Analysis of melt ejection during long pulsed laser drilling

Abstract

In pulsed laser drilling, melt ejection greatly influences the keyhole shape and its quality as well, but its mechanism has not been well understood. In this paper, numerical simulation and experimental investigations based on 304 stainless steel and aluminum targets are performed to study the effects of material parameters on melt ejection. The numerical method is employed to predict the temperatures, velocity fields in the solid, liquid, and vapour front, and melt pool dynamics of targets as well. The experimental methods include the shadow-graphic technique, weight method, and optical microscope imaging, which are applied to real-time observations of melt ejection phenomena, measurements of collected melt and changes of target mass, observations of surface morphology and the cross-section of the keyhole, respectively. Numerical and experimental results show that the metallic material with high thermal diffusivity like aluminum is prone to have a thick liquid zone and a large quantity of melt ejection. Additionally, to the best of our knowledge, the liquid zone is used to illustrate the relations between melt ejection and material thermal diffusivity for the first time. The research result in this paper is useful for manufacturing optimization and quality control in laser-material interaction.

Effects of Beam Mode on Hole Properties in Laser Processing

“…and βr is the retro-diffusion coefficient assumed to be 0 at the beginning of evaporation, while 1 at steady state [25]. ρ is the mixture density [kg/m 3 ], l ρ is the liquid density [kg/m 3 ], δ(φ) is the delta function, and φ is the level-set function.…”

“…K is the isotropic permeability in a porous medium model [2], describing the solid/liquid phase-change process. F is the gas/liquid interface force [N], including surface tension, recoil pressure, and Marangoni force [25], which mainly influences the properties of the fluid flow in the melt pool.…”

“…At the moment, there is no systematic study in the literature highlighting the effects of the GS, TH, DH, and MH on melt-flow phenomena, such as spatter, the recast layer, and the hole shape, during laser drilling. In this work, an experimentally verified numerical laser-drilling model [25,26] was tested on aluminum alloy, and the dynamic process of GS, TH, DH, and MH laser-matter interaction was studied.…”

Amplitude and phase controlled absorption and dispersion of coherently driven five-level atom in double-band photonic crystal

“…Following the previous work in Ref. [34], for the isotropic PBG reservoir, the Green's functions can be expressed as…”

Spontaneous emission from Λ-type three-level atom driven by bichromatic field in anisotropic double-band photonic crystals

“…Zhang et al found that the density of states of photonic crystal determined the relative height of the middle peak in the spontaneous emission spectrum of Λ-type and V-type three-level atoms. [22] It made a two-peak structure with wide dark lines appearing in the spontaneous emission spectrum of Λ type three-level atom which located at the defect position in the defect photonic crystal. [23] In the presence of the driving field and defect mode, the nature of quantum interference was depended on the initial atomic coherence.…”