`Boeing Friction-Stir Welding Machine Investment`

$10 million capital investment for friction stir welding of aluminum wing component attachments. Used to illustrate that aluminum's 6% solidification shrinkage drove industry toward solid-state joining.

One of the big problems with aluminum is that it has a 6% volume change on solidification. It will tend to distort on you much more severely than steel — steel's like two and a half percent. So even though aluminum is lower melting, you get tremendous distortion problems when you're fusion welding. When friction stir welding came along, NASA was pushing it — one of my students who worked at NASA gave me this sample. Boeing spent $10 million on a friction stir welding machine for some aircraft wing component attachments. You have to have big heavy fixturing because you're basically just forging things under very high pressure while spinning. There's been a lot of research done on friction stir welding in the last 20 years, partly because it is a new process.