Sequencing in mixed model assembly lines: A genetic algorithm approach

The mixed model assembly lines are becoming increasingly popular in a wide area of industries. The authors consider the sequencing problem in mixed model assembly lines, which is critical for efficient utilization of the lines. They extend standard formulation of the problem to allow a hybrid assembly line, in which closed and open workstations are intermixed, and sequence-dependent setup time. A new approach using an artificial intelligence search technique, called genetic algorithm, is proposed. A genetic representation suitable for the problem is investigated, and genetic control parameters that yield good results are empirically found. A new genetic operator, Immediate Successor Relation Crossover (ISRX), is introduced and several existing ones are modified. An extensive experiment is carried out to determine a proper choice of the genetic operators. The performance of the genetic algorithm is compared with those of heuristic algorithm and of branch-and-bound method. The results show that the present algorithm greatly reduces the computation time and its solution is very close to the optimal solution. The authors have identified the ISRX operator to play a significant role in improving the performance.