Spot Welding in Modern Auto Body Repair, Explained
Spot welding in modern auto body repair, properly called squeeze-type resistance spot welding, or STRSW, is fast becoming the joining method automakers require instead of the old MIG plug weld. In an interview with BodyShop Business, Brian Wasson, manager of I-CAR Program Delivery, laid out why the two processes are not the same and why the difference matters for the safety of your vehicle after a collision.
The confusion starts with terminology. A plug weld, done with gas metal arc welding equipment, joins two panels by filling a punched or drilled hole with molten filler metal. STRSW joins the same flanges with no holes at all. Two electrodes squeeze the metal under high pressure and pump high amperage through it to form a weld nugget. After decades of running a torch, I can tell you the equipment for that second process is a different animal entirely, often needing three-phase power to even run.
Why Automakers Are Moving From Plug Welds to STRSW
The push toward STRSW comes straight from how vehicles are built now. To hit safety ratings and fuel economy targets while adding weight from every new feature, engineers lean on higher-strength steels that do the same structural job with less mass. The catch with those steels is that heat changes their properties. Traditional MIG welding gets the metal very hot, and that heat can quietly rob a high-strength panel of the exact strength it was engineered to provide in a crash.
STRSW joins the parts with minimal heat, which is why the factory uses it on the assembly line and increasingly writes it into repair procedures. It is common for an outer replacement panel to be a low-strength steel welded to an inner panel made of high-strength steel, and getting that joint right without cooking the metal is the whole point.
Welding Around ADAS and Electronic Components
Any welding process throws off a magnetic field, and because STRSW is a high-current process, that field can be large. Wasson notes you can actually see the proof of it.
You may have noticed the welding machine's cables move or jump when the machine is triggered.
That same field can push voltage into a vehicle's electronic systems and fry them if precautions get skipped. For advanced driver assistance system components, the precautions look a lot like handling any electronic module: remove sensors, modules, and wiring harnesses before you strike an arc. Sometimes the part sitting in the path of that magnetic field is several feet from the actual repair, which means extra disassembly. That is exactly why a repair plan built at the start of the job matters so much. You want to know what has to come off before the sparks fly, not after.
Which Steels Call for Spot Welding
As a rule, any hot stamped or boron alloyed steel requires STRSW, though the process can be applied to nearly any steel. Those boron parts are the backbone of the safety cage, and they are unforgiving of the wrong method.
Equipment, Training, and Maintenance
Modern spot welders are smart. Many will set their own parameters automatically to produce a quality nugget. Even so, some OEMs specify exact clamping pressure, hold time, and amperage for certain areas, and hitting those numbers means switching the machine into manual mode. Knowing when and how to do that is not something a machine does for you.
STRSW is procedure-based, and like any procedure, skip or fumble a step and the result suffers. Good training covers real headaches like shunting and material coatings that interfere with a clean weld. Having the right tool is one thing, knowing how to use it correctly is everything, and most equipment makers run their own training, some in partnership with I-CAR.
Maintenance is where shops quietly get burned. Two items get missed most often. Electrode tips flatten with use and need to be redressed or replaced, since they are consumables that wear out by design. And the welder's internal coolant has to be changed on schedule, or the machine's life gets cut short. The owner's manual spells out the intervals, and if the paper copy is long gone, the manufacturer almost always posts it online.
What This Means for Your Vehicle After a Collision
The only way to preserve a vehicle's as-built crash performance is to follow the manufacturer's own repair information, using the joining method it specifies. A shop that plug welds a joint the factory says to spot weld may leave a car that looks perfect and performs worse than designed in the next accident. That is why proper equipment, current training, and OEM procedures are non-negotiable on modern steel. At AW Collision, that discipline is the baseline our OEM-certified teams work from, and if you want your repair done to the standard your vehicle was built to, you can start with an estimate.
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