Old welder to young welder: “OK, now we’re going to check your welds to see if they hold.”
Young welder: “They’re tight, they’ll hold up to anything.”
Old welder: “We’ll see about that.”
Don’t blink!
Explosive welding and explosive forming are old techniques if by “old” you mean “since we had high explosives available.” I’m endlessly amazed by the concept and I have to admit that I’d love to try explosive welding. Out here where I live there’s a lot of mining activity so there are suppliers that sell blasting materials. I just don’t want to go through all the regulatory headaches and the risk of making myself into a fine, pinkish, paste.
When I started working on wet plate photography in 2007, I was very concerned about the difficulty of getting my hands on stuff like ether and cyanide, but it turned out that in Pennsylvania what’s really hard to get is: anhydrous ethanol. Because the college kids like to drink it so it’s highly regulated. The cyanide took a phone call and a credit check. And that was how I learned that security on materials is spotty, at best. For another example: you can buy crystal iodine on ebay (used to sensitize silver for photography) but if you do, the sellers are most likely FBI agents trolling for meth cookers. But tincture of iodine, sold on amazon.com, just has a bit of alcohol in it and it doesn’t affect the dilution for your film. It’s really goofy, how security is a whack-a-mole game based on the last failure, and no forethought for the next.
I’m not sure if this is an application of high explosive, or low explosive, really. It could be a low explosive and the forming is done by gas pressure, e.g.: gunpowder. Whatever it is, it sure is a great test for the quality of your welds!
I am unsure of the term “hydroforming” for this process. I suppose it’s because there are fluid/gas dynamics at play, but isn’t there a more appropriate term?
Do you know of any other delightful applications of explosives?
It’s hydroforming because the blast wave is propagated through water, remember that liquids are to all intents and purposes incompressible, therefore they channel the blast wave evenly. Think of it as a HEAT charge but with water instead of a copper cone.
Basically they would just fill the sphere with water, put the charge in the middle, blow it and drain out the water.
And yes, you had better make damn sure your welds are good!
Patric Slattery@#1:
I didn’t realize it was also full of water; that makes a lot of sense. Thanks for explaining.
I guess the water also helps absorb the energy of the explosive, so they’ve got a carefully calculated amount of power in the charge and presumably they have to make sure there are no air pockets in the water or the forming will be lumpy.
And I imagine the failure mode, if the welds don’t hold, involves a certain amount of flying steel and a whole lot of water going in all directions. The video appears to be from an enclosure designed for observation – I expect that nobody is anywhere near that thing when it goes off. Funny to imagine that after a while it becomes routine for the people doing it.
I guess that making sure the explosive charge is centered within the object is also really important.
Marcus@#2:
The main reason (AIUI) for using water rather than air is the benign failure mode – split and slosh rather than violent disintegration. Partly because the incompressible water cannot convert pressure into velocity as gas can. Partly because of the sheer mass of the water – the charge doesn’t remotely have the joules to accelerate it, so you get your monstrous pressure pulse but low bulk velocity. The remaining danger is that a failed seam could flick off little high speed fragments.
I do recall seeing somewhere over the years that many parts for the Blackbird were formed using this or similar techniques, I couldn’t find a citation for it though when I searched.
I did however find this incredible document from NASA about the Blackbirds:
Design and Development of the Blackbird: Challenges and Lessons Learned
https://ntrs.nasa.gov/api/citations/20090007797/downloads/20090007797.pdf
Here is what I was looking for:
https://authors.library.caltech.edu/105515/14/AE107%20SR-71%20Case%20Study%20121-320.pdf
Page 19 – TITANIUM SHEET METAL/PART FAB.
They mention a hydro press, which is a similar technology, just no explosives…
I’ve heard of hydro-forming bicycle frames, which I haven’t spent too much time looking up, but after a brief googling/wikipeding, I think basically consists of taking a fairly uniform tube, putting it in a mold, and then using liquid of some sort under really high pressure to deform it in the desired fashion.
I imagine manufacturing the set up to do that isn’t easy, but it seems like it has a lot of potential (to someone who is completely unfamiliar with the manufacture process), to make asymmetrical hollow parts in a repeatable and consistent manner.
There’s an application of this to fine art, check out Evelyn Rosenberg who does low reliefs by exploding sheet metal into forms.
https://www.evelynrosenberg.com/
“Detonography is a method for sculpting metal with plastic or other explosives.” – https://en.wikipedia.org/wiki/Detonography
Works by Evelyn Rosenberg at https://www.evelynrosenberg.com/ .
Evenly transmit, not absorb. It’s incompressible. In order to absorb the energy it would need to be able to compress. Pretty much the point is that it doesn’t.
At work I’m not allowed to pressure test vessels or pipes using gases because of the energy buildup and potential for damage on failure. Hydraulic testing is standard.
can’t you get everclear and molecular sieves over there? or i’m sure one of your neighbours can help out with some 95% ethanol.
once again, security based on the last failure rather than thinking through the problem