ON THE SHAPE AND LOCATION OF THE KEYHOLE IN PENETRATION LASER-WELDING

A simple quasi one-dimensional self-consistent model of the keyhole in penetration laser welding has been given previously. By considering t he equation of heat conduction and the pressure balance at the keyhole wall, the radius of the keyhole was obtained. The keyhole was assumed to be a circle, concentric to the laser beam. In the present paper we drop these restrictions. The keyhole boundary is considered to be a f ree curve, adjusting itself to the physical mechanism previously formu lated. The so obtained Stefan problem is solved numerically with a fin ite element method. The keyhole boundary deviated only slightly from a circle but was shifted with respect to the laser beam, depending on w elding speed and laser power. The temperature is found to be nearly co nstant at the keyhole boundary. Our results give justification to prev ious investigations, which considered a constant temperature along the keyhole wall as a boundary condition for the equation of heat conduct ion.