Application Note: On the Beam
Weld pool flow structure
Several methods of joining material employ an energy beam to melt material in a narrow region where the joining is to take place. For example, arc welding and laser welding use this approach as part of their strategies. The deposition of sufficient thermal energy onto the surface of a solid will cause it to melt. For joining purposes, one would like to know how much power is needed to produce a melt pool of a given size and shape.
If the target material is highly conductive, more power will be needed to compensate for the heat conducted away from the beam area. In most cases, the melted material will also have surface tension that is influenced by temperature. If the surface-tension strength increases with reduced temperature, for example, the liquid in the melt pool will develop a circulation that convects heat to the sides of the pool. This results in a pool that is wider than it is deep. Conversely, if the surface tension is larger in the hotter region at the center of a beam, a surface-tension-driven flow develops in the opposite direction and generates a deeper pool.
In the accompanying figure the former case is shown; a larger value of surface tension near the outside edge of the liquid pool has generated an outward radial flow of liquid. The width of the pool is clearly greater than its depth. Color in the figure indicates the fraction of solid material, where blue is completely solid.
The beam energy deposition model is a user-customizable routine that can be downloaded from the Flow Science Support section. Want to circulate more and stir things up? Get on the beam and make an impression.