materials for the future of lightweight construction · 2013-08-08 · lightweight construction and...

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© Carl Hanser Verlag, Munich Kunststoffe international 3/2012

CLAUS DALLNER ET AL.

Lightweight construction is not a newconcept; indeed it is a well estab-lished strategy in vehicle construc-

tion (Title picture). New momentum hashowever come on the one hand from theintensive efforts being put into alterna-tive drive systems, particularly electriccars, but on the other also from conven-tional vehicles that will dominate Eu-rope's roads for decades, where light-weight construction is vitally importantsince every kilo counts: From 2020 theEuropean Union will require every Euro-pean vehicle manufacturer to achieve anaverage fleet emission level of 95 gCO2/km. For comparison the actual val-ue achieved in November 2011 was still

around 143 g CO2/km. This means a re-duction of around a third in just under adecade. Exceeding this value will lead tolarge fines for the automotive industry.Alongside optimized traditional and al-ternative drives as well as improvedrolling and air resistance lightweight con-struction is a lever in meeting the reduc-tion targets: Every 100 kg of weight savedmeans 0.4 l less fuel consumption per100 km traveled or around 10 g less car-bon dioxide emissions.

Following the large scale uptake ofshort glass fiber reinforced polymers forlightweight construction and the accept-ance of the advantages of long glass fiberreinforced material by the market the au-tomotive industry now has to face thenext challenge: continuous fiber rein-forced composites for mass production.The ambitious weight and associated fu-el consumption reductions of the nextgeneration of vehicles can be achieved

with these material and componenttypes.

Short, Long and ContinuousReinforcement

Short Glass Fiber Reinforcement: Sincethe beginning of the 70s when the firstmass produced polyamide (PA) air intakefrom Dr. Ing. h.c. F. Porsche AG, Stuttgart,Germany, saw the light of day, short glass

Materials forthe Future ofLightweightConstruction

Composites. Continuous fiber reinforced

composites allow the automotive industry to achieve

weight savings that were previously not possible. In combi-

nation with different matrix polymers as well as various types

of fiber and fabric architecture they also offer a high level of design

freedom for component parts. At the same time cost efficient processes that are

suitable for mass production are the prerequisite for market success.

The greatest challenge for lightweight construction with fiber reinforced

polymers today is the development of mass production capable – that is

fast and cost effective – manufacturing techniques for large area compo-

nents such as doors, roof modules or tailgates as well as structural com-

ponents such as B pillars, sills or underbodies with the required mechani-

cal performance (figures except Fig. 4: BASF)

BASF SE

Trade press office

Performance Polymers

D-67056 Ludwigshafen

Germany

TEL: +49 (0)621 60-43348

> www.plasticsportal.eu

Contacti

Translated from Kunststoffe 3/2012, pp. 60–67

Article as PDF-File at www.kunststoffe-

international.com; Document Number: PE110992

� 2012 Carl Hanser Verlag, Munich, Germany www.kunststoffe-international.com/archive Not for use in internet or intranet sites. Not for electronic distribution

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fiber reinforced polymers such as PA andpolyurethane (PUR), as well as

polyethylene (PE) and polypropylene (PP) havecontinuously advanced

automotive lightweightconstruction in demanding ap-

plications. They will also continue toadvance it on a broader and more globalscale through the proliferation of innova-tive components. Amongst the most in-teresting examples of the past few years isthe replacement of metals by engineeringthermoplastics in engine mounts, stabi-lizers and transmission cross beams.However, ten years ago it was also notpossible to produce bumper supportsmade from polyamide or front ends, Bpillar inserts or oil and seat pans inpolymeric materials.

Success was not only madepossible by the continuous de-velopment of the matrix poly-

mers, but also by the increasingability to predict the behavior of

polymer parts under loading usingcomputers, e.g. advanced simulationtools such as Ultrasim from BASF SE,Ludwigshafen, Germany. Furthermore,these material developments are not overyet: Polyamides such as the now evenstiffer Ultramid Endure grades, whichhave continuous service temperatures ofup to 220°C for components near to tur-bo charge engines, or even more cus-tomizable crash optimized PA6 gradessuch as Ultramid B3ZG10 CR show thata great deal of potential within short glassfiber reinforced materials remains to beunlocked. In addition there are alterna-tive raw materials with new combinations

Kunststoffe international 3/2012

of properties such as for example Ultra-mid Balance (PA610) with high chemicaland hydrolysis resistance.

