Tool Life of Small Diameter Ball End Mill for High Speed Milling of Hardened Steel - Effects of the Machining Method and the Tool Materials -

We studied tool life, flank wear, and machined surface roughness in the high-speed milling of hardened steel on a small ball end mill using a high-speed milling machine. We found that: (1) Cutting edge flank wear increases in proportion to cutting length and the flank wear shape gradually has a resembalance to the shape of the actual cutting length. (2) Long tool life depends on stepdown pick-feed and down-milling conditions. (3) Surface roughness increases in proportion to cutting length, but a low surface roughness of 1.4 μm is obtainable for a 3,800 m cutting length in down-milling. (4) CBN tool flank wear is very low -- at least 1/15 th that of carbide tools under down-milling conditions, and a surface roughness of 1.6 μm is obtainable for a 67.2 km cutting length. We verified the effectiveness of CBN tools in high-speed milling of hardened steel under cutting conditions.