Mechanical and Aerospace Engineering Colloquium Series

December 2, 2020
December 2, 2020        
Speaker: Christopher Kube, PhD
                Pennsylvania State University 
Topic: "Advancing the science of metallic 3D printing through ultrasonic characterization of laser generated melt pools" 
Time: 3:30 pm to 4:15 pm (Q&A 4:15 pm to 5:00 pm)                
Meeting ID: 935 0150 9391 
Password: seminars

Abstract: Fundamental to metallic additive manufacturing (AM) is the laser-powder-substrate interaction that leads to localized melting of metallic powder to a previously solidified substrate. The formation of the melt pool and the subsequent solidification dictate the resultant microstructures and, thus, the properties of the processed materials, which then influence both part quality and performance. Open ended questions involving the optimization of process parameters for defect free and high performing parts remain at the heart of AM science. Further understanding of melt pool and solidification behavior is required to help answer these questions and enable the next generation of AM adoption. This presentation will highlight a real-time in situ ultrasonic scattering method sensitive to melt pool initiation and solidification in addition to formation of porosity and solidification cracking. The method utilizes 25 MHz ultrasonic transducers for generating and receiving the field scattered from the melt pool volume. The method was validated by simultaneously monitoring melt pools using ultrasound and X-ray imaging in real-time. The ultrasonic signal capture rate was precisely synced to the X-ray frame rate at 28 kHz or 28 waveforms collected in 1 millisecond. The X-ray imaging provides the opportunity for a side-by-side comparison between a dynamically evolving melt pools and the ultrasonic response. Results will be presented showing sensitivity to melt pool dynamics, keyhole initiation, solidification rates, porosity formation, and solidification cracking. The flexibility of ultrasonic sensors supports the potential to move the technique into individual AM machines for calibration of optimal processing parameters.

Bio: Christopher Kube is an assistant professor in the Department of Engineering Science and Mechanics at Penn State University. Along with other faculty members in the department, Kube is a co-founder of the Penn State Ultrasonics Laboratory (PennSUL). PennSUL is dedicated to ultrasound related research with a core focus on research in nondestructive evaluation. Prior to joining Penn State in 2018, Kube was a contract researcher at the United States Army Research Laboratory where he specialized in the nondestructive characterization of additively manufactured (AM) parts and structural health monitoring for fatigue awareness in rotorcraft vehicles. In 2014, Kube received his PhD in Mechanical Engineering and Applied Mechanics from the University of Nebraska-Lincoln where he studied the influence of residual stress and deformation on the scattering of ultrasound from inhomogeneities. Kube’s research interests include experimental and theoretical modeling of resonant ultrasound, acoustic microscopy, nonlinear ultrasonics, and ultrasonic scattering. Currently, he is leading several active research efforts spanning the use of ultrasound to monitor melt pool dynamics in 3d printing of metals, constitutive modeling of soft and deformed piezoelectric materials, and is investigating the combined influences of texture and residual stress on the resonant behavior of AM parts.

For additional information please contact Professor Andrew Norris at or at 848-445-3818.