In the case of polyurethanes PUR-RRIM technology has been further devel-oped and in 2009 had its most spectacu-lar success with the world’s first all PURmass produced vehicle body shell (Fig. 1).The in part large area bodywork compo-nents of the low volume Artega GT sportscar from Artega Automobile GmbH, Del-brück, Germany, were produced usingRRIM (Reinforced Reaction InjectionMolding). In this process the PUR basecomponents which contain short glassfibers are mixed at high pressure in a mix-ing head. After this the low viscosity re-action mixture is injected into the closedtool within 1 s and just 30 s later the fin-

ished part is demolded. Elastolit gradesR8, R8HT, K4 and D from BASFPolyurethanes GmbH, Lemförde, Ger-many, were used for the Artega GT andindividually optimized for the require-ments of the door skins, wings, bumpers,tailgate and roof frame. Particularly forlow volume mounted parts that requirelow cost tooling, PUR systems can prevaildespite competition from metal or ther-moplastics. In this case the very good flowproperties stemming from the processingof liquid components and low internalmold pressures are a clear advantage.Stiffness, dimensional stability, toughnessand low thermal expansion are some ofthe benefits of the material. PUR body-work led to a weight saving of around40 % for the Artega GT.

Long Glass Fiber Reinforcement: Atthe same time however a trend towardslong glass fiber reinforced polymers canbe seen for special applications and re-quirements. BASF has therefore beenmarketing Ultramid Structure since2010. This material was chosen in 2011for the wheel of the smart forvision con-cept car (Fig. 2). What is special about thislong glass fiber reinforced (LGF)polyamide is that during the injectionmolding process a three dimensionalfiber network of about 3 to 6 mm longfibers is created which acts as a skeletonfor the component, as can be seen herewith the example of an internally devel-oped crash absorber (Fig. 3, center). Thisskeleton structure ensures very good me-chanical properties: creep behavior,warpage and energy absorption are sim-ilar to metal without losing the tradition-al advantages of a thermoplastic. In or-

Fig. 1. The bodywork of the Artega GT, a low volume sports car made in Delbrück, Germany, consists

mainly of polyurethane reinforced with short mineral and carbon fibers

Fig. 2. The new smart forvision concept car presented at the IAA 2011 was equipped with the world’s

first thermoplastic wheels that have the potential to be mass produced. They are made from long

glass fiber reinforced polyamide and with a weight of 6 kg they are some 30 % lighter than mass

produced aluminum wheels reducing the overall weight of the vehicle by 12 kg


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der to give a complete description of the(failure) behavior of components madefrom LGF polyamide BASF has onceagain expanded its simulation tool: Theprecise failure during a collision with theUltramid Structure crash absorber canbe predicted using Ultrasim (Fig. 3, bottom).

Long glass fiber reinforced compositematerials made from polyurethane foamwhen combined with thermoplastic filmoffer options for the roof module as wellas other mounted parts of commercial ve-hicles such as radiator grills (Fig. 4). This isan application area for Elastoflex E fromBASF Polyurethanes. In the roof moduleof the smart fortwo a thermoformed mul-tilayer film is long-fiber injection (LFI)back foamed with a long glass fiber rein-forced polyurethane. What is importanthere alongside the individually adjustablelevel of stiffness and strength is the lowand isotropic thermal expansion of thePUR system.

Continuous Fiber Composites: Forall of these short or long fiber reinforcedvehicle components the weight savingper component compared to metal is be-tween 30 and 50 %. These already allowhigh stiffnesses and strengths to beachieved. The future of lightweight con-struction, particularly for the bodyworkand the chassis, however lies in continu-ous fiber reinforced components. In re-spect of finished component propertiesand process technology, ContinuousFiber Reinforcement (CFR), goes a fun-damental step further. It will thereforelead to a further increase in the propor-tion of polymer in vehicles. In the case ofthermoplastic processing, injectionmolding or compression processes arecombined with localized continuous

fiber reinforcement, thereby allowing asignificant increase in strength, stiffnessand energy absorption (Fig. 5).

