Nov. 7, 2017—3M released a detailed report offering techniques on how to complete rivet repairs on heavy duty trucks. The report outlines rivet selection, bonding, installation and removal.
There are several factors to consider when repairing with rivets. Rivets alone are great for holding panels together in the shop; but with movement and vibration, fatigue and corrosion can result, leading to panel bond failures.
When an aluminum panel comes into contact with a steel rivet, galvanic corrosion can easily occur. If the joint is not properly sealed, an electrolyte such as an acid, moisture or road salt can quickly start the corrosion process.
Heavy duty truck OEMs can apply anti-corrosion coatings on aluminum and other metal panels where the rivets attach. However, the technician may remove this corrosion protection during panel removal or surface preparation, leaving bare metal exposed.
Sometimes, these panels may get riveted back together without the corrosion protection restored. This can result in a compromised repair and a mark on the reputation of the repair facility.
Working with aluminum also requires special precautions related to worker safety and substrate preparation, as well as proper process mapping and site and workplace hygiene. Use OEM and vendor information to help educate yourself on best practices when working with aluminum and mixed metal repairs.
Rivet Selection
Selecting the correct type of rivet for a specific repair can be confusing. Heavy duty truck OEMs use several types of rivets including self-piercing rivets, blind rivets, countersink rivets, solid rivets, Magna Bulbs, Monobolts and many more.
Rivets and fasteners also come in a variety of metals such as aluminum, steel, stainless steel and high strength steel. Each rivet type has a specified shear strength, tensile strength, grip range, clamping force, application technique and tool requirement.
Other considerations, such as the length, size, and shape of the rivet as well as the location of the repair and accessibility to the repair area, can have a significant impact on which rivet is right. OEM specifications, technical bulletins, and repair recommendations as well as information from rivet and fastener manufacturers are helpful resources.
Rivet Bonding
The use of an adhesive such as 3M PN8115 Panel Bonding Adhesive in addition to rivets when performing a repair can result in higher bond strength versus rivets alone.
It can also provide leak prevention, reduced rivet vibration and lower point stress which can reduce fatigue and cracks. The adhesive can also serve as an isolator between dissimilar metals, which can reduce the potential for corrosion.
The Process of Rivet Bonding with Adhesives
In this process, the adhesive is being used as a bonder and as an isolator.
- Straighten the host panel mating flange on the truck to ensure proper fit-up of the service part.
- If using rivets that require drilling: clamp the panels, drill the holes and deburr the drilled holes as needed.
- Clean with an approved low-VOC compliant surface cleaner on the truck body and the service part.
- Sand the mating flanges on the truck and the service part using a 3M 80 grade abrasive and a dual action sander. (Remember, on aluminum the surface needs to coated within one hour to avoid surface oxidation.)
- Re-clean both surfaces with an approved low-VOC wax and grease remover.
- Apply a thin bead of adhesive to the mating flange(s). Using a filler spreader or acid brush, cover bare metal on the mating flange completely.
- Apply a second bead of adhesive to achieve adequate bond-line thickness, and clamp the part into place. Apply a thin coat of adhesive on the edges of the drilled holes to cover exposed metal before inserting rivets.
- Apply a second bead of adhesive to achieve adequate bond-line thickness, and clamp the part into place.
- Install the proper rivet recommended by the OEM.
- Remove the clamps. Remove excess squeeze-out before the adhesive cures, as grinding cured adhesive can create corrosion hot spots and collateral damage.
The Process of Rivet Bonding using an Adhesive Only as an Isolator
The adhesive in this process is only being used as an isolator between dissimilar metal panels. When would this be beneficial? When bonding large panels with rivets or fasteners when the addition of an adhesive bond is not needed but the need to isolate dissimilar metal panels is necessary. Handling large panels with wet adhesive or sealers can be a challenge.
- Straighten the host panel mating flange on the truck to ensure proper fit-up of the service part.
- Clean the truck body and the service part with an approved low-VOC compliant surface cleaner.
