Frequency Domain Measurements of Melt Pool Recoil Force Using Modal Analysis

Abstract

Recoil pressure is a critical factor affecting the melt pool dynamics during Laser Powder Bed Fusion (LPBF) processes. Recoil pressure depresses the melt pool, providing layer-to-layer fusion without introducing porosity. If the recoil pressure is too low, the process operates in a conduction mode where layers will not properly fuse, while excessive recoil pressure leads to a keyhole mode, which results in gas porosity. Direct recoil pressure measurements are challenging because it is localized over an area proportionate to the laser spot size producing a force in the mN range. This paper reports a vibration-based approach to quantify the recoil force exerted on a part in a commercial LPBF machine. The measured recoil force is consistent with estimates from high speed synchrotron imaging of entrained particles, and the results show that the recoil force scales with applied laser power and is inversely related to the laser scan speed. These results facilitate further studies of melt pool dynamics and have the potential to aid process development for new materials.

Understanding the effects of temporal waveform modulation of the laser emission power in laser powder bed fusion: Part I - Analytical modelling

“…Experimental measurements by Cullom et al reported values for the recoil pressure in the range of tens of kPa which were found to be in agreement with the results reported by Yin et al [37,61]. Although, the recoil pressure levels reported in the current work are well beyond values reported in literature they still confirm the predominance of the recoil pressure over other dynamic components.…”

“…to be smaller in orders of magnitude and may be considered as secondary effects over the fluid motion [37,38].…”