Research On Characteristics Of The Key Component Of System Keeping Transmission Stiffness Of Ball Screw Invariant

High-speed&high-precision is the eternal problem towards CNC lathe. With theconstant improvement of the spindle speed, the feed velocity must grow more and morerapidly to meet the high CNC machine tools requirement. The high feed velocity inevitablycause the ball screw to rotate in a high speed, which will generate a lot of friction heat andcause thermal extension deformation. This thermal extension deformation is the main reasonof positioning error for machine tool feeding system, and can reduce the transmission stiffnessof the ball screw transmission system, which restrict the high-precision of CNC machinebadly. In order to meet the requirement of key research project “research on high-speed&high-precision CNC lathe” of Jiangxi provincial department of education, this dissertationstudies on the factors which influence the transmission stiffness of ball screw, and confirmsthe key component and the scheme of system keeping transmission stiffness of ball screwinvariant, and then analyses the features of hydraulic cushion.In allusion to the GSCK200A type CNC lathe of the project “research on high-speed&high-precision CNC lathe”, this dissertation completes the design of ball screw of feedingsystem under the low-speed rough turning and high-speed hard turning conditions accordingto the total design requirement of Z-axis ball screw of feeding system, and works out the keycomponent of system keeping transmission stiffness of ball screw invariant——geometricstructure and specific parameters of hydraulic cushion, and then applies the finite elementanalysis software ANSYS to study its strain characteristic. The result suggests that controllinghydraulic pressure can bring relevant axial strain to hydraulic cushion which will ensure theprestretching invariant, thus keeping the transmission stiffness invariant.This dissertation contains following parts:(1)Consulted and studied the related literatures widely which influence the transmissionstiffness of ball screw, and ensured the scheme of system keeping transmission stiffness ofball screw invariant.(2)According to the design requirements for Z-axis feeding system of GSCK200A type CNC lathe, this dissertation analyses every parameter of ball screw worked out the ball screw,and then analyses the stress of ball screw considering low-speed rough turning and high-speedhard turning conditions.(3)According to the condition and precision requirement of Z-axis ball screw of feedingsystem for GSCK200A type CNC lathe, this dissertation worked out the geometry sizes ofhydraulic cushion which is the key component of system keeping transmission stiffnessinvariant according to the stress and strain theory, and analyzes and calculates the compositestrain, and then initially confirmed several basic structures and parameters.(4)This dissertation establishes the finite element model for the hydraulic cushionapplying the finite element analysis software ANSYS, and analyses its composite stress andstrain characteristics, and then calculated the axial strain output of hydraulic cushion underdifferent hydraulic pressure(5)This dissertation applies MATLAB obtained the input equation of hydraulic pressureand the output equation of axial strain for hydraulic cushion, and then calculated the linearcorrelation coefficient and stiffness of hydraulic cushion.