Abstract Scope |
After decades of intense research and development, laser powder bed fusion (LPBF) has advanced from a rapid prototyping tool for shortening the design cycle towards a manufacturing technology for producing end-use metallic components. While some industries fully embrace LPBF now, others are taking cautious steps to integrate it into their product lines. As a primary metal additive manufacturing (AM) technique, LPBF is capable of fabricating parts with extreme geometric complexities and fine features, which cannot be rivaled by conventional manufacturing or even other AM technologies. However, LPBF still needs to improve in a few areas before it can reach its full potential as a disruptive manufacturing technique. The fast scanning of high-power laser creates far-from-equilibrium thermal conditions which trigger transient phenomena and complex structure dynamics, including but not limited to, fluctuations of melt pool and vapor depression, powder entrainment and spattering, rapid solidification and phase transformation, etc. These highly dynamic processes often lead to build anomalies such as dimension inaccuracy and structure defects.
Understanding the laser-metal interaction and the dynamic interplays between the solid, liquid and gas phases involved in LPBF holds the key for improving its capability for building parts more reliably. Recently, we applied high-speed synchrotron x-ray imaging technique to probe the structure dynamics in LPBF with unprecedented high spatial and temporal resolutions. The high-flux high-energy x-rays afforded by Advanced Photon Source allowed us to directly visualize the morphological evolution of the melt pool and vapor depression zone during scanning laser melting. With these time-resolved quantitative measurements, the conduction, transition, and keyhole modes laser melting were re-defined with rigorous physics underpinning. Also, novel mechanisms were discovered that are responsible for the generation of various defects. |