Jeff Ding introduced friction stir welding (FSW) to NASA in 1995. He currently holds 6 U.S. patents for FSW, including one for an automatic retractable pin tool that solves the troublesome “keyhole” problem. He is also credited with inventing two new solid state welding processes called thermal stir welding (TSW) and ultrasonic stir welding (USW). Ding was Marshall Space Flight Center’s Inventor of the Year in 2000, was awarded the Medal for Exceptional Technology Achievement in 2003, and recently received the 2009 Federal laboratory Consortium Award for Excellence in Technology Transfer.
NASA Tech Briefs: Jeff, you are considered to be NASA’s foremost expert in the field of friction stir welding (FSW). What is friction stir welding, and how does it work?
Jeff Ding: Friction stir welding is a solid state weld process, meaning you do not melt the material when you weld. The material is heated into a plastic state – a temperature between solidus and liquidus – using a rotating FSW pin tool. The pin tool has a larger diameter shoulder (approximately three times material thickness) from which a smaller diameter threaded pin protrudes. The threaded pin diameter is approximately equal to the thickness of material being welded and the pin length is approximately .025-in shorter than the thickness of material being welded. Essentially, if you’re welding aluminum, you slowly plunge the rotating, protruding pin into the weld joint until the shoulder comes in contact with the surface of the weld piece. After dwelling for a short period, the shoulder’s frictional energy creates enough heat to allow the aluminum to become soft, pliable, and “mushy” (plastic). At this time, the rotating pin tool (shoulder and pin) traverses the weld joint allowing the threaded pin inside the weld joint material to “stir” the abutting joint material. For .300-in thick aluminum, the pin tool rotates approximately 250 to 300 rpm and traverses the weld joint approximately 6 inches per minute.
NTB: I see. Although you’re credited with introducing friction stir welding to NASA in 1995, the technology was actually invented in 1991 by a man named Wayne Thomas and his team of researchers at The Welding Institute (TWI) in Great Britain. How did you get involved with friction stir welding?
Ding: Back in 1995 I was working in the space shuttle main engine (SSME) chief engineer’s office. I had been there for seven years. It was kind of ironic because I hired into the welding group in 1986 here at Marshall and spent my first two years completing the professional internship program (PIP), a program all new engineers fresh out of college must complete. During those two years, several three month rotations are spent in other MFSC organizations. I rotated to the SSME Office, where, after completing my PIP program, I was offered a permanent job. I guess they liked my welding background; at the time there were over 10,000 welds in a space shuttle main engine. So, I worked there for seven years, and through the years the welding people periodically asked me to come back to the welding organization because they were busy and needed help. So after seven years I thought, “Yeah, I’m going to head off back to the welding group.”
I believe it was in October of that year (1995) that I heard about this new welding process. To be able to do long, linear welds without melting the material seemed very intriguing, because when you don’t melt the material you get much higher properties out of the weld joint as compared to those weld processes where you melt the material. By the way, the processes where you melt material are referred to as fusion weld processes. Metal inert gas (MIG), tungsten inert gas (TIG), variable polarity plasma arc (VPPA), electron beam (EB) are all fusion weld processes, whereas friction stir welding is solid state.
I heard about this and the first thing I did was I called Edison Weld Institute (EWI) in Columbus, Ohio. At the time, EWI was a sister organization to The Welding Institute (TWI) in Cambridge, UK. By belonging to EWI, we could call TWI over in England for consultation. They were sister organizations, so being a member of one allowed you to use the services of the other. So I called Edison and they really didn’t know much about FSW. There were very few people back in 1995 who knew about this process. They said, “You’re going to have to call TWI.” So I called TWI and spoke with Dave Nicholas, who gave me a brief education, and I thought, this is great stuff!