Method And Technology Of Straightness Retentivity Improvement For CNC Machine Tools

Accuracy retentivity is a key performance index for evaluating CNC machine tools,and the main factor restricting the performance and market competitiveness of domestic CNC machine tools.As a key component of CNC machine tools,the accuracy retentivity of the basic components after installation is a key factor affecting the accuracy performance of the whole machine.Straightness accuracy is one of the important indicators to characterize the geometric accuracy of basic components.Affected by the assembly process of basic components and various factors in the service process of machine tools,straightness accuracy tends to decline slowly,which directly affects the machining accuracy of machine tools.Relying on the major national science and technology projects.this dissertation carries out the research on the methods and techniques of improving straightness retentivity of CNC machine tools from three aspects:accuracy retentivity evaluation,retentivity improvement and retentivity monitoring.A quantitative evaluation method for accuracy retentivity is proposed and the key error sources affecting accuracy retentivity is identified.Considering the actual working conditions of CNC machine tools,the definitions of accuracy retentivity and accuracy retentivity time are defined.The concept of "accuracy retentivity degree" is proposed to measure accuracy retentivity to solve the problem that accuracy retentivity time can not reflect the ability of accuracy to remain in the original state within the prescribed range.The model of volume accuracy retentivity degree of CNC machine tools is established to reveal the relationship between the volume accuracy retentivity degree of machine tools and the time-varying state of geometric errors.Based on the theory of sensitivity analysis,the identification method of key error sources affecting the volume accuracy retentivity degree is studied.A method for predicting straightness error of guideway mounting surface considering elastomer characteristics of basic components is studied.The straightness error model of the guideway mounting surface is proposed.The relationship between the pretightening force,the pretightening sequence and the straightness error of the guideway mounting surface is established by considering the elastic interaction between the bolts.An analytical model of interaction stiffness between bolts is proposed to reveal the connotation of elastic interaction between bolts,and the numerical model is used to verify the proposed model.On this basis,the influence of elastic interaction between bolts on the change of residual pretightening force is quantitatively analyzed,the influence range of elastic interaction is defined,and the measures to reduce the influence of elastic interaction between bolts on pretightening force are put forward.The optimization method of pretightening process for basic components oriented to straightness retentivity is studied.In order to meet the requirement of accuracy and stiffness of the basic component directly in the pretightening stage,an optimized pretightening process for straightness retentivity is proposed.The influence of bolt pretightening sequence on the connection stiffness of basic components is analyzed,and the constraint model of bolt pretightening sequence and the strategy of reasonable pretightening sequence are put forward.Particle swarm optimization(PSO)algorithm for bolt pretightening sequence optimization is studied.Combining with the mating operation in genetic algorithm,the strategy of updating the number and position of particles is proposed,and the optimization process of bolt pretightening sequence is formulated.The method of straightness retentivity increment is applied and verified.Taking the heavy CNC roll lathe of a machine tool factory as the experimental object,the accuracy of the straightness error model of the guideway mounting surface is verified by field testing.Comparing the straightness errors of guideways of machine bed after assembling according to different pretightening processes and evaluating the effect of optimizing pretightening process for the basic component.The straightness retentivity monitoring method of the mounting surface of the guideway of machine bed based on distributed strain on-line acquisition is studied.Based on the plane stress theory of elasticity,a straightness error prediction algorithm of the mounting surface of guideway suitable for arbitrary strain measurement point distribution is developed.The strategy of strain gauge arrangement is established.The multi-channel strain remote monitoring software and hardware system for long-term monitoring of straightness error of the mounting surface of the guideway of machine bed is developed.The proposed method has been formulated as the enterprise standard,which has improved the linear accuracy retentivity ability of several series of basic products,and has been popularized and applied in many kinds of machine tools,making a positive contribution to steadily promoting the overall improvement of the accuracy retentivity of domestic CNC machine tools.