Influence of Hatch Spacing On Thermal Stress of Multi-Track Melt Pool During Additive Manufacturing Of Ti-6al-2zr-1mo-1v Alloy

Abstract

Selective laser melting (SLM) is an additive manufacturing technique that has gained acceptance in the aerospace industry. However, persistent challenges related to defects have been encountered. Therefore, in-depth research on thermal stress during the manufacturing process is required. Traditional studies have been limited to solving heat transfer equations on a continuum to obtain thermal stress and strain using the Finite Element Method (FEM). This study proposes a novel approach that combines the multi-physic thermal fluid model with the mechanical model to investigate the thermal stress distribution characteristics in multi-track melt pools on the mesoscale. Additionally, the temperature field obtained from the thermal fluid model enables the investigation of the thermal stress of different order tracks at the same hatch spacing and the characteristics of thermal stress at different hatch spacing. The study presents numerical results on the distribution characteristics of thermal stress in SLM of Ti-6Al-2Zr-1Mo-1V alloy under selected process parameters. The analysis indicates that the thermal stress on the melt pool surface increases initially and then decreases along the laser scanning direction, with a peak value of approximately 170 MPa. While the peak values of thermal stress among different tracks are not significantly different, the area affected by thermal stress increases gradually in subsequent tracks due to heat accumulation. The reduction of hatch spacing from 110 µm to 70 µm causes a minimal increase of 1.9% in the peak value of thermal stress in the melt pool but a significant increase of 76.7% in the area of thermal stress above 167 MPa on the melt pool surface. The proposed coupled multi-physic model provides a more precise and comprehensive understanding of the thermal stress distribution.

Keywords: selective laser melting, Multi-track molten pool, Computational fluid dynamics, Finite Element Method, Thermodynamics and thermal stress