day 2 1.05 phil weber, sika corporation - lbcg · phil weber practical considerations of mixed...

PHIL WEBER

PRACTICAL CONSIDERATIONS OF MIXED MATERIAL BONDING IN SUPPORT OF LIGHTWEIGHT VEHICLE DESIGN & MANUFACTURING.

§  A Global Footprint with a Local Presence.

§  Localized Manufacturing, Engineering, and R&D activities operating in all four regions

§  Global Management / HQ in Detroit with Global Key Account management focused on needs of customers.

SIKA AUTOMOTIVE

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August 18, 2015 3

LIGHTWEIGHTING PRODUCTS & INTIATIVES

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Body Shop

General Assembly DVD Modules: (Dampfung Verstarkung Dach)

§  Facilitate mass reducCon via reduced panel thickness

§  Improved NVH / panel sCffness

High Modulus Assembly Adhesives: §  “Cold” Body Shop Concept §  Roof Modules/ Structural components

Structural Inserts: Lightweight composite inserts for: §  Crash resistance §  Global SCffness / NVH §  Local Durability

Structural Adhesives: Heat cured Epoxy adhesives: §  ConvenConal Steel / AHSS construcCon. §  Aluminum / Rivet Bonded Aluminum §  Mixed Material bonding

LIGHTWEIGHTING PRODUCTS & INTIATIVES

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Body Shop

General Assembly

High Modulus Assembly Adhesives: §  “Cold” Body Shop Concept §  Roof Modules/ Structural components

Structural Adhesives: Heat cured Epoxy adhesives: §  Mixed Material bonding

Unique consideraCons when bonding dissimilar materials in body shop: §  Substrate chemistries, morphologies, and surface tensions. §  Thermal Expansion differenCals

Review Example of structural bonding in Trim / GA §  Understand capability of understanding newer adhesive capabiliCes

MIXED MATERIAL BONDING

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Advantages of Using Adhesives: §  Bonding steels, aluminums, & heat

resistant composites.

§  Supplement performance of convenConal fastening methods (welds, rivets, etc;)

§  High strength / sCffness achievable

§  No pretreatment-‐ adhesion on oily substrates (Body Shop).

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Bonding mixed metals and/or plasCcs or composites in the body shop with high performance hot curing adhesives allows: §  Bond areas only accessable during build. §  Speed: Heat accelerates curing . §  Easy applicaCon (roboCc 1 or 2 component

materials). §  IntegraCon in exisCng body shop process.

MIXED MATERIAL BONDING Body Shop

Challenge with oven curing process: §  DifferenCal coefficients of thermal expansion (CTE) of

substrates. §  Curing of adhesive at 180°C & subsequent cooling

leads to stress in the joint / distorCons / part failures.

Coefficient of Thermal Expansion §  Steel: 12.6 x 10 mm/mm/ °C §  Alum. (6061): 24.3 x 10 mm/mm/ °C §  CFRP: 1.0 x 10 mm/mm/ °C

What does this mean?....... §  For a 1.0 meter long bondline, the differential

expansion b/w aluminum & steel is 2.0 mm at typical Body Shop bake conditions.

§  Results in stress in adhesive/substrate at RT. §  From a design / process perspective, these

differentials must be accounted for.


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-‐6

-‐6

-‐6

Steel

Aluminum Adhesive

Adhesive Failure

Substrate Failure

Substrate Buckling


Temperature °C

0.00

1.00

2.00

3.00

4.00

5.00

60 80 100 120 140 160 180 160 140 120 100 80 60

CFRP

Steel

Alum

§  ResulCng stress locked into adhesive bead & adjacent substrates is in determined by :

where: Gx = Shear Modulus ΔLx= Differential Thermal Expansion t = Adhesive Bead Thickness

§  Thermal expansion of the substrates (ΔLx) is controlled by the temperature

differenCal and the length of the parts & associated bond lines.

§  Stress can be managed by 1.  Changing properCes of adhesive 2.  Bond line design / thickness 3.  Rate of cooling as BIW exits ovens *

↓ΔL𝑥 = 𝐺x/𝑡  Δ𝐿𝑥

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ΔLx

t

SikaPower® MBX – Mixed Bonding eXcellence §  Family of adhesives designed to reduce failure & residual stress. §  Better elasticity, but maintains strength properties for structural applications:

Std. Crash MBX Class I Class II Modulus [MPa] 2000 600-1000 300-600 Elongation at break [%] 8 15-30 30-80 Tensile strength [MPa] 32 18-30 12-18 Lap shear strength1) [MPa] 32 20-30 15-20 Crash, impact peel2) 23°C [N/mm] 43 35-50 -30°C [N/mm] 33 30-45


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Adhesive ContribuKon to SoluKon ↓ΔL𝑥 = 𝐺x/𝑡  Δ𝐿𝑥

Influence of bondline geometry

where: Gx = Shear Modulus ΔLx= Differential Thermal Expansion t = Adhesive Bead Thickness

↓ΔL𝑥 = 𝐺x/𝑡  Δ𝐿𝑥

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t =1.0 mm→ Stress 100% t= 0.25 mm → Stress 400%

Movement tolerance through slojed hole

§  Increasing bondline thickness can reduce stress in adhesive bead, but addiConal design consideraCons would be required to eliminate stress from substrates.

