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125yearsVol. 199 • Issue 2

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CHANGING GEAR
from quality of miles toquality of coverage

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DebunkingC-V2X myths

Structural adhesives
tailor-made to bondmultiple materials

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visit ai.com.ai“Our message to automotive designers is that you now havemore freedom in designing body structures with a wider array ofmaterial choices, and we welcome collaboration to make design
challenges from dreams into reality. Example, the F-150.”– Leslie Wolschleger VP R&D Sika Automotive USA. Page 22

innovation

Advanced structural
adhesives keep pace with vehicle
bodies of the future
By: Tony Davidson

Adhesives are replacing mechanical joins across an increasing number of components andapplications as OEMs strive to reduce weight for both internal combustion and electricpowered vehicles. An example is the 2021 Ford F-150, which has an aluminum-alloy body.
Automotive Industries (AI) asked Leslie Wolschleger VP
R&D Sika Automotive USA to tell us how SikaPower ®-550 Gcame to be specified for the new F-150.
Wolschleger: Sika has been a global supplier to Ford Motor
Company for decades. We have been working with the Ford
Research Center on innovative projects for many years, supplying
a full range of acoustic, reinforcement and direct glazing products
to Ford globally.
SikaPower ® -550 G structural adhesive was developedwith Ford to provide increased durability, superior open
time in an uncured state and a wider cure process window(mainly time and temperature). The developmental targets
were verified together with Ford, first by screening previousgenerations of SikaPower ® products and then throughfurther development for both aluminum and steel
bodies with improvements to meet new andLeslie Wolschleger
VP R&D Sika
Automotive USA.

higher standards for crash performance. Fordconducted benchmark studies on many of these
SikaPower ® samples at both lab and full vehicle scale. This
enabled the material property requirements at a lab level tobe verified in real world conditions.
The collaboration process involved other Tier suppliers andsubstrate coating companies. Coatings of the crash grade
aluminum substrate is a critical aspect for durability in the F-150.
Our partnership with the coating supplier helped to ensure ouradhesives are compatible with the coating. It provided confidence
that we had the correct chemistry to enable chemical bonding to
the substrate that stood up the loads seen in a crash event. We
were able to fine-tune intimate property relationships between
50

the adhesive and the substrate to ensure a cohesive fracture
profile and eliminate substrate failure.
AI: What design challenges did the adhesive help toovercome?
Wolschleger: The targets for adhesive performance werechallenging as specifications normally met by multiple adhesives
were condensed into one. A vision for the adhesive was that it
could be used on both aluminum and steel applications, and in allareas of the vehicle. While adhesion and impact modifications wereneeded to meet crash performance criteria, we also needed toensure full coverage in hem applications. Thus SikaPower®-550 G
contains glass beads to ensure full wet out of the bonded area
after application. The beads also ensure there is a constant bondline thickness in the adhesive joint guaranteeing consistentbond performance. The addition of glass beads alongwith fine tuning of mechanical performance, while
maintaining corrosion resistance, makes theSikaPower®-550 G suitable for hem-flange
bonding applications as well.
During the vehicle development phase, CAE
modelling was heavily used to predict overallvehicle performance and has an influence on
adhesive joint design and usage. The use ofglass beads enabled the final vehicle crashperformance to match CAE predictive results.
Further, weldability and rivetability screening wasneeded with material that contained glass beads toensure the presence of the beads would not interfere withtraditional mechanical joining methods.
Humidity resistance is also a key factor for adhesive performance.
The new SikaPower®-550 G demonstrates an improvement inhumidity resistance prior to cure and excellent stress durability ofthe bond under static load in a corrosive environment after cure.
The durability of the adhesive when subjected to both static
loading and a corrosive environment introduced a new challenge for
the SikaPower®-550 G development team. This required maximum
corrosion resistance and the ability of the adhesive to withstand a staticload while being cycled through corrosion accelerated conditioning.
This stress durability test inflicts maximum and challenging

