Development of ultra-fine-grain binderless cBN tool for precision cutting of ferrous materials

A new cutting tool was developed from ultra-fine-grain (<100 nm), binderless cubic boron nitride (cBN) material fabricated by transforming hexagonal boron nitride to cBN by means of sintering under an ultra-high pressure of 10 GPa at 1800 °C. The cutting edges of the newly developed cBN tool can be made as sharp as those of single-crystal diamond tools. In this experiment, cBN and single-crystal diamond tools of the same shape were compared by precision cutting tests using stainless steel specimens and steel specimens coated with an electroless Ni-P layer. The surface roughness (Rz) of specimen surfaces cut with the cBN tool by means of planing was approximately 100 nm for both the Ni-P-coated steel and stainless steel specimens. Though similar Rz values were obtained for Ni-P layers cut by the cBN and diamond tools, an Rz value exceeding 2000 nm was obtained for stainless steel cut by the diamond tool. High-precision surfaces with Rz values of 50–100 nm were obtained for stainless steel specimens cut with the cBN tool under high-speed milling (942 m/min) conditions. These results indicate that the newly developed cBN tool is useful for the ultra-precision or precision cutting of ferrous materials.