The mixed-model U-line balancing problem

Many manufacturers are switching their production lines from single product or batch production to mixed-model production, often as a consequence of implementing just-in-time (JIT) principles into their operations. In mixed-model production, different products or models are produced on the same line with the models interspersed throughout a production sequence. This helps manufacturers provide their customers with a variety of products in a timely and cost-effective manner. The mixed-model U-line balancing (MMULB) problem assigns the tasks required to produce all models to a minimum number of stations on a U-shaped line. U-lines are widely used and well-suited to mixed-model production. A model of the MMULB problem is developed in this paper. The problem is NP-hard. An approximate solution algorithm is presented, and an illustrative example is worked. Areas where more research is needed are identified.