How Adhesives Drive Safety and Comfort in Vehicles The adhesives used in vehicles keep drivers safe, comfortable, and in control by bonding materials that have opposite but complementary properties. Adhesives hold together the diverse parts of our cars, from the dashboard to the windshield to door panels and carpet to the exterior trim and brakes and suspension—to name a few. The list of where adhesives are applied is long and growing. One advantage to using adhesives in cars is that they make it possible to successfully bond materials with different mechanical properties, such as steel and rubber. Successful bonding of different materials is critical for automotive applications. Take the permanent application of rubber to an engine mount, for example. If an engine was mounted on metal, drivers would feel its constant shaking and firing. That shaking and vibration would affect how well they control the car and would certainly make the car less comfortable to drive and ride in. Instead, the rubber absorbs the vibration so drivers can drive safely and comfortably. In this blog, we’ll discuss how adhesives successfully bond metal with so many different substrates, where adhesives shine as excellent alternatives in automotive design, and why adhesives are essential to automotive design. The Problem of Bonding Two Very Different Materials Bonding two materials together should be easy. Just get out the glue, put it on one or both surfaces and stick them together. Except—what if the two materials have very different mechanical properties, like metal and rubber? When bonded, those unique mechanical qualities of each material will concentrate stress on particular points of the bond. And that is important because materials deform differently. That means they will respond to moisture and chemicals differently, the materials will be affected by temperature differently, and, in general, be subject to dynamic fatigue, like pulling apart, which could lead to failure. Adhesives that Retain Mechanical Properties The key to bonding materials with different mechanical properties is to retain and optimize those desired capacities from each material. Flexibility and strength are two prized qualities when bonding using adhesives, and H.B. Fuller’s CILBOND® adhesive is designed to achieve both of those ends—especially when compared with spot welds. CILBOND® chemically bonds rubber and polyurethane elastomers during the molding and casting processes to a number of substrates (from elastomers and rubber to metal to polyurethane). The adhesive provides flexibility to allow for how each material responds to stress, temperature, and frequent loading and unloading effects. CILBOND® is strong enough to withstand years of deformation while continuing to adhere to each material. Because the adhesive is lightweight, it is a perfect fit for the automotive industry, where weight must be shrewdly cut wherever possible. Examples of Automotive Bonding Vibration and shock isolation are key benefits of using CILBOND® adhesives. Engine gaskets and seals are critical examples of rubber bonded to metal that positively affect automobiles. H.B. Fuller’s Automotive Electronics Adhesive and Glass Adhesives groups also help complete the full picture of automotive bonding with a variety of materials. Body Panels: Adhesives bond aluminum or steel body panels to the frame or to each other, reducing the need for welding and allowing for the use of lighter materials. Windshields and Windows: Glass windshields and windows are bonded to the vehicle’s frame using adhesives, providing structural integrity and ensuring proper sealing against the elements. Interior Components: Dashboards, door panels, and center consoles often involve bonding plastics, composites, and metals together for a seamless finish. Trim and Moldings: Exterior trim pieces and moldings, made from plastics or metals, are often adhered to the car’s body to enhance aesthetics and improve aerodynamics. Seats: Different materials used in seat construction, including metal frames, foam padding, and fabric or leather coverings, are bonded together with adhesives to ensure durability and comfort. Composite Panels: Carbon fiber or fiberglass components, such as hoods, trunk lids, and roof panels, are bonded to the vehicle’s structure using adhesives to reduce weight while maintaining strength. Electronics and Sensors: Adhesives attach sensors, wiring, and other electronic components to various parts of the vehicle, ensuring secure placement and protection against vibrations. Roof Liners and Insulation: Adhesives bond roof liners and insulation materials to the car’s roof, enhancing acoustic performance and interior comfort. Automotive Applications where Adhesives Provide Superior Bonding Let’s explore examples of disparate materials bonded together to improve the safety, comfort, and ease of control in a car. Safety Friction brakes are one example of how adhesives make cars safer. A friction brake forces brake pads against a rotor surface to slow the speed of the wheel (Figure 1) and the car. A friction brake’s pads rely on strong and durable adhesives, which are used in the production of composite materials that are designed to withstand high temperatures and pressures. The adhesive used allows the composite material on the brake pad to lose microscopic amounts of material with each use and still remain durable by minimizing material loss. The pad must also distribute heat and pressure, which is why pads have a large surface area. Adhesives are the heroes of friction brakes because they securely bond the composite material to the metal, which is subject to high stress with every use. Adhesives also distribute stress evenly across the composite pad surface. The adhesive used also helps the components withstand heat. Stress, heat, and vibrations could all contribute to brake wear and failure, but adhesive slows that whole process. Control Brakes are critical features for safety and driver control. Clutches and slip differentials also play a role in automobile control. They provide predictable control features for drivers despite quickly changing driving conditions, such as weather and traffic. Engine mounts, where adhesives are used to bond rubber to metal, isolate vibrations, improving vehicle control. The steering wheel, signals, levers, gear shift knob, the dashboard and the screens and controls, door knobs, window switches—just about everything a driver or passenger touches—contain components bonded together using adhesives. Comfort Fabrics above the driver’s head are attached to the roof with adhesives from H.B Fuller’s Automotive Adhesive group. Sun visors, mirrors, door panels, armrests, and carpet are all held together with adhesives. Foam padding is bonded to the seat frames, and upholstery is affixed with adhesives. The list of comfort parts requiring adhesive is extensive. Why Adhesives Are Essential to Automotive Design Adhesives are essential tools for bonding parts together because they reduce overall vehicle weight, which improves fuel efficiency and provides for more nimble handling and acceleration. As we’ve seen, adhesives also have the advantage of dispersing stress evenly across a bonded area—something spot welds cannot do. Distributed stress improves fatigue resistance by reducing localized stress concentrations. Enhanced structural rigidity is another benefit of adhesives. For instance, continuous bonding along a seam can increase the overall stiffness of the vehicle, which also improves handling. How Bonding Is Evolving in Automotive Applications For years, effective use of adhesives required a two-coat process. The first coat was typically primer, which featured a different set of qualities and characteristics than the second coat. The first coat made the material ready for bonding and also provided extras like water and corrosion resistance. After drying, the second coat, or top coat, was applied to achieve the desired bond. CILBOND® is available in a one-stop bonding formulation, which removes the priming step, though it is important to prepare the surface before applying the single coat. Bonding in a single coat removes the drying step and allows for a faster process—a critical need in automotive assembly processes. Proper application of the one-coat or two-coat CILBOND® formulation enables the bond to have the full range of viscoelastic behavior (stress distribution, energy distribution, durability).