Degradation Modeling And Reliability Assessment Of Coordinate Boring Machine Accuracy Based On Creep Analysis Of Key Parts

In the environment of transformation and upgrading of the manufacturing industry,the domestic CNC coordinate boring machine tool is gradually developing towards highend reliability,the requirements for the design and manufacturing reliability of its key parts are becoming more and more stringent.The release of residual stress in manufacturing process with the service time of key parts leads to the change of geometric accuracy,which is one of the key factors affecting the accuracy reliability of the machine tool.At present,the residual stress analysis of machine tool is mostly used for aging treatment evaluation,however,the mapping relationship between the residual stress of key parts and the accuracy reliability of machine tool is not clear,and the problem that the residual stress elimination standard cannot be quantified has long plagued the machine tool manufacturing enterprises.To this end,this paper analyzes the residual stress distribution of the key parts of the precision coordinate boring machine,and establishes the geometric accuracy degradation model of the machine tool and evaluates the accuracy reliability of the machine tool from the point of view of creep deformation of key parts,which is of great significance for adjusting and optimizing the design and manufacturing process of current machine tool structural parts and improving the accuracy retention of precision coordinate boring machine.The main research contents of the paper are as follows:(1)Continuous simulation analysis and tracking test of residual stress in the manufacturing process of key parts are carried out.The theory of finite element simulation and blind hole test of residual stress in casting,roughing and thermal aging of key parts is analyzed.The continuous simulation of the residual stress of the casting,first thermal aging,roughing and second thermal aging of the bed,column and slide are carried out by utilizing the finite element software,and the variation law of residual stress in multi-process during the manufacturing process of key parts in coordinate boring machine is obtained.Then the residual stress in the manufacturing process of the bed,column and slide are tested by blind hole test,and the simulation and test values of residual stresses are compared and analyzed to verify the validity of finite element simulation.(2)The creep of the key parts of coordinate boring machine during service is simulated and analyzed.The creep constitutive model of coordinate boring machine bed,column,and slide are determined according to the material characteristics and working environment of the key parts.The creep numerical simulation of three key parts are carried out by finite element software,the creep deformation values of three key parts of machine tool during two years of service are obtained,and the variation law of displacement deformation of the key points on the guide rail surface of the key parts with the change of service time is analyzed.(3)The geometric accuracy degradation model of the key parts of coordinate boring machine is established.The general law of machine tool performance degradation is analyzed;the statistical model of degradation data at each time of machine tool geometric accuracy is constructed,and the degradation process based on power law model is proposed,the parameters are estimated by maximum likelihood estimation and least square method.Finally,based on the assembly relationship of the adjacent parts of coordinate boring machine,the mapping relationship between the guide surface deformation of the bed,column,slide and Z,X and Y geometric accuracy of machine tool is established,and the geometric accuracy degradation trajectory of the machine tool's three coordinate axes is obtained.(4)The accuracy reliability of coordinate boring machine under the multi-part geometric accuracy degradation is assessed.Taking the TGK4680 coordinate boring machine as an example,the spatial error model of the coordinate boring machine is established by using the theory of multi-body system.The state function of machine tool machining accuracy reliability is constructed,and the initial machine tool spatial machining accuracy reliability mean value is solved by the Mento Carlo method,based on the geometric accuracy degradation model,the law of the decline of the machine tool spatial accuracy and the kinematic accuracy of X,Y and Z axes in the two-year service period is obtained in the form of power law function.So as to realize the prediction and assessment of the machine tool accuracy reliability.