Machining is the process of removing unwanted material from a workpiece in the form of chips. If the workpiece is metal, the process if often called metal cutting or metal removal. U.S. industries annually spend $60 billion to perform metal removal operations because the vast majority of manufactured products require machining at some stage in their production, ranging from relatively rough or nonprecision work, such as cleanup of casting or forgings, to high-precision work involving tolerances of 0.0001 in. or less and high-quality finishes. Thus machining undoubtedly is the most important of the basic manufacturing processes .
 DeGarmo, E.P.; Black J.T.; Kohser, R.A.; and Klamecki, B.E. "Materials and Processes in Manufacturing, Ninth Edition." Hoboken, N.J.: John Wiley & Sons, 2003.