Heat accumulation effect in metal droplet-based 3D printing: Evolution mechanism and elimination Strategy

Uniform morphology and good metallurgical bonding between neighboring droplets are crucial in metal droplet-based 3D printing. However, this technique is usually accompanied by a heat accumulation effect during the printing process, leading to poor forming accuracy and non-uniform microstructure and properties of the formed parts. Since the heat accumulation effect is an intrinsic physical property in metal droplet-based 3D printing technique under fixed-parameter conditions, morphological deterioration or even instability phenomena are still common defects in this technique. Herein, a set of pillar printing experiments based on the 7075 aluminum alloy were conducted to demonstrate the influence of the heat accumulation effect on the forming accuracy in metal droplet-based 3D printing. A semi-quantitative analysis of the heat accumulation effect was also carried out based on the one-dimensional thermal conductivity theory. To further reveal the evolution mechanism of the heat accumulation effect during the aluminum micro-droplet printing, this paper develops a 3D numerical model of aluminum micro-droplet printing based on the volume of fluid (VOF) method. The evolution of the temperature field, heat flux, solid fraction, velocity field, and solidified morphology, during the continuous deposition of aluminum micro-droplets, were systematically investigated. The evolution mechanism of the heat accumulation effect and its influence on the forming accuracy was revealed. Finally, based on the thermal equilibrium theory, this paper proposed a variable frequency printing strategy to effectively eliminate the heat accumulation effect. This study provides a foundation for further development of metal droplet-based 3D printing technology.