LB-ALBP: The lexicographic bottleneck assembly line balancing problem

Abstract

The classic assembly line balancing problem (ALBP) basically consists of assigning a set of tasks to a group of workstations while maintaining the tasks' precedence relations. When the objective is to minimise the number of workstations m for a given cycle time CT, the problem is referred to as ALBP-1; if the objective is to minimise CT given m, then the problem is called ALBP-2. The only objective in ALBP-2 is to minimise CT, i.e., the workload of the most heavily loaded workstation (the bottleneck). However, considering the second-biggest, third-biggest, etc. workloads, can be important. Distributing a workload among six workstations as 10, 10, 10, 4, 3, 3, is not the same as distributing it as 10, 6, 6, 6, 6, 6. The CT value is the same, but the second distribution is beyond question more reliable and balanced. In this paper, we present and formalise a new assembly line balancing problem: the lexicographic bottleneck assembly line balancing problem (LB-ALBP). The LB-ALBP hierarchically minimises the workload of the most heavily loaded workstation (CT), followed by the workload of the second most heavily loaded workstation, followed by the workload of the third most heavily loaded workstation, and so on. We present two mixed-integer linear programming (MILP) models designed to solve the LB-ALBP optimally, together with three heuristic procedures based on these MILPs. © 2011 Taylor & Francis.