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Research progress on heteromorphic structure parts fabricated by additive manufacturing based on inside-laser coaxial powder feeding

Inside-laser material feeding laser cladding deposition (IMF-LCD) is a directed energy deposition technology featuring “hollow beam, annular spot, centered powder, and coaxial powder feeding.” IMF-LCD offers distinct advantages over traditional outside laser material feeding laser cladding deposition (OMF-LCD), such as a good laser-powder coupling effect, high powder utilization, high forming flexibility, uniform thermal field distribution in molten pools, and excellent forming surface quality. IMF-LCD would significantly improve forming efficiency and surface quality while it was applied to rapid direct manufacturing and repair of complex metallic parts compared to OMF-LCD. In this manuscript, the working principle of IMF-LCD technology is briefly introduced. Mostly, the research progress on heteromorphic structure parts fabricated by IMF-LCD was summarized, focusing on layered design, posture change, forming strategy optimization, and process parameter adjustment. The heteromorphic structure included a twisted thin-walled structure, variant height/width structure, overhanging structure, and closed structure. Based on the excellent characteristics of this technology, the exploration of high forming quality heteromorphic structural parts is carried out by changing the process parameters and forming processes such as the variable attitude stacking method, the conformal discrete layering method and the normal layering method, and the surface roughness is as low as 1.323  μm, the dimensional accuracy is as high as 1.6%. Simultaneously, the powder utilization rate of IMF-LCD reached 60%–80% on average, in accordance with the advantages of the laser-powder coupling effect. Finally, the remarkable research and application of IMF-LCD technology in high flexibility, high precision, high surface quality, and high material utilization would further promote the development of additive manufacturing with higher performance, higher quality, and lower cost in the future.