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

arhutchinson@brookes.ac.uk

www.mems.brookes.ac.uk

Thank you for listening