By Curt Harler
Chemistry is replacing physical welds in many sectioning procedures. In fact, according to the Federal Motor Vehicle Safety Standard 301 crash tests, adhesive bonding and MIG welds will do the job of joining body parts equally as well.
"I think it's the wave of the future," says Dan Frohlich, owner of A.R.S. Automotive in Pittsburgh, Pa. However, he adds, for the shop owner it can be a double-edged sword. He is concerned that the insurance companies will see the savings in time that is possible with adhesives and forget about adding back the additional cost of the chemical materials.
Chemical adhesives can repair and bond metal and plastics. Among the materials available are the Fusor family of urethanes, acrylics and cyanoacrylates manufactured by Lord Corporation; Panel Bonding Adhesive from 3M; epoxies such as Nonsag from SEM Products; 2000 Flex-Filler 2 or 2020 SMC Hardset Filler from Urethane Supply Company; and Epoxy Door Skin Adhesive from Dominion Sure Seal. The latter four firms all make door skin products that rely on two-part epoxy chemistry. The materials also serve to dampen vibration and seal against the elements.
In all cases, chemical adhesives are recommended only for secondary panels. Posts, frames and other structural members should be welded.
The procedures for doing a repair with bonding materials are fairly simple - almost instinctive for anyone who has been around cars. Ed Staquet, senior development representative for Lord, is a master I-CAR instructor with 34 year's of experience working in body shops. "When we were developing this product, I was insistent that there be no major procedural changes," he says. "The only difference is that, instead of welding, the technician is applying adhesive."
Be aware, however, that using adhesives in all applications is not universally approved. "There is not a global acceptance," says Tom Fleming, vice president and database developer for Mitchell International. While agreeing that doing door skins with adhesives "is not an issue," he notes that there are still some differences of opinion on jobs like quarter-panel replacement. "We see that changing with time," says Casey Knobel, 3M's auto aftermarket liaison manager. 3M recommends its materials for non-structural uses like quarter-panels, tailgates and box sides, but not structural applications such as rocker panels or struts. In some cases, 3M recommends welding with its product.
Knobel notes that some OEMs are using adhesives in some of their cars today. "The reason they do not use adhesives more is the assembly line time factor at the factory," he says. In this instance, it is the time to cure that is the hang-up. "OEMs are going to be cautious," he adds. 3M's product is a heat-activated adhesive designed for the demanding aircraft business. "You have the luxury of working with it, clamping it and making sure it is right before curing it," he says. The material can be heat or air cured.
"I can sometimes beat flat-rate time by using these materials," Frohlich says. "Of course, it depends on the technician _ if they are familiar with the materials and procedures, then they can do a 10-hour quarter-panel job in about eight hours," he said.
No matter what product is used, replacing a door skin is a good place for a technician to start using bonding materials. After all, most door skins are bonded from the factory. After doing a door or roof skin, rear body panels are a good place to build a comfort level with chemical adhesives.
The initial steps to sectioning with an adhesive chemical bond are identical to those for welds. The car must be square. All grease, dirt or other foreign material should be removed. Any rust or twisted and broken metal should be air chiseled or sawed away from the repair area.
Next, the technician should pre-fit the replacement to the existing metal. This step is especially important for chemical bonding, since metals - once placed together - should never be pulled away from the vehicle.
The mating surfaces on both pieces should be ground to bare metal. Next, the technician should prepare to put a one-quarter to three-eighths inch bead of bonding material on the metal panel. There are notches on the bonding tube so the proper bead size can be applied. The applicators work like caulking guns and material runs out easily.
Follow these two tips to get a better bond. First, purge the tube to assure an even flow from the applicator. Second, "waste" a mixer's-length of the material, squeezing it out onto a piece of cardboard. This will assure an accurate mix of the chemicals. Any unused material can be saved for the next job.
Lord makes two types of metal bonding adhesives. The medium set requires 90 minutes to two hours to set up. The fast-set material takes about 30 minutes to set and is appropriate for smaller jobs. Once a sectioning panel has been set on the vehicle, it should never be pulled away or lifted from the surface. Should a slight adjustment be required, slide the metal into position, but maintain contact between the two surfaces at all times.
