Repeated experiments show that weld beads made by keyhole PAW typically have relatively large and irregular ID(inner diameter) reinforcements associated with a considerable amount of spatter.
On the other hand, those made by melt-in PAW show large ID weld beads that may cause excessive convexity around 12 o’clock and concavity around 6 o’clock.
To resolve these issues, the authors propose the double-stage PAW process, which combines keyhole and melt-in mode into a single welding procedure.