Abstract
This review focuses on the current state of the art in liquid metal additive manufacturing (AM), an emerging and growing family of related printing technologies used to fabricate near-net shape or fully free-standing metal objects. The various printing modes and droplet generation techniques as applied to liquid metals are discussed. Two different printing modes, continuous and drop-on-demand (DOD), exist for liquid metal printing and are based on commercial inkjet printing technology. Several techniques are in various stages of development from laboratory testing, prototyping, to full commercialization. Printing techniques include metal droplet generation by piezoelectric actuation or impact-driven, electrostatic, pneumatic, electrohydrodynamic (EHD), magnetohydrodynamic (MHD) ejection, or droplet generation by application of a high-power laser. The impetus for development of liquid metal printing was the precise, and often small scale, jetting of solder alloys for microelectronics applications. The fabrication of higher-melting-point metals and alloys and the printing of free-standing metal objects has provided further motivation for the research and development of liquid metal printing.
Highlights
Functional composite materials, e.g., piezoelectric ceramic composites, have been printed via several methods including a BaTiO3 -based ceramic composite via digital light processing [33]; a polyvinylidene fluoride composite loaded with BaTiO3 nanoparticles and carbon nanotubes printed through fused filament fabrication (FFF) [34]; and Pb(Zrx Ti1-x )O3 (PZT) ceramics by the selective laser sintering (SLS) method [35]
Liquid metal printing may overcome the limitations of beam-based metal Additive manufacturing (AM) especially as it pertains to reduction of temperature related defects such as hot cracking
Jiang et al investigated the relationship between the diameter of micro-droplets and processing parameters of liquid metal alloy jetted with a continuous inkjet printing (CIJ) printer
Summary
Polymers were among the first materials to be AM fabricated. Two of the early polymer printing technologies include stereolithography and fused deposition modeling or fused filament fabrication (FFF). In EPBF, a high vacuum (at least in the range of 10−5 mbar) is a requirement as an electron beam will be scattered by atmospheric gases These powder-based AM techniques generally lead to materials with unique microstructures. This microstructure formed due to the high cooling rates encountered in the SLM process [38,39]. Balling leads to rough surfaces due to formation of balls of material caused by high surface tension and inhomogeneous thermal distribution [51,52,53] Cracking is another commonly encountered defect, especially when fabricating “nonweldable” alloys with laser powder bed fusion, electron beam melting, or other-directed energy deposition method. Liquid metal printing may overcome the limitations of beam-based metal AM especially as it pertains to reduction of temperature related defects such as hot cracking
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