Mechanisms of Increasing Weld Depth during Temporal Power Modulation in High‐Power Laser Beam Welding

Understanding the fundamental mechanisms of action for increasing weld depth during temporal power modulation in laser beam welding could allow dissimilar rotational welding without the introduction of concomitant turbulence, but with enhanced intermixing. The investigations are conducted on 30 mm‐diameter round bars of stainless steel alloy 1.4301 and nickel base alloy 2.4856 utilizing a 16 kW disk laser beam source. Modulation frequencies are 0/50/100/200 Hz at low, medium, and high amplitudes of laser beam power. The influence on the process and weld characteristics is investigated through high‐speed imaging with grayscale analysis, keyhole depth measurements, metallographic sections, and energy‐dispersive X‐ray spectroscopy analysis. The objectives are successfully achieved, and the underlying mechanism is maintaining the keyhole depth at a higher level for modulation frequencies of 200 Hz and a high amplitude of laser beam power, which is related to the keyhole inertia. Based on this, a novel welding mode with a constant keyhole depth is proposed. Furthermore, up to 20% increase in weld depth is achieved, a saturation limit for the modulation frequency is identified, intermixing within the weld is enhanced, and a model for predicting the weld depth based solely on measurements of the surface width is developed.