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Aluminum
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Structural
Inserts»PRODUCTS + PROCESSES
By Denis Souvay, global product manager structural reinforcers, Sika Automotive+ Michael Meier, head structural systems, Sika Automotive

REINFORCINGTHE TRENDS IN
LIGHTWEIGHTING
Adding NVH and crash performance

38

Lightweighting worlD / JUL+AUG 2019The challenges in vehicle design andassembly are getting bigger. Lightweight construction, increasing
requirements for crash safety, costpressures, design of derivative car
models on the same platform, material
flexibility and shortened development
times are aspects that are often difficult to reconcile.
Added to the equation, efforts to reduce mass for increased fuel economy,
emissions reductions or to increase
range through the reduction of metals
or metal thicknesses can fundamentally modify structural performance ofthe car body.
Within the last several years, the integration of heavy batteries of electricvehicles with additional crash-safety
requirements have expanded fromjust the occupants to the batteries
themselves, while adding a growing
material mix in the car bodies. Noengine noise means higher demand
for acoustic and noise, vibration andharshness (NVH) performance. Put
together, these challenges lead tobrand-new solutions to achieve thecombined targets for vehicle performance requirements.
Sika has solutions to help vehicle
designers address these challenges.
One of many solutions is a focus onengineered structural inserts used forreinforcement. Increasingly, plasticcomponents with structural foams
or structural adhesives are used toachieve structural performance, whichhave their final properties only aftercuring in the e-coat ovens.
The concept and real-world results
are long proven—precise reinforcement placements for car-body stiffness

Lightweighting worlD / JUL+AUG 201939

PRODUCTS + PROCESSESEngineered injection molded reinforcer inserted
to B-pillar application during assembly process
mirrors cavity section, strategically placed forcrash durability.

improvement (NVH applications) orfor better crash performance (structural enhancements). SikaReinforcer
technology has been used successfully for more than 15 years. Plastic
reinforcement elements, called SikaStructure, are adhesively bonded tothe surrounding substrates by molded
structural foam or through a growing
concept, liquid epoxy adhesives.
As mentioned, the usage field for
NVH applications is focused on theimprovement of the dynamic stiffnessof a car body. By reinforcing the bodystructure section at specific emplacement zones, SikaReinforcer parts will
act as a block to dynamic bending ortorsions of the car body, which will
limit the “pumping effect” of the sections. The result is a stiffer body leading to better handling and increased
cabin comfort.
Reinforcer components can beintegrated into the already existing
structures in late development phases,

40

for instance when technical requirements arise. At this late stage, changesof existing sheet-metal tools usuallylead to high costs. Even greater are theadvantages of early incorporation of
SikaReinforcer technology into the predesign of a vehicle. Then, lower steel
grades and lower material thicknesses
can be used because the reinforcementof critical zones by structural parts withReinforcer takes place.
For Crash Applications—By using
reinforcer components in crash-sensitive sections, a collapse of the subject
profiles is prevented. Crash energy isabsorbed through the reinforcer insert
and adhesive, whereby the deformation of the subject component can besignificantly reduced. The failure ofa structure due to high local forces isspecifically prevented.
The crash resistance of the applied
epoxy foam or structural adhesive
guarantees the transmission of highforces to tension and shear. Plastic-Lightweighting worlD / JUL+AUG 2019

The crash resistanceof the applied epoxy
foam or structural
adhesive guarantees
the transmission ofhigh forces to tension
and shear.

reinforcing elements open up completely new possibilities for the designof the bodyshell.
In addition to the improved deformation performance and occupantcompartment penetration reductionin the event of a crash, in most cases,
there is a double benefit—an increased
stiffness of the body is achieved, asmentioned, for NVH applications.
Further, by using crash-resistantadhesives instead of structural foams
to secure the reinforcement element,
the performance of the reinforcing
solution can be massively increased.
This technology is called HSB (HighStrength Bonding).

¾ High performancextensive use of UHSS to increase
Ecrash performance of body structure
results in loss of NVH performance.
Expanding reinforcers placed
at structural nodes increases
static torsional stiffnessby 3200 KNmm/° *(*: performance of the NVH
package with 10 reinforcers/car)¾L
 ightweight solution

 uge weight reduction compared toH
equivalent performing steel solution
saving > 10 kg¾D esign freedom

Injection-molded parts show very
high freedom of design to fulfill all
customer requirements.

