Schmelztauchveredeltes Feinblech.Hot-dip coated sheet.

Formability
All forming processes for the cold-rolled
steel can be used for hot-dip coated
sheets, if tool surface and geometry are
suited to these materials. The last finishing
operation of the tool surface must
take place in the direction of the sheet
metal flow. This also applies to the
drawing beads and draw radii. The
drawing opening and draw radius may
have to be somewhat enlarged. The tool
surface must be absolutely scratch-free
to avoid abrasion from the coating
which commonly occurs at high forming
unit cycle times. The abrasion can be
minimized by using a suitable drawing
aid or a phospate-treated strip surface.
If possible a thin metallic coating should
always be chosen, as far as the corrosion
protection requirements allow.
The resulting friction forces are significantly
lower than with cold-rolled sheet
of comparable roughness because of
the metallic coating. Thus the forming
efficiency is increased, which often
results in a higher limiting drawing ratio
or in a greater depth of draw. Due to the
lower friction, higher blank holder forces
Abrieb der Beschichtungen bei verschiedenen
schmelztauchveredelten Feinblechen
Coating abrasion of different hot-dip coated sheets
Abriebmenge/Mass of abrasion [g/m 2 ]
6
5
4
3
2
1
0
are required when deep drawing than
with cold-rolled sheet, with the result
that, although the applicable working
range shifts in terms of level, it is not
restrictive. Just as for cold-rolled sheet,
a certain roughness of the hot-dip galvanized
sheet surface permits optimal
production conditions and safe transportation
of parts through suction cups.
This roughness is adjusted during
temper-rolling.
Hot-dip galvanized sheet Galvannealed
is just as suitable for all deep drawing
processes as normal hot-dip galvanized
sheet. Due to the iron content in the zinc
layer, the frictional behaviour is more
similar to that of cold-rolled sheet.
Because of the higher frictional values,
smaller blank dimensions can be chosen
with stretch forming parts. The fact that
the zinc-iron layer is somewhat less
ductile than the pure zinc layer has to
be borne in mind when lubricating,
maintaining tools and designing the
radii.
All the above-mentioned criteria relating
to hot-dip galvanized sheet apply
correspondingly to GALFAN ® and
Werkzeugstahl gehärtet;
Ziehgeschwindigkeit = 6 m/min;
Schmiermittel: RP4107S;
2 g/m 2 Oberfläche
Hardened tool steel;
Drawing speed = 6 m/min.;
Lubricant: RP4107S;
2 g/m 2 surface
Kaltfeinblech/Cold-rolled sheet
Feueraluminiert/Hot-dip aluminized
GALVALUME ®
GALFAN ®
Feuerverzinkt/Hot-dip galvanized
Galvannealed
Galvannealed und vorphosphatiert/
Galvannealed and pre-phosphated
GALVALUME ® . GALFAN ® has especially
good forming properties because the
bending angle shows fewer hairline
cracks than hot-dip galvanized sheet
even with narrow radii. The reason lies
in the structure of the very ductile coating.
GALVALUME ® is more liable to
cracking due to the brittle ternary ironaluminium-silicon
layer. Usually these
fine hairline cracks, e.g. when roll-forming
with narrow radii, do not reduce the
corrosion protection, as here too the
zinc content in the coating protects the
steel underneath cathodically. Nor are
appearance and paintability diminished.
The formability of the various hot-dip
coated products is always the same for
comparable steel grades. Although the
values of the tensile test tend to be
worse for products with a harder coating,
i.e. galvannealed and GALVA-
LUME ® , the coating itself does not influence
formability. Because of a certain
sensitivity of the GALVALUME ® surface
to damage in general and especially with
regard to fingerprints, the surface
should be sealed during production (see
page 13). This sealing protects against
surface damage during forming and
against unsightly signs of handling,
works as a lubricant so that it can be
roll-formed without oil and reduces tool
abrasion. The sealed surface can be
painted without problem.
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