Sandwich materialsHylite

Automotive Applications

Vehicle weight

Vehicle weight

Materials on the moveMetal plastic sandwiches

Combine the best properties of metal and plastic in a single product

Hylite: developed for non load bearing car body parts (bonnet, boot lid, roof)

Steelite: can we do the same thing with steel and would that be profitable?

aluminiumpolypropylenealuminium

Material choice: Ashby diagram

Material choice: weight optimisation

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hylite 1.2/0.8

graphs atfixed rigidity

Material Weight Stiffnesskg/m2 Nm/unit width

Hylite 1.8 72001.2/0.8Steel 5.8 71000.74 mmAluminium 3.0 66641.10 mm

Mechanical properties for equal flexural stiffness

Material properties

Hylite total skin core YS skin A50 skinquality thickness thickness

[mm] [mm] [mm] [MPa] [%]

1,2/0,4 HYL 6.6.6 1,2 0,20 0,80 140 18 deep drawable

1,2/0,8 HYL 4.6.4 1,2 0,20 0,80 380 4 full hard

1,4/0,92 HYL 6.6.6 1,4 0,24 0,92 140 18 deep drawable

2,0/1,6 HYL 4.6.4 2,0 0,20 1,60 350 4 full hard

max. painting temperature 145C

Hylite history Development started in European project

Skin AA5182; core ABS

Lab produced panels successfully pressed into bonnets

Development of industrial production method

Replace ABS with PP for better form stability at high temperature

Pre-validation project with Volkswagen and Grau Werkzeugsysteme

Commercial production

Hylite product information

The Hylite laminate can be made in various gauges with a maximum width of 1540 mm and a maximum thickness of 2,5 mm.

The manufacturing process is set up in such a way that the thickness ratio and therefore also the stiffness, dent resistance and formability can be adjusted depending on the application.

Hylite is delivered as standard with a chromated surface, possibly with one or more layers of paint as required.

A moulded part made from Hylite maintains its shape during a coating treatment of 30 minutes at a maximum temperature of 150 c.

Hylite properties

(1,2 mm thick, with soft aluminium outer layers) Weight 1,8 kg/m2 Maximum stretch 22 % Plain strain stretch 18 % Peel strength 4 N/mm Flexural stiffness 7,1 kNmm (equal to 0,74 mm steel and 1,06 mm aluminium sheet

Aluminium yield point 140 MPa Aluminium tensile strength 280 MPa Shape retention to 150 C (for 30 minutes) Expansion coefficient 28*1 0-6/K Heat

conduction 0,3 W /mK Deep drawing also possible on soft tools

Product Variations Hylite is available in sheets with standard thickness between 1,2 mm and 2,5 mm. Maximum width is 1540 mm. The following aluminium outer layers are available:

AA 5182 (soft) for applications such as the deep drawing of bodywork panels AA 5182-H 18 (hard) for applications such as flat panels Precoated (primer)

Hylite processing

Hylite can be worked in the same way and using the same machines as steel or aluminium sheet, although the process parameters need to be adjusted.

The forces exerted on the blank-holder during deep drawing must not be too large and the angles in the die must not be too sharp.

The formation speed may be up to 60 mm per second (research is still being carried out on higher speeds).

The radius of the bending equipment must be 4-5 mm (with 1,2 mm Hylite). If a smaller bending radius is needed, for example for hemming, the specially developed hot bending technique can be applied.

Hylite processingMachining Hylite lends itself to machining as well as aluminium does; the vertical

movement speed must be slower with drilling.

The advantage of laminate over solid materials is that no burrs are formed when cutting takes place.

The clearance must be approximately 4 % of the thickness of the sheet.

Punching, to which this rule of thumb also applies, is another process to which Hylite lends itself admirably.

Formability

Lab scale stamping experiments with deep drawn pots

Biaxial stretched products

Forming limit diagram

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AA5182Hylite 1.2/0.8Hylite 1.4/0.92

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local necking curve

cracking curve

Formability

Flanging and hemming

Flanging Pre-hemming Hemming

Flanging and hemming

Hem flange example with 15 mm rib geometry

flange

pre-hem

hem

Hot ribbing

Preheating stage Cycle time Specific force

Hot ribbing stage Cycle time Specific force

2D Simulations

Reasons:

possibility to look into details

fast set up of the simulation possible

Goal:

to determine the behaviour of the different material layers of the sandwich

to investigate the effect of different tooling on the behaviour of the sandwich

only possible with plain strain processes

FEM Codes

2 codes used in modelling:

DiekA: University code

core shear only

skin membrane only (no bending)

PAM-stamp

3 layers shear, but independent

basically 3 stacked Mindlin elements!

