Fundamental Milling Principles
Milling is a machining process that uses a rotating multi-tooth cutter to remove material from a workpiece fed against the tool. The cutter teeth engage and disengage with the workpiece during each revolution, producing interrupted cutting action that differs fundamentally from continuous-cutting processes like turning. This interrupted engagement requires rigid machine construction and secure workholding to maintain accuracy.
Classification of Milling Machines
Milling machines are classified by spindle orientation into vertical and horizontal types. Vertical milling machines mount the cutter on a vertical spindle and are versatile for end milling, face milling, and drilling operations on smaller workpieces. Horizontal milling machines position the cutter on a horizontal arbor, providing superior rigidity and chip evacuation for heavy slab milling, slot cutting, and gang milling operations.
Common Milling Operations
Face milling produces flat surfaces perpendicular to the spindle axis using cutters with teeth on both the periphery and face. Peripheral milling generates surfaces parallel to the cutter axis and includes slab milling, slot milling, and side milling variations. End milling combines both actions to create pockets, profiles, and complex contours using end mills with cutting edges on the tip and sides.
Cutting Tool Selection for Milling
Choosing the correct milling cutter involves considering workpiece material, required surface finish, slot or profile geometry, and machine rigidity. Carbide inserts dominate modern milling for their hardness and heat resistance, while high-speed steel cutters remain cost-effective for low-volume work. Coated tools with titanium nitride or aluminum titanium nitride layers extend tool life and permit higher cutting speeds in demanding applications.
