3 Fundamentals of press design

Die design
ledeburitic 12 % chromium steels (1.2379) and carbides fully comply
with these requirements.
Coatings are applied mainly by specialized companies. This means
that particular attention must be paid to the preparation of dies by the
die manufacturer. Prior to coating, the work surfaces must be free of
grooves and polished to a surface roughness of R z < 1 mm. The limit for
optimum coating of internal holes is around l (length) = d (diameter)
when using the PVD technique. With the CVD technique, there are no
known limitations. The limits for the ratio between the diameter D and
thickness H of coated panels in cases where a “deflection” of < 0,02 mm
is required after treatment, are as follows when using the CVD technique:
D < 7 · H for steels and
D < 15 · H for carbides
and when using the PVD technique
D < 20 · H
It is only possible to coat pre-stressed dies in cases where the insert is
pressed out, coated and pressed in again after coating. In order to prevent
the formation of beads, sharp edges must be broken beforehand.
In cases where a mean deviation of the mandrel length L and diameter
D after coating of < 0.01 mm is required, the CVD process should be
used in preference for the following dimensions
L < 10 . D in the case of steel
L < 15 . D in the case of carbide
and the PVD process for the length
L < 20 . D
Reliable improvement in die life, as a result of coating warm forming
dies with the CVD or PVD techniques, has not been demonstrated yet,
classical nitriding and welding-on techniques are generally used to
enhance performance. The problem faced here is that the base materials
have lower degrees of hardness compared to the requirements of
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
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