5. Conclusion and future work
This paper proposed an MILP model (without heuristics) for an ice cream multi-week production scheduling problem. The model adopted the makespan objective and a number of constraints including start/stop interval formulation, and processed product arranging constraints. Multi-week constraints were formulated to address the unique arrangements required to transfer products from week to week. This included constraints for integrating products from preceding production week, proper break-up points of products processing for the weekend break, and end of the week clean-up session. The model is implemented in CPLEX and three sets of optimization experiments were conducted. The first set of experiments showed that proposed MILP model was capable of solving problem instances that necessitated the use of heuristics to an MILP model in the past. The second and third sets of experiments compared the run results for cases with transferred products from prior week as well as added weekly clean-up and process break-up points for weekends. Proper break-up of process affected the final makespan value and hence would have to be integrated into the model. In particular, these runs showed that adding the clean-up sessions at the end may not give the same result as scheduling the sessions with proper break-up points
