The causal relationship between melt pool geometry and energy absorption measured in real time during laser-based manufacturing
Brian Simonds, Jack R. Tanner, Aly Artusio-Glimpse, Paul A. Williams, Niranjan Parab, Cang Zhao, Tao Sun
During laser powder bed fusion additive manufacturing, a protean pool of molten metal governs a complex energy absorption process as it presents as either a highly reflective surface, a deeply absorbing cavity (a keyhole), or some amalgamation thereof. To date, high temporal resolution studies of this relationship have only been possible using multiphysics simulations that combine optical ray tracing with fluid dynamics. These suggest that melt pool dynamics influence energy absorption and can affect solidified metal quality through pore formation and defect generation. However, direct observation in real-time under realistic manufacturing conditions has been elusive due to the extreme environment surrounding the laser-generated melt pool. In this work, we quantify the time-dependent, absolute energy absorption by monitoring omnidirectional backscattered laser intensity while simultaneously observing cross-sectional melt pool geometry with high-speed synchrotron x-ray imaging for a focused laser incident to Ti-6Al-4V bare plate and powder. At a microsecond timescale, we find that the backscattered laser intensity is indicative of keyhole cavity instability induced by either increasing laser power or oxygen content in the processing atmosphere. Furthermore, under nominally stable keyhole conditions, rapid and relatively large changes in the backscattered laser intensity are correlated to momentary obfuscations of the keyhole opening – a mechanism shown to lead to porosity in manufactured parts. Lastly, we find that a normalized enthalpy model is effective in quantifying the relationship between the laser absorption and keyhole depth, which has never been tested under transient conditions. In addition to providing data for simulation calibration, the correlation of melt pool geometry with laser absorption during realistic process conditions shows the promising implementation of a total integrated backscattered detection system for real-time process control. This would
, Tanner, J.
, Artusio-Glimpse, A.
, Williams, P.
, Parab, N.
, Zhao, C.
and Sun, T.
The causal relationship between melt pool geometry and energy absorption measured in real time during laser-based manufacturing, Applied Materials Today, [online], https://doi.org/10.1016/j.apmt.2021.101049, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=930868
(Accessed October 4, 2022)