application report BMW0 pages

Technical article: Conversion enables early detection of faults in BMW‘s light metal die casting

Josef Gibis, Helmut Ambros - January 2014

Conversion enables early detection of faults in BMW‘s light metal die casting

Sliding gate valves optimise the process reliability of light metal die casting
In low pressure die casting, e.g. light metal
engine blocks, the casting machines are filled
by pressurising the furnaces. This requires
highly precise pressure control along defined
pressure curves in order to be able to produce
a high quality casting and, for example, to
prevent the metal pillars from moving around
in the mould. In each case, BMW replaced the
pressure control previously used for this purpose in its Landshut light metal foundry with a
single sliding gate valve from Schubert & Salzer
Control Systems. The outstanding control quality
and the rapid reactive ability of the sliding gate
valves have allowed the pressure head curves
to be followed in a precisely reproducible manner.
In addition, they offer the possibility of compensating for process influences when furnaces of
different sizes are used.
In the low pressure die casting process, the casting
furnace is pressurised so that the molten metal flows
up a riser tube into the casting machines. To ensure
that the complete shape of the part is filled uniformly,
it is absolutely essential to have a controlled rise in
pressure. The pressure profile is crucial for quality in
the casting process.
Sensitively adjustable pressure control is needed in
order to reproduce these pressure curves time after
time. It not only prevents pressure fluctuations, but
also facilitates different mould filling speeds to optimise
the filling of castings with different cross sections.
BMW has all-round know-how in this area and is
achieving a high degree of success in working with
precisely defined casting pressure curves for the
different versions of the component parts. Previously,
a so-called valve organ with 13 digitally actuated
valves of different sizes had been used to follow
the pressure curve. While this pressure control was
precise, there was a problem in that it was not
immediately evident when a valve failed. The critical
issue here was that the pressure curve was no
longer being followed according to the reference
data andthe operator was not in a position to detect
this. Therefore, a valve failure of this type could only

be picked up by defects in the finished casting.

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Josef Gibis, who has worked at BMW for 25 years
and is currently the person responsible in Landshut
for process development and design in the area
of light metal foundry work, could not rest with this
constraint. He searched for a valve solution that offered
more process reliability. This would have to
display a high level of quality with a very rapid control
response,
detect faults itself and flag them up immediately,
be low on maintenance and
offer a good price-performance relationship.
The company HISTA Elektroanlagenbau GmbH in
Neutraubling, charged with the job of upgrading the
foundry operations and developing new software
for the comprehensive control processes, proposed
that the 8021 sliding gate valve from Schubert &
Salzer Control Systems, used already in other facilities,
should be used here.
Flow-related advantages and variable Kvs values
The sliding gate valve offers a simple opportunity to
modify the valve operating characteristics, which is
the Kvs values as a function of the valve opening,
almost infinitely. This can be done simply and in
almost any conceivable number of ways by an
appropriate configuration of the shape of the slit in
the sliding discs.
After just two short project discussions on site,
Schubert & Salzer‘s specialists calculated a Kvs
value of 1.7 for BMW‘s foundry in Landshut.
However, since different sizes of furnaces ranging
from 1,000 to 2,500 kg serve a casting facility interchangeably, making it imperative that any process
effects would have to be compensated, the sliding
gate valve was selected at a Kvs value of 5 on an
equal characteristic. As a result, not only does the
sliding gate valve make it possible to follow the
pressure curves precisely but it also has sufficient
capacity with a larger opening to react to leakages,
yet still be able to meter to the finest degree
possible.

Technical article: Conversion enables early detection of faults in BMW‘s light metal die casting

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