Mechanism of pore formation during keyhole laser spot welding

Alexander F. H. Kaplan; Masami Mizutani; Seiji Katayama; Akira Matsunawa

doi:10.1117/12.497914

3 March 2003 Mechanism of pore formation during keyhole laser spot welding

Alexander F. H. Kaplan, Masami Mizutani, Seiji Katayama, Akira Matsunawa

Proceedings Volume 4831, First International Symposium on High-Power Laser Macroprocessing; (2003) https://doi.org/10.1117/12.497914
Event: LAMP 2002: International Congress on Laser Advanced Materials Processing, 2002, Osaka, Japan

Abstract

Theoretical and experimental studies have been carried out in order to improve the understanding of the mechanism of pore formation in keyhole laser spot welding in a qualitative and also quantitative manner. A semi-analytical mathematical model of the keyhole collapse illustrates the different characteristic time scales of the contributing physical processes: post-vaporization (order of magnitude: 100 ns typically), excess keyhole vapor relaxation flow 10 μs), inertia driven collapse (100 μs), followed by bubble contraction, re-condensation and rising (10 ms), and re-solidification (10 ms). The conditions of the keyhole just before switching off the laser beam, observed by X-ray imaging, are essential for the subsequent collapse mechanism. In case of a bottleneck-shaped keyhole, which can easily form due to the paradox of vapor flow inversion, bubble formation is likely to occur due to necking. When the thermally contracting bubble is trapped by the re-solidification front, a pore is formed. The model is complementary to high speed X-ray observations of the keyhole shape, particularly in liquid Zn that enables investigation of keyhole and bubble formation not constrained by surrounding solid.

Citation Download Citation

Alexander F. H. Kaplan, Masami Mizutani, Seiji Katayama, and Akira Matsunawa "Mechanism of pore formation during keyhole laser spot welding", Proc. SPIE 4831, First International Symposium on High-Power Laser Macroprocessing, (3 March 2003); https://doi.org/10.1117/12.497914

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