On March 3, Henkel AG & Co. KGaA (Düsseldorf, Germany) announced the successful fabrication of a composite automotive leaf spring by Benteler SGL Composite Technology GmbH (Ried im Innkreis, Austria), using a specially developed resin transfer molding (RTM) process. Compared to conventional leaf springs made of steel, these composite leaf springs are up to 65 percent lighter.
The resin, Loctite MAX 2, a polyurethane-based composite matrix resin, is said to cure significantly faster than the epoxy products usually employed in the RTM process. Due to its low viscosity, the polyurethane resin reportedly penetrates and impregnates the fiber reinforcement more easily and with less fiber displacement, thus enabling very short injection times. Henkel holds that Loctite MAX 2 has an exceptionally high stress-intensity factor, which is a measure of toughness. The toughness has, says Henkel, a positive effect on the fatigue behavior under load. Leaf springs in cars are constantly subjected to dynamic loading under driving conditions, so the use of flexible materials with a high fatigue tolerance prolongs component life.
Resin injection processes such as RTM predominate in the manufacture of automotive composites for mass-produced automobiles because they make it possible to control the cure reaction more reliably, either by adjusting the temperature or adding an accelerator. Furthermore, the risk of local overheating and the resulting shrinkage is reduced because the polyurethane generates less heat, overall, during cure than epoxy resins do. As a result, even thick components with many fiber layers cure quickly. The RTM process is especially attractive for volume production of cars because fast curing of the matrix resin permits short cycle times.
The product range of Benteler-SGL, a joint venture of Benteler Automobiltechnik (Salzburg, Austria) and the SGL Group (Meitingen, Germany), includes body shell components, such as side blades, doors and visible carbon components. The composite components, which are designed specifically for mass-production, consist mainly of carbon and glass fibers in various textile forms, such as stitched or woven fabrics. Customers include almost all the big names in the automotive industry, primarily in the premium class.
“While developing these composite leaf springs, the competencies of Benteler-SGL and Henkel complemented each other perfectly,” says Frank Deutschländer, global market manager, automotive at Henkel. “With our matrix resin technology, Loctite MAX 2, we were able to establish a new process at Benteler-SGL that is tailored to the automotive industry and gives this fiber composite component an attractive properties profile.”
Given the more stringent CO2 exhaust standards, lightweight construction is becoming ever more important for the automotive industry. Reportedly, the composite components from Benteler-SGL help to reduce fuel consumption yet offer a high level of safety. “Thanks to our intensive collaboration with Henkel, we have succeeded in producing a resin transfer molded, glass fiber-reinforced leaf spring for the automotive industry that not only combines low weight with high strength but is also mass production capable. It thus also satisfies the highest expectations in terms of cost-efficiency and process reliability,” says Frank Fetscher, head of sales and marketing at Benteler-SGL
For more information, contact Lisa Kretzberg, Tel.: +49 211 797 5672; Fax: +49 211 798 9832.