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    Balancing straight and U-shaped assembly lines with resource dependent task times
    (TAYLOR & FRANCIS LTD, 2011) Kara, Yakup; Ozguven, Cemal; Yalcin, Nese; Atasagun, Yakup
    The basic assumption of assembly line balancing is that every task's time is fixed. However, in practice, different processing alternatives may be available to process a task with different times. The problem in this case is to assign tasks and resources to work stations that minimise total cost and so-called resource dependent assembly line balancing (RDALB) in the literature. This study proposes a new integer programming formulation for RDALB. This formulation is then modified to develop a formulation for RDULB problem in U-shaped assembly lines. To the best knowledge of the authors, this study is the first RDULB study and the developed formulation is the first RDULB formulation. The proposed formulations are illustrated and validated using several examples. An experimental analysis is also conducted to examine the percent improvement in total cost when the line layout is switched into the U-shaped from the straight line shape. Experimental results show that an improvement in total operating cost is obtained when the straight line is switched into the U-shaped line configuration. Results also show that percentage improvement in total operating cost is significantly greater for problem instances having a large number of tasks and having greater values for the strength of the precedence relationships among tasks.
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    Multi-objective approaches to balance mixed-model assembly lines for model mixes having precedence conflicts and duplicable common tasks
    (SPRINGER LONDON LTD, 2011) Kara, Yakup; Ozguven, Cemal; Secme, Nese Yalcin; Chang, Ching-Ter
    The existence of common tasks for model mixes is the main characteristic of the mixed-model assembly lines. The decision problem considered in this study is how some common tasks can be duplicated to improve the efficiency of a mixed-model assembly line under the assumption that some of the precedence relationships among common tasks for different products are conflicting. This decision problem is called by the authors as "mixed-model assembly line balancing with precedence conflicts and duplicable common tasks (MALB-CD)." Although precedence conflicts have been mentioned in some of the earlier studies, to the best knowledge of the authors, this is the first study that deals with precedence conflicts by mathematical modeling. In the first step of this study, a new binary mathematical model with single objective for MALB-CD is developed where the single-objective is to minimize the number of workstations. Three goals relevant to MALB-CD are then incorporated into this single-objective model to give rise to two pre-emptive goal programming models, one with precise and the other with fuzzy goals. Minimizing the number of workstations, the cycle time and the total cost required to duplicate common tasks are the goals in question. The proposed mathematical models are illustrated and validated by means of a number of numerical illustrations.