Major improvements in the rate at which workpieces are machined usually result from the development and application of new tool materials. In the past several years, there have been major advancements in the development of cutting tools including coated carbides, ceramics, cermets, cubic boron nitride, and polycrystalline diamond. These have found useful applications in the machining of cast irons, steels, and high-temperature and aluminum alloys.
Unfortunately, none of these or other new materials has improved the removal rate of titanium alloys. In studies conducted as early as 1950, the straight tungsten carbide (WC) cutting tools, typically C-2 grades, performed best in operations such as turning and face milling, while the high-cobalt, high-speed steels were most applicable in drilling, tapping, and end milling.
Today, the situation is much the same. C-2 carbides are used extensively in engine and airframe manufacturing for turning and face milling operations. In recent years, in the United States as well as in Europe, solid C-2 end mills and end mills with replaceable C-2 carbides are finding applications, particularly in aerospace plants. Today, the M7 and, more frequently, the M42 and M33 high-speed steels are recommended for end milling, drilling, and tapping of titanium alloys.