Effect of press depth on defect formation in friction-rolling additive manufacturing

Friction-rolling additive manufacturing (FRAM) is a solid-phase additive manufacturing technology that relies on the insertion of a high-speed rotating toolhead into a previous layer to generate heat for deposit formation. Press depth is a key parameter of FRAM, and insufficient press depth may result in defects that affect the mechanical properties of the deposited material. In this study, the effect of press depth on heat generation and defect formation in materials was revealed for the first time using the Coupled Eulerian-Lagrangian method. The results showed that at a small press depth, the temperature and stress of the material on both sides of the interface are low, and the plastic deformation produced by the toolhead does not affect the interface; thus, two types of bonding defects: voids and tunnels, appear easily at the interface position. With an increase in the press depth, material flow along the travelling direction and the toolhead direction was enhanced, and the temperature, stress, and plastic deformation at the interface gradually increased, resulting in the disappearance of the defects, and the order of disappearance was related to the morphology of the toolhead. When the press depth was 1.90 mm, the materials on both sides of the bonding interface reached 70 % of the melting point, resulting in an almost defect-free interface. The simulation results were consistent with the experimental results. This study provides a better understanding of the defects formation during FRAM and provides guidance for regulating the defects in the future.