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.
- Hardest (Suitable for plain diameters only)
- Medium (Suitable for moderate interruption)
- Toughest (Suitable for machining gear o/d)
Typical cutting data for CBN:
- 315 – 335 feet per minute (96-102 m/min)
- .008″ – .010″ (0.2-0.25 mm) depth of cut
- .004″ IPR (0.1 mm/rev) feedrate
The size of the insert nose radius determines the surface finish achieved within the limits of machine and component rigidity. CBN is undoubtedly the best option, provided the workpiece material is uniformly hard. It will work on steel with a hardness above 50Rc.
