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
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
D
C
B
A
20
40
60
80
100
120
140
1996 1998 2000 2002 2004 2006
Year
Met
res
of A
dhes
ive
per N
ew M
odel
s
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
BMW i3
A MULTI-MATERIAL FUTURE?
Aluminium: passenger cell and front supporting structure CFRP: crash structures, inner sills, central tunnel, bulkhead, floor supports GFRP: panels
Hybrid: 1.5l,3-cyl 2 motors 1.1l/100km 26g/km
Audi Crosslane Coupe concept 2012
BMW APPROACH
Life + Drive Modular cfrp body-on-aluminium chassis structure
Mass of battery offset by lightweight structure
i3
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 spot-
heating 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
0
1
2
3
4
5
6
7
0 10 20 30 40 50Overlap (mm)
Nor
mal
ised
she
ar s
tress
Low modulus adhesive (A)High modulus adhesive (B)
1. Use lower modulus, or variable modulus, adhesive
2. Use tapers and fillets
-4
-2
0
2
4
6
8
0 10 20 30 40 50
Overlap (mm)
Nor
mal
ised
pee
l str
ess
Low modulus adhesive (A)High modulus adhesive (B)
THE BONDING OPERATION
AUTOMATION IS THE KEY
RESOURCES: WASTES RESULTING FROM VEHICLES
0
50
100
150
200
250
300
350
400
450
2010 2020 2030 2040 2050
Mat
eria
ls m
asse
s m
illio
n to
nnes
per
an
num
Production wastes Use phase (aftermarket) End-of-life
0
2
4
6
8
10
12
14
16
18
Cum
ulat
ive
mas
s to
nnes
x 1
0^9
Year in which vehicles were produced Cumulative from 2010
§ 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.
RESOURCE RECOVERY DISASSEMBLY OF ADHESIVE-BONDED JOINTS
Concepts § Brute force (and heat)
§ Modifications to chemistry of adhesive / primer
§ Additions to adhesive / primer
Considerations Ø Type & nature of substrates Ø Scale of components Ø Location of bonded assembly Ø Restrictions associated with manufacturing environment Ø Re-use of substrates Ø Safety
Requirements Ø Low cost Ø Straightforward to implement Ø Rapid Ø Clean separation, preferably at interface Ø Minimal damage to substrates Ø No hazardous by-products Ø Minimal effect on performance of bonded joints in service
DISBOND-ON-DEMAND ADHESIVE SOLUTIONS FOR AUTOMOTIVE APPLICATIONS
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
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
DISBONDING TECHNOLOGY – FUNCTIONAL ADDITIVES
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 temperature
05101520
26°C 80°C 90°C 100°C 110°C 120°C
Temperature
Lap
Shea
r St
reng
th
110°C 115°C 120°C
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.
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
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.
Sustainable Vehicle Engineering
Prof Allan Hutchinson
www.mems.brookes.ac.uk
Thank you for listening