3 Fundamentals of press design

4 Sheet metal forming and blanking
4.4 Sheet metal forming lines
4.4.1 Universal presses
Universal presses are characterized by their high degree of flexibility.
They are suitable both for blanking and forming operations (Fig.4.4.1).
In combination with individual, progressive blanking, compound and
transfer dies, this opens up a wide range of application possibilities for
the production of small to medium-sized parts (cf. Sect. 4.1.1). To
increase the number of formed parts and so enhance the cost-effectiveness
of the production process, universal presses are equipped with coil
lines (cf. Fig. 4.3.1), scrap disposal systems and stacking units for finished
products (Fig. 4.4.41). Fully automatic die change plays an important
role in ensuring economical production (cf. Sect. 3.4).
Comparison: mechanically and hydraulically driven universal presses
Generally speaking, universal presses are driven either mechanically or
hydraulically. In the case of mechanical universal presses, the movement
of the eccentric shaft is transmitted to the slide by means of the
connecting rod. Accordingly, the sinusoidal curve of the stroke is prescribed
by the geometry of the eccentric or crank shaft (cf. Fig. 3.2.3).
For a mechanical and a hydraulic press with a forming stroke of
approx. 100 mm, the stroke versus time, the time required for one work
cycle (cycle time) and the time available for part handling (transportation
time), are shown in Fig. 4.4.2. It is seen that the handling time
available is 2.4 s, the cycle time of the mechanical press is 3.6 s, so that
the corresponding stroking rate is around 17 strokes per minute.
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998