Optimal process adjustment with considering variable costs for uni-variate and multi-variate production process

This paper investigates a single-stage and two-stage production systems where specification limits are designed for inspection. When quality characteristics fall below a lower specification limit (LSL) or above an upper specification limit (USL), a decision is made to scrap or rework the item. The purpose is to determine the optimum mean for a process based on rework or scrap costs. In contrast to previous studies, costs are not assumed to be constant. In addition, this paper provides a Markovian model for multivariate Normal process. Numerical examples are performed to illustrate the application of the proposed method.