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Milling

Why?
milling machine features a rotating cutter.  It is a machine tool used to machine a variety of solid materials.  The cutter path can vary in 3 axes to create a high definition often complex 3D surface. It should also be noted that 2 or more processes can be employed on a single machine, e.g. turning and milling on a machining centre, using 5 or 6 axes are relatively common.
 
How?
The machined part can have a number of features including slotscavitiesholes and profiles. The process is a wasting process, creating swarf as it removes material. To reduce heat, wear and distortion a coolant and cutting fluid are generally used to lubricate and wash away swarf from the cutting area.
Milling machines are often classed in two basic forms, horizontal and vertical, which refer to the orientation of the main spindle. The work piece or raw material is clamped firmly on a bed that can be moved radially ( x-y axis) against the rotating milling cutter, which cuts on its sides as well as its tip. The milling cutter can be moved in the z axis to create contours and forms and to drill down into the work piece.  The cutter is often multi-toothed creating several swarf chips with each rotation.

Milling machines can be manually operated but most are automated via computer numerical control (CNC).  Both the bed and cutter can be controlled to move in complex paths.  Tool changes are automated and speed and feed rates changed continuously to suit cutter size and materials.
For complex forms, face and end milling use a cutter pointing down (perpendicular) into the material rotating in the z axis. Almost all cutters have attached teeth made from carbides.  These teeth are called inserts.

For creating flat true surfaces, peripheral or slab milling uses a rotating cutter parallel to the work piece and can cut ‘up’ through the material (up milling).  While work has to be held really firmly it creating a quality flat surface, especially on forging and castings.  Thin materials and softer materials can often be machined better by down milling where the cutter tip approaches the work from above.  The workpiece while held in place is pushed firmly down on the machine bed.

Workpiece and cutter movement are precisely controlled and moved in the three axes to less than 0.001 in (0.025 mm), usually by means of precision ground slides and leadscrews.

Milling machines can perform any number of operations, from simple (e.g., slot and keyway cutting, planing, drilling) to complex (e.g., contouring, die sinking).