| The machine tool industry is a basic equipment industry that provides working machines for all fields of the national economy.As a high-precision heavy-duty machine tool,the floor-type boring and milling machine plays an important role in industrial production.As an important part of the floor-type boring and milling machine,the feed system has a decisive influence on the positioning accuracy and machining accuracy of the machine tool.At present,most of the researches on feed systems in China are concentrated on the single-screw drive feed system.The research on the double-drive feed system is mostly for the horizontal feed system,and the research on the vertical double-drive feed system is relatively few.The Y-direction double-drive feed system of FMXT-2000 floor-type boring and milling machine is the research object,and its static and dynamic characteristics are analyzed,and some optimization schemes are proposed.These studies provide references for the design and improvement of vertical drive dual-drive systems for similar machines.(1)The stiffness model of the Y-direction double-drive feed system is established.The static analysis of the system 3D model is carried out by using Workbench software,and the accuracy of the stiffness model is verified.It is concluded that the static deformation of the feed system is mainly affected by the mass and stiffness of the spindle box system and the stiffness of the ball screw,and the influence of the cutting force is small.The influence of the screw diameter on the stiffness of the system is analyzed.It is concluded that increasing the diameter of the screw can effectively reduce the deformation of the system.The deformation of the feed system in the Y direction is analyzed when the headstock is at different positions.The maximum deformation is 47.75?m and the minimum deformation is 18.22?m.The deformation at different positions is plotted as a curve and used as the basis for numerical control compensation.(2)The various types of joint surfaces in the Y-direction double-drive feed system are analyzed and the dynamic model of the system is established.The modal and harmonic response characteristics of the feed system are analyzed by Workbench software,and the first six modes of the system are obtained.In the modal state,the first-order natural frequency of 124.73 Hz is significantly higher than the excitation frequency of 100 Hz,indicating that the system structure has good stability.According to the mode shape of the modal analysis,the screw diameter is increased by 10 mm,and the first six natural frequencies are increased by about 11 Hz on average.According to the harmonic response analysis results,the system damping ratio is increased from 0.05 to 0.1,and the maximum amplitudes in the three directions are reduced by 39.54%,39.39%and 41.06%,respectively.These studies provide a theoretical basis for structural optimization design to improve the dynamic characteristics of machine tool feed systems.(3)The axial contact stiffness model of the double nut preloaded ball screw pair is established by the Hertz point contact theory,and the expression of axial contact deformation and stiffness of the Y-axis ball screw pair is obtained.According to the derived axial contact stiffness equation of the ball screw pair,the influence of some structural parameters and preload on the stiffness is analyzed.It is concluded that increasing the elastic modulus of the ball screw pair,the number of balls and appropriately increasing the preload can effectively improve the axial contact stiffness of the double nut preloaded ball screw pair,and the corresponding change relationship curve is drawn.(4)The positioning accuracy of the Y-axis of the floor-standing boring and milling machine after numerical control compensation is 8.33?m,which verifies the effectiveness of the compensation.At the same time,the straightness of the Y-axis in the X direction is 7.81?m,and the straightness in the Z direction is 4.22?m.The variation curve is similar to the deformation in the X and Z directions in the static analysis.Through the milling experiment,the machining accuracy of the machine is measured.The maximum deviation of the Y-direction straightness of the workpiece is 5.32?m,and the deviation of the Y-direction of the four-corner hole is 2.49?m.It is verified that the cutting force has little influence on the deformation of the system,and the feed system has good dynamic performance.(5)An optimization scheme for the hydraulic balance device of the spindle headbox is proposed,and the relevant parameters required for the selection are calculated.The static analysis of the optimized Y-direction double-drive feed system shows that the overall deformation of the optimized feed system is reduced by 50.8%,the deformations in the X,Y and Z directions were reduced by 38.4%,52.1%and 23.1%,respectively,and the deformation of the ball screw was 4.98?m,which was reduced by 80.3%.,that is,the optimization scheme greatly improves the static characteristics of the Y-direction double-drive feed system.The results of static and dynamic characteristics analysis show that the deformation of the system is mainly concentrated on the headstock and ball screw.Increasing the ball screw diameter to increase the rigidity of the ball screw pair,adding the hydraulic balance device of the headstock,and increasing the damping of the system can effectively improve the static and dynamic performance of the Y-direction dual-drive feed system.Increasing the elastic modulus of the ball screw pair,the number of balls and appropriately increasing the preload force can effectively improve the axial contact stiffness of the double nut preloaded ball screw pair.These studies provide a reference for the design and improvement of vertical drive dual-drive systems for similar machines. |
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