¾J oining of inaccessible areas

Possibility to join several metal sheets
where welding is not possible

Applications and noted performance improvements through targeted use of reinforcers on the Volvo V90

Typical assembly process for Sika high-strength bonding application couplingcrash-durable adhesives with SikaStructure engineered inserts

Lightweighting worlD / JUL+AUG 201941

PRODUCTS + PROCESSES

Application target¾Side crash of electric Golf
derivative with 300 kg additionalweight (batteries)¾G
 lobal reduction of sheet-metal

thickness in roof frame ightweight solutionL W¾
 eight reduction (vs. steel solution)> 2.5 kg
Design freedom¾ Injection molded parts show very
high freedom of design to fulfill
all customer requirements
Cost reduction¾S
 heet metals and crossing on
B-pillar head discharged(downsizing possible)¾S
 teel weight reduction

provide savings

Application of reinforcements and benefits gained by using Sika HSB concept in VW E Golf modelFirst Development Phase—In thisphase of the solution, feasibility, performance and weight are determined
by CAE simulation. This phase cantypically be realized within a couple
of weeks, which gives the designer
multiple choices for solving a crashor stiffness issue. In the optimization
phase, the ratio of power and weight isusually significantly improved. Here,the development engineer can fallback on a variety of technical options.
A first step is the selection of thesuitable material, usually a technicalplastic. Due to the specific choice ofthe glass-fiber content in the material, the optimal structural designand other parameters, it is possible
to achieve the best balance between
strength, ductility, weight and costs.
Plastic components with their highdegree of design flexibility offer possibilities that can’t be realized withsteel parts or can be realized onlywith greater effort.
While there are other possibilities
currently available, such as intensive
use of press-hardened steel (PHS)or ultra high-strength steel (UHSS)in the high-loaded crash areas of theoccupant safety cell and a switch toaluminum for external panel or doors,
or complete aluminum car bodies forlightweighting, the material makeup
and design are much more expensive
and complex particularly for highvolume car models.
Additionally, while trials have been
made and continue to intensify theuse of carbon fiber reinforced polymer(CFRP), the material currently faces
difficulties in penetrating the market
in high volume due to challenges inrecycling capability and a very highcost level. In comparison, SikaRein-Plastic components with their high degree of design flexibility offer possibilities
that can’t be realized with steel parts or can be realized only with greater effort.
42

Lightweighting worlD / JUL+AUG 2019forcer engineered plastics technology
is ready to use, easy to integrate withvast user experience and many applications in production.

Why don’t advanced
reinforcement technologies
gain more attraction?
Simply put, a lack of awareness of thepossible performance enhancements
such technology approaches can offer.
At present, we rarely observe the introduction of this technology in the strategic development of new car models. We
mainly see that designers are tending
to use alternative materials to standard
steel, like PHS, UHSS, aluminum andsometimes CFRP. We do see heavy
activity introduced when traditional
design factors fail after the initial design.
It is time to reverse this trend.
Many reasons are at the sourceof this current situation, as many
designers are entrenched in selecting
traditional solutions.
•	For decades, the use of steel has
been a proven technology, using
existing and proven production
equipment, with strong voluminous
experience and knowledge sets todesign car bodies.
•	The suppliers of raw material aremainly focused on their own material and are competing against theraw material of their competitor(e.g., steel against aluminum).
•	More and more, automotiveengineers are deploying efforts tobuild up a symbiosis of all available materials, with the main target

to use “the right material at theright place” in the body structure,balancing the costs, the material
performances and the technicalstate of art of each technology.
Plastic components are still seen as“low value” components—assumed
as correct by considering the raw
material alone—without knowing its
interaction and performance potential
with other known raw materials, particularly when combined with specificengineering advantages and knowledge of material integrations.
•	Finally, there is a lack of awarenessand knowledge of non-traditional
reinforcement techniques. One reason they are featured in this article
is to inform. There also may be atrust factor. Designers don’t like todepend on plastic components for
traditional metal applications.
In any case, when such technology
could be necessary to solve crash or
stiffness issues, we can assume OEM
engineers are migrating to the mostconvenient solution (in terms oftechnology accessibility and confidence) because they are challenged
by a development timeline. Sika has
an experienced team and can support
finding the best location, CAE methods, process integration and support
with a high level of flexibility for any
customer request.

