Browsing by Subject "Production planning."
Now showing 1 - 20 of 23
Results Per Page
Sort Options
Item Open Access Aggregate production planning with linear programming: a case study(Bilkent University, 1991) Alperat, HalukThe aim o f A g g r e g a t e P r o d u c t io n P la n n in g i s t o b a la n c e th e e x p e c te d denuind and s u p p ly f o r a company. I f demand i s g iv e n , p ro d u c t io n r a t e s , w o rk fo r c e s i z e s , and in v e n t o r y l e v e l s a r e d e te rm in ed f o r e v e r y p e r io d in th e p la n n in g h o r iz o n in o rd e r t o m in im ize th e t o t a l p r o d u c t io n c o s t . In t h i s s tu d y . A g g r e g a t e P r o d u c t io n P la n n in g i s a p p l i e d t o a sm a ll company th a t p ro d u c e s s p a r e p a r t s f o r T o fa ^ and F o rd f a c t o r i e s . L in e a r Progranun ing i s one ap p ro a ch t o s o l v in g th e A g g r e g a t e P ro d u c t io n P la n n in g p ro b lem w ith l i n e a r c o s t fu n c t io n s . T h is s o p h i s t i c a t e d t e c h n iq u e , wh ich i s v e r y s im p le t o a p p ly , y i e l d s a c c u r a t e r e s u l t s in a r e l a t i v e l y s h o r t p r o c e s s in g tim e . In s o l v in g t h i s p ro b lem , th e r e q u i r e d d a t a f o r th e company a r e c o l l e c t e d and p r o c e s s e d . The c o s t fu n c t io n s a r e fou n d t o be l i n e a r wh ich e n a b le s th e u se o f LP. F i n a l l y , s e n s i t i v i t y a n a ly s i s i s p e r fo rm ed t o f i n d th e a l lo w e d ra n g e s f o r demand f o r e c a s t s a s w e l l a s r e g u l a r and o v e r t im e w o rk in g h o u rs .Item Open Access Aggregate production planning: an application in Özkaşıkçı Flour Mill(Bilkent University, 1996) Çağan, AlpasAggregate planning is medium-range capacity planning that typically covers a time horizon of anywhere from 3 months to 18 months. The goal of aggregate planning is to achieve a feasible production plan that will effectively utilize the organization’s resources to satisfy expected demand. In this study. Aggregate Production Planning is applied to 0zka?ik9i Flour Mill in order to maximize the total profit by using the optimal allocation of export and domestic sales to the plant capacity. A nonlinear programming (NP) model is developed and the proposed model is run on GAMS (General Algebraic Modeling System) software package. Alternative scenarios are applied to the model in order to find optimal allocation of export and domestic production and to maximize the total profit.Item Open Access Analyzing the effect of consumer returns in a multi-period inventory system(Bilkent University, 2012) Erikçi, İsmailReturn of a sold item by a customer becomes tremendously common situation in many industries. Increase in the amount of returned items promotes return information to be a critical factor for inventory control. Undoubtedly another critical parameter for an inventory system is the length of the review period. Effect of the review period or length of the time-bucket is amplified with returned items, because available return information at a decision point is related to the frequency of the review. In this study, we analyze the effects of these two parameters over a multiperiod inventory system where the length of a time horizon is fixed. Dynamic programming approach is used to calculate the optimal inventory positions. In dynamic programming, it is assumed that a fixed proportion of sold items are returned. Computational results are obtained to compare the effects of return information under different return proportions and period lengths. These results are used to conduct various analyses to explore the level of the advantage gained by using return information.Item Open Access An application of Silver Meal Heuristic to MRP lot sizing decisions at Turk Traktor Fabrikasi(Bilkent University, 1995) Esmer, Berkhan N.MRP does not consider setup and inventory holding costs for lot sizing but very quick algorithms like Silver-Meal can be used for lot sizing decisions. A module to apply Silver-Meal Heuristic to manufacturing work order releases at Türk Traktör Fabrikasy, Ankara, Turkey is designed and tested for 3 months. The module processes demand for finished goods, determines lot sizes, checks capacities by loading machines according to the schedule and reports the setup, inventory holding and overtime costs. These cost figures are compared with the MRP lot sizes. It is observed that, the planning time decreased by 90% by designing module in PCs connected to the main databases, and the total costs decreased by 50%.Item Open Access Application of the critical path method to the planning of a technology transfer project using linear programming(Bilkent University, 1993) Emirli, ElifThe main purpose of this thesis is to utilize the critical path method in the planning of a technology transfer project by using linear programming. LINDO software is practiced in establishing the linear programming formulation and a matrix generator is written in C language to input the formulation into LINDO format. In this way, the schedule of the project is created, the completion time of the project is calculated and the activities forming the critical path are determined. Also by applying