If it is absolutely necessary to remove a patch, Staquet recommends re-applying a bead of adhesive over the existing wet material. This will prevent any bubbles from forming. If the job sits long enough that the adhesive dries, it must be taken back to bare metal.
The repaired surface should be clamped evenly for a half hour. The same clamps or vise-grips that are used for a weld job can be used for adhesives. Another tip: do not cover the clamp area. Too much force will prevent proper bonding and is just as bad as under-clamping.
Once the material has had proper time to set up, grind away any excessive adhesive. Bevel the edges around the work area. Then apply body filler and proceed to paint as on any other repair.
When dealing with problem plastics like TFO and polypropylene, Urethane Supply recommends using a filler prep material before applying the epoxy.
"One of the big advantages with adhesives is that there is no clean-up, no spatter from the welds," Staquet says. It is important to apply the correct bead size for the job. "The big thing is to follow the instructions," he adds.
Staquet says one place people often go astray is on sizing the section to be replaced. On a butt joint with insert, use the size recommended in the paperwork. "If the instructions say to overlap one inch, then overlap one inch," he says. "Do not try a three- or four-inch overlap 'just to be safe.' It will not work." For complex chemical reasons, the extra overlap will distort the curing process and could lead to failure.
Properly done, chemical bonding passes the government crash tests. Three 1990 Nissan Sentras were crash-tested; one had the driver-side quarter panel and rear body panel MIG welded; one was adhesive bonded; and one was in OEM condition. All three vehicles successfully passed the FMVSS 301 test.
There can be as much as 20 percent to 25 percent less time involved in doing a job with chemical bonding than with welds, Frohlich said. The trade-off is in a higher cost of materials. Overall, experts say there is not a lot of difference time-wise between welding and bonding in getting a car out of the shop. But since the dry-time from an adhesive is about two hours, the technician can be doing something else during that time. Some jobs can be done with both chemicals and welds. Frohlich has looked at compression welding. "I have friends who like it, but right now I'd have a hard time justifying the $12,000 for the machine," he said.
Because adhesives have a lower peel strength vs. overlap shear, welding is usually recommended for anchoring and to resist the tendency for bonded panels to peel under certain failure modes. On the plus side for adhesives is the elimination of damage to glass or the interior upholstery that welding sparks or spatter can cause. "Panel warpage is eliminated and in many cases the need to paint adjacent panels is done away with," Knobel said.
Neither Lord nor 3M have done meticulous time studies on repairs using adhesives vs. welding. In general, adhesives are faster, but the materials are more expensive, said Knobel. "The time saved on the job is more valuable than the materials cost," he said. Mitchell has monitored and done studies on door skins. "We haven't seen any big variance in labor times," Fleming said. However, where the OEM does chemical bonding, it is the preferred method for prepare. In the quarter-panel area, however, Fleming says the jury is still out. "We haven't seen too much actual application under shop conditions," he said. "Some OEMs are not buying into it."
"Adhesive makes a better repair," Knobel maintains. "Look for more adhesives in future cars."
Frohlich is also convinced that adhesives are here to stay. It is the difference in the cost of materials that Frohlich worries about. He sees the information providers accounting for the quicker flat-rate shop time and not adding in the greater expense of materials. "If they cut us down on our time and don't add in for the materials, our profits will go right out the window," he said. For the present, though, he figures he is able to beat flat-rate time on some of the jobs by using adhesives, even if some of that difference is eaten up by the cost of materials.
Another key area to consider is job warranty. "We stand behind the repair," Staquet says, noting that no warranty comes with a spool of welding wire or a tank of argon. In fact, chemical manufacturers may have an easier time of it since they are able to control the quality of adhesive and the mix ratios.
"Testing has shown the overlap shear strength of our adhesive to be much stronger than welding," Knobel said.
The new sectioning procedures are fairly straight-forward. There is the potential for speeding up jobs. In most cases, the adhesives are ready to use. "As a last resort -- should there be a problem -- pull the instructions out of the trash and read them," says Staquet.
| Curt Harler is a freelance writer based in Strongsville, Ohio.
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