Measurement of beam attenuation by the vapor plume during full-penetration laser welding of stainless steel, aluminum and copper

During deep-penetration laser welding, the associated vapor plume attenuates the laser beam through scattering and absorption, resulting in a reduction of laser power contributing to the welding process. In the present study, the attenuation of the laser beam was measured in detail for stainless steel, aluminum, and copper under various atmospheric conditions. To achieve this, a novel beam configuration is employed, in which a coaxially aligned probe laser beam propagates along the same path as the processing laser beam through the interaction zone and the bottom opening of the keyhole during full-penetration welding. After separation from the residual processing beam, the laser power of the transmitted probe beam was measured using an integrating sphere and a photodiode. The results show that the attenuation was highest for stainless steel, followed by copper, and then aluminum. For all three materials, the attenuation occurred primarily within the keyhole and in its immediate vicinity. Furthermore, in the overall attenuation resulting from absorption and scattering, absorption was identified as the dominant effect. Mie–theory calculations for single–particle interactions matched the measured attenuation, confirming the experimental findings. Finally, lowering the ambient pressure noticeably reduced the total attenuation.