About I-CAR - Current Events/News: e-newsletters: Advantage Online: October 30, 2006

Figure 1 - Rivets used for steel-to-steel application have notches along the body for defined compression purposes.

Figure 2 - Rivets used for Usibor applications have a larger head than the steel-to-steel rivets.

Figure 3 - The style of cleco is not as important as its ability to hold the panel tightly together during rivet installation.

Figure 4 - This deburring tool is guided around the edge of the hole.

MERCEDES-BENZ AND BLIND RIVETS

When it comes to steel vehicle construction, technicians are used to seeing vehicle maker recommendations to replace factory installed squeeze-type resistance spot welds (STRSW) with STRSW or GMA (MIG) plug welds. Replacing spot welds in steel construction with blind rivets? That’s different.

Mercedes-Benz currently recommends using blind rivets during repairs to replace spot welds on specific models. Riveting is the predominant repair method with spot welds and plugs welds following. There are some areas where using GMA (MIG) plug welds is the only option and therefore recommended.

Recommendations are provided for the repair attachment method that should be used in specific areas. As a matter of fact, STRSW, rivets, and GMA (MIG) plug welds may all be recommended when installing a single part.

Collision repair information for Mercedes-Benz vehicles can be found at www.startekinfo.com for a fee. Rivets are recommended when replacing steel, aluminum, and Mega-Hard Steel (Usibor). This article will focus on steel-to-steel and Usibor steel applications. Examples of vehicles that use rivets for panel replacement include the:

Rivets are recommended instead of GMA (MIG) plug welds for strength and to avoid heat-affect and deformation. Mercedes-Benz research finds that the blind rivet they recommend has the same strength as a spot weld or a GMA (MIG) plug weld. Also, with blind rivets, a technician is able to more effectively ensure corrosion protection following repairs because coatings have not been burned off.

Mercedes-Benz has specific rivets that are recommended for repairs. The rivets are available through Mercedes-Benz dealership parts departments. There are different types of rivets depending on the visibility of the repair and the materials that are being attached. The head of the rivet may be a standard protruding-type or flush-mounted. Flush-mounted rivets require the hole in the part to be countersunk. The rivet may have an aluminum body with a steel mandrel (see Figure 1), which is the standard rivet, or a steel body with a steel mandrel (see Figure 2), which is used when working with Usibor steel.

When working with steel, aluminum or Usibor steel, Mercedes-Benz may recommend using adhesive with rivets. The repair procedure identifies when adhesives should be applied. With the new model 221 S-Class, which is a steel-bodied vehicle, rivets are used in conjunction with adhesives for repairs.

The replacement blind rivet is installed in a different location than the original spot weld. This is done for the same reason that a repair spot weld is made in a different location. The original spot welding process changed the characteristics of the metal at the heat-affect zone in regards to strength, thickness, and malleability of the metal.

Before removing the damaged panel, it is important to identify if rivets will be used for replacement. Tools and methods must be used to prevent damaging or making holes in the part that will remain on the vehicle. When drilling out the factory installed spot welds, use caution to avoid drilling the inner panel. The holes left behind will be too big for the rivets and in the wrong locations.

Mercedes-Benz has rivet guns available with adapters for gaining access to recessed areas. In Usibor steel applications, a specific rivet gun is recommended to obtain the necessary pulling force to compress the rivet.

Panel fit-up and cleanup are crucial to proper rivet installation. Flanges should be smooth and straight. A special panel clamp called a “cleco” is used to hold panels firmly together (see Figure 3). Burrs can also be a problem. It is recommended that both sides of each panel of the joint be chamfered, or deburred. A deburring tool works well for this task (see Figure 4). Burrs around the edge of a rivet hole can scratch the coating of the rivet which in turn can cause corrosion, cause the rivet to fail, or prevent proper panel fit-up.

Corrosion protection is important when working with dissimilar metals, such as when attaching a steel part with an aluminum-bodied rivet. Corrosion protection is also important when working with bare steel. The main objective is to seal out moisture. When using rivets, Mercedes-Benz recommends applying a zinc dust paint, part number 000 986 34 42, to all bare metal surfaces before attaching the panels, including the edge of the hole. This weld-through primer is the same product recommended for spot welding. Weld-through primer is not recommended when GMA (MIG) welding.

Following rivet installation, seam sealer should be applied to both sides of the flange. A wax-based anti-corrosion compound should be used for enclosed areas.

Mercedes-Benz recommends using blind rivets for attaching parts on certain vehicles in specific areas. This is preferred over GMA (MIG) plug welds, since GMA (MIG) welding can damage corrosion protection and produce damaging heat. These factors are a growing concern especially when working with advanced high-strength steels, such as Usibor steel.

We can no longer repair collision-damaged vehicles as we have in the past. With today’s complex vehicle bodies containing different alloyed parts, the technician must follow the vehicle maker’s recommendations during repairs and to do that, must have access to the vehicle maker-specific web site for the latest repair guidelines.

For comments or suggestions on the Advantage Online, please contact I-CAR Senior Instructional Designer Bob Jansen at bob.jansen@i-car.com.

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