Hole-defects in soluble core assisted aluminum droplet printing: Metallurgical mechanisms and elimination methods

Abstract

Using droplet-based 3D printing to directly fabricate microwave devices with smooth inner surfaces remains an elusive goal, because of the naturally scalloped shapes of solidified droplets and the staircase effect in 3D printing. In order to address this issue, a novel manufacturing process involving deposition of molten metal droplets on soluble cores is proposed. However, complete elimination of hole-defects formed during this manufacturing process is very challenging. This paper presents the study on the transport phenomena among four neighboring droplets using both numerical modeling and experimental methods. The formation mechanisms of hole-defects and their elimination are also discussed. The results show that the hole-defects on the inner surfaces are caused by the incomplete fusion and filling of residual liquid metal between neighboring droplets. Furthermore, these defects can be effectively eliminated by selecting the proper temperatures of droplets and substrates. Finally, a modified parameter mapping of solidified morphologies about the inner surfaces is established to help with printing temperature selection.