Lightweighting. Nick Warrior Polymer Composites Group University of Nottingham

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1 Lightweighting Nick Warrior Polymer Composites Group University of Nottingham

2 Fuel consumption is directly proportional to vehicle weight Steel vehicle structures are currently highly optimised Greatest potential for weight saving is in novel materials (carbon fibre reinforced composites) Our two current EPSRC grants in lightweighting are: CIM Comp: Centre for Innovative Manufacturing in Composites TARF LCV: Towards Affordable Closed Loop Recyclable Future Low Carbon Vehicles

3 Young's Modulus (GPa) Material selection Equivalent plate bending stiffness Automotive grade steel Aluminium & Magnesium Glass Moulding Compounds Advanced Moulding Compounds Glass Prepregs DCFP Foams Carbon Prepregs Better Density (g/cm 3 )

4 Material selection Stiffness limited plate Based on equivalent stiffness plate design aluminium offers 50% weight save and composite up to 80% 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%

5 Ultimate Tensile Strength (MPa) Material selection Ultimate tensile strength Automotive grade steel Aluminium & Magnesium Glass Moulding Compounds Advanced Moulding Compounds Glass Prepregs DCFP Foams Carbon Prepregs Better Density (g/cm 3 )

6 Material selection Strength limited plate High strength steels and aluminium show advantage in high stress areas - can the advantages of composites be carried over to real parts with complex stress states? 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%

7 TARF LCV: carbon fibre recycling motivation Carbon fibre is valuable - 10,000 - > 50,000 /T Carbon fibre production is very energy intensive GJ/T Increasing global pressure on OEM s to provide recycling routes Hot gases to high temperature clean up Cyclone to separate carbon fibre Recycled Carbon Fibre Collection Hot Air Supply Fan Hot gas stream with carbon fibre in suspension Scrap Shredded Composite Feed Fluidised Bed 550 C UoN Fluidised Bed process

8 TARF LCV: carbon fibre reinforced Al and Mg CF reinforced Al Nickel coated CF reinforced Al Nickel coated CF reinforced Mg Woven CF/Al 12Si Random CF/Al 12Si Random CF/Mg 3Al 1Zn

9 TARF LCV: carbon fibre reinforced thermoplastics Low cost thermoplastic matrices may hold the key to affordability of recycled carbon fibre composites UoN pilot scale thermoplastic fibre coating rig Thermoplastic CF/PP composites produced on UoN fibre coating rig

10 Young's Modulus (GPa) CIM Comp informs Manufacturing Process selection Automotive grade steel - DP300/500 Automotive Aluminium 6016-T4 Conventional advanced SMC Compression moulded prepreg UD as QI Compression moulded prepreg UD Prepreg based Advanced SMC (HexMC) Triaxial braiding [0/30/-30] equal weights DCFP Random DCFP Aligned NCF QI - 800gsm NCF UD - 600gsm UD materials 10 Loadcase optimality 1 10 Density (g/cm 3 )

11 CIM Comp Resin Transfer Moulding (RTM) Typically high injection pressures for large automotive components to minimise voids (100bar+) High CapEx:Tooling cost comparable to compression moulding + cost of injection system and large scale press Short cycle times (<10 mins) with highly reactive resins Process bottleneck is separate preforming operation required for fibres Tool design can be challenging for complex parts potentially high reject rates Local preform permeability introduces variability in the moulding process Class A finish achievable

12 CIM Comp Compression Moulding Short cycle times compared with autoclaved charges prepreg (15-20mins) Advanced moulding compounds require higher charge coverage than glass based materials. Higher touch labour. Limited mechanical properties, E=50GPa, σ=400mpa Properties are thickness dependent Trade off between performance and surface finish Excellent option for complex parts with intricate details. Integral stiffeners.

13 CIM Comp Hybrid Architectures: Compression Moulding Aim: Produce structural components from a combination of UD and randomly orientated fibre architectures Align continuous prepreg with principal stresses for primary load cases ASMC for secondary stress states or damage tolerance requirements Evaluate cycle time/cost/performance Application 1: High volume semi-structural/structural components for the aerospace industry. e.g. cleats/clips/brackets (6000 per 10/month) Application 2: Medium-high volume automotive structures. e.g. BIW components UD and/or woven prepreg ASMC Mould complex geometries with ASMC

14 CIM Comp Compression moulding capability Working temp up to 180 C Limited to 85 bar mould pressure Mould closure speeds between 0.5mm 25mm per second Pneumatic part ejection NI LabView used for data acquisition and logging: 4 zone PID heating control Kistler pressure and clamping force transducers HMI at press and web interface for remote monitoring

15 CIM Comp Compression Moulding: Directed Fibre Charge Fibre delivery system On-the-fly variable fibre length (6-90mm) Deposition rates up to 12kg/hr (per 12K tow) Resin metering system Two servo driven displacement pumps ensure a precise mix of each resin component. Heated transfer lines to maintain viscosity. Atomiser; solid spray cone.