Development andIndustrialization of Reinforcers
Our development engineers construct
the specific lightweight structural ele-

Automotive engineers
are deploying efforts tobuild up a symbiosis of
all available materials,
with the main target touse “the right material
at the right place.”

ments in close cooperation with thecar manufacturer. This includes thedefinition of concepts for the respective application, the iterative optimization of design and connection, andthe release of the overall solution bymeans of experiments. This verification includes the implementation ofcrash tests for the validation of themechanical properties and on the other hand, the verification of the processcapability under series conditions.
The full benefit of engaging reinforcer solutions as outlined can berealized in the most relevant mannerby engagement at the start of the design process, which allows for optimization/iteration of the part design,production and assembly methods.
When engaged early in the process,our reinforcer high-performance solu-Lightweighting worlD / JUL+AUG 201943

PRODUCTS + PROCESSES

Applications and noted performance improvements throughtargeted use of reinforcers on the Volvo V90

tions normally result in favorable cost
parameters over traditional materialsolutions.
With the freedom of design ofinjection-molded support elements,
stiffness jumps can be avoided, as they
are almost always present at the endsof steel inserts. These stiffness jumps
often lead to undesired stress localization under load.
By using these measures, the vehicle
body can be designed specifically forthe needs of different model variants
and targeted segment markets. Throughthe combination of crash-resistantadhesives or structural foam and lightweight structures, the efficiency of thereinforcing elements can be raised toan unprecedented level.

Application Areasand Possibilities
The implementation of SikaReinforcer
often lets the OEM meet additional
requirements without changing thebasic design of steel components andtools. Such reinforcement increases
performance compared to pure steel
structures, enhances the dimensional
stability of the body in the event of acrash and yields a lower weight than asteel reinforcement.

44Not least in variant design, the useof reinforcers is interesting. Advantages arise where a basic construction
can cover a large part of the applications and only individual vehicle
derivatives can be upgraded withstructural elements as necessary. With
SikaReinforcer, the vehicles needing
increased requirements are selectively reinforced, while the rest of thevehicles will not be burdened by extra
weight and additional costs.
Examples of this are hybrid andelectric vehicles, which due to theirhigher mass load, the vehicle structure
plays more heavily in the crash event
than those with an internal combustion engine. Selective reinforcement
can also be used for protection in
vehicle component structures including metal extrusions, vehicle rocker
panels and battery enclosures.

Conclusion
The molded reinforcer elements,
coupled with structural foams, orperformance-enhancing special crashresistant adhesives enable a new levelof performance of structural elements.
It results in new design and assembly
options in body construction, which

Lightweighting worlD / JUL+AUG 2019

With the freedom ofdesign of injectionmolded support
elements, stiffness
jumps can be avoided,
as they are almost
always present at theends of steel inserts.
contributes to stiffer, crash-optimized,
weight-reduced and cost-efficient
vehicles. lw
ABOUT THE AUTHORS
Denis Souvay is theglobal product manager,
reinforcement technologies
at Sika Automotive AG. He is a generalmechanical engineer with more than
30 years’ experience in the automotive
industry, including 15 years in program
management. Since 1999, he has
focused on the introduction of lightweighting plastic solutions for car
bodies, driven by growing customer
needs of lightweighting solutions.
Since 2010, Mr. Souvay has led global
product management for automotive
reinforcing solutions at Sika Automotive.
He graduated from École Nationaled’Ingénieurs in France and completed
his technical studies with a specialization
in industrial marketing management.
Michael Meier, headstructural systems, Sika
Automotive, is leading
an international teamof engineers and isresponsible for the virtual
development of structural inserts,
mechanical characterization of theproducts and onsite support ofcustomers. He has been with Sika
Automotive for more than 11 years,
during which time he has successfully
brought more than 200 applications
onto the market.