Quantitative Evaluation of Quality Loss for Nominal-the-best Quality Characteristic

Abstract

The traditional way of measuring quality loss had the interpretation that any value within the specification is equally good for the customer and that, as soon as it exceeds the specification, the product is bad. Products that do not meet the specifications inflict a quality loss to the manufacturer. This loss is visible in the form of scrap or rework in the industry, which the manufacturer adds to the cost of the product. However, products that meet the specifications also inflict a quality loss, which is visible to the customer and that can adversely affect the sales of the product and the reputation of the manufacturer. Taguchi's way of measuring quality loss has the interpretation that, as the quality characteristic deviates from the target, even though it is within the specification, the quality loss becomes more visible to the customer. In this paper, Taguchi's Quality Loss Function (TQLF) is applied to evaluate the quality loss for Nominal-The-Best (NTB) type of quality characteristic of a rotary driving shaft. It also compares the performance of shafts manufactured by five different industries, with the same customer specifications and tolerance but with different diameter distributions.