a parametric analysis to the right-hand sides of the constraints (activity durations) for the noncitical activities, the times when the critical activities became critical are determined.Item Open Access Carbon restricted newsvendor problem under CVAR objective and resource constraints(Bilkent University, 2014) Korkmaz, ÖzümNewsboy problem has been studied in the literature extensively. The classical newsvendor, representing the risk neutral decision maker, determines the optimal order/production quantity by maximizing the expected profit or minimizing the expected total cost of a single period with stochastic demand. This approach is not suitable if one also aims to reduce the chances of facing unexpected losses due to demand uncertainty. In this thesis, two problems are investigated with a single product newsvendor under CVaR maximization objective. The first problem addresses the newsvendor model with two different carbon emission reduction policies, namely, mandatory emission allowance and carbon emission trading mechanism. In the second problem, as an extension of the first one, a newsvendor with multiple resource constraints is considered for the cases where the resources have quotas with trade options. Analytical expressions for optimal order/production quantities are determined together with the optimal trading policy and numerical examples are provided.Item Open Access Continuous time control of make-to-stock production systems(Bilkent University, 2010) Bulut, ÖnderWe consider the problem of production control and stock rationing in a make-tostock production system with multiple servers –parallel production channels--, and several customer classes that generate independent Poisson demands. At decision epochs, in conjunction with the stock allocation decision, the control specifies whether to increase the number of operational servers or not. Previously placed production orders cannot be cancelled. We both study the cases of exponential and Erlangian processing times and model the respective systems as M /M /s and M /Ek /s make-to-stock queues. We characterize properties of the optimal cost function, and of the optimal production and rationing policies. We show that the optimal production policy is a state-dependent base-stock policy, and the optimal rationing policy is of state-dependent threshold type. For the M /M /s model, we also prove that the optimal ordering policy transforms into a bang-bang type policy when we relax the model by allowing order cancellations. Another model with partial ordercancellation flexibility is provided to fill the gap between the no-flexibility and the full-flexibility models. Furthermore, we propose a dynamic rationing policy for the systems with uncapacitated replenishment channels, i.e., exogenous supply systems. Such systems can be modeled by letting s --the number of replenishment channels-- go to infinity. The proposed policy utilizes the information on the status of the outstanding replenishment orders. This work constitutes a significant extension of the literature in the area of control of make-to-stock queues, which considers only a single server. We consider an arbitrary number of servers that makes it possible to cover the spectrum of the cases from the single server to the infinite servers. Hence, our work achieves to analyze both the exogenous and endogenous supply leadtimes.Item Open Access Design and implementation of an MRP-II system in electronics industry(Bilkent University, 1991) Cankat, A BurçManufacturing Resource Planning (MRP II) system is a modern production planning and control method that is relatively new in our country. In today's competitive and continuously improving industrial scene MRP II systems play an important role in increasing productivity. Electronics industry is a field that is highly suitable for MRP applications and can easily set a good example for further improvements. This work aims at applying a professional MRP II softv>^are to a relatively large electronic equipment manufacturer. In this aspect the semi-formal operating system of the company is totally reconstructed and formalized to meet the requirements of the new system. To achieve these a phased implementation plan is developed and executed and thus a successful implementation is performed. Finally, the initial results of the new system are discussed.Item Open Access Essays on non-cooperative inventory games(Bilkent University, 2012) Körpeoğlu, EvrenIn this thesis we study different non–cooperative inventory games. In particular, we focus on joint replenishment games and newsvendor duopoly under asymmetric information. Chapter 1 contains introduction and motivation behind the research. Chapter 2 is a preliminary chapter which introduce basic concepts used in the thesis such as Nash equilibrium, Bayesian Nash equilibrium and mechanism design. In Chapter 3, we study a non-cooperative game for joint replenishment of multiple firms that operate under an EOQ–like setting. Each firm decides whether to replenish independently or to participate in joint replenishment, and how much to contribute to joint ordering costs in case of participation. Joint replenishment cycle time is set by an intermediary as the lowest cycle time that can be financed with the private contributions