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FULL SET OF INNOVATIVE TOOLS FOR THE PREDICTION OF LASER WELDED BLANK FORMABILITY IN SIMULATION

Daniel Duque Múnera (a)ArcelorMittal – Noble International

Sadok Gaied (a)(c), Fabrice Pinard (b), Francis Schmit (a), Jean-Marc Roelandt (c), Kalyan Palanisamy (b)

(a) ArcelorMittal R&D, Automotive Applications Research Center, France(b) Noble International (c) Université de Technologie de Compiègne, Laboratoire Roberval, UTC/CNRS, France

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OUTLINE

• Laser Welded Blanks (LWB) overview• LWB fracture modes overview• Forming Limit Curve for LWB

– Problem of the application of FLC concept to LWB– Formability testing– Experimental results– Numerical modeling– Industrial application

• A new model for the prediction of Laser assemblies’maximum elongation– Results comparison between experiments and model– Industrial application

• Conclusion

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LASER WELDED BLANK OVERVIEW 1/3

• Characteristics– Various steel grades Laser welded

together • Different strengths• Different gauges• Different coatings

– Single blank prior to the forming process

• Benefits– “The best material in the right place”– Cost savings– Mass savings– Crash management– Reduction in number of parts– Reduced off-cuts

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LASER WELDED BLANK OVERVIEW 2/3

• Applications

Bumperbeam

Shocktower

Floor panel

Front Rail

Fire wall /dash panel

Crossmember

Pillars

Roof reinforcement

Wheel house

Body side innerBody side outer

Doorinner

Tailgate

Side member

HSSHSS

DUALDUALPHASEPHASE

DDQDDQ

TRIPTRIP

MULTIMULTIPHASEPHASE

USIBORUSIBOR

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LASER WELDED BLANK OVERVIEW 3/3

• Market Example: Renault Laguna III 2007, 18 LWB

A-Pillar innerL&R

Lateral floorpanel L&R

Front railclosing plate

L&R

Rear Door InnerL&R

Cradle closingplate*

Up & Down

Fire wall

Front Door InnerL&R

Front railL&R

Rear rail*L&R

* For some models

Cross member

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LWB FRACTURE MODES OVERVIEW

Fracture in base material

Fracture in the welding seam

– Mode 1– Fracture in base material with propagation parallel to

weld line– This model is related to the interaction between the two

materials– Already well-known, ArcelorMittal and Noble Forming

Limit Curve (FLC) specific model

– Mode 2– Fracture in weld seam with propagation in base materials– This mode is related to the mechanical properties of the

Laser seam– A new model for the prediction of Laser assemblies’

maximum elongation has been developed

• Two principal fracture modes

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FORMING LIMIT CURVE FOR LWB 1/6

Fracture in base material

• Problem of the application of FLC concept to LWB

0,00

0,10

0,20

0,30

0,40

0,50

-0,40 -0,30 -0,20 -0,10 0,00 0,10 0,20 0,30 0,40

Minor

Maj

or

FLC of weaker material Experimental dataStrain measurement

– Monolithic FLC of weaker material does not predict any rupture

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FORMING LIMIT CURVE FOR LWB 2/6

• Formability testing– The Nakazima method has been used – A carrier blank has been used to compensate the different gauges

between the thinner and the thicker sheets– The Bragard method is used in order to obtain the FLC points

0

10

20

30

40

50

60

-50 -30 -10 10 30 50

Minor Strain

Major Strain

Forming Limit Curve

ε10C : Major strain in

plane-strain path

Die

Thicker Blank

ThinnerBlank

Carrier Blank

Blank Holder

Punch

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FORMING LIMIT CURVE FOR LWB 3/6

• Experimental results– The experimental set-up has been used for various

configurations• Same thickness and different grade specimens• Same grade and different thickness specimens• Both different thickness and grade specimens

– The interaction between weaker and stronger materials plays a determining factor in LWB forming processes

• Ductile failure by plastic instability process– A specific Laser Welded Blank FLC model is required

to accurately predict the onset of necking

LWB MS(0.8) / HSS(1.2) MS(0.8) / MS(1.5) MS(0.8) / HSS(1.2)

