Effect of electric arc on laser keyhole behavior based on direct observation during low power pulsed laser–arc hybrid welding process

• An illumination laser is used to observe the laser keyhole in laser–arc welding.
• After a laser pulse action the laser keyhole outlet does not close immediately.
• The extension of arc plasma column hinders the laser keyhole from collapse.
• Arc plasma with large current intensity promotes the keyhole collapse.
• Surface tension difference and arc pressure helpfully keep the keyhole open.

This paper presents an investigation on effect of electric arc on laser keyhole behavior based on direct observation during pulsed laser–arc hybrid welding process. Direct and synchronous observation of laser keyhole outlet and arc plasma is achieved by means of an assistant illuminating laser and corresponding optical modulation. Experimental results show that after laser pulse action the keyhole outlet does not close immediately and the time depends on the welding parameters. Larger arc current will decrease the existing time of keyhole outlet. Extension of arc plasma column into the laser keyhole gives the pressure to the inner keyhole wall, and consequently hinders the keyhole from collapse, resulting in the longer existence of keyhole outlet. The surface tension of the liquid metal around the keyhole outlet increases due to the extension of arc column into the keyhole, which also prevents the keyhole outlet from collapse.