Collision Repair Training | Australia
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Collision Repair Training | Australia
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Current Events/News: Advantage Online: 2005 Archives
FORD MOTOR COMPANY PROVIDES WELD BONDING PROCEDURE
April 18, 2005 - Ford Motor Company recently released two bulletins addressing the issue of weld bonding (TSB 04-26-16 and TSB 04-26-17). These procedures address weld-bonded panel replacement for all Ford, Lincoln, and Mercury vehicles. To ensure that all weld-bonded panels are repaired according to Ford’s guidelines, follow the procedure as outlined in these technical service bulletins. This procedure is performed only on panels that have been weld-bonded during vehicle assembly. Do not attempt this procedure on other areas of the vehicle. TSB 04-26-16 states that the door shells are manufactured with adhesives only. Therefore, weld-bonding door skins is not recommended. Weld Bonding Defined Weld bonding is the process of using both adhesives and squeeze-type resistance spot welds (STRSW) or GMA (MIG) plug welds to attach a panel to the vehicle. During vehicle assembly, the adhesive is first applied to one of the panel flanges. The flange is then mated with the adjoining flange and welded in place. The purpose of weld bonding is to create an area with good soundproofing that is leak-free, and corrosion resistant without seam sealer. Restoring these properties ensures that the original vehicle design, function, and appearance are maintained following collision repairs.
Recommended Welding Equipment and Adhesive When weld bonding, STRSW is the preferred method and should be used whenever possible. There are several resistance spot welders that have been approved by Ford to be used for the weld-bonding process. The recommended welders can be found in TSB 04-26-16 and TSB 04-26-17. When choosing one of the approved resistance spot welding machines, make sure that the tips are able to deliver the proper pressure at the tips (see Figure 1). If there is too little pressure, there will not be enough contact between the flanges, causing excessive throw-out, burnthrough, cracks, or pinholes. There are instances when a GMA (MIG) welder is recommended in place of a resistance spot welder. These areas include any area that is inaccessible to the STRSW tips. For example, the bottom third of the A-pillar on the 2004 F-150 has no access to the panel backside. Therefore, this area is GMA (MIG) welded to the vehicle structure (see Figure 2). Ford has provided a specific product requirement regarding the use of adhesive. Motorcraft metal bonding adhesive TA-1 50 ml or TA-1-B 225 ml are the only adhesives currently approved by Ford Motor Company for weld bonding (see Figure 3). Flange Preparation and Application The flanges must be properly prepared to accept the adhesive and ensure a strong bond between the adhesive and the metal substrate. The adhesive recommended by Ford requires that the flange be clean to bare metal, so it must be ground to ensure that all coatings, including the E-coat and galvanizing, have been removed from the bonding area (see Figure 4). The metal should appear shiny once all the coatings have been removed (see Figure 5). Follow the adhesive maker’s recommended procedure for cleaning the prepared flange. The adhesive application instructions require dispensing a small amount of adhesive from the cartridges to ensure an even flow. Install the applicator tip, and dispense a mixing-tip length of adhesive to ensure the product is properly mixed. Before applying the adhesive, make sure the resistance welder is properly tuned for welding through adhesive. To make sure the welder is properly tuned, make practice welds and destructively test the welds using the peel test and measure the remaining nugget (see Figure 6). Ford has developed a Weld Nugget chart that shows what the recommended nugget size should be when welding a specific thickness of metal. Keep in mind that this is an important step that must be performed BEFORE the preparation and application of adhesive. Next, apply a 6-9 mm bead of adhesive to the bare metal mating surface of the vehicle flanges. Spread the adhesive, making sure all of the bare metal is covered. With the E-coat and galvanizing removed, the adhesive now provides the only corrosion protection for the flange. Therefore, it is critical that all the bare metal is covered. Clamp the two panels together, making sure to slide the panels against each other if adjustments need to be made. Do not lift the panel; separation between the flanges can create air pockets that weaken the adhesive bond. The working time of the recommended adhesive is 40–50 minutes, depending on the air temperature. Temperature warmer than 20° C (70° F) will reduce cure time and a cooler temperature will increase cure time. Also, while welding takes place, the heat of the welding process reduces the actual working time and cure time. Resistance Welding Resistance welding can either be done while the adhesive cures or after the adhesive has fully cured. Welder settings will vary depending on the cured state of the adhesive. Use the welder manufacturer’s recommended settings for welding through wet or cured adhesive. To begin the welding process, install a shunt to assist with the first weld (see Figure 7). Shunting is only required when there is no metal-to-metal contact on the weld mating surfaces. With this shunting effect, the current flows through the clamp before making the weld between the electrode tips. Once the first weld is made, the shunting clamp is no longer required for additional welds because the initial weld creates a conductive path between the workpieces. If, however, there is a portion of the panel that must be welded and it is far enough away from a spot weld, shunting may be required to create a weld in a new area. Clamps that are not used for shunting should have tape over the ends for insulation when welding (see Figure 8). When welding, be sure to maintain the original spot weld spacing. Welds should be placed as close as possible to the original spot weld location, however, do not place a new spot weld in the original spot weld location. GMA (MIG) Welding When resistance spot welding is not possible (i.e. no access to the panel backside), than GMA (MIG) plug welding may be used in its place. When using this method, the flange preparation procedures are similar. However, the main difference between the two procedures is that when GMA (MIG) welding and bonding, make sure the adhesive stays out of the weld zone. Before applying adhesive, attach 25 mm (1") tape to the area that will be plug welded (see Figure 9). Apply and spread the adhesive on the flange. After the adhesive has been spread out, remove the tape. This should leave an adhesive-free area to weld. Adhesive in the weld zone will create problems with excessive porosity and weld integrity. Another consideration when GMA (MIG) welding is the creation of plug weld holes in the replacement panel. Like the squeeze-type resistance spot welding procedure, these holes should be close to, but not on top of, the original spot welds. Make sure that the E-coat is ground around the plug weld hole to ensure weld integrity. Conclusion The practice of combining adhesive bonding and welding is not a difficult process, and doing so helps restore the original vehicle design. When doing weld bonding, remember these key points:
For a step-by-step procedure for weld-bonding Ford vehicles, refer to the technical service bulletins which can be obtained online at http://www.motorcraft.com/ or at your local dealership.
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