Just about anyone who spends time serving in the military eventually learns the meaning of the old expression "hurry up and wait." Service members spend long hours training to meet specific deadlines at precise locations, often to be left waiting once they've completed their tasks. This isn't accidental. It's the military's way of stressing the importance of continuous preparation and timeliness even when the need isn't always immediate.
Collision repair businesses are going through their own version of "hurry up and wait" as they prepare to work on aluminum, specifically on the 2015 version of the top-selling Ford F-150 pickup truck. ABRN recently spoke with several successful MSOs who had taken aluminum training and invested in new tools and equipment. Not one had worked on the vehicle yet, nor did they expect to use their new training and tools any time soon. That's to be expected. The aluminum-intensive truck is brand new, and until significant numbers hit roadways, very few will be rolling into shops needing repairs.
Still, the investment should pay off handsomely.
According to a 2015 North American Light Vehicle Aluminum Content Study by industry analysts Ducker Worldwide, over the next 10 years “seven out of 10 new pickup trucks produced in North America will be aluminum-bodied” and “every leading automaker will have several aluminum body and closure panel programs."
In the meantime, repairers can continue honing their skills and preparing for aluminum work by keeping up to date on the latest repair information and equipment. Here's a look at what your shop will need to know about prepping to paint and weld aluminum, along with the basics of adhesive rivet bonding and some tools to add to your inventory.
Clean finishes
For the most part, finishing aluminum parts will differ very little from those made of steel. The major departure comes in the prep work.
With its light weight, aluminum offers the additional benefit of being highly corrosion resistant. That's because aluminum resists rust by spontaneously forming a thin but effective oxide layer when it contacts moisture. This layer prevents further oxidation. Unfortunately, it also can contaminate any finishes applied to the aluminum so it must be removed during paint prepping stage.
Notable here is that fact that some of the cleaning done during prepping to remove shop contaminants picked up during body work will produce this oxide layer. Repairers will remove this layer mainly by sanding.
I-CAR offers the following directions for preparing bare aluminum parts for refinishing.
- Begin by cleaning bare metal surfaces with soap and water to remove any water-soluble contaminants. Next, apply a wax and grease remover. These steps will ensure a clean, contaminant-free part.
- If required, apply a metal cleaner and conversion coating made specifically for aluminum.
- Remove the oxide layer by sanding or abrading the surface. Never use grits coarser then P80 since aluminum scratches easily.
Bonding principles
Aluminum’s light weight also makes it an ideal candidate for rivet bonding, which provides a remarkably strong bond that further reduces vehicle weight. Some shops are already performing rivet bonding since it also can be performed on steel, as it is on some BMWs.
Rivet bonding utilizes structural adhesives and a variety of different rivets, either specially coated HSS steel, specially coated boron alloyed steel or aluminum rivets in different designs, such as but not limited to SPRs, domed, flat, counter-sunk blind rivets and solid rivets.
Refer to the following rivet instructions supplied by 3M for standard aluminum panel replacement on domestic vehicles. (Note that OEM information will include additional steps for specific models, such as information on de-burring drilled holes and using clecos to hold panels in place.)
Step 1.Prepare the host panel. Use a grade 80 abrasive belt to remove any remaining rivet material from this panel. Prep the remaining mating flanges with a coarse durable flex belt.
Step 2: Prepare the mating flange panel. Remove the e-coat from replacement panel mating flange areas using a clean strip sanding disk.
Step 3. Dry fit the replacement panel and complete any necessary metal straightening at the flange areas.
Step 4. Clean the host panel and replacement panel mating flange areas with a VOC compliant surface cleaner.
Step 5. Identify the replacement rivet sites and prepare the surface for the rivet type recommended by the manufacturer. (For solid or blind rivets, drill all necessary holes.) Once complete, remove the panel.
Step 6. Pre-assemble the NVH replacement. If the vehicle construction requires this step, apply an NVH dampening material or flexible foam at the original locations.
