What materials are appropriate for hard turning? When are CBN cutting inserts the appropriate choice?
If the hardness ranges between 50-68 Rc and the depth of hardness is greater than the depth of material to be removed, then Cubic Boron Nitride (CBN) is the best medium. CBN will give good tool life and wear properties. Surface finishes of 11-15 micro-inches can be achieved and maintained. ISO inserts are available with multiple grades to suit different machining requirements. Insert hardness and, therefore, wear rate are traded for toughness and ability to withstand shock loading from interrupted cuts, i.e., keyways.
