Milling is opposite to that of turning. When milling the workpiece is stationary and the tool is rotated. As the tool rotates one or more of the cutting edges engages with the workpiece and removes material. Therefore due to the action of the cutting edges coming into and out of contact with the workpiece the machining is interrupted machining. As the cutting edges engage and disengage with the workpiece the cutting edges are subjected to severe thermal shock. This is due to the rapid temperatures increase due to friction during the cut and rapid cooling as this cutting edge disengages from the workpiece.
Recent years have seen a large step forward in the technologies revolving around the manufacturing of workpiece materials and the development of new workpiece materials. Therefore, to enable and achieve high-efficiency machining, cutting tool manufacturers strive to improve and develop tool materials and cutting edge geometries.
In contrast to turning, milling is an operation in which a rotating tool engages the workpiece. Material is removed as the workpiece moves past the rotating cutting edges. Milling is interrupted and non-uniform machining as one or more teeth engages the workpiece one after another. One of the main characteristics of milling is the impact when one or more teeth engage the workpiece. When this occurs the cutting edge is subject to severe thermal shock.
Thermal shock is the term given to the extreme temperature changes experienced at the cutting edge. The cutting edge temperature increases rapidly due to friction when machining the workpiece. After machining the teeth disengage from the workpiece and are cooled rapidly as the teeth pass through air. Therefore, for milling, it is important to select a tool grade material that can withstand severe working conditions and a cutting edge geometry that can maximize the performance of the cutter.
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Generally milling is divided into face milling, to machine wide surfaces, and end milling to machine complicated shapes.
The picture shows a variety of milling tools.