To bond or not to bond: That is proving to be a sticky question for some dealership body shops.
As its name implies, adhesive bonding involves the use of specially designed adhesive products to bind two surfaces - in this case, vehicle panels - together.
Adhesive product manufacturers say their products offer a lot of benefits. It's faster than welding (some estimate it can reduce repair time by 50% over traditional welding) yet as durable and more corrosion resistant, they say. But only a few of the vehicle manufacturers have endorsed the use of adhesive bonding.
"We're familiar with it and use it some, but not on Ford vehicles because to my knowledge Ford does not recommend the use of adhesive to bond panels," says Gary McCann, manager of the Joe Madden Ford body shop in Downers Grove, IL.
Mr. McCann says that no matter what dealership body shop managers hear from adhesive product manufacturers, they need to understand what repair methods have been approved by the automakers for use on the vehicles they are repairing.
Adhesive bonding has received a lot of attention recently because the product manufacturers have been touting its benefits.
"Unlike welding, which concentrates stress at specific points, adhesives distribute stress uniformly, which makes it very durable," says Jim Perritt of Lord Corp., makers of Fusor Metal Bonding Adhesive. He says adhesives also form a moisture barrier that minimizes the chance of corrosion. And his company's product can be used on bare or primed metals, and can be used to bond dissimilar materials with less risk of corrosion.
He says shops using adhesive bonding report it can improve productivity, and reduce vehicle noise and vibration. Compared to welding, it also is relatively easy to learn and master.
"It is easy and saves time," says Ron Rose, body shop manager at Reuther Jeep/Chrysler in Creve Coeur, MO. "You just need to have everything ready to put together before it sets up, but it has a pretty good working time. We always combine it with some welds, but from what we've seen, the structural integrity holds up and there's less chance of a rust problem."
Although the process for using adhesive bonding varies by product manufacturer, all products require cleaning of the surfaces to which the adhesive will be applied. For some adhesives, cleaning with a wax and grease remover followed by scuff-sanding is adequate. Others require removal of topcoats, primers and e-coat. Still others require priming the area with a self-etching or epoxy primer, leaving the factory e-coat or primers intact.
With such a degree of variation just in preparation recommendations, it's easy to understand why it is critical to know how the product you choose should be used.
The adhesive manufacturers also differ in their recommendations for the thickness and width of the bead to be applied. This, in turn, affects recommended cure times.
One common mistake made in adhesive bonding is squeezing the joined panels too tightly. That can squeeze much of the adhesive out of the joint, reducing the strength of the bond.
Given its overall ease-of-use and potential benefits, why isn't adhesive bonding more widely used than it is today? One big reason is that vehicle manufacturers haven't endorsed the repair technique. Ford, GM and Toyota all say they are looking at it but are waiting for more research.
"At the present time, our engineers in Japan do not endorse adhesive bonding as a replacement for welding," says Roger Foss, national dealer support manager for Toyota. "I see no signs that that's going to change."
In 1999, DaimlerChrysler published a technical booklet giving a "thumbs-up" to the use of adhesive welding on cosmetic panels. Until then, Nissan was about the only major manufacturer to recommend structural adhesives to repair some parts and assemblies on its cars.
When the auto manufacturers appear slow to endorse a repair methodology that seems promising, insurers and repairers often turn to the industry training organization, I-CAR (the Inter-Industry Conference on Auto Collision Repair), for recommendations based on its research. The fact that I-CAR has developed a class on adhesive bonding indicates that it foresees a trend. But officially, I-CAR has stood by its general guidelines of following the auto manufacturers' recommendations.
"During collision repairs, replacement panels should be attached to the vehicle using procedures recommended by the vehicle manufacturer," an I-CAR statement reads. "If a repair facility chooses to use adhesive bonding for panel installation, tested procedures should be used that have been validated by a reliable product maker or testing facility."
The adhesive product makers have not been shy about developing procedures based on such testing.
In 1996, for example, Lord Corp. released the results of crash testing by an independent research facility. In one test, several rear body panels were removed from two undamaged vehicles. Factory replacement parts were attached to one using bonding adhesive, and to the other using standard welding procedures. A third undamaged vehicle (the same year, make and model) was left unaltered. All three vehicles were measured before and after a crash test that involved hitting the stationary vehicles from behind by a 4,000-pound barrier moving at 30 mph.
A similar test was done on front-end body panels of three other vehicles crashed into a 30-degree barrier wall at 8 mph.
"The bottom line is that we were able to demonstrate, in both instances, that the structural integrity of the vehicle was not compromised in any way by reattaching the panels with structural adhesives rather than welding," Richard Jones of Lord Corp. says.
The following year, Lord reported crash testing a Nissan Sentra with a roof panel installed using the company's bonding adhesive. The vehicle was subjected to a 32 mph rollover test with similar successful results.
More recently, a Canadian insurer, Manitoba Public Insurance, announced the preliminary results of its crash testing of adhesive-bonded roof panels.
The testing involved full roof replacements on four-door sedans. The roof panels of the test vehicles were replaced using adhesive alone, or with adhesive and spot welds as the product manufacturers recommend. A similar vehicle with its OEM welds intact was also crashed for comparison. The testing included 30- and 40-mph offset frontal crashes into a barrier.
The resulting damage to the vehicles was severe enough to total them. Factory spot welds on the undercarriage had let go, and the floor pans often had large tears. But the adhesive bond held on all vehicles tested, says Denis Pinette, Manitoba Public Insurance's technical services coordinator.
"Because different makes of vehicles react differently under the same test conditions, it is impossible without testing every make to be certain of the adhesive's performance in all cases," a report on the crash testing states.
It adds, "We are satisfied, however, that this type of frontal crash provided sufficient stress to the adhesive bonds to allow us to draw the following conclusions: Roof panels replaced with...panel bonding adhesive and strategically placed plug welds perform at an acceptable level in even the most severe of frontal crashes.
"We find that in repair situations where a uniform adhesive bond line is possible, that the manufacturer's recommended adhesive bonding system can provide an acceptable process when replacing cosmetic, non-structural parts."
Will such testing convince repairers, insurers and vehicle manufacturers that adhesive bonding is a viable alternative to welding? Perhaps. DaimlerChrysler's shift to a more-accepting view of it is welcome news at some dealerships.
"Bonding is the coming thing," says Matt Congdon, body shop foreman at Ed Murdock Chrysler in Lavonia, GA. "Now that DaimlerChrysler has approved it, if we have to put on a roof panel or a door panel or skin, we prefer to use bonding instead of welding. It's stronger, it distorts the metal less, and it's quicker - there's less body work to do afterward. I think those people who don't switch over are going to be far behind in the next couple of years as more and more manufacturers move toward bonding."
Mr. Congdon and others point out, however, that until manufacturers make that move, dealership body shops can best avoid a sticky situation by knowing and following automakers' recommendations.