Technological Innovation and Market Application of Machining Centers: Analysis of the Differences between Four-Axis and Five-Axis

Three-axis machining center

Vertical machining centers (three-axis) are mainly used for processing the top surface of workpieces and have high processing efficiency. Horizontal machining centers, on the other hand, achieve efficient processing of the four surfaces of workpieces through rotary tables. However, with the continuous development of high-end machining centers towards five-axis control technology, now a workpiece can complete the fine processing of a five-sided body in a single clamping. If a high-end numerical control system with five-axis linkage is further equipped, high-precision processing of complex spatial curved surfaces can be further achieved.

Four-axis linkage machining technology

Introduction to Four-Axis Linkage Technology

Four-axis linkage machining, simply put, is to add a rotating axis, namely the fourth axis, on the basis of the traditional three-axis machining. On a regular machine tool, we only have the movement of three axes, including the left and right movement of the workpiece platform (axis 1), the front and back movement (axis 2), and the movement of the spindle tool head (axis 3), which are used for cutting the workpiece. The addition of the fourth axis involves installing an electric dividing head capable of 360-degree rotation on the mobile platform. This enables functions such as automatic indexing for drilling inclined holes and milling inclined edges without the need for secondary clamping, thus ensuring processing accuracy.

Technical features

Four-axis linkage machining has significant advantages over the traditional three-axis machining. First of all, it can easily handle complex workpieces that three-axis machine tools cannot process or situations that require cumbersome clamping. Secondly, the four-axis technology has significantly enhanced the processing accuracy, quality and efficiency of free-space curved surfaces. A larger processing range is achieved by adding a rotating shaft. Furthermore, the core difference between four-axis and three-axis lies in the addition of a rotating axis, thereby expanding the processing range and flexibility. In the establishment of four-axis coordinates, the Z-axis is usually set in the direction of the machine tool's spindle axis or the vertical direction of the worktable where the workpiece is clamped, while the X-axis is selected in the horizontal plane parallel to the workpiece installation surface, perpendicular to the workpiece's rotation axis, and away from the spindle axis as the positive direction.

Design of vertical five-axis machining center

Two types of rotary shaft configurations

The vertical five-axis machining center has two types of rotary axis configurations. One type is the worktable rotary axis, which is set on the bed and can rotate around the X-axis, defined as the A-axis. Its working range is usually ±30 degrees to ±120 degrees. In addition, a rotary table is equipped in the middle of the workbench, which can rotate 360 degrees around the Z-axis and is defined as the C-axis. Through the coordinated action of the A-axis and the C-axis, the five surfaces of the workpiece fixed on the worktable, except for the bottom surface, can all be processed by the vertical spindle. The minimum dividing values of the A-axis and C-axis are usually 0.001 degrees, which enables the workpiece to be subdivided at any Angle, thereby processing complex shapes such as inclined surfaces and inclined holes. The configuration of the A-axis and C-axis enables the vertical five-axis to achieve processing on five surfaces.

Spindle rotation design

Another spindle rotation design is more flexible. The front end of the main shaft is equipped with a rotary head that can rotate 360 degrees around the Z-axis by itself, which becomes the C-axis. The rotating head is also equipped with an A-axis that can rotate around the X-axis, and its rotation Angle can generally reach ±90 degrees or more. This design makes the spindle highly flexible during processing and allows the worktable to be designed to be larger, thereby meeting the processing requirements of large workpieces, such as the huge fuselage and large engine casings of passenger aircraft. Provide better flexibility to adapt to large workpieces and high-precision surface processing capabilities. In addition, this spindle rotation design has another major advantage. When processing curved surfaces, by adjusting the Angle of the spindle, the problem of the vertex linear velocity of the spherical milling cutter being zero can be avoided, thereby improving the processing quality of the workpiece surface. This structure is particularly suitable for high-precision curved surface processing of molds, which is difficult for worktable rotary machining centers to achieve. To achieve high-precision rotation, the high-end rotary shaft is equipped with circular grating ruler feedback to ensure that the indexing accuracy is within a few seconds. Of course, the manufacturing structure of this type of spindle is relatively complex and the cost is also high.

Horizontal five-axis machining center

Two types of rotary shaft Settings

There are two ways to set the rotary axis for horizontal five-axis machining centers. One type uses the horizontal spindle swing as the rotary axis, supplemented by a rotary axis of the worktable, to achieve five-axis linkage processing. Its structure is simple and flexible. If the spindle needs to be converted between vertical and horizontal positions, it only requires the indexing and positioning of the worktable, and then it can be easily configured as a three-axis machining center for vertical and horizontal conversion. This horizontal five-axis type has high flexibility and is suitable for processing complex curved surfaces. By coordinating the vertical and horizontal conversion of the main shaft with the indexing of the worktable, five-sided processing of the workpiece can be carried out, reducing manufacturing costs and making it highly practical. In addition, CNC axes can be set on the worktable, with a minimum graduation value of 0.001 degrees, but they are not linked. This makes it a four-axis machining center that can be converted between vertical and horizontal positions, meeting different processing requirements and offering highly competitive prices.