Quantification of Interdependent Dynamics during Laser Additive Manufacturing Using X‐Ray Imaging Informed Multi‐Physics and Multiphase Simulation

Abstract

Laser powder bed fusion (LPBF) can produce high-value metallic components for many industries; however, its adoption for safety-critical applications is hampered by the presence of imperfections. The interdependency between imperfections and processing parameters remains unclear. Here, the evolution of porosity and humps during LPBF using X-ray and electron imaging, and a high-fidelity multiphase process simulation, is quantified. The pore and keyhole formation mechanisms are driven by the mixing of high temperatures and high metal vapor concentrations in the keyhole is revealed. The irregular pores are formed via keyhole collapse, pore coalescence, and then pore entrapment by the solidification front. The mixing of the fast-moving vapor plume and molten pool induces a Kelvin-Helmholtz instability at the melt track surface, forming humps. X-ray imaging and a high-fidelity model are used to quantify the pore evolution kinetics, pore size distribution, waviness, surface roughness, and melt volume under single layer conditions. This work provides insights on key criteria that govern the formation of imperfections in LPBF and suggest ways to improve process reliability.

Correlative spatter and vapour depression dynamics during laser powder bed fusion of an Al-Fe-Zr alloy

“…The intense vapour flow (blue solid arrow) induces vapour pressure towards the rear keyhole wall (figure 2(d)). Previous work estimates that the vapour jet velocities can reach from 20 m•s −1 [43] to 300 m•s −1 [29] whereas the melt flow can only reach up to 5 m•s −1 [43]. The differences in velocities and densities between metal vapour and liquid metal induce a perturbation at the gas/vapour-liquid interface, a.k.a.…”

Mapping of lithium ion concentrations in 3D structures through development of in situ correlative imaging of X-ray Compton scattering-computed tomography

“…X-ray computed tomography (XCT) has been used for studying internal structures of materials during solidification (Withers et al, 2021), battery operation (Huang et al, 2021), additive manufacturing (Leung et al, 2019) and many other processes (Karagadde et al, 2021). Using high-flux synchrotron X-rays, the acquisition time of XCT has sped up from a matter of minutes to milliseconds (Garcı ´a- Moreno et al, 2021;Leung et al, 2022), capturing dynamic processes close to real time in most situations (Mokso et al, 2017;van Aarle et al, 2016). Tomoscopy is a technique that pushes temporal resolution down to just 1 ms (1000 tomograms per second are acquired) while maintaining spatial resolutions of micrometres and running experiments for minutes without interruptions (Garcı ´a-Moreno et al, 2021;.…”

Quantifying the effects of gap on the molten pool and porosity formation in laser butt welding

“…To determine the optimal conditions and improve the welding quality, the molten pool behavior in the welding process needs to be further studied. With the development of science and technology, the in-situ observation method based on X-ray imaging technology is an effective way to obtain the information inside the molten pool [6][7][8][9]. A lot of work has been done to investigate the dynamics of keyhole and molten pool, spatter and pore in the laser welding [10][11][12][13][14][15].…”

“…Numerical simulation is an economical and effective method that has been widely adopted in the research of molten-pool dynamic simulations in the presence of heat transfer and fluid flow [9,[19][20][21][22][23][24][25][26][27]. Cho et al [20] investigated the temperature distribution characteristic of weld bead and molten flow by simplifying the multi-phase problem into a single-phase problem using finite volume method (FVM).…”

“…They demonstrated that the larger keyhole opening and larger melt flow velocity under a lower pressure is responsible for the reduction of porosity. Leung et al [9] also revealed that the pore and keyhole formation mechanisms are driven by the mixing of high temperatures and high metal vapor concentrations in the keyhole using a combination of in situ X-ray imaging and high-fidelity multiphase simulation.…”