72
Putting ideas into shape
SIEBER gained a name for itself, particularly through its founder Karl Sieber, who introduced new ideas for using ‘shrunk
tools’ in cold solid forming processes more than 50 years ago. Here Seiber explains the latest developments in its
technology.
Shrunk, pre-stressed tools were able to kind of induction process is used to provide the After 20 minutes the core temperature was
absorb far higher forces and this provided an heat. This allows the tool to be ready for use further increased to approx. 350°C and the
enormous boost to the cold solid forming within less than 5 minutes after a cold start temperature of the outer member was
sector. This has been part of standard technology and it guarantees almost real time performance adjusted by the same ratio. After 45 minutes,
for a long time now. The challenge today for open loop or closed loop control of the the temperature ratio was set at approx. 300°C
involves machining products with even greater diameter of the drill hole. to approx. 50°C, which creates a drill hole
degrees of precision, forming materials that In contrast to other solutions available on opening of only approx. 0.02mm. Despite the
have an even greater strength, coping with the market, which are only able to set the size 300°C in the core, the huge temperature
short entry curves and naturally introducing a of the drill hole by the initial stress that is difference of more than 200°C between the
greater degree of flexibility so as to be able to exerted, this concept largely enables the core and the outer member now provides a
produce smaller batches in an economical initial stress load to be maintained or used to greater degree of initial pressure, which makes
manner. extend the working area. the opening in the drill hole smaller.
The experiment uses a combined tool
where the core drill hole measures 27.8mm
and the diameter of the outer member
200mm. The graph on the right shows a test
run that lasted 75 minutes. The dark blue line
shows the temperature of the core and the
light blue line the outward temperature of the
outer member.
The temperature of the core was as high as
250°C after approx. 7 minutes. The temperature
of the outer member was set at approx. 80°C,
which means that the drill hole expands by
0.05mm. Tungsten carbide is used as the core
material. On the one hand, this tool concept opens up
Tungsten carbide would only expand by opportunities for handling new dimensions
approximately 0.035mm in the drill hole at and responding to process or material
these temperatures. By heating up the outer fluctuations in a much more flexible manner.
member to 80°C, the pressure on the shrink fit But it also allows users to gain access to a
Shrunk die – laboratory design
is reduced approx. by a further 20% and this new class of precision, integrated in a closed
enables the core to open even further by about loop. The closed loop also compensates for
It would be preferable if the tool, which 0.015mm. This means that the core drill hole the effect produced by the innate heat in the
needs to be very stiff, could be somewhat has already opened by approx. 0.05mm at process, i.e. start-up processes are much
more flexible, particularly to provide greater temperatures below 300°C. shorter.
precision or even cater for dimensions in a Given the temperatures that are reached,
closed loop in a sensitive and flexible manner
it is now possible to combine cold and
or be able to respond to material properties.
semi-hot forming processes, with the
Prompted by the process of pressing
result that other materials with higher
inserted gear tooth designs, where the cores
degrees of forming can now be used.
normally have to be remoulded – this is done
The prototype of this development
by altering the drilling dimensions to a minute
is currently being tested. The
degree in order to provide the necessary levels
company plans to offer a complete
of precision to cope with the effects of the
assembly group, which can be
material or the heat treatment processes – a
retrofitted to any press in a practical
tool concept has been developed where the
drilling process can be adjusted in a flexible
manner. A patent for the patent and
manner by up to 0.06mm without having to
the process has been applied for.
remove the tool.
This concept opens up a
This problem was resolved by heating and
completely new product group for
cooling at the same time to provide a shrink fit.
SIEBER and this will enable the
While the core can be heated to a temperature
company to continue the extremely
of up to 500°C, the outer member is cooled at
positive developments that it has
the same time to provide the shrink fit. A new Development team
enjoyed over the past 3 years.
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