Serrated Chip Formation Induced Periodic Distribution of Morphological and Physical Characteristics in Machined Surface During High-Speed Machining of Ti6Al4V

Abstract

Difficult-to-cut materials are widely used in aerospace and other industries. Titanium alloys are the most popular ones among them due to their high strength-to-weight ratio and high temperature resistance. However, in high-speed machining, the alloys are prone to produce serrated chips, which have a serious influence on surface integrity. In this study, a coupled Eulerian–Lagrangian method is used to simulate the orthogonal cutting of Ti6Al4V due to its advantages of avoiding element distortion and improving the data extraction efficiency. The internal relationship between serrated chip formation and periodic profile of machined surfaces is analyzed by the simulation results and experimental data which are obtained by optical microscope and white light interferometer. Furthermore, thermal–mechanical loads on machined surfaces are reconstructed based on the simulation results, and a coupled finite element and cellular automata approach is used to describe the dynamic recrystallization process within the area of the machined surface during the formation of a single serration. According to the results, the periodic fluctuation of cutting forces is attributed to the serrated chip formation phenomenon, which then leads to the periodic profile of machined surfaces. The period is about 60–70 µm, and its amplitude decreases with the increase of cutting speeds. Moreover, the loads on machined surfaces also show the same period due to serrated chip formation. As a result, the grain refinement layer thickness (about 2 ∼ 5 µm) in machined surfaces is related to the surface temperature and exhibits the same periodic characteristics along the cutting direction.