Balancing assembly line with skilled and unskilled workers

In this paper, we present the process of rebalancing the line at motorcycle-assembly plant. The company found it necessary to rebalance its line, since it needs to increase production in the spring and summer months. The main characteristics of the problem are as follows: (i) the company hires temporary staff, who need more time to carry out their tasks than permanent workers; (ii) there must always be at least one skilled employee working alongside an unskilled one; and (iii) different task groups are incompatible with each other (clean-hands tasks and dirty-hands tasks). The goal is to minimise the number of temporary workers required, given a cycle time and the team of workers on staff. The problem is modelled as a binary linear program (BLP) and solved optimally by means of the ILOG CPLEX 9.0 optimiser. The solution provided, namely 12 permanent workers (skilled) and two temporary workers (unskilled), is an improvement on the solution implemented by the business, which involved 12 permanent workers and four temporary workers.