ε10C Weaker material 0.33 0.33 0.38

ε10C LWB 0.2 0.187 0.29

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FORMING LIMIT CURVE FOR LWB 4/6

• LWB Forming Limit Curve

0,0

10,0

20,0

30,0

40,0

50,0

-20,0 -15,0 -10,0 -5,0 0,0 5,0 10,0 15,0 20,0

Minor

Major

LWB Forming Limit Curve MS (0.8mm) / HSS (1.2mm)LWB Forming Limit Curve MS (0.8mm) / MS (1.5mm)LWB Forming Limit Curve MS (1.2mm) / HSS (1.2mm)

Welded seam

Necking zone

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FORMING LIMIT CURVE FOR LWB 5/6

• Numerical modeling– Abaqus model

Necking zone

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FORMING LIMIT CURVE FOR LWB 6/6

• Necking zone– The numerical simulation

shows that the fracture occurs in the weaker material next to the Laser seam

• The plastic instability process is directly related to the interaction between the two materials

• The deformation during this phase is localized in the necking region of the specimen

Thicker blank

Thinner blank

Carrier Blank

Necking zone

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INDUSTRIAL APPLICATION 1/2

• LWB fracture prediction

A1 B1A1 B1

LWB FLC allows prediction of rupture by stamping simulation

Fracture on real part

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INDUSTRIAL APPLICATION 2/2

• LWB fracture prediction– Thanks to the FLC LWB model, an excessive stretching

area near the weld line is identified

A1 B1

Simulation without LWB FLC for material A1 and B1

Simulation with LWB FLC for material A1 and B1

LWB FLC for material A1 and B1 Monolithic FLC for material B1

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PREDICTION OF LASER ASSEMBLIES’MAXIMUM ELONGATION

Mechanical analysis

UE1, Ts1, t1,

UE2, Ts2 , t2…

Thermal analysis

P, V…

Metallurgical analysis

C1, P1, C2, P2 …Base metal HAZ WZ

Ductile fracture

Plastic instability, fracture criteria

HAZ and FZ geometry

Thermal history

Percentage of various phases

0

0,2

0,4

0,6

0,8

1

1,2

0 Time (s)

% p

hase

FerriteB ainiteMartensiteAustenite

Weld line mechanical behaviour

0200400600800

100012001400

0 0,005 0,01 0,015 0,02Strain (%)

Str

ess

(MP

a

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0

2

4

6

8

10

12

14

16

18

0 2 3 4 5 6 7 8 9 0 2 3

UE

(%)

Experimental results

Model prediction

RESULTS COMPARISON EXPERIMENTAL vs. MODEL

Difference ± 1%

Assembly configurations

• Various configurations of assembly have been tested with a large variety of thickness and various steel grades such as Dual Phase 600, Dual Phase 780, Dual Phase 980, TRIP 700, TRIP 800, Multiphase 1000…

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INDUSTRIAL APPLICATION 1/2

• Fracture prediction of Laser seam

– Major strains are almost parallel to weld seam as shown by simulation

– Uniform elongation obtained during LWB assembly tensile test is 13 %

– Margin = -2.3 %. There is not enough margin to avoid fracture in the Laser seam

Major strain value: 13.3 %

Fracture on real partMajor strains direction and value analysis on

stamping simulation

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CONCLUSIONS

• Laser Welded Blank Forming Limit Curve– Weaker material FLC may not predict the onset of necking of

LWB though fracture actually occurs in weaker material– LWB FLC allows accurate prediction of fracture in the interaction

zone in stamping simulations• Maximum elongation

– In the cases where crack initiation appears at the weld seam (major strain parallel to weld seam), maximum elongation model for LWB assemblies allows prediction of fracture in stamping simulations

• These two models may be used to analyze stamping simulations of LWB in order to guarantee part feasibility

• They are particularly suitable for AHSS-based LWB solutions

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Great Designs in Steel is Sponsored by:AK Steel Corporation, ArcelorMittal, Nucor Corporation,

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