Flanging and hemming: Set up of model

3 seperate layers, connected at the outer nodes; this to preventthat the stresses at the edge of each material are smoothed

Simulation of hot ribbing

High viscosity Low viscosity

Strains and stresses

Equivalent plastic strain Bending stresses (MPa)

Different Simulations, tooling

Flanging and hemming

calculations of pre-hemming after flanging

spring back calculations after hemming

5 mm rib geometry 15 mm rib geometry

The 5 mm rib can not be closed completely Strain distribution of the 15 mm rib is more favourable.

Strains and stresses

Equivalent strains

Deformed mesh

2D Simulations

2D simulations have shown:

main deformation mode core: shear

main deformation mode skins: membrane (= no bending)

Development & Testing show:

no delaminations

3D Simulations

For motor car industries, it is mandatory to perform and validate simulations before a new material can be introduced

Predictions from FE calculations were compared with strain analyses of parts pressed from Hylite

3D simulation product

Press with tool

Hylite product with grid for strain measurements

Tool geometry

Process model

Blanksize & mesh

Thickness outer skin

Thickness core

Shear strain core

DiekA results

Mini car bonnet Sharp feature near middle Low Blank Holder Force Extra lubrication in corners

Buckling simulations

locationof buckles

Rm

Rp

Rd

Free space

Tooling + Blank

40 [mm] draw depth

140 [mm] draw depth

Strain, 40 [mm]

Distribution of major strain, outer skin

Revised model

Distribution of minor strain, outer skin

PAM-Stamp results

Hemispherical cup

300 [mm] diameter

Sensitive to buckling

Find BHF buckling limit

FLD

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Minor strain

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BHF 1280 [kN]; 83 [mm];ESI results

BHF 1280 [kN]; 83 [mm],HR&D old results

FLC Hylite

SWLC

FEM Conclusions

Dieka

Good experience

Labour intensive

PAM-Stamp

User friendly

Buckling not so good

ESI working on Sandwich formulation

CRD&T working on material properties

Tool Wear Comparison was made of the tool wear

after deep drawing TiSulc and Hylite.

Samples have been deep drawn in a draw bead tester and wear patterns were measured with a profilometer on draw beads

Tool wear is significantly less for Hylitethan for steel.

Deep drawing forces are also much lower: with Hylite the punch force was approximately half the value for steel.

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Conclusions

The formability of Hylite is 20% in plane strain and 25% in biaxial strain.

The formability of Hylite is determined by the skin material, not by the core material.

Deep-drawing forces are much lower than for steel since only two skins of total thickness 0,4 mm will be deformed. This may lead to less tool wear and hence lower tool maintenance costs.

Bending Bending of Hylite

Cold free bending of Hylite is theoretically limited by the maximumuniaxial strain of the outer skin

However the position of the neutral line is also of importance in practical situations

Minimum inner bending radii for various products:

Joining Mechanical joining of Hylite proves a good alternative for spot

welding as applied for aluminium and steel.

The tested joining methods are: self-piercing rivet and blind rivet. The self piercing rivet is a 5mm length, 3,3mm diameter steel rivet, currently in use in Audi's A8. This rivet has obviously not been optimised for Hylite yet. The standard automotive Hylite quality 1,2mm has been tested.

self piercing rivet blind rivet

Joining

Punch side

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Die side

When mechanical joining methods are used in Hylite, they should preferably be used with Hylite on the die-side of the joining tool

To simulate the coating sequence specimen have been heat-treated for half an hour at 140C. This has no negative effect on the tensile strength of the joint.

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After heatingBefore heating

Self piercing river Blind river

Joining

After ageing

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Before ageing

To acquire some data on joint characteristics after a few years of service, some specimen have been subjected to mechanical ageing. Like the heat treatment the ageing has no negative effect on the tensile strength

Self piercing river Blind river

Clinching of Hylite is possible but will have a limited number of applications. The strength of clinched joints was about 400N. Itcan therefore only be used for fixing parts, e.g. during paint baking.

Joining conclusions

Both the self piercing rivet and the blind rivet prove to be good joining methods for Hylite

Hylite should, when mechanically joined, preferably be placed on the die-side of the joining tool

Neither a heat treatment (coating the panel) nor mechanical ageing has any negative effect on the tensile strength of the joint

Product performance In many automotive applications besides the flexural rigidity a certain

product stiffness and dent resistance will be required

The following materials will be compared:

The product stiffness is the elasticity of a curved panel expressed in N/mm elastic displacement

The static dent resistance is the force where a permanent dent of 0,1 mm depth has been formed.

