dry cleaning and pretreatment of aluminum sheets using ... · 4-step wet-chemical pretreatment...

© Fraunhofer IWS KLZ: 22.10.2019 P2C - Forum

DRY CLEANING AND PRETREATMENT OF ALUMINUM SHEETS USING HIGH-RATE LASER PROCESSING

Annett Klotzbach, Tom Schiefer, Robert Kühne, Jens Standfuß

Fraunhofer Institut für Werkstoff- und Strahltechnik Dresden


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Fraunhofer IWS Dresden Application-adapted research for industry and society


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Fraunhofer IWS Dresden Working group: Bonding and Composite technology


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AGENDA

Fiber metal laminate / GLARE processing

Requirements for pretreatment

Process overview

Pretreatment by laser

Results of mechanical testing

Conclusion © fokker.com

© CTC Staade

Dry cleaning and pretreatment of aluminum sheets using high-rate laser processing


Fiber metal laminates (FML)

GLARE®

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Glass fiber reinforced aluminum (GLARE)

Aluminum sheets (AA2024), 0.3 mm – 0.4 mm

uni-directional S-glass fiber prepreg + epoxy resign 0.13 mm

Fiber orientation based on loading condition

Schematic image of splice

Cross section

©: theatlasgroup.biz

GLARE - Advantages

Density of GLARE approx. 10% lower than monolithic aluminum

High corrosion stability

Corrosion attack will be limited by prepreg layer

Higher damage resistance

Higher fatigue properties based on reduced crack growing


GLARE production steps

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-> Lay-up (manually)

Coil delivery ->

Source: Fokker

Part cutting by milling-> PSA-treatment -> Primer-coating ->

-> Autoclav -> Finished GLARE part


Requirements for surface pretreatments

SOA

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Phosphoric acid anodizing

State of the art pretreatment:

4-step wet-chemical pretreatment

Cleaning, etching, anodizing, primering

Specific surface (~4 µm ablation), defined oxide layer

Treatment time, human safety, costs, environment protection, legal requirements

Requirement:

Pretreatment with dry (physical ) processes

Active (oxide layer) and passive (adhesion) corrosion resistance

Production factors (automation, time in m²/min, costs, safety)


Laser pretreatment

Principle

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Pulsed laser ablation

Interaction of light energy and part surface

Material melting, vaporizing and/or ablation

Material and wavelength specific interaction

Removal of layer thicknesses up to some 100 µm

Laser processes realize:

surface cleaning (removal of oil, dust, paint, rust,…)

Surface enlargement (topography change)

Surface activation (new oxide layer)

Treatment of points, lines, areas, contours (easy to automate)

Process productivity is determined by average laser power


Laser pretreatment from PRECISE to PRODUCTIVE

Laser setups

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2D - pulsed laser ablation

ns - laser vscan: 5 m/s typical, Plav.: up to 500 W

2D - cw laser processing

cw - laser vscan: 15 m/s typical, Plav.: up to 3 kW

cw - laser vscan: 300 m/s typical, Plav.: up to 5 kW

1D - cw laser processing (R2R)


R2R laser pretreatment

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Principle

Combination of „laser beam scanning“ and „laser beam switching“

Proven technology: laser treatment of electrical ferritic sheets („laser magnetic domain refinement“)


R2R laser pretreatment

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Experimental setup

quick 1D-beam deflection (up to 300 m/s)

continuous material movement (up to 80 m/min)

Programmable line distance and length

Modified laboratory system

Parameter

Wavelength 1070 nm

Laser power 2000 - 5000 W

Scan speed up to 300 m/s

Fokus diameter ellipse (a = 18 µm, b= 460 µm)

Step-by-step material transport


Structuring results@AA2024uc, 0.3 mm thickness

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Results

Parameter setup

P = 5000 W

Scan speed: v = 150 - 300 m/s

Line distance: 50 µm

Results

Line width: 28 - 41 µm

Ablation depth: 8 – 15 µm

500 µm

Complete line processing with artificial oxide layer


Structuring results@AA2024uc, 0.3 mm thickness

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Enlargement of oxide layer thickness

Results

Parameter setup

P = 5000 W

Scan speed: v = 150 - 300 m/s

Line distance: 50 µm

Results

Line width: 28 - 41 µm

Ablation depth: 8 – 15 µm


Testing of adhesion properties

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Adhesion tests

Pk. Pretreatment Primer B Non treated --- LM Solvent Yes TSA Wine-sulfur-anodizing Yes pw1 pw-Yb:YAG (fiber laser) Yes pw2 pw-Nd:YAG (rod laser) Yes cw1 1D-cw-Remote Yes cw2 1D-cw-Remote yes

Cross section tensile test specimen

Tensile shear test specimens (DIN EN 2243-1) thickening on both sides

Peel test specimen (DIN EN 2243-2)

Material: AA2024 uc ; 0.3 mm

Adhesive: GF-Epoxy resin

Primer: Cr(VI) - Primer

Thickening: 1.6 mm

Thickening: 1.6 mm

Pre-treated

foils

Autoclav - run



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LM (adhesion) TSA (cohesion) cw1 (cohesion)

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5

10

15

20

25

30

35

40

45

50

B LM TSA PSA* pw1 pw2 cw1 cw2

Ten

sile

sh

ear

stre

ng

th

[MPa

] *) PSA-reference AA2024 unclad

Adhesion tests





Primer: Cr(VI) - Primer



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B LM TSA PSA* pw1 pw2 cw1 cw2

Peel

res

ista

nce

[N

/mm

] comparison (cw1- TSA)

cw1 (cohesion)

TSA (adhesive failure between AA2024/Primer)

Adhesion tests





Primer: Cr(VI) - Primer *) PSA-reference AA2024 unclad


Comparison of processes

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Comparison

© Fraunhofer IFAM

Treatment Lap Shear [MPa]

Peel Test [N mm-1]

FFT 2nd-6th fil. / mm

SST 3000h 3)

2nd -6th del. / mm

Requirements 30 7.21) 2 1.25

Laser 375) 7.85) 1.75) 0.2

Plasma 355)/256) 2 > 56) >> 2

Anodising tape

315)/306) 4.25)/7.26) 1.4 – 4.86, 2) 0.5.. > 3.02)

PSA 315)/366) 9.55)/8.76) 0.75)/1.06) 0.5

1) IPS 10-01-008-01 issue 3 (Structural adhesive film for GLARE application FM94K.06) 2) Depending on surface treatment 3) AA2024 uc, chromate loaded coating system 5) AA2024 uc 6) AA2024 c


Fatigue and damage tolerance properties

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Fatigue testing

Fatigue crack initiation life

Crack propagation

Residue strength as function of fatigue damage


Fatigue and damage tolerance properties

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Fatigue testing

Fatigue crack initiation life

Crack propagation

Residue strength as function of fatigue damage


Conclusion - Outlook

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Conclusion

Processes can fulfill the adhesion requirements (strength, FFT, SST)

Material removal is needed for good adhesion and corrosion behavior

Good fatigue properties

Processing speeds of up to 1 m²/min possible

SOA

Laser treatment R2R


Conclusion - Outlook

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Conclusion

Processes can fulfill the adhesion requirements (strength, FFT, SST)

Material removal is needed for good adhesion and corrosion behavior

Good fatigue properties

Processing speeds of up to 1 m²/min possible

The presented work was funded within the aviation research project „AUTOGLARE“ (FKZ: 20W1517D), leading by AIRBUS.

Annett Klotzbach

[email protected]

Mobile: +49 1722414077

dry cleaning and pretreatment of aluminum sheets using ... · 4-step wet-chemical pretreatment...

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