PROCESS DEVELOPMENT AND OPTIMIZATION FOR LASER POWDER BED FUSION OF PURE COPPER

Abstract

Pure copper is widely employed as the primary metal in thermal management and electromagnetic applications due to its exceptional electrical and thermal conductivity. Laser powder bed fusion (LPBF) is a versatile additive manufacturing technique that utilizes high laser energy to selectively melt and fuse successive layers of metal powder to create metallic components with intricate geometries. Nonetheless, LPBF of pure copper is known as a challenging manufacturing process attributed to low optical absorptivity, rapid dissipation of laser energy, and affinity to oxidation. This thesis focuses on the process development and optimization for LPBF of Cu. Firstly, the Process-structure-property relation was examined by assigning a wide range of process parameters to print Cu-LPBF coupons. The optimum process parameters were defined based on maximum relative density, which was obtained at the full laser power of the EOS M280. The results emphasized the significant impact of laser power and hatch spacing on the part quality. Second, Cu oxide exhibits higher optical absorption than pure copper, as reported in the literature. Therefore, the thin film of oxide that was created either on recycled or intentionally oxidized power particles would be a possible easy way to increase the heat energy absorbed from the laser beam. However, the current work emphasized the adverse effects of oxide presence on part quality, particularly when using a medium laser power machine. In this regard, a new method of in-situ Cu oxide reduction during LPBF was proposed to develop an easy and environment-friendly approach to recover the contaminated powder. Applying laser ablation on the powder surface and the solidified layers results in considerable improvement, where the oxygen content is reduced by 70% in the LPBF samples compared to the initial state of the oxidized powder. Finally, the power density of Cu-LPBF coils was improved by enhancing the filling factor and increasing the electrical conductivity. The dimensional limitation of Cu-LPBF fabricated parts was initially identified. The power of utilizing sample contouring was highlighted to upgrade surface quality. Adjusting beam offset associated with optimum scan track morphology upgraded the minimum feature spacing to 80 um. The electrical impedance of full-size Cu-LPBF coils, newly reported in this study, was measured and compared with solid wire. It can reflect the performance of Cu-LPBF coils (power factor) in high-frequency applications.