3 Fundamentals of press design

Mechanical presses
In crossbar transfer presses, flywheels of up to 2,500 mm in diameter
and a weight of 25t are used. The mounting and lubrication of this
type of flywheel in roller bearings are highly demanding, as a large
quantity of lubricant and continuous temperature monitoring are
required (cf. Sect. 3.2.11). The flywheel is driven by the main motor via
a flat belt or high-performance V-belt. When the main drive system is
switched off, the flywheel is brought to a standstill within a maximum
of 30 s by reverse braking of the motor and by an additional pneumatic
brake.
In isolated cases, normal car body presses and tri-axis transfer presses
are equipped with mechanical creep speed drive systems of one stroke
per minute. In this case, the drive is achieved by a threephase motor
acting on a worm gear which actuates the drive shaft via the brake
flange of the main brake. The transmitted torque generally falls short of
the nominal drive torque. However, by means of a pneumatic or
hydraulic servo system in the brake, the nominal force may be achieved
for distances of up to 10 mm. This is generally sufficient for set-up
operation.
3.2.4 Clutch and brake
One of the characteristics of mechanical presses is the clutch used to
transmit the motor and flywheel torque to the gear shaft and, after
clutch release, the brakewhich is used to decelerate the slide, the top die
and the gear. Particularly when working in single-stroke mode, the
masses in translational or rotational motion must be brought to a standstill
after every stroke within an extremely short time: 200 to 300ms for
large-panel presses and 100 to 150ms in universal presses. Conversely,
after engaging the clutch, the same masses must be accelerated from
zero to operating speed.
For safety reasons, braking is generated mechanically by spring power.
The clutch torque is calculated from the nominal press force and the
required working distance, generally 13 to 25mm above bottom dead
center.
Pneumatic single-disk clutch and brake combinations with minimum
rotating masses have been in successful use for decades (Fig. 3.2.7).
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
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