Hi!
Stumpled upon this technology: HEATForming. Have two halves that are the negatives of some vaguely tube-shaped piece. Heat a tube to 500..600°C (for Al), put it into the two halves and blow it up with air (at least 20 atm). Push the tube in from one or two sides to give more material to deform.
Difference to hydroforming is the usage of gas, which allows for hot workpieces and thus much more forming. This includes threads (yes, threads)!
*Impressive* -not to say incredible- samples here:
Nick