A Bonding Experience

Body shops will embrace different tools and techniques to repair high-tech cabs.Crafted to cutting-edge designs with space-age materials, many newer trucks will require special handling when they hit the body shop.Where truck-body repairs once called for popping rivets and grinding metal, they may now require heating and separating "bonded" surfaces to replace panels or make spot repairs. Or as one

Body shops will embrace different tools and techniques to repair high-tech cabs.

Crafted to cutting-edge designs with space-age materials, many newer trucks will require special handling when they hit the body shop.

Where truck-body repairs once called for popping rivets and grinding metal, they may now require heating and separating "bonded" surfaces to replace panels or make spot repairs. Or as one body-shop veteran puts it, the new repair procedures will convert technicians "from metal sculptors to part-time chemists."

The specialized repair techniques and tools required will be different from what's needed for typical riveted or welded cabs. But the actual work performed won't necessarily be more difficult. And once technicians gain proficiency, these procedures may be completed in less time than traditional body repairs.

Nonetheless, what fleet managers might expect to do -- or expect an outside repair outlet to do for them -- can appear daunting at first glance at what's under the surface of many new cabs.

"The materials used in constructing a bonded cab, such as our T2000, require an entirely different repair procedure than riveted or Huckbolted cabs," points out John Lindemann, a senior district service manager at Kenworth Truck Co.

"However," he continues, "it's actually a simple process. A structural panel is removed by applying a heat gun and prying with a putty knife to `cut' the adhesive bond. The surfaces are then prepped, new adhesive applied, and a replacement panel clamped into position. The heat gun or a heat lamp can then be used to accelerate the cure time for the repair bond."

Fixing scratches, cracks, and holes in hoods, doors and other parts made of SMC (sheet-molded compound) or other rigid plastics involves sanding the flaw and applying one or more layers of adhesive, according to Lindemann. If needed, he notes, structural "backing patches" may be added to the reverse side of the repair area.

Lindemann says the next step is to apply pressure to counter tape placed over the adhesive. After the set time elapses, the tape comes off, the area is sanded and air-blown, and any remaining imperfections are filled before priming and refinishing complete the job.

That's just a shorthand account of two procedures developed by one truck maker for repairing certain areas on a single model. OEMs should be contacted directly for repair recommendations based on the specific materials and methods used in building their cabs.

Think Vette The non-metallic composite or "plastic" materials increasingly being incorporated into cab construction are forcing body shops to adapt. To varying degrees, major truck makers are replacing steel and aluminum with composites, including fiberglass and SMC materials. The use of adhesives -- or glue, as the body guys call it -- is coming on strong as a replacement for mechanical fasteners in cab assembly and subsequent repairs.

OEMs report the new materials and fasteners deliver several advantages. Those using them affirm that composite parts weigh less than metallic ones yet offer the durability expected by fleets.

Truck builders -- including some that make primarily steel or aluminum cabs -- contend that applying high-tech glue to bond plastic or metal body panels in place enhances vehicle aesthetics and reduces assembly time. However, even highly plastic cabs still use metal fasteners to support or align body panels during installation.

Experts in plastic surgery abound in auto-body shops. They've gained hands-on knowledge as car makers have switched over to composite body parts. But in trucking, the composites-and-adhesives learning curve remains steep. Even experienced truck-body technicians will benefit from additional training before the first composite guinea pig limps into the shop.

For example, according to KW's Lindemann, the OEM wrote a new collision-repair manual and conducted seminars to bring dealer personnel up to speed on T2000 cab-repair techniques before the new truck hit the market.

Freightliner, says Larry Warr, manager of technical training, offers customers and dealers two-week training on cab repairs. "Our schools explain how much of an adhesive bead to use and how to clamp SMC repairs without denting," he remarks.

Warr points out that door frames and aluminum side panels on the OEM's Century Class trucks are attached with adhesives. These models sport multi-piece SMC hoods and also use adhesives to secure the fiberglass Raised Roof on sleepers so equipped. "Freightliner selects factory adhesives by spec," he notes, "which can be translated by aftermarket suppliers so warranty work can be done with original-type material."

"Most people are skeptical of the new procedures at first," reports Walt DeWolfe, truck-shop foreman for Knipsher Inc., a Fort Wayne, Ind.-based body-and-paint works. "A lot of these repairs do require giving the technician something to read up on before they'll know how to do it."

DeWolfe, who served as a consultant to Navistar on SMC repairs, knows whereof he speaks. "Once technicians get the hang of it, the work will be completed much more quickly. The key is to learn the basics first and then develop shortcuts as your experience increases."

For example, he places glass beads or monofilament line alongside a repair to contain the adhesive applied. "That keeps you from squeezing or clamping the repair so tightly the glue's forced out before it sets."

