As a former Design Engineer at Newport News Shipbuilding I worked extensively with titanium alloys in the design of submarine components. Titanium is an excellent material for a number of reasons and is especially well suited to a marine environment because of it's corrososion resistance and strength.
Some time back the Russian navy produced a class of subs with a titanium hull. They were welded in a large inert gas filled chamber with welders in moon suit like gear and oxygen supplied through hoses. The issue at the time as far as my understanding goes was that in order to prevent contamination of the weld material the hot weld must be shielded with argon gas until the weld is below around 650 degrees F.
@Ivan: Friction stir welding is a solid-state welding process and doesn't require either fill metal or a shielding gas. So you don't need to wear a space suit in order to do it. It also results in some beneficial microstructural changes which improve material properties. (Sometimes the process is applied to a surface specifically to induce these microstructural changes, rather than to weld one surface to another). It's a very promising process, and it's great to see this collaboration between industry, government, and academia to develop it.
Ivan, the Soviets were willing to take chances with people's lives in all kinds of situations. It is good to see that a safer process is being developed.
The issue, as the article states, is with the tools. They have to operate in very adverse conditions.
As for the cost, most military systems that would use this technology and material have a very long life time. Just look at the B-52. My father worked on the design of it around the time I was born (and you can see that was a while ago). They are still flying and projected to be around for a long time.
I believe I saw soemthing on TV about the Airbus A380 using some stir welding processes as well. I don't recall if it was on titanium pieces or Aluminum but it was interesting. The video of the actual process was impressive in how little it affected the workpieces being joined.
It would be interesting to note the limitations of the process as applied now and also to see what is being undertaken to make it more versatile. stir welding a 4 inch thick piece of Titanium hull section would certainly be an impressive feat.
Does anyone have details on this process? What I saw in the video on Airbuss looked like a spinning tool being forced into the intersection of two sheets of materials. As the tool progressed along the interface the rapid spinning created friction to plasticise the metals and it closed up around the tool on the trailing side. It made a very neat and clean looking bond. Presumably full strength.
Sorry, but we evloved from using the old heat it up and smash it togther process of welding many decades ago. The current most popular processes use an electrical arc to create a metal puddle, if you will, to melt two metal pieces together. There are several forms of this, Arc welding, TIG and MIG just to name a few. The new process you mentioned in the article is still a very impressive development, however, if it tests out that it indeed has the long term structural integrity needed for ship building.
From the article, I didn't get a sense if the weld joint strength was stronger than/weaker than/or same as the surrounding material. There are obvious manufacturing advantages to this new friction welding, but I wonder how does the resulting material properties of this new process compare to the more traditional methods?
Friction stir welding is a process that is quite a bit more complex than ordinary arc welding and far more complex than gas flame welding. The result being that it will cost quite a bit more to do it. So ships made with titanium will be exspensive indeed.
The fact that a process can be done in a manner to produce good rsults does not prove that it can be done in a cost-effective manner. So we should wait and watch and see if the process becomes economicly viable.
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