Abstract:

In order to master the control methods of welding porosity on laser-arc hybrid welding for high nitrogen steel, the effect of weld porosity on arc energy and laser energy and the vibration frequency are studied. Causes of welding porosity are analyzed in terms of porosity rate, and its effect is investigated on stability of welding processes through waveforms of current and voltage and droplet transfer. There is certain relevance between fluid flow in the melt pool and formation of welding porosity, and the influence on welding porosity is analyzed in terms of fluid flow in the melt pool. The keyhole is generated when laser power reaches up to a certain extent and condition of keyhole will affect porosity rate. Influence of porosity rate on condition of keyhole is analyzed according to keyhole's stress situation. The results shows that porosity rate of welding seam increased first and then decreased with the increasing of arc energy or laser energy, and porosity rate of welding seam is reduced to the lowest for just 0.49% while arc energy is 4 800 J (I=200 A, U=24 V) and the porosity rate of welding seam is only 0.14% when laser power is 2.8 kW, but porosity rate of welding seam is reduced greatly after work pieces are vibrated during hybrid welding. Porosity rate of welding seam decreased first and then increased with the increasing of vibration frequency. The number of welding porosity is inhibited efficiently by suitable arc energy or laser power, and inhibitory effect of welding porosity is best while vibration frequency amount to 35 Hz.

Key words: control methods, high nitrogen steels, welding porosity, hybrid welding