Product stiffness In a Schenck- Trebel tensile testing machine, the product

stiffness of curved panels of 180mm diameter has been measured. The slope of the force-displacement diagram is the product stiffness

Dent resistance

Static dent resistance resistance against remaining deformation large mass, low speed ( hand palm pressing, luggage ) def: force to obtain a dent of 0.1 mm

Dynamic dent resistance resistance against cosmetic damage low mass, high speed ( stone chipping, hail) def: energy to obtain a dent of 0.4 mm

Dent resistance

Geometry standard product

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Static dent resistanceSchematic set up

Indenter (D = 127 mm)

ProductClamping

Height gauge

test speed 2mm/min

Static dent resistance

Displacement

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Static dent resistance

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Definition: Force to obtain a dent of 0.1 mm

Static dent resistanceHylite compared to steel and aluminium

YP product171 MPA

YP product235 MPa

YP product249MPa

YP product317 MPa

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Hylite1.4/0.92

1.5 mmAA6016

1.5 mmAA6016

0.75 mmSteel

0.75 mmSteel

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Static dent resistance In a Schenck-Trebel tensile testing machine, the static dent

resistance of curved panels of 180mm diameter has been measured. Dent depth was measured with a 3D measure machine

Dynamic dent resistance

Impact energy determines the resulting dent

Dynamic dent resistance

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Dent shape and dent depth measurement

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Hylite 1.4/0.92Hylite 1.2/0.8AA6016 1.15 mm 286MPaAA6016 1.15 mm 171MPa

Definition: Energy needed to create a dent of 0.4 mm depth

Dynamic dent resistance

Dynamic dent resistanceHylite compared to steel and aluminium

YP product 235 MPa

YP product171 MPa

YP product 249 MPa

YP product317 MPa

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0.75 mmSteel

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Dynamic dent resistance Dynamic denting with 25 mm ball of 64g has been carried out on

plane circular specimen of 50 mm clamped along its outer contour

Product performance results

The static dent resistance of Hylite is strongly influenced by its thickness

An extremely high dent resistance at low weight can be achieved using 2,4 mm Hylite

Hylite is the lightweight solution even when additional to flexural rigidity demands upon dent resistance are made

Corrosion resistance

Since paint coatings largely prohibits corrosion, the intrinsic corrosion resistance of Hylite has been measured on the bare material.

Two methods have been applied: Corus Cyclic Test (CCT) Salt Spray Test (SST)

A comparison with hot dip galvanised steel (HDG) was made

(The CCT is an accelerated cyclic corrosion test of a total duration of 5 weeks per cycle, simulating one year including seasonal effects. These 5 weeks are divided into 140 periods of 6 hours to simulate day-night cycles. Humidity (50-100%), chemical attack and temperature (25-50C) are set for each period of 6 hours. As standard practice the test will be run for 10 weeks, thus simulating 2 years of car use. Criteria for evaluation are delamination and rust formation.)

Corrosion of HDG after 10 weeks CCTCorrosion of Hylite after 10 weeks CCT

Corrosion Resistance

Corrosion of Hylite after SST Corrosion of HDG after SST

Corrosion resistance

After SST no deterioration could be observed in Hylite

After CCT only slight pit corrosion could be observed in Hylite, no perforation appeared

For Hylite the adhesion between aluminium and polypropylene has not been affected

Hylite shows superior corrosion resistance when compared to HOG-steel

Pre-validation To validate the suitability of this material for the mass production

of automotive body outer panels, a pre-validation project of producing a bonnet was conducted.

Focus was on cycle time, quality and cost. The component selected needed to be of complex, modern and sophisticated design in order to provide a true test of the material's suitability for use in the manufacture of to day's automotive body outer panels.

Project was joint undertaking of former Hoogovens (supplier, management, know-how), Volkswagen (bonnet design, processing) and Grau Werkzeugsysteme (tooling)

Pre-validation

To produce the steel bonnet, 10 processing operations are required, which are determined by the complexity of the design.

To make a well-defined hem in steel, it takes six process operations.

In the case of Hylite it takes two preparatory ribbing operations, followed by four hemming operations.

Pre-validation process

500 bonnets were stamped. Grau engineered, built and installed a complete set of tools for this purpose

From flat sheet to car bonnet in 10 operations:1. Stamping blanks: blanks were trimmed and supplied by former

Hoogovens2. Deep-drawing: Press forces were lowered, design of drawbeads were

adjusted to hylite. Speed of 12 cycles/minute (transfer not included) using standard lubricants

Pre-validation process

3/4. Ribbing: needed for sharp hem. Pad retainer and ribbing die are applied to inside of bonnet. Heated ribbing die (250C) is then pressed into Hylite. Operation takes 20s.

