Flex Work Research Centre

Flexibility in workforce planning is one of the best ways to respond to fluctuations of the demand. This paper proposes a flexible mixed integer linear programming (MILP) model to solve a multiple-shift workforce planning problem under annualized working hours. The model takes into account laws and collective agreements that impose constraints on overtime and holidays. The authors consider possible gradual hiring of full time and partial time workers. Several objectives are pursued such as balancing the workload of the employees or minimizing the workforce size.

Annualizing working hours is a good economical way of adjusting productive capacity to seasonal demand and obtaining flexibility in the distribution of annual working hours. The authors have presented a flexible mixed integer linear programming (MILP) model to solve a multiple-shift workforce planning problem under annualized working hours and without capacity shortage. The model includes many options such as gradual hiring, and part time work. Different restrictions on sets of consecutive weeks are considered such as imposing the same type of week schedule each week on each employee, or bounding the workload on consecutive weeks. While the model does not take into account temporary workers, it would not be difficult to introduce them in the model.

The authors have tested the model on a real life industrial problem and compared different solutions obtained with various parameter settings. The experiments reported in Section 4 clearly demonstrate that the proposed model, once implemented as a black box in a user friendly software, is an interesting tool for managers facing demand fluctuations. They can use our model to generate several solutions corresponding to different options and then negotiate with the workers to choose the most appropriate solution for both.