Handling multi-lean measures with simulation and simulated annealing

This paper describes a simulation-based approach for developing a lean production system of multi-lean measures. Three lean measures are defined to characterize the leanness of the underlying production system: productivity, cycle time, and work-in-process inventory. An optimized setting to certain operational parameters is determined so that a best tradeoff of the three lean measures is reached. The problem formulation results in a multi-objective optimization problem with no closed-form definition of problem objective functions and constraints. The solution approach utilizes Discrete Event Simulation (DES) to deploy lean techniques and model lean measures under process variability and plant constraints and dynamics. A direct search method (i.e., Simulated Annealing (SA)) is used to search of problem domain. A model-based Value Mapping (VM) is used for combining the conflicting multi-lean measures and guiding the SA search for optima. The DES model is also used to develop a future state dynamic Value Stream Map (VSM) of the optimized production process. The approach is applied to an example production system where the capacity of material handling conveyors and the size of maintenance crew are optimized to develop a lean system in terms of three lean measures. Little's formula is used to verify the simulation assessment of lean measures. Optimization results are also used to demonstrate the conflict among lean measures, the impact of process variability on lean measures, and the role of VM in reaching an efficient tradeoff of multi-lean measures.