BMW Group has been recommending bonding and rivet bonding techniques to replace damaged aluminum parts for over a decade. The recommendation has now been brought to repairs on steel vehicles. The theory behind the repair of both aluminum and steel parts is similar, although the adhesives and preparation Figure 2 - The repairs on this aluminum front end are similar to the repairs on steel vehicles.material used can vary by the repair situation and the materials being joined (see Figure 2).

Reasons for the Change
There are several reasons that BMW has made the transition from conventional welding and STRSW to bonding and rivet bonding. One of the main reasons is the use of heat-sensitive steel. With bonding and rivet bonding, there is no heat generated that would weaken the steel, allowing the steel to retain its strength.

Another reason for bonding and rivet bonding is the increased corrosion resistance of the repair joints. Corrosion protection is extremely important during repairs because BMW offers a 12-year corrosion warranty.

Repair Overview
The recommended BMW sectioning joint on outer body panels requires a pre-fabricated E-coated reinforcement plate, available from BMW, along with VIN-specific repair information. The sectioning joint locations are in a similar area as the previously recommended weld joint, but may have moved to accommodate the reinforcement plate. The reinforcement plate has studs built into the part. This requires notches to be placed into the existing part and the new part.

Special plastic lock nuts are used to hold the parts in position until the adhesive cures. If the joint calls for them, rivets, which may be special blind rivets or punch rivets (also called self-piercing rivets or SPRs), are then installed on mating flange areas where applicable. When the adhesive is cured, the studs on the reinforcement plate are removed and the surface is prepared for the application of the BMW-recommended epoxy metal filler.

Figure 3 - The repair elements for aluminum repair that are shown are the same concept for repairs on steel rails.The sectioning procedure for a rail is similar to an outer body panel. The difference is this repair joint uses a repair element that fits into the rail. A bolt is inserted into the repair element. When the bolt is tightened down, the repair element expands against the inside of the rail, causing the adhesive to emerge. The bolt is removed once the rivets have been installed and the adhesive is cured (see Figure 3).

Still Some Welding
Bonding and rivet bonding does not replace all welding procedures for BMW. There are some areas that will still require welding to be done. These areas can only be identified with the correct repair information.

Tools and Equipment Availability
All of the tools and parts, including the reinforcement plates, repair elements, rivets, and adhesives needed to complete bonding and rivet bonding procedures for BMW are available to independent collision repair facilities. It is highly recommended, however, that before any repairs are attempted, the technician acquire training from BMW on the tools and techniques to correctly perform these repairs. It is also critical to have access to the most current and up-to-date repair procedures and sectioning locations from BMW.

Conclusion
BMW recommends primarily using adhesive bonding and rivet bonding to replace exterior body panels, frame rails, and when sectioning. The repairs are vehicle specific and require special tools, equipment, and procedures. BMW recommends specific training before doing these repairs, and having access to their specific repair information.

The recommended change in repair procedures from BMW is just one of the many examples of the challenges that collision repairers face on today's HSS and UHSS vehicles. While traditional repair methods are still used on these vehicles, how and where those repair methods are used is constantly changing.

This article first appeared in the April 26, 2012 edition of the I-CAR Advantage Online.

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