A mathematical programming approach for walking-worker assembly systems

Abstract

Purpose – It has become increasingly critical to design and maintain flexible and rapid assembly systems due to unpredictable and varying market conditions. The first stage of developing such systems is to restructure the existing assembly system. After designing the manufacturing system, efforts should be made for capacity adjustments to meet the demand in terms of allocating tasks to workers. Walking-worker assembly systems can be regarded as an effective method to achieve flexibility and agility via rabbit chase (RC) approach in which workers follow each other around the assembly cell or line and perform each task in sequence. In this paper, a novel mathematical programming approach is developed with the aim of integrating RC in assembly processes. Therefore, this study is thought to add value to industrial assembly systems in terms of effectively raising engineering control for task allocation activities. Design/methodology/approach – Two consecutive mathematical models are developed, since such a hierarchical approach provides computational convenience for the problem. The initial mathematical programming model determines the number of workers in each RC loop for each segment. In addition, the number of stations and the distribution of station times in the segments is essential. Therefore, the succeeding mathematical programming model generates stations in each segment and provides convenience for the workflow in RC loops. The output of mathematical programming models are the parameters of simulation model for performance assessment. Findings – The effectiveness of the proposed approach was validated by an application in a real-life chair production system. The application resulted in performance improvements for labour requirement (12.5 per cent) and production lead time (9.6 per cent) when compared to a classical assembly system design (CASD) where one stationary worker exists in each station. In addition, it is worth to note that RC leads to a reduced number of workers for a considerable number (39.4 per cent) of test problems. What is more, input as well as output factors have been determined via discriminant analysis and their impacts to the utilization of RC were analyzed for different levels. Practical implications – This study is thought to add value to the industry in terms of effectively providing convenience during production planning and task allocation in assembly lines and cells. Originality/value – To the best knowledge of the author, optimization models for RC considering a real industrial application have not yet been developed. In this context, this paper presents an approach which models RC by the use of mathematical programming in manual assembly processes to address this research gap. The contribution of the paper to the relevant literature is the development of hierarchical mixed integer linear programming models to solve RC problem for the first time.

Walking worker vs fixed worker assembly considering the impact of components exposure on assembly time and energy expenditure

“…& WW number of operators/stations analysis and optimization. [38] observe the interrelationships between the number of workstations and the number of walking workers for their minimization, while [39] proposes a methodology for minimizing number of workers and smoothing workload among stations, and [40] analyze multi-manned assembly with walking workers for minimizing the number of workers and workstations. & WW and lean principles analysis.…”

A novel optimization approach for segmented rabbit chase oriented U-type assembly line design: an application from lighting industry

“…Formulating work congestion and idle times under worker performance differences, Wang et al (2009) also simulated WWAL for some design rules with the aim of preventing congestions. Cevikcan (2014) attempted to solve single model WWAL balancing problem by using a pre-emptive MILP approach. Subsequently, Cevikcan (2016) provided an approach for the same problem for multi model WWAL using heuristics.…”

“…As right-hand side of takt time constraint (constraint set 9) is relaxed in line balancing with RC when compared to classical line balancing (Cevikcan, 2014), the tendency of exposing balance loss-sourced idle times can be avoided in RC applications. Moreover, RC prevents the effects of workload imbalances which deteriorate line performance in terms of capacity utilization and work satisfaction in classical assembly lines (Wang et al, 2009;Al-Zuheri et al, 2012).…”

Sequencing of mixed models on U-shaped assembly lines by considering effective help policies in make-to-order environment

“…Boysen et al [17] investigated the more realistic sequencing problem by considering real availability of utility workers and presented a binary linear program along with a complexity proof. Cevikan [18] considered walkingworker assembly systems as an e ective method to achieve exibility. Mirzapour et al [19] used bypass subline to reduce stoppages of assembly line and to level the part usage rates.…”