3 Fundamentals of press design

Methods of forming and cutting technology
Expanding is tensile forming to enlarge the periphery of a hollow
body. As in case of deep drawing, rigid (Fig. 2.1.17) as well as soft tools,
active media and active energies are also used.
Stretch forming is a method of tensile forming used to impart impressions
or cavities in a flat or convex sheet metal part, whereby surface
enlargement – in contrast to deep drawing – is achieved by reducing the
thickness of the metal.
The most important application for stretch forming makes use of a
rigid die. This type of process includes also stretch drawing and embossing.
Stretch drawing is the creation of an impression in a blank using
a rigid punch while the workpiece is clamped firmly around the rim
(Fig. 2.1.18). Embossing is the process of creating an impression using a
punch in a mating tool, whereby the impression or cavity is small in
comparison to the overall dimension of the workpiece (Fig. 2.1.19).
punch
s
0
mandrel
workpiece
Fig. 2.1.18 Stretch forming
s