Browsing by Author "Kalay, Serkan."

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    Campaign planning under sequence dependent family setups and co-production in process industry
    (Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2020., 2020.) Kalay, Serkan.; Taşkın, Zeki Caner.
    We investigate tactical level production planning problem in process industries, with float glass manufacturing being the specific application domain. Process industries are cost intensive, and as a result, efficient usage of capacity through planning is necessary. In the presence of high sequence dependent family setup costs, the need for planning production in batches, or campaigns as named in the float glass industry, arises. Campaign planning is determining timing and duration of each product family, which translates into setups. Moreover, availability of input data in different resolution, i.e. setup times in continuous time whereas customer demand forecast are available in discrete time, increases the complexity. Co-production is a phenomenon that exists in several industries including float glass manufacturing. Usually due to some special characteristic of the manufacturing process some products need to be produced by necessity. This is another challenge for efficient capacity usage as well as inventory management. We study the problem for different complexity levels. We start with single machine instance and develop two formulations. A novel branch-and-price algorithm is proposed for the parallel machine extension. Finally, we extend the problem to multiple product hierarchy levels and network structure including customer locations. We demonstrate the efficiency of our methods through extensive numerical experiments as well as some further tests to analyze the sensitivity of the cost components.
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    Stochastic programming based sales operations planning in television manufacturing industry
    (Thesis (M.S.)-Bogazici University. Institute for Graduate Studies in Science and Engineering, 2014., 2014.) Kalay, Serkan.; Ünal, Ali Tamer.
    Planning in TV manufacturing industry contains significant risks originating from rapid changing technology and high demand volatility. Within this scope, S&OP (Sales and Operations Planning) can be an enriching method for business plans via associating different levels of planning such as supply, demand and operational level planning. The main goal here is to prevent lost sales as much as possible while balancing inventories in terms of critical materials. For competitive business purposes, a make-to-order business model with mass customization allowance can be quite attractive for customers but in the meantime provokes planning complexity. In this study, we propose an S&OP model for a TV manufacturer in Turkey based on stochastic programming that will try to handle demand uncertainty while attaining better inventory compositions. After reviewing concepts of S&OP process and methods of stochastic programming, the planning problem is defined in detail followed by the formulation of optimization model. To inspect the effects of stochastic programming on S&OP process in TV manufacturing industry, a practical implementation from Vestel Electronics is analyzed.