The milling cutter's cutting edge is subjected to an impact load each time it is plunged. In order to successfully mill, you must consider the correct contact between the cutting edge and the material during cutting in one cut. In the milling process, the workpiece is fed in the same or opposite direction as the rotation direction of the milling cutter, which will affect the cutting in and out of the milling and whether the method of up milling or down milling is adopted.