3 Fundamentals of press design

80 Fundamentals of press design
– their nature inevitably results in a standardization process: the valve
blocks do not need to be redesigned for each different press,
– all the valves are brought together to create a functional assembly on
a single block,
– integrated valves are sensibly combined with space-saving, low-cost
auxiliary valves,
– troubleshooting is simplified by the presence of drilled-in functional
and test connections.
3.3.3 Parallelism of the slide
The capacity of the press frame to absorb eccentric loads plays a major
role. Eccentric forces occur during the forming process when the load of
the resulting die force is not exerted centrally on the slide, causing it to
tilt (Fig. 3.3.5). The standard press is able to absorb a maximum eccentric
moment of load of
M 0075 . m F kNm
= ⋅ [ ]
x N0
M Mx y kNm
2
= [ ]
via the slide gibs. This results in a maximum slide tilt of 0.8 mm/m. If a
higher off center loading capability is desired, then the press design
must be more rigid. In this case, the slide gibs will have greater stability,
the press frame will be more rigid, and the slide will be higher.
If it is not economically possible to achieve the allowable amount of
slide tilt within the required limits by increasing press rigidity, it is necessary
to use hydraulic parallelism control systems, using electronic
control technology (Fig. 3.3.5), for example in the case of hydraulic
transfer presses (cf. Fig. 4.4.14). The parallelism control systems act in the
die mounting area to counter slide tilt. Position measurement sensors
monitor the position of the slide and activate the parallelism control
system (Fig. 3.3.5). The parallelism controlling cylinders act on the corners
of the slide plate and they are pushed during the forming process
against a centrally applied pressure. If the electronic parallelism monitor
sensor detects a position error, the pressure on the leading side is
increased by means of servo valves, and at the same time reduced on
the opposite side to the same degree. The sum of exerted parallelism
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998