Development and manufacturing of cost efficient highly integrated composite structures

Christina Altkvist, Jonas Wahlbäck, Per Hallander, Tonny Nyman

Stockholm 2010-10-19

Flygteknik 2010

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Flygteknik 2010

Development and manufacturing of cost efficient highly integrated composite structures

Saab research activities has been carried out within the FP6 European project ALCAS

ALCAS – Advanced Low Cost Aircraft Structures

The objective is to reduce the operating costs of relevant European aerospace products by 15%, through the cost effective application of carbon fibre composites to aircraft primary structure, taking into account systems integration

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2010-10-19

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Agenda

Background

Material down selection

Airliner Wing Platform• Hot Drape Forming

• Manufacturing Center Wing Box Rear Spar

• Summary and Conclusions

Business Jet Wing Platform• Target and assumptions

• Manufacturing of Sub Scale Wing Box

• Testing

• Cost & Weight

• Summary and Conclusions

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ALCAS Overview

60 partners from 18 European countries

A total budget of 101.64 million euro

Duration: 2005-02-01 - - 2011-01-31

Coordinated by Airbus

Organized into four technical platforms

Airliner Wing Airliner Fuselage Business Jet Wing BJ Fuselage

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The Airliner Wing Platform

WP1.2 Lateral Wing Box

Global Spar deformation

Saab: Analytical prediction of deformation after curing for Lateral Wing Box Rear Spar

WP1.3 Centre Wing Box

Saab: Design and cost efficient manufacturing of Centre Wing Box Rear Spar

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A BJ Wing reference model was defined

The Business Jet Wing Platform

Saab (Sweden) Partner 4Partner 1 Partner 2

Four teams - four different technologies

Test set-up

Saab: Design and cost efficient manufacturing of BJ Sub Scale Wing Box with high level ofstructural integration

One shot curing

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Material down selection

For CWB Rear spar and BJ Wing SSWB cost savings can be achieved by

Less expensive raw materials → Investigate ”non aircraft grade” carbon fiber

Innovative prepreg processing methods → Investigate ”out-of-autoclave” cure

Less expensive prepreg handling & layup → Investigate ”thick plies” and use ATL

Initial concept

Prepreg system, MTM44-1 from ACG with an out-of-autoclave process. FAW=268 g/m2

Processing trials to

determine a suitable cure cycle and investigatelaminate quality when moving from thin flat laminateto thick complex structures

Back-up solution

Autoclave process with Airbus qualified prepreg system M21 Porosity problems in C-shaped spar

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The Airliner Wing Platform

Design, manufacturing and testing of an inner wing and centre wing box

Overall objective: 20% weight saving in the wing structure, with zero increase in recurring cost against the reference state-of-the-art metallic wing. 

Various composite materials and processes used indifferent components

Structural test will be carried out to validate the design

Saab: CWB rear spar

• Length: 2.5 m

• Web height: 0.9 m

• Flange width: 300 mm

• Thickness: 16-22 mm

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Hot Drape Forming Trials

Hot drape forming of flat laminates with fully interleaved layup was very challenging

ux = 0 along line

ux corresponding to 1% global strain

uy = 0 along line

Manufacturing concept:

Flat layup of a stack of prepreg

Hot Drape Forming on male tool

Curing in autoclave

Manufacturing trials to:

develop the HDF process and to investigate influene of lay-up sequence

A patch layup design preferable from a manufacturing point of view

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Manufacturing – Full Scale CWB Rear Spar

1) Manual Lay-up

2) Set up in female tool 3) After Curing 4) Loaded into assembly jig

Design: Monolithic inward facing ‘C’ section spar with fully interleaved lay up

Integration: Bolting selected for spar to skin attachment and for stiffener to spar attachment

Material: Prepreg T800/M21

Tooling: Invar/Steel female mould tools

Process: Hand lay up on male tool. Autoclave curing in female tool.

