3 Fundamentals of press design

142 Sheet metal forming and blanking
4.1.3 Die materials
The processing of high strength sheet metal, which is becoming more
widely used in stamping technology, calls for higher pressing forces.
This means higher loads on the dies and greater overall wear on the
tools. In order to meet the requirements for long die life, while maintaining
acceptable component quality, special materials – most of
which have been hardened or coated – must be used in the construction
of the dies. The basic structure of different types of dies and their
most important components are shown in Figs. 4.1.16 and 4.1.17.
Table 4.1.2 lists the various components of dies used for drawing,
blanking, folding and flanging as well as the materials used to manufacture
them. Table 4.1.3 lists various surface hardening processes and
coating methods for dies. Coatings, for example through hard chromium
plating, can improve the sliding characteristics in deep drawing, so
that the need for lubrication is greatly reduced.
4.1.4 Casting of dies
The casting process is one of the steps in the overall process of manufacturing
production dies for sheet metal forming where the highest
standards are required by die makers. In contrast to castings used in
general machinery manufacture, in die manufacture, multiple usage of
a model is not possible, as no two tools are exactly the same. A disposable
pattern made from polystyrene (polyester, hard foam) is therefore
used for the die casting process (Fig. 4.1.18).
The casting is carried out as a full form casting process: the polystyrene
pattern stays in its resin-hardened quartz sand form. The liquid
metal, which is poured in, evaporates or rather melts the pattern. With
the full form casting process, the foundry industry has developed a production
method which offers a large measure of design-related, technical,
economic and logistical improvements in die making. For the
designer, there is the possibility of precise measurement and functional
control, as the full form pattern is identical in shape to the piece being
cast. Product development is made easier, as the pattern can be altered
without any problems by means of machining or gluing processes.
Furthermore, the costs of core box, core production, core transport and
core installation are reduced.
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998