Ann, this is an interesting twist on an old technology. Welding has been around for a long time. By improving the process new things are possible. Isn't it interesting what some of these engineers will come up with?
Welding dissimilar materials -- especially dissimilar materials with very different thermal characteristics (sheet vs. foam) -- can be a big challenge. The closest I've come to this is inertia welding a hollow carbon steel tube to a solid stainless steel shaft. That's challenging enough, but it's child's play compared to the process described in this article.
It wasn't immediately clear to me how trimming the edges of the foam prevents intermetallic formation. I know that intermetallic formation can be prevented by keeping heating times short, and maybe precise alignment between the aluminum foam and the steel sheet prior to welding helps with this. The high heating and cooling rates made possible by laser welding might also help.
Thanks, naperlou. I thought the combination of technologies to improve this process was especially interesting. Seems like we're seeing more of that: combining different assembly or manufacturing-related techniques to solve new materials and/or process problems. For instance, yesterday's robots plus lasers in composite repair story http://www.designnews.com/author.asp?section_id=1392&doc_id=243715
Thanks for weighing in on this subject, Dave, with your background in metals. From the description, I visualized lasers trimming away the aluminum foam so it doesn't contact the edges of the panel's top steel sheets, only its internal steel sheets. I saw it somewhat like the peanut butter that slops over the side of a sandwich. Here, the "peanut butter"--perhaps a slice of cheese is a better metaphor-- is cut back so it doesn't stick out that far. Then the "bread slices" are positioned so there's no gap and welded. This may be inaccurate, but that's what I thought it meant. A video sure would be helpful.
I wonder about repairs underway? When you are at sea, you are on your own when trouble occurs. Can repairs be made without a 6kW laser? How about standard aluminum welding processes? Can you store on board replacement sections that can be used to reinforce or replace?
And does the sandwich material come with pickles? Just curious.
As excited as I was by the headline, as someone who has spent a lot of time in the marine industry, once I read about a dissimilar metal construction I lost my enthusiasm. The main place where ships need to save weight is in the superstructure (to make them less "tippy") and that problem has been solved by using all aluminum construction. An explosion welded bar of steel/aluminum is used to provide a transition from the deck to the superstructure. Other than that, I have to agree with Warren that the ability to repair stuff easily at sea is paramount. Structures corrode, crack and come apart due to the constant barrage of vibration, sea spray and racking stresses. Probably best to keep this sandwich either in the air or on solid ground.
I also spend many years in the marine industry, and the dissimilar metal issue arose all the time. And the center of gravity would certainly rise, but surely this is taken under consideration.
i wonder where they are on using this new material? I am sure better minds than ours have figured out what the issues are. Just like they did on the Titanic, er I mean the center fuel tank on the 747s, er I mean the solid-state booster on the space shuttle, er, well, you know what I mean.
The first word that pops into my head when I hear the words dissimiar metal is corrosion. When I pull an aluminum wheel off my car which pushes against a steel brake disc, you can see the pattern of the contact patch because the contact patch is rusted.
I am fascinated by the technology to do this and how wavelength was important to the process. ("Say gurl, see if vermillion will work. Or maybe a chartreuse, I'm partial to greens.) I had a manufacturing rep in our design group when I first went to work (his name was Edsel Buick Dodge and I'm not kidding) who said we had some welders who were good enough to make welds which looked like they had welded aluminum to steel.
If there is no oxygen in the structure is there no corrosion? Is so, then keeping the honeycomb sealed would be really important. Water never sleeps, though.
I'm with ChasChas, my materials professors must be spinning in their graves.
As the article states, the demonstrator, at least, was a marine gear unit foundation. I also thought about corrosion, but because the aluminum and steel aren't touching, there are no intermetallic phases, so there are, presumably, no corrosion issues. Thanks for the points about repair at sea. I can't speak to that, except to note that the laser welds occur only on specific welds, as stated in the article: butt welds and fillet welds. Again, a video sure would have helped.
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