The deployment of temporary production workers in assembly operations: a case study of the hidden costs of learning and forgetting

The dynamics of workforce skill levels has a considerable impact on plant-level performance that is commonly overlooked by managers of manufacturing operations. In this study, we present a discrete event simulation model inspired by and validated in an actual manufacturing setting that includes short product life cycles, mid-volume production quantities, and a production environment consisting of assembly, inspection and testing.The effect of worker skill dynamics is analyzed using a factorial experimental design that contrasts the use of temporary versus permanent workers on manufacturing cost performance. The manufacturing costs assessed include labor, inspection and testing. The cost of reworking a defect is captured as an increase in the labor consumption. Materials costs are not assessed. At the core of the analysis, it is assumed that temporary workers have relatively less skill and therefore have higher average production times, higher average defect rates associated with their assembly activity, and lower rates of learning. In addition, the variance of the production time is higher for the temporary workers. Despite these indicators of performance problems, temporary workers may be used because of the considerably lower wage rate compared to permanent employees.Our in-depth case analyses shows that assigning skilled permanent workers to upstream build operations was superior to other policies deploying temporary workers, regardless of lot size or product complexity. Attesting to the importance of the labor mix component of manufacturing strategy, workforce deployment policies tended to dominate product switching frequency (a proxy variable for lot size and product mix) in impacting costs.