Taguchi Risk and Process Capability

Abstract

Process control methods, in general, and quality, in particular, most often refer to the measures taken especially to the finished product, as well as to the technological process, in order to maintain its performance within certain statistical parameters. Genichi Taguchi is the first who developed a quality control approach, used first in Japan and later in industrialized economies, a procedure widespread in quality under the name Taguchi method. Within the Taguchi method, he imposed a key term average loss attached to a process /characteristic in case it deviates, compared to a target value/objective, considered optimal. The Taguchi methodology is especially oriented towards the design phase, different from the classic approach oriented towards the final control phase upon delivery, or towards the supervision of the processes. This new approach aims to design processes and products so that they are as insensitive as possible (robust) to the influence of external, disruptive factors of the processes. In our paper, the capability indicators of the processes and their connection with the Taguchi risk are also presented. A link is also made between the statistical measurement of uncertainty and the Taguchi risk with an example in a process from the mechanical industry.

Process Capability Evaluation Using Capability Indices as a Part of Statistical Process Control

“…The "loss-based" or Taguchi index was proposed in the context of the loss function used in Taguchi's approach to quality assessment. It compares the maximal allowable variability of the observed quality trait, determined by the width of the specification interval, with its actual variability around a target mean T. It considers the variability of the values of the quality attribute of interest and the rate of attainment of the optimum value [56,57]. It is calculated according to the formula…”