- Sand the mating flanges on the truck and the service part. Use a 3M 80 grade abrasive on a dual action sander. (Remember, on aluminum the surface needs to be coated within one hour to avoid surface oxidation.)
- Re-clean both surfaces with an approved low-VOC wax and grease remover.
- Apply a thin bead of adhesive to the mating flange(s). Using a filler spreader or acid brush, cover the bare metal area of the mating flange completely. Spread the adhesive to achieve a thin, uniform layer. Do not add any additional adhesive.
- Allow the adhesive to cure per the manufacturer’s recommendation.
- If using rivets that require drilling, clamp the panels, drill the holes and deburr the drilled holes as needed. Apply a thin coat of adhesive on the edges of the holes to cover any exposed metal before inserting the rivet.
- Install the proper rivet recommended by the OEM.
- Remove the clamps and remove excess squeeze-out before the adhesive cures. Grinding cured adhesive can create corrosion hot spots and collateral damage.
For help choosing the correct adhesive, visit 3M Collision.com and select “Heavy Duty Truck” under the “Products” or “Applications” tabs.
Rivet Installation
Installation techniques vary from one type of rivet to another. For example, solid rivets and blind rivets require holes to be drilled in both panels. Drilling can cause burrs which, if not removed, can prevent the panels from fitting up properly.
Countersink rivets are also used in solid rivets and blind rivets. Many countersunk rivets have a head angle of 90 degrees, so when setting the rivet it is very important to use the proper countersink bit to prevent thinning of the aluminum.
Self-piercing rivets (SPRs) are made of specially coated high-strength steel. SPRs don’t require pre-drilled holes or deburring, since they are designed to pierce the panels and spread outward.
Similarly, some rivets are designed to be compressed at a specified speed using a specific tool. This compression causes the rivet body material to flow out and properly fill the intended space.
However, if compressed too fast, voids may be created or the metal can become work hardened and cause the rivet to fail over time.
If manual tools are used and multiple compression attempts are made, the rivet or fastener can work harden, fatigue crack, or unevenly compress, causing a potential failure.
Rivet Removal
As with rivet installation, removal methods vary from one type to another. For example, solid rivets are installed using a bucking bar and an air hammer. The backside of the rivet is flared out which creates a “bucktail.”
It’s common when removing solid rivets to grind off this bucktail with a 2” or 3” 3M Roloc abrasive disc. However, especially in the case of aluminum, this can also remove excess material around the rivet and weaken the host panel. Instead, a technician can use a 3M File Belt Tool equipped with a 60 grit belt to grind the rivet bucktail down with minimal damage to the surrounding metal.
An SPR may be removed by pressing out the rivet with a special removal tool. You can also remove an SPR by drilling from the backside of the rivet—its shape makes it must easier to keep the drill bit centered on the rivet.
If you choose to drill the front side of the SPR, you must center-punch the rivet head to hold the drill bit in place.
Remember, SPRs are made of high strength steel and can therefore be difficult to drill out. An electric drill can be useful, but be sure to reduce the speed to prevent quickly dulling the drill a bit.
SPRs can also be ground from the backside, commonly done with a 2” or 3” 3M Roloc abrasive disc. As with solid rivet removal, the 3M File Belt Tool equipped with a 60 grit belt can be very effective: the SPR can be ground off on the front or backside with very little damage to host panel.
Accessibility, integrity of the host panel, tool availability, rivet or fastener type, and technician safety are factors to consider when choosing a removal method.
Rivet Bonding is a fast and effective way to join panels together. As with other repairs, size is the main difference between repair procedures in automobiles versus heavy duty trucks. The key is understanding the heavy duty truck OEM design and then determining what is needed and recommended for a proper repair.
There are many factors that can affect an individual repair, so the technician and repair facility need to evaluate each specific application and repair process and determine what’s appropriate. Visit 3mcollision.com/HDTruck for more product and process information on heavy duty truck repair.