of participating firms. We consider two variants of the participation-contribution game: in the single–stage variant, participation and contribution decisions are made simultaneously, and, in the two-stage variant, participating firms become common knowledge at the contribution stage. We characterize the behavior and outcomes under undominated Nash equilibria for the one-stage game and subgame-perfect equilibrium for the two-stage game. In Chapter 4, we extend the private contributions game to an asymmetric information counterpart. We assume each firm only knows the probability distribution of the other firms’ adjusted demand rates (demand rate multiplied by inventory holding cost rate). We show the existence of a pure strategy Bayesian Nash equilibrium for the asymmetric information game and provide its characterization. Finally, we conduct some numerical study to examine the impact of information asymmetry on expected and interim values of total contributions, cycle times and total costs. quantities for all firm types except the type that has the highest possible unit cost, who orders the same quantity as he would as a monopolist newsboy. Consequently, competition leads to higher total inventory in the industry. A firm’s equilibrium order quantity increases with a stochastic increase in the total industry demand or with an increase in his initial allocation of the total industry demand. Finally, we provide full characterization of the equilibrium, corresponding payoffs and comparative statics for a parametric special case with uniform demand and linear market shares.Item Open Access Final phase inventory management of spare parts under nonhomogeneous poisson demand rate(Bilkent University, 2013) Çay, Sertalp BilalIn product lifecycle, there are three phases, initial phase, normal phase and final phase. Final phase begins when the product is out of production, and ends when the last contract expires. It is generally the longest period in the lifecycle. Although the product is not manufactured any more, spare parts of the product need to be supplied to the market. Firms need to provide these parts at the retailer level until the end of the phase due to legal responsibilities. Because of lack of historical data and unavailability of forecasting, retailers need a systematic policy to decide replenishment quantity and time to prevent excessive holding, backordering, unit and setup costs. In our problem, we assume that demand of the spare part is a non-homogeneous Poisson process where the rate parameter is a non-increasing function of time. We consider all costs and lead time are fixed and known. Due to characteristics of the final phase, the planning horizon is taken as finite and known. In this study, we developed two alternative heuristics for retailer’s problem to minimize total cost during the final phase. First heuristic is a continuous-review policy based on estimation of future replenishments by solving series of deterministic demand subproblems. Second heuristic is a periodic-review policy with variable period lengths, which solves myopic problems, by selecting subsequent time points to check inventory position. We also developed a simulation model to evaluate performances of the heuristics. This study provides an efficient way to decide on replenishment quantity and time. Limited numerical results show that heuristics provide near-optimal results for homogeneous cases studied in the literature. Moreover, this is one of the initial studies that considers final phase with non-homogeneous demand rate. In that sense, it makes a contribution to the literature of final phase problems and provides a systematic way of replenishment decisions for the retailers.Item Open Access Impact of product variety on inventory performance : an empirical analysis of pharmaceutical and medical device industries(Bilkent University, 2012) Aydınlı, Ali YağmurIn this thesis, we construct empirical models to analyze the effect of various financial measures and product variety on inventory performance. We apply multiple regression models and simultaneous equations models using 2010 financial data for 128 U.S. firms in pharmaceutical and medical device industries. Using multiple regression models, we investigate the correlation of inventory turnover with product variety, gross margin, capital intensity and type of the firm. Product variety data are obtained from U.S. Food and Drug Administration. The best multiple regression model explains 38.50% of the total variation in inventory turnover and we observe that inventory turnover is negatively correlated with product variety. Since inventory turnover is the ratio of cost of goods sold (sales) to inventory level, a change in product variety might have an effect both on inventory level and cost of goods sold. In order to investigate the effects of product variety on cost of goods sold and inventory level separately, we employ simultaneous equation models. The best simultaneous equation model explains 96.22% of the variation in inventory level and shows that inventory level is positively associated with product variety.Item Open Access The impact of reengineering in manufacturing companies: a methodology for operations improvement and manufacturing productivity(Bilkent University, 