Milling is the process of machining using rotary cutters to remove material by advancing a cutter into a work piece. CNC milling, or computer numerical control milling, is a machining process which employs computerised controls and rotating multi-point cutting tools to progressively remove material from the workpiece and produce a custom-designed part or product. This may be done varying direction on one or several axes, cutter head speed, and pressure.
Milling 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. CNC machines also include laser cutters, plasma cutters, press brakes, etc.
The milling process usually comprises of a few different operations, but this depends on the shape of the final product and the state of the raw piece. Often, milling is necessary for giving a precise finish and adding a few features like slots or threaded holes.