By Brian Simonds – Welding is said to be more art than science. In part, this is a nod to the vital, skilled work that welders perform. It’s also recognition of the fact that the physics of the process is really, really difficult to understand.
The laser welding process begins, as one might imagine, when a laser is focused to the surface of a metal. Although the surface initially reflects most of the light, it absorbs enough to cause significant heating. This heating slightly changes the way the metal interacts with the light, which in turn causes more absorption and even more heating.
Once the metal gets hot enough, it begins to melt and evaporate. The now-molten metal pool reacts to this evaporation by recoiling and creating a depression in the surface, like a trampoline reacting to a heavy load. When this depression is deep enough, it sends some of the reflected light back onto itself, which increases the absorbed light, creating more melting, generating more evaporation, making a deeper depression, creating more absorption, then more melting, and so on.
This continues until all the light is absorbed and a deep hole, called a keyhole, forms. In cross section, this looks something like a molten metal tornado with a hollow cavity surrounded by a turbulent funnel of very hot liquid. This all happens within the first few milliseconds.
In their textbook Modern Welding Technology, which has been metaphorically welded to my neocortex, H.B. Cary and S. Helzer estimate that as much as 50 percent of the U.S. gross domestic product relies on welding in some form or another.
The obvious applications of welding are in the manufacturing of big things like cars and trains, but there are less obvious ones like the battery casing in your mobile phone or the metal stents used to reopen clogged arteries. more> https://goo.gl/ngG3hh