Impact of Lot Arrival Density Fluctuations on Cycle Time Control : IE: Industrial Engineering

For optimized cycle time control, a precise under-standing of lot arrival times is critical. Queueing theory has been used as a lightweight model for estimating WIP (work-in-progress) arrivals in fabs, typically under the highly simplified assumption that lot arrivals follow the Poisson process. This paper investigates the impact of lot arrival density fluctuations on manufacturing cycle time. Motivated by the observation that actual lot arrival times often exhibit clustering behavior, we propose using the Hawkes process to describe the stochasticity of lot arrivals. Our empirical evaluation on NY CREATES fab data shows that: 1) the Hawkes process offers a better fit than the Poisson process, and 2) this clustering behavior leads to increases in both WIP and cycle time, as demonstrated through WIP simulation.