Research On Laser Welding Melting Technology

It is appropriate to use a combined heat source model consisting of a rotating Gaussian body heat source and a double ellipsoidal body heat source to simulate the formation of small holes in the laser deep-melt welding of titanium alloys as well as the flow velocity field of the welded molten pool. The body heat source model can reflect the basic physical process of the laser deep-melt welding process, and also reflects the simulation characteristics of the control volume method.
In the fully penetrating laser deep-melt welding process, the diameter of the small hole is not very sensitive to the laser power, while the tilt angle of the small hole changes very significantly with the increase of the laser welding speed. Under the condition of constant airflow pressure in the small hole, the surface tension pressure caused by the curvature of the free surface of the small hole has a great relationship with the welding speed. With the increase in welding speed, small hole stability is gradually reduced.
Laser deep melting welding molten pool of the flow rate of the upper surface for the maximum, Marangoni force on the surface of the molten pool of convective heat transfer plays a dominant role. Under the action of the moving heat source, Marangoni flow from the symmetrical form around the laser heating center evolved into a tadpole shape of the melt pool long axis direction parallel to the welding direction. In the melt pool surface to melt pool width 1/2 as the radius of the speed of the "virtual circle, the melt pool flow rate is larger, in this 'virtual' circle, the melt pool fluid flow rate gradually decreases. Inside the weld pool, the fluid flow rate is significantly lower than the surface of the pool, but much greater than the welding speed value. The value of the fluid flow velocity at the back of the melt pool is greater than the value of the flow velocity of the metal inside the melt pool.
The shape and size of the weld pool have a good correspondence with the size and position of the melt pool flow velocity vortex. Melt pool vortex is Marangoni flow and solid-liquid interface of the recoil of the joint action of the results, buoyancy and gravity only play a supporting role. The existence of the molten pool fluid flow vortex, greatly enhanced the convective heat transfer between the high-temperature metal fluid and cold fluid, which directly affects the size of the shape of the weld pool.
The parameters of the laser deep melting welding side blowing auxiliary air flow is one of the main factors to determine the size of the welding pool protected area and reduce the plasma smoke flow from the small hole eruption. Increasing the flow velocity near the plasma smoke stream is conducive to convective heat dissipation, which in turn increases the probability of compounding between positive and negative plasma ions, thus facilitating the improvement of welding quality. There is a large difference between the component flow field where the auxiliary gas stream is helium and the flow field where the auxiliary gas stream is xenon. From the point of view of the protected area size, the protection of gas is superior to that of gas.