3 Fundamentals of press design

Hydraulic presses
F 4
I P
(F )
max
slide tilt
pressing force F1 parallelism
control
a (b)
x (y)
I P
Fig. 3.3.5 Control system for maintaining slide parallelism
F 2
center of die force
F= 1 F 2 + F3
with
F= F + F
3 4 5
control forces remains constant, and the slide tilt balance is restored.
Depending on the deformation speed, a slide parallelism of 0.05 to 0.2
mm/m is achieved. A central device adjusts the system to different die
heights by means of spindles at the slide.
Full-stroke parallelism control involves the use of parallel control cylinders,
with their pistons permanently connected to the slide (Fig. 3.3.6).
These act over the entire stroke of the slide so that no setting spindles
are required to adjust the working stroke. Two cylinders with the same
surface area, arranged well outside the center of the press, are subjected
to a mean pressure. The tensile and compressive forces are balanced out
by means of diagonal pipe connections. The system is neutral in terms
of force exerted on the slide. If an off-center load is exerted by the die on
the slide, a tilt moment is generated. The slide position sensor detects a
deviation from parallel and triggers the servo valve. The valve increases
the pressure on the underside of the piston acting on the leading side of
the slide, and thus also on the opposite upper side of the piston. At the
same time, the pressure in the other connecting pipe is reduced. The
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
F 5
(F )
min
displacement
monitoring
slide stroke
250 bar
81