A study of wear on coated PCBN tools when turning hardened AISI 4340 using FEM simulation

Turning hardened steels can be a very challenging task, although it has been a preferred operation, in many cases to replace grinding. PCBN tools have been a good choice especially if coating can be added to further enhance its surface physical and mechanical properties. In the present work two TiAlN and one AlCrN coatings were tested, comparing with uncoated PCBN on turning hardened AISI 4340. Tests assessed tool wear, cutting forces and surface roughness. FEM simulation was also applied to explain some of the results. The use of coating extended tool life, comparing to uncoated tool and AlCrN coating provided the best combination for both feed rates tested. AlCrN coating performs better when temperatures at the chip formation zone reaches 1,000 °C, usually using high feed rates, according to FEM simulations. For cutting conditions where temperature remains around 800 °C TiAlN is the best choice, being those results related to the Al2O3 formation at the coating surface. Cutting force follows the some tendency as tool wear, being the highest when using uncoated PCBN. Surface roughness were between 0.7 and 2.0 μm Ra, as a general range for all tests. The experimental Ra results were comparable to theoretical ones, being above when using low feed rate and closer when using high feed rate.