Automotive body panels

01

Choose the material grade for drawability and dent resistance

ArcelorMittal describes its bake-hardening (BH) steels as designed for visible parts — door, hood, tailgate, front wing and roof — and structural parts, with a bonnet example in CR180BH and a door in CR240BH. Their yield strength rises during paint curing, giving improved dent resistance in parts with low forming strains (hood, roof, doors and wings) or weight reduction at equal dent resistance. Rolling-direction yield strength Rp0.2 is 180–240 MPa for CR180BH (tensile 290–370 MPa), 210–270 MPa for CR210BH (320–400 MPa), 240–300 MPa for CR240BH (340–440 MPa) and 270–330 MPa for CR270BH (360–460 MPa). BH2 is the yield-strength increase between a 2% plastic pre-strain and a heat treatment of 170 °C for 20 minutes. The grades cross-reference to EN names such as HC180B and HX180BD and VDA 239-100 names such as CR180BH. [1]

The AHSS Guidelines (WorldAutoSteel) note that bake-hardening steels are used for exposed panels because of the extra strength from paint curing. Their example 340 BH has 242 MPa yield, 354 MPa tensile, 41% elongation, 33 MPa work hardening and 35 MPa bake hardening, for a formed-and-baked strength (YP') of 310 MPa; a 440 DP exposed-quality dual-phase steel reaches 376 MPa, allowing a thickness reduction of 0.05 mm while still improving dent resistance. [3]

For deeper drawn panels, SSAB Form 04 meets and exceeds DC04 in EN 10130, with yield strength Rp0.2 of 210 MPa maximum, tensile strength of 270–350 MPa, elongation A80 of 38% minimum, r90 of 1.6 minimum and n90 of 0.18 minimum, tested in the transverse direction, in thicknesses of 0.40–3.00 mm and widths up to 1500 mm. [4] For aluminium closures, a Corus Aluminium SAE paper names AA6016 the preferred outer-panel alloy in Europe for its hemming performance, low FFC susceptibility and formability; pre-bake 6016 T4P with improved bake-hardening response removes dent resistance as the limit on downgauging, and a 6016 outer with a 5182 inner gives the best weight saving where torsional rigidity is critical. [5]

Editorial calculation: in the AHSS Guidelines table, the 440 DP formed-and-baked strength of 376 MPa is 66 MPa above the 310 MPa of 340 BH (376 − 310), which is the margin that permits the 0.05 mm thinner panel. [3]

Give the supplier the panel drawing or CAD data, the part (hood, door outer, wing, roof, tailgate or inner), material and grade with standard (for example DC04 to EN 10130, CR210BH to VDA 239-100, AA6016 outer and AA5182 inner), nominal thickness, coating and coating mass, exposed or unexposed surface, dent-resistance or stiffness requirement, paint-bake cycle, hemming and joining method, dimensional tolerances and checking fixture, packaging, and annual volume.

02

Set the surface quality and corrosion coating

ArcelorMittal recommends its Extragal hot-dip pure-zinc galvanized steel for exposed and non-exposed automotive parts: the zinc crystal structure is not visible to the naked eye and the painted appearance meets requirements for exposed bodywork parts. Standard coatings are Z100 (100 g/m² minimum both sides; 7.0–9.0 µm, 50–65 g/m² per side), Z140 (140 g/m²; 70–85 g/m² per side), Z200 (200 g/m²; 100–120 g/m² per side) and Z225 (225 g/m²; 112.5–132.5 g/m² per side). Zinc acts as a sacrificial anode, protecting even where the coating is damaged by impact, scratches or stone chipping; the friction coefficient is about 0.10 to 0.20 depending on oiling, and the coating can be phosphated and painted with tri-cation processes. [2]

ArcelorMittal's BH grades are offered uncoated, electrogalvanized (+ZE), galvannealed (+ZF), hot-dip galvanized Extragal or Ultragal for visible parts (+Z) and Zagnelis (+ZM), under EN 10268, EN 10152 and EN 10346 designations. [1]

Editorial note: ask each supplier which surface class and coating mass applies to each exposed panel, how surface defects are inspected before and after paint, and for salt-spray or cyclic corrosion results on the painted panel, since none of the reviewed sources states a test duration for a finished panel.

03

Compare panel types, bumper reinforcement and suppliers

No manufacturer record has been reviewed for this product yet.

Reinforced bumpers sit behind the bumper cover on a beam and crash boxes. SSAB suggests Docol CR CP 1180, CR MS 1500-1700 or PHS 2000 for bumper and cross beams, HR CP 800 or HR DP 800 for crash boxes, and HR420LA to HR1000CP for anchor plates. In its examples, a CR1300 martensitic beam was upgraded to a 1.0 mm thick 1500 MPa martensitic beam that was roll formed, laser welded and 3D bent; a PHS 2000 beam reduced bumper system weight by 17%; and eliminating two crash-box anchor plates saved 2.5 kg on a front bumper system. [6]

When requesting quotations, ask each supplier for the material certificate and grade, stamping and hemming capability, coating data, surface inspection method, dimensional reports against the checking fixture, and samples.

04

Trace the panel

This is a functional reference built from the sources cited; it is not one maker's design.

05

Fill the specification fields with values for your project

A body panel quotation needs values for your vehicle. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

06

Send the panel, grade and surface together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Panel: [hood; door outer; wing; roof; tailgate; inner; bumper beam]
Material: [grade; standard; thickness]
Surface: [exposed; unexposed; coating mass]
Performance: [dent resistance; stiffness; crash requirement]
Process: [stamping; hemming; joining; paint bake]
Quality: [tolerances; checking fixture; inspection]
Volume: [parts per year]

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