20th October 2015
A study released today by WorldAutoSteel, the automotive group of the World Steel Association, showed a wide variation in efficiency among steel components in vehicles on the road today. The study, “A New Paradigm for Automotive Mass Benchmarking,” further revealed that when aluminium closure components, such as doors, bumpers, hatchbacks, and decklids, are compared to efficient steel components of similar size, the 40 percent mass savings currently accepted as a standard measure of aluminium lightweighting capability is not nearly reached.
The study also showed that while use of aluminium may achieve mass savings at the component level, that mass savings is lost when an entire system is measured. The study, conducted by EDAG International, Inc., uses the A2Mac1 vehicle tear-down database of approximately 200 vehicles along with a benchmarking methodology. The methodology uses statistical regression analysis to isolate mass-efficient designs and compare lightweighting, as presented in a paper by Dr. Donald Malen, University of Michigan, and Jason Hughes, A2MAC1 Automotive Benchmarking at the Society of Automotive Engineering World Congress in April 2015. A component structure that is identified as efficient is one that stands out statistically as much lighter than others of its kind of the same size, structural performance and material. For efficient steel, this could be due to the use of Advanced High-Strength Steels and/or because of a fully optimized design.
According to Malen, statistical benchmarking opens a whole database of today’s vehicles to the benchmarking process. With it, engineers can identify better, more realistic targets, saving time and money. “First, this benchmarking method revealed a broad disparity in levels of efficiency among the steel component designs of similar size. But when comparing aluminium component designs to their efficient steel counterparts, the results were startling,” said Cees ten Broek, director, WorldAutoSteel. “For example, the Malen and Hughes paper documented a 22 percent mass savings when comparing efficient aluminium doors to efficient steel doors. Our study confirmed that calculation. A similar comparison of front bumpers shows just an 11 percent savings. And when comparing an average aluminium design to an efficient steel bumper design, the aluminium bumper was 26 percent heavier.”
Ten Broek noted that this is very different than currently accepted predictions in the industry. An approximate analysis of the total vehicle curb weight change was conducted using the mass reductions shown in the steel and aluminium efficient designs. The efficient steel subsystems reduced vehicle curb weight by 6.5 percent compared to average steel subsystems. Aluminium subsystems reduce curb weight by 9.3 percent compared to average steel subsystems, a 2.8 percent difference.
Further, when the aluminium door component is added to the door system, the study shows that the aluminium door system was equal in weight to the steel door system. Most of the systems in the database do not fully benefit, or show no benefit, from the mass savings achieved at the component level, the study indicates. Though identifying the cause of this was not part of the study scope, it did investigate whether this loss was due to premium vehicle features, with the results showing no such correlation. It is a reasonable deduction that the efforts made to reduce component mass are being lost along the vehicle design chain. Said ten Broek, “While steel has come a long way, the study shows additional lightweighting can be achieved through design optimization and advanced steels and steel technologies.” A2MAC1’s benchmarking database, paired with statistical analysis, enables automotive designers to see where their own vehicles stand in terms of mass efficiency against a larger database of vehicles and evaluate opportunities for greater efficiencies.