Laser Foil Printing and Surface Polishing Processes

摘要

A foil-based additive manufacturing technology for fabricating metal parts, called Laser Foil Printing (LFP), was proposed and developed in this dissertation. The manufacturing sub-processes comprising the LFP technology were comprehensively studied, which include the laser spot welding of foil, laser raster-scan welding of foil, laser cutting of foil, and laser polishing processes. The fabricated free-form parts were demonstrated and own better mechanical properties (micro hardness and tensile strength) than the raw material, because of the rapid-cooling process of laser welding. The full and strong bond between layers was formed by the laser welding process, with no micro-cracks or pores observed. The clean and accurate cutting edges were produced by the laser cutting process, with no burr or thermal distortion. The study of laser polishing shows that the width and depth of polished track have significant impacts on the polishing capability. The numerical analysis of laser polishing process shows that the convection flow in the melting pool can deepen the polished track. Three different scan paths were studied to polish the side surface of LFP parts. The finally resulted side surface roughness can be reduced to 0.72 microm in Sa, for both the vertical side surface (with the initial surface roughness of 4.39 microm) and the 45º-inclined side surface (with the initial roughness of 24.22 microm). And the foil bonding defects on the side surface can be completely repaired in the post-processing of laser polishing. Finally, the bulge structure along polished track was noticed in the experiments and studied on Ti-6Al-4V slabs. The spatial spectra analysis shows that the overlapping process of polished tracks can effectively reduce the induced bulge structures.