Theory And Method Of Hybrid Dimensional Part Surface Modeling And Its Application In Prediction Of Product Assembly Quality

The quality of part surface is a key factor in analysis and prediction of product performance, and the geometric topography of part surface has a great influence on various performance indexes of products and parts. In product design and manufacture stage, evaluating the characteristic parameters of a real part surface from its local measured data, simulating the realistic topography which reflects the surface microstructures and the geometric structural parameters of the real part surface, and obtaining the influence of the topography on product working efficiency will make sense for the improvement of assembly quality and product performance. Basing on analysis and overview of the literature of modeling and simulation of part surface topography, the technologies and methodologies including part surface modeling, characteristic parameter identification, assembly positioning and fitting performance analysis are deeply studied. According to the research achievements, the software system for modeling and analysis of part surface topography is developed and applied successfully to the related projects.The dissertation is organized as follows:In chapter1, the history and state-of-art of modeling of part surface topography are reviewed. The key technologies for analysis of part surface topography and performance prediction are discussed, and the shortages of present similar researches are proposed. Then the research contents and architecture of the dissertation are presented.In chapter2, the separation and revision methods of multi-scale part surface topography altitude field are proposed. A multi-fractal characteristic function of part surface altitude field is defined to describe the microstructures of a spatial rough surface, and the surface topography is decomposed into four scales by the multi-scale information extraction method. Then the multi-resolution optimization method and the part surface consistency evaluation method are studied, and the information transmission model of multi-scale part surface is also built. The revision technology of part surface topography based on multi-scale parameter driving is proposed, so the part surface topography is generated, which meets the structural parameters at each scale of a real part.In chapter3, the hybrid dimensional fusion and characteristic parameter identification methods of part surface topography are proposed. The innovative concept of Hybrid Dimensional Impact Factor is defined which reflects the influence of the micro topography on the practical topography of a part surface. The constitution and fusion methods of integral dimensional component and fractal dimensional component of part surface topography are studied, and the established hybrid dimensional surface model can express both the integral dimensional information of part surface in macro level, and the fractal dimensional detail in micro level. Moreover, the hybrid dimensional characteristic parameter identification method for the part surface topography model is proposed, so the machining quality of part surface can be evaluated in both macro level and micro level.In chapter4, the hybrid dimension based feature construction and assembly positioning methods of part realistic geometric solid are proposed. The innovative concept of part realistic geometry is defined which integrates ideal geometry, variational geometry and fractal geometry. The hierarchical representation method of part realistic geometric feature information is proposed, and the specific generation method of part realistic geometric solid feature is presented. Then the assembly positioning and contact analysis methods of part realistic geometric model are studied, so the accuracy of assembly simulation is improved.In chapter5, the realistic geometry based fitting performance analysis and its application in leakage characteristic prediction of electro-hydaulic servo valve are studied. The realistic geometric feature model of precision couplings is built which includes the fitting surfaces with dimensional discrepancy and form error, and the influence of realistic geometric fitting surfaces of precision couplings on fitting performance is investigated according to the evaluation index of interval sectional area. Then the realistic geometric model based fluid leakage prediction method of electro-hydraulic·servo·valve is proposed, so the fluid leakage of precision couplings under various factors can be predicted according to the calculated interval sectional area.In chapter6, the software system for modeling and analysis of part surface topography is developed. The architecture of the software system, the design idea of each function and its programming realization are discussed. The efficiency of modeling and analysis of part surface topography can be improved effectively by the software system, which shows the validity and feasibility of the new theories and methods proposed in this dissertation. In chapter7, the conclusions and innovations of this dissertation are given along with future prospects of these research topics.