MANUFACTURING CELL-FORMATION IN THE PRESENCE OF LOT SPLITTING AND MULTIPLE UNITS OF THE SAME MACHINE

We present a realistic cell formation problem in the design of cellula r manufacturing systems which includes three important features. First , when multiple units of a machine type are considered due to processi ng time requirements, the model accounts for assigning the units to di fferent cells if such an assignment contributes to reducing material h andling costs. Second, the model accounts for the possibility of perfo rming two or more nonconsecutive operations of a part on the same mach ine. Finally, the model allows for splitting the lot into two if the t otal workload required of a part's operation on a machine exceeded its daily unit capacity expressed in manned hours. We refer to this featu re as 'lot splitting'. Consequently, the operation required of each sp lit lot of the part can be performed on a separate unit (machine). The model formulated for the problem falls into the class of generalized quadratic binary programming models. As the problem is shown NP-hard i n the strong sense, a higher level heuristic algorithm based upon a co ncept known as tabu search is presented. Results obtained from solving an example problem demonstrate the application of the proposed algori thm when either of the two features-lot splitting or nonconsecutive op erations, exist. The applicability of the proposed algorithm has furth er been extended to solving a test problem consisting of both features -lot splitting and non-consecutive operations. The results obtained sh ow a reduction of > 50% in total moves (material handling costs) betwe en the initial solution and the final best solution.