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Direct Processes have been developed in recent years. Resin Transfer Moulding (RTM), Resin Film
Infusion (RFI) and Vacuum Assisted RTM (VaRTM), also frequently called liquid resin infusion (LRI), are
probably the most significant processes to mention, of which many variants have been developed.
Typical Advantages of Direct Processes
• Potential for lower overall cost of finished parts
• Reduced lay-up times, trimming and assembly operations
• Integration of functions
• Savings in capital expenditure – reduced investment in refrigeration, automated lay-up equipment
and autoclaves
• Lower energy costs - refrigeration and heat cure not always necessary
• Shorter processing cycles
• Control of thickness and surface aspect in the mould
Hexcel has developed materials for the Direct Processing of composites for over twenty years, with much
of the work focusing on RTM for aerospace. RTM, RFI and VaRTM are Direct Processes, where the preshaped
reinforcement, commonly termed the preform, is placed in a mould, and then infused with the resin.
Hexcel’s Injectex® woven carbon fabrics and HexFlow® RTM6 epoxy resin have been widely qualified for
aerospace programmes around the world, and the use of Direct Processes is advancing further with new
aircraft programmes, such as the Airbus A380, which has Direct Process parts, including fittings, struts,
beams, spars, ribs and fuselage frames.
With plans for the next generation of aircraft to have full composite wings and even a composite fuselage,
cost and performance become key drivers. Recent breakthroughs have been achieved by Hexcel’s R&T
team and the new package of materials (reinforcements, binders and resins) for cost-competitive Direct
Processing methods is able to meet the overall requirements of primary aircraft structures.
Targeting the performance of the latest generation
UD prepregs, this new materials package allows
fibre volume ratios approaching 60% to be
achieved using an Out of Autoclave resin infusion
technology.
Man Technology has recently built a giant
booster demonstrator part for Ariane 5 using
1.2 tons of Injectex® reinforcements and
HexFlow® RTM6 resin.
RESIN TRANSFER MOULDING
RTM has the potential to produce high quality parts at lower cost than prepreg/autoclave based
processing
• Automated process for relatively high volumes
• Net-shape and close tolerance component fabrication
RTM is a moulding process in which catalysed resin is pumped into a matched mould in which a fibrereinforcement
known as a preform has been placed. The process is already well known for the
manufacture of composite components and is used in numerous applications. The RTM process has been
recognised as a cost-effective alternative to manual composite processes, traditionally used by the
aerospace industry for the production of selected secondary and primary structures. Hexcel has developed
a range of resins for this process along with a broad family of structural reinforcements.
3
Airbus A380 aileron spar, manufactured by Airbus
France (Nantes), using HexFlow® RTM 6 resin and
Injectex® woven carbon reinforcement.
Airbus A380 door hinge arm manufactured
by Eurocopter Deutschland GmbH using
HexFlow® RTM 6 resin and HexForce™
G0926 carbon fibre fabric. There are 16
door hinge arms on each A380. As well as
saving weight, they provide better thermal
insulation in the cabin, reducing heat loss.
4
ADVANCED FIBRE-REINFORCED MATRIX PRODUCTS FOR DIRECT PROCESSES
The RTM process is as follows:
1. The dry reinforcement is assembled and pre-shaped to resemble the geometry of the desired part,
which is called a preform.
2. The preform can be stabilised to make it handleable by applying a binder or by textile technologies
such as stitching
3. The preform may be consolidated by applying heat and pressure which activates the binder.
4. The preform is inserted into a matched mould
5. The mould is then closed and a full vacuum applied. A RTM resin system (which can be mono- or
bicomponent) is then injected into the tool. During the injection the resin fills the mould cavity and
fully impregnates the fibre preform.
6. Heat is applied to the mould, activating the polymerisation/curing mechanism of the RTM resin.
7. The cure is completed and the part develops sufficient strength to be demoulded safely when cooled.
Advantages of RTM
• Separating the moulding process from the fibre architecture allows the designer to create a uniquely
tailored material
• Good quality parts – tight dimensional tolerances
• Good surface quality on all sides
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