DeWolfe recommends debonding panels with a heat gun, set between 250deg F and 350 deg F, depending on the repair. "Don't overheat the area, especially not the undamaged piece that will remain. Take a putty knife and tap into the glue. As you heat the glue, the panel will start to lift. Apply more pressure and the piece will walk right off."

Already versed in working on the plastics and glue found in the T2000 is Dan Davis, body-shop leadman at Trebar Kenworth of Boise. "Shops definitely need retraining for body repairs. The technician must be able to identify four of five different composite materials, know which adhesives will work best on each, and know how to follow recommended repair procedures."

While training will be critical at the outset, Davis points out that labor-hour savings will accrue. "Repair time will get shorter as technicians get experience," he asserts. "Eventually, debonding should be comparable to or quicker than replacing damaged riveted panels."

David Ebert, senior training instructor for Freightliner, says that body shops should consider how "user-friendly" a formula is when selecting the appropriate repair adhesives. "Some things to look at," he advises, "include whether the material is consistent enough not to run off; how many pads will it take to sand it; how easy is it to clean up; and whether it will classify as hazardous waste for disposal."

According to Ebert, technicians should know the specific cure time of adhesives used to bond aluminum. "Adhesive that is precured," he notes, "means it won't shrink and thereby weaken the repair as it dries.

"Using preassembled replacement panels improves aesthetics and reduces repair time," Ebert continues. "Or the damaged area can be hammered out and puttied. However, I don't advise cutting and splicing in pieces because it can decrease the resale value of the vehicle."

Steel fan Despite such acceptance of plastics, metal cabs are not yesterday's news. Convinced of the safety benefits of a welded-steel structure, Volvo Trucks North America elected to construct its new VN Series cab out of HSS (high strength steel).

According to Jeff Priddy, Volvo's manager of diagnostic & service engineering, HSS is a light but strong galvanized product that allows a "competitive" vehicle weight while supporting a safe driver environment.

"The VN cab is spot-welded," relates Priddy, "and the HSS body panels provide some of the structural integrity. This design means standard body-shop equipment and repair procedures can be used. We recommend replacing complete panels to maintain the cab's structural integrity." He says a new Volvo repair manual will tell how to cut out a spot-weld from one side so there won't be any holes where a new panel is joined.

On some sleeper models, Volvo glues an SMC roof to the cab module. "SMC is very versatile and easy to work with," Priddy says. "Small areas can be patch-repaired, although we advise replacing the entire roof if damage is extensive. Starting about three inches above the joint, a technician would cut off the bulk of the roof and use a heat gun on any remaining adhesive. Attaching a new roof requires a few rivets to align it on the cab, but the glue applied will actually hold it down."

While its cabs are structured of steel or aluminum, Navistar International uses SMC for hoods, air fairings, fender extensions, and other cab components. According to Tom Barkimer, manager of non-metallic materials engineering, Navistar mainly uses SMC on parts that require more styling than can be achieved by stamping metal.

"SMC materials save weight over steel but not vs. aluminum," he states. "The biggest advantage of composites is to production cost. It's less than half the price to tool a hood in SMC than in metal. Economics are an issue when OEMs select cab materials," Barkimer remarks. "A high-volume cab can be built in steel or aluminum for less than in fiberglass or plastic."

As to glue, Barkimer relates that Navistar is "looking at new adhesives for structural bonding of cab panels. If used to eliminate some fasteners, adhesives would save labor-hours on the factory floor." He says adhesives may prove more durable as well, since the "biggest potential for service failure is at rivetheads."

However, Barkimer cautions truck buyers to weigh that gain in durability against potentially higher repair costs. He holds to the "theory that adhesive bonding is meant to be permanent. Heat will soften adhesives but it's still not an easy task to remove a fiberglass roof that was bonded on for good. It may be easier to repair the damaged sections than replace the complete roof."

Like their customers, truck builders march to different drummers. A case in point is an OEM where the familiar Huckbolt is holding firm.

"Because of its corrosion resistance and weight performance, aluminum is our primary cab material," says Rick Harris, Peterbilt's cab & systems engineering manager. "And to make cabs and sleepers easy to repair, the Huckbolt is our primary fastener." He says the bolts lend themselves to panel replacement "as opposed to body work."

According to Harris, Pete makes use of fiberglass, "a readily repairable material"-- in cab cowls, hoods, sleeper roofs, and aerodynamic devices. "Fiberglass pieces are Huckbolted," he points out, "with a sealant used where they attach to metal parts."

"We find the bolts provide consistent clamp-loading during production and won't loosen over a vehicle's lifetime," Harris continues. "Dealing with welded joints involves far more extensive repair work than drilling out some Hucks to install a replacement body panel."

Beauty is only skin deep. But knowing how to fix a cab, no matter what it's made of, is a thing of beauty that will last as long as there are trucks on the road.

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