Energy optimization to reduce residual warping in laser powder fusion

In additive manufacturing (AM), metal parts are often 3D printed using a fabrication technique known as “laser powder fusion” (LPBF). LPBF involves rapidly repeatedly melting and solidifying metal powders using a laser heat source to form a 3D object. Locally high-temperature molten metal conforms to the surrounding solid due to thermal expansion.

However, molten metal produces negative thermal stress after solidification, creating an inner plane residual stress. This residual stress builds up towards the upper layer with repeated forming per layer and often leads to undesirable effects such as delamination, cracking and warping. Furthermore, the curvature and residual strain are asymmetrical in nature and proportional to the size of the metal being fabricated. As a result, the integrated derivation of metal partssuch as rocket nozzles, is extremely difficult.

To solve this problem, a team of researchers from Japan and the US, led by Professor Akihiro Takezawa from Waseda University, has now proposed an optimal design strategy for AM. “LPBF metal 3D printing, which has been the focus of much attention in recent years, suffers from large warping in cast parts. In this study, we developed a method to reduce residual strain by simultaneously optimizing the internal structure of the fabricated part, and Takezawa explains the laser scanning direction.

In their study offered online at Additive productionThe research team, which includes Dr. Qian Chen and Professor Albert C. To from the University of Pittsburgh, USA, has been working on reducing the amount of remnants while focusing on layer-by-layer residual stacking and using the technique. grid infill distribution.

They used a numerical method called the “repetitive formula inherent strain method” to analyze residual strain. In it, they modeled the lattice based on the effective stiffness and inherent anisotropic strain using a gradient-based optimization algorithm.

In LPBF AM, the team optimized two aspects of the fabrication process simultaneously: the “expansion direction” or laser scanning direction using residual stress asymmetry and the internal structure of the fabricated material. or “lattice density distribution” by considering the layer -ordering residual stress clockwise. Accordingly, they refined their methodology to ensure the synergistic effect of concurrent optimization.

In addition, the team performed experiments to verify their new methodology using semi-2D plates, 3D racks, and 3D connecting rods. Compared to the standard benchmark designs being used, their design strategy has reduced longitudinal edge distortion by 23–39% in semi-2D panels. In the case of 3D brackets and connecting rods, the curvature reduction ranges from 13–20%.

Overall, the method proposed in this study could herald a great development in 3D printing using LPBF fabrication. Reducing warping and residual distortion is important for casting large metal components. Takezawa concludes: “Recent improvements in metal 3D printing technology have made it possible to produce larger molded parts. Following this approach, our methodology should ideally allow for 3D printing of any part. any big metal,” concluded Takezawa.