Pratt & Whitney 1975 laser disk additive manufacturing experiment

Office of Naval Research contract at Pratt & Whitney around 1976-77 to build up turbine discs with high-power laser. 15 lb/day deposition rate. Tom frames this as the predecessor of today's additive manufacturing hype: "a whole new generation of people who refuse to believe that the people before them were not completely stupid."

People have looked at building things up — back around 1976 or '77, when they first had some high-power lasers, they tried to build up things. There was a research contract at Pratt and Whitney from the Office of Naval Research to use this very proprietary high-power laser to build things up like we were doing with electron beams, to try to make turbine discs. A turbine disc could be worth $100,000 a piece. The problem was you're laying down such thin layers and you have residual stresses. They were laying down 15 pounds a day, which is not very much when you start talking about a thousand-pound turbine disc that you're going to machine to a smaller weight. People are still trying. After 35 years, there's a whole new generation of people who refuse to believe that the people before them were not completely stupid. They believe they were stupid and they can make it work. So today additive manufacturing is one of the buzzwords. People are trying to do what we were trying to do 20 years ago with electron beams.

The historical precedent for laser-based additive manufacturing — Pratt & Whitney demonstrated in 1975 that going slowly enough you can achieve 100% density. Tom uses this to anchor the claim that the physics has been known for over 40 years; what's new is the commercial packaging.

Depending on whether it's electron beam or laser powder bed — if you go back to Alex's chart of all the companies, and to his website, he actually has a video of laser powder bed or maybe electron beam, where you've got the powders, and you can see the process in a video. It's a very violent process. You're spitting out powders as you're melting powders, and you say, what kind of defects is that going to produce? But go look on the blog, and you'll see that because you're melting the metal, you get a better surface finish than a lot of things in the powder bed fusion. That's not a bad surface finish, better than most additive manufacturing parts. But the precision goes to hell because of the shrinkage. If you melt by directed energy deposition — which is what he calls what you're talking about — this surface actually should be better, except you've got all this little spatter of molten metal drops that land on the surface and introduce defects. Should it be a hundred percent dense? You can get close to a hundred percent if you go slow enough. If you try to go fast, you start getting molten metal spatter all over the place. But if you go slow enough, you can get 100 percent dense. Pratt & Whitney showed that in 1975 when they tried to make the laser disk — this is called laser glazing, and they just went around and around.

brief historical anchor — first attempt to additively manufacture a turbine disk, 1975, Pratt Whitney's 75 kW research laser, six-inch disk contract. Tom truncates and ends the lecture.

The first time they ever tried to make a disk by additive manufacturing was 1975. Pratt Whitney had the 75 kilowatt laser, sort of a research thing — it wasn't in the public domain, but he could really buy one. They had a big contract to make a six inch turbine disk. Anyway. Any questions in the class? No? Thanks for coming, Dave. Dave: Thank you, thanks for having me.