Two-dimensional Quality Function Deployment: An Application for Deciding Quality Strategy Using Fuzzy Logic

Abstract

A traditional Quality Function Deployment (QFD) has two shortcomings that are seldom considered. First, the relation in a traditional QFD matrix is frequently regarded only as a positive one. Therefore, the negative effect, which may be hidden in the blank cell (the category of ‘No relation’) of the QFD matrix, is neglected when computing the absolute importance of some design parameters, thus undermining the precision. Second, how to decide quality strategy, in view of limited resources, is not considered. The proposed method, called two-dimensional quality function deployment (2D-QFD), is developed from the ideas of Kano's model and fuzzy logic. The relation in the QFD matrix is distinguished through a questionnaire that consists of a pair of positive and negative questions. Furthermore, the qualitative relation, according to Kano's two-dimensional quality classification, in the QFD matrix is quantified by fuzzy logic. The negative relation in the QFD matrix may be derived when the membership function of fuzzy set ‘R (reverse attribute defined in Kano's model)’ is located in the negative score range. Under the consideration of limited resources, 2D-QFD is employed to decide quality strategy as basic type, competitive type or attractive type, by adjusting the membership functions of fuzzy sets in the output variable. This study finds that 2D-QFD is more precise and flexible than a traditional QFD.