While automakers are evaluating the use of lightweight materials, such as aluminum, composites and magnesium, they are also trying to make better use of traditional materials to lower vehicle weight. As a result, the use of sheet steel in automobiles may not decline rapidly, but be replaced using thinner grades of high-strength, low-allow steels.
Despite recent rumors, steel is not dead. In fact, it appears to be more popular than ever in the auto industry.
“Steel is here to stay,” says Richard Schultz, a consultant at Ducker Worldwide (Troy, MI). He believes steel will continue to be a major component in automobiles for quite some time.
The steel industry has made a major commitment to developing high-strength steel, which is more expensive than traditional mild steel, but can reduce weight by at least 10 percent because parts can be made thinner. Although the average vehicle is now 50 percent heavier compared to 40 years ago, “the use of advanced high-strength steel has provided solutions for cost-effective lightweighting on vehicles over the last 10 years,” says Jon King, director of automotive engineering at Corus Engineering Steels (Rotherham, England).
According to King, that has helped make today’s vehicles “up to 60 kilograms lighter, despite the huge improvements in structural safety.” During a recent conference on “lightweighting for carbon-free vehicles” in Birmingham, England, King predicted that steel will continue to be “the benchmark material in vehicle body construction” for quite some time.
“In North America, medium- and high-strength steel will continue to replace mild steel and blunt aluminum’s growth for most bumper beams, body structures, wheels, closures other than hoods,” adds Ducker.
While automakers are evaluating the use of lightweight materials, such as aluminum, composites and magnesium, they are also trying to make better use of traditional materials to lower vehicle weight. As a result, Ducker says the use of sheet steel in automobiles may not decline rapidly, but be replaced using thinner grades of high-strength, low-allow steels.
“The use of high-strength steel and micro-alloy steel sheets is very popular,” notes Ken Gomes, vice president of marketing and engineering at Research Engineering & Manufacturing Inc. (REM, Middletown, RI). “Automotive seat makers have tried to use aluminum and magnesium to replace sheet steel to reduce weight. These materials reduce weight in certain seating applications, but increase size in doing so, in order to have the same strength as the sheet steel being replaced.
“The use of high-strength, low-alloy (HSLA) steel provides weight reduction by allowing thinner sheet steel to be used without sacrificing strength or increasing component size,” adds Gomes. “The strength of the component is increased even further by the cold work-hardening that occurs during the stamping process. The use of HSLA has had a dramatic weight saving effect in other areas of the vehicle, as well.”
However, HSLA can create assembly problems. “In the past, many automotive seat components have been fabricated using punch-extruded holes suitable for use with Taptite 2000 thread-rolling screws,” explains Gomes. “This is still the method used in many grades of HSLA steel. The higher strengths require [engineers to reevaluate] the fastening method being employed.
“With higher strengths of HSLA, due to work hardening, punch extruding the sheet steel is often not possible as the hole size and shape are inconsistent due to the extreme work hardening that occurs,” claims Gomes. “In some cases, the hardness due to cold working prohibits consistent performance when forming threads in the punch-extruded hole. Welding pretapped weld nuts is also difficult, due to the work-hardened material.”
REM has worked with RB&W Manufacturing Inc. (Park, OH), a leading nut manufacturer, to provide a solution for this problem. “These pierce and clinch nuts have the ability to pierce very hard sheet steel,” says Gomes. “SpacNuts are produced with a straight bore that is sized to accept Taptite 2000 screws, which resist vibrational loosening. The joint can provide Class 10 strength in thin sheet steel.”