A master scheduling model with skilled and unskilled temporary workers

A new model called MPS-T is presented for the scheduling of temporary workers in mixed model flow lines with both skilled and unskilled workstations. We classify workers in two dimensions: (i) permanent or temporary, and (ii) skilled or unskilled. While all permanent workers are skilled, temporary workers can be either skilled or unskilled. Two workstation restrictions are modeled in the MPS-T: (i) some workstations may be limited to only skilled workers if there is a significant operational complexity, (ii) each workstation is limited to a minimum ratio of permanent to temporary workers. Such workforce models are commonly seen in labor intensive export oriented factories located in the Far East. These factories experience an order behavior that is characterized by high variance and short lead times. Distinguishing between worker types, permits management to limit their fixed workforce costs and also rapidly access a cheaper labor pool to meet demand surges. MPS-T is modeled as a mixed integer program and the key decisions are: (i) What type of temporary workers to hire or layoff in each period, (ii) the number of workers to hire or layoff in each period, (iii) the assignment of the work time of workers to the work stations, and (iv) the usage of overtime hours. A case study example to study model behavior under different parametric conditions is reported.