In this project, we collaborated with Tronos Jet Inc. to assess the feasibility of using ultrasonic testing to detect the defects that might arise during the additive manufacturing (3D-printing) of functional metallic components. We first explored typical defects that arise during selective laser melting (the most common technique to print metals). The defects were generated intentionally by lowering the laser power during printing at certain locations in the part. We first characterized the nature of the defects that gets generated using optical microscopy as well as X-ray computed tomography (CT-scaning). We then used an ultrasonic phased array system (from Verasonics) to image the samples. Multiple imaging algorithms were tested including TR-Music, traditional B-Scans, and the total focusing method (TFM). The 10-MHz 64 element phased array used was able to detect partially fused defects down to 0.25 mm in diameter.
We also explored the use scanning laser Doppler vibrometery to detect unfused defects inside thin functional components. A bonded piezoelectric transducer was used to excite guided waves (Lamb waves) in the part and root mean square imaging was used to detect the defects. Thin defects down to 1 mm in diameter was detected using this approach.
Please feel free to send me any questions you might have about this work.