16 CIM Comp Compression moulding: Directed fibre charge Maximum fibre volume fraction ~55% Good resin wet-out and low void content (~0.3% average)

17 Mechanical Properties: Directed fibre charge Comparable to commercial ASMCs Fibre orientation bias due to spray process

18 CIM Comp Hybrid Fibre Architectures Cut fabric (using ply cutter) Spray liquid resin Robotic DFC deposition Drape forming Transfer DFC charge and staged plies to compression mould tool Isothermal cure Eject hybrid part Stage De-mould

19 CIM Comp Discontinuous Carbon Fibre Studies Fibres are robotically chopped and sprayed onto a tool surface - can be sprayed with binder onto a perforated tool and part moulded using liquid resin methods - can be sprayed with resin directly into the mould tool Advantages Rapid cycle (5 minutes preforming) Low cost raw materials Low use of intermediates Low wastage (2-5%) Complex geometry Parts integration Locally variable thickness

20 Modulus Retention (ROM) Discontinuous Fibre - homogeneity Performance of meso-scale discontinuous fibre architectures is largely governed by homogeneity 100% 80% 60% 10mm 30mm 60mm 90mm 24K 12K 30mm tows, 10%vf, 3mm thick specimen 40% 20% 6K 0% Homogeneity (Bundles/m 2 ) 3K

21 Discontinuous fibre studies strength variability Unstructured B-basis 196MPa Mean = 225MPa Structured (Weibull) B-basis 189MPa Structured (normal) B-basis 176MPa 90% Confidence 13 samples tested Mean = 225MPa, St.dev = 22.9MPa

22 Discontinuous Fibre Alignment opportunities Smaller tows offer greater alignment levels at 30mm length Homogeneity influences final results ~2:1 increase in properties with alignment Still not a laminate Fibre deposition rate maintained 20kg/hr per 24K tow (lab scale)

23 Discontinuous fibre - Process modelling Integrated optimisation environment under development Import of tooling geometry Import of robot programs Robot kinematics Fibre flight simulation Homogeneity analysis

24 Bentley Motors Study - Structural Optimisation Performance von Mises Stress (MPa) Max.Deflection (mm) Glass/carbon NCF benchmark Carbon NCF benchmark Optimised DCFP Total Strain Energy (kg) 837 Max Deflection (mm) 2.62 Total Mass (kg) 3.56 Norm Specific Stiffness* (unity) 1.7 Total Strain Energy (kg) 1023 Max Deflection (mm) 3.01 Total Mass (kg) 3.16 Norm Specific Stiffness* (unity) 1.6 Improvement in deflection over benchmark Reduction in total mass (non ply based solution) Comparable specific stiffness to carbon NCF

25 Jaguar Land Rover Composite BIW Study Roof assembly Bodyside assembly L&R Tailgate surround Footwell assembly Rear shock tower L&R Cross car beam Boot Floor assembly Front shock tower L&R Floor assembly Over 220 steel pressings =12 composite components

26 JLR Composite BIW Study Detail Front shock towers 36 steel pressings Steel part thicknesses vary from 1.5 to 2.4mm 4 composite components Combination of compression moulding and RTM Front fender support (3mm RTM/braid with foam core) Shock mount 2 preforms co-moulded via RTM Main preform (3.5mm DCFP) Spring tower upper preform (5mm QI NCF) Side member (3mm braid/rtm + 2 cores)

27 JLR Composite BIW Study Detail Front shock towers Materials CF 50K Split tow RTM resin Type TBD NCF (Type TBD) Core Inserts ASMC (Roll) Premould / Preform DCFP Preforming (2x) NCF???? Preforms Braided preforms Core machining ASMC Charge Moulding Post-moulding HP RTM moulding HP RTM Moulding HP RTM Moulding 2x ASMC Moulding Shock mount tower (LH & RH) Front fender support (LH & RH) Sidemember (LH & RH) Sidemember mount Sub assembly name Number metal parts Front Shock Tower RH_Front Fender Support_RTM/Braid/Core (green) 9 Foam Core (Rohacell 110) Front Shock Tower RH_Shock Mount_RTM/DCFP 10 SPRING_TWR_UPR_RH_VCC preform 1 Front Shock Tower RH_SideMember_RTM/Braid (blue) 12 Foam Core 1 (Rohacell 110) Foam Core 2 (Rohacell 110) Front Shock Tower RH_SideMemberMount_SMC (yellow) 4 Assembly Demould CNC trim Robot edge seal Front Shock towers ( LH & RH) Place in assembly jig Robot adhesive Close assembly jig Heat Demould Local QA Total metallic mass Composite mass Target mass %age weight save 52%

28 JLR Composite BIW Study - summary Weight Saving of 51% Parts designed on an equivalent stiffness basis Viable unit cost of 3855 at 65,000 units