A cyclic versus flexible approach to materials ordering in make-to-order assembly

This paper presents and compares two different approaches for material ordering in make-to-order assembly: the independent or fixed-cycle ordering with stationary order intervals and stationary order quantities, and the flexible ordering with variable (nonstationary) order intervals and quantities. Mixed-integer programming formulations and enumeration schemes are proposed to find the optimal schedule of material supplies for the two approaches. In addition, simple formulae are derived to evaluate feasibility conditions for the fixed-cycle approach, when a finite capacity input buffer is considered. Numerical examples modeled after a real-world make-to-order assembly are provided and some computational results are reported.