Abstract: Taguchi defines product quality as a loss that a product imparts to society from the time the product is shipped, and describes the loss with a quadratic function, but does not indicate what the loss is specifically. The product quality characteristics are continually changing because of pressure, movement and attrition after the product is put into use, which will cause loss because of the product rejected and scrapped. The paper defines product quality losses as present worth of a loss caused by product obsolescence because its quality characteristics are out of specification after it’s put into service. On the basis of this view on quality, it establishes the present worth of quality losses model based on service life distribution with the principle of discounted cash flow, and proposes the calculation method of product service life distribution density function based on the technical requirements for tolerance of quality characteristic. It takes the interior diameter dimension characteristic of the shaft sleeve as an example to analysis the impact of various factors of the new model on the present worth of shaft sleeve quality losses, and contrast with Taguchi quality loss model and Teran present worth of quality loss model. The results show that the new model describes an actual loss that a product imparts to society after the product is put into service, and can reflect quality loss of different products in the different service conditions and environment, and is more realistic than Taguchi quality loss model and Teran quality loss model. The new model extends product quality assurance and tolerance design from the manufacturing stage to the service stage, and provides new perspective for quality variation in the life cycle of product design, processing, operation, et al.

Key words: Quality characteristic, Quality loss, Service life distribution(SLD), Taguchi