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

Transcription

1 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

2 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

3 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

4 LASER WELDED BLANK OVERVIEW 2/3 Applications Roof reinforcement Tailgate Pillars Side member Wheel house Body side inner Body side outer USIBOR TRIP Cross member MULTI PHASE Fire wall / dash panel DUAL PHASE Bumper beam Shock tower Front Rail Floor panel Door inner HSS DDQ

5 LASER WELDED BLANK OVERVIEW 3/3 Market Example: Renault Laguna III 2007, 18 LWB Fire wall Front rail closing plate L&R Front rail L&R Cradle closing plate* Up & Down Cross member Rear rail* L&R Rear Door Inner L&R Front Door Inner L&R A-Pillar inner L&R Lateral floor panel L&R * For some models

6 LWB FRACTURE MODES OVERVIEW Two principal fracture modes 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

7 FORMING LIMIT CURVE FOR LWB 1/6 Problem of the application of FLC concept to LWB Monolithic FLC of weaker material does not predict any rupture Fracture in base material 0,50 0,40 Major 0,30 0,20 0,10 Strain measurement 0,00-0,40-0,30-0,20-0,10 0,00 0,10 0,20 0,30 0,40 FLC of weaker material Experimental data Minor

8 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 Blank Holder Thicker Blank Punch Thinner Blank Die Carrier Blank Forming Limit Curve 0 Major Strain ε 10C : Major strain in plane-strain path Minor Strain

9 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) ε 10C Weaker material ε 10 C LWB

10 FORMING LIMIT CURVE FOR LWB 4/6 LWB Forming Limit Curve Welded seam Necking zone 50,0 40,0 Major 30,0 20,0 10,0 0,0-20,0-15,0-10,0-5,0 0,0 5,0 10,0 15,0 20,0 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) Minor

11 FORMING LIMIT CURVE FOR LWB 5/6 Numerical modeling Abaqus model Necking zone

12 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 Carrier Blank Thinner blank Necking zone

13 INDUSTRIAL APPLICATION 1/2 LWB fracture prediction A1 B1 A1 B1 Fracture on real part LWB FLC allows prediction of rupture by stamping simulation

14 INDUSTRIAL APPLICATION 2/2 LWB fracture prediction Thanks to the FLC LWB model, an excessive stretching area near the weld line is identified LWB FLC for material A1 and B1 Monolithic FLC for material B1 A1 B1 Simulation with LWB FLC for material A1 and B1 Simulation without LWB FLC for material A1 and B1

15 PREDICTION OF LASER ASSEMBLIES MAXIMUM ELONGATION Thermal history HAZ and FZ geometry Thermal analysis P, V Metallurgical analysis C1, P1, C2, P2 Mechanical analysis UE1, Ts1, t1, UE2, Ts2, t2 Plastic instability, fracture criteria % phase 1,2 1 0,8 0,6 0,4 0,2 0 0 Time (s) Base metal HAZ WZ Percentage of various phases Ferrite Bainite Martensite Austenite Weld line mechanical behaviour Ductile fracture Stress (MPa ,005 0,01 0,015 0,02 Strain (%)

16 18 16 Difference ± 1% RESULTS COMPARISON EXPERIMENTAL vs. MODEL Experimental results Model prediction UE (%) 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

17 INDUSTRIAL APPLICATION 1/2 Fracture prediction of Laser seam Major strain value: 13.3 % Fracture on real part Major strains direction and value analysis on stamping simulation 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

18 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

19 Great Designs in Steel is Sponsored by: AK Steel Corporation, ArcelorMittal, Nucor Corporation, Severstal North America w w w. Inc. a u and t o s United t e e States l. o r gsteel Corporation