| As an important precision transmission functional component in defense industrial fields such as large mechanical equipment,high-speed CNC machining center and aerospace,the transmission precision and service life of ball screw are directly related to the precision and life of high-end equipment.With the support of the National Science and Technology Major Project,the ball screw products have made significant progress in transmission precision and service life,but there is still a gap with foreign high-end products.At present,the demand of domestic equipment manufacturers for high-end ball screw is still dominated by foreign imports,which has become a prominent bottleneck problem restricting the application of domestic high-end ball screw in the field of defense industry.In the operation process of ball screw with applied load,considering the position and direction difference of the load and the different options of installation forms under different working conditions,the contact load of each ball is different.As a result,the contact deformation consistency of the contact micro-zone for all balls is poor,the lubrication form of contact interface for each ball is different,and the contact friction and wear between ball and raceway is different,and high period contact fatigue of ball and raceway can occur.These are the important factors that affect the transmission precision loss and degradation,precision life and fatigue life of ball screw,and lead transmission accuracy,life and reliability of ball screw to lag behind foreign products,and make imported ball screw products for the high-grade CNC equipment in the dominant position,and become the key problem for the domestic ball screw to catch up or catch up with the level of foreign high-end products.According to the above problem,this paper aims to explore transmission precision loss（including the precision loss of contact deformation and the precision degradation of contact wear）and life prediction（including wear precision life and contact fatigue life）as the main line.The full load distribution model of ball screw under different load condition is constructed,and the prediction method for precision loss caused by contact deformation is proposed based on full ball load distribution,and the friction moment calculation method considering the thermal elastohydrodynamic lubrication is proposed,and the prediction method of precision degradation caused by time-varying wear of raceway is analyzed,and the prediction method of fatigue life considering the non-Newtonian mixed lubrication effects is proposed.The full load distribution coupled to the precision loss and life prediction analysis of ball screw is achieved,and theoretical verification and result analysis are carried out by relying on the loading test platform of ball screw integrating drive loading and performance testing,which provides a new theory and method for precision loss and life prediction of ball screw pair,and lays a foundation for replacing imported high-end ball screw with domestic product.（1）The main contact parameters of the contact point between ball and raceway are discussed,and the elastic-plastic contact deformation model is established.On this basis,the relationship model between overload load and residual deformation is established.The contact characteristics of different contact materials are analyzed and the residual plastic deformation at the contact point is compared.The velocity at the center of the ball,the relative slip velocity at each contact point,the entrapment velocity and the sliding-roll ratio are solved,and the relationship between them is analyzed.（2）The loading modes of ball screw under different mounting modes are analyzed.The contact load distribution model of ball screw under the axial load,composite load and combined load is established.The change of the contact load distribution under the assumption of the ball geometric error by using the statics and dynamics analysis method is analyzed,and the effect of the axial load,radial load,torque and radial displacement of ball screw on load distribution for all balls is analyzed,and the relation between contact deformation coefficient and manufacture error coefficient is established.The position accuracy calculation model of ball screw during the cycle is established,which is of great significance to improve the driving accuracy of ball screw and the digital compensation of the positioning error.（3）The kinematics and thermal elastohydrodynamic coupling analysis model of ball screw is established.Based on the Reynolds equation considering the influence of lubrication temperature rise,the lubrication performance between ball and screw raceway or nut raceway is studied,and the film pressure,shear stress,film thickness and temperature rise at the contact points between ball and raceway are compared,and the failure area caused by insufficient lubrication is analyzed.On this basis,the full load distribution of the double-nut ball screw under the action of preload is analyzed.The friction moment calculation method of ball screw considering viscous friction,elastic hysteresis friction and sliding friction is proposed.The coupling relationship between the preload and friction torque of ball screw is established.The proposed friction moment calculation method considering the thermal elastohydrodynamic lubrication has a guiding significance for the fatigue life analysis of ball screw.（4）The contact forms of the double-nut ball screw under different axial loads are studied.The ball load distribution of the double-nut ball screw with applied load is analyzed.A time-varying wear calculation method for ball screw based on fractal contact surface and improved Archard theory is proposed.The friction and wear of the ball contact area and the dynamic evolution of interface coupling field are studied.The wear condition of ball screw is analyzed.The coupling effect between the raceway wear depth and the preload loss is studied,and the precision life model of ball screw is established based on numerical iteration method,which provides the theoretical basis for the prediction of precision life.（5）The mixed lubrication model of ball screw based on full ball load distribution model is established considering non-Newtonian effect of lubricant and fatigue life prediction method is provided baed on maximum secondary surface stress,and the lubrication performance of the ball with applied maximum load distribution is discussed based on full ball load distribution,and the effects of full load distribution,curvature ratio,temperature rise on the fatigue life is analyzed.Two kinds of ball screw including BT GD8020 and NSK DFD8020 are used for running test of fatigue life,and the fatigue life calculation method based on the maximum secondary surface stress is verified.The hardness distribution of the transition zone between ball and raceway is analyzed,and the fatigue failure modes of two ball screw are explored. |
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