• Title/Summary/Keyword: Laser power modulation

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Prevention of Back Side Humping in Laser Welding of Al 5J32 Alloy by Using Laser Power Modulation (Al 5J32 합금의 레이저 용접에서 레이저출력 모듈레이션을 이용한 이면 험핑 비드의 안정화)

  • Ahn, Do-Chang;Kim, Cheol-Hee;Kim, Jae-Do
    • Journal of Welding and Joining
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    • v.29 no.4
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    • pp.80-84
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    • 2011
  • In the 5xxx series Al-Mg alloy, magnesium addition can increase the strength of aluminum alloy by solid solution strengthening but it has a relatively low melting and boiling temperature. During full -penetration laser welding of the Al-Mg alloys, its low boiling point and high vapor pressure brings about the spiky humping bead on the bottom side. Under back-side shielding, the spiking of back bead can be reduced but it restraints the process flexibility. In this study, a square pulse waveform modulation was employed to stabilize keyhole and back bead surface without back-side shielding. By using an experimental design, the bead shapes were evaluated for various process parameters such as the focal position, welding velocity and waveform parameters and the smooth back bead shape could be achieved.

Weld Quality Quantification through Chaotic Analysis (카오스 분석을 통한 용접 품질 정량화)

  • Cho, Jung-Ho;Farson, Dave;Kim, Cheol-Hee
    • Journal of Welding and Joining
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    • v.28 no.1
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    • pp.72-76
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    • 2010
  • Irregular fluctuation of penetration depth in CW single mode fiber laser welding is analyzed statistically and chaotically. Among various chaos theories, one of the basic concept referred as Lyapunov exponent is applied to the analysis to quantify the irregularity of penetration. Especially, maximal Lyapunov exponent (MLE) is known as the representative value indicating chaotic degree of the system dynamics. MLE calculation method of experimental data is applied to longitudinal spiking defect in fiber laser weld. Laser power modulation is suggested as a remedy then the computed MLE value is compared to CW case. It is shown that the adoption of chaos theory, MLE computation, can be used as a measurement standard to prove the validity of the solutions to prevent the unexpected chaotic behavior of weld through this work.

CONTROL OF LASER WELD KEYHOLE DYNAMICS BY POWER MODULATION

  • Cho, Min-Hyun;Dave Farson
    • Proceedings of the KWS Conference
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    • pp.600-605
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    • 2002
  • The keyhole formed by high energy density laser-material interaction periodically collapses due to surface tension of the molten metal in partial penetration welds. The collapse sometimes traps a void at the bottom of the keyhole, and it remains as welding defects. This phenomenon is seen as one cause of the instability of the keyhole during laser beam welding. Thus, it seems likely that improving the stability of the keyhole can reduce voids and uniform the penetration depth. The goal of this work is to develop techniques for controlling laser weld keyhole dynamics to reduce weld defects such as voids and inconsistent penetration. Statistical analysis of the penetration depth signals in glycerin determined that keyhole dynamics are chaotic. The chaotic nature of keyhole fluctuations and the ability of laser power modulation to control them have been demonstrated by high-speed video images of laser welds in glycerin. Additionally, an incident leading beam angle is applied to enhance the stability of the keyhole. The quasi-sinusoidal laser beam power of 400Hz frequency and 15$^{\circ}$ incident leading beam angle were determined to be the optimum parameters for the reduction of voids. Finally, chaos analyses of uncontrolled signals and controlled signals were done to show the effectiveness of modulation on the keyhole dynamics. Three-dimensional phase plots for uncontrolled system and controlled system are produced to demonstrate that the chaotic keyhole dynamics is converted to regular periodic behavior by control methods: power modulation and incident leading beam angle.

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