Reasonable selection of structural form of CNC machine tool steel components
Due to the complexity of the instantaneous change of CNC machine tool processing status, structural stiffness is usually difficult to calculate theoretically. Designers can only calculate the stiffness of some parts (such as shafts, screws, etc.)
Shape, joint surface contact deformation, etc. can only be calculated approximately after simplification. The calculation results are always very different from the actual situation and can only be used as a reference for qualitative analysis. In recent years, although the finite element method is often used for analysis and calculation in the structural design of machine tools, generally speaking, it is still necessary to use
Conduct testing, analysis, and comparison through models, physical objects, or similar prototypes to determine a reasonable structural plan. However, by following the following principles and measures, the structural stiffness of the machine tool can still be reasonably improved.
(1) Correctly choose the cross-sectional shape and size
After a member is subjected to bending and torsional loads, its deformation depends on the bending and torsional moments of inertia of the section. The greater the bending and torsional moments, the greater its stiffness. For cross-sections of the same shape, while maintaining the same cross-sectional area, the wall thickness should be reduced and the cross-sectional outline size should be increased. circular cross-section torsion
The stiffness is greater than that of a square section, while the bending stiffness is smaller than that of a square section; the stiffness of a closed section is much greater than that of an unclosed section; openings in the wall will reduce the stiffness, and adding a flange around the hole can restore the bending stiffness.
(2) Reasonably select and arrange partitions and ribs
By rationally arranging the partitions and reinforcements of supporting components, the static and dynamic stiffness of the components can be improved. Several column structures are equipped with longitudinal, transverse and oblique stiffening aids, and static and dynamic stiffness tests were conducted on them, and the static and dynamic stiffness test results were obtained. For some thin-walled components, in order to
To reduce wall warpage and component cross-section distortion, honeycomb stiffeners are more effective, which can not only increase component stiffness but also reduce shrinkage stress during casting.
(3) Improve the local stiffness of components
The connection between the CNC machine tool guide rail and the support is often the weakest local stiffness, but the connection method has a great influence on the local stiffness. Several connection types between the guide rail and the bed are given below. If the guide rail is wider, a double-wall connection type should be used. If the guide rail is narrow, a single-wall connection or a reinforced one can be used.
Thick single wall connections, or adding vertical stiffeners to single walls to increase local stiffness.
(4) Welded structural parts
The bed, columns and other supporting components of CNC machine tools are all welded from steel plates and shaped steel, which has the significant advantages of reducing mass and improving stiffness. The elastic modulus of steel is about twice that of cast iron. Under the premise of the same shape and dimensions, if the stiffness of the weldment and the casting are required to be the same, the wall of the weldment will
The thickness only needs to be half of the casting; if the local stiffness is required to be the same, the local stiffness is proportional to the cube of the wall thickness, so the wall thickness of the weldment only needs to be about 809 times the wall thickness of the casting. In addition, whether the rigidity is the same and the mass is reduced, or the mass is the same and the rigidity is increased, the resonant frequency of the component can be increased.
Make it less likely to resonate. By welding steel plates, the components can be made into a fully enclosed box structure, which is beneficial to improving the rigidity of the components.
