Laser – CMT (cold metal transfer) hybrid welding can increase penetration depth

enhance efficiency

and improve weld formation

yet the laser power is crucial for weld formation and process stability. In this study

high-speed imaging and electrical signal method were employed to investigate the weld formation and process stability during laser–CMT hybrid welding of a 6 mm medium-thick aerospace ultra-high-strength steel plate. The results show that the addition of laser shortens the droplet short-circuiting process

prolongs the boost and waiting times

and the droplet diameter slightly increases with laser power

yet the transition frequency remains essentially unchanged at 97 Hz. As laser power increases

the frequency of current instability increases

affecting the stability of the welding process. Analysis indicates that during the detachment and boost phases

the impact force of the droplet and the arc pressure impact and squeeze the keyhole

which is the main cause of keyhole instability. When the laser power is at 5000 W

the keyhole is fully penetrated

and the metal vapor force maintaining keyhole stability maintains a dynamic balance with the droplet impact force and arc pressure

resulting in the best formation with a porosity rate only 0.14%. However

when the power is increased or decreased

the formation deteriorates and porosity defects increase.