Owing to heavy dynamic and thermal loads, PCBN tools are seriously worn during hard cutting, which largely constrains the improvement of their machining performance. Therein, the chamfered structure of a cutting edge has a notable influence on the tool wear. Thus, a comparative study was carried out on the wear morphology and wear mechanism of PCBN tools with either a variable chamfered edge or an invariable chamfered edge. The results indicate that, for a PCBN tool with a variable chamfered edge, the rake wear area is far from the cutting edge and slowly extends toward it. A shallow large-area crater wear occurs on the rake face, and the flank wear area has a long triangular shape with a smaller wear area and width, and the cutting edge remains in a good state during the cutting process. In contrast, for a PCBN tool with an invariable chamfered edge, a deep small-area crater appears on the rake face, and the wear area is close to the cutting edge and quickly extends toward it. Thus, it is easy for chips to accumulate in the crater, resulting in large-area and high-speed wear on the flank face. In addition, the tool shows a weak wear resistance. In the initial wear stage, the rake wear mechanism of the two cutting tools is a mixture of abrasive, oxidation, and other types of wear, whereas their flank wear mechanism is dominated by abrasive wear. With an aggravation of the tool wear, the oxidation and diffusion wear mechanism are both increasingly strengthened. The rake wear of the cutter with a variable chamfered edge showed an obvious increase in the oxidation and diffusion wear, as did the flank wear of the cutter with an invariable chamfered edge. This study revealed the wear mechanism of the PCBN tool with a variable chamfered edge and provided theoretical and technological support for its popularization and application in the machining of high-hardness materials.

The edge chamfered structure not only enhances the strength of cutting edge, but also increases the thermal load in the cutting process, which affects the chip flow, tool wear and machining surface quality in hard cutting. The high-speed photography is used to compare the characteristics of chip flow from the two PCBN tools respectively with variable strengthening edge and invariable chamfered edge, and it is found that the variable strengthening edge can effectively coordinate chip flow, and get rid of chip accumulation in hard cutting. Through the hard cutting experiment, the wear characteristics of the PCBN tool with variable strengthening edge are researched. The results indicated that the wear zone is relatively concentrated for the tool with invariable chamfered edge, while the one is narrow and long for the tool with variable strengthening edge, and especially the flank wear belt is a long triangle. Thus, the latter has better cutting edge retention and tool durability. When the edge form got to change, the flank wear mechanism gradually is changed into a mixture of abrasive, oxidation and diffusion wear from the abrasive wear. The tool with variable strengthening edge is obviously advantageous in improving chip flow and increasing tool life. Thus its widespread application is promising.