Study Of The Three Tridimensional Functional Toleracne Analysis Method Of The Complex Product

The manufacturing accuracy of the mechanisms affects performance, working lifeand manufacturing costs of the products. The functional tolerancing is now widelyaccepted by industry, as this approach contributes to a reduction of manufacturingcosts while improving product quality. The process of tolerancing and the toleranceaccumulation have become main concerns of designers, manufacturers and qualityinspectors. The designer must determine the influential parts and consider theinfluences of the geometric deviations on each part and the contact conditionsbetween the parts. Tolerance analysis plays an important role in the stage of productdesign and has great influences on the assembly quality and manufacturing costs ofproducts. In a three-dimensional dimension chain, several angular or radial defects ofthe same part can be influential on a functional requirement, and the assemblyjunction between the parts also affect the tolerance accumulation, which requires aunified method to handle these problems.Based on the research of National Nature Science Fund Project “Study for thethree-dimensional tolerance design and optimization method of product function (No.51005002)”, the method for3D functional tolerance analysis is studied from thefunctional requirement of the complex product and based on the new-generationgeometrical product specification. Considering the geometrical deviation of the part,assembly clearance and precedence of position characteristic, the3D geometricaldeviation transfer and accumulation relationship are studied based on the analysis ofthe assembly junction of the product and the assembly connection of the part.The existing problems of the first generation geometrical product specifications(GPS) are analyzed and the significance of the new-generation GPS is summarizedand its principle is introduced simply. The current achievement and the existingproblem of the CAT system composed by the three modules (tolerance specification,the tolerance analysis and tolerance synthesis) are analyzed. Then the method of3Dfunctional tolerance analysis is proposed. The result of the tolerance accumulation isobtained according to the influence accumulation of the displacement of the supportsurface on the ending point based on the analysis line method.The transfer relationships of several classical junctions are analyzed then. Theexpression of the maximum displacement of the point in the terminal surface isobtained using the transfer equation according to the displacement of the supportsurface. The expression of the tolerance model is obtained by the analysis for thediscretization of the several classical terminal surfaces. The equation of the tolerancetransfer relationship is deduced according to the tolerance principles such as the precedence of location and the material requirement.A simple mechanism composed of two parts is selected as an example for thetolerance accumulation. The influence of the precedence of the datum on the toleranceaccumulation is analyzed. The advantage of the method is verified according to thecompare with the small displacement torsor method. And then a three-part mechanismis selected as an example for the tolerance accumulation to obtain the tolerance of theassembly according to the studied requirement with the precedence of the datum andthe assembly clearance considered. For the mechanism composed of three or moreparts, the analysis for the entirely junction is conducted first and then the analysis ofthe separate part, which makes the process of tolerance analysis perfect and is thefoundation of the tolerance synthesis following.