Hydroforming is kind of like blow-molding, except instead of air blowing into plastic, water is pumped at high pressure into aluminum or steel. As the water pressure increases, the steel part is deformed outwards, taking the shape of the mold it's inside of.
Hydroforming can be used for furniture and bike frames...
...but its biggest proponent is the auto industry.
The part shown above starts out as a mere tube, and its "journey" is pretty interesting. In this "How It's Made" video, we see how hydroforming is used to economically create a complicated part--in this case, the sub-frame for the suspension system on an Acura--that would not be feasible using more traditional methods:
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We know that "affordable" for the auto industry means "Totally out of reach" for the independent designer. However, next we'll show you a guy who's been experimenting with DIY hydroforming. Stay tuned.