ねずみ鋳鉄材の高速旋削加工におけるバインダレスcBN工具の損傷特性

抄録

The wear mechanism of a binder-less cBN tool on the high speed turning of the gray cast iron was investigated. The tool material was characterized to have excellent both mechanical and thermal properties, owing to microstructure consisting of single phase cBN with extremely fine grain, resulting in confined flank wear in the initial stage of turning at condition of V=33.33m/s. The confined flank wear extended the tool life as long as 16 times compared to that of the conventional type of cBN tool. According to the precise observation of the tool surface in the course of the turning operation, an A1 ₂O ₃ based adhered layer from workpiece was build-up on the tool flank face. The adhered layer became to exert as a protective film which prevented direct contact between tool and workpiece, resulting in a significant decrease in tool flank wear. In the turning of the workpiece material with lower Al content, the tool life was shortened because of lower possibility of formation of the adhered layer. The tool life was also shortened at the turning speed higher than V=40.00m/s. X-ray diffractometry and scanning electron microscopy of the adhered layer formed in the higher speed conditions, clarified that the layer consisted of a spinel type MgAl ₂O ₄ crystal which has inferior mechanical properties compared to A1 ₂O ₃