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The five axes of a five-axis machine tool are usually composed of three linear axes and two rotational axes, but the structural styles can vary greatly. Different structural forms can cause differences in the machine tool's rigidity, dynamic performance, and precision stability. This article mainly analyzes and compares the two different structures of vertical spindle swing and vertical spindle stationary table swing (cradle type) of the CNC five-axis machine, so that users can fully understand their structural forms, and thereby select the appropriate machine tool according to the characteristics and economic capacity of their products.
During the machining process of a spindle swing type machine tool, the rigidity of the spindle is relatively poor due to the swing of the spindle, while in a stationary table swing type machine tool, the rigidity of the spindle is not affected due to the swing of the table.
Due to the different rotation points, the spindle of a spindle swing type machine tool needs to swing a larger angle to achieve the same displacement of the cutting edge, so when machining the same parts, the efficiency of a spindle swing type machine tool is lower.
For a spindle swing type machine tool, the tool length is part of the swing arm. In other words, the length of the tool affects the length of the swing arm and amplifies the error. The error increases as the length of the tool increases. For a cradle-type stationary table swing machine tool, the tool length is not relevant to the length of the swing arm.
With the swing, both types of CNC five-axis machines will produce position errors, but the spindle swing type machine tool will also produce shape errors, while the stationary table swing type machine tool does not produce shape errors. The rotary motion of the spindle of a spindle swing type machine tool generates position errors. At the same time, the feed direction of the machined hole and the rotation center of the cutting tool deviate, so the machined hole not only produces position errors but also shape errors with a wedge-shaped hole.
The position error of the stationary table swing machine tool is caused by the swing of the table, but the feed direction of the spindle and the rotation center of the cutting tool always coincide, so there is no additional shape error. This is another obvious advantage of the cradle-type stationary table swing machine tool compared to the spindle swing type machine tool.
With the swing of the spindle of a spindle swing type machine tool, the range of the diameter of the workpiece that can be machined in the radial direction will be reduced. In other words, the range of the diameter of the workpiece that can be machined by a CNC five-axis machine with spindle swing is smaller than that of a three-axis CNC machine tool due to the reduction of travel caused by the spindles swing angle. The table swing of a cradle-type machine tool does not affect the size of the workpiece in the horizontal direction. In this sense, the size range of the workpiece for five-axis machining and three-axis machining is the same in a cradle-type machine tool. In general, given the same travel, the five-axis machining range of a machine tool with a cradle-type stationary table swing structure is larger than that of a spindle swing type machine tool.
Therefore, the cradle-type stationary table swing machine tool has better spindle rigidity and higher machining efficiency. The length of the tool does not affect machining accuracy, and no shape errors are generated during machining. The machining range of the CNC five-axis machine with a cradle-type mechanism is larger than that of a spindle swing type machine tool for the same travel.
The rigidity of the spindle of the head pendulum machine is relatively poor, and the machining efficiency is relatively low; the machining accuracy will decrease with the growth of the tool length; the machining will produce shape errors; the angle of spindle swing will eat up the stroke, thus resulting in the maximum size of the workpiece that can be machined becomes smaller.
In addition, it should be added that the table swing machine needs to overcome the self-weight of the workpiece, if the workpiece is very heavy, the clamping has higher requirements; also, when processing large and heavy parts, the machine cannot achieve the table swing, it can only use the head swing method.
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