You may have come across this word, as hydroforming is a process utilized by many bicycle manufacturers when building their frames. So, what does it mean?
In brief, hydroforming means forming and processing of metal using a high-pressure fluid. The process is also known as die molding. The straight tube is placed in a negative mold having the final form the manufacturer wants to obtain for that segment of the frame.
The liquid pumps from inside out at a very high pressure. This process causes the frame tube to adapt the form of the mold as it actually relies on the fluid ability to always apply a perpendicular force to the metal.
Engineers choose a curved shape for areas requiring additional reinforcement, such as those around seat-tube or down tube frame. Manufacturers say that this process gives the frame extra-strength without adding weight, as the amount of raw material stays the same. Also stiffness to weight ratio is increased.
Hydroforming can be used for steel and aluminum frames as well.