One option is conventional injectionmolding which uses light continuousfiber inserts for local reinforcement ofcomponents. These are unidirectionalthermoplastic impregnated rovings (UDtapes) or fabric reinforced prepregs calledthermoplastic laminates. Whilst thermo-plastic laminates (or organo sheets) areparticularly suitable for large area hybridparts, UD tapes are advantageous for lo-cal reinforcement. With their help com-ponent properties can be very effectivelyoptimized through the nearly limitlesschoice of layer construction and its asso-ciated fiber orientation. In both cases theprepregs are thermoformed to three di-mensional shapes, after this they are in-jection overmolded for example with aglass fiber reinforced polyamide and thusmade into hybrid components with highstiffness and strength. A seat back devel-oped jointly by BASF and Faurecia is closeto mass production (Fig. 6). This process ishowever also in principle suitable for oth-er structural components such as the Bpillar or the sills (see Title picture). As ina pure injection molding application thefirst step in the development process withcontinuous fiber reinforcement is estab-lishing the ability to simulate the compo-nent behavior including crash perform-ance. Based on component tests CAE ma-terial models of the overmolded contin-uous fiber structures were developed.

In terms of process technology over-molding of the pre-formed laminate fiberstructure offers all the advantages of ther-moplastic injection molding, such asshort cycle times, high levels of automa-

tion, reproducibility, modularity, func-tional integration as well as recyclability.Thermoplastic laminates utilize theirstrengths as 2-D components: They areused as semi finished products and arethermally formable either during orshortly before the overmolding step.

An additional novel technology is cur-rently being developed for componentswhich are manufactured by injectionmolding with steel cord reinforcement(EASI technology). Access to structuralapplications is possible through the jointdevelopment partners Bekaert, Kortrijk/Belgium, and voestalpine Plastics Solu-tions, Putte & Roosendaal/the Nether-lands. By using polyamide as the injectionmolding material the components can becathodic dipped and so are suitable asmounted parts as well as for use in unfin-ished bodywork (BIW: body in white).These components combine the necessaryperformance for structural requirementssuch as strength and stiffness with the duc-tility of highly resilient materials so that ina crash extremely high energy absorptionand structural integrity are guaranteed.

BASF is available as a developmentpartner for the automotive industry forall these thermoplastic reinforcementtechnologies.

Fig. 3. Long glass fiber reinforced polymers form

a three dimensional glass fiber network during

injection molding (center of picture), which

gives the component its exceptional mechani-

cal performance for instance as a bodywork

crash absorber. The behavior of such demand-

ing components can now also be calculated

and predicted via computer simulations

Fig. 4. Long fiber

reinforced

polyurethane is

already being used

for the MAN

radiator grills

(photo: MAN-Truck)


Bodywork and StructuralComponents Using RTM

Through the polymer applications beingtargeted by the automotive industry forbodywork and chassis,which should makethe next step change in weight reductionpossible, new demands are being placedon the performance of materials as well astheir processability. It was for this reasonthat BASF set up the cross departmentaland material Lightweight CompositesTeam in 2011. They are investigating thepotential of the three polymer matrixcomponents epoxy resin, polyurethaneand polyamide in respect of the mass pro-duction use of continuous reinforcementin resin injection processes. In this way thecompany can make targeted use of its ex-tensive portfolio of all three classes of ma-terial along with the associated processingknow-how in partnership with represen-tatives of various parts of the automotivevalue added chain and create synergies.

Fiber Composites with RTM: One ofthe processing technologies behind the

new materials is resin transfer molding(RTM) with the help of which large andcomplex composite components are cre-ated in a resin injection, press and moldprocess. In doing so, after being placed ina temperature controlled mold which issubsequently closed, dry multilayer fiberor textile structures are impregnated witha very low viscosity polymer resin. Due totheir low starting viscosity all of the newmatrix systems display very good impreg-nation and wetting properties even dur-ing rapid mold filling processes. Depend-ing on the tool temperature chosen in thecase of the thermosetting systems a fast

cross-linking reaction occurs whilst thethermoplastic polyamide polymerizesand crystallizes in a short period of time(Fig. 7).Alongside the mechanical perform-ance of the finished fiber composite partthe good flow properties of the matrixsystems (even with long flow paths), thedegree of impregnation and the short cur-ing time of the polymer components arehighly important factors for all three ma-terial types (Fig. 8).

