Douglas Craig, Technical Application Engineer & Collision Industry Liaison, Structural Adhesives Tech Service, LORD Corporation, also contributed to this article.
As more aluminum-bodied vehicles enter the automotive market, the auto collision repair business must also prepare itself for repairing these vehicles. Aluminum’s light weight makes it an ideal auto-body substrate as an environmentally-friendly, cost-effective method for increasing performance, boosting fuel economy and reducing emissions while maintaining or improving safety and durability.
A crash durable adhesive being applied to a Cadillac ATS strut tower. Flexible crash durable adhesives have the ability to stretch without losing their effectiveness.
Auto OEMs are utilizing impact-toughened adhesives in the manufacturing process, and will be recommending similar type adhesives for repair operations. The prevalence of aluminum-bodied vehicles will necessitate changes in how repairs are made and in the products used to make the repairs.
Crash durable adhesives
Recently, two-component crash durable adhesives for repair have been formulated to replace all OEM one-component crash durable adhesives, which are used to return vehicles to pre-accident condition. In the repair process it is necessary to restore a vehicle to its pre-loss condition. To accomplish this, you need to duplicate the original vehicle down to the adhesive, and that is where crash durable adhesives come into play.
Reference is often made to one-component and two-component, or even 1K and 2K, materials. This designation refers to how many materials are applied as a bead or are mixed to be applied as a bead in vehicle body assembly or repair. A one-component material is applied as received from the supplier, whereas a two-component material is mixed together during the application. The 1K/2K designations are derived from the German word “komponente” meaning component and thus 2K means two-components.
Most of the vehicles produced today, whether aluminum- or steel-bodied, are assembled with a one-component crash durable adhesive. So why is the repair version of the crash durable adhesive a two-component formulation? The answer is in how the original vehicle is manufactured.
When OEMs assemble cars with crash durable adhesives, the vehicles go through a heat-curing process for the adhesive, along with drying processes for the paint and/or e-coating. The one-component crash durable adhesive is made to withstand temperatures up to 400° F. All of this heat allows the chemistry in the one-component adhesive to cure.
In the collision repair shop, it is not possible to place a repaired vehicle into such high temperatures for the curing process. The two-component epoxy formulation allows repairs to be made to vehicles that match the original adhesive application.
Strong and tough
So what exactly is a “crash durable adhesive” and how does it differ from a conventional structural adhesive? Crash durable adhesives not only have the strength of structural adhesives, they also provide exceptional toughness. This is why they are sometimes referred to as “impact-toughened” adhesives. Crash durable adhesives are extremely flexible, with the ability to stretch without losing their effectiveness.
A crash durable adhesive being applied to a Taurus rear frame rail and trunk prior to installation of a rear body panel. Crash durable adhesives offer the impact resistance, corrosion protection and sealing needed for the life of the car.
Flexibility is especially crucial in crash mode situations. Crash durable adhesives will not “micro-fracture” in a “crush-and-crash” mode as with standard structural adhesives. Therefore, joints will hold together better and not lose their strength during a crash. This is especially important when considering that thinner substrates, such as aluminum, tend to “move around” more during a crash, and the flexibility of the adhesives helps to hold the joints together.
Everything that occurs in a crash event happens very quickly – sometimes within one-half of a second. The vehicle’s metal is crushed, the airbags are deployed – the crash is over. During the crash event the adhesive must be strong and flexible enough to hold all the vehicular parts together. Crash durable adhesives offer the impact resistance, corrosion protection and sealing that is necessary for the life of the car.
Adhesive Impact Testing
An Impact Wedge Peel (IWP) test is used to measure the effectiveness of structural adhesives, and shows the value of crash durable adhesives. The IWP test is an International Standard (ISO 11343) method for assessing the fracture performance of adhesive-bonded joints when exposed to impact. In the test procedure, two bonded substrates are drawn over a small, v-shaped wedge to determine the force required to push through the assembly. Crash durable adhesives have been shown to have not only high lap-shear strength but also an extremely high IWP strength.
Impact wedge peel measures a key characteristic of the crash durable adhesive which the automobile manufacturer has factored into their overall design to protect the vehicle occupants during a crash event. Replacement during repair with an OEM approved material is critical to accurately restore a collision-damaged vehicle.
Repair procedures
Crash durable adhesives, for repair procedures, are used to replace all the original equipment locations of OEM-applied crash durable adhesives. Typically, these areas are between all the metal panels and in sections such as A-, B- and C-pillars, and other locations including roof joints and engine box joints. They can be used for panel bonding, weld bonding and rivet bonding of aluminum panels.
Crash durable adhesives offer both strength and sealing functions, providing a sealant to the vehicle‘s body structure and a bonding method. If there is any doubt as to whether the OEM adhesive is crash durable, use a crash durable adhesive in the repair.
‘Colorful’ adhesive
Though application methods for crash durable adhesives are similar to conventional structural adhesives, technicians might be “startled” by their appearance. Crash durable adhesives are highly pigmented and come in colors such as purple, orange, red, and blue.
A “drop tower test” depicting a collapsible section “with and without adhesive.” The component on the right shows how the addition of a crash durable adhesive keeps the axial crush in a more controlled and consistent fashion. Whereas the component on the left, without the adhesive, appears to have splayed or ripped open; an undesirable effect of a crash situation.
The coloration of crash durable adhesives began not only as a marketing tool, but also as an error-checking method during OEM vehicle production. In order to easily view and validate that the correct materials are being employed, OEMs developed crash durable adhesives in various colors. Crash durable adhesives for repair procedures also come in colors, and the colored adhesive is either hidden in the repair process or painted so as to not be visible to the customer.
For repair, it is important to understand that colors do not need to be matched. For example, a purple OEM adhesive can be replaced with a blue repair adhesive as long as that repair adhesive meets the OEM requirements.
Meeting repair requirements
To meet the needs of collision repair shops for an impact-toughened adhesive, and for an OEM-approved, crash durable adhesive, LORD Corporation has introduced a structural metal bonding adhesive that replaces OEM one-component crash durable adhesives for panel- and weld-bonding of aluminum vehicle parts. LORD Fusor® 2098 crash durable adhesive offers high impact strength performance and lifetime corrosion protection. It will return vehicles manufactured with one-component crash durable adhesives back to pre-accident condition as recommended by the OEM.
In an IWP test, Fusor 2098 provided 30N/mm or 11.7Joules as opposed to most adhesives which are only in the 5-to-6 N/mm range.
Fusor 2098 requires little pre-repair preparation. It retains profile stability after extrusion and offers a working time of approximately 90 minutes. The crash durable adhesive provides weld-through ability within 60 minutes, along with improved body stiffness and safety performance.
The product was developed to meet, or exceed, OEM requirements for crash durable adhesives, and has been tested by several OEMs for collision repair. It has been approved for repair operations on vehicles manufactured by Tesla, Ford Motor, General Motors, Fiat, and PSA Peugeot.
Aluminum and repairs
The increased use of aluminum (and other materials such as carbon fiber, new plastics, and advanced high-strength steels) and adhesives to develop stronger and lighter weight vehicles, mandates the use of OEM collision repair information in the blueprinting process to ensure proper repairs are made. Errors in choosing the right adhesive, attachment method (welds, rivets, screws, etc.), and ancillary parts can have a negative impact on repair quality, safety and vehicle value.
Auto OEMs are recommending specific repair products for returning vehicles to as-built condition. Crash durable adhesives provide the high strength impact performance needed to guarantee secure repairs over the lifetime of the vehicle.
