Wednesday, 24 February 2016 22:21

Glue and Rivets Have Replaced Welding in Many Newer Vehicles -- Part 1

Written by Toby Chess

Recently, I was conducting the I-CAR Steel welding certification test at a collision repair center when I saw a 2014 BMW 3 Series having a quarter panel being installed. The tech was welding in the quarter panel instead of using glue and rivets. I asked the tech if he had the OEM replacement procedures, which he produced from his tool box. I showed him that the proper procedure was to rivet and glue the quarter panel in See accompanying photos for the proper installation method and recommended tools.

DOWNLOAD THE PDF TO VIEW FIGURES AND DIAGRAMS

 

I spoke with the person in charge and explained that there was a problem with the repairs that were being performed.

First, the corrosion protection warranty could be voided by the factory.

Second, a state violation could be imposed for not following OEM repair procedures (Fine, loss of license, and court litigation.)

Finally, diminished value could be imposed and/or the shop could be compelled to purchase the vehicle. But I am getting ahead of the game. Let’s take a look at why adhesives and rivets are being used more frequently today and in the future.

The major reasons for rivet-adhesive bonding are two fold. First, Corporate Average Fuel Economy or CAFÉ standards. Starting in 2015, trucks and automobiles are classified together. In the past, Cars and trucks were separate, but now they are combined. Substituting aluminum for steel, Ford was able to achieve a 700 lb weight reduction in its F150 Truck. That translates in 3½ gallon better gas mileage. The current average for 2016 is 34.1 miles per gallon with a goal of over 50 miles per gallon by the year 2025. Second is vehicle safety.

With stronger and lighter materials being used in today’s vehicles, we are seeing a combination of several different types of steels, together with aluminum, magnesium, plastics and carbon fiber. It should be noted that not everything can be welded, so we are seeing a number of new and different joining methods Remember, heat will weaken high strength steels and destroy ultra high strength steels. For example, Honda began using ultra high strength steel in “A” pillar, “B” pillar and rocker reinforcements on its 2013 Accord. Honda states in the repair statement (https://techinfo.honda.com)

“Parts made of Ultra-High-Strength Steel (UHSS/1,500MPa/USIBOR) must be installed as a complete part. No sectioning allowed. Ultra HighStrength Steel requires special welding equipment, procedures, and settings. See the welding section of the appropriate body repair manual. Failure to use the proper equipment or follow the proper procedures can result in an unsafe repair.”

It goes on to state “Never do MAG-MIG welding on 1,500 MPa steel.” The repair industry is being asked by the OEMs to invest in new equipment and training to repair their vehicles properly to OEM pre loss specifications. I could go on about this trend, but lets get back to adhesive-rivet bonding or a some refer to it as cold bonding.

Like I stated previously, welding will be used less and less and the alternative is adhesive. Look at Fig 7 taken from the web site http://www.adhesive test.com.

Adhesive has excellent tensile strength and extremely strong when conducting a peel test, but is weak when conducting a shear test. To overcome this deficiency, a mechanical fastener or some form of rivet needs to be used. The rivet will prevent the panels from shearing apart.

Fig 8h taken from www.bolt products.com/images shows the definition and term when discussing rivets.

The two most important items in Fig 8h are the material thickness (also material type) and the shank size. The vehicle engineers will determine everything needed for their particular repair operation, but you need to know the proper shank size to drill or punch the hole in the material. If the hole is wrong size, the rivet could be loose and shear movement could occur. Too small a hole could cause the metal to distort and again the panels will not be full contact with each other. Let’s look at the various types of rivets.

There are 3 major types of rivets that are used in the repair process, which are self piercing rivets (SPRs), solid, and blind rivets (we will look at Hemlock, Monobolt and Pop rivets in this category).

A self piercing rivet as the name implies does not need pre-drilled holes for installation. The process starts by clamping the sheets of materials between the die and the blank holder. The rivet is driven into the materials to be joined between a punch and die in a press tool. The rivet pierces the top sheet and the die shape causes the rivet to flare within the lower sheet to form a mechanical interlock. The rivet may be set flush with the top sheet when using a countersunk rivet head.

The die shape also causes a button to form on the underside of the lower sheet. In the repair process, it is necessary to have access to the back side of the material. It should be noted that SPRs are made from high strength steel and coated with a tin-zinc coating to prevent galvanic corrosion. Moreover, the install gun must have enough pressure to set the rivet (more on this later on). Dave Gruskos from Reliable Automotive Equipment furnished me a diagram on the installation of a SPR. 

The rivet is put into the dies (1st diagram on the left). Next, he tool clamps the panels together. The third diagram the rivet pierces the top sheet and radially expands into the bottom sheet. Finally, the high joint strength is achieved by the interlock between rivet and material. Removal of an SPR can be done by welding on a cylinder and removed with a special tool, can be drilled out or using a different set of dies with the install tool and punched out.

Part 2 of this article will run in the November issues of Autobody News. 

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