BASF already offers solutions based onepoxy resin and polyurethane systems un-der the brand names of Baxxodur andElastolit R. Both thermosets use innova-tive curing mechanisms so that theycross-link within a few minutes. They canbe processed on conventional high andlow pressure equipment. The newpolyamide systems, which are currently >

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Time

700

J

500

400

300

200

100

00

Energ

y

10 20 30 40 50 60ms

Ultramid B3G10 (GF)

Ultramid Structure B3ZG8 (LF)

Ultramid CompoSIT (CFRT)

Fig. 5. Energy absorption

of driver’s seat backs

made from PA6 with short

fiber reinforcement (GF),

long fiber reinforcement

(LF) and a hybrid of short

glass fiber with UB tape

inserts (CFRT) respective-

ly: During drop tests the

energy absorption over

time was recorded (all

measurements at 23°C)

© Kunststoffe

ε-Caprolactam

ε-Caprolactam

Activator

110 °C

150 °CCF or GF textile

50 vol.-% (60–70 wt.-%)

Catalyst

Additives

Reactivesystem

Fig. 7. Resin Transfer Molding (RTM) process sequence for the case of polyamide

© Kunststoffe

Fig. 6. The prototype SUSCO 1.5 seat from Faurecia was developed jointly with BASF and uses con-

tinuous fiber thermoplastic tapes in the seat back (white in the picture) which in a second process

are overmolded with a special polyamide (black seat back parts). The replacement of the existing

metal structure in the seat backs with a single piece polymer component reduces the weight of the

back by about 20 %

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under development, are based on the verylow viscosity caprolactam, a precursor ofPA6, and highly advanced activator andcatalyst systems. In contrast to classic PAprocessing they react only once they arewithin the mold. These thermoplasticcomposite materials can then be molded,welded and recycled. The large effort thatBASF has put into the development of thethree systems is aimed at additional re-ductions in cycle times and improvedprocessability. It is accompanied by theextension of simulation tools for the pre-diction and component layout of evensuch complex continuous fiber compos-ite structures.

Continuous Fibers for StructuralComponents: Continuous fibers are al-ready being used in aircraft construction,wind energy generation, plant construc-tion, prototyping and in low volume au-tomobile applications. Carbon fibers of-fer a very high specific stiffness andstrength as a reinforcing material and aretherefore of particular interest. In com-parison glass fibers offer a large potentialas widely available cost effective materi-als: There are also new systems whichshow that the performance envelope ofthis traditional reinforcing material hasin no way been fully exploited yet. Thepossibility of combining the various ma-trix polymers with the various types offiber and textile architecture offers a highlevel of design freedom (Fig. 9). However,alongside the performance of the rein-forcing materials the mass productionsuitability and cost effective processesbased on fast matrix systems are impor-tant factors for the market success of con-tinuous fiber reinforced components.

In contrast to injection molded com-ponents with local continuous fiber rein-forcement the performance of such RTMcomponents is even better since the con-tinuous fiber reinforcement extends overthe entire part. The initially dry fibers androvings can also be processed to tailormade pre-forms and large 3-D compo-nents. Amongst these are highly loadedstructural vehicle components as well as

mounted parts such as doors, tailgatesand roof modules (see Title picture).

Up to now RTM technology has beenused for low volume runs in the luxuryvehicle sector such as Porsche spoilers orthe roof of the BMW M3 and racing carsas well as trucks and agricultural or con-struction machinery. In those applica-tions roofs, cowlings and cabin parts areproduced in 2K epoxy systems with glassand carbon fibers. At between 10 and20 min, depending on the part size, cycletimes with conventional matrix systemsare however still rather long.

