The study on crack evolution mechanism of TiAlN-coated tool in milling TC4 titanium alloy

Abstract

This study aims to investigate the effects of thermo-mechanical coupled stresses on crack initiation and propagation in coated cutting tools during milling processes. TiAlN-coated tools machined TC4 workpieces, and a comprehensive analysis of cutting forces, cutting temperatures, and tool stresses was carried out through finite element simulation. By decoupling thermal and mechanical stresses, the study aimed to identify the different forms and effects of both types of stresses on the coated tools. Experimental results revealed that an increase in cutting speed resulted in higher tool surface temperatures, leading to elevated thermal stresses that facilitated the propagation of “comb-like” thermal cracks. Additionally, mechanical stresses induced by impacts during milling operations were found to initiate and propagate mechanical cracks in tools. The research observed that mechanical cracks, running parallel to the cutting edge, and thermal cracks, propagating perpendicular to the cutting edge, eventually result in coating spalling. The primary modes of tool failure identified were the propagation of micro-cracks and coating spalling, with the direction of crack propagation closely linked to the stress state distribution within the tool. The research highlights the intricate interplay between thermal and mechanical stresses in the evolution of cracks in coated cutting tools during milling processes.