An integer programming mathematical model with line balancing and scheduling for standard work optimization: A realistic application to aircraft engines assembly lines

Abstract

Aircraft Engine Maintenance Repair and Overhaul (MRO) companies face intense global competition that requires effective management of maintenance costs, TAT (turnaround time), and accurate job standards. These indicators can be improved through methodologies such as line balancing and scheduling of assembly tasks. The main objective of this article is to propose models for standard work definition that can optimize companies’ indicators – TAT, the number of operators, training costs, and load balancing – considering the specificities of the aircraft engine assembly lines. First, a literature review identified features of line balancing and scheduling integrated problems relevant to aircraft engine assembly and highlighted the integer programming mathematical models already proposed. Second, four new MILP models were developed in order to combine some of the features identified during the literature review and include new relevant ones: the multi-skilled operators can work in more than one engine per takt time, and each task may start in one takt time, and finish in the next. Lastly, the models were implemented in the AIMMS system and hierarchically solved by the CPLEX on data of two different assembly lines from a Brazilian MRO company. The results were considerably better than those obtained empirically by the firm. They include a 14.3% reduction in TAT for one assembly line and a 15.4% reduction in the number of operators for another, confirming a suitable decision support tool for the company, which can also help other firms.