3 Fundamentals of press design

Force and work requirement
dies) (cf. Fig. 6.1.2). If upsetting is carried out in a closed die without
flash formation, for example in order to press cylindrical or lens-shaped
pre-forms, this is referred to as sizing.
(Free) upsetting (cf. Fig. 2.2.1) is characterized by three process limits:
Depending on the material, the maximum true strain of � = 1.6 can be
achieved. The upsetting ratio h 0/d 0 (height to diameter of the starting
workpiece) may not exceed 2.3 for single pressing, 4.5 for dual pressing
and 8.0 for triple pressing, as otherwise buckling may occur and the
fiber flow is interrupted (cf. Fig. 6.2.1). The maximum die pressure is
2,300 N/mm 2 .
In contrast to upsetting in which the exterior contour and dimension
are free formed, in sizing the workpiece is fully enclosed (trapped
die). The same process limiting values exist as for free upsetting.
However, the same magnitude of the upsetting punch load is reached at
lower levels of deformation, as the material leans against the die wall.
6.5.7 Lateral extrusion
Lateral extrusion generates shapes with flanges, collars or other geometric
features (teeth, protrusions), whereby the die opening which
gives the workpiece its shape remains unchanged during the entire
forming process (cf. Fig. 6.1.1). This is achieved by closing the dies with
a high force before the slide reaches the bottom dead center. After the
dies are closed, the material is pressed into the impression by the penetrating
punch. It is possible to produce for example flanges with a diameter
ratio D 1/d 0 �2.5 in a single forming operation. The ratio between
flange thickness and starting s/d 0 should not exceed 1.4 because the
material may separate at the neutral surface.
The required forces are substantially lower than for upsetting, in particular
when pressing secondary geometric features. To date, the actual
force requirement has been estimated only through experimental tests.
Because of the state of compressive stress, acting on all sides, local
levels of true strain of up to � = 5 have been achieved using this nonstationary
process.
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
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