1993) Atceter, MuzafferMany manufacturing companies today are facing the problem of loosing their competitive edge in international markets. This is partly due to the outdated manufacturing processes. This study is examining the improvement methods and suggesting a methodology whose scope is wider than small changes. This type of improvements requires a radical change in the manufacturing processes. The word reengineering, meaning process redesign, is used to describe this method for achieving the manufacturing productivity considering the cost, quality, customer service, time and management issues. First chapter is defining reengineering. The techniques, methods and a step-bystep approach for productivity projects are explained in the second chapter. Chapter three includes an analysis of a Turkish case company with the methods given in chapter 2. The thesis questioning the applicability of reengineering projects for manufacturing companies in Turkey in chapter 4. It is examining the difficulties that the project teams would face.Item Open Access Integrated machine-scheduling and inventory planning of door manufacturing operations at OYAK Renault factory(Bilkent University, 2012) Bozkaya, NurcanA car passes through press, body shell, painting and assembly stages during its manufacturing process. Due to the increased competition among car manufacturers, they aim to continuously advance and improve their processes. In this study, we analyze planning operations for the production of front/back and left/right doors in body shell department of Bursa Oyak-Renault factory and propose heuristic algorithms to improve their planning processes. In this study, we present four different mathematical models and two heuristics approaches which decrease the current costs of the company particularly with respect to inventory carrying and setup perspectives. In the body shell department of the company, there are two parallel manufacturing cells which produces doors to be assembled on the consumption line. The effective planning and scheduling of the jobs on these lines requires solving the problem of integrated machine-scheduling and inventory planning subject to inclusive eligibility constraints and sequence independent setup times with job availability in flexible manufacturing cells of the body shell department. The novelty in the models lie in the integration of inventory planning and production scheduling decisions with the aim of streamlining operations of the door manufacturing cells with the consumption line. One of the proposed heuristic approaches is Rolling Horizon Algorithm (RHA) which divides the planning horizon into sub-intervals and solves the problem by rolling the solutions through sub-intervals. The other proposed algorithm is Two-Pass Algorithm which divides the planning horizon into sub-intervals and solves each sub-problem in each sub-interval to optimality for two times by maintaining the starting and ending inventory levels feasible. These approaches are implemented with Gurobi optimization software and Java programming language and applied within a decision support system that supports daily planning activities.Item Open Access Integrated scheduling and tool management in flexible manufacturing cells(Bilkent University, 1997) Özkan, SerkanA flexible inanufaciuring cell (l''M(J) is designed to combine the efiiciency of a liigli j)roduction line and the ih'xibility of a job shop to best suit the batch production of ruid-volume and mid variety of products. In view of the high investment and operating costs of h'lVICs, attention should be pa.id to their eifective utilization. Their eircctivc'iiess is, however, directly related to their design and operational strategies. In this study, we propose a.n iutegra.ted algoritlim tliat will solve the scheduling and the tool management problems in an FMC. There will be three stages in the algorithm. The first stage will perform the tool allocation. The second stage will find an initial schedule, and the final stage will finalize tlie schedule via cojitrollable proc(Wsiug times. The main objective of the ju'oposed aigorithiu is to minimize' total pioductiou cost coiisisting of tooling cost, operaXional cost and tardiness cost..Item Open Access Medium range production planning of "Tacer" company: a case study(Bilkent University, 1994) Süer, BurakIn order to foresee the potential problems related with production, a production plan is undertaken for the year 1994. Product classification is determined according to the annual sales volume of the company "Tacer". A production schedule is prepared in relation with the forecast data of 1994. The schedule is examined by capacity requirements and financial analysis. Some capacity problems that are highlighted were investigated in the analysis section. Short and long term solutions were made to overcome the insufficient capacityItem Open Access Minimazing the total completion time in a two stage flow shop with a single setup server(Bilkent University, 2012) Kolay, MuhammetIn this thesis, we study a two stage flow shop problem with a single server. All jobs are available for processing at time zero. Processing of a job is preceded by a sequence independent setup operation on both machines. The setup and processing times of all jobs on the