Computational analysis of metal transfer mode, dynamics, and heat transfer under different pulsating frequencies in pulsed wire-arc additive manufacturing

Abstract

A numerical model of the metal transfer process was developed using the thermomagnetohydrodynamic equations and the phase-field method to investigate the influence of pulse frequency on the metal transfer mode, dynamics, and thermal behavior in the pulsed wire-arc additive manufacturing (WAAM) process. The control of droplet transfer mode, dynamics, and thermal behavior is essential in WAAM; otherwise, several potential defects such as high residual stresses and distortion, poor dimensional accuracy, and surface quality may occur due to uneven heat input condition and process instability. Therefore, in this study, eight sets of pulse frequencies ranging from 50 to 225 Hz, in steps of 25 Hz, using identical power source parameters, such as pulse duty cycle and average current of 25.4% and 152 A, respectively, were considered and compared for a nearly square current waveform. The results reveal that only the current pulses with a medium frequency regime (100–175 Hz) achieve the one-droplet-per-pulse mode of metal transfer. Moreover, an increase in pulse frequency leads to a shorter necking length of the pendent droplet and a significantly lower average speed and temperature of the detached droplet. The results for the heat flux analysis indicate that Joule heating and arc heating decrease due to the increase in pulse frequency, whereas the sheath heating remains almost constant using different pulse frequencies. The proposed numerical scheme provides a detailed understanding of controlling and tailoring the different metal transfer modes and their metal transfer stability during WAAM, which benefits further process optimization and control.