Tolerance Design And Analysis Based On Finite Element For Flexible Parts

Tolerance design is one of most important factors that cannot be ignored in the modern manufacturing process. It not only affects the machining accuracy of parts and the quality of the product, but has a vital significance in the processing craft route, testing,manufacturing cost and the final product assembly, etc. In the mechanical designing of manufacturing and assembly process, the tolerance design is mainly used to determine the geometric parameters of parts(size error, location, shape, position error) whether it meets the design requirements or not. The ultimate goal is to control the target geometry tolerance changes within the range of set, so that we can get the interchangeability between parts, coordination and general goals.Scholars at home and abroad have been analyzed tolerance mathematical modeling and representation, tolerance analysis and synthesis, computer-aided tolerance design,concurrent design, function tolerance research, and have achieved certain results. But the general tolerance research theory is based on an assumption that the parts are absolutely rigid, which holds that assembly with no elastic deformation between cooperate or connection between parts. But in the automotive, aerospace and other industrial exist a lot of metal thin wall parts, these parts are often low stiffness, the assembly force or elastic deformation under the action of gravity relative to the size and tolerance can no longer be ignored.This paper proposes a flexible parts oriented tolerance analysis method, based on the finite element mathematical model of flexible parts tolerance based on flexible parts tolerance mathematical definition to establish flexible parts tolerance representation model,main content has the following several aspects:(1) Making the key nodes and flexible part geometry element(point, line, face)control points, control point position variation according to the geometric elements to represent the size and geometric tolerance. Similarly to the finite element grid nodes into flexible parts geometry elements of control points, using flexible parts of key node position changes to indicate size and geometric tolerance.(2) The proposed modeling method based on generalized directed graph of theassembly tolerance, first build tolerance representation model, based on graphical computing component assembly tolerance model, using the generalized directed graph said assembly tolerance.Tolerance representation model based on key characteristics and figure can tolerance, according to the process design experience can be mapped and built on the tolerance chain graph search algorithm, in the unit vector in the direction, conducive to the accumulation of error and tolerance analysis.(3) Using the finite element to the flexible parts tolerance analysis, based on the deviation of the finite element analysis model, research the deviation distribution under certain load, and defines the boundary conditions of assembly parts and fixtures, using the finite element simulation analysis was carried out on the model, get the flexible parts assembling deviation, and to validate the result.(4) By using Taguchi quality loss function to optimize the tolerance, tolerance optimization design method of quality loss function is introduced to set up the minimum manufacturing cost and quality loss sum as the optimization design model of the target, can improve the parts interchangeability, reduce manufacturing cost, is of important guiding significance for tolerance allocation and optimization for the related parts.Tolerance based on the finite element of finite element analysis is applied in this article, to build the finite element analysis model of flexible body assembly, realize flexible parts assembly tolerance of numerical analysis and prediction, control and compensation mechanism research of assembly error, on the whole tolerance development has certain innovation.