With the use of structural adhesives in vehicle manufacturing increasing, many OEMs now call for using adhesives when replacing structural parts on a vehicle.
There are a variety of adhesive bonding methods used when replacing automotive body components, including squeeze resistance spot welding or MIG/MAG welding, and sometimes a combo of self-piercing rivets and blind or solid rivets.
There are many specific techniques that are either overlooked by repairers or are described in ambiguous terms in repair guides. In this article, 3M Automotive Aftermarket Division technical experts offer best practices and practical information to help ensure the best repairs possible.
OEM repair procedures are your most-important resources when using adhesives automotive repair. Repairers should get year- and model-specific procedures from a reliable source, such as the automotive manufacturers’ web sites and reputable 3rd-party providers of consolidated OEM procedures.
Be aware repair procedures vary by OEM and sometimes between models built by a single company. Some vehicle manufacturers use general statements that recommend a list of applicable adhesives. This type of information, though general, follows a “repair it as it was built” philosophy. Additional content may include specific instructions on combining welding with adhesives to mimic assembly line construction. Weld bonding is the most common of these. Welds may follow a “replace with same number” approach.
Other manufacturers are specific about the adhesive used, generally OEM branded. They may specify the exact locations where adhesive should be applied, specified cleaners, adhesion primers, the number and location of the welds—even the grades of abrasives used for preparation. Some manufacturers advise rivet bonding procedures to replace welding that was performed on the assembly line.
It is rare for OEMs to advise the use of adhesives alone. In those rare cases one or two joints on a panel may be bonded with adhesives only, but the remaining joints are spot-welded or weld-bonded. Always consult specific model and year information to determine the correct procedure.
If repairers are following OEM guidelines, they should ask themselves what other considerations they might have. Whether the OEM guide was developed with very specific details or not, repair professionals should always follow some general best practices around the use of adhesives and panel preparation.
Avoiding cross-contamination of metallic substrates is especially important when working with dissimilar metals. Often you may be joining steel to aluminum—don’t grind/sand both the panels with the same disc or belt
You may see the use of the phrase “or equivalent” language in the repair manual. Unless you have some written proof of equivalency that has been published by a manufacturer, be careful deviating from the prescribed adhesive.
They have determined the procedures, methods of preparation and application at which the adhesive performs optimally and meets their specific required standards.
Most companies use expiration dates that are easily identifiable to the public. If not, consult the adhesive manufacturer for identification of the code.
Not all tools are created equally, and the varying designs can cause improper mixing.
Always consult the OEM repair procedures even when models appear to be identical.
Some OEMs have different adhesive advisements related to specific panels on the same vehicle.
Body repair is more complicated and requires more knowledge now than it ever has. Be sure to get proper training and familiarize yourself with necessary procedures.
The temperature for determining the work time, clamp time and cure time displayed on an adhesive’s package is typically 70°F to 75°F. If you turn off the heat in your shop at night and the temperature drops to 40°F for eight hours after you bonded a panel, you will have to raise the temperature back to 70° to 75°F and then wait the specified clamp time.
If host panels have corrosion that cannot be removed, it is best to consult the customer and consider replacing the host panel as well. If nothing else, be sure to document the corrosion damage with photos.
Adhesives may have the ability to prevent corrosion on uncorroded panels, but if heavy corrosion is already present, bond strength will be lost, and corrosion growth will—at best—only be slowed.
Most OEMs advise the use of corrosion protection internally and externally even when bonding procedures have been used. This ensures the bond is protected and if any bare metal was exposed during the placement of the new part, it has been protected.
Remember, you are the frontline decision maker when it comes to doing the repair. Your customer is trusting you to do things the right way. Following the OEM repair procedures combined with ongoing training is the foundation for performing safe repairs that benefit both your customers and your business.
Written by: Dennis Keicher, Advanced Application Development Specialist 3M Automotive Aftermarket Division