brief history of its evolution. Following this, supply chain in the food sector is explained and cold chain that is specific to the food sector is examined further in details. In the third section of this thesis project, building supply chain, limitations, and decision factors are explained followed by optimization of different supply chain components and related articles in this department. The study also emphasized the importance of the supply chain. In the absence of effective supply chain, the factors such a low cost, high quality, just in time distrubution provide advantage temporarily. The changing economy, market and the dynamic enviromental conditions should be taken in consideration and new supply chain networks and strategies should be developed. Thus, firms can survive by protecting their future. In the forth section of the project which is the applied portion of the thesis, a model to improve the exiting system in the cold chain of a company in Turkey was developed. The model was applied in two periods in an attempt to determine the amount of the product that needs to be produced, the amount of the product that needs to be sent from factory to the warehouses, and the amount of the product that needs to be delivered to the customers from the warehouses. The goal of the model is to reduce the total cost of the production, transportation, storing, and refrigerating. The percentage of defective product during transportation were taken into the consideration in this model. As a result of the uncertainty of the percentage of the defective products, limitations are taken based on stochastic, and turned into deterministic form. Results are calculated by using software called Lindo 6.1. Similarly, results from the deterministic and stochastic models are compared and analyzed to determine how much the uncertainty is affected. Based on our examinations, the cost in the stochastic model is much higher. Additionally, the more uncertainty there is, the more cost associated with it. In the fifth section of the thesis, the results taken from this study are explained and suggestions are made. In this study, the model was applied to a distribution network which includes one factory, two depots, seven customers, three products and two-term plan. However, indexes in the model were created to receive the value from 1 to n, so more complicated problems which contain more factories, depots and customers can be solved with this model. Although the model established in this study was solved using lineer programing, the complicated problems are solved using genetic algorithms. In this study, the changes in the objective function were analysized by increasing the standart deviation of the percentage of defective products. With the increase of the standart deviation, the value of the objective function also increases. In other words, the uncertainty results in high cost. It is similar to bullwhip effect which is observed phenomenon in forecast-driven distribution channels. The bullwhip effect occurs when the demand order variabilities in the supply chain are amplified as they moved up the supply chain. Because customer demand is rarely perfectly stable, businesses must forecast demand to properly position inventory and other resources. Forecasts are based on statistics, and they are rarely perfectly accurate. Moving up the supply chain from end-consumer to raw materials supplier, each supply chain participant has greater observed variation in demand and thus greater need for safety stock. In addition to greater safety stocks, the described effect can lead to either inefficient production or excessive inventory as the producer needs to fulfill the demand of its predecessor in the supply chain. This also leads to a low utilization of the distribution channel. In this model, as the producers do not know the amount of waste during transportation, they produce and transport more than it should be and then, it results in high cost. Hereby, understanding and managing the uncertainty in a parameter is important in reducing the total cost of the supply chain. If the quality control is done more often and this values are decreased to a certain limits, it would be for the benefit of all stakeholders involved in the supply chain. With the establishment of systems to minimize risks, production, quality control, distribution, sale and consumption may be checked in stages. In the real life, supply chain takes place in the uncertain environment. The main reason of uncertainty is that the activities through the supply chain are performed by people. In practical applications, it is difficult to predict some of the data such as the percentage of the defective product. Stochastic programming is useful for uncertain problems. For this reason, the constraint including the percentage of the defective products were established as a stochastic constraint and then, they were converted to deterministic equivalent. The results were presented to the firm and has been also accepted by the firm. In addition to the scientific method applied in this study and the development of the information technology, new software programs are used for the supply chain management but many businesses are not aware of this software programs. Therefore, it can be said that the optimization studies of the supply chain will provide an advantage if the supply chain is not set at its optimum. The main aim of cold chain is to extend the shelf life of foods. Producers should be careful in terms of controlling the temperature through the cold chain from production to consumption. The changes of temperature in the cold chain may result in growing of microorganism and changes of physical, sensual and chemical structures of foods. There are two main problems in cold chain : breaking of cold chain and the cost of cold chain. Improving of additional cost and finding solution to the problems could affect the firms budget positively. It is possible to create a new system for foods with longer shelf life by decreasing the cost of warehousing and transportation. In addition to the machine and equipment used in the cold chain, staffs should be trained in terms of principles and procedures. For example, the drivers of vehicles should know why they carry food product at the same temperature or they should know the risks if there are temperature fluctuations. In this study, it has been assumed that the demands of customers were known and they are constant through the period. In further research, demand constraint and objective function could be established as a stochastic structure by assuming the customer demand as uncertain. Although lineer programming models gives the optimal solution, meta heuristic methods can be used as a complemantary method.