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Manufacturing Result Layup started in April 2007

Assembly completed in June 2007

Final inspection and delivery in September

Good geometrical tolerances with female tool

Waviness and porosity in some areas of the spar corners due to insufficient debulking of the lay-up

To verify the manufacturing process testing of travellers cut out from the spar was carried out.

This testing together with supporting stress analysis resulted in an approval of the rear spar.

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Summary and Conclusions

One piece C-spar with metal stiffener most optimal from weight- and cost point of view

Initial manufacturing with out-of-autoclave material gave raise to a high degree of porosity. Further development needed but tight time schedule made it impossible

Hot drape forming of prepreg material without wrinkles difficult in tapered areas when fully interleaved design rules applies

The female tool gives a good outer surface and the tolerance is more or less given by the spring back of the flanges. Machining of the outer surface is not needed. The height of the spar is controlled by using Invar in the web of the tool.

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PreambleThe Business Jet Wing Platform

Sub Scale Wing Box - SSWB

• Design a composite wing box with 10 % reduced weight and 20% reduced RC compared to a metallic reference.

• 4 teams – 4 different approaches.

• Common approach: High level of integration – less assembly.

• Demonstrate each technology through manufacturing and verification.

LRI ”Mix”RTM Prepreg

F7X

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Target and assumptions

• Manufacture a wing box with Skin, stringers and spars integrated and cured in one operation.

• Further cost reductions:

• Thick prepreg

• ATL Automated Tape Laying

• HDF Hot Drape Forming

• Design philosophy:

• No use of fasteners between upper skin and adjacent spars.

• To have rigid surrounding tools and ”adjustable” internal tools.

• Have Recurring Cost as top priority during the design phase.

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Manufacturing• Lay up started In mid January.

• Demolding end of January.

• Inspection and trimming in February.

• Assembly with metallic structure from end February to end of April.

• Strain Gauge installation beginning of May.

• Delivery to Prague for verification mid May.

• Notably: 4 month from manufacturing start to delivery.

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Manufacturing ResultComposite Box

Prepreg solution in combination with this tool concept seems to be robust.

• First attempt successful.

• Geometrical tolerances acceptable.

• Scale up should be possible. (Tools are low weighted)

• Both tool surface and ”bag” surface of smooth condition.

Laminate quality very good.

• No delaminations.

• No “porosity” detected. (Edge areas)

Rear Spar difficult to manufacture due to shape.

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Test and Test result.

Test started end of July 2009 and final testing was performed at lunch time 11 September 2009. 200% LL was reached without failure.

• Static and fatigue.

• To test the critical spar/skin splice area, artificial defects and Impact damages was introduced.

• Impact damages were introduced after the limit load test. No damage propagation was detected during the fatigue load session.

• The innovative design concept without fasteners between forward and rear spar and upper skin was verified by this test.

• Overall good agreement between the measured and predicted strain values from FEM.

Test set up in Prague

Two very satisfied engineers.

(Without helmets)

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Cost & Weight

• Cost and Weight Assessment is on going together with Dassault and involved partners.• Initial results indicated a rather high weight but on the

other hand, a very low cost which was in line with the design approach.

• The initial results were “considered” to include too much company specific skills and advantages. Due to this, efforts have been taken to harmonize the manufacturing values. (Common standardized values to be used for all 4 concepts)

• With harmonized values it can be concluded:• The prepreg box has the lowest manufacturing cost.

• The prepreg box has (together with Dassault’s LRI) the lowest weight.

• Number and type of fasteners have a huge impact on the total cost.

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Summary & ConclusionsThe Business Jet Wing Platform

Composite Box

• We do see a potential of this design concept specially from a cost point of view.

• With a redefined design principles we believe the weight could be reduced significantly.

Assembly

• The assembly cost could be reduced with use of more robotic drilling and relaxing of (harmonizing) sealing requirements.

Questions!Thank you for your attention!