Click Image to Enlarge
A fiber-reinforced leaf spring made by Benteler-SGL (benteler-sgl.com) with Henkel’s Loctite MAX 2 polyurethane-based resin. Compared with a steel leaf spring, the composite component, made with resin transfer molding, is as much as 65% lighter.
Although there was probably a seemingly endless period of time when operating in the fields of adhesives and composite materials for automotive was not all that encouraging, it is hard to imagine what might be a better time than now, when every automaker in the world is concerned with meeting regulatory demands for improved fuel economy or reduced emissions (which can be achieved, in part, by becoming more fuel efficient) within the next few years. With the stroke of a pen in the several
global capitals, suddenly alterna-tive approaches to designing, engineering, and building cars and trucks have become more viable. This is not only a move under the hood, where spark-ignition and compression-combustion engines are being fitted with an array of new technologies to increase their efficiency, but they are being joined with or replaced by electric motors. In the U.S., getting to a corporate fuel efficiency average of 54.5 mpg isn’t going to be achieved via the status quo. But another big part of hitting that number (or the regulations in Europe and China) is going to be through the lightweighting of vehicles.
Which brings us to Henkel (Henkel.com/automotive), a company that specializes in a variety of adhesives for putting things together as well as epoxy materials that can be used to produce fiber-reinforced composite components.
Henkel engineers have calculated that were OEMs to use its technology in place of that which is typically used, there could be a weight-save per vehicle on the order of 209 lb. Of course, that would be all in, which is not likely to happen. However, there can certainly be incremental savings.
One of the means by which OEMs are reducing weight is by using more than one type of material to build structures. Two of the materials that are often paired are steel and aluminum. Chris Liddiard, director of Acoustics & Structures, Henkel automotive group, “You can’t join aluminum to steel without adhesive.” Among the reasons is the coefficient of expansion difference between the two metals, which can be accommodated by the bonding provided by high-performance adhesives.
A bigger boost for automotive lightweighting, however, is the substitution of metals with fiber-reinforced composites. While these materials exhibit strength and are generally light, an abiding problem with their introduction into auto applications that aren’t, say, low-volume Formula One cars, is that processing time is way too long to be practical for the jobs per hour characteristic of passenger cars.
Henkel’s Kevin Roslinski, senior application engineer, says that process speed is one area that they’ve been keenly focused on. He says that the company’s Loctite MAX 2 resin, a poly-urethane based material, can be readily applied in resin transfer molding (RTM) better than epoxy-based matrices because the polyurethane has extremely low viscosity, which means that (1) there can be fast injection without having an adverse effect on fiber orientation and (2) there is better wetting of the fibers in the mold. In addition to which, cure times are faster.
Roslinski says that while epoxy-based composites have a cycle time that would make them applicable for volumes on the order of 20,000 to 30,000 per year, the Loctite MAX 2 resin with glass or carbon fibers can produce parts at a 200,000 to 300,000 per year volume, thereby making process time less of an issue when making the calculations of overall part cost.
In addition to which, the mech-anical properties—toughness, in particular—make the polyurethane matrix resin-based composites well suited to automotive application, as they exhibit high fatigue tolerance.
In efforts to achieve even greater improvement in the area of composites, Henkel introduced a new three-component polyurethane-based resin, Loctite MAX 3, which, Roslinkski says, not only offers higher temperature resistance than MAX 2-based composites, making them more aligned with epoxy-based parts, but which also includes a mold release agent to further reduce processing time. Once out of the mold, the part is ready for paint-ing and/or bonding.
To assure that the material is production ready for automotive parts, Henkel engineers have been working with those of plastic equipment manufacturer KraussMaffei (kraussmaffei.com).
And the aforementioned high-performance adhesives: they can be employed to help make composites part of the hybrid structure mix, too.