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RESEARCH PAPERS: Heat Transfer in Manufacturing

Transport Phenomena and Keyhole Dynamics during Pulsed Laser Welding

[+] Author and Article Information
Jun Zhou

Department of Mechanical and Aerospace Engineering, University of Missouri-Rolla, 229 Mechanical Engineering, 1870 Miner Circle, Rolla, MO 65409jzhou@umr.edu

Hai-Lung Tsai

Department of Mechanical and Aerospace Engineering, University of Missouri-Rolla, 122 Mechanical Engineering Annex, 1870 Miner Circle, Rolla, MO 65409tsai@umr.edu

Pei-Chung Wang

R & D Center, General Motors Corporation, Warren, MI 48090Pei-chung.wang@gm.com

J. Heat Transfer 128(7), 680-690 (Dec 07, 2005) (11 pages) doi:10.1115/1.2194043 History: Received August 22, 2005; Revised December 07, 2005

Numerical and experimental studies were conducted to investigate the heat transfer, fluid flow, and keyhole dynamics during a pulsed keyhole laser welding. A comprehensive mathematical model has been developed. In the model, the continuum formulation was used to handle solid phase, liquid phase, and mushy zone during melting and solidification processes. The volume-of-fluid method was employed to handle free surfaces. The enthalpy method was used for latent heat. Laser absorptions (Inverse Bremsstrahlung and Fresnel absorption) and thermal radiation by the plasma in the keyhole were all considered in the model. The results show that the recoil pressure is the main driving force for keyhole formation. Combining with the Marangoni shear force, hydrodynamic force, and hydrostatic force, it causes very complicated melt flow in the weld pool. Laser-induced plasma plays twofold roles in the process: (1) to facilitate the keyhole formation at the initial stage and (2) to block the laser energy and prevent the keyhole from deepening when the keyhole reaches a certain depth. The calculated temperature distributions, penetration depth, weld bead size, and geometry agreed well with the corresponding experimental data. The good agreement demonstrates that the model lays a solid foundation for the future study of porosity prevention in keyhole laser welding.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Experimental setup and schematic sketch of static keyhole laser welding process

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Figure 2

A sequence of liquid metal evolution during the keyhole formation process

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Figure 3

The corresponding temperature distributions for the case shown in Fig. 2

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Figure 4

The corresponding velocity distributions for the case shown in Fig. 2

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Figure 5

Surface tension and its gradients as a function of temperature for the pseudo-binary Fe-S system with 300ppm sulfur

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Figure 6

Coefficient of Inverse-Bremsstrahlung absorption as a function of plasma temperature from Ref. 16

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Figure 7

Keyhole depth and keyholing speed as a function of time

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Figure 8

A sequence of liquid metal evolution during the keyhole collapse and solidification processes

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Figure 9

The corresponding temperature distributions for the case shown in Fig. 8

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Figure 10

The corresponding velocity distributions for the case shown in Fig. 8

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Figure 11

The comparison of the weld bead geometry between experimental result and model prediction

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Figure 12

The comparison of the temperature history at location “A” between experimental result and model prediction

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