WEAR-RESISTANCE OF PLASMA-NITRIDED AND SPUTTER-ION-PLATED HOBS

Hobs and test substrates made of high speed steel were plasma nitrided and coated using a sputter ion plating technique in a reactive mode. The morphology and composition of the surface layer have been investigated by scanning electron microscopy and optical microscopy, X-ray and Auger spectroscopy and energy-dispersive X-ray analysis. The results of industrial tests on (Ti,Al)N-coated hobs in gear cutting are given concerning the tool life and productivity. A tool life enhanced up to five times with respect to the uncoated tool was found at approximately 55% increased cutting speed and 25% increased cutting feed before the first resharpening. By applying plasma nitriding after resharpening, crater wear was significantly reduced. The experiment clearly demonstrated the excellent wear properties of the (Ti,Al)N coating. Plasma-nitrided hobs were tested under the same machining conditions as the uncoated tool. The wear intensity diagram shows that the service life of plasma-nitrided hobs, compared with that of an uncoated hob, is enhanced by a factor of four for the standard cutting speed. It has been concluded that both a (Ti,Al)N coating as well as a post-plasma-nitriding treatment after resharpening may be especially successfully applied in order to obtain better performance of hobs for gear cutting. © 1990.