JEC COMPOSITES MAGAZINE - Issue #100 - Special JEC Asia - October 2015 - 51

adjustability of microwave absorption,
reached by this method, can be seen in Figure 5. Through consequent development of
absorbing layers and the according tooling
technologies, the huge benefits of microwave heating regarding heat-through time,
heat-up rates, and energy consumption can
be used freely. With its ongoing work, the
LCC will contribute to this aim. n
More information:
www.ifb.uni-stuttgart.de
www.lcc.mw.tum.de
Fig. 5: Adjusting the dielectric properties of epoxy resin by addition of different particles with varying
filler contents

is made possible. The next step to exploit
the potential of microwave heating for
composites involves tooling concepts
and design guidelines for complex parts.
Since the microwave applicator can only
generate a homogenous electric field,
the heat input into different part areas
has to be adjusted by the tooling used.
Summarizing, the main challenges are
the right set of mind, a controllable
multi-mode microwave applicator, and
adaptable tooling. Since the first comes
with time, the second is already overcome, the last is the final stepping stone
to introduce this promising technology
into widespread industrial use.

Tooling technology: a key factor
for microwave success
While the direct interaction between the
microwaves and the material enables fast
heat-up rates with a higher temperature
homogeneity for simple parts, this direct
interaction causes temperature differences in complex parts. Industrial products,
however, not only consist of flat or uniform
parts, but of parts with variable thickness,

with radii, or several combined materials.
For the cure of such applications, the right
tooling is the key to success in microwave
curing. Thicker areas of the part absorb
more (or less) energy, different materials
don't show the same heat-up characteristics, and bends and radii have a higher
irradiated area and therefore absorb more
energy. Potential temperature inhomogeneities can be countered by introducing
shielding and absorbing areas into the
mould. For the latter, absorbing layers with
properties according to the part's thickness,
the part's geometry, and the local thermal
conductivity and capacity can be attached.
The shielding can be achieved using a
closed conducting layer, i.e. a metal film.
Considering the flexible tooling concept
needed to achieve temperature homogeneity in any circumstances, the LCC works
in close collaboration with the Institute
for Pulsed Power and Microwave Technology (IHM) of the KIT to manufacture
adaptable absorbers. In order to tailor these
absorbing layers for tooling applications,
different particles are mixed in varying
volume contents into epoxy resins. The

Acknowledgements
The authors would like to acknowledge
Vasileios Ramopoulos (KIT) for his support
in measuring the dielectric properties. The
research and development project that
made this work possible was funded by
the German Federal Ministry of Education and Research (BMBF) as part of the
SME-Innovative: Resources and Energy
Efficiency funding action (funding number
02PJ2130) and managed by the Project
Management Agency Karlsruhe (PTKA).
This work would not have been possible
without the research and development
project supported by the public sector and
the participating companies.
References
[1] Meredith RJ. Engineers' handbook of
industrial microwave heating. London:
Institution of Electrical Engineers; 1998.
[2] Thomas Herkner. Microwave curing of
composites: The 25th annual international
SICOMP conference. Pitea Sweden; 2014.
[3] Link G (ed.). Faserverbund-Leichtbau
mit Automatisierter Mikrowellenprozesstechnik hoher Energieeffizienz (FLAME):
Schlussbericht des BMBF-Verbundprojektes. Karlsruhe: KIT Scientific Publishing;
2015.

No100 October 2015 / jec

composites magazine 51

http://www.ifb.uni-stuttgart.de http://www.lcc.mw.tum.de http://www.eastmancuts.com

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #100 - Special JEC Asia - October 2015