3 Fundamentals of press design

136 Sheet metal forming and blanking
of ongoing collision testing, which clearly contributes to the reduction
of errors. Jaw layout plans, die construction plans and single part drawings
can be made available by this system. The general use of CAD/CAM
systems in tool making have many inherent advantages that are linked
to the process. Therefore, in the medium term, CAD/CAM techniques
will be increasingly used to increase the total cost effectiveness of part
production.
Mechanical processing
Today’s technical possibilities in NC processing require ever more easy
to manufacture designs from the die designer. In particular the use of
five-axis milling machines allows to machine completely complex
castings with a single fixturing operation. In the past, because of
restricted conditions, extended operating and assembly activities were
carried out with fixtures and additional clearances. Today, for example,
three-dimensionally located sliding and guiding components can be
cast (Fig.4.1.17).
High speed milling (HSM) is used increasingly for machining of
sculptured surfaces in which economical cutting speeds of 2,000
m/min are attainable. Even strongly patterned surfaces for inner parts
can still be machined with medium feed rates of around 5m/min.
Cermets and special PVD-coated carbides are capable of attaining surface
qualities of R t = 10mm, which reduces the need for secondary manual
polishing to a minimum.
Assembly and try-out
More accurate machining and finishing operations together with the
above-mentioned advantages of a CAD supported die design, simplify
the assembly task considerably. The general processing of data gives
access to further theoretical and error-free blanking and contour information
without having to resort to the use of costly aids. The expert
knowledge of the qualified diemaker is, however, still necessary. In particular,
in the pre-run or try-out phases when the die developer tries to
produce a good part after the installation of the dies in the press, it
becomes evident whether or not the theoretical design effort has been
correct (cf. Sect. 4.1.5). Prototype tools or simulation methods provide,
of course, considerable help. There are, however, additional factors
which contribute towards the quality of the stampings obtained with
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998