Root collapse suppression in thick-plate laser welding using steady-state electromagnetic force.

• The steady-state EMF is the body force and has self-regulating characteristic. • The maximum welding thickness of the plate is up to 30 mm in the steady-state EMF assisted laser welding in a single pass. • The intensity of the magnetic field and the density of the DC have the equivalent effect to control the magnitude of the steady-state EMF. Root collapse is the major problem in laser welding of the thick plate, limiting the maximum welding thickness in a single pass. The steady-state electromagnetic force (EMF), produced by direct current (DC) and rectangular magnets, greatly improve the welding stability at the root. Aiming to understand the influence of the EMF on the root collapse suppression, the transient simulation model of the EMF assisted laser welding is developed and deeply discusses the inner flow behaviors. The simulation results show the weld morphology has a great influence on the magnitude and orientation of magnetic field. The EMF is the body force and has self-regulating characteristic. The direction of the EMF is confirmed based on the Fleming's rule and mainly directed vertical. The experimental tests are implemented in full penetration laser welding of thick stainless steel. The EMF is the real working force on improving the welding stability, not the DC or magnetic field alone. The maximum thickness of the plate is up to 30 mm in a single pass. The intensity of the magnetic field and the density of the DC have the equivalent effect to control the magnitude of the EMF. The vector control of the EMF is more flexible. [ABSTRACT FROM AUTHOR]