Step 7. Apply adhesive to mating flange areas on host panel and replacement panel covering all bare metal areas. Apply additional bead of adhesive at the mating flange area to ensure proper bond line thickness
Step 8. Install the replacement panel to host panel, making sure to avoid scraping off any of the adhesive. Clamp the panel in place.
Step 9. Install the replacement rivets to all areas per manufacturer recommendations. Note: Rivets must be installed while the adhesive remains uncured. Weld or insert bond the cosmetic joints/splices as recommended by the manufacturer.
Step 10. Clean up the adhesives. Remove the clamps and "tool" the excess adhesive squeeze out from the repair area before curing to seal the repair. Use an acid brush to remove adhesive from between clamps. Warning: Grinding to remove excess cured adhesive can expose bare metal, causing corrosion.
Step 11. Post-assembly foam replacement. Apply foams at the original locations as required
Worry free welding
Welding aluminum--namely aluminum joints--requires the same level of preparation as refinishing. Repairers again need to address removing the oxide layer since it has a greater melting point than the base metal. Shop also must clean any moisture, dirt, grease or oil that might contaminate the welding area.
Miller Electric Manufacturing Company recommends the following directions for preparing aluminum welds using their tools.
- Oftentimes aluminum arrives from the factory with grease and oil on it. To clean the joint, begin by degreasing the surfaces with a solvent. Next, use a cheesecloth or lint-free cloth to clean and dry the welding joint (their materials tend to be porous and will absorb more oils/moisture). Do not use shop rags to clean welding joints because they can transfer oil and dirt to the welding surface.
- Always wipe the opposite side of the joint clean since impurities can be pulled through the aluminum and into the weld puddle.
- Use residue-free solvents. Avoid chlorinated solvents in the welding area since they can form toxic gases in the presence of a welding arc.
- Never blow off the joint using compressed air. Compressed air contains moisture and oil contaminants.
- Clean the joint with a stainless wire brush but only after solvent cleaning. Wire brushing prior to cleaning will embeds hydrocarbons and other contaminants in the metal surface. It also transfers these undesirable elements back to the brush, making it unsuitable for cleaning.
- The by-product residuals from etching must be removed prior to welding. Use a stainless steel wire brush to clean all metal that has been etched.
- Clean all wire brushes frequently to prevent the transfer of contaminants to the weld joint. Dedicate specific brushes solely for aluminum work to reduce the chance of cross contamination with steel and other materials.
Miller also recommends the following rules for storing aluminum parts and filler materials to prevent contamination:
- Store all base metals and welding filler in a dry location with minimum temperature fluctuation (to minimize condensation). Welding filler metals should be stored in a heated and dry cabinet or room.
- Store aluminum pieces vertically to reduce condensation and the absorption of water contamination between layers.
- Whenever possible, bring all filler and base metals into the welding area 24 hours prior to welding so they may reach room temperature. Again, this minimizes condensation
- Keep filler metals covered at all times prior to welding. This includes a spool cover for MIG wire.
New tools
Along with the tools absolutely necessary for aluminum work--a MIG welder, clean room apparatus and a rivet gun--shops also would be well served to investing in an aluminum dent pulling kit or system. These systems typically include an anodized aluminum pulling bar kit (with suction cups, tie-rods and multi-hook gripping heads), an assortment of hammers, a heat gun and an infrared laser thermometer.
The thermometer is necessary to help technicians identify when a part has been adequately heated. Aluminum, unlike steel, does not change color when heated to its melting point. Heat shield gel usually is included in a system because it creates a barrier to protect undamaged portions of the aluminum panel.
Manufacturers now offer these systems as part of mobile aluminum workstations that feature additional tools such as stud welders and die grinders, allowing repairers to stretch their tool budgets a bit farther. These systems and workstations can be good investments for shops that are still putting together the funds to fully convert their shops for F-150 work.
A number of vehicles already sport aluminum hoods that need dent work. And affording dent pulling system allows any shop to get into the aluminum game as it prepares for the inevitable day when vehicles like the new F-150 will no longer be the exception, but the norm. Although most of the repair work for cosmetic aluminum panels, if repairable, can be accomplished with a map-pro gas. Then you may need to apply one or two pins to finish the repair.
