Fitting-Free Diagnosis of Conduction-Model Breakdown in Laser Powder Bed Fusion

Area of Science:

• Materials Science
• Manufacturing Engineering
• Additive Manufacturing

Background:

• Melt-pool depth is critical for interlayer bonding and porosity in laser powder bed fusion (LPBF), directly impacting part qualification.
• Accurate prediction of melt-pool depth is essential but remains a significant challenge for current models.
• Existing fast conduction models often require absorptivity fitting, limiting their predictive power and turning them into calibration tools rather than validation models.

Purpose of the Study:

• To validate a moving-source conduction model for predicting melt-pool depth in LPBF by independently fixing absorptivity.
• To assess the model's accuracy across different alloys (IN718, IN625, 316L, Ti-6Al-4V) and identify regimes where it excels or underpredicts.
• To investigate the role of unmodeled transport phenomena, such as Marangoni flow, in melt-pool dynamics and their influence on absorptivity inference.

Main Methods:

• Utilized a physics-based, moving-source conduction model with independently fixed absorptivity values.
• Employed root-finding to locate the melt boundary, avoiding grid discretization errors.
• Analyzed 231 single tracks across various alloys, comparing model predictions with experimental depths and half-widths.

Main Results:

• The model accurately reproduced conduction-regime melt-pool depth and half-width to within a few percent.
• Underprediction increased significantly in the keyholing regime, suggesting the influence of unmodeled transport.
• Inferred absorptivity values were non-physical (above unity) for keyhole tracks, supporting the need for additional physics.
• Emulating downward convection as anisotropic effective diffusivity did not fully explain keyhole tracks, even with Marangoni flow enhancements.

Conclusions:

• The validated physics-based model offers a reliable method for predicting melt-pool depth in the conduction regime, with advantages for cross-alloy extrapolation.
• Keyholing behavior requires further investigation into unmodeled transport phenomena, with evidence suggesting Marangoni flow plays a role.
• The study provides a framework for fitting-free diagnosis of melt-pool dynamics and highlights the limitations of simple conduction models in keyholing regimes.