Analysis of YAG laser lap-welding of zinc coated steel sheets

Schmidt, Michael; Otto, Andreas; Kägeler, Christian

doi:10.1016/j.cirp.2008.03.043

Cited by 66 publications

(30 citation statements)

References 4 publications

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“…The keyholes with modified shapes shown in figure 7 are similar to those reported by Fabbro et al [7] and Schmidt [29], which show that the keyhole shape is strongly influenced by the dynamic pressure of the zinc vapour. In order to develop a statistical evaluation of the keyhole geometry, a continuous video sequence of 10 240 images (representing a time period of 0.34 s) for steady-state welding was analysed for each parameter combination.…”

Section: Keyhole Elongation Behaviour During Weldingsupporting

confidence: 76%

Keyhole behaviour during laser welding of zinc-coated steel

Pan¹,

Richardson²

2011

J. Phys. D: Appl. Phys.

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The production of consistent, high-quality laser welds on zinc-coated steels for the automotive industry remains a challenge. A simple overlap joint geometry is desirable in these applications but has been shown to be extremely detrimental to laser welding because the zinc vapour formed at the interface between the two sheets expands into the keyhole and disrupts fluid flow in the melt pool, which often leads to metal ejection. In this work, laser welding on sheets with various coating thicknesses has been performed and it is observed that the sheets with thick coatings (∼20 µm) show surprisingly good weldability. High speed video camera visualizations of the keyhole provide insight into the keyhole dynamics during the process. It appears that the dynamic pressure of zinc vapour can effectively elongate the keyhole and the process can reach a stable state when an elongated keyhole is continuously present. A simple analytical model has been developed to describe the influence of zinc vapour on keyhole elongation.

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Section: Keyhole Elongation Behaviour During Weldingsupporting

confidence: 76%

Keyhole behaviour during laser welding of zinc-coated steel

Pan¹,

Richardson²

2011

J. Phys. D: Appl. Phys.

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“…It disturbs the pressure equilibrium, leads to strong perturbations of the melt pool and can even cause collapses of the keyhole, what consequently leads to the formation of pores and melt ejections (see Fig. 9a) [17,[24][25][26][27]. Figure 8 shows the simulation results for the welding process of two sheets of a thickness of 0.6 and 0.7 mm with defined gaps of different widths.…”

Section: Influence Of a Gap On The Welding Of Zinc Coated Sheetsmentioning

confidence: 99%

A 3D transient model of keyhole and melt pool dynamics in laser beam welding applied to the joining of zinc coated sheets

Geiger

Leitz

Koch

et al. 2009

Prod. Eng. Res. Devel.

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140

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In order to get a deeper understanding of laser beam welding, a process model was developed at the Chair of Manufacturing Technology. It is based on the continuity equation, the equation of heat conduction and the NavierStokes equation. The model includes effects of Fresnel absorption, vapor pressure, surface tension, melting and evaporation enthalpy and energy loss due to evaporating material. This paper presents the results of a three-dimensional, transient finite volume simulation of a laser beam deep penetration welding process based on this model. The simulations show periodic keyhole oscillations and the complex fluid dynamics of the melt pool. A comparison of the evaporation rates calculated from the simulations and the experimentally observed process emissions shows good correlation. Furthermore, the simulations show pore formation at higher feed rates, the influence of a gap on the welding process and give an explanation for the welding behavior of zinc coated steel sheets.

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“…During the welding process the generated zinc vapor will not have a direct way to escape, and will therefore vent into the liquid phase zone of the molten pool, resulting in a sever fluctuation of the molten pool generating spatters and blowholes. During the solidification phase, the surface tension of the liquid steel increased, and the blowholes cannot be closed (Schmidt et al, 2008). The defects can be observed in the welds (see Figs.…”

Section: On-line Monitoring Of the Molten Pool And The Keyhole Dynamicsmentioning

confidence: 98%