Array Eddy Current Technology for Evaluation of Laser Powder Bed Fusion Additive Manufacturing Process. New Possibilities

The additive manufacturing (AM) process has numerous advantages in comparison to conventional subtractive machining technologies. A laser beam supplies the energy to melt the metal powder and build the component layer by layer in a typical laser powder bed fusion (L-PBF) system. Monitoring techniques and non-destructive evaluation (NDE) is relied upon to provide monitoring, material property measurements (e.g., phase composition, microstructure, residual stresses, defects), and geometry layer by layer in real time. The lack of adequate NDE techniques for examination before, during, and after AM component fabrication was identified as one of the main current challenges. Small features and discontinuities that may be generated during L-PBF pose unique challenges for process inspection and monitoring.

Array eddy current (AEC) is one of the techniques that has capabilities to directly scan the component without physical contact with the powder and fused layer surfaces at low and high temperatures. The technique can detect discontinuities, surface irregularities, and undesirable metallurgical phase transformations in magnetic and nonmagnetic conductive materials used for laser fusion.

Trials with AEC system were conducted to verify the detection of typical discontinuities and conditions in AM specimens. Four, 10-mm thick solid AM experimental specimens in two “sandbox” arrangements were fabricated for technique development and standardization. Two types of materials were used for the demonstration: typical carbon ferromagnetic steel 4140 and nonmagnetic alloy Inconel 625. The solid experimental specimens were fabricated with typical process core parameters. The top two layers of the Inconel 625 specimen were fabricated with parameters that produced a smoother surface (common practice) than core-layer surfaces. Artificial and natural discontinuities such as notches and holes were fabricated with electrical discharge machining process, machining, and by varying the laser fusion parameters. The AEC technology demonstrated very good sensitivity and resolution to surface and subsurface discontinuities and conditions.