Squeeze-Type Resistance Spot Welding (STRSW) Equipment and Setup
How STRSW makes a nugget
Squeeze-type resistance spot welding passes current through stacked panels held by copper-alloy electrodes. The cycle has squeeze, weld, hold, and sometimes cool time. Force must be applied before current and held while the nugget solidifies. Nugget size depends on current, time, force, tip diameter, coating, and shunt paths.
Setup rules
Use the OEM-approved welder and electrode tips; dress tips regularly and replace them at the OEM limit. Verify tip alignment and force with a gauge, and confirm current calibration. Set parameters from the OEM weld chart for the steel grade and thickness. Test on a coupon of the same stack before welding the vehicle. Clean coatings only as the OEM permits; weld-through primer and adhesive can change resistance.
Worked example
A coupon of two 1.0 mm mild-steel panels is welded, then peeled. The nugget measures 4 mm, but the OEM requires 5 mm. The reasoning: first confirm tip condition and force, then increase current or weld time within the OEM window; do not simply increase force, which can reduce nugget growth and cause expulsion.
Traps
Using a spot welder on ultra-high-strength steel without OEM approval; welding through structural adhesive; ignoring shunting when welds are close together; skipping tip dressing; assuming a “click” means the force is correct.