An economic inspection interval for control of defective items in a hot rolling mill

The article addresses a real-life problem on determining the optimum sampling interval for control of defective items in a hot rolling mill. Having observed that the pattern of appearance of mill defects indicates a geometric process failure mechanism, an economic model is developed in line with the method suggested by Taguchi and critically examined by Nayebpour & Woodall. An expression for the expected loss per product as a function of the sampling interval is derived and the optimum interval is obtained by minimizing this loss function. The practical issues involved in this exercise, such as estimation of various cost components, are also discussed and the effect of erroneous estimation of cost components is studied through a sensitivity analysis.