The rigidity of CNC machine tools and the measures to improve the rigidity of CNC machine tools (2)
October 26, 2022
2. Reasonable structural layout can increase stiffness
Take the horizontal boring machine or horizontal machining center as an example for analysis. In the layouts of Figure 7-4, (a), (b),
(c) The headstock of the three schemes is suspended on the side of the column on one side. The weight of the headstock will cause bending deformation of the column; the cutting force will cause bending and torsional deformation of the column. These deformations will affect the machining accuracy. The center of the headstock of the scheme (d) is located in the symmetry plane of the column, and the self-weight of the headstock no longer causes the deformation of the column, and the bending and torsional deformation of the column caused by the same cutting force are greatly reduced, which is equivalent to The rigidity of the machine tool.
Due to the limitation of structural size, the thickness and size of the CNC machine's carriages and worktables cannot be designed too large, but the width or span cannot be reduced, so the rigidity is insufficient. To compensate for this defect, in addition to the main guide rail, in the overhanging part The addition of auxiliary guide rails can greatly improve the rigidity of the carriage and the workbench.
3. Take structural measures to compensate for deformation of components
When the magnitude and direction of the relative deformation of the force point can be measured, or the deformation law of the component is predicted, the corresponding measures can be taken to compensate the deformation to eliminate the influence, and the compensation result is equivalent to the rigidity of the machine tool. As shown in Figure 7-5(a), the large-scale portal milling machine has the largest bending deformation of the beam when the spindle component is moved to the middle of the beam. For this purpose, the beam guide can be made "arched", that is, the central portion is a convex parabolic shape, which can compensate for its deformation. Or pre-correct the main rail by means of auxiliary beams and pre-correction screws mounted inside the beam. It is also possible to reduce the deformation caused by the self-weight of the beam and the headstock by adding a counterweight, as shown in (b) of the figure. When the floor boring machine main shaft sleeve is extended, the self-weight sag, and the horizontal milling machine spindle ram sag when the self-weight hangs, the balance weight can be used to reduce or eliminate the sagging.
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