3 Fundamentals of press design

3 Fundamentals of press design
3.3 Hydraulic presses
3.3.1 Drive system
Hydraulic presses operate on the physical principle that a hydrostatic
pressure is distributed evenly through a system of pipes, and that a pressure
p [N/m 2 ], acting on a surface A [m 2 ], produces a force F [N]:
The force acting on the slide of the press depends on the forming or
blanking process performed. For this reason, the pressure p acting on
the piston surface is also a function of the deformation process conducted.
Its measurement may be used directly to calculate the force acting
on the slide. The maximum slide force can be selected by limiting
the maximum hydraulic pressure through a relief valve at any position
of the slide.
The drive power P [W] of a hydraulic press depends on the volumetric
·
F = p⋅A flow of hydraulic fluid V [m 3 /s] and therefore on the speed of the slide
as well as on the hydraulic pressure p, the forces at the slide, and the
mechanical and electrical losses � ges:
V˙ ⋅ p
P =
η
In contrast to mechanical presses, there is generally no reserve of energy
available in hydraulic presses. Thus, the entire power must be
applied when carrying out the forming operation. For this reason,
hydraulic presses require a significantly higher drive power than in
mechanical presses, with comparable force capacity (cf. Sect. 4.4.1).
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
ges