Day 2, Manufacturing Stream ADHESIVE TECHNOLOGY Light-weighting vs resource recovery Prof Allan Hutchinson Head, Sustainable Vehicle Engineering Centre Department of Mechanical Engineering and Mathematical Sciences
MULTI-MATERIALS APPROACH TO LIGHT-WEIGHTING POSES CHALLENGES IN ASSEMBLY.. AND DISASSEMBLY
SOME LOW CARBON VEHICLE DESIGN ISSUES Light-weighting reduces overall energy consumption. This can be achieved by smaller vehicles, and using different designs and materials Design vehicles for ease of disassembly (and repair) BUT note that they may be heavier because of the design and extra joining requirements Cost-effective methods for separating high value components. Stop shredding, to enable materials recovery! Recovery and recycling of metals and plastics closed-loop recycling
LIGHT WEIGHT DESIGN STRATEGIES FOR VEHICLES Design strategies space frame structures bonded aluminium chassis sandwich panels fewer parts, modularisation design for disassembly exploitation of stressed skin concepts with bonding of panels Joining structural adhesives self-piercing rivets welding: laser spot, FSW, laser weld/brazing hybrid joining Refinement use of composites, structural foams, absorbers increased vehicle stiffness istream technology Simple tubular steel structure clad in 14 adhesive-bonded CF reinforced thermoplastic sandwich panels
METRES OF ADHESIVE BONDING FOR NEW VEHICLE MODELS BY YEAR OF LAUNCH BMW i3 140 D Metres of Adhesive per New Models 120 100 80 60 40 A B C 20 1996 1998 2000 2002 2004 2006 Year A Mercedes Benz S-Class B Range Rover, VW Polo, VW Touran, Mercedes Benz E-Class, Mercedes Benz S-Class, Jaguar XJ, BMW 7-Series C BMW 1-Series, Skoda Octavia, Audi A6 D Audi Q7, Mercedes Benz S-Class
A MULTI-MATERIAL FUTURE? Aluminium: passenger cell and front supporting structure CFRP: crash structures, inner sills, central tunnel, bulkhead, floor supports Audi Crosslane Coupe concept 2012 GFRP: panels Hybrid: 1.5l,3-cyl 2 motors 1.1l/100km 26g/km
BMW APPROACH Life + Drive Modular cfrp body-on-aluminium chassis structure i3 Mass of battery offset by lightweight structure
BMW i3 ASSEMBLY Adhesive bonding of body shell (Life module) Process temperatures never exceed 100C 160m of structural adhesive bonding using a 2K PU, cured at 100C for 30 mins. Typical lapped joints have a 1.5mm thick bondline and 20mm overlap Bonded joints are cfrp-cfrp, cfrp-thermoplastic, cfrp-aluminium, cfrp-steel Surfaces prepared for bonding by dry grit-blasting A felt pad, impregnated with an activator, is wiped over the areas just prior to bonding. Flame treatment is also used. Bonded components are held in jigs during cure but local IR spotheating is also used selectively to provide handling strength within 90 sec.
FUNDAMENTAL CONCEPTS Surface pre-treatment Adhesive selection Joint design Process control Training! Surface treatment is probably the most important aspect of adhesive bonding technology Surface treatment is the key to long-term bond durability www.adhesivestoolkit.com
SURFACE PRE-TREATMENT Surface pretreatments generally have less effect on initial strength than on bond durability Surface pretreatments are used as a minimum to provide a clean surface. Surfaces can be made very much more 'receptive' towards adhesives by altering their surface chemistry, energy and morphology Different materials warrant different types of treatment. Further surface treatments include the use of adhesive-compatible primers and/or chemical coupling agents such as silanes and titanates.
