Browsing by Subject "Warm/cold process"

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    Dynamic lot sizing for a warm/cold process: heuristics and insights
    (Elsevier, 2013-09) Toy, A. Ö.; Berk, E.
    We consider the dynamic lot sizing problem for a warm/cold process where the process can be kept warm at a unit variable cost for the next period if more than a prespecified quantity has been produced. Exploiting the optimal production plan structures, we develop nine rule-based forward solution heuristics. Proposed heuristics are modified counterparts of the heuristics developed previously for the classical dynamic lot sizing problem. In a numerical study, we investigate the performance of the proposed heuristics and identify operating environment characteristics where each particular heuristic is the best or among the best. Moreover, for a warm/cold process setting, our numerical studies indicate that, when used on a rolling horizon basis, a heuristic may also perform better costwise than a solution obtained using a dynamic programming approach.
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    Single item lot-sizing problem for a warm/cold process with immediate lost sales
    (Elsevier, 2008-06-16) Berk, E.; Toy, A. Ö.; Hazır, Ö.
    We consider the dynamic lot-sizing problem with finite capacity and possible lost sales for a process that could be kept warm at a unit variable cost for the next period t + 1 only if more than a threshold value Qt has been produced and would be cold, otherwise. Production with a cold process incurs a fixed positive setup cost, Kt and setup time, St, which may be positive. Setup costs and times for a warm process are negligible. We develop a dynamic programming formulation of the problem, establish theoretical results on the structure of the optimal production plan in the presence of zero and positive setup times with Wagner–Whitin-type cost structures. We also show that the solution to the dynamic lot-sizing problem with lost sales are generated from the full commitment production series improved via lost sales decisions in the presence of a warm/cold process. 2006 Elsevier B.V. All rights reserved.