Programming Difference between Three-axis and Five-axis Machining Centers

Five-axis machining center workpiece can be clamped once to complete the pentahedron processing, but also to complex space surface for high-precision processing. The most effective processing surface of vertical machining center (three axes) is only the top surface of the workpiece. Horizontal machining center can only complete the four-sided processing of the workpiece with the help of rotary table.

　　I. Vertical Five-Axis Machining Center

　Ⅰ. Workbench Rotary Shaft

The worktable set on the bed can revolve around the X axis, which is defined as the A axis. The A axis generally has a working range of + 30 degrees to - 120 degrees. There is also a turntable in the middle of the worktable, which revolves around the Z axis in the position shown. It is defined as the C axis, and the C axis is 360 degrees revolving. In this way, through the combination of A axis and C axis, the workpiece fixed on the worktable can be processed by the vertical spindle except the bottom. The minimum indexing value of axes A and C is generally 0.001 degrees, so that the workpiece can be subdivided into arbitrary angles and the inclined surface and hole can be machined. If Axis A and C are linked with XYZ three linear axes, complex space surface can be machined. Of course, this requires the support of high-grade CNC system, servo system and software. The advantages of this method 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. But the general worktable can not be designed 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 cutting will bring a great bearing moment to the worktable.

2. Relying on the Rotation of Vertical Spindle Head

The front end of the spindle is a revolving head, which can revolve 360 degrees around the Z axis and become the C axis. The revolving head is also equipped with an A axis which can revolve around the X axis. Generally, the revolving head can reach more than 90 degrees, which achieves the same function mentioned above. The advantage of this method is that the spindle processing is very flexible, the worktable can also be designed very large, the huge airplane body, the huge engine shell can be processed in such processing centers. This design also has one big advantage: when we use spherical milling cutter to process surface, when the center line of the cutter is perpendicular to the machining surface, because the vertex linear velocity of the spherical milling cutter is zero, the surface quality of the workpiece cut by the vertex will be very poor. The design of spindle rotation makes the spindle rotate an angle relative to the workpiece, so that the spherical milling cutter avoids the vertex cutting and ensures a certain linear speed. It can improve the quality of surface processing. This kind of structure is very popular in high precision surface processing of dies and dies, which is difficult for rotary machining centers of worktables. In order to achieve high accuracy of rotation, the high-grade rotary shaft is equipped with grating ruler feedback, and the accuracy of indexing is within a few seconds. Of course, the rotation structure of this kind of spindle is more complex and the manufacturing cost is higher.

The spindle speed of horizontal machining center is generally over 10,000 rpm. Because of the self-gravity of the horizontal spindle in the radial direction, the radial force of bearings is uneven in high-speed air running. In addition, the larger BT50 tool holder is used, which can generally reach up to 20,000 rpm. Horizontal Machining Center has a fast feed rate of 30-60 m/min, a spindle motor power of 22-40 KW or more, and a tool library capacity of 160 can be increased from 40 to 160 as required. Its processing capacity is far beyond that of general vertical Machining Center. It is the first choice for heavy machinery processing.