430铁素体不锈钢薄板激光焊接背面飞溅和熔池动态的数值模拟OACSTPCD

Since a small deviation in the off-focus value can lead to an unstable weld pool,the laser welding of thin plates is highly susceptible to this parameter.Based on numerical simulation,effects of off-focus on the dynamic behaviors of the weld pool in laser welding of 430 ferritic stainless-steel plates in 0.6mm thick were investigated.The reasons behind the for-mation of spatters on the back of the weld bead were examined.The results show that the position and distribution of laser heat input in the weld pool are primarily determined by the off-focus.As the off-focus value decreases,the keyhole in the weld pool gets deeper.A negative off-focus(-0.1 mm)creates a fully penetrated keyhole,while zero(0 mm)and positive(0.01 mm)off-focus creates smaller keyholes.All off-focuses form weld pools with a same waist structure,and the maxi-mum flow velocities are observed on the surfaces of the weld pool and keyhole.Two eddy currents flowing from the middle waist to the upper and lower surfaces exist in the weld pool,and the molten metal on the upper surface of the weld pool flows forward from its rear to its front.Due to the evaporation force and high surface flow velocity,the keyhole continu-ously seals off in its middle,leading to closed bubbles at the bottom.Only negative off-focus causes back spatter,while zero and positive off-focus do not cause it.In the case of negative off-focus,small droplet spatters form on the back of the weld during the initial formation of the weld pool,chiefly caused by the gravity and surface flow.Jet spatters resembling large par-ticles are formed due to bubble rupture during the final stage of the formation of the penetrated keyhole.There is a relatively stable shape and flow of the weld pool in the case of positive off-focus,and the predicted profile of the weld bead on the cross-section is in good agreement with the experimental results.