EFFECT OF FRP SURFACE TREATMENT ON BONDED JOINT STRENGTH Woven carbon epoxy composite 2-part room temperature curing epoxy
ADHESIVE SELECTION AND JOINT DESIGN New generation adhesives, eg acrylics, for low energy surfaces (thermoplastics) require no surface treatment(?) Flexible and tough (high strain to failure) adhesives are desirable Fast curing adhesives are needed Repositionable adhesives are desirable (see later)
BONDED LAP JOINT BEHAVIOUR FRP
APPROACHES TO STRESS MANAGEMENT WITH FRP 1. Use lower modulus, or variable modulus, adhesive Normalised shear stress 7 6 5 4 3 2 1 Low modulus adhesive (A) High modulus adhesive (B) Normalised peel stress 8 6 4 2 0-2 Low modulus adhesive (A) High modulus adhesive (B) 0 10 20 30 40 50 0 0 10 20 30 40 50 Overlap (mm) -4 Overlap (mm) 2. Use tapers and fillets
THE BONDING OPERATION
AUTOMATION IS THE KEY
RESOURCES: WASTES RESULTING FROM VEHICLES Currently the majority of this waste is steel which is readily recyclable. Many alternative powertrains employ large quantities of different materials, which are often mixed and far harder to recover. Materials masses million tonnes per annum 450 400 350 300 250 200 150 100 50 0 0 2010 2020 2030 2040 2050 Year in which vehicles were produced Production wastes Use phase (aftermarket) End-of-life Cumulative from 2010 18 16 14 12 10 8 6 4 2 Cumulative mass tonnes x 10^9
RESOURCE RECOVERY DISASSEMBLY OF ADHESIVE-BONDED JOINTS Concepts Brute force (and heat) Modifications to chemistry of adhesive / primer Additions to adhesive / primer
DISBOND-ON-DEMAND ADHESIVE SOLUTIONS FOR AUTOMOTIVE APPLICATIONS Considerations Ø Ø Ø Ø Ø Ø Type & nature of substrates Scale of components Location of bonded assembly Restrictions associated with manufacturing environment Re-use of substrates Safety Requirements Ø Ø Ø Ø Ø Ø Ø Low cost Straightforward to implement Rapid Clean separation, preferably at interface Minimal damage to substrates No hazardous by-products Minimal effect on performance of bonded joints in service
REQUIREMENTS OF A DISBONDABLE ADHESIVE Hutchinson A, Liu Y and Lu Y (2016). Overview of disbonding technologies for adhesive bonded joints, J Adhesion, on-line
DISBONDING TECHNOLOGIES AND MECHANISMS
DISBONDING TECHNOLOGY FUNCTIONAL ADDITIVES Micro-encapsulated solvents, acids & bases Induction heating activated liquid release adhesive degradation Expanding inorganic additives Dilated graphite, vermiculite, pearlite, mica, Wermlandite, Thaumasite, Hydrotalicte Oxidising agents Self burning bondline (ammonium perchlorate, slow process) Physical Foaming Agents, PFAs polymer and internal agent composition, geometry & concentration Chemical Foaming Agents, CFAs Generates gases/acids & ammonia Effectiveness: chemical nature, purity, size distribution & concentration
PFAs or THERMO-EXPANDABLE MICROSPHERES (TEMs)
PFA CONCEPTS Thermally-expanding microspheres (TEMs) are present in the adhesive or in the primer /surface cleaner A range of sizes (10-30 micron), expansivities and shell types are available Typically 10% wt in primer or 20% wt in adhesive Dormant for long periods Triggered by thermal energy typically 100-140C Works in 2-3 minutes Low cost, for the TEM and the energy source Microspheres can also be surface treated to enhance adhesion
INITIAL EXPERIMENTAL EVALUATION Shear strength against tem perature Lap Shear Strength 20 15 10 5 0 26 C 80 C 90 C 100 C 110 C 120 C Temperature 110 C 115 C 120 C Joint disbonds at predetermined temperature Failure occurs at epoxy/ steel interface Solid state foaming of matrix can efficiently separate substrates, BUT additives generally lead to a reduction in short- and long-term joint performance Hutchinson, Winfield and McCurdy (2010). Automotive material sustainability though reversible adhesives, J Advanced Engineering Materials, 12 (7) 646-652. McCurdy, Hutchinson & Winfield (2013). The mechanical performance of adhesive joints containing active disbonding agents. Int. J. Adhesion & Adhesives 46,100-113.
EXPANDABLE GRAPHITE (EG) Pausan N, Liu Y, Lu Y and Hutchinson A (2016). The use of expandable graphite as a disbonding agent in structural adhesive joints, J Adhesion, on-line
EXPANDABLE GRAPHITE (EG)
EG WORKS AT LOW ADDITION LEVELS Pausan N, Liu Y, Lu Y and Hutchinson A (2016). The use of expandable graphite as a disbonding agent in structural adhesive joints, J Adhesion, on-line
COMPARISON OF TEMs AND EG (UNAGED LAP SHEAR JOINTS) Hutchinson A, Liu Y and Lu Y (2016). Overview of disbonding technologies for adhesive bonded joints, J Adhesion, on-line
SUMMARY Low carbon vehicles: Light-weighting through design and alternative materials Design of vehicles for ease of disassembly (and repair) Cost-effective methods for separating high value components Adhesive bonding and disbonding: New generation tough and surface-tolerant adhesives are good news Disbonding systems need to be optimized to avoid significant reductions in joint performance. Microencapsulation techniques are effective but add complexity EG is better than TEMs for auto applications because smaller amounts are needed, the activation temperature is higher, it works in PU, and seems to be environmentally stable.
Thank you for listening Sustainable Vehicle Engineering Prof Allan Hutchinson arhutchinson@brookes.ac.uk www.mems.brookes.ac.uk