Panel bonding you can trust

New technology makes panel bonding quicker and more profitable

Panel bonding just might be the great overlooked craft in collision repair. Custom paint elicits passion; high-strength steels elicit controversy and technical acumen, and frame work immediately calls up patience and accuracy. Yet, panel bonding is key both to a thorough repair and the appearance of the final product.

It also has gotten a whole lot easier. This month, with a little help from the manufacturers of adhesive bonding products, we look at the latest bonding technologies that can save you time and help you produce a superior repair.

Growing popularity of adhesives

Is your shop making the most of its adhesive bonding possibilities? There's a good chance you're not, according to Jason Scharton, marketing manager – Adhesives, Coatings & Sealers for 3M Automotive Aftermarket Division. Scharton explains that history has a good deal to do with this.

Panels almost always are welded into place at the factory. In recent years OEMs have recognized the value and quality of adhesives and have included their use in technical repair bulletins. Scharton says these technical bulletins usually apply only to newer vehicles. For vehicles 10 years of age or older, the manufacturer's recommended repairs often don't include adhesives. But that's not because adhesives won't function here. "The OEMs just haven't updated their information," explains Scharton, who says adhesive bonding works fine on these vehicles.

The same history that is preventing some shops from using adhesives on older vehicles also seems to be preventing other shops from getting into the adhesives game at all. Scharton points to some numbers that show these shops probably are costing themselves significant savings in work quality and cycle time. Scharton said welding is a challenging craft to pick up and excel in.

Meanwhile, he said, technicians can learn proper adhesive panel bonding techniques after several hours of training (I-CAR offers a course on adhesive bonding). For shops wary of using adhesives, he suggests they start in an area such as the inner wheel arch area of the wheel well since it's one of the toughest vehicle areas to weld in. Scharton said using adhesives here is far easier. He said shops also will discover, should the vehicle return again after being in another collision, how well the adhesive bond holds.

Shops looking into adhesives should find two other factors even more compelling. According to Scharton, adhesives cut cycle times on panel bonding an average of 2.8 hours versus traditional plug welding. Scharton also said OEMs increasingly are turning to adhesives during manufacturing. He said the redesign of the Ford F-150 in 2004 featured 10 times more adhesive usage in the panel bonds than the previous model. "They found that adhesives significantly increased stiffness and structural rigidity without adding weight," says Scharton.

Bonding basics: Deciding how to bond

When is the right time to use an adhesive versus welding? The first step in any panel bonding operation is determining whether the panel is structural or non-structural. Non-structural panels typically include quarter panels, roof panels, door skins, cab side panels and rear body panels. Non-structural operations can include repairing corrosion and tears or holes in the metal and repairs on parts that don't affect the structural integrity of the vehicle. Structural parts typically include frame rails, rocker panels, pillars, aprons, core supports, inner quarter panels and floors.

According to adhesive manufacturers, because methyl methacrylate (acrylic) type metal bonding adhesives are trusted by many auto manufacturers for the assembly and replacement of non-structural metal bonding panels, technicians only have to identify the structural characteristic of the part when deciding the best method of repair. For example, a door skin is a non-structural part so it can be bonded completely with most metal bonding adhesives without the need for welding.

For structural areas, the best method of joining metal panels can vary. Using adhesives has become commonplace in structural areas when used in conjunction with traditional metal joining methods. In some repairs, frame rails, aprons and pillars are assembled in the factory with adhesive and welds. Metal bonding adhesives, combined with squeeze-type resistance spot welding (STRSW) equipment, can be utilized when installing structural members and panels (more on this operation to follow). Rivet bonding also can be used with adhesives.

Panel bonding step by step

Once you've decided adhesive panel bonding is the right operation, you'll need to decide upon an adhesive and follow the specific manufacturer instructions for it. You should find them fairly straightforward and uncomplicated. Consider these instructions for adhesive bonding of a door skin supplied by adhesive manufacturer Valvoline.

Panel removal and preparation:

1. Grind the outer edge of the door skin with an angle grinder.

2. Drill out factory spot welds.

3. Remove outer skin from door shell.

4. Remove remaining flange with an air chisel.

5. Straighten any damage to the flange with a hammer and dolly.

6. Grind the door shell flange to bare metal, removing all adhesive, paint, galvanized coating and e-coats. Note: Continue to grind until a constant flow of sparks is observed coming off the grinding disc to ensure all the galvanizing coating is being removed.

