Evaluation of the mixed-model assembly line balancing problem with variable operation times and product mix

In order to make production systems more versatile and flexible, there has been a transition in the last decades towards mixed-model assembly lines, where all the products are variations of the same base product and only differ in specific customisable attributes. A mixed-model environment presents balancing problems (Mixed-model Assembly Line Balancing Problem or MALBP) that can normally be solved by transforming the mixed-model system into a Single Assembly Line Balancing Problem (SALBP), and simplified by creating a 'virtual average model'. In this case, a general average model not dependent on the characteristics of the real system can represent a considerable restriction since the reality is characterised by high variability in the operation times and product mix between different product models. A comparative evaluation of eight different methodologies to reduce a MALBP into a SALBP is presented, using several randomly generated problems, to test operation time fluctuations and the product mix. Their evaluation is based on five different performance measures.