Contour milling and rock climbing milling
Figure 6-26a is a simple schematic of solid surface milling. Surfaces are not too complex, but they can be selected from a variety of paths. If you use a machine tool with more than three-axis linkage, you can choose a wider area, and you can use the approximate contour path with a small inclination as shown in Figure 6-26b (the contour line is originally used for the ground map, and the concept is borrowed from the three-dimensional surface milling), but if it is only a CNC machine tool with two-axis linkage, there are usually only two alternative milling methods: contour milling (see the red trajectory in Figure 6-27a) and rock climbing milling (see the red trajectory in Figure 6-27b).
Contour milling is to treat the shape of the three-dimensional surface as a three-dimensional landform, and the milling cutter mills along the contour line of the "landform". Rock climbing milling also treats the shape of the three-dimensional surface as a three-dimensional landform, and cuts along the surface in the direction perpendicular to the contour line with a trajectory similar to that of a rock climber. In the process of rock climbing and milling, both the steep downward slope (see Figure 6-28) and the corner (see the blue arrow in Figure 6-27) are prone to problems. The downward steep slope is very easy to cause the ball nose cutting edge of the ball nose milling cutter to be close to the chipping edge at the circumferential cutting edge, because the cutting working angle of the tool here has changed greatly compared with the static angle, the axial working rake angle of the milling cutter becomes very large, and the axial working rear angle is very likely to become a negative value, or even a small negative value, and this situation is easy to cause chipping. Therefore, the feed value must be reduced for downwards steep slopes. Figure 6-30 shows the relationship between the feed per tooth and the feed direction of rock climbing milling.
The corners of the climbing mill are prone to chipping at the center of the ball nose milling cutter (see Figure 6-29). These corners are prone to gouging, especially at high speeds.
It is recommended to machine the three-dimensional surface on a two-axis machine, using contour milling, and using the climb milling method. At the same time, at the corners of the contour lines, the trochoidal milling, sheet milling or dynamic milling methods described below are used. After each contour milling is completed, a new contour machining is started in an arc form.
On machines with three or more simultaneous axes, it is recommended to use an approximate contour path with a small inclination, and it is also recommended to use the climb milling method. This results in fewer plunges and smoother cuts.
