Study of solid carbide end mills for machining workpieces with hardness gradient

The present paper sets out to investigate the service life of solid carbide end mills for machining workpieces with an HRC 40 base hardness and a surface layer hardness of HRC 65 and greater. For machining, solid carbide end mills with four and nine teeth were used; control mills were uncoated. The studied mills were coated with 5 µm thick multilayer nanostructured coatings applied using the condensation method with ion bombardment in a Bulat unit. Three types of coatings were studied, including titanium carbonitride with titanium nitride layer (TiCN+TiN); a mixture of titanium and aluminum with aluminum oxide, mixed titanium and aluminum nitride, and aluminum oxide layers (TiAl+Al2O3+(TiAl)N+Al2O3); titanium carbonitride with mixed titanium and aluminum nitride, aluminum oxide, and titanium carbide layers (TiCN+(TiAl)N+Al2O3+TiC). The surface layer hardness of workpieces exceeded HRC 61. The surfacing was applied using a TST 350 arc welding machine equipped with a PDG0–527-4A semiautomatic welding device with a PP-AN167 flux-cored wire. The service life of a nine-tooth mill, both coated and uncoated, was found to exceed that of a four-tooth mill. Experimental results show that TiCN+(TiAl)N+Al2O3+TiC coating is more appropriate for a nine-tooth mill. This coating surpasses the (TiAl)N+Al2O3+(TiAl)N+Al2O3 coating for the resistance period in the entire range of milling speeds. The dependencies of the tool life on the milling speed were separately obtained for solid carbide nine- and four-tooth end mills with various multilayer nanostructured coatings. The identified dependencies can be used to establish the most appropriate operating conditions for these mills. The research results can be used to develop technologies for manufacturing parts with a surface layer hardness above HRC 65.