Vertical five-axis machining center

There are two ways for the rotary axis of this type of machining center:

One is the rotary axis of the table.

The worktable set on the bed can rotate around the X-axis, which is defined as the A-axis. The general working range of the A-axis is +30 degrees to -120 degrees. There is also a rotary table in the middle of the worktable, which revolves around the Z-axis at the position shown in the figure, which is defined as the C-axis, and the C-axis rotates 360 degrees. In this way, through the combination of the A-axis and the C-axis, except for the bottom surface of the workpiece fixed on the worktable, the remaining five surfaces can be processed by the vertical spindle. The minimum division value of the A-axis and C-axis is generally 0.001 degrees so that the workpiece can be subdivided into any angle, 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 curved surfaces can be processed. Of course, this requires the support of high-end CNC systems, servo systems, and software. The advantages of this arrangement are that the structure of the spindle is relatively simple, the rigidity of the spindle is very good, and the manufacturing cost is relatively low.

However, generally, the worktable cannot be designed too large, and the load-bearing capacity is also small, especially when the rotation of the A-axis is greater than or equal to 90 degrees, the workpiece cutting will bring a large load-bearing moment to the worktable.

The front end of the main shaft is a rotary head, which can surround the Z-axis 360 degrees and become the C axis. The rotary head also has an A-axis that can rotate around the X-axis, generally up to ±90 degrees or more, to achieve the same function as above. The advantage of this setting method is that the spindle processing is very flexible, and the worktable can also be designed to be very large. The huge body of the passenger plane and the huge engine casing can be processed at this type of machining center.

This design also has a big advantage: when we use a spherical milling cutter to process a curved surface when the centerline of the tool is perpendicular to the processing surface since the linear velocity of the vertex of the spherical milling cutter is zero, the surface quality of the workpiece cut out by the vertex will be very poor. The design of the spindle rotation is adopted, so that the spindle rotates at an angle relative to the workpiece, so that the spherical milling cutter avoids the vertex cutting, and ensures a certain linear speed, which can improve the surface processing quality. This structure is very popular for high-precision surface machining of molds, which is difficult to achieve with rotary machining centers. To achieve the high precision of rotation, the high-grade rotary shaft is also equipped with a circular grating scale feedback, and the indexing accuracy is within a few seconds. Of course, the rotary structure of this type of spindle is relatively complex, and the manufacturing cost is also high.

The other is to rely on the rotation of the vertical spindle head.

The gravity of the main shaft of the vertical machining center is downward, the radial force of the bearing in high-speed idling is equal, and the rotation characteristics are very good, so the speed can be increased. Generally, the high speed can reach more than 1,2000r/min, and the practical maximum speed has reached 4,0000 rpm. The spindle system is equipped with a circulating cooling device. The circulating cooling oil takes away the heat generated by the high-speed rotation, reduces it to a suitable temperature through the refrigerator, and then flows back to the spindle system.

X, Y, and Z three linear axes can also use linear grating feedback, and the bidirectional positioning accuracy is within the micron level. Because the rapid feed reaches more than 40～60m/min, the ball screws of the X, Y and Z axes are mostly cooled by the center. Like the spindle system, the refrigerated circulating oil flows through the center of the ball screws to take away the heat.

Horizontal five-axis machining center

There are also two ways for the rotary axis of this type of machining center. One is that the horizontal spindle swings as a rotary axis, plus a rotary axis of the worktable to achieve five-axis linkage processing.

This setting method is simple and flexible. If the spindle needs to be converted vertically and horizontally, the worktable can be simply configured as a three-axis machining center with vertical and horizontal conversion only by indexing and positioning. The vertical and horizontal conversion of the main shaft cooperates with the indexing of the worktable to realize the pentahedral processing of the workpiece, which reduces the manufacturing cost and is very practical. CNC axes can also be set on the worktable, with a minimum index value of 0.001 degrees, but without linkage, it becomes a four-axis machining center for vertical and horizontal conversion, adapting to different processing requirements, and the price is very competitive.

The other is the traditional rotary axis of the worktable. The A-axis of the worktable set on the bed generally has a working range of +20 degrees to -100 degrees. There is also a rotary table B-axis in the middle of the worktable, and the B-axis can rotate 360 ​​degrees in both directions. This horizontal five-axis machining center has better linkage characteristics than the first method and is often used to process complex curved surfaces of large impellers. The rotary axis can also be equipped with circular grating feedback, and the indexing accuracy can reach several seconds. Of course, the structure of this rotary axis is more complicated and expensive.

Conclusion

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