A Look at Advanced Resistance Welding

In our article, "Introduction to Resistance Welding" (H&D, Sept. 2010), we gave an overview of the origins of Squeeze-Type Resistance Spot Welding (STRSW), the types of equipment used today, electrical requirements and basic usage. In this article, we are going to delve deeper into the procedures for making proper resistance welds every time, which in turn will ensure proper, safe repairs.

Due to the advanced material usage in today's vehicles, many OEMs are developing their own certified collision repair programs — not just for their aluminum-intensive vehicles, but for their steel-intensive vehicles, too. OEMs with certified programs and equipment requirements are Audi, BMW, Chevrolet Corvette Z06/ZR1, Chrysler/Jeep, Ferrari, Jaguar, Lamborghini, Mercedes Benz, McLaren, Nissan GT-R, Porsche, Toyota and Volkswagen. Additionally, almost every OEM, at the least, makes a suggestion in their collision repair information as to what welding equipment to use.

As with any specific repair program, there are going to be requirements as to what equipment can and cannot be used; this holds true for Resistance Spot Welders (RSW), too. After reviewing the recommended and/or required RSW from the OEM repair manuals, we found one common denominator: The requirement of a 3-Phase inverter, water-cooled welder. Some OEMs recommended non-water cooled units, but all the OEMs with a certified repair program required water-cooled units only. The most commonly approved welders are the Car-O-Liner CR-510 and CTR-12000, Celette-Elektron MultiSpot MI-100, ProSpot i4, TECNA 3664 SMART and Wieländer and Schill InvertaSpot GT.

As many of you already know, most of today's RSW machines will ask you to choose the type of substrate (steel) you will be welding, such as High-Strength Steel/Galvanized (HSS/Galv.), Mild Steel, Weld-Bond (using adhesives), Boron Steel, Advanced High Strength Steel (AHSS), Pulse Mode, OEM-specific settings and even custom modes for your own preference. Many of the required RSW will have a flash drive, SD card or memory card with pre-set weld settings built into the onboard computer of the RSW. The pre-installed weld parameters and settings make it easier for the technician to make the correct settings every time.

The required RSWs have been tested by the OEM to meet their stringent weld parameters and destructive testing to ensure that the replaced components will react in the manner they were designed to in a subsequent collision event. As we all know, no matter how great RSWs are, they cannot make seam welds on sectioned components, so most OEMs allow Metal Active Gas (MAG) seam welding to reattach the panel at the sectioned joint, although many OEMs are requiring MIG Brazing or structural adhesive bonding in these areas and STRSW on the flanges where the electrode arms can reach both sides of the matting flange. But the use of MAG welding is for another article.

The first thing you must do, after getting your welder by the vehicle, is to unwind the electrical cord completely off the machine; otherwise, you risk turning the cord into an electromagnet during operation. The next thing to do is plug the unit in and check your power lamp(s). Now for the most important step: Check your electrode tips. The electrode tips come in basically two versions: Shafts and caps. The shaft type generally can be sharpened multiple times before the shaft must be replaced. The cap type is generally not sharpened and is usually replaced after a few jobs. The important thing here is to ensure the tips are clean and properly shaped. Never use a file or a grinder on the tips; use only the sharpener provided by the equipment maker. If the tips are clean, then you can proceed to your practice welds; if not, then either re-sharpen or replace them. During your welding operations, sand (clean) the tips every five to eight welds with a piece of P120 sandpaper or emery cloth. Doing this will ensure that no metal particles or dirt will build up on the electrode tips. Most manufacturers have picture charts or vector drawings of the electrode tips that show their profiles and dimensions. These will assist you in knowing when to discard a tip.

The next thing you will need to do is to make some practice welds. Cut some metal coupons (pieces) from the damaged or unused portion of the replacement part. Set the coupons up exactly the same way the flanges are set up on the vehicle. Make the sure that the weld edge and pitch that will be used on the vehicle flanges are duplicated on the practice coupons. Clamp the coupons together; the first clamp should be a metal-to-metal contact (a shunt) and all the other clamps must be insulated. Insulating the clamps is easy; you can either use duct tape or electrical tape wrapped around the jaws. Not insulating the clamps can cause the electrical current to pass through the clamp, causing progressively weaker welds. Now, weld the coupons together by making two welds. After the coupons cool off (a minute or two), destructively test them by peeling them apart. Measure the tear out hole, which generally needs to be five times the metal thickness of the thinner piece for a two-layer flange and the middle thickness on a multiple layer flange. After passing the visual and destructive tests, take a photo of the coupons, attach the photos to the file and save the coupons for liability protection.

Each OEM has different requirements for RSWs that are replacing OEM spot welds. Some examples are 1.3 times the amount of OEM spot welds = the amount replacement RSW required; a ratio of 1:1, 1.5:1 or 2:1 might be required, or one replacement RSW every 22mm.

As you can see, each OEM has very different repair procedures and equipment requirements for replacing OEM Spot Welds. This is why it is very important to look up the proper collision repair information, either at the OEM website or at www.AlldataCollision.com.

Feel free to contact us at any time if you have any questions.

Larry Montanez, CDA is co-owner of P&L Consultants (with Peter Pratti Jr) and is a founding member of IACDA. P&L Consultants work with collision repair shops on estimating, production and proper repair procedures. P&L conducts repair workshops on MIG & resistance welding, measuring for estimating and advanced estimating skills. P&L also conducts investigations for insurers and repair shops for improper repairs, collision reparability and estimating issues. P&L can be reached by contacting Larry at Office (718) 891–4018; Cell (917) 860–3588; Fax (718) 646–2733 or email at larrygoju@aol.com.

Jeff Lange, PE, is president of Lange Technical Services, Ltd. of Deer Park, New York (www.LangeTech.net) and is a founding member of IACDA. Jeff is a Licensed New York State Professional Engineer, ASE certified and I-CAR Trained. Jeff specializes in investigating vehicle and component failures. Lange Technical Services, Ltd. is an investigative and forensic engineering firm performing forensic vehicle examinations and analysis for accident reconstruction, products liability and insurance issues. Jeff can be reached at 631-667-6128 or by email at Jeff.Lange@LangeTech.net.