Transient Laser Energy Absorption, Co-axial Melt Pool Monitoring, and Relationship to Melt Pool Morphology

Area of Science:

• Materials Science
• Additive Manufacturing
• Optical Metrology

Background:

• Melt pool monitoring (MPM) in laser powder bed fusion (LPBF) uses in-situ sensor signals to detect defects and assess part quality.
• Melt pool phenomena correlate with laser energy absorption and emission, which are key parameters in MPM.

Purpose of the Study:

• To investigate the utility of dynamic laser energy absorption measurements for understanding melt pool dynamics in LPBF.
• To correlate dynamic laser absorption with coaxial MPM signals and surface features.
• To analyze the transition between conduction and keyhole modes during laser scanning.

Main Methods:

• Utilized a reflectometer-based instrument to measure dynamic laser energy absorption during single-line scans on IN625.
• Synchronously measured incandescent melt pool emission using a co-axial photodetector.
• Performed metallographic cross-section and topographic measurements of solidified tracks.

Main Results:

• Observed relationships between dynamic laser absorption, coaxial MPM, and surface features, illustrating melt pool dynamics.
• Demonstrated that time-integrated laser absorption measurements correlate well with MPM signals.
• Confirmed the transition between conduction and keyhole modes using laser absorption data, corroborated by cross-section and topographic analyses.

Conclusions:

• Dynamic laser absorption measurements provide valuable insights into the physical nature of melt pool dynamics.
• This technique enhances the interpretation of process monitoring signals in LPBF.
• Dynamic laser absorption measurements can inform process control and defect prediction in additive manufacturing.