The cutting edge of a milling cutter is subject to impact loads every time it cuts in. For successful milling, the correct contact between the cutting edge and the material during the cut must be considered. During the milling process, the workpiece is fed in the same or opposite direction as the milling cutter's rotation, which affects the milling cut-in, cut-out, and whether to use down milling or up milling.I: Definitions
Down milling: refers to the direction of the cutting speed of the tool in the same direction as the workpiece's movement. Up milling: refers to the direction of the cutting speed of the tool in the opposite direction of the workpiece's movement. The golden rule of milling - when milling from thick to thin, always consider chip formation. The determining factor in chip formation is the position of the milling cutter. Always strive to form thick chips when the cutter cuts in and thin chips when the cutter cuts out to ensure a stable milling process. Remember the golden rule of milling "from thick to thin" to ensure that the chip thickness when the cutter cuts out is as small as possible. 2. Identification method
When milling the outer contour of the workpiece, feeding and programming along the outer contour of the workpiece in a clockwise direction is down milling, and programming and feeding along the outer contour of the workpiece in a counterclockwise direction is reverse milling; when milling the inner contour of the workpiece, feeding and programming along the inner contour of the workpiece in a counterclockwise direction is down milling, and programming and feeding along the inner contour of the workpiece in a clockwise direction is reverse milling. 3. Characteristics of down milling and reverse milling 1. During down milling, the cutting thickness of each cutter changes gradually from small to large. When the cutter teeth just come into contact with the workpiece, the cutting thickness is zero. Only when the cutter teeth slide a certain distance on the cutting surface left by the previous cutter teeth and the cutting thickness reaches a certain value, the cutter teeth really start cutting. Reverse milling makes the cutting thickness change gradually from large to small, and the sliding distance of the cutter teeth on the cutting surface is also very small. Moreover, during down milling, the distance traveled by the cutter teeth on the workpiece is shorter than that of reverse milling. Therefore, under the same cutting conditions, when reverse milling is used, the tool is easy to wear. 2. In reverse milling, since the direction of the horizontal cutting force of the milling cutter on the workpiece is opposite to the direction of the workpiece feed movement, the worktable screw and the nut can always keep one side of the thread tightly fitted. However, this is not the case in down milling. Since the direction of the horizontal milling force is consistent with the direction of the workpiece feed movement, when the force of the cutter teeth on the workpiece is large, the worktable will move due to the gap between the worktable screw and the nut, which not only destroys the stability of the cutting process and affects the processing quality of the workpiece, but also damages the tool in serious cases. 3. In reverse milling, due to the large friction between the cutter teeth and the workpiece, the cold hardening phenomenon of the machined surface is more serious. 4. In down milling, the cutter teeth start cutting from the workpiece surface every time, so it is not suitable for processing workpieces with hard skin. 5. The average cutting thickness in down milling is large, the cutting deformation is small, and the power consumption is less than that in reverse milling (power consumption can be reduced by 5% when milling carbon steel and by 14% when milling difficult-to-process materials). The feed direction of the workpiece fixture tool puts forward different requirements for the workpiece fixture. It should be able to resist the lifting force during up milling. It should be able to resist the down force during down milling.
