Global Automotive Lightweight Materials
Applications of Adhesive Bonding To Enable
Joining Of Multi-Materials
April 25th 2013
©
Cars
Limited
©Lotus
Lotus
Cars
Limited
Daryl Greig
Introduction – Lotus Cars
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2
Overall Construction
Elise / Exige:
Volume: 1500 – 2000 p.a.
Tub:
Anodised aluminium
Upper:
Composite Panels
Rear:
Steel subframe – bolted
Front:
Composite front module – bonded
Evora:
Volume: 1000 – 1500 p.a.
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Tub:
Anodised aluminium
Upper:
Composite Panels
Rear:
Steel subframe – bolted
Front:
Aluminium front module – bolted
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Tub Construction
•  Semi monocoque tub concept
•  Multi material construction
•  No primer or overall paint finish
•  Bolted and bonded structural interfaces
•  3 types of Bonded joints:
• Al / Al, Elise/Exige
• Dow XD4600 single part heat cure
• 1.95kg adhesive, Evora 3.5kg
• Al / composite
•  Dow Betamate 2810
• Composite / composite
• Dow Betamate 2810
•  Panels bonded and bolted to complete BIW
•  Possible common features to higher volume multi material BIW
designs – depends on E-coat & paint provision
Kerb weights:
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Elise:
720kg (Mk1)
Exige:
1176kg
Evora:
1390kg
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Evora - Torsion and Bending Stiffness Contribution
Full GBIW
Bare Tub
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Stiffness
Torsion
kNm/deg
Bending
kN/mm
Baseline Roadster
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8
Coupe (GBIW)
26
10.5
5
Evora Structural Composite Panels
Key
CSM – Chopped strand mat
FV - Fibre volume
RTM - Resin transfer moulding
ICS - injection compression
system
UD - Unidirectional
Windscreen surround (WSS)
ICS/RTM 3mm-5mm Foam
cored
CSM and 0/90 UD Stitch mat
in A pillar and header. 23%
FV
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Roof panel ICS/RTM
2.5mm CSM and +/-45
UD Stitch Mat.
23% FV
Rear Bulkhead RTM
3.5mm CSM
23% FV
Body Side ICS/RTM 2.5mm-5mm.
Foam cored cant rail
CSM and 0/90 UD Stitch mat in A
pillar and cantrail. 22% FV
•
•
Bonded composite body panels are structural unlike Elise
Bonded to tub with Betamate 2800 series and large bond
areas
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Bonding Similar / Dissimilar Materials – Challenges
1. Joint design for functionality – Stiffness and strength
•  Design for load bearing joints
•  Predictive analysis of joints – static and dynamic behaviour at extremes of performance envelope
•  Testing to back up engineering – static / dynamic / high / low temp.
2. Pretreatment / Surface prep for Durability
•  Prediction of useful life through accelerated test
•  Component tests
•  Chamber tests – whole structures
•  Vehicle Test
•  Correlation to recognised standards of life – Welded steel to bonded aluminium
3. Manufacturing Process control & Repeatability
•  Substrate surfaces and surface preparation
•  Adhesive contact
•  Manufacturing variables – Extrusion, pretreatment, curing, open time, contaminants, transport…….
•  Tracability
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1. Design - Composite Front Module- Multi Functional Component
7.5kg, 75kJ absorbtion
Protects tub up to speeds of 25 mph
420mm crushable length
Replaceable in service
Front impact energy absorber –
0 deg, offset and 30 deg
Variable wall thickness front to rear
Cooling Module
support
Clamshell Support
Auxiliary light
mounting
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Radiator duct
intake / exit
Tow Bar Mount
Heater Intake
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Bonded Joint Design – A Closer Look
Section1 – Al/Al
Section2 – Al/ Composite
Section 3 – Comp / Comp
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Section 1 – Al / Al
Surfaces SAA anodised for pretreatment,
corrosion protection and visual finish
Bracing ribs
Interlock detail
for adjoining
extrusions
Spew fillet wiped
for moisure
expulsion
0.2mm Ribs Bond gap
control
Cutback detail for fastener
access and progressive
failure mode from front
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Mechanical
Fasteners – Riv
bonding
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Section 2 – Al / Composite
Corner load
distribution braces
Shear / compression planes
for joint
Bond gaps
controlled by
assembly
fixture
Mechanical attachment
plane
Design features aligned
correctly for load bearing
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Composites
Surfaces primed
for bonding
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Section 3 – Composite / Composite
Load bearing
corners – Hex made
of 2 mating sections
Low modulus adhesive with
large bond areas
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Bond gaps controlled by
assembly fixture
Composites Surfaces
primed for bonding
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1. CAE - Riv Bonding Development – Adhesive Strength
Correlation
Lap Shear Strength Analysis and Test
Dynamic Strength – Test data
Static Strength
– Test Data
Dynamic Test
Drop Rig
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Dynamic Strength
– FE Model Correlation
Upper Bound
Dynamic Strength
– FE Model Correlation
Lower Bound
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1. CAE - Riv Bonding Development – Adhesive Strength
Correlation
T Peel Strength Analysis and Test
Dynamic Strength
– Test data
Dynamic Strength
– FE Model
Correlation Upper
Bound
Dynamic Strength
– FE Model Correlation
Lower Bound
•
Upper and Lower bound values used in crash
FE models to envelope possible failure modes
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Static Strength – Test Data
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1.Tests for Joint Functionality – Box Joint Tests
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2.Durability and Life prediction
•  Technology project to develop bonded aluminium tub.
•  Set up to work with partners:
•  Suppliers:
Hydro, Ciba
• Technologists:
TWI, AEA, Alcan,
•  Key Universities
UK and Europe
•  Others
OEMs, Professors……..
•  Preliminary testing for adhesives, fastener and pretreatment selection
•  8 Major phases of core testing to Explore effect of manufacturing variables on performance
•  Confirmatory corrosion tests to complete correlation of life prediction and confirm production
specs for anodising, coatings , fixings, interfaces for galvanic protection and transport
packaging materials
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2.Durability and Life prediction
Stress Humidity & SWAAT
Proving Ground Rig Tests
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87 days
exposure
2. Durability - Link Proving Ground to Test exposure (Steel)
Component test
SWAAT / Stress
Humidity /
Dynamic impact
System test
Proving
ground
Vehicle test
Proving
Ground
Correlation
SWAAT / Proving
ground
Proving Ground
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2.Durability and Life prediction
Correlation – SWAAT to Proving Ground
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3.Manufacture
•  Supplier is a wholly owned subsidiary of Group Lotus - LLS
•  Supply chain for extrusions and surface treatment is tightly controlled e.g. SAA chemistries
controlled by manufacturing specification. Test parts bonded and tested with every batch
•  Adhesive contact – Adhesive robot applied to approved patterns for complete coverage
•  Tracability – Trace on adhesive, aluminium, pretreatment and curing. Parallel tests of parts with
every assembly made.
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The future at Lotus
•  Functional integration – Careful design
•  Sandwich materials – Lightweight and quiet
•  Overall mix of materials
•  Reasonable cost of ownership – service / repair
•  Credible supply partners
•  Tooling to allow adventurous design
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Conclusions
•  Multi material constructions are possible, even without e-coating and painting the final assembly
•  Bonding durability life can be simulated to an extent by accelerated ageing
•  Durability of bonded joints is achieved in real time exposure
•  Innovation in automotive architectures involves design innovation as well as materials technology
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END
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