3 Fundamentals of press design

5 Hydroforming
5.5 Materials and preforms for
producing hydroformed components
5.5.1 Materials and heat treatment
Basically the same materials which can be used for other cold forming
techniques such as deep-drawing (cf. Table 4.2.3) are suitable for
hydroforming applications. The material should have a fine-grained
microstructure and be soft-annealed.
The best forming results are achieved using materials with a high
degree of ultimate elongation, whereby the ultimate elongation at right
angles to the longitudinal direction of the tube – i.e. generally at right
angles to the rolling direction of the sheet metal – is important for the
configuration of hydroform components. A high degree of strain hardening
is beneficial.
The tube manufacturing process and pre-forming bring about a
strain hardening effect which may have to be eliminated by annealing
for certain components prior to the hydroforming process. If the formability
of the material is exceeded during a production step in the manufacturing
process, forming must be performed using several stages
(progressive forming) with intermediate annealing. However, due to
the additional costs involved, heat treatment should only be carried
out when all other possibilities, for example design or material modifications,
have been exhausted.
The preferable method of heat treatment for austenitic steels is solutionizing
– ideally using inert gas. For small parts, a continuous furnace
can be used.
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998