5/6. Trimming: Cutting clearance is slightly less than with aluminium. Cut edge is smoother due to less formation of burrs

7/8. Flanging: Conventional9. Pre-hemming: Conventional10. Finish-hemming: Conventional

Ribbing Hemming Finished bonnet

Pre-validation

Pre-validation used industrial tooling and manufacturing in industrial environment

Successful completion of 500 bonnets demonstrates that Hylite is suitable and ready for mass production of automotive body outer panels

Deep-drawing and hem flanging takes same number of steps as steel and aluminium. Cycle-times: 5s for deep-drawing, 20s for ribbing in assembly line

Reproducible process that meets OEMs requirements

Design studies bonnet

Bonnet with Hylite outer part and aluminium inner part

Demanded: better torsion stiffness

Alternative rib designs inner part

There is no universal optimum design there is always interaction with the materials used

Automotive Applications

Hylite is used in the bottom of the two latest models of the Aixam microcar, the Aixam 300 and 400.

One square meter of Hylite, 50% lighter bottom sheets than aluminium

Automotive Applications

1999 IAA: announcement of Audi A2 as world-wide first aluminium mass-produced car

Contact arose from bonnet pre-validation

Panels were originally of aluminium (550-600g a piece), but the current Hyliteproduct weights 350g.

1998 trials, 1999 supply with 3x1.54m large plates, 1.4mm thickness

Top floor panels are located under the front seats

Future production aims at 50.000 cars per year

Automotive Applications

Sound dampening

Using Hylite for certain panels can be a useful way of avoiding 'metallic' sound, and obviates the need for damping materials which add to both weight and cost.

Sound dampening has been tested in a car sliding sun roof panel.The material tested is deep drawable 1,2mm Hylite.

Tapping a Hylite panel produces a less 'metallic' sound than steel sheet or aluminium. This is because the damping factor of the laminate is 18,5dB higher than for steel and 20dB higher than for aluminium.

Hylite is a low-noise material; replacing steel or aluminium with Hylite enhances sound comfort in certain applications where contact noise is a problem.

Sound dampeningSliding sunroof The sliding sun roof of certain cars is finished on the underside with a

steel trim panel. This panel produces a metallic, hollow sound when tapped. This contact noise is sometimes not acceptable.

The complaint was resolved at considerable expense by sticking sound damping material onto the panel.

Study In an experimental set-up the contact noise of this steel trim panel was

compared with a Hylite version. Both an undamped and a damped version of the steel panel were tested.

Contact noise from the three different versions of the trim panel was assessed in a test involving a group of volunteer listeners.

Sound dampeningResults The overall sound level of Hylite was 3,4dB(A) lower than that of the

steel panel.

The Hylite panel and the damped steel panel produced a comparable noise spectrum when tapped.

Conclusions Using Hylite in the sliding roof panel avoids undesirable (metallic)

sound coloration from the trim panel. Adding damping material isthen no longer necessary.

In general Hylite can be useful in metal panels in very poorly damped constructions in which the contact noise produces an unacceptable sound, for example in various roofing panels and sliding car door panels.

Transport applications

Super light panels with Hylite skins

Super-light panel construction

For the Super-Light Panels a Hylite quality with aluminium layers of 0,2 mm and an inner layer of 0,8 mm thickness has been chosen (total thickness of 1,2 mm)

Aluminium or plastic honeycomb core The core of the panel consists of an aluminium or plastic honeycomb, depending on the actual application. Also a hard foam core is possible

The panels are bonded by a 2-component epoxy.

Super-light panel construction The internal shape of a honeycomb structure results in high stiffness

and strength but low deformation and weight

The combination of Hylite skin and the honeycomb core results in a very flat panel

The weight reduction compared to more traditional panels with analuminium skin ranges from 15 - 35%, as indicated in the table on the backside of this leaflet

Applications:Ship building industry (floor and wall panels), Air cargo industry (floor and wall panels), Car industry (floor panels), Coach work industry (panels)

Transport applications

Extreme low weight is of special importance in aircraft industry.

Hylite is used for airfreight containers catering trolleys due to its low weight and good dent- and damage resistance.

Non-automotive applications

Transport containers, airplane trolleys, train doors, x-ray film cassettes, laptop holders, note blocks

Hylite can be easily folded: just remove the skins on both sides

Special Hinge

Just remove the aluminium skins by grinding or machining on opposite sides of the Hylite sheet. The polymer core is exposed and the sheet can be folded

This principle is used in the foldable sheets for the vehicle market

The sheets are also functionally tested by RWTUV in a broad temperature range: After 80.000 folding movements no deterioration could be observed

Hinge application

Examples of our design studies

Laptop case

Chair

Examples of our design studies

Portable exhibition stand

Hylite: Best of both metals