7. Dry fit for proper alignment.

Installing new door skin:

1. Scuff the inside of the door skin with a scratch/scuff pad to remove the shiny surface of the e-coat.

2. Blow off with clean, dry air, and wipe with clean, dry rag.

3. Remove the cap of the adhesive cartridge by prying the uppermost slot with a flat screwdriver. The cap may be retained for future storage.

4. Properly place the cartridge into the gun. Prior to attaching the mixer, dispense a small amount of adhesive to ensure both sides flow evenly.

5. Attach mixer, and dispense out two inches for proper mix.

6. Apply a 1/4- to 3/8-inch bead of adhesive to bare metal door shell, then tool or brush the adhesive evenly, making sure to cover all surfaces of the bare metal. Note: This eliminates exposed metal, which would be susceptible to corrosion.

7. Align the new skin in place, and apply even pressure. After the panel has been positioned, do not pull it away from the shell. If repositioning is required, slide the panels against one another to ensure no air is trapped in the bond line.

8. Clamp tightly in place every 4-6 inches, then roll the hemmed flange.

9. Tape off hemmed seam, and apply the same adhesive for seam sealing. This will allow the seam sealer to cure at the same time. Clamp times may be accelerated by use of a heat gun or lamp for 10-15 minutes at 180 degrees F.

10. Prime and paint per paint manufacturer's recommendation.

Weld bonding: The best of both worlds

Weld bonding, as its name suggests, is a method of joining metals together using STRSW in conjunction/combination with a structural adhesive. According to Bob Zweng, senior technical service representative for LORD Corporation, it can improve strength and stiffness; allow for additional fixturing capabilities; permit fewer welds; improve fatigue and impact resistance as well as cycle time; and increase corrosion protection and NVH (noise, vibration and harshness) control properties.

Ed Staquet, senior technical service representative, Automotive Aftermarket, LORD Corporation notes, "The increased usage of weld bonding has armed body shops with a repair method that restores damaged vehicles to pre-accident condition better than ever before."

Gerry Bonanni, paint and body technical engineer at Ford Motor Company, says weld bonding offers the body shop the ability to duplicate proven factory processes in the auto body repair field, and the value of improved repair quality by utilizing weld bonding is enormous.

"With the advent of near-future vehicles utilizing ultra high-strength steels, aluminum and alternative structures, the progressive body shop will do well to explore the opportunities of weld bonding and squeeze type resistance spot welding equipment," says Bonanni.

Zweng says any automotive part (structural and/or non-structural) originally welded or weld bonded by the manufacturer with adhesives and/or sealers can be repaired using weld bonding. STRSW welders often are used with advanced high-strength steels (AHSS) since there is minimal heat affect damage compared to MIG welding.

There are different types of STRSW equipment that can be used for weld bonding. The most common compression welder options are transformer and inverter. Transformer welders change AC power to DC current to obtain higher amperage, while inverter welders change the wave pattern from a sine wave to a square wave. Inverter welders often are considered a better choice since they provide a high-powered weld in a very short amount of time, which minimizes the heat-affect zone on the adhesive and metal.

MIG weld bonding can be used, but the procedure may be cumbersome. The technician applies adhesive to the bond locations of the part but skips areas where a MIG weld would be placed. MIG weld bonding offers some of the same benefits of STRSW weld bonding, such as corrosion protection in the bond areas and NVH advantages. The increased heat and other factors produce longer repair times, making STRSW weld bonding a better choice.

Zweng explains that when choosing between MIG and STRSW, technicians must consider the joint design of the part and the type of equipment on-hand. STRSW has been proven to work well with weld bonding, but not all metal joints allow for STRSW gun access.

Before implementing weld bonding, shops must consider a few factors. They must be electrically equipped to handle resistance welders. They must have a dedicated circuit with a minimum of 60 amps, three-phase and 208/220-volt service to handle most resistance welding equipment. The welder should be UL/CSA approved and conform to the local electrical code. Shops need to remember that voltage drop can cause performance problems.

Final word: The right choice

If you're still relying on welding for the majority of your panel bonding operations, it's time for a change. Adhesives can both cut your cycle times dramatically and provide the kind of fit, finish and structural rigidity that OEMs are building into their vehicles. In fact, if you haven't gotten on board with adhesives and started looking at weld bonding, you run the risk of falling dangerously behind your competitors. It's time to put your trust into some new technology.