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Vertical five-axis machining center

There are two types of rotary axes for this type of machining center. One is the table rotary axis. 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 workbench, which rotates around the Z-axis at the position shown in the figure, which is defined as the C-axis. 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 workbench, the remaining five surfaces can be processed by the vertical spindle.

The minimum indexing value of the A-axis and C-axis is generally 0.001 degrees, which allows the workpiece to be subdivided into any angle and to process inclined surfaces, inclined holes, etc. If the A-axis and C-axis are linked with the XYZ three-linear axis, complex spatial surfaces can be processed. Of course, this requires the support of high-end CNC systems, servo systems and software. The advantage of this arrangement is that the spindle structure is relatively simple, the spindle rigidity is very good, and the manufacturing cost is relatively low. However, the general workbench cannot be designed to be too large, and the load-bearing capacity is also small. Especially when the A-axis rotation is greater than or equal to 90 degrees, the workpiece will bring a large load-bearing moment to the workbench during cutting.

The other one relies on the rotation of the vertical spindle head (picture). The front end of the spindle is a rotary head, which can circle the Z-axis 360 degrees on its own to become the C-axis. The rotary head also has an A-axis that can rotate around the X-axis, generally up to ±90 degrees, to achieve the same function as above. The advantage of this setup is that the spindle processing is very flexible and the workbench can be designed to be very large. The huge fuselage of the passenger aircraft and the huge engine casing can be processed on this type of machining center.

This design also has a major advantage: when we use a spherical milling cutter to process a curved surface, when the tool center line is perpendicular to the processing surface, since the vertex linear speed of the spherical milling cutter is zero, the surface quality of the workpiece cut out by the vertex will be very poor. The spindle rotation design is used to rotate the spindle at an angle relative to the workpiece, so that the spherical milling cutter avoids vertex cutting, ensuring a certain linear speed and improving surface processing quality. This structure is very popular for high-precision curved surface processing of molds, which is difficult to achieve with table rotary machining centers. In order to achieve high rotation accuracy, high-end rotary axes are also equipped with circular scale feedback, and the indexing accuracy is within a few seconds. Of course, the rotation structure of this type of spindle is relatively complex and the manufacturing cost is also high.

Vertical five-axis machining center with rotating spindle

The gravity of the spindle of the vertical machining center is downward, and the radial force on the bearings during high-speed idling operation 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 high-speed rotation, reduces it to the appropriate temperature through the refrigerator, and then flows back to the spindle system. The three linear axes of X, Y and Z can also use linear grating feedback, and the bidirectional positioning accuracy is within the micron level. Since the rapid feed reaches more than 40~60m/min, most of the ball screws of the X, Y, and Z axes adopt central cooling. Like the spindle system, the refrigerated circulating oil flows through the center of the ball screw to take away the heat. .

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