يك مدل چند هدفه چند دوره اي براي تخصيص سفارش به تامين كنندگان در يك زنجيره تامين همراه پيشنهادات تاخير در پرداخت ها و تخفيف

چكيده انگليسي :

A Multi Objective Multi Period Model for Allocating Orders to Suppliers in a Supply Chain with Delays in Payments and Discount Offers Banafshe Taghaodi b taghaodi@in iut ac ir Date of Submission 2012 Department of Industrial and Systems Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Seyed Reza Hejazi rehejazi@cc iut ac ir Abstract Globalization in our modern times is giving rise to a multitude of continual changes and developments inthe business environment including regulatory changes increasing competition intensity increasinglydemanding customers new information technologies mergers and acquisitions among others The supplychain management SCM is the term used to describe the management of materials and information acrossthe entire supply chain from suppliers to component producers to final assemblers to distribution warehouse and retailers and ultimately to the consumer In fact it often includes after sales service andreturns or recycling as well Supplier selection and material procurement planning are the most importantissues in supply chain management This function involves evaluation of many factors such as cost ofparts materials size of order quality and delivery performance Therefore this problem is categorized asmulti criteria decision making problems Different approaches have been applied in order to assess and selectthe suppliers when suppliers offer discount on the unit price Price discounts provide a reduction in the priceper unit as the number of units purchased increases Large quantity orders lower the unit cost but mayincrease inventory which conflicts with the financial department s goal of investing fewer dollars ininventories The introduction of price discounts complicates the determination of the optimal purchasingquantities with minimum cost for an item It is the task of the purchasing department to evaluate all of theconsiderations and make profitable buying decisions under different conditions In real situation eachsupplier may apply different methods such as different types of discount schedules and various types ofpayment in order to increase market share In this situation buyers try to select the best supplier byconsidering all tangible and intangible factors which may be included in this decision problem Besides inmulti period planning inventory management may be considered as an important issue for supplier selectionin lot sizing decision A bi objective model is proposed for multiple item multiple period supplier selectionand lot sizing problem This model includes all unit discount and delay in payments which ordinary may beproposed by each supplier Traditionally supplier selection should simultaneously take into accountnumerous heterogeneous criteria and then is a tedious task for the purchasing decision makers Under suchmanner most studies often formulate such a problem as a Multi Objective Linear Programming MOLP problem This work applied a mixed integer programming approach to solve the sourcing and orderallocation problem with multiple products and multiple suppliers in a supply chain The decision process isdriven by multiple objectives and a set of constraints We used the weighted sum of objective functions sincebuyers usually look for a unique decision to follow The problem is to determine which products to order inwhich quantities from which suppliers in which periods Considering the complexity of these models on theone hand and the ability of genetic algorithms to obtain a set of Pareto optimal solutions we apply a geneticalgorithm to solve the model Finally several sample problems have been solved by the proposed GA and theexact branch and bound method The results illustrate slight relative errors to compare with reasonablesaving in computational times Keywords Supplier selection Lot sizing All unit discount Shortage Genetic algorithm

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