Development of cBN ball-nosed end mill with newly designed cutting edge

In this study, we aimed at developing cBN ball-nosed end mills for cutting and finishing hardened steel for practical use. That is, we developed cBN tools with a higher tool shape accuracy, a higher chipping resistance, and a lower fabrication cost than conventional tools. We succeeded in developing two types of ball-nosed end mill with a unique cutting edge. One has a very simple no-flute unchamfered cutting edge with a large negative rake angle of approximately −45°. A high finishing accuracy was obtained using this tool. The other has the same cutting edge shape as the tool mentioned above and its rake angle is approximately −20°. We realized a relatively large-depth cutting and a high cutting efficiency using this tool. By developing these tools, the high-accuracy and high-efficiency finish machining of hardened die steel was realized.