Development and Application of Thermoplastic Welded Structures

The information in this presentation is proprietary and confidential and shall not be disclosed to or

used by a third party unless specifically authorised by the relevant GKN plc group company.

Development and Application of Thermoplastic Welded Structures

3AF – Association Aéronautique et Astronautique de France| June 13th, 2018

Michel Brethouwer GKN/Fokker Aerostructures

Lead Stress Engineer Papendrecht, The Netherlands

Proprietary and confidential restrictions on title slide apply throughout this presentation

Acknowledgements

The following persons have contributed to the information included in this presentation:

Arnt Offringa Head of R&D Department GKN/Fokker Hoogeveen (NL)

Jaap Willem van Ingen R&D Engineer GKN/Fokker Hoogeveen (NL)

Marco Doldersom R&D Engineer GKN/Fokker Hoogeveen (NL)

Johan Meuzelaar Lead Stress Engineer GKN/Fokker Papendrecht (NL)

Sylvain Chabot M&P Engineer GKN/Fokker Papendrecht (NL)

3AF – Association Aéronautique et Astronautique de France 2


Overview of GKN


Mexico

4 locations

China

2 locations

Landing Gear

Electrical and Wiring

Services

Aerostructures

Office locations

USA

26 locations

Netherlands

7 locations2 2 1 3

2 2

1 1

India

2 locations1 1

Romania

2 locations2

Turkey

1 location1

Belgium

1 location

Canada

1 location

1

Singapore

1 location

Thailand

1 location

United Kingdom

8 locations

1 4 3

Sweden

4 locations2

Norway

1 location

1

Germany

1 location1

Engine Systems

Transparencies

and Special Products

13 1 2 71 2

2

1

1

12015 sales

£3 billion*

Number of employees

17,000

Number of locations

62 in 15 countries

* 2015 sales include Fokker

Fokker Aerostructures

The Netherlands


GKN/Fokker Aerostructures – Hoogeveen, The Netherlands



Characteristics of Thermoplastic Materials

Part manufacturing by consolidation is a (reversible) ‘melting’-process

Unlimited storage of pre-production material at RT-conditions

Matrix material is typically tougher than epoxies, good out-of-plane properties. Beneficial for;

GIC & CAI

Post-buckled structures & acoustic fatigue resistance

Moisture uptake is typically less than expoxies, with more favorable EKDF

Manufacturing of composite parts by;

Consolidation

Press-forming (using pre-forms)

Welding & co-consolidation


Great benefit in relation to efficient part-integration:

Reduction of assembly cost and lead-time

Allows for optimized conceptual design for low weight


GKN/Fokker Roadmap - Development of Thermoplastic Structures


20001990 2010

A380 wing

fixed

leading

edges

First large

scale

assembly:

Welded fixed

wing leading

edges A340

Glass/PPS

First

welded

assembly:

MUC door

Fokker 50

Carbon/PPS

First

primary

structure:

bonded

GV

pressure

floors

First series

production:

press-formed

Dornier ribs

Carbon/PEI

First co-

consolidated

torsion box,

AW169

First Induction

welded

control

surfaces,

G650

Carbon/PPS

Co-consoli-

dated floor

beam

Carbon/PEKK

Ca/PEKK

CS2 ALFA

NLF HTP C/PEKK Demonstrator

2012 2018

Induction

welded

control

surfaces,

Falcon

Business Jet

Single Aisle

Rudder Skin

C/PEKK HTP Stiffened Skin

C/PEKK Fuselage Panel

Conduction Welded Frames


Welding of Thermoplastic Materials

The welding of thermoplastic structures allows;

Reduction or elimination of costly mechanical fasteners:

No drilling & countersinking of holes

No placement of fasteners

More weight optimized conceptual design

The following thermoplastic welding processes are applied at Fokker;

Ultrasonic welding

Resistance welding

Induction welding

The following thermoplastic welding processes are currently under development at Fokker;

Conduction welding

Resistance welding 2.0



Ultrasonic Welding

Main applications:

Fast joining of inserts to CFRP Floorpanels

Ply fixation during hand lay-up of Glass/PPS semi-preg plies

Features:

Established and robust technology

Locally applied, less suited for long welds



Ultrasonic Welding – Joining of Inserts


Joining of inserts to CFRP Floorpanels


Ultrasonic Welding – Ply Fixation during Hand Lay-Up


Accurate ply positioning using

Laser Projection System (LPS)

Ply fixation using ultrasonic ‘point’-welding


Resistance Welding

Main applications:

Airbus A340-500/600 Fixed Leading Edge J-Nose (inboard section)

Airbus A380-800 Fixed Leading Edge J-Nose (mid / outboard sections)

Features:

Joining of non-electrical conductive materials;

Thermoplastic glass material

Thermoplastic carbon material with insulation between heating element and carbon fibers

Heating element: metallic grid or wire at joint-interface heated by an electric current

Weld-line can be curved but weld-length is currently limited (electric voltage limitation)

