All machining processes remove material to form shapes. As metals are still the most widely used materials in manufacturing, machining processes are usually used for metals. However, machining can also be used to shape plastics and other materials which are becoming more widespread. Basically all the different forms of machining involve removing material from a component using a rotating cutter. The differences between the various types arise from the relative motion between cutting tool and work piece and the type of cutting tool used. Typically machining will be done using a machine tool. This tool holds the work piece and the rotating cutting tool and allows relative movement between the two. Usually machine tools are dedicated to one type of machining operation, although some more flexible tools allow more than one type of machining to be performed. The machine tool can either be under manual or automatic (Computer Numeric Control - CNC) control. Automatic control is more expensive because of the need to invest in the necessary control mechanisms however it becomes more desirable as the number of components produced increases and labor costs can be reduced. The speed at which a machine tool can process individual components is a function of the cutting speed of the tool and the downtime involved in changing the work piece and maintaining the tool (this will usually involve changing the cutting edges of the tool). Some very flexible tools allow automatic changing of components and cutting tools, however they greatly add to initial purchase price of the machine tool. The cutting speed of the tool is usually dictated by the type of material being machined, in general the harder the material, the slower the machining time. Machining speed can be increased by increasing the rotational speed of the cutter; however this will be at the expense of the tool life. Hence for machining processes there is an optimum cutting speed that balances tooling costs with cutting speed.
In order to dissipate the heat generated between the work piece and the cutting tool, cutting fluids are sprayed onto the tool. The cutting fluid also acts to remove cut material away from the cutting region and lubricates the tool - work piece interface but may require that the component is cleaned afterwards.
It is important to view machining, as well as all manufacturing operations, as a system consisting of the work piece, the tool and the machine. The introduction topic in this section covers primers on topics like mechanics & shear bending in machining, and heat in machining. The traditional machining includes primers on turning, milling, drilling, and grinding.