Roof Module as a Concept Study: Thefirst demonstration part based on the var-ious materials from BASF suitable forRTM is the convertible roof module madeup of several sections in a sandwich con-

struction with carbon fiber reinforcedcover layers and a polyurethane foam core(Fig. 10). This roof segment forms the for-ward part of a three section RHT foldingroof concept (RHT: retractable hard top)which was conceived and designed byEDAG GmbH, Fulda, Germany, as a fea-sibility demonstrator for a generic fibercomposite sandwich concept with systemcomponents from BASF optimized witheach other.

The central layer of the demonstratorsandwich structure is a closed cell PURstructural foam from the Elastolit Drange. It serves as a low weight separatorfor the laminate cover layers which leadsto an exceptionally high component stiff-ness. In addition it gives the roof modulegood insulating properties. On the exte-rior the component is protected from UVradiation and other environmental influ-ences by a paint that contains the BASFTinuvin CarboProtect additive.

Upscaling this to a mass production ca-pable process will require a pre-formedfoam insert containing all the additionalinserts, covered on both sides with thechosen textile structure that is laid intothe mold and fully impregnated in a sin-gle operation. The PUR foam system spe-cially developed for this by BASF has a


Fig. 8. Scanning electron

microscopy: The picture

shows the multilayer con-

struction of a unidirection-

al carbon fiber epoxy lami-

nate. What can be identi-

fied is the layer thickness

homogeneity and high

quality of impregnation

Fig. 9. Various glass and carbon fiber textile structures based on wovens and non-wovens (left);

various RTM fiber composite laminates based on polyamide, polyurethane and epoxy resin (right)


high pressure and temperature resistance as well as low densi-ty. This ensures that the foam core is not compressed during theinjection phase.

The RHT roof segment as a fiber composite sandwich con-cept weighs 2.6 kg in total, which represents a weight reductionof 40 % compared to an aluminum construction and more than60 % compared to one made from steel, whilst offering a com-parable loading capacity under all typical design loading casesfor vehicle roofs.

Conclusion

With light but sophisticated high performance fiber compositecomponents and the associated composite raw materials it ispossible to replace even more metal, save weight and thus, in-dependent of the vehicle drive system, reduce energy consump-tion and CO2 emissions still further. In regard of cost-benefitconsiderations various matrix materials, fiber types, reinforc-ing techniques, joining technologies, predictive modeling andprocessing technologies are currently being researched and de-veloped in parallel and rigorously investigated for their suitabil-ity for mass production. Depending on the customer require-ment profile one or the other of these system solutions will beused so that it is likely that several technologies with establishthemselves in the marketplace side by side. Raw material man-ufacturers, part suppliers and OEMs will have to work togeth-er to establish the necessary competence required to fully ex-ploit the potential they offer. Without such multiple materialsystems the next leap in automotive lightweight constructionwill however not be possible.�

THE AUTHORS

DR. CLAUS DALLNER heads the multi-disciplinary Lightweight Composites

Team at BASF SE, Ludwigshafen, Germany.

JÖRG SCHNORR works in Business Development Automobile for the Engineer-

ing Plastics Europe business unit at BASF SE, Ludwigshafen.

DR. ANDREAS WOLLNY works in the marketing department of the Engineering

Plastics Europe business unit at BASF SE, Ludwigshafen.

DR. ANDREAS RADTKE works in the marketing department of the Engineering

Plastics Europe business unit at BASF SE, Ludwigshafen.

DR. MICHAEL HENNINGSEN works for the Global Epoxy Systems unit of the

Operating Division Intermediates at BASF SE, Ludwigshafen.

DR. GUIDO VANDERMEULEN works for the Global Epoxy Systems unit of the

Operating Division Intermediates at BASF SE, Ludwigshafen.

ANDREAS WOLF heads the Exterior/Composites segment within the European

Business Unit Automotive of BASF Polyurethanes GmbH, Lemförde, Germany.

DR. JAN K.W. SANDLER is Head of Materials and Systems Research for auto-

mobile fiber reinforced composites within the polymer research section at BASF

SE, Ludwigshafen.

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Fig. 10. RTM process demonstrator: The convertible roof module concept

study is made in sandwich construction with carbon fiber reinforced cov-

er layers and a polyurethane foam core


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