Abstract
Laser powder bed fusion (LPBF) is a promising additive manufacturing technology for producing metal parts with complex geometric features. However, the issue concerning process stability and repeatability still hinders its future acceptance by the industry. Gaining a better understanding of the behavior and stability of the evaporation process is an important step towards further insights into the complex interaction between laser and material. In this study, we used off-axis high-speed camera to observe vapor plume evolution in single-track formation on bare Ti-6Al-4V plates; the results showed that evaporation has a strong effect on melting quality even if the keyhole is not developed. We then expanded the experiments to multi-track level and found that the melting mode can change as the result of heat accumulation. The results show the possibility that keyhole regime may be reached even if it starts with a combination of parameters below the threshold for keyhole formation in single-track-level observation.
Highlights
Laser powder bed fusion (LPBF) is considered one of the most successful and promising additive manufacturing (AM) technologies because it can produce end use metal structures directly from a computer-aided design (CAD) model with reasonable part quality and attractive design freedoms [1,2]
The laser material interaction in LPBF is a complex process related to multiple interdependent factors [5], and a combination of complex phenomena can be observed during laser irradiation on a powder bed
The main interest of this study is to identify a regime that can be used in LPBF to avoid complex keyhole instability, and evaluation to what possible extent the results at single track level will be influenced by the heat accumulation in LPBF
Summary
Laser powder bed fusion (LPBF) is considered one of the most successful and promising additive manufacturing (AM) technologies because it can produce end use metal structures directly from a computer-aided design (CAD) model with reasonable part quality and attractive design freedoms [1,2]. If a certain threshold is reached and exceeded, the recoil pressure can overcome the surface tension, penetrate deep into the melt pool surface, and lead to a keyhole melting mode. In this regime, laser absorption is significantly enhanced by the multi-reflection on the keyhole wall and the melt pool can be much deeper than in conduction mode [7,8]. Besides keyhole formation process and porosity, vapor behavior is closely related to complex phenomena during laser–material interaction, such as powder layer denudation [1,12] and spattering [13,14,15], and final part quality [14,16]
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