PLASMA DIAGNOSTICS IN WELDING WITH CO<sub>2</sub> LASERS

Albert, David; Taibi, Abdennasser; Robin, M.; Laurent, Matthew A.

doi:10.1051/jp4:1991743

Cited by 1 publication

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“…There are several papers reporting and analysing plasma, melting pool and keyhole fluctuations observed during welding with the use of cw CO 2 lasers [5,6,[13][14][15][16][17][18][19][20][21][22]. There were attempts to look for characteristic modes and eigenfrequencies of these fluctuations.…”

Section: Introductionmentioning

confidence: 99%

Searching for chaos in fluctuations of a plasma induced during cw- laser welding

Kurzyna

1998

J. Phys. D: Appl. Phys.

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Fluctuations of cold ( eV) and dense plasmas which burn above metallic surfaces during welding with a cw laser are registered in monochromatic radiation. The aim of the present work is to check whether low-dimensional deterministic chaos can be an explanation for the irregular, random-like oscillations of the surface plasma induced during laser welding. The standard procedures of nonlinear time series analysis like the embedding technique, noise reduction by projection on the local manifold, calculations of the correlation dimension using the G-P algorithm, and looking for the largest Lyapunov exponent are applied. After cleaning original time series from the noise, 3D phase portraits displaying more or less regular structures of attractors were reconstructed. The values of the estimated fractal dimensions of these attractors lay in the range , for various cleaning conditions. The plots of the average orbits' `divergence' calculated for the estimation of the largest Lyapunov exponent display behaviour which is typically observed in chaotic systems. The value of the largest Lyapunov exponent obtained from the slope of the orbits' divergence curves is for our welding conditions, about and the average `period' of the plasma oscillation is estimated to be s. This means that the system is highly unpredictable. These results indicate that fluctuations of laser induced plasmas represent deterministic chaos and a nonlinear dynamical system consisting of several ordinary differential equations can be used for modelling laser welding.

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