Recent Developments in Quality Control: An Introduction to "Taguchi Methods”

Abstract

This paper discusses a set of ideas which have come to be known as "Taguchi Methods". It firstly suggests that the decline in U.S. industrial power, coincident with Japanese takeover of world markets, is the fundamental reason why American manufacturers have been, receptive to quality control ideas emanating from Japan. It sets out Taguchi's philosophy of off-line quality control, i.e. design the product: to be insensitive to normal manufacturing variation, component deterioration and environmental variation, and illustrates this with one of Taguchi's best known case studies. It then shows that the statistical experimental designs (orthogonal arrays) advocated by Taguchi are superior to the traditional engineering approach of investigating one parameter at a time. Some experimental design ideas introduced by Taguchi are described. In particular, his use of "inner' and "outer" arrays and the distinction he draws between "control" and "adjustment" factors are illustrated by examples from the literature. Finally, his performance measures, which he calls "signal-to-noise ratios", are described and related to his concept of a loss function which is fundamental to his philosophy of quality engineering.