High-Fidelity Optical Monitoring of Laser Powder Bed Fusion via Aperture Division Multiplexing

TL;DR

This paper introduces aperture division multiplexing (ADM), a novel optical method enabling high-resolution, in situ monitoring of laser powder bed fusion (LPBF) processes to detect microscopic pores that affect component fatigue life.

Contribution

The paper presents the design and implementation of an ADM optic for real-time, high-resolution infrared imaging of LPBF, demonstrating its ability to detect sub-5 micron pores.

Findings

ADM achieves 50 micron spatial resolution in infrared imaging.

Infrared video correlates with micro-CT data for pores as small as 4.3 microns.

ADM enables in-process defect detection for improved quality control.

Abstract

Qualification of high-performance metal components produced by laser powder bed fusion (LPBF) must identify process-induced porous defects that reduce ductility and nucleate fatigue cracking. Detecting such defects via optical monitoring of LPBF provides a path towards in-process quality control without downstream testing such as by computed tomography. However, integration of in-process sensing with LPBF is hampered by geometric and optical complications and, as a result, it has yet to be proven that the finest pores that limit component fatigue life can be resolved via in situ data. We present aperture division multiplexing (ADM) as a method for simultaneously focusing the process laser and providing unobstructed optical access for high-fidelity process monitoring using a common optic. Construction of an ADM optic of achieving imaging at 50 micron spatial resolution in the mid-wave infrared is described, and this optic is demonstrated on a production-representative LPBF testbed. High-speed infrared video data are correlated to micro-CT measurement of pores as fine as 4.3 microns, through multiple process signatures, establishing the promise of ADM for qualification of LPBF component fatigue performance.