Repairing today, preparing tomorrow?
Composites have had a long and ever-changing history. But today’s composites promise to offer lighter, more durable hoods and creative panels that won’t rust or dent as easily as in the past. Moreover, continued improvements in adhesive technology are making repairing composites even easier. Understanding some of the basics behind the evolution of composites and their current state will help ensure a complete repair each time. From the late 1930s and into the 1940s, fiberglass, or FRP, was available but only being considered in very limited applications. At the time, one of the OEMs considered making deck lids of fiberglass, but it returned to using sheet metal—mainly because the molding and production process was done exclusively by hand lay up. By the late 1940s and into the 1950s, the process of molding fiberglass had undergone some serious improvements. The process had improved to the point where, in 1953, General Motors Corp. (GM) was able to introduce the first all-fiberglass body vehicle—the Corvette. During the 1950s and 1960s, fiberglass was primarily used on the Corvette, although a few manufacturers did use fiberglass for fender or quarter panel extensions. The “enduro” bumper, which was developed in the 1960s, was the first bumper that used plastic composite in its production application, and it was designed to take a minor hit with little or no damage. During the 1970s, plastic composite bumper covers—or fascias—came into the industry in somewhat limited quantities. Today, almost all cars worldwide use composite bumper covers. But by early 1980s, the OEM manufacturers switched from fiberglass to a new material known as Sheet Molded Compound (SMC). This material has been used in header panels since 1973. At the time, the collision repair industry was repairing this new “fiberglass” just like it had repaired the original fiberglass and having a great deal of repair failures. However, as we now know, SMC has a very different chemical makeup and needs to be repaired with the appropriate repair material. Many modern-day repairers believe this is where the new age of automotive composites begins. The Trend to Composites Keeping all of this in mind, we need to accept that plastic composite—when used in an appropriate application—is an improvement from the parts once made of glass and metal. The automotive design engineer of today has the composite materials available to create a lighter, more durable hood and a door outer panel that can take a shopping cart bump without a dent. And let’s not forget the added bonus—it won’t rust. This technology came about with sheet-molded compound, and now there is a new material coming into the picture—carbon fiber. Carbon fiber is only being used on what are often considered exotic cars, such as Ferrari and other extremely high-end sports cars and with some limited use on low-production vehicles. However, carbon fiber will be incorporated into the manufacturing of several Corvette parts in the near future—making carbon fiber repair more mainstream. As far as repairing carbon fiber, the good news is that from the repair side, we will deal with it much in the same way as SMC. What about composites that are showing up on the sides of today’s vehicles? A vehicle that normally had a fairly smooth and plain side can take on a completely new appearance when cladding is added to the side of it. Cladding are large side moldings made of the same materials as the fascias. These moldings can serve two or more purposes. The first is to enhance the appearance of the side of the vehicle. The second, less-obvious purpose, is to protect against stone chips on the lower portion of the doors and rockers. DaimlerChrysler uses cladding on its Grand Cherokee, Ford is adding cladding to the Explorer and Excursion, and Chevrolet pickup trucks have large wheel opening moldings or flairs made of composite that will protect from stone chipping. These parts are repaired in the same way as bumper covers. Repairability of Composites Now let’s discuss some composites and their repairs. We’ll start with SMC, which includes carbon fiber. The most important idea to remember is that these composites are fiber-rich materials. I constantly get calls asking why a backing patch can’t be put on the backside and the front or cosmetic side filled with body filler. The problem is something called thermal expansion and contraction. Think about this: if you have a fiber rich part and you do a resin rich repair in the middle of that part, you can’t expect the repair area to expand and contract at the same rate as that part. You must control thermal expansion in the repair area by using a repair adhesive made for SMC repair and packing as much fiberglass cloth into the repair as you can. This will simulate the fiber-rich part and expand and contract similar to the original material. When this is not done you end up with a “bull’s eye,” or “halo” or whatever term you use to describe the repair a few weeks after it is completed. This is a failed repair, redo or replace that should not have happened. With whatever repair material you use in the repair, it is urged that you do the repair exactly as the adhesive manufacturer’s instructs. This means paying attention to the curing time. There are a few issues that may make fiber-rich parts not repairable. The fibers in these materials are not 100 percent saturated with resin, and this can be an issue if the part has been contaminated with an outside substance. Consider a moderate front-end accident on a vehicle with an SMC hood. The hood sustains minimal damage but the core support is damaged, severing one of the air-conditioning high-pressure lines. The freon escapes, wetting down the SMC. It also carries the lubricating oils to the backside of the SMC and the fibers wick in the oil. Even though the damage to the hood was minimal, it may not be repairable due to this saturation. The use of silicone-based products such as interior dressings may also cause a nonrepairable situation. Some show car owners will spray the engine compartment with these products to achieve that shiny look under the hood. But this causes the silicone to leach into the SMC, rendering the part nonrepairable. Bumper cover repairs have become very simple during the past two years. Several repair material manufacturers now have one or two repair products used with surface modifier or adhesion promoter to repair any composite bumper. Many covers that could be saved with minor repairs are unnecessarily scrapped. One of the most repairable parts of a cover is the mounting tab. There are repair materials on the market that you can use to easily create a tab even if the tab is not there. It is appropriate to mention the repair of side cladding with bumper covers since they are made of the same composites as the bumper covers. We are now finding composite pickup-truck beds on the market, with some made of SMC and others made of S-RIM or R-RIM. These materials will be repaired similarly to SMC. Whatever the composite, consult your adhesive manufacturer for their repair procedures. Repair or Replace? The Future of Composites |
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