The Application of Multiphase Steel in the Body-in-White Dr.-Ing. Markus Pfestorf BMW AG
1. Demands on materials 2. Functionality 3. Mechanical data of sheet materials 4. Material grade application 5. Forming 6. Joining 7. Summary and outlook
Demands on Material Process and Product Forming Formability Punch force Forming limit diagram Cutting Cutting forces Spring back Joining Spot Welding Adhesive Bonding MIG welding MIG brazing Laser welding Riveting Surface/ Corrosion Class A surface Adhesive bonding Paint adhesion Contact corrosion Functionality Ductility during crash (R p0,2, R m, A 80, ) Fatigue strength E-Modulus (stiffness) Weight (density) Frequency attenuation Acoustics Process: Press-Shop Body-in-White Paint Product
BMW Functionality Parameters for Crash Performance BMW rear, 50 km/h, 40 % US-FMVSS 301, 80 km/h, 70 % - IIHS low speed, 8 km/h, others, AZT-front/rear, 15 km/h, 40% FMVSS 201 FMVSS 208 Roof hitting test Roll over EURO-NCAP, 64,4 km/h, 40 % US-NCAP, 56,3 km/h, 100% Pole (front), 50 km/h, middle JAPAN-NCAP, 55 km/h, 90 US-LINCAP, 62 km/h Pole (side), 29 km/h IIHS side, 50 km/h www.autosteel.org
Functionality Crash Testing (BMW 6 series coupé) Data for rear crash Car weight: 1978 kg Barrier weight: 1365 kg Barrier speed: 81,7 km/h Results: No impact of fuel tank No impact in passenger cabin No brittle fracture of trunk lid
Functionality Stiffness 32 Hz Torsion 29 29,8 28 Hz Bending 26 26,5 1. Torsion 28 26 24 22 22,8 24,8 1. Bending 24 22 20 20,6 21,8 E28 (1981) E34 (1988) E39 (1995) E60 (2003) f ~ c m E28 (1981) E34 (1988) E39 (1995) E60 (2003) Inflated scale
Functionality Stiffness Bending Torsion
Mechanical Data Sheet Steel Elongation at fracture A 80 50 % 40 35 30 25 20 15 10 5 0 deep drawing steel 6xxx (T4) IF 5xxx Stainless steel 6xxx (T6) TWIP-steel phosphorus alloyed steel Bake Hardening TRIP Micro alloyed DP Work hardened 0 200 400 600 800 1000 N/mm² 1400 CP MS Yield strength R p0,2
Mechanical Data Comparison: H400T H420LA Yield strength R p0,2 1200 N mm² 800 600 400 200 H400T (TRIP700) H420LA (ZSTE420) 0 0 0,1 0,2 0,3 0,4 Forming rate
Mechanical Data Work and Bake Hardening Effects Delivery values before forming Forming Work hardening Paint oven Bake hardening Final value of finished products 800 Yield strength Rp0,2 N mm² 400 200 H300LA (Micro-alloyed) H300B (Bake-hardening steel) 0 H300X (Dual-phase steel) (Supplier data)
Material Grade Application Increasing Utilization of HS Steels BMW 3 Series (SOP 1997) BMW 7 Series (SOP 2001) BMW 5 Series (SOP 2003) BMW 3 Series (SOP 2004) Percentage of material (body in white incl. hang on parts) Deep Draw Steels 180 N/mm² 200-220 N/mm² 260 N/mm² 300-340 N/mm² 380-420 N/mm² 500-680 N/mm² > 900 N/mm² Plastics Others AlMg aluminum AlSi aluminum
BMW Material Grade Application Detailed Case Study: BMW 3 Series 180 N/mm² 19% Deep drawing steel 19% Others 1% >900 N/mm² 1% 500-800 N/mm² 6% 380-420 N/mm² 12% 200-220 N/mm² 11% 260 N/mm² 9% 300-340 N/mm² 22% www.autosteel.org Steel Other steel DC 03/04 DX 54 DX 56 H180B, H180Y H220B, H220Y H260B, H260Y, H260LA H300B, H300LA, H300X H340LA, H340X H400T H420LA D680C Docol1000 Plastics/others Plastics Others
Material grade application Impact load path at the BMW 3 series Load path for frontal impact Deformable front Rigid passenger cabin Load path for side impact Multi-phase steel grades
Material grade application Benefit of Multiphase steel Weight body in white Low strength steel < 180N/mm² 300 kg 200 150 100 50 0 averaged min. yield strength: 178 N/mm² 45% 55% Previous 3 series weight: 284 kg, functionality 98 (size of new 3 series) High strength steel Multiphase steel 69% 31% New 3 series weight: 296 kg, functionality: 2004 26% 42% 32% Averaged min. yield strength: 294 N/mm² New 3 series weight: 267 kg, functionality: 2004 Weight saving + 12 kg 0 1 Weight saving by multiphase steel and high strength steel: 29 kg - 17 kg
Forming Formability H420LA (ZStE 420) H400T (TRIP700) Severe risk of cracks Formable without cracks Rp0,2: 420 560 N/mm² A80: > 17% Rp0,2: 400 500 N/mm² A80: > 24%
Forming Spring Back and Buckling Spring back and buckling Steps to prevent spring back and buckling (required increase in package volume) Opening of the profile by a certain angle stiffening bead stiffening bead
Forming Deep Draw Tooling Considerations Conventional deep drawing tool material: GGG70 insert not essential not hardened interactive surface Deep drawing tool for TRIP 700 inserts essential CVD coated + hardened inserts cooling system increased stiffness
Joining Electrode Considerations Normal steel: 0 15 Multiphase steel: 0 t 5,5 mm 6-7 mm Multiphase steel: increase the diameter of the electrodes increase the electrode forces adaptation of the weldability range
Joining Adhesive Spot Welding Vibration test with H400T + Z100 (hot dip galvanized) 10000 N 6000 4000 Amplitude 2000 k=4,27 1000 1,0E+04 1,0E+05 1,0E+06 1,0E+07 Number of cycles