How to improve the structural rigidity of CNC machine tools

Increasing the static and dynamic stiffness of the machine tool The positioning and machining errors caused by the deformation of the support parts such as the bed, base and column of the machine tool depend on their structural rigidity, and these errors cannot be artificially adjusted and compensated during the machining process. Therefore, the elastic deformation caused by the mass of the moving part and the cutting force must be kept to a minimum to ensure the required machining accuracy and surface quality. For this reason, measures must be taken to improve the structural rigidity of CNC machine tools.

1) Reasonable selection of the structural form of the support member After the support member is subjected to bending and torsion, the deformation size depends on the bending and torsion moment of inertia of the section. For sections with the same cross-sectional area and the same cross-section, the wall thickness should be reduced, and the profile size of the cross-section should be increased: the torsion should be rounded, and the cross-section should be selected for the bending; the cross-section of the support should be closed as much as possible. Adding a flange around the hole increases the bending stiffness. Reasonably arranging the ribs of the baffle of the support member can improve the rigidity of the member, and the baffles and the brace can be arranged laterally, longitudinally or diagonally, which is beneficial to improve the bending and torsional moment of inertia of the member. For the layout of the bed of the horizontal machine tool, the partitions and ribs should be considered for convenient chip removal. The joint between the machine guide rail and the support member is often the weakest part of the local stiffness. The Asahi guide rail is narrow in size, and can be connected by single wall or thick single wall, or by adding vertical ribs on a single wall to improve local stiffness; When the size is wide, it should be double-walled. Increasing the contact stiffness of various parts of the machine tool can increase the load carrying capacity of the machine tool. The scraping method is usually used to increase the contact point per unit area; applying a sufficiently large preload between the bonding faces can also increase the contact area and reduce the contact deformation.

2) Reasonable structural layout The heavier moving parts on the bed and column should be placed in the middle of the component as much as possible to reduce the deformation caused by the dead weight and cutting force. Taking a horizontal boring machine or a horizontal machining center as an example, if the headstock is suspended on one side to explain the side, the weight of the headstock will cause bending deformation; the cutting force will cause bending and torsional deformation.

3) Measures for compensating deformation If the relative deformation magnitude and direction of the force point can be measured, or the deformation law of the component is predicted, corresponding measures can be taken to compensate the deformation to remove the influence of the force deformation, and the result is equivalent to an improvement. The rigidity of the machine.

4) Reasonable selection of materials such as material bed and column of the component, welded by steel plate or section steel, has the remarkable feature of reducing weight and improving wind. The modulus of elasticity of steel is twice that of cast iron. If the rigidity of the welded part is the same as that of the casting, the wall thickness of the welded part is only half of that of the casting. If the required local stiffness is the same, since the local wind is proportional to the cube of the wall thickness, the wall thickness of the welded part is only about 80% of the wall thickness of the casting. Filling the damping material of the sand or concrete into the wall of the support member can effectively improve the damping characteristics and increase the dynamic wind of the support member. The material directly using concrete, resin concrete or artificial granite as the support member can significantly improve the vibration resistance of the support member and improve the machining accuracy of the numerical control machine tool.