A Comparative Study of Pulse Wave and Continuous Wave Laser Patterns During Laser Powder Bed Fusion

Abstract

AbstractLaser powder bed fusion (LPBF) of metallic components is used across a wide range of industrial domains. Commercial LPBF machines utilise pulse or continuous laser systems; however, research on the underlying physical phenomenon in the pulse wave mode remains limited. Here, we developed a powder-scale computational fluid dynamics (CFD) multi-physics model to reveal the effect of the pulse wave mode on the thermal behaviour and molten pool evolution of 18Ni-300 maraging steel during LPBF. A model was also developed under the equivalent continuous wave mode to reveal the differences between these two modes. The results indicated that a fish-scale surface morphology of the melted track formed under the pulse wave mode, with deep penetration of the laser energy underneath the baseplate material. The instability of the molten pool in the pulse wave mode led to the formation of keyhole pores. Quantitative analysis showed that the molten pool was deeper and narrower under the pulse wave mode than under the equivalent continuous wave mode. The maximum temperature of the molten pool was significantly higher than the boiling point in both modes. The temperature slightly fluctuated under the continuous wave mode; however, a significant temperature drop occurred under the pulse wave mode when the laser source was switched off within one pulse. These findings demonstrated that the simulations developed for the continuous wave mode do not accurately model the equivalent pulse wave mode. This study also offers initial insights into the thermal and molten pool behaviours during pulse wave LPBF.KeywordsLaser powder bed fusionPulse and continuous waveComputational fluid dynamics (CFD)Molten poolTemperature history