What is the difference between 3-axis and 5-axis CNC milling machines?
The five-axis machining center has the characteristics of high efficiency and high precision, and the pentahedron can be processed in one clamping of the workpiece. If equipped with a five-axis linkage high-end numerical control system, it can also perform high-precision processing of complex spatial surfaces, and is more suitable for processing modern molds such as auto parts and aircraft structural parts. There are two ways for the rotary axis of the five-axis vertical machining center. One is the table rotary axis. The table 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 A-axis and C-axis, except for the five-axis machining center (7 sheets) on the bottom surface of the workpiece fixed on the worktable, the remaining five surfaces can be processed by the vertical spindle. The minimum graduation value of 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 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 structure of the spindle is relatively simple, the rigidity of the spindle is very good, and the manufacturing cost is relatively low. However, the general worktable 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, it will bring a large bearing moment to the worktable when the workpiece is cut. The other is to rely on the rotation of the vertical spindle head. The front end of the main shaft is a revolving head that can circle the Z axis 360 degrees to become the C axis. The revolving head 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 arrangement is that the spindle processing is very flexible, the worktable can also be designed to be very large, and the huge fuselage and huge engine shell of the passenger aircraft can be processed on this type of machining center. This design also has a big advantage: when we use a spherical milling cutter to process curved surfaces, when the center line of the tool is perpendicular to the processing surface, since the linear velocity of the apex of the spherical milling cutter is zero, the surface quality of the workpiece cut by the apex will be poor. The spindle rotation design is adopted to make the spindle rotate an angle relative to the workpiece, so that the spherical milling cutter avoids the apex cutting, guarantees a certain linear speed, and improves the surface processing quality. This structure is very popular for high-precision surface machining of molds, which is difficult for rotary table machining centers. In order to achieve the high precision of rotation, the high-end rotary axis is also equipped with circular grating scale feedback, and the indexing accuracy is within a few seconds. Of course, the rotation structure of this type of spindle is more complicated and the manufacturing cost is also high.
Three-axis CNC machine tools
Generally speaking, the X axis refers to the direction of the worktable, the Y axis is the up and down movement direction of the headstock, and the Z axis is generally the feed direction of the boring bar or milling head.
The five axes are X, Y, Z, W, B or U axis. For the boring machine, it corresponds to the straight line of the worktable, the headstock, the boring bar, the ram and the rotation of the worktable.
The axis of rotation is the main drive, of course the Z axis. Up and down is the Y axis.