Henkel – Developing high performance bonding technologies
As manufacturers worldwide look to reduce weight to overcome increasing fuel costs, reduce emissions and improve manufacturing processes, they find themselves challenged to set aside the mindset that has dictated traditional material and process choices and to look openly at new and emerging technologies. This includes adhesives and other joining options.
Today, each passenger vehicle contains on average 15 kg of adhesives. Components such as instrument panels, fenders, windshield wipers, gears and the cross members on frames are now secured by various types of adhesives.
Growth in the use of adhesives can be attributed manufacturers turning to polymer-based composites to replace steel and aluminum, which in turn has created a growing need to find effective methods of bonding these types of mixed materials. In some applications, adhesives need to provide structure and rigidity, and in others they need to be flexible and pliable – all while providing a nearly unbreakable bond.
While initially it might seem counter-intuitive, testing has shown that adhesive bonds are more stable than welded joints. This makes them viable options in such demanding uses as in civil infrastructure, recreational vehicles, swimming pools, transport, piping, storage tanks and architecture. Traditional joining methods such as welding and riveting are costly and also compromise the strength of polymer based composites. Adhesives can also help to seal scratches and joints, while also reducing noise.
Lightweight leaf springs made for the Volvo V90 estate, S90 and 60 series models.
In automotive, overcoming the different coefficients of thermal expansion (CTE) of hybrid multi-substrate systems in modern, lightweight bodies is a significant challenge facing designers. The market requires an adhesive that offers both high strength and high elasticity at the same time while ensuring the bond line will last for many years between very different materials.
Henkel developed the new adhesive Loctite UK 2015 to address the challenge. It is based on two-component polyurethane technology and is ideally suited for use on structural body parts, regardless of whether they are made of fiber-reinforced plastics, painted/e-coated steel or painted/e-coated aluminum.
Composite springs
An innovative example of where plastics composites are taking over from steel is one recently implemented by Volvo for use in its new top-line, crossover SUV model, the XC90, as well as in its premium V90 estate, S90 and 60 Series models. Henkel partnered with Austrian automotive composites specialist Benteler- SGL to redesign the vehicles' rear suspensions.
The aim was to replace the usual helical springs mounted on the rear axle. The team involved did this by using high-pressure resin transfer molding, or HPRTM, to produce lightweight leaf springs made from an advanced, glass-fiber-reinforced polymer composite material.
The transverse leaf spring enables a more compact axle design than with the bulky helical steel springs it is replacing. The transverse leaf spring allows the elimination of the coil springs, which means the axle protrudes less into the trunk area, leaving more loading space. In addition, the new design provides a smoother ride and improved NVH (noise, vibration, harshness) behavior.
Even more important is that the composite leaf spring offers significant weight savings compared with their metallic counterparts. The new axle system weighs 4.5 kg less than the conventional helical spring construction.
Henkel's flagship product, the Loctite MAX 2 two-component polyurethane composite matrix resin system, is what enabled Benteler-SGL to develop these innovative leaf springs. Loctite MAX 2 has very low initial viscosity, which enables fast injection of the resin into the mold and excellent penetration between the tightly packed reinforcing glass fibers.
Once injected into the mold, the matrix resin cures very quickly, much faster than standard epoxy resins, for demold times as low as one minute per part. The production system installed at Benteler-SGL, which uses a multicavity tool, is designed for a production output of more than 400,000 pieces per year.
Henkel have also developed a new epoxy resin system, the Loctite Max 5 which is incorporating high fracture toughness with the benefits of improved curing processes.
Henkel is working with numerous companies in all industrial sectors with its high-performance composite matrix resins and adhesives. These include structural parts such as body components, exterior paintable parts, structural members and tube, piping applications.
Across numerous industries, the ability to leverage process know-how while also integrating and matching products within an overall package is essential for successfully applying this type of lightweight technology.
Increasing development activity
In 2016, Henkel opened the Composite Lab, a state-of- the-art test facility, in Heidelberg, Germany. A second Composite Lab has also opened in Japan in 2017 to help increasing customer requirements. Here manufactures can work with Henkel experts to develop and test composite parts and optimise series production process conditions. Companies can carry out trials with different test molds on Henkel's own HP-RTM equipment, which has resin injection units for polyurethanes and epoxies coupled to a 380-tonne press.
www.composite-lab.com
The Volvo V90 estate.
Issue 49: December, 2018
Author: Konrad Brimo-Hayel– Henkel Germany
Co-Author: Brad Smith – Henkel Australia
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Connection Magazine is the official magazine of Composites Australia Inc.