Milling is the machining process of using rotary cutters to remove material from a workpiece by advancing (or feeding) the cutter into the workpiece at a certain direction. The cutter may also be held at an angle relative to the axis of the tool. That processing covers a wide variety of different operations and machines, on scales from small individual parts to large, heavy-duty gang milling operations. It is one of the most commonly used processes for machining custom parts to precise tolerances.
Milling can be done with a wide range of machine tools. The original class of machine tools was the milling machine (often called a mill). After the advent of computer numerical control (CNC), machines evolved into machining centers: machines augmented by automatic tool changers, tool magazines or carousels, CNC capability, coolant systems, and enclosures. Centers are generally classified as vertical machining centers (VMCs) or horizontal machining centers (HMCs).
The integration of milling into turning environments, and vice versa, begun with live tooling for lathes and the occasional use of mills for turning operations. This led to a new class of machine tools, multitasking machines (MTMs), which are purpose-built to facilitate milling and turning within the same work envelope.
This cutting process that uses a cutter to remove material from the surface of a workpiece. The cutter is a rotary cutting tool, often with multiple cutting points. As opposed to drilling, where the tool is advanced along its rotation axis, the cutter in milling is usually moved perpendicular to its axis so that cutting occurs on the circumference of the cutter. As the milling cutter enters the workpiece, the cutting edges (flutes or teeth) of the tool repeatedly cut into and exit from the material, shaving off chips (swarf) from the workpiece with each pass. The cutting action is shear deformation; material is pushed off the workpiece in tiny clumps that hang together to a greater or lesser extent (depending on the material) to form chips. This makes metal cutting somewhat different (in its mechanics) from slicing softer materials with a blade.
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