Review of the stereolithographic 3D printing of metals

Stereolithographic three-dimensional (3D) printing of metals is a new additive manufacturing technology. The metal parts prepared by this technology have the characteristics of complex shape and precise structure, and no post-processing is required. It is an advanced manufacturing technology that has enormous potential in fabricating complex parts owing to the considerable progress of stereolithography, digital light processing, liquid crystal displays, continuous liquid interface production, and two-photon polymerization in recent years. This paper summarizes the current research progress on stereolithographic 3D printing of metals and defines four major methodologies, namely, curing sintering, curing coating, mixed curing, and curing mold. Of these, the curing sintering method is the primary technique to prepare metal parts by mixing metal powder with photosensitive resin and forming parts through degreasing and sintering at high temperatures. In curing coating, a metal film is coated on the surface of a solidified resin matrix, which is often used to prepare precision electromagnetic equipment. The mixed curing process is used to directly cure metal slurry without sintering to complete the one-step formation of parts. The curing mold technique is used to realize the multistep formation of parts by using the resin matrix or the ceramic matrix as the mold, followed by subsequent treatments such as casting. In this review, the composition of metal slurry and the resulting properties of the stereolithographic 3D printed metal parts are summarized. Key scientific questions on the property difference between metals and polymer in the slurry, immature processing parameters, lack of reliable compositions for photosensitive resin are still unresolved. The direction of future development is forecasted by studying on the influence of process parameters on the performance of parts, on the new formulas of photosensitive resin, and on more suitable equipment for the stereolithographic 3D printing of metals.