Highspeed laser weld instabilities

Abstract

Laser welding has firmly entrenched itself as an attractive manufacturing process technology in the industry. Despite its role of a viable manufacturing process, its overall efficiency is not significantly higher than other joining processes in particular resistance welding. It is imperative that the high traverse speed of laser welding would increase the manufacturing productivity. But it is observed that the high speed laser welds are associated with defects such as bead protrusion commonly known as humping, hole formation, undercutting, etc. Though these phenomena have been observed previously, in highspeed laser, electron beam and arc welding, there is a scarcity of reported physical explanation of the cause of these highspeed weld nonlinearities. A mathematical model is developed to correlate the instabilities of highspeed weld melt pool. The weld molten pool behavior is explained in terms incompressible Newtonian fluid flow. The continuity and momentum equations are formulated for surface perturbation of the melt. The surface perturbation is defined as the quasi-periodic protruded bead structure measured after solidification.The surface perturbation is not measurable within the weld speed that does not create weld defects and is distinctive of striations. The onset of instability is determined employing dynamic similitude that correlates the weld penetration and weld speed.A comparison of experimental welding speed showed good approximation to the weld surface perturbation. This paper detailed the mathematical formulation of propagation of the perturbation on the melt at high weld speed and experimentally determine the instability criteria.Laser welding has firmly entrenched itself as an attractive manufacturing process technology in the industry. Despite its role of a viable manufacturing process, its overall efficiency is not significantly higher than other joining processes in particular resistance welding. It is imperative that the high traverse speed of laser welding would increase the manufacturing productivity. But it is observed that the high speed laser welds are associated with defects such as bead protrusion commonly known as humping, hole formation, undercutting, etc. Though these phenomena have been observed previously, in highspeed laser, electron beam and arc welding, there is a scarcity of reported physical explanation of the cause of these highspeed weld nonlinearities. A mathematical model is developed to correlate the instabilities of highspeed weld melt pool. The weld molten pool behavior is explained in terms incompressible Newtonian fluid flow. The continuity and momentum equations are formulated for surface perturbati...