Loose powder detection and surface characterization in selective laser sintering via optical coherence tomography

Area of Science:

• Additive Manufacturing
• Non-Destructive Testing
• Optical Metrology

Background:

• Selective Laser Sintering (SLS) parts often contain defects like un-melted powder, compromising integrity.
• Post-build defect detection in SLS typically requires X-ray methods, limiting real-time assessment.
• Layer-by-layer integrity assessment is crucial for reliable SLS applications.

Purpose of the Study:

• To investigate Optical Coherence Tomography (OCT) for non-destructive, in-situ defect detection in SLS parts.
• To correlate OCT measurements with SLS process parameters for variable density regions.
• To evaluate OCT's capability for surface texture profiling.

Main Methods:

• Utilized OCT to scan SLS samples with embedded graduated porosities simulating defects.
• Performed simulated in-situ measurements and correlated them with SLS process parameters.
• Compared OCT surface texture data with focus variation microscopy after spatial bandwidth matching.

Main Results:

• OCT successfully detected sub-surface un-melted powder and differentiated densities within ±5% at depths up to 300 μm.
• Simulated in-situ OCT measurements correlated effectively with SLS process parameters.
• OCT surface profiling yielded comparable results to focus variation microscopy.

Conclusions:

• OCT is a viable non-destructive method for in-situ layer-by-layer defect detection in SLS.
• OCT enables the identification of critical defects like porosity and un-melted powder.
• This technique enhances quality assurance for SLS additive manufacturing.