I just watched it a second ago, and need to go back and rewatch it. But, the short story is the Mythbusters crew was able to set up a hydroforming rig with a just a pressure washer and a couple of steel plates! They actually provided a pretty good "how to" on tonight's show (5/04/11). Now, I know they say "don't try this at home", but they seemed VERY successful in making some steel torpedoes. Would be excellent for forming sheet metal bubbles for various body work situations. Of course, not without risk, any time you have confined pressure there can be consequences. On the other hand, it seems like with the rig they used, it would be pretty easy to do this for not a ton of money. Maybe I can link up a clip later.... **Update** If this works, the hydroforming part comes in at about 1:00 minute <iframe id="dit-video-embed" width="640" height="360" src="http://static.discoverymedia.com/videos/components/dsc/5223244ccce91f4c67e4052e5eade47d000d8ea2/snag-it-player.html?auto=no" frameborder="0" scrolling="no" allowtransparency="true"></iframe> The show actually gave a little bit better description of the set up, but this shows the hydroforming really well...
I saw it too...... Really very impressive. Made me wonder how complex a form you could make. Very similar principle to blowing a bubble top ...
If you managed to record the full episode, the hydroforming set up explanation is about 27 minutes in. It obviously took some set up and practice, but it looks like it worked pretty well when they got it dialed in. Now, it looks like they were using something in the neighborhood of 1/2" steel plates, and a forklift to lift the top plate into position. Which would probably exceed the capabilities of some folks' garages. But they were also forming pretty large sections. So, if you wanted to form a belly tank, you'd need some pretty heavy duty equipment. But something like a blister for a hood side, or maybe sections of a motorcycle fuel/oil tank might be pretty "plausible" for a garage build. Just another reason to get a pressure washer... I'm thinking the forms would have to be fairly simple. The edges would have to be pretty round to keep the metal from kinking or tearing, so probably just forms of ellipses or circles. You'd have to do some testing to figure out how small a radius would work, I'm guessing it'd be related to the thickness and type of metal too.
hmmm.... i've got a monster pressure washer... and i must have some luck on my side as i've managed to avoid loosing a finger or an eye with any of the other stuff they've said to not try at home...
Did you pay any attention to the first attempt? The one where they tried to use a cannonball on a jackhammer? Crude as it looked, the main reason it failed was because the sheet was welded to the framework. The outer edges couldn't move. Compare that to when you start forming on a shot bag or a stump. Draw dies clamp the outer edge but still allow some slippage so the metal can "flow" into the cavity.
http://www.jalopyjournal.com/forum/showthread.php?t=77692&highlight=hydroforming Tech from 2005, gotta love the hamb
^^^^^^^^^^^^^^^^^^^^We had a tech week winner from Scandinavia a few years back where the guys made a tuned exhaust for a motocycle or moped using hydraulic fluid and sheetmetal.
yeh I saw that last night! wow, i.m not usually into watching mythbusters but, I just happened to take a look and it was pretty good show, gotta start watchin them more.
Hydroforming is very safe as liquids are not compressible. If something fails it goes spurt and its all over. No explosion. I had a scuba tank fail a tip inspection at 3800 psi. It barely stirred up the water in the test tank.
I was actually wondering if someone would mention this today. Caught it lastnight myself. Very cool stuff.
Hydroforming can be used to produce very complicated shapes, provided one has a die. The die are similar to the ones used for stamping of sheet steel into three dimensional objects. Some chassis/body components of cars today are manufactured using hydroforming rigs. Note that hydroformed metals flow into the die. This is in contrast to stamping, which is more of a stretching process. The distinction is relevant when considering work hardening.
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