Automotive Applications Stamping

Sandwich materials Hylite

Automotive Applications

Vehicle weight

Vehicle weight

Materials on the move Metal 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) aluminium polypropylene aluminium

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

Material choice: Ashby diagram

Material choice: weight optimisation 1

graphs at fixed rigidity

steel

relative sheet weight

0.8

Material 0.6

Weight Stiffness kg/m2

Nm/unit width

aluminium

Hylite 0.4

1.8

7200

5.8

7100

3.0

6664

1.2/0.8

Steel 0.74 mm

hylite 1.2/0.8

0.2

Aluminium 1.10 mm

0 0

20

40

60

80

plastic volume fraction [%]

100

Mechanical properties for equal flexural stiffness

Material properties Hylite quality

total thickness [mm]

skin core thickness [mm] [mm]

YS skin

A50 skin

[MPa]

[%]

1,2/0,4 HYL 6.6.6

1,2

0,20

0,80

140

18

1,2/0,8 HYL 4.6.4

1,2

0,20

0,80

380

4

1,4/0,92 HYL 6.6.6

1,4

0,24

0,92

140

18

2,0/1,6 HYL 4.6.4

2,0

0,20

1,60

350

4

max. painting temperature

145°C

deep drawable full hard deep drawable full hard

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 processing Machining • 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 0.4

e1 (major strain)

cracking curve 0.3 local necking curve

0.2

AA5182 Hylite 1.2/0.8 Hylite 1.4/0.92 0.1

0 -0.2

-0.1

0

0.1

e2 (minor strain)

0.2

0.3

0.4

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 prevent that 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 5 mm rib geometry

15 mm rib geometry

• calculations of prehemming after flanging • spring back calculations after hemming

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

Strains and stresses

• Deformed mesh

• Equivalent strains

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

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

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 “Free” space

Rm

Rd

Rp

location of buckles

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

0,30 0,25

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

Major strain

0,20

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

0,15

FLC Hylite

0,10 SWLC 0,05

-0,10

0,00 -0,05 0,00

0,05

Minor strain

0,10

0,15

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.

• Tool wear is significantly less for Hylite than for steel. • Deep drawing forces are also much lower: with Hylite the punch force was approximately half the value for steel.

Wear [µm]

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

Length of steel metal [m]]

Tool Wear 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 maximum uniaxial 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

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

Force [N]

Joining

Die side

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

Blind river

Force [N]

Self piercing river

Punch side

Before heating

After heating

• 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

Force [N]

Joining

Before ageing

After ageing

Self piercing river

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

Blind river

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

r =r=20 20 mm mm

hh=50 = 50mm mm r = r=20 20 mm

RR 0

-200

-150

-100

-50

0

50

distance (mm)

R = 2000 mm

100

150

200

Static dent resistance Schematic set up

Indenter (D = 127 mm)

Product Clamping

Height gauge test speed 2mm/min

Force

Static dent resistance

dent depth

Displacement

Dent depth (mm)

Static dent resistance

0.2

0.1

0 0

150

F0.1

300

Force (N) Definition: Force to obtain a dent of 0.1 mm

Static dent resistance Hylite compared to steel and aluminium YP product 235 MPa

static dent resistance (F0.1) [N]

300

YP product 171 MPA

200

YP product 317 MPa YP product 249MPa 100

0

Hylite 1.2/0.8

Hylite 1.4/0.92

1.5 mm AA6016

1.5 mm AA6016

0.75 mm Steel

0.75 mm Steel

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 Dent shape and dent depth measurement 1 0 -100

-50

0

50

100

-1 -2

before denting

-3

after denting

-4

0.05 -100

-50

-0.05 0

50

-0.15

dent shape -0.25 -0.35

100

Dynamic dent resistance 1.8

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

1.6

dent depth [mm]

1.4 1.2

1 0.8

0.6 0.4

0.2 0 0

0.2

0.4

0.6

0.8

1

1.2

1.4

impact energy [J]

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

1.6

Dynamic dent resistance Hylite compared to steel and aluminium dynamic dent resistance (E 0.4) [Joules

0.8

YP product 235 MPa

0.7

0.6

YP product 249 MPa

YP product 317 MPa

0.75 mm Steel

0.75 mm Steel

YP product 171 MPa

0.5

0.4

0.3

0.2

0.1

0

Hylite 1.2/0.8

Hylite 1.4/0.92

1.5 mm AA6016

1.5 mm AA6016

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 (25-50°C) 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 Resistance

Corrosion of Hylite after 10 weeks CCT

Corrosion of Hylite after SST

Corrosion of HDG after 10 weeks CCT

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. 2.

Stamping blanks: blanks were trimmed and supplied by former Hoogovens 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 (250ºC) 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: Conventional 9. Pre-hemming: Conventional 10. 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 OEM’s 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 (550600g a piece), but the current Hylite product 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 dampening Sliding 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 dampening Results • 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 is then 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 an aluminium 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

• Chair

• Laptop case

Examples of our design studies • Portable exhibition stand

Hylite: Best of both metals