Laser powder bed fusion processes are driven by scanned, focused laser beams. Along with selectively melting the metal powder, laser energy may be converted and transferred through physical mechanisms such as reflection from the metal surface, heat absorption into the substrate, vaporization, spatter, ejection of heated particles, and superheating of the metal vapor/condensate plume generated by laser-metal interaction. Reliable data on energy transfer can provides inputs for the process modeling, as well as help validate computational models results. Additionally, some related process signatures can serve better process monitoring and optimization. Previous studies have shown that the proportion of the transfer mechanisms depend on laser power, spot size, and scan speed. In the current investigation, the energy conservation principle was used to validate our measurement of reflected energy, absorbed energy, and energy transfer by vaporization on bare plates of Nickel Alloy 625 (IN625). Heat absorbed into the substrate was measured by calorimetry. The mass transfer from the sample was measured with a precision balance and used to establish an upper bound of energy transfer by mass transfer. In addition to measurement of total reflected energy, the reflected laser power was time-resolved at 50 kHz in an integrating hemisphere, which provided insight into the process dynamics in conduction, transition, and keyhole modes.
Proc. SPIE Photonics West
February 1-6, 2020
San Francisco, CA
SPIE Photonics West
Laser powder bed fusion, laser coupling, energy transfer in laser melting