Methods Research Of Mechanical Product Quality Loss Model And Tolerance System Optimization Design

Mechanical product quality and manufacturing cost are the important factors that affect its competitiveness. From the perspective of product level, the relationships between product quality characteristics and parts quality characteristics are analysed, and then the methods of product quality loss model and tolerance system optimization design is proposed for the product quality characteristics with multiplicity, dynamic nature and complexity, which improve product quality, reduce product cost, and quickly respond to market demand change.Firstly, three hierarchical modeling method of product quality loss for multi-quality characteristics is proposed. Making full use of the historical test data recorded in the whole production process, the weights among parts quality, product quality characteristic and product quality are determined with neural network method and analytic hierarchy process. Considering the rework cost and scrap cost during parts manufacturing process, the piecewise function theory is used to improve Taguchi quality loss function. The corresponding parts quality loss is deduced with the different distribution of parts quality characteristic, and product quality loss for multi-quality characteristics is established. A micro-motor is used as an example to calculate and analyse product quality loss with multi-quality characteristics, which show that the developed method is effective, and provides a comprehensive evaluation approach solution of product quality with multi-quality characteristics.Secondly, modeling method of product quality loss based on service life distribution is proposed. For product whole life cycle, Product quality loss is defined as present worth of a loss caused by product obsolescence because its quality characteristics are out of specification after it is put into service. On the basis of this view on quality, the present worth of quality loss model based on service life distribution is established with the principle of discounted cash flow, and the calculation methods of product service life distribution density function based on the technical requirements for tolerance of quality characteristic are proposed for the quality characteristics with different distribution. Combining with three cases, the fatigue strength in the dangerous cross-section of rotation shaft, the product quality loss of nominal-is-better, smaller-the-better and larger-the-better quality characteristics are calculated and analysed, respectively. The impacts of various parameters of the new model on product quality loss are discussed, and the new model is contrasted with Taguchi quality loss model and Teran present worth of quality loss model. The results show that the new model describes an actual loss to society, which is caused by product obsolescence because its quality characteristics are out of specification after it 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 provides new perspective for researching product quality variation in product whole life cycle.Thirdly, product tolerance system optimization design method based on data mining is proposed. From the perspective of general tolerance, the product tolerance system model is established after analysing the interaction relationships among the quality characteristics of product levels. The support vector non-linear regression relational model between parts quality characteristic deviations and product quality characteristic deviations is established by using the historical test data in the product manufacturing process, and a micro-motor is used as an example to structure the support vector non-linear regression (SVNR) model between parts quality characteristic deviations and product quality characteristic deviations, and compare with the Regress Function method. The relationship between non-dimension tolerance and product cost is analysed, and the product manufacturing cost model based on product general tolerance is set up. Then, the optimal design model of product tolerance system is established by minimizing product manufacturing costs as target. The results show that the developed method is effective and provides a new way for the product tolerance design.Finally, tolerance system redesign method for user performance requirements is proposed. For the users often change product performance requirements or the new user requirements are added, the product tolerance system redesign model for user performance requirements is established on the basis of optimal design method of product tolerance system based on data mining. A micro-motor is used as an example, its assembly relationship and influence factors of performance are analyzed, and micro-motor tolerance system model is established. The micro-motor tolerance system redesign model for user performance requirements is established by minimizing product manufacturing costs as target and user performance requirements as constraint. The micro-motor tolerance system redesign is optimized according to the different user performance requirements. The change rule between product tolerance and cost is analysed. The proposed tolerance system redesign optimization method can directly improve and optimize product tolerance system according to user performance requirements change, so that the manufacturers can shorten product design and manufacturing cycle, and respond quickly to market change. The manufacturing enterprises can manufacture the products that can not only meet the user requirements, but also minimize its manufacturing total costs because they only need to appropriately adjust manufacturing system and quality inspection system on the basis of the original product manufacturing system. The new method expands product tolerance design from the product development stage to the product whole market cycle.