Laser-welded aluminum window frames (circa 1980)

Illinois plant, 10 lasers, 300 million feet/year, double-pane window aluminum frames. Tom's favorite "the exception that proves the rule" example: laser-welding aluminum is unreliable, but the *inherent* unreliability produced the slightly-porous breathing weld the application needed. Eventually supplanted by mechanical stitching.

One of the problems I didn't mention when we were talking about reflectivity on aluminum: the reflectivity problem on aluminum is worse than it is on steel because aluminum reflects about 95% of the light coming in. It's a very good electrical conductor, which means it's got lots of free electrons, which means it's a very good mirror. People generally would say it's not practical to laser weld aluminum, except — the exception that proves the rule — at one time about 30 years ago, the largest application in the world for laser welding was laser welding of aluminum, in a plant in Illinois. They were turning out 300 million feet a year of a piece of sheet metal that had a cross section like 10 or 15 thousandths sheet, and it had a shape formed like this to make a box. The thickness is 10 or 15 thousandths, and they put a weld along here to seal up that seam. This was about 2 to 3 mm on this land.