JEC COMPOSITES MAGAZINE - Issue #86 - January/February 2014 - 46

tool

Innovative benzoxazine prepregs for tooling

In the summer of 2010, GKN Munich selected Airtech
Advanced Materials Group's Beta prepregs to manufacture
a carbon fibre composite stringer support tooling for the
production of Airbus A350 flap skins. Although this was only
a few months after the Beta prepreg materials had been
launched at the 2010 JEC Exhibition in Paris, the decision to
select them was based on their strong technical and commercial benefits over the BMI tooling system which had
been used up to that point.
Philip Lunn,
Global Technical Manager,
Airtech Advanced Materials Group

he design of the stringer support
tooling was a relatively simple
U-section channel approximately
10 cm x 10 cm and 8 m long, with a
requirement for smooth and flat inside
and outside surfaces. In addition to the
demanding dimensional requirements,
the tooling needed to be stable during
autoclave cure at 180°C with 9 bar of
pressure. As the tooling was needed for
high-volume production, the selected
tooling material needed to demonstrate
long life at elevated temperatures to avoid
costly tooling repairs and rebuilds during
the production life cycle.

Tooling design
The tooling design placed great demands
on the composite materials. The tooling

sections had to be moulded off a male
tool to achieve a smooth, flat "A" inside
surface (Figure 1). Then the "B" external surface had to be post-machined to
achieve a smooth, flat and close-tolerance
surface. The composite material needed
to be moulded in a thick section without
a runaway exothermic reaction and then
be machined without delaminating or
twisting, and with an acceptably smooth
surface finish.
Another major consideration was the
amount of springback of the moulded
laminate. This is the phenomena where
moulded sharp angles spring in after curing, producing a dimensional mismatch
with the designed shape. Previous tools
produced by GKN with BMI tooling
materials had exhibited a springback of
the order of 1°; this could not be exceeded and any improvement was desirable.

Fig. 1: A section moulded on a male tool - Courtesy of GKN Munich

46 jec composites magazine / No86 January - February 2014

GKN planned to build the U-section
composite tooling in-house as they had
the expertise available. However, more
than 100 tools had to be built and the
company wanted to limit the impact on
production by only using the autoclave
on weekends.

Resin technology
The Airtech Beta prepreg is a composite
tooling prepreg that uses the latest benzoxazine resin technology from Henkel.
Airtech and Henkel started working
together on applications for benzoxazine
technology in 2005, which resulted in
the launch of the Beta 8610 film adhesive that was immediately adopted by a
major airframe manufacturer for bonding
large BMI tooling assemblies. After the
successful launch of the Beta 8610 film
adhesive, Airtech continued to work with
Henkel to optimize the technology for a
tooling prepreg material for the manufacture of carbon composite moulds.
Airtech Advanced Materials Group proposed the Beta prepreg to GKN Munich
as a solution providing technical and
commercial benefits including:
- Outstanding toughness, high temperature stability and high Tg
- Low resin shrinkage

JEC COMPOSITES MAGAZINE - Issue #86 - January/February 2014

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #86 - January/February 2014