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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.

Thanks to its good specific strength and modulus, carbon fiber-reinforced plastic (CFRP) is widely used in such fields as aerospace and automotive. Nonetheless, it is very likely that the serious tool wear and some surface quality defects occur in machining, such as delamination, tear, burr, and so forth. Thus, this paper carried out the experimental research into the tool wear in milling carbon fiber composites with spiral staggered diamond-coated milling cutter. According to the evolution of tool wear micro-morphology, the tool wear process was obviously divided into two stages, i.e., coating particle wear and coating shedding. It was found that the former was dominated by the abrasive wear mechanism and the latter the fatigue wear mechanism. In addition, wear mechanism and cutting force variation of each stage were analyzed. In addition, the coating shedding happened obviously in advance with the increase of milling speed. In the period of coating particle wear, the tool was in good cutting performance, and its cutting force changed slowly, while after it came into coating shedding period with the aggravation of tool wear, the cutting force increased greatly and the cutting performance worsened obviously. Thus, the appropriate control over the tool wear of spiral staggered diamond-coated milling cutter is the key to improving the machining quality of carbon fiber composites.

In this paper, high-speed cutting tests for hardened steel were carried out where PCBN inserts with variable chamfer and fixed chamfer were employed. The aim of the tests was to investigate the influence of cutting speed and tool wear of variable chamfer insert on the machined surface topography, micro-characteristics and micro-hardness, where comparison and analysis of the machined surface properties were also carried out for the surface produced by the fixed chamfer tool. Experimental results showed that machined surface morphologies become more complex and rough, and peaks appear to a trend towards steepness, with the flank wear increase of the variable chamfer tool. At the same time, the thickness of white layer, hardening depth and hardening degree of the machined surface increase dramatically. With the increase in cutting speed of the variable chamfer tool, it is of primary importance to consider phase transition effects caused by thermal load, which will result in increase in the thickness of white layer on the machined surface. Moreover, it will also lead to decrease in the thickness and deformation degree of plastically deformed layer caused by mechanical load. Compared to the fixed chamfer tool, the cutting force generated by the variable chamfer tool is relatively small, where the flank wear area is also smaller and the groove wear marks is shallower. Therefore, better surface roughness can be obtained by utilizing the variable chamfer tool. In particular, the gap between the roughness of the machined surface formed by two tools becomes more pronounced in the scenarios of high speed and severe wear. Moreover, the thickness of white layer, the depth and degree of hardened layer are relatively small for the variable chamfer tool. Therefore, the surface properties produced by the variable chamfer tool would be more desirable.

Hard turning and fatigue tests are conducted to study the influence of cutting process on the fatigue properties of hard machined components in this work. The specimens are machined under various cutting speeds and tool wear condition. Tension-compression fatigue tests of the specimens are performed. The typical fatigue fracture patterns are observed and discussed. The fatigue life of the specimens is recorded and compared. The mechanism of the influence of white layer on fatigue properties is proposed, and the effects of white layer on the fatigue life are obtained. The changing process of tensile and compressive residual stresses is discussed. The effects of surface residual stress and maximum residual stress on the fatigue life are clarified.

This work investigates the cutting performance of chamfered PCBN tools in hard turning of GCr15 bearing steel. Experimental study was performed on a NC lathe. Cutting forces were measured by using a dynamometer. Cutting temperature was measured by using an infrared thermal imager. The variation of cutting forces and cutting temperature with the chamfer angles are investigated and discussed. The surface roughness of the workpiece and flank wear of the tool during the machining is concerned, and the relationship between the surface roughness and flank wear is studied. The tool rejection criteria for the hard turning of GCr15 steel is proposed considering surface roughness and flank wear. The wear patterns of the tool were investigated using scanning electron microscope (SEM), and the wear mechanism is discussed. It is found that crater and adhesion are the dominant wear mechanism of the rake face, and abrasive wear is the dominant wear mechanism of the flank of the PCBN tool in hard turning of GCr15 steel.