Perforated metal sheets - Production process
Sectional presses
Sectional presses can perforate single metal sheets which are fixed on a
progress table. Metal sheets are larger than the tool. After the first
longitudinal perforating pass, there is a lateral displacement which has
the same length of the tool. At this point a second perforating pass is
performed; the second pass is followed by another lateral displacement,
and so on to reach the full perforation of the metal sheet.
Pros of this system:
- great versatility of the presses;
- perforated and/or unperforated areas (even very patchy ones, e.g.
disc-shaped) can be made;
- Reasonable tooling cost;
- Very thick metal sheets can be perforated,
by reducing the number of punches and by increasing the passes;
- quick preparation of the machineries;
Cons:
- long perforation times, and thus high incidency of labor costs;
- coils cannot be perforated;
- high investment cost.
Sectional presses are basically used for small series, high thickness,
very irregular perforated areas.
Perforating lines
Pitch-to-pitch feed presses, or "perforating lines" consist of:
-
an unwinding reel with straightener;
-
an
all across
perforating press
-
a shearing machine for lengthways cuttings or a winding reel.
The tools on these presses cover the entire width of the strip (or coil)
that is dragged thanks to feeding rollers in couples.
Every down stroke of the tool is followed by a movement of the rollers,
which corresponds to the perforating pitch.
When the plate reaches the desired length, the equipment stops working
and the shearing machine cuts the plate.
If on the contrary an
uninterrupted perforated stripe is required, the shearing machine is
disconnected and the metal strip is re-winded thanks to a suitable
winding reel.
This system has the merits of...
-
having a great perforating speed (and thus reduced costs of labour);
-
making possible the perforation from coils (resulting in lower raw
material costs);
- making possible the
supplying of metal sheets with or without edges on the short sides;
... and some drawbacks:
-
high tooling cost;
-
limited possibilities of irregular perforated areas;
-
limited possibilities regarding the thickness of the sheet to be
perforated;
- relatively high costs
of the line setting.
Perforating lines are mainly used for large series, to obtain continuous
perforated strips, and on thin and medium thicknesses.
Flattening of perforated metal
sheets
Perforation
causes
tensions to the
metal sheet,
deforming it. It is therefore necessary a subsequent flattening performed by
suitable multi-cylindrical flattening machines. For large metal sheets,
wide unperforated areas, broad or irregular edges, or materials that are
very hard or with “difficult” perforated areas, the tension can be so
strong to compromise the flattening process. Perforated metal strips
winded in coils are not flattened, therefore when the coils are unrolled
the flatness is not guaranteed.
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