two machines are given. All setups are performed by the same server who can perform one setup at a time. Setups cannot be performed simultaneously with job processing on the same machine. Once the setup is completed for a job, processing can automatically progress without any further need for the server. Setup for a job may start on the second machine before that job finishes its processing on the first machine. Preemption of setup or processing operations is not allowed. A job is completed when it finishes processing on the second machine. The objective is to schedule the setup and processing operations on the two machines in such a way that the total completion time is minimized. This problem is known to be strongly NP-hard [3]. We propose a new mixed integer programming formulation for small-sized instances and a Variable Neighborhood Search (VNS) mechanism for larger problems. We also develop several lower bounds to help assess the quality of heuristic solutions on large instances for which optimum solutions are not available. Experimental results indicate that the proposed heuristic provides reasonably effective solutions in a variety of instances and it is very efficient in terms of computational requirements.Item Open Access On the newsvendor problem with multiple inputs under a carbon emission constraint(Bilkent University, 2012) Sözüer, SibelIn this thesis, we consider two problems in the newsvendor setting with multiple inputs, under a carbon emission constraint and non-linear production functions. In the first problem, we assume a strict carbon cap and find the optimal production quantity and input allocation that will maximize the expected profit under this constraint. In the second problem, we consider an emission trading scheme where an advance purchase of carbon emission permits is made at an initial price before the random demand is realized. When the demand is realized and new carbon trade prices are revealed, it is possible to buy additional permits or to sell an excess amount. The aim is to decide on the optimal allocation of the inputs as well as the carbon trading policy so as to maximize the expected profit. In both problems, the production quantity is linked to multiple inputs via the Cobb-Douglas and Leontief production functions. Optimal policy structures are derived and numerical examples are provided.Item Open Access Order timing for seasonal products with demand learning and capacity constraints(Bilkent University, 2009) Demirci, Ece ZelihaOrder time and order quantity of seasonal products significantly affect profits gained at the end of the period due to high demand uncertainty. Delaying order time enables a company to gain more information on demand, while decreasing the possibility of realizing the best order quantity due to capacity constraints. This thesis analyzes the problem of determining the best order time for a seasonal product manufacturer in an environment, where there exists a single opportunity for ordering and capacity is a decreasing function of the order time. Main feature of the study is utilizing demand information collected until the order time for resolving some portion of the demand uncertainty. A Bayesian update procedure is utilized to capture the essence of the gathered demand information. Three models are proposed for determining the order time, each having a different level of flexibility with respect to possible order times considered. Analytical results for structural properties, as well as extensive numerical results are obtained. A computational study is carried out in order to compare the performance of the models under different settings and to identify the conditions under which the demand learning is most beneficial.Item Open Access A producer survey on Turkish furniture industry(Bilkent University, 1996) Öğün, Emir PolatTurkish furniture industry has been growing steadily since the liberalization of Turkish economy in early 1980’s. However, the industry faces some technological and economical problems which affects the competitiveness of the firms in the global market. The major problems of the firms in the furniture sector is availability and quality of raw materials, and the productivity of labor. Turkish furniture manufacturers can be classified into two categories; small job-shops (workshops) and big firms. Small job-shops are scattered all over the country and their major market is domestic. Whereas big firms market their products domectically, and internationally. In this thesis we have investigasted Turkish furniture industryItem Open Access Robust solutions to single and multi-period machine layout problems with interval flows(Bilkent University, 1997) Tüfekçi, Özgür AtillaDesign clecisous are genevcUly given in the early stages when there is a great deal of inexactness in the data gathered. In this study, we consider the plant Uiyout problem witli inexactness in material flow quantities with the aim of designing robust layouts. Material flow quantities are assumed to lie in a priori specified intervals based, for example, on low ¿md high demands. The robustness criterion we use is to minimize the maximum I’egret. We extend our work to the multi-period case where a distinction is made between reversible and irreversible layout decisions.