3 Fundamentals of press design

Basic terms
cation of an exterior force. This requires surfaces to move directly against
one another under pressure, for example when upsetting and rolling.
Indirect application of force, in contrast, involves the exertion of a force
some distance from the actual forming zone, as for example when the
material is drawn or forced through a nozzle or a clearance. Additional
stresses are generated during this process which induce the material to
flow. Examples of this method include wire drawing or deep drawing.
In the direct application of force, the force F is given by:
where A is the area under compression and k w is the deformation resistance.
The deformation resistance is calculated from the flow stress k f
after taking into account the losses arising, usually through friction.
The losses are combined in the forming efficiency factor η F:
The force applied in indirect forming operations is given by:
F A k A k
A w
fm
id
= ⋅ wm ⋅ ϕg
= ⋅ ⋅ ϕg
= ⋅
η
η
where A represents the transverse section area through which the force is
transmitted to the forming zone, k wm is the mean deformation resistance
and k fm the mean stability factor, both of which are given by the integral
mean of the flow stress at the entry and exit of the deformation zone.
The arithmetic mean can usually be used in place of the integral value.
The referenced deformation work w id is the work necessary to deform a
volume element of 1mm 3 by a certain volume of displacement:
ϕ g
∫ 0
F = A⋅kw ηF = k
k
w = k ⋅dϕ ≅ k ⋅ϕ
id f fm g
The specific forming work can be obtained by graphic or numerical
integration using available flow curves, and in exactly the same way
as the flow stress, specified as a function of the deformation j g.
Figure 2.2.2 illustrates the flow curves and related work curves for different
materials.
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
f
w
F
F
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