1. Choose the structural form of components reasonably
For some components, the rigidity is calculated by calculation method, while the bending and torsional deformation of parts such as lathe bed, column, operating table and box body, contact deformation of joint surface, etc. can only be simplified for approximate calculation. In the design, it is necessary to test, analyze and compare the model, physical object or similar prototype to determine a reasonable structural scheme.
(1) Correct selection of the shape and size of the section
After bearing bending and torsion loads, the deformation of a member depends on the bending and torsion moments of inertia of the section, and the higher the bending and torsion moments of inertia, the higher its stiffness. When the cross-sections with the same shape keep the same cross-sectional area, the wall thickness should be reduced and the outline size of the cross-section should be increased. The torsional stiffness of the circular cross-section is greater than that of the square cross-section, while the bending stiffness is smaller than that of the square cross-section. The stiffness of closed section is much greater than that of non-closed section; Opening a hole in the wall will reduce the stiffness, and adding a flange around the hole can restore the bending stiffness.
(2) Reasonable selection and arrangement of baffles and ribs
Reasonable arrangement of baffles and ribs of supporting parts can improve the static and dynamic stiffness of members, and longitudinal, transverse and diagonal ribs are arranged inside to carry out static and dynamic stiffness tests on them, among which the cross ribs are the best. For some thin-walled members, in order to reduce the warping of the wall surface and the distortion of the section of the member, ribs can be set on the wall plate, among which honeycomb ribs are better, which can not only improve the stiffness of the member, but also reduce the shrinkage stress during casting.
(3) Improving the local stiffness of components
The connecting parts between the guide rail and the supporting parts of machine tools are often the parts with the weakest local stiffness, but the connection mode has a great influence on the local stiffness. If the size of the guide rail is wide, the double-wall connection type should be applied, and if the guide rail is narrow, the single-wall or thickened single-wall connection can be used, or vertical ribs should be added to the single wall to improve the local stiffness.
(4) Choose welded structural components
The lathe bed, columns and other supporting parts are welded by steel plates and section steel, which has the obvious advantages of reducing mass and improving rigidity. Whether the stiffness is the same to reduce the mass or the mass is the same to improve the stiffness, the resonant frequency of the component can be increased and the * * * vibration is not easy to occur. It is possible to make the component into a fully enclosed box structure by welding with steel plates, which is beneficial to improve the stiffness of the component.
second, a reasonable structural layout can improve the stiffness
Take a horizontal boring machine or horizontal center as an example. The self-weight of the headstock hanging on the side of the column will cause bending deformation of the column, and the cutting force will cause bending and torsion deformation of the column, which will affect the accuracy. The center of the headstock is located in the symmetrical plane of the column, so the self-weight of the headstock no longer causes the deformation of the column, and the bending and torsion deformation of the column caused by the same cutting force are greatly reduced, which greatly improves the rigidity of the machine tool.
Due to the limitation of structural size, the thickness of the carriage and the operating table of CNC machine tools can't be designed too large, but the width or span can't be reduced, which leads to insufficient rigidity. To make up for this defect, an auxiliary guide rail is added at the overhanging part, which can greatly improve the rigidity of the carriage and the operating table.
Third, take structural measures to compensate the deformation of components
When the magnitude and direction of the relative deformation of the focus point can be measured, or the deformation law of the components can be predicted, corresponding measures can be taken to compensate the deformation to eliminate its influence, and the compensation result is equivalent to improving the rigidity of the machine tool. Or pre-correct the main guide rail through the auxiliary beam and pre-correcting screw installed inside the beam, or use the method of adding balance weight to reduce the deformation caused by the dead weight of the beam and the spindle box. The self-weight sag of the spindle sleeve of the floor boring machine when it is extended and the self-weight sag of the spindle ram of the horizontal milling machine when it is extended can be reduced or eliminated by adding balance weight.