0.0

0.5

1.0

1.5

2.0

2.5

0.3 mm 1.0 mm

Dis

plac

emen

t at f

ailu

re, m

ax. Δ

L

Adhesive layer thickness

Standard adhesive New adhesive, type I New adhesive, type II


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0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

40°C/min 30°C/min 15°C/min

Dis

plac

emen

t at f

ailu

re, m

ax. Δ

L

Cooling rate

New adhesive, type I

New adhesive, type II

Influence of Bake Process §  Slow Heat-up: Uniformity of temps across

bondline during e-coat cure.

§  Polymer crosslinking occurs starting at 140°C – above Tg of cured material.

§  Slow Cool Down: improves adhesive relaxation – reduces stress locked into bondline.

§  Mixed Material Bonding in Body Shop operations is achievable, and desirable from a process perspective.

§  Requires some consideration / management of the stress that can be built into the bondline due to thermal expansion differentials of the materials.

§  Special adhesives are under development to facilitate – but may not be able to totally compensate for differentials.

§  Additional influence of design & process that may require future focus. -  Bondline design -  Bake/ cooling process


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Body Shop

§  Long history of bonding in Assembly for both structural & non-structural applications:

-  Antennas, small non-structural components -  Fixed Glass -  Roof Modules.

§  Typically not preferred due to management of Open Time and Cure Time of adhesive systems.

§  Growth in bonding applications in GA associated with use of mixed materials:

-  Review one unique application launched within last year.


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General Assembly

§  Historical use of structural bonding in GA is limited •  Glass adhesives •  Roof modules: - Conventional, Top mount / panoramic roof systems.

§  Primarily cold applied single component Polyurethanes •  Robotically applied •  Slow strength builds, and 3-7 days to full cure

§  Expanding structural bonding applications in GA requires alternate methods

to improve strength build.


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General Assembly

Single Component (1C) Two Component (2C) Boosted (1C)


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General Assembly

Adhesive Options

Appl. Temp

Strength Build

Cure time

E’ (MPa)

Elong. % Comments

Single Comp.(1C)

Single Comp.(1C)

Boosted (1C)

Two Comp.(2C)

Cold Slow 7 D 5-‐10 100-‐500 Simple implementaCon/control Insufficient Strengths

Cold Bejer 1 D 5-‐10 100-‐500 Fast cure Insufficient Strengths

Warm 50°C

Bejer 7 D 100-‐500 5-‐10 Simple implementaCon/control Insufficient Strengths

Cold Bejer/ Good 1 D 15-‐25 10-‐100

Fast Cure / Low ElongaCon ProperCes sensiCve to mix raCo Tg: ProperCes vary w/ temp

Warm 50°C Good 1 D 40 350

Fast Cure / Good ElongaCon ProperCes in-‐sensiCve to raCo Tg (-‐69°): ProperCes stable

Boosted UHM (1C)

EFFECTIVE OF GLASS TRANSITION

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§  Comparison of typical 2C urethane modulus in comparison to Single component UHM technology over temperature range of -‐40°C to 80°C.

§  Bonding of carbon fiber body structure to e-coated aluminum chassis

§  Need structural bond with capability to

survive thermal expansion differentials over service temperature range:


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General Assembly

CalculaKons: OperaCng Temp Range: 60°C Adhesive Bead Length: 1900 mm Bead Thickness (compressed): 5.5 mm ElongaCon: ΔLx = : 2.6 mm Adh. Elongation = 2.6/5.5  = 47 %


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Open Time for Handling of Uncured Adhesive: 6 Min. Strength Build (Lap Shear – 4 hours): 1.0 MPa Full Adhesive Cure: < 24 Hr. Build Rate: 35,000/Yr


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Application has now grown to include C & S Class vehicles. Total of 250,000 units per year

§  Alternate lightweight materials being utilized bring new challenges from an adhesives perspective.

§  Some consideration / management of the stresses induced by thermal expansion differentials of the materials is required:

•  Either built into bondline during assembly process. •  Experienced during normal service life the vehicle

§  Challenges can be met, either in Body Shop or in Trim / GA. Specialty adhesives are under development to facilitate – but may not be able to totally compensate for differentials.

§  Additional influence of design & process that may require future focus – Early involvement with material supplier is key for success.


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day 2 1.05 phil weber, sika corporation - lbcg · phil weber practical considerations of mixed...

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