COREON - Faserinstitut Bremen eV

COREON:
Integrated heating system for water-soluble mandrels
Motivation / Aims
The use of lost mould mandrels enables a production process
where these mandrels can be released without residue by using
plain water. The material is made of a ceramic based granulate
combined with hollow glass balls and a chemical binder to form
the geometry. An additional advantage is, that even complex
component geometries with undercuts can be realized without
a division of the mandrel.
Mandrels from a porous moulding material are used to have a lower thermal conductivity
than metallic tools. The heating process can therefore be positively influenced. When warming
the cavity, a high temperature gradient in the mandrel material results in a heated outer layer
directly on the fiber preform.
To additionally counteract inhomogeneous heating through the outer cavity, the Faserinstitut
Bremen has developed an integrated heating system called COREON that generates a regulated heat emission at the surface of the water soluble mandrel.
Process
No additional element such as a heating coil or similar is added to the mandrel for heating.
Instead, the approach of the new patented method is to use the water soluble mandrel material itself as an electrical resistance heater. For this, the outer area of the mandrel is reinforced with an additive, which enables it to produce a defined or specifically varying electrical
conductivity in the mandrel material. The amount of locally adjusted electrical power which is
converted to heat emission, results from the locally adjustable thickness and locally adjustable
electric conductivity of the electrically conductive layer, which can be adapted to suit the local
heat requirement. The variation of the supplied electrical power results in a regulated heating
profile on the mandrel surface. Due to multi-layered construction, the heat in the edge layer is
also directly generated at the preform and only partly flows off into the inner mandrel, as the
thermal conductivity of the base material is very low.
Schematic view for
resistance heating of water
soluble mandrels
The process of heating a mandrel can be established by means of a thermo-electrical simulation. Furthermore, from the locally varying heat requirement that comes from the heating
profile at the component as a result of the external heating, an adjusted mandrel construction
is being derived. The calculated optimal layer structure of a mandrel can therefore also take
into account a complex cavity design and produce a homogeneous heating profile. A significant reduction of cycle time and temperature gradient at the cavity is achieved through local
adjustment of the emitted heat flow in the heating phases.
A temperature of 180°C can be achieved at the mandrel within three minutes (laboratory
scale) for curing resins for aircraft or automotive production.
Process Results
Due to low heat capacity the process is very energy efficient compared to the use of metal
mandrels:
Example for mandrel dimensions of
1000 mm x 100 mm x 100 mm
passively heated aluminum mandrel
COREON - Water soluble mandrel
heating system
27 kg
5 kg
Specific heat capacity
880 J/(kg K)
610 J/(kg K)
Heat up to 180°C
3800 kJoule
480 kJoule
2°C/min
40° C/min
Mandrel weight
Heating rate
For this example the following results are calculated at:
 Acceleration of heating phases by 95 %*
 Heating cycle acceleration by 45 %*
 Application of energy reduced by 85 % *
 Thermal mass reduced by 80 %*
*Compared to component manufacturing process by RTM with a passive heated mandrel insulated by
fibre preform (2K/min).
The porous structure of these mandrel materials must generally be sealed against resin penetration. This sealing consists of a PA film or adhesive tape coated with Teflon. Both sealing types
also offer electrical insulation that prevents the mandrel coming into direct contact with the
fiber material or the component. Therefore no additional expense is required to decouple the
mandrel from the remaining system.
Precise temperature control on the mandrel surface is achieved automatically by setting the
electrically conductive layer thickness and regulating the electrical voltage and current. The
laboratory tests were conducted at a voltage of ca. 15 volts, so that the system can be operated
safely.
Airbus Operations
ThyssenKrupp
Systems Engineering
Haindl Kunststoff
verarbeitung
Supported by:
Wirtschaftsförderung
Bremen
InnoWi
Contact person
Dipl.-Ing. André Stieglitz· Telephone: +49 (0)421-218-58657 · stieglitz@faserinstitut.de
Faserinstitut Bremen e.V.
The Faserinstitut Bremen e.V. is active in research and development tasks in areas of testing, development
and processing of fibres, textile preforms and carbonfibre reinforced plastics. The department of Composite Structures and Processes has its focus on the examination of continous process chains and the design
of components for aircraft and automotive industry and other industrial fields.
Faserinstitut Bremen e.V. · Am Biologischen Garten 2 (IW3) · D-28359 Bremen
Telephone +49 (0)421-218-58700 · Telefax +49 (0)421-218-58710 · www.faserinstitut.de
03/2012
Project Partners: