Managing task processing time variations in manufacturing systems

Managing the variation in task processing time has been a critical problem in manufacturing systems design. We present three research papers for systematic evaluation and handling manufacturing time variations. The manufacturing time variations addressed in the first paper are product-change dependent variations in task times and inter-task times in multi-product manufacturing lines with known production schedule. The problem of unexpected variations in manufacturing times is addressed in the second and third papers. The first paper of this study is focused on incorporating non-value added activities, namely inter-task times, in optimal configuration of multi-product manufacturing lines. The contribution of this paper includes explicit consideration of intra-model inter-task times in station times, optimal assignment of tasks to stations for increased task recurrence between different product models, analysis of batch size effect on station time variation, and selection of machine types according to the flexibility of stations. In the second paper, a moderate robust optimization approach is implemented for systematic evaluation of buffer times in synchronous manufacturing lines. The effect of conservatism level on the minimum cycle time at the bottleneck station and the required buffer time in each station is analyzed. The non-productive time in each station is characterized based on its effect on handling task time variations. The efficiency of the robust optimization approach based on the variation level of uncertain times is verified. The third paper represents the work-sharing approach for managing task time variations in the bottleneck station of synchronous manufacturing lines. The stochastic Chance-Constrained models of this paper provide sufficient pure idle time in the immediate downstream station to finish the incomplete work form the overloaded bottleneck station. The approaches of the third paper prevent extra cost of utility workers for offline completion of incomplete work. Moreover, the probability of line stoppage due to overload in the bottleneck station is reduced and the cycle time is minimized with the utilization of work-sharing approach.