A high speed digital camera with a spatial resolution of 64×64 pixels and a temporal resolution of 40,500 frames/sec has been employed to observe the melt dynamics and the keyhole oscillations in laser welding. Illumination of the interaction zone was provided by a secondary probe laser beam delivered through a multimode diffused fiber. High speed melt flow and wave patterns were observed to have originated from the keyhole region. The keyhole drives fluctuations in the interior of the melt. As a result, multimode volumetric wave patterns were observed. Quantification of the wave velocity and characterization of keyhole oscillation have been attempted. It is observed that as the translation speed increases, the keyhole oscillates more rapidly, leading to faster wave motion. The fluctuatuions in the flow field significantly influence the solidification process at the melt pool tail. Attempts have been made to establish a correlation between the keyhole oscillation and the fluctuations in the solidification process. However, no apparent correlation appears to exist.

Topics
Wave mechanics, Lasers, Solidification process, Welding
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1997
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