Optimal allocation of empty load carriers in multi-site automotive manufacturing during ramp-ups

This paper addresses the operational planning problem of redistributing empty load carriers (ELCs) across multiple production sites of an automobile manufacturer during the ramp-up of a new vehicle model. With the increasing prevalence of platform and modular production concepts, identical component groups are produced and consumed in parallel at several sites, creating significant challenges for ELC allocation. To analyse this problem, we formulate a discrete-time, finite-horizon stochastic inventory model with discounted costs. We show analytically that, for each production site, there exists a cost-optimal policy for repositioning ELCs. Based on operational data from a major German car manufacturer, we evaluate alternative ramp-up strategies across vehicle plants. The results demonstrate that overlap-free ramp-ups can reduce costs by up to two orders of magnitude relative to fully synchronised ramp-ups without offsets. Compared to the company’s existing ELC control system, our approach achieves average cost savings of 33% and substantially lowers cost variance. These findings highlight not only the cost-efficiency of the proposed model but also its robustness, providing stable solutions that can be effectively applied across diverse operational scenarios.