The front end of the main shaft is a back, which can circle the Z axis 360 degrees to become the C axis. The back back also has an A axis that can rotate around the X axis, which can generally reach more than ±90 degrees to achieve the same function as above. The advantage of this setting method is that the spindle processing is very sensitive, and the worktable can also be designed to be very large. The huge fuselage of the passenger aircraft and the huge launcher casing can all be processed on this type of vertical machining center.
This kind of planning also has a major advantage: when we use spherical milling cutters to process curved surfaces, when the center line of the tool is perpendicular to the processing surface, since the linear velocity of the pole of the spherical milling cutter is zero, the surface quality of the workpiece cut from the pole will be poor. The plan of spindle reversal is adopted to make the spindle rotate a point of view relative to the workpiece, so that the spherical milling cutter avoids the pole cutting, guarantees a certain linear speed, and improves the surface processing quality.
Secondly, this structure is very popular for high-precision surface processing of molds, which is difficult for vertical machining centers with inverted worktables. In order to achieve the high precision of reversal, the advanced reversal axis is also equipped with circular grating feedback, and the indexing accuracy is within a few seconds. Of course, the reversal structure of this type of spindle is more complicated and the production cost is also high.
Reverse axis of worktable
The work table set on the bed can be reversed around the X axis, defined as the A axis, and the A axis generally operates from +30 degrees to -120 degrees. There is also a reversing table in the middle of the worktable, which reverses around the Z-axis in the orientation shown in the figure. It is defined as the C-axis, and the C-axis is 360-degree reverse. In this way, through the combination of the A-axis and the C-axis, all five surfaces of the workpiece fixed on the worktable of the vertical machining center can be processed by the vertical spindle except for the bottom surface.
The small division values of A-axis and C-axis are generally 0.001 degrees, so that the workpiece can be subdivided into arbitrary viewpoints, and inclined surfaces, inclined holes, etc. can be processed. If the A-axis and C-axis are linked with the XYZ three linear axes, complex spatial surfaces can be processed. Of course, this requires the support of advanced CNC systems, servo systems and software. The advantage of this setting method is that the structure of the main shaft is relatively simple, the rigidity of the main shaft is very good, and the production cost is relatively low.
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