Foreign material (metallic wire) remains at joint interface

Simple welding equipment



Resistance Welding


+

-Glass laminate

Weld strip

Weld pressure

Electric current

Glass/PPS Rib

Glass/PPS Skin

Weld-strip is placed between the thermoplastic parts

Electric current heats the joint from the inside

Weld-strip remains in the welded joint

No further rivets are required

(except at weld-ends where applicable)


Resistance Welding at Fokker: In Production Since 2000


A380-800

Fixed Leading Edge J-Nose

Significant weight reduction achieved against acceptable cost-level


Resistance Welding process: A380 FLE J-Nose


Welding of multi-rib stiffened Leading

Edge Skin;

Joining of Glass/PPS Ribs and Skin

Simple welding equipment

Curved weld-line

No bolts needed

Elimination of shimming


A380-800 Fixed Leading Edge J-Nose Assembled to Wing


Fixed Leading Edge J-Nose

A380-800


Resistance Welding of Carbon/PPS: Development


+

-Carbon Laminate

Insulated Weld Strip

Carbon/PPS Rib

Carbon/PPS Skin

Insulated weld-strip

Welded joint

Due to electric conductivity of carbon, electric insulation of

weld-strip is required to prevent short-circuit (current leakage)

Most robust solution developed: insulation of metallic mesh

weld-strip with glass-layers

Drawbacks of this solution;

Welding-strip is difficult to industrialize due to cost

Additional glass-insulation layers add weight to the joint

Applied to single Fokker 50 MUC, not further industrialized


Induction Welding

Main applications:

Gulfstream G650 Elevators & Rudder

Dassault Falcon F6X Elevators & Rudder

Features:

Based on KVE Composites Group patented technology liscensed to Fokker, industrialized by Fokker

Material to be welded requires to be electrically conductive with resistive nodes (fiber-crossings)

Heating element: induction head (coil / ‘torch’) to deliver an alternating magnetic field at weld area

Magnetic field induces an alternating current in the carbon fabric creating resistive heating allowing the

thermoplastic parts to fuse together

No foreign material at joint interface (no inclusion of separate welding-strip)

No contact between heating element and material (no imprint visible after welding)

No weld-length limitation

Highly automated process significantly reducing assembly cost, but more complex and heavy weld-tooling



Induction Welding


Generated

heat

Alternating

current in

C/PPS

laminate

Induction coil

C/PPS

laminate

Alternating magnetic field induces alternating current in

laminate

Alternating current generates heat within carbon fabric

due to joule heating (resistive heating)

Weld direction

Temperature vs time in a weld

0

50

100

150

200

250

300

350

400

0 25 50 75 100 125 150 175 200

Time [sec]

Tem

pera

ture

[oC

]

14C/s

5C/s

2C/s

2C/s

Resistance weld

Induction weld


0

50

100

150

200

250

300

350

400

0 25 50 75 100 125 150 175 200

Time [sec]

Tem

pera

ture

[oC

]

14C/s

5C/s

2C/s

2C/s

Resistance weld

Induction weld

Time [sec]

0 25 50 75 100 125 150 175 200

400

350

300

250

200

150

100

50

0

Tem

per

atu

re[º

C]


Resistance weld

Induction weld

Time [sec]Tem

pera

ture

[ºC

]

Temp vs time in a weld


Research on Induction Welding of Carbon/PPS (2006 – 2008)


A KVE Composites Group patented induction weld set-up was used to perform research on feasibility on induction welding technology on thermoplastic Carbon/PPS moveable structures

No metal weld strip

C/PPS skin

C/PPS rib


Research on Induction Welding of Carbon/PPS (2007)


A typical Torsion-Box section 1.2 [m] x 0.7 [m] was designed and built

Feasibility was successfully demonstrated and it was decided implement the induction welding technology as joining method for Carbon/PPS Moveable Torsion-Box Parts

KVE Composite Group weld technology was licensed to Fokker


Induction Welding Tool Principle

3AF – Association Aéronautique et Astronautique de France

Weld jig contour boards contain

slots for the induction coil at rib and

beam positions

The contour boards define the

outside of the product

The rib or beam is pressurized from

the inside

The coil is moved by a robot

A heat sink cools the outside of the

skin


Industrialized Full-Scale Development – Business Jets Moveables


Robot installed on a 24 [m] track

Fully automated welding process

Significant assembly lead-time reduction per ship-set


Optimal Conceptual Design of Elevators & Rudder

High torsional stiffness;

Control surface effectivity

Flutter behavior

Low bending stiffness;

Low hinge interface loads (as a result of enforced displacement by HTP or VTP)

Sufficiently high to tolerate single hinge-failure

Low weight;

Multiple rib chordwise stiffened post-buckled thin skin with stable sub-structure allows weight

efficient compliance to the above conceptual requirements;

Post-buckled skin reduces bending stiffness (occurence of shear-buckles above flight loads)

Chordwise stiffnening maintains aerodynamic profile

Shear stiffness is maintained

Challenge to produce such a multiple-part concept against acceptable assembly cost and lead-time





