CBN tool wear in hard turning: a survey on research progresses

Direct machining steel parts at a hardened state, known as hard turning, offers a number of potential benefits over traditional grinding in some applications. In addition, hard turning has several unique process characteristics, e.g., segmented chip formation and microstructural alterations at the machined surfaces, fundamentally different from conventional turning. Hard turning is, therefore, of a great interest to both the manufacturing industry and research community. Development of superhard materials such as polycrystalline cubic boron nitride (known as CBN) has been a key to enabling hard turning technology. A significant pool of CBN tool wear studies has been surveyed, in an attempt to achieve better processing and tooling applications, and discussed from the tool wear pattern and mechanism perspectives. Although various tool wear mechanisms, or a combination of several, coexist and dominate in CBN turning of hardened steels, it has been suggested that abrasion, adhesion (possibly complicated by tribochemical interactions), and diffusion may primarily govern the CBN tool wear in hard turning. Further, wear rate modeling including one approach developed in a recent study, on both crater and flank wear, is discussed as well. In conclusion, a summary of the CBN tool wear survey and the future work are outlined.