Low Carbon Vehicle Technology Project (LCVTP) · PDF fileROPS – reinforced A-pillar ....
Transcript of Low Carbon Vehicle Technology Project (LCVTP) · PDF fileROPS – reinforced A-pillar ....
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Low Carbon Vehicle Technology Project (LCVTP)
WS 7 Lightweight Structures - Technology Review
November 17th 2011
Geraint Williams
WMG
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Manufacturing UHSS (boron steel)
Developing joining solutions for composites
Rahul Bhattacharya, Dave Cooper, Mike Cromarty, Richard Dashwood, Darren J. Hughes, Dave Mossop, Mark Pharaoh, John Pillier, Neil Reynolds,
Darren Stewardson, Geraint Williams, Terry Wheeldon
Associate Partner: Alpha Adhesives – David Shaw, Darryl Taylor
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Presentation overview
A – Processing boron steel 1 – Applications 2 – Manufacturing considerations 3 – Facility development 4– Initial results
B – The joining challenge for thermoplastic composites 1 – The options available 2 – A fitting solution? 3 – Matching to existing processes 4 – Optimisation and results
Demonstrator components (next talk)
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UHSS (boron steel)
Significant opportunities in using UHSS > Light-weighting via down-gauging
> Improved crash performance
HOWEVER : Challenges to forming > Limited RT formability (low elongation, high forces)
> High spring-back
Hot forming – die quenching > Eliminates spring-back > High ductility > Fully hardened (cooling rate
dependent)
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Hot-forming route
‘Direct process’ 1 –Austenitisation of blank @ 850-950 C 2 – Rapid transfer 3 – Forming-cooling operation
Austenitization in
furnace
As-received
Ferrite-Pearlite
Forming & quenching
Fully hardened
part
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Typical applications
Typically A/B-pillar, roof, side rails....
Ford Fiesta (2011) A-pill a r
Volvo C70
ROPS – reinforced A-pillar
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Challenges: tailored microstructure
Best crash performance achieved with different properties
- B-pillar Can be achieved by:
tailor welded blanks Differential tool cooling
- Tailored microstructure
Fully hardened microstructure
Controlled cooling
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Challenges
Differential tool cooling Heat flow – final microstructure
–thermal control mechanisms
Interplay between forming strain and microstructure
Controlling oxide – tool wear –joining implications
Addressing information needs of partners for designing with UHSS
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Facility development at WMG
Main aims: Develop a facility capable of forming UHSS To create a facility to fabricate demonstrator hardened parts in boron steel for
input to LCVTP test programme
Hot forming requirements
FURNACE - rated to ~ 1000 C
PRESS - high forming speed
TOOL - integral cooling
INSTRUMENTATION- thermal tracking
MATERIALOGRAPHY - microscopy, hardness
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Facility
Furnace
Blanksto1m 2
To1200 C Up-and-over door
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Facility
Press and tool
500 tonne press Final forming sp Water-cooled to LCVTP top-hat d accounted for
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Facility
Facility
Part transfer critical
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Spring-back
First parts – short top-hats tool time~30s
Degree of spring-back obtained using
GOM scanner
Virtually zero spring-back observed in hot-formed part
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Hardness and microstructure
Hardness (macro-Vickers)
As-received stock - 253 VHN 30
Average test-part 1 - 396 VHN 30
Average test-part 2 - 393 VHN30
Microstructure : to come...
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Progress-to-date
Press facility commissioned - Industry relevant forming speed (100 mms -1 over 125 mm via accumulators)
Controllable tool temperature via channels
Initial parts are hardened – thermal instrumentation needed
Spring-back effectively zero
Full length parts into test programme next week
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Joining solutions for composites
Principal aims > Evaluate the state-of-the-art for joining processes > Investigate appropriate (production-relevant) joining methods for the
candidate materials selected in WS7
> Provide timely input for demonstrator (top-hat/seat) testing
Candidate material – recap!
PA – GF composite (aligned glass fibre reinforcement – thermoplastic matrix)
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Joining is critical
Jaguar X350 (XJ) monocoque
284 stampings
35 extrusions
15 castings
Majority rivets + adhesive
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Joining TPC’s?
