3 Fundamentals of press design

406 Hydroforming
p i
axial force
p i = internal pressure
closing force
a b c
Fig. 5.2.1 Process variants of hydroforming: afree hydroforming; btool-dependent hydroforming,
transversely divided die; ctool-dependent hydroforming, longitudinally
divided die
The example used here to explain the hydroforming process is the
production of a T-fitting (Fig. 5.2.2). This type of component can be
either a copper fitting or a joint element in a load-bearing structure. A
special hydraulic press is equipped with a two-part multiple purpose
die. Depending on the workpiece, the dies have two seal punches (horizontal
cylinders) positioned axially relative to the tube ends and a
counterpressure punch. The tubular preform is in the bottom die and
the die is closed. The ends of the tube are sealed by the axial punches,
and the tube is filled with pressure medium. In the actual forming
process, the punches compress the tube, while the pressure medium is
fed to inflate the part until the part wall rests against the die contour.
The counterpressure punch controls additionally the material flow.
The calibration pressure forms the workpiece in such a way that its
contour corresponds to that of the die accurately and reproducibly. The
die is finally opened and the formed component is ejected.
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
p i
p i