Optimizing distance between laser and ultrasonic vibration points for additive manufacturing of HG785 steel with the assistance of ultrasonic vibration

The formation of pore defects in the HG785 steel produced by wire and laser additive manufacturing (WLAM) limits their safety applications in the engineering fields, which can greatly deteriorate the mechanical properties of the additive manufactured parts. Ultrasonic vibration is a novel technology to reduce product defects. In this study, finite element method and experimental researches of WLAM assisted with ultrasonic vibration have been taken to investigate the effect of ultrasonic vibration on the pore defects, surface deformation and hardness of HG785 steel for the first time. The simulation results confirm that the temperature fluctuation of deposition layers along depositing height direction becomes smaller as the distance between laser and ultrasonic vibration point increases. The experimental results show that pore defects of deposition layers can be effectively melted assisted with ultrasonic vibration. The microstructure observation results have shown that large deformation can promote to form the granular bainite induced by ultrasonic vibration. Hardness induced by ultrasonic vibration is strengthened at the top layers, while the strengthen effect still exists after the deposition of the upper layers.