|Material selection for the Venza aluminum BIW. Click to enlarge.|
A new study by EDAG Group, commissioned by the Aluminum in Transportation Group of the US Aluminum Association, finds that an all-aluminum body in white (BIW) can deliver potential mass savings in the 35 – 40% range over a base steel BIW. This, when combined with secondary mass savings and other design changes, could boost fuel economy by around 18%.
The study built upon research EDAG performed last year for the US Environmental Protection Agency (EPA) examining mass reduction, safety and cost variables in a mid-size crossover Toyota Venza. The EPA study aimed to reduce vehicle mass by 20% while meeting all NHTSA and IIHS safety standards, and maintaining or improving performance, handling and braking.
That study found that using a maximized high-strength steel (HSS) Venza body resulted in a body mass reduction of only 14% over the baseline production vehicle body, and that the study’s total vehicle mass reduction target could not be met without the use of aluminum closures and chassis components.
The new study focused on taking the steel Venza BIW (body in white) and developing a CAE concept for an aluminum BIW with equivalent performance but with a target BIW mass reduction of more than 30% over steel, within the following boundaries:
Project is a “feasibility study” only.
Concept was to be of riveted / bonded construction (with use of extrusions/sheet/castings).
The use of castings in the BIW was to be minimized (for cost / complexity reasons).
Aluminum materials used in the study will be “current technology” only.
No detailed manufacturing feasibility will be performed in this stage of the project.
As per the base Venza, the following load cases were defined for the project:
For crashworthiness, FMVSS 208 Frontal Crash; IIHS 35mph ODB Frontal Crash; FMVSS 301 Rear Impact; FMVSS 214 Side impact (MDB); and FMVSS 216 Roof Crush.
For NVH, Static torsion and bending stiffness; and BIW normal modes (1st structural).
For the purposes of the feasibility study, EDAG selected four basic aluminum materials: 6022 T6 Alloy Sheet; 5754 O Alloy sheet; 6082 T6 Extrusion; and generic casting. Properties of the metals were supplied by the Aluminum Association and a basic material model created in LS-DYNA using MAT 24 (PWL or BL stress strain curves only).
EDAG emphasized that this was only a structural feasibility study (i.e., formability / environmental factors were not considered).
The cost increase was about $1 per kilogram of weight saved, which consumers will recoup in fuel savings in less than two years of operating the more efficient vehicle.
The research was presented at the Society of Automotive Engineers (SAE) World Congress during a panel discussion on advances in lower weight materials. It comes at a time when automotive aluminum use is at an all-time high, with automakers announcing plans to incorporate more of the metal into vehicle designs—doubling aluminum’s 2008 share of the automotive metals mix by 2025.