A joint scheduling approach for production and material handling under customized manufacturing paradigm

Responsiveness is the core competitiveness of customized manufacturing (CM) systems. Motivated by a real-world smart CM system where the sequential scheduling of the flexible assembly line (FAL) and material handling robots (MHRs) creates a responsiveness bottleneck, this paper investigates a joint scheduling problem that integrates production and material handling decisions while explicitly accounting for the limited carrying and battery capacities of MHRs. We first derive the optimal feeding and charging policies for MHRs, which streamline the associated decision-making process. The problem is then formulated as a mixed-integer programming model, in which time constraints couple production and material handling activities, and we prove that it is NP-hard. Despite this inherent complexity, we analyze the problem’s structural properties by decomposing it into two simpler subproblems under a Lagrangian Relaxation framework. Analytical results derived from these subproblems elucidate the interplay between production and material handling decisions, facilitating the development of an efficient joint FAL and MHR scheduling (JFMS) algorithm. The algorithm not only strengthens the lower bound but also incorporates a tailored local search procedure to improve the upper bound. Numerical experiments demonstrate that the JFMS algorithm outperforms multiple benchmarks in both computational efficiency and solution quality, with gaps between the strengthened lower bounds and the upper bounds typically below 10% in most instances. Moreover, the advantage of the algorithm is more pronounced when logistics resources are scarce. Finally, the paper provides managerial insights into the integration of production and material handling scheduling in CM systems.