3 Fundamentals of press design

34 Fundamentals of press design
– presses for solid forming, such as forging, extrusion and coining
presses (cf. Sect. 6.8),
– presses for internal high-pressure forming (cf. Sect. 5.6),
– pressure forming, stretching and stamping presses.
Shears are also commonly used, generally in separate lines, for the manufacture
of sheet metal blanks (cf. Sects. 4.6.1 and 4.6.2).
3.1.1 Press frame
The function of the press frame is to absorb forces, to provide a precise
slide guidance and to support the drive system and other auxiliary
units. The structural design of the frame depends on
– the pressing force – this determines the required rigidity,
– the dimensions of dies influencing the size of the tool area,
– work area accessibility that determines on the shape of the press
frame,
– the degree of guidance precision. This influences both the shape and
the rigidity of the frame.
Presses with relatively low press forces, up to 2,500 kN, frequently make
use of the open-front press design (cf. Fig. 4.6.14). This construction is
characterized particularly by the easy access to the tool area. However,
its drawback lies in the asymmetrical deflection of the frame, which
contributes to reductions in part accuracy and die life, particularly in
blanking applications. Inclined or horizontal designs permit faster part
ejection making use of gravity following the forming process, for example
when forging or coining (cf. Fig. 6.8.20). As a rule, open-front presses
are used in conjunction with single dies.
Presses with a nominal pressing force over 4,000 kN are constructed
exclusively in a gantry-type design. These are known as straight-side
presses (Fig.3.1.1). In this press type, the press bed with the bed plate,
the two uprights and the crown form the frame. The application spectrum
of straight-side presses ranges from small parts produced using
progression dies, compound progression dies or transfer dies through to
individual dies for varying part sizes (cf. Sect. 4.1.1). When using progression
tools, the parts are conveyed by the sheet strip itself. Con-
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998