Glass-fiber composite foam sandwiches are already used in aircraft manufacturing to help planes shed weight, and carbon composite sandwiches using foam or honeycomb cores are also on the rise in planes and trains. Now, a laser-welded metal sandwich with a metal foam core has been demonstrated for lightweighting ships.
Along with its project partners, the German Laser Zentrum Hannover research and development center laser welded a demonstrator for marine gear unit foundations made of steel and aluminum foam sandwich material. The demonstrator was on display at the Hannover Messe 2012 show.
A new process for laser-welding steel-aluminum foam sandwich structures for lightweighting ships has been demonstrated. Shown here is a laser fillet weld support for structures such as marine gear unit foundations. (Source: Laser Zentrum Hannover)
Using metal foam sandwiches to make ships lighter isn't a new idea. The metal foams are highly porous materials, often made of aluminum, that can also more easily absorb noise because of their cellular structure. Noise reduction is a growing trend in car interiors, and both the inside and outside of planes, in those cases usually employing non-metal foam or metal or non-metal honeycomb cores.
Metal foams are not only light in weight and sound-absorbing, but also heat-resistant and provide good insulation against electromagnetic waves. In sandwich constructions, they have a much higher bending stiffness than solid sheets. Because of their lighter weight, they are also applicable for parts that undergo high amounts of stress, such as rudders or machine foundations. In those applications, large-scale metal foam sandwich constructions can reduce weight by as much as 20 percent.
The problem with this technology has been the difficulty in welding steel and aluminum. This is caused by different material thicknesses, and the inhomogeneity of the foam core. Aside from problems such as the distortion caused by the thermal effects of foaming the aluminum core in mixed sandwich materials, cracks in the welding seam can also occur, caused by intermetallic phases due to welding.
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.
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 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.
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.
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
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.
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?
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