Milling is a mechanical processing method that uses a milling cutter as a tool to process the surface of an object. Milling machines include horizontal milling machines, vertical milling machines, gantry milling machines, profiling milling machines, universal milling machines, and bar milling machines. The characteristic of curved surface parts is that the machining surface is a spatial curved surface, and during the machining process, the machining surface and the milling cutter are always in point contact. Ball end milling cutters are often used for surface finishing.