The details of the melt flow dynamics in deep-penetration welding as well as in laser cutting are still not completely understood. In addition, control of the melt flow might help to suppress or eliminate defects such as spattering, humping or dross formation.
The present paper describes the use of a short-pulse laser to influence the behavior of the melt flow. First results show that the melt pool dynamics can be influenced very significantly with less than 1% of additional average power of pulsed laser radiation.
A 4’000 W lamp-pumped cw solid-state laser focused to a spot diameter of 450 µ m was used as heating source to generate a keyhole and the melt pool. A diode-pumped Q-switched (QS-) laser delivering 20 ns, 4 mJ pulses at 4 kHz was used to influence the melt pool. The two lasers were overlapped in the interaction region by angular multiplexing. The position of the QS-laser could be adjusted arbitrarily with respect to the cw-laser. The experiments were made on sheets of stainless steel and aluminum and analyzed by means of a high-speed camera.
Completely different effects were observed depending on the position of the QS-laser with respect to the keyhole proving that the melt pool dynamics can significantly be influenced with the additional short laser pulses. These preliminary results allow for estimations on the physical quantities such as short pulse absorption, energy transfer and melt flow speed.