Surface modified tool fabricated by radical nitriding

High speed and high efficiency machining are required in the production area. Investigation was carried out on improving tool properties such as hard film coating and surface modification. Radical nitriding is one of many surface modification methods, and it is possible to improve surface hardness by maintaining the roughness of the initial surface by control of the plasma. To improve the cutting performance of tools, we studied the fabrication of radical nitrided tools and their cutting performance for Cr–Mo steels. Radical nitriding was performed using an external heating plasma apparatus. The reaction gas was a mixture of NH3 and H2; reaction time was 1 h. As a result, the hardness of the SKH tool surface changed from 800 to 1200 Hv after radical nitriding. Subsequently, the intial surface roughness was kept constant. On the cutting performance for Cr–Mo steels, non-treated, ion- and radical-nitrided end mills were used, and the cutting length and torque was measured. In the cutting test of radical-nitrided end mill, wear increased slowly. Ion-nitrided end mill showed more wear from the beginning of cutting, and wear increased quickly. The cutting torque of radical-nitrided end mill was constant, and there was only a small change in torque. Moreover, the cutting torque of the ion-nitrided end mill was high and irregular at the beginning of cutting, and increased significantly. Radical-nitriding was effective for improving the performance of the cutting test of Cr–Mo steels using surface modified tools.