Pace making and worker reassignment for assembly line rebalancing

Abstract

The objective of this article is to develop a mathematical model that helps foremen rebalance assembly lines in real time. Assembly lines with a large number of workstations go through extensive line balancing to determine production rates. Once production begins, one or more workstations may not operate at predetermined production rates due to disturbances, and the assembly line requires rebalancing. Previous research largely focused on task reassignment for rebalancing. Effective and efficient tools for real-time line rebalancing are needed. This research focuses on rebalancing of unpaced and asynchronous assembly lines through pace making and worker reassignment. A mixed integer programming model is developed and its optimal solution determines which workstations pace up (increase production rates) and the amount of increase, which workstations pace down (decrease production rates) and the amount of decrease, and whether workers from certain workstations are reassigned to work at other workstations to decrease the production rates of the former and increase the production rates of the latter. Foremen may use these recommendations to rebalance assembly lines by adjusting production rates and reassigning workers. Numerical results show that the solution time of the model is less than one second, which enables real-time line rebalancing for large assembly lines.

A detailed review and analysis of assembly line rebalancing problems

“…In the reviewed papers, worker-dependent task times occur in two studies (Çimen et al, 2022;Fattahi and Samouei, 2016). Moreover, the worker assignment problem was also incorporated in the ALRBP in nine publications (Budak and Chen, 2020;Çimen et al, 2022;Corominas et al, 2008;Fattahi and Samouei, 2016;Karas and Ozcelik, 2021;Michels and Costa, 2021;Sikora et al, 2017;Yang et al, 2013;Yang and Gao, 2016). Corominas et al (2008) tried to minimize the number of temporary (unskilled) workers who should work alongside skilled workers and cannot perform some tasks, leading to worker assignment restrictions.…”

“…The first column of Table 5 indicates the related references. The second column specifies articles that have a constraint related to the number of workstations (Budak and Chen, 2020;Çimen et al, 2022;Fattahi and Samouei, 2016;Girit and Azizo glu, 2021;Hu et al, 2020;Karas and Ozcelik, 2021;Li, 2017;Michels and Costa, 2021;Mokhtari and Mozdgir, 2015;Otto and Scholl, 2011;Zhang et al, 2016). Task zoning constraints are categorized as negative zoning and positive zoning in the literature, which are used to forbid or force the assignment of specific tasks to the same workstation.…”

“…Finally, the last column of Table 3 states whether there exists an additional problem accompanying the rebalancing problem. For instance, some papers study worker reassignment problems together with the rebalancing problem (Budak and Chen, 2020; Çimen et al , 2022; Corominas et al , 2008; Fattahi and Samouei, 2016; Karas and Ozcelik, 2021; Michels and Costa, 2021; Sikora et al , 2017; Yang et al , 2013; Yang and Gao, 2016), while some others incorporate ergonomic aspects into the rebalancing problem (Çimen et al , 2022; Otto and Scholl, 2011). AL rebalancing problems classification, which is summarized above, is illustrated in Figure 4.…”

“…The task times are deemed to be dynamic if processing times fluctuate over time as a result of learning effects or advancements in the production process. Yang and Gao (2016), Li and Boucher (2017); and Budak and Chen (2020) used dynamic task times in their studies.…”

“…Moreover, the worker assignment problem was also incorporated in the ALRBP in nine publications (Budak and Chen, 2020; Çimen et al , 2022; Corominas et al , 2008; Fattahi and Samouei, 2016; Karas and Ozcelik, 2021; Michels and Costa, 2021; Sikora et al , 2017; Yang et al , 2013; Yang and Gao, 2016).…”