Interrupted hard turning with cryogenically cooled ceramic tools

Interrupted hard turning is an extremely difficult operation, but is increasingly becoming popular in automotive, powder metal, bearings and other industries. Even though hard turning offers higher material removal rate than grinding process, interrupted cutting of hard materials could be an expensive proposition, due to the slowness of the cutting process and cost of tooling. PCBN inserts are almost always used, due to their higher fracture toughness, compared to Al2O3 ceramics. Usually, no coolant is used in the cutting process, as the coolant hardens the free edges of the interruptions, causing detrimental effects on tool life. The present work explores a new way of cryogenically cooling the insert, using liquid nitrogen (LIN) and eliminating the interaction between the coolant and the work material. Ceramic inserts cooled by this indirect cooling method, have been shown to significantly outperform conventional PCBN/Dry operations. For very severe interruptions, PCBN/LIN is shown to be the best choice, outperforming PCBN/Dry and Al2O3/LIN operations.