Hard turning is defined as turning hardened steel with a hardness of up to approximately 63 HRc (Rockwell hardness). For this to be possible at all, the cutting edge or turning tool must be harder than the steel to be machined. When hard turning, therefore, cutting materials made of boron nitride are predominantly used. Due to very high shearing forces and the fact that hard boron nitride reacts sensitively to impact, very stable and robust machines are used for hard turning. High-quality parts can be machined on high-precision lathes, which limits costly grinding operations on many projects.
Sources: En.wikipedia.org, Internet, own documentation (Werder limited compagny) Back