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SPR for composites?
SPR – Self Pierce Riveting
Cold-forming process
Widely used in AA bodies
" No pre-drilled hole
Y Valid for a range of materials
" Readily automated
( Excellent repeatability
x Two-sided access required
x Recycling issues
x Weight x Aesthetics
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Joining proposal & questions
Proposal: Combine the advantages of adhesives and mechanical (SPR) fixtures
High fail strength (adhesive) Improved energy absorption (mechanical)
Good peel strength (mechanical) Environmental performance (adhesive) Immediate fixing – no jigging (mechanical)
? Can we use the e-coat process to cure a 1-k adhesive?
simpler tooling/automation mechanical fixture holds form
? Is SPR relevant to TPC’s?
? Can we combine it with a (1-k) adhesive without modifying existing processes? (paint line)
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> Current status
Alpha Adhesives signed as ‘associate’ (adhesive supply and advice)
Initial tests performed to establish appropriate adhesive
Lap-shear coupon testing (JLR standard geometry) + ageing
DSC – cure kinetics
DMTA – adhesive strength development and thermal resistance
CT–joint integrity
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μCT analysis
Initial results show applicability to hybrid and similar joints
X-ray μCT in WMG can show integrity of joint (NDT)
- same concept as medical scanner
3000 images over 180 degs
1s per2D image
Relies on X-ray contrast between phases
Reconstruction takes 5 mins
‘Fly through’ analysis possible
15 μm voxel
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SPR joint – suitable for composites?
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μCT data
Fibres into plane Fibres horizontal
Fibre layup: 90,0,0,90,90,90,0,0,90
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μCT data
Suitable flare – could be optimised
Fibre layup: 90,0,0,90,90,90,0,0,90
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Cure of 1-k via paint line?
Thermal simulation of paint line profile (thermocouple data) using DMTA
Work with Alpha Adhesives to
optimise properties of 1-k
(epoxy) adhesive
> Initial adhesive – cures (but
only just)
> Alpha re-formulated
adhesive for LCVTP
> Lower temp cure – OK
(reduced shelf-life)
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Composite surface finish – peel ply or
not?
finish Peel ply cloth
Surface
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Composite surface finish – peel ply or
not?
Is the peel ply useful?
> Aesthetically better
> May give better bond – literature disagrees
Investigated by lap-shear testing of:
1k epoxy and methyl-methacrylate
P60 abraded surface Aligned glass – PA composite (P60 prep)
Aligned glass – PA composite (peel ply)
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Lap-shear tests – peel ply worth it?
Tests using 1-k epoxy and MM
>Approx two-fold increase in
UTS using peel ply
Joint efficiency (η) = Joint UTS/Parent UTS
1-k epoxy
Peel ply
Non- Peel ply
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Lap-shear tests – peel ply worth it?
Tests using 1-k epoxy and MM Joint efficiency (η) = Joint UTS/Parent UTS
Substrate failure with peel ply
Substrate
failure
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Lap-shear tests – peel ply worth it?
Tests using 1-k epoxy and MM Joint efficiency (η) = Joint UTS/Parent UTS
BUT
> Results not replicated
using 2-k or MM
Recall DMTA....
- initial viscosity drop
- flow into ‘pores’
- strong interlock on cure
MM
Peel ply
Non- Peel ply
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Lap-shear tests – peel ply worth it?
Tests using 1-k epoxy and MM Joint efficiency (η) = Joint UTS/Parent UTS
Summary
Highlights:
> Identified mechanical (SPR) and adhesive as a route to usage in automotive structure
Adhesive and SPR systems already in use – minor changes to incorporate composites
> Optimisation of 1-k adhesive achieved with Alpha Adhesives – cure within 15 minute bake
> Proven usefulness of peel-ply finish
> Excellent joint in hybrid structures. Further work needed to optimise similar joints. >
System used for demonstrator longitudinal parts (NEXT TALK....)
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Thanks for listening!