A metal additive manufacturing method: semi-solid metal extrusion and deposition

Different existing metal additive manufacturing (AM) processes have many shortcomings and a lot of activities are centered on improving the final printed metal product. A new method of metal additive manufacturing has been proposed in this paper. Unlike most of the metal additive manufacturing processes, it does not use metal powder. The proposed method utilizes semi-solid metal (SSM) forming combined with deposition process as used in the most common additive manufacturing process for polymers. SSM forming is a promising near net shape technology with several advantages, such as being a porosity-free product and having reduced shrinkage, controlled microstructure, and excellent mechanical performance. Implementation of this technology in metallic additive manufacturing improves the mechanical properties and cost savings. Complicated time-dependent behavior of SSM makes it a challenging issue to utilize in additive manufacturing. A wire feedstock as a metallic filament was employed for the proposed process. However, some material preparations were necessary to get the desired rheological properties at the deposition head. In this study, the strain-induced melt-activated (SIMA) process was applied on a low-melting-temperature Sn-Pb alloy to obtain the desired globular feedstock microstructure. Then, preconditioned wire was fed in a thixo-extruder, which was designed and built for the proposed method in this research. A semi-melted alloy was deposited on the moving substrate to build a metallic part layer by layer. Various parameters of SIMA and thixo-extrusion processes, including wire thermomechanical cycle, feed rate, solid fraction, nozzle and chamber geometry, and others, were examined experimentally, and a sustainable semi-solid metal extrusion and deposition (SSMED) process was achieved. Finally, an acceptable metallurgical layer bonding was obtained at the interface of the deposited layers, with good mechanical properties of the fabricated parts. The new proposed method seems to have great potentials for metal additive manufacturing parts.

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