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punishments on a cured adhesive in a lap geometry that is held undera constant static load. Lap specimens are cycled, each cycle lasting
one day, through humidity and salt conditions. SikaPower®-550 G
surpasses the previous generation performance in the number ofcycles it can hold its’ bond at both low and high temperature cureconditions. It also not only meets the specification but exceeds it.
AI: Has this paved the way for increased use ofadhesives in the automotive industry?
Wolschleger: The automotive industry and supplier networks
are becoming more aware of how structural adhesives can beused to improve not only crash performance of the vehicle, but also
durability and resulting occupant comfort. We have seen a significant
number of automotive manufacturers and vehicle platforms using
SikaPower® structural adhesives throughout the vehicle body.
Not coincidentally with that we are embracing more collaboration
between Sika and our OEM customers, especially in the early vehicle
design phase to maximize the benefit of our products that enable
their program goals: lightweighting, ease of manufacturing (cycletime reductions) and improvement of overall vehicle performance.
AI: What about at the component level?
Wolschleger: We have observed an increase in the use ofstructural adhesives at the component level. As sub-assemblies
are often prefabricated outside the OEM assembly plant at aTier supplier, the superior pre-cure open time performance of

AI: Do you think adhesives will replace mechanical bonds?
Wolschleger: We will see more mixed material bonding
in the future, where adhesives will be used with a wider arrayof substrates, both metallic and non-metallic. For metallic
applications, the mechanical properties can be fine-tuned to theapplication and have an added benefit of preventing galvanic
corrosion when bonding metal substrates.
In mixed metal/ non-metal joining, already there are production
vehicles which use adhesive to bond carbon fiber reinforced plastic(CFRP) with metal substrates in their body structures to achieve
lower weight targets. Sika believes there will more instances ofsimilar applications as automakers get more aggressive withlightweighting efforts.
While the use of adhesive can help to decrease mechanicaljoining points, and to add strength to the joints by transferring
energy across the total bond surface, the approaches servecomplementary purposes in assembly.
AI: What else should automotive designers know about
advanced structural adhesives?
Wolschleger: Advanced structural adhesives are built on
chemistry that is proven in the industry and enables durability
and corrosion resistance over the life cycle of the vehicle. Whatexcites me is that this technology is used to not only improve
driver comfort, but more importantly safety. An impact modified

SikaPower ®-550 G is more resistant to humidity uptake inan uncured state.

Improvement in stress durability under a corrosive
environment with SikaPower ®-550 G.

SikaPower®-550 G becomes important. SikaPower®-550 G wet
out and coverage performance remains constant and moisture
uptake resistance is improved during transport. Once processedand cured at the OEM, resulting material performance andcohesive failure modes meet industry standards and requirements.
While SikaPower® 550 G is a shining star, additional SikaPower®
adhesives have been developed for component level assembly.
To address the growing number of mixed material bondingapplications, we have introduced an entire line: SikaPower®
MBX (Mixed Bonding eXcellence) structural adhesives for suchuse. Our latest innovation is SikaPower®-510 G MBX. It is used
to join the boron steel torque box (designed to strengthen thevehicle's unibody construction) to an e-coated aluminum front
rail assembly on the 2020 Ford Explorer and Lincoln Aviator.
SikaPower® MBX also enabled corrosion mitigation for themixed metal combination, as well as protection from thermaldelamination during the e-coat process.

adhesive in a joint, such as SikaPower®-550 G, absorbs moreenergy in less time than a mechanical weld in a crash event. Theenergy is transferred as designed by the OEM to facilitate the best
possible outcome in a crash event.
Automotive design is an iterative process enabled bytechnology advancements; vehicles throughout history havebecome lighter, stronger, more comfortable and safer for theiroccupants. By progression recent body structural designs have
evolved from all-steel, to a mix of aluminum and steel, and withthe latest advancements, a mix of different metal and non-metal
substrates. The use of advanced structural adhesives helps these
newest vehicle designs to come to life.
Our message to automotive designers is that you now havemore freedom in designing body structures with a wider array ofmaterial choices, and we welcome collaboration to make design
challenges from dreams into reality.

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51

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AND SEALING SOLUTIONS. PERIOD.
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