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Keyhole stability during laser welding—part I: modeling and evaluation

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Abstract

The keyhole is a requirement in order to establish the energy efficient process of laser deep penetration welding. However, the process is highly unstable which results in unwanted pore and spatter formation. In order to avoid process defects, the physical effects in the keyhole have to be better understood to find ways for compensation. This work aims to describe the keyhole properties at different welding parameters for welding of aluminum (EN AW 1050) with the help of a semi-analytical model based on energy and pressure equations and differential equations. The resulting dynamic characteristics of different keyholes are evaluated with frequency analysis of optical observations during the welding process. The spring coefficient, that describes the radial pressure change at radius deviation, is a good indicator for the resulting keyhole dynamics. Dynamic behavior is influenced by the spatial laser intensity distribution, while higher frequencies at lower amplitudes are found at a Top Hat distribution compared to a Gaussian intensity profile.

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Acknowledgments

This work was accomplished within the Center of Competence for Welding of Aluminum Alloys (Centr-Al). Funding by the DFG—Deutsche Forschungsgemeinschaft (VO 530/52-2) is gratefully acknowledged. The “BIAS ID” numbers are part of the figures and allow the retraceability of the results with respect to mandatory documentation required by the funding organization.

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Authors and Affiliations

  1. Bremer Institut für angewandte Strahltechnik GmbH, Klagenfurter Straße 2, 28359, Bremen, Germany

    Jörg Volpp & Frank Vollertsen

  2. University of Bremen, Bremen, Germany

    Frank Vollertsen

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  1. Jörg Volpp
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Correspondence to Jörg Volpp.

Appendix

Appendix

The modelled results for the Top Hat beam intensity distribution are shown in Figs. 20, 21, 22, 23, 24, 25 and 26.

Fig. 20
figure 20

Keyhole properties at different laser powers (Top Hat beam, EN AW 1050 base material, reference parameters)

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Fig. 21
figure 21

Keyhole properties at different welding velocities (Top Hat beam, EN AW 1050 base material, reference parameters)

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Fig. 22
figure 22

Keyhole properties at different focal positions (Top Hat beam, EN AW 1050 base material, reference parameters)

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Fig. 23
figure 23

Dynamic keyhole properties at different welding parameters (Top Hat beam, EN AW 1050 base material, reference parameters)

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Fig. 24
figure 24

Comparing experimentally recorded frequency spectrums and calculated frequency-amplitude-points at different laser powers (Top Hat beam)

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Fig. 25
figure 25

Comparing experimentally recorded frequency spectrums and calculated frequency-amplitude-points at different welding velocities (Top Hat beam)

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Fig. 26
figure 26

Comparing experimentally recorded frequency spectrums and calculated frequency-amplitude-points at different focal positions (Top Hat beam)

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Volpp, J., Vollertsen, F. Keyhole stability during laser welding—part I: modeling and evaluation. Prod. Eng. Res. Devel. 10, 443–457 (2016). https://doi.org/10.1007/s11740-016-0694-3

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