Effect of the surface morphology of solidified droplet on remelting between neighboring aluminum droplets

• Published in: International journal of machine tools & manufacture Vol. 130-131; pp. 1 - 11
• Main Authors: Yi, Hao, Qi, Lehua, Luo, Jun, Zhang, Daicong, Li, Hejun, Hou, Xianghui
• Format: Journal Article
• Language: English
• Published: Elmsford Elsevier Ltd 01.08.2018; Elsevier BV
• Subjects: 3D printing; Aluminum; Aluminum droplets; Blocking; Computer simulation; Droplets; Effects; Experiments; Mathematical models; Melting; Metallurgical bonding; Metallurgy; Morphology; Ripples; Solidification; Solidification angle; Substrates; Thermal conductivity; Three dimensional models; Three dimensional printing; Aluminum droplets; Solidification angle; Ripples; Metallurgical bonding; 3D printing
• ISSN: 0890-6955; 1879-2170
• DOI: 10.1016/j.ijmachtools.2018.03.006

Good metallurgical bonding between neighboring droplets is essential in droplet-based 3D printing. However, although the mechanism of remelting has clearly been mastered, cold laps are still common internal defects of formed parts in uniform aluminum droplets deposition manufacturing, which is due to the overlook of the surface morphologies of solidified droplets. Here, for the first time, the blocking effect of ripples and solidification angles on the fusion between droplets is revealed. To investigate the detailed process of remelting, a 3D numerical model was developed, basing on the volume of fluid (VOF) method. Experiments and simulations show that the remelting process between neighboring droplets can be divided into two stages according to the transient contact between the second droplet and the substrate. In the first stage, a non-intuitive result is observed that cold laps can also be formed even if the remelting conditions are satisfied in theory. Ripples on the surface of previously-deposited droplet block its direct contact with the new-coming droplet. In the second stage, cold laps on bottom surface are formed due to incomplete filling of liquid metal when the solidification angle is greater than 90°. Furthermore, these cold laps are difficult to be completely avoided by improving the temperature parameters. To address this problem, a novel strategy of decreasing the thermal conductivity coefficient of the substrate is proposed. This method effectively promotes remelting between droplets by eliminating ripples and decreasing solidification angles. •Surface morphologies of solidified droplets influence the remelting behavior.•Ripples on the droplets block the direct contact between neighboring droplets.•Incomplete filling of metal occurs if the solidification angle is greater than 90°.•Remelting is promoted by eliminating ripples and decreasing solidification angles.