Process quality improvement based on the application of rectifying sampling inspection plan

In 1996, Pulak and Al-Sultan provided a rectifying sampling inspection plan for determining the optimal process mean, by assuming that the quality characteristic is larger-the-better and is normally distributed. In their inspection plan, the 100% rectifying inspection is executed when the quality of the lot is rejected. Pulak and Al-Sultan obtained the optimal process mean by maximizing the expected profit per item. Quality investment setting, e.g., new equipment, new software system, new material and parts, etc., is usually considered a long-term method for reducing the bias and variability of the product characteristic when the process improvement is required. The major objective of the present paper is to involve the effect of quality investment on the expected profit per item, where the original Pulak and Al-Sultan's model is modified. Numerical results show that our modified model yields the higher expected profit per item than the original model.