A model of deep penetration laser welding based on calculation of the keyhole profile

Abstract

A model describing the process of deep-penetration laser welding has been developed by calculating the keyhole profile using a point-by-point determination of the energy balance at the keyhole wall. A formula for heat conduction was derived from the model of a moving line source of heat. The various absorption mechanisms were modelled. The corresponding absorbed power transferred to the keyhole wall balances the conduction losses, which yields the local inclination of the wall. The thermodynamics and the flow of metal vapour inside the keyhole have been calculated. Accordingly, beam damping due to the plasma plume above the workpiece and the mean plasma absorption coefficient in the keyhole could be estimated. The keyhole profile tends to a geometry that distributes the major part of the beam to the front wall owing to higher conduction losses at the upstream side. The reasons for decreasing energy absorption with increasing welding speed are discussed.

Investigation of Precision Large-Caliber Slot Cutting of Sheet Steel Using Single-Mode Fiber Laser Radiation

“…In the waveguide propagation zone, the intensity of radiation absorbed by the uppermost metal layer in a "step" is I w =P l ⋅η t ⋅η a ⋅(1-ε)/(Δx⋅b)≈1.3⋅10 5 W/cm 2 , which is lower by two orders of magnitude than the value necessary for the onset of intense metal evaporation observed, e.g., in laser welding, but is quite sufficient for effective heating of the metal (Gladush & Smurov, 2011;Kaplan, 1994;Goncharov et al, 2010).…”

“…For K≥ 30, the static gas pressure in the near-wall jet is close to atmospheric (isobaric jet), and the large hydraulic losses of pressure (proportional to ∼h/b) together with jet divergence (in proportion to ∼1/z) with allowance for gas heating lead to several-fold decrease in the initial subsonic gas flow velocity (to ~50 m/s) and dynamic pressure (to ≤10 3 Pa) (Panchenko, 2009;Vitshas et al, 2014). In this case, the removal (blowing away) of melted metal from the "step" surface can only be ensured by creating a pressure pulse similar to that in the case of laser welding (Kaplan, 1994). Therefore, the process of laser cutting must proceed in a periodic-pulsed regime, in which the formation of a layer of liquid metal with thickness Δz 1 on the surface of "step" with dimensions Δx⋅b takes place rather slowly (within several microseconds, see below) while its subsequent removal (blowing away) is much (ten fold) faster.…”

Benefits And Prospects Of Laser Welding Application In Vacuum

“…The mechanism of pro-melting depth increase (the decrease of external pressure is still the debatable issue) and the complexity of the occurring phenomena require most up-todate numerical experiments. The method for the determination of a steam-gas channel form based on the calculation of energy balance by step-by-step approach has been proposed in work [11]. In the work [12] the authors has described the application of this technique for electron beam welding.…”

Progress in Numerical Simulation of Thermal Processes and Weld Pool Behaviors in Fusion Welding

“…一些研究者假定激光深熔焊熔池达到准稳态 后小孔的形状不再发生动态变化，通过预先假定小 孔形状的方法来考虑小孔对熔池行为的影响，研究 激光深熔焊中熔池传热与流动行为。预置的小孔有 圆柱形 [57] 、圆台形 [58] 或是基于能量或力平衡方程计 算的特定形状 [59][60][61] 。目前较为常用的预置小孔形状 确定方法是 KAPLAN [59] 提出的点对点能量平衡模 型。张转转等 [60] 、BACHMANN 等 [61] 在 KAPLAN [65] 。图 16b 为使用 DSM 法计算的激光束反射路径 [66] 。 CHO 等 [67] 采用 VOF 法对动态小孔界面进行追踪， 并结合基于 光线追踪法的多重反射 Fresnel 吸收模型计算了激 光能量在小孔壁面的分布规律，模拟了小孔的形 成、塌陷过程及气孔缺陷的形成，如图 17 所示。 近期， HAN 等 [68] 提出了基于逐步搜索法(Progressive …”