Highly automated induction

welding of ribs and spars to skins

C/PPS Spars: Autoclave

consolidation on male tool

C/PPS Skins:

Autoclave consolidation

C/PPS Ribs:

Press-formed flat laminates

Press

Industrialized automated induction

welding assembly tooling




C/PPS induction welded Torsion-Box:

1. Torsion-Box Skins

2. Front Spar

3. Rear Spar

4. Torsion-Box Ribs

C/PPS removable bolted parts:

5. Leading Edge

6. Trailaing Edge

Aluminium parts:

7. Leading Edge Ribs

8. Hinge / Actuator Brackets

9. Hinge Brackets


Parameters Influencing Quality of Induction Weld

Heating profile during welding process;

Weld peak-temperature to achieve good melting conditions

Specific window of temperature & time to obtain good entanglement of the PPS chains

Cooling-down rate of weld-bath to achieve semi-crystalline PPS

Weld-bath position relative to web / radius of rib;

Weld-bath center corresponds to position of induction coil (guided by weld-tooling in all directions)

Weld-bath width is a function of temperature

Gaps between the parts before welding;

Welding process can accomodate different gaps during welding to a certain extent

This control accurate assembly dimension after welding

Flanges of internal parts are pressured form inside

Skin controlled by contour boards on outside



Heating Profile During Welding Process


Weld-peak temperature

(to achieve good melting conditions)

Window of temperature & time

(to obtain good entanglement of PPS chains)

Cooling-down rate

(to achieve semi-crystalline PPS)


Effect of Weld Temperature on Weld-Bath Width


Relation between weld-bath width

and weld peak-temperature

Weld-bath width measurement example: phased-array

scan of an induction weld (with thermo-couples)


Full-Scale Welding Qualification Test

After released weld-tool and equipment available;

Pre-production component is manufactured

Thermo-couples are installed in each weld (around 5 per weld)

All weld recipes are verified by measuring and recording weld temperatures

After welding, full assembly is NDI scanned and melt-bath is measured

Coupons are machined from pre-production component and strength tested in peel to verify weld-strength

and process

After successful manufacturing & confirmation the weld-process is qualified for series production


C-Scan of Rudder Rib-to-Skin welded

joints including thermo-couples


Quality Control of Induction Welding in Series Production

NDI;

100% NDI is performed on all welds

Recording of coil power consumption and weld-speed per weld

Relationship between weld-bath width and temperature is used, i.e. weld-bath width is measured through

NDI as demonstration of suffient applied temperature and weld-joint integrity

In-Process control: Test welds on regular (sampling) basis are performed to monitor process over

time to detect unknown variables and demonstrate consistent weld-strength and process



Test-Pyramide Welded Joints: Carbon/PPS


Sonic Fatigue ‘shaker’ Tests

Peel & Shear Welded Joint

Static & Fatigue Tests

Lightning-Strike Test

Full-Scale Component Test

Open Hole, CAI &

Single Lap-Shear Tests

Fokker approved material

Qualification by supplier

Coupon Level

Element Level

Detail Level

Sub-Component Level

Component Level

Lamina & constituents (fiber / resin)


Conduction Welding – Under Development

Targeted applications (in research status):

Thermoplastic Carbon/PEKK Fuselage Panels with welded frames

Thermoplastic Carbon/PEKK Moveables (Flaps & Control Surfaces)

Features:

Also applicable to thermoplastic Carbon UD-tape material (in addition to fabrics)

Heated stamp: provides external heating and pressure

No foreign material at joint interface (no inclusion of separate welding-strip)

Contact between heating element and material

Tooling requires more space-envelope (to apply heat & pressure)

Potential for highly automated process significantly reducing assembly cost



Conduction welding

C/PEKK: Ortho-Grid Fuselage Panels


Automated Fiber Placement of Skin (AFP) Ortho-grid fuselage panelCo-consolidated butt-joint


Conduction Welding of Frame to Ortho-Grid Panel


Grid Blade-Stringer

Ortho-grid fuselage panel

Frame

Automated conduction welding process

Welded frame to ortho-grid panel,

no additional fastners added


Possible Future Applications of Conduction Welding


Welding of rib- and spar

webs to ortho-grid skins


Summary & Conclusions


Application of composite structures offers opportunities to weight optimize conceptual designs,

but traditionally came at a higher cost

Innovative solutions have been and must be continuously developed to reduce part-

manufacturing cost and assembly cost & lead-time

Application of thermoplastic materials can support the realization of optimized conceptual

designs at acceptable cost-levels;

Unlimited storage at room-temperature, no clean room required

Cost efficient production of high part-counts by press-forming, i.e. stiffeners and ribs

Good out-of-plane properties and more favorable EKDF

Cost efficient integration of parts by means of co-consolidation & automated welding processes

Further development of welding technologies ongoing

Thermoplastic composite materials are maturing from secondary structure to primary structure

Challenge: expand application of thermoplastic materials on primary structures

Development and Application of Thermoplastic Welded Structures

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