Installation form of ball screw

The ball screw pair is used as the feed transmission chain of the CNC machine tool. Its assembly form and accuracy determine the positioning accuracy of the CNC machine tool, and also affect the smoothness of the feed axis interpolation operation.

1. Installation form and force of ball screw

Common lead screw supports for controlling machine tool feed axes have the following forms:

1. One end is fixed-one end is free

    One end of the screw is fixed and the other end is free. The fixed end bearing bears both axial force and radial force. This support method is used for short lead screws with small stroke or for fully closed-loop machine tools, because the mechanical positioning accuracy of this structure is the least reliable, especially for The lead screw with a large aspect ratio (the ball screw is relatively slender) has obvious thermal degeneration. It is normal for a 1.5m long lead screw to change 0.05~0.10mm under different cold and hot environments. However, due to its simple structure and convenient installation and debugging, many high-precision machine tools still adopt this structure, but must be equipped with gratings and adopt full closed loop feedback.

2. One end is fixed-the other end is supported

    One end of the screw is fixed and the other end is supported. The fixed end bears axial force and radial force at the same time; the supporting end only bears radial force, and can make a small amount of axial floating, which can reduce or avoid bending due to the weight of the screw, and the thermal deformation of the screw can be free Stretch to one end. This structure is the most widely used. At present, domestic small and medium-sized CNC lathes and vertical machining centers use this structure.

3. Fixed at both ends

    Both ends of the screw are fixed. Both the fixed end bearings can bear the axial force at the same time. This support method can apply appropriate pre-tightening force to the screw, improve the support rigidity of the screw, and partially compensate the thermal deformation of the screw.

    This solution is often used for large-scale machine tools, heavy-duty machine tools, and high-precision boring and milling machines. However, the adjustment of this kind of screw is cumbersome. If the pre-tightening force at both ends is too large, the final stroke of the screw will be longer than the design stroke, and the pitch will be larger than the design pitch. If the pre-tightening force of the lock nut at both ends is not enough, it will cause the opposite result, and easily cause the machine tool to vibrate and reduce the accuracy. Therefore, this type of screw must be adjusted according to the original manufacturer's instructions during disassembly or assembly, or adjusted with the aid of an instrument (dual frequency laser measuring instrument).