Both weight and NVH (noise, vibration and harshness) in cars can be reduced through design changes and the use of specific steel processing technologies, such as tailor-welded blanks (TWB).
The TWB allows for greater thicknesses in weaker areas as opposed to using an over-designed beam.
According to a study commissioned by WorldAutoSteel, bead designs were implemented on a firewall that showed potential to bypass expensive damping sheet treatments, commonly applied to reduce the amplitude of vibrations. The noise contribution of the firewall was improved by 0.9 dB, its mass reduced by 5.1 percent and the structure maintained the same level of crashworthiness.
âThis is a good result considering that we only had access to the firewall and were testing a front-end design that is already quite advanced,â says Juliette Florentin of LMS International, who helped conduct the study on behalf of WorldAutoSteel. âIf this approach were applied early on in the design process, we might be able to achieve additional weight reduction.â
The study was presented at the SAE 2009 World Congress by Florentin and Toyoki Yamamoto of Nippon Steel, who provided steel technical expertise to the project.
The new approach was applied to a BMW 1-Series firewall with integrated cross beam and the study was done with a virtual firewall structure with a test-based body model. The vibro-acoustic model includes the firewall structure, trim elements, full vehicle boundary conditions and an acoustic model of the passenger cabin. It can predict structure-borne engine noise in the 40- to 400-Hz range.
The short calculation time of this setup allows a wide range optimization, where multiple design iterations can be completed quickly. A significant number of modifications to the firewall and associated transverse beam were modeled to determine the impact on weight and NVH.
âWe focused on a firewall, as it is a dominant panel for noise and vibration concerning the structure-borne engine noise,â says Yamamoto. âAnd we chose the BMW 1-Series firewall because it is already a superior design that would be difficult to improve upon, therefore creating a proper challenge for this new approach.â
WorldAutoSteel is the automotive group of worldsteel Assn., a trade organization that includes 15 major steel producers, including Nucor and U.S. Steel.