Milling is the process of using revolving cutters to remove material from an object advancing in a certain direction at an angle with the axis of the tool. This covers a variety of machines and operations, on small individual parts to large heavy-duty gang milling operations. Milling is one of the most common processes in industry and machine shops today.

Computer numerical control or CNC is a relatively new invention that has transformed the manufacturing industry. Manufacturing units use CNC milling machines to make sophisticated and accurate parts of machinery from various materials which include steel, plastic and aluminum. These machines can accurately manufacture complicated parts for aeronautical applications as well as simple parts for consumer good and toys.

CNC milling machines were first invented in mid 20th century. Manufactures involved in making parts for airplanes discovered that they could make parts more accurately and efficiently by using a computer to move the cutting spindle. For more than a century all mills had been manually operated.

• The invention of the CNC allowed manufacturing units to manufacture objects more accurately. This invention had a large impact on the manufacturing industry, as these machines could cut objects repeatedly with absolute accuracy. Once the program is entered into the computer, the machine will cut every piece of the desired object exactly the same as long as the tools are sharp.
• Previously it took a skilled mill operator a lot more time to cut parts and these parts were never exactly the same. The invention of CNC machines reduced the cost of manufacturing and allowed for fewer rejects.
• NC milling machines are first set-up by trained operators after which these machines can be run by less-skilled workers. Operators place the raw materials inside the machines and monitor the machine for errors and tool breaks. Since the CNC milling machines are fully automatic the machine operators are free to take on other tasks in the manufacturing units. Before the invention of CNC machines an operator had to make all the parts by hand and hence was seldom able to multitask.