| Geometric deviation of parts has a great influence on the function of products,so it must be analyzed and controlled.The skin model proposed in the new generation of GPS(Geometrical Product Specifification and Verifification)represents a part of the imperfect model with geometric deviation.It has developed into a new computer aided tolerance method.At present,the research on the construction of skin model is not perfect.It seldom considers the influence of mechanical processing method and processing system(load,temperature)on the surface performance of parts,which makes it unable to guide tolerance design in an all-round way.In addition,most of the studies on tolerance analysis only focus on dimension tolerance,and don’t reflect geometric tolerance information such as shape and position on the matching characteristics between parts,which leads to inaccurate results of tolerance analysis and can not provide reliable basis for the optimal allocation of tolerances.Aiming at the above problems,this paper makes a deep and systematic study around the technology of skin model construction and tolerance analysis based on GPS.(1)Research on skin model construction technology based on GPS.Firstly,based on the new generation of GPS operation technology and random process theory,this paper proposes a method to construct a skin model that can characterize the micro-morphological characteristics of parts,and simulates and generates three-dimensional random Gaussian surfaces with different autocorrelation functions.Then,the Johnson transformation system is used to study the simulation method of three-dimensional non-Gaussian surface,and the surface topography error feature models of different processing methods are simulated and generated.Finally,typical skin models of plane and cylinder are constructed based on CAD/CAE integration technology and reverse engineering technology.(2)Skin model construction and evaluation technology considering mechanical processing mode.Using the principle of homogeneous coordinatetransformation,this paper establishes the trajectory equation of relative motion between milling cutter and workpiece,and establishes the product skin model under different cutting parameters in MATLAB software.The evaluation technology of skin model is studied,and a flatness error evaluation method based on projection transformation is proposed.This method can achieve the minimum area evaluation of flatness error without using optimization algorithm.The experimental results show that the method has strong generality and high accuracy.(3)The tolerance analysis technology based on Jacobian spinor model is studied.Mathematical models of different tolerance band shapes are established based on SDT theory.Considering the geometric deviation and the constraint between feature vectors,the Jacobian spinor model is modified.Taking the tailstock of machine tool and the simple assembly of two blocks as examples,the results of Worst-case method and Monte Carlo method are compared,and the accuracy and reliability of the model are verified.(4)The problem of skin model construction considering processing technology system is studied.The key problem is to solve the skin model construction of typical processing technology such as turning,longitudinal grinding,cross grinding,longitudinal grinding and cross grinding under the influence of stress deformation and thermal deformation.On the basis of the above research,a skin model simulation system is developed on the platform of MATLAB GUI,and an example is given to verify the system. |
