Research on the Surface Characteristics of Hardened Steel with Variable Chamfer Edge PCBN Insert by High-Speed Hard Turning

Abstract

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.