Applications of Adhesive Bonding To Enable Joining Of Multi-Materials

Transcription

1 Global Automotive Lightweight Materials Applications of Adhesive Bonding To Enable Joining Of Multi-Materials April 25 th 2013 Lotus Cars Cars Limited Limited Daryl Greig

2 Introduction Lotus Cars Lotus Cars Limited 2

3 Overall Construction Elise / Exige: Volume: p.a. Tub: Anodised aluminium Upper: Composite Panels Rear: Steel subframe bolted Front: Composite front module bonded Evora: Volume: p.a. Lotus Cars Limited Tub: Anodised aluminium Upper: Composite Panels Rear: Steel subframe bolted Front: Aluminium front module bolted 3

4 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: Elise: 720kg (Mk1) Exige: 1176kg Evora: 1390kg Lotus Cars Limited 4

5 Evora - Torsion and Bending Stiffness Contribution Full GBIW Bare Tub Stiffness Torsion knm/deg Bending kn/mm Baseline Roadster 14 8 Coupe (GBIW) Lotus Cars Limited 5

6 Evora Structural Composite Panels Key CSM Chopped strand mat FV - Fibre volume RTM - Resin transfer moulding ICS - injection compression system UD - Unidirectional Roof panel ICS/RTM 2.5mm CSM and +/-45 UD Stitch Mat. 23% FV Rear Bulkhead RTM 3.5mm CSM 23% FV Windscreen surround (WSS) ICS/RTM 3mm-5mm Foam cored CSM and 0/90 UD Stitch mat in A pillar and header. 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 Lotus Cars Limited 6

7 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 Lotus Cars Limited 7

8 1. Design - Composite Front Module- Multi Functional Component 7.5kg, 75kJ absorbtion 420mm crushable length Protects tub up to speeds of 25 mph Replaceable in service Variable wall thickness front to rear Clamshell Support Front impact energy absorber 0 deg, offset and 30 deg Cooling Module support Auxiliary light mounting Radiator duct intake / exit Tow Bar Mount Heater Intake Lotus Cars Limited 8

9 Bonded Joint Design A Closer Look Section1 Al/Al Section2 Al/ Composite Section 3 Comp / Comp Lotus Cars Limited 9

10 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 Mechanical Fasteners Riv bonding Lotus Cars Limited 10

11 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 Composites Surfaces primed for bonding Lotus Cars Limited 11

12 Section 3 Composite / Composite Load bearing corners Hex made of 2 mating sections Bond gaps controlled by assembly fixture Low modulus adhesive with large bond areas Composites Surfaces primed for bonding Lotus Cars Limited 12

13 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 Dynamic Strength FE Model Correlation Lower Bound Dynamic Strength FE Model Correlation Upper Bound Lotus Cars Limited 13

14 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 Static Strength Test Data Lotus Cars Limited 14

15 1.Tests for Joint Functionality Box Joint Tests Lotus Cars Limited 15

16 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 Lotus Cars Limited 16

17 2.Durability and Life prediction Stress Humidity & SWAAT Proving Ground Rig Tests Lotus Cars Limited 17

18 2. Durability - Link Proving Ground to Test exposure (Steel) 87 days exposure Component test System test Vehicle test Correlation SWAAT / Stress Humidity / Dynamic impact Proving ground Proving Ground SWAAT / Proving ground Proving Ground Lotus Cars Limited 18

19 2.Durability and Life prediction Correlation SWAAT to Proving Ground Lotus Cars Limited 19

20 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. Lotus Cars Limited 20

21 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 Lotus Cars Limited 21

22 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 Lotus Cars Limited 22

23 END Lotus Cars Limited 23