Research On Quality Evaluating Technology For The Assembly Process Of CNC Machine Tools

As the basic strategic equipment for the realization of national industrialization and modernization, CNC Machine Tools' quality and reliability are the significant symbols of the country's comprehensive strength. And as the last stage of the whole manufacturing process, assembly is the key process to realize the design quality, which determines the product quality directly. Regarding CNC Machine Tools as the research object, the quality evaluating technologies of different assembly stages were studied systematically in this paper, providing new ideas for assembly process quality control technology research and implementation, with great theoretical and practical significance.Supported by the National Major Scientific and Technological Special Project for “High-grade CNC Machine Tools and Basic Manufacturing Equipment” and the National Natural Science Foundation, the main work of the paper are as follows.(1) The basic theories of the assembly quality of CNC Machine Tools were expounded. And the purposes and meanings of evaluating different stages' assembly quality were analyzed. Then the assembly sequences quality evaluation, the importance evaluation of assembly processes and the assembly quality evaluation of the whole machine, etc. were studied. Finally, the assembly quality evaluating technology technical framework of CNC Machine Tools was established.(2) Since there were various quality-influenced factors in assembly sequence chosen process and the quality level was very hard to be evaluated, a fuzzy evaluation method based on relative entropy was proposed in this paper. Firstly, based on the content definition of assembly sequence quality, the evaluation system was established to present comprehensive quality of assembly sequences by using Interpretative Structure Model, and the index attribute values were calculated quantitatively; Then in order to get the index weight, the vague set was used to concentrate experts' opinion; Thirdly, a new decision-making method based on entropy theory was founded to evaluate comprehensive quality of all feasible assembly sequences.(3) There were enormous processes in CNC Machine Tools assembly, of which the importance degrees were different. Firstly, assembly processes' importance degrees were respectively calculated by gray entropy correlation analysis and grey relation projection method. Then fuzzy Borda method was proposed to combine the two evaluation results, so as to get the final evaluation result, from which the key assembly processes could be extracted to be carried on the point management. The sorting order and score difference were considered in this method, which made the evaluation result more scientific and effective, and overcame the limitations of traditional single evaluation methods.(4) In order to meet the requirements of CNC Machine Tools assembly quality evaluation, the evaluation index system of assembly quality was established completely. Then EAHP was used to calculate the weight of each index. Thirdly LS-SVM was applied to evaluate the comprehensive assembly quality of CNC Machine Tools. At the same time, the PSO was proposed to optimize the parameters of LS-SVM, which could improve the accuracy of assembly evaluation model. Finally, case study indicated the rationality and effectiveness of this method.