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Solutions for Burn-Through Defects When Welding High-Strength Steel & Nuts with Capacitor Discharge Spot Welders
Jul 10,2026
High-strength steel features high tensile strength and rigidity, widely used for load-bearing parts such as automotive structural components and equipment brackets. Nut projection welding is the mainstream processing method for these parts. Compared with ordinary steel sheets, high-strength steel dissipates heat slowly and heats up rapidly, making heat accumulation inevitable during welding, which easily causes sheet burn-through and other defects.
I. Common Burn-Through Defects
1.Complete Burn-Through: Through holes at welding spots, rendering workpieces unreworkable and scrapped.
2.Hidden Partial Melting: Weld surface looks intact, but the back of the sheet turns black and thins, nearly penetrated; cracks or fracture easily under force.
3.Overburn Collapse: Sunken welding spots with metal loss and ablation at nut roots.
II. Material Characteristics Prone to Burn-Through
1.Slow heat dissipation of high-strength steel leads to continuous heat buildup at nuggets;
2.Poor plasticity under high temperature prevents outward metal flow;
3.Hardening and embrittlement after cooling easily generate cracks and pinholes; inconsistent welding quality also occurs between dissimilar materials.
III. Root Causes of Burn-Through
1.Welding parameters set for ordinary steel generate excessive energy and accumulated heat that pierce sheets;
2.Insufficient pressure results in poor fitting and concentrated current burn-through; excessive pressure crushes molten pools to cause extrusion-type burn-through;
3.Instant high-energy discharge without buffer creates rapid heat concentration; continuous welding accumulates heat and repeatedly triggers burn-through defects;
4.Worn, eccentric or poorly cooled electrodes cause uneven current load and local overheating that burns sheets;
5.Thin sheets matched with large nuts require high energy, resulting in sheet burn-through while nuts remain unwelded;
6.Oil stains, scale and dust left on welding spots create uneven resistance and local overheating perforation.
IV. Radical Optimization Solutions to Eliminate Burn-Through
1.Optimize welding parameters: Adopt low-voltage slow discharge mode with stepped buffered energy release to disperse heat. Control heat input while meeting torque requirements to avoid heat accumulation burn-through.
2.Rational welding pressure control: Maintain stable moderate pressure. Increase pre-pressure to eliminate gaps if pressure is insufficient; lower pressure appropriately if overpressure occurs. Enable pre-press & hold function: compress tightly before discharge to prevent gap-induced arcing and overheating.
3.Standardized electrode management: Use large flat-surface electrodes to disperse current. Grind and calibrate concentricity daily, keep unobstructed water cooling to avoid electrode heat buildup.
4.Reinforce fixture support: Do not weld thin sheets suspended; install backing plates underneath. Use dedicated jigs to center nuts and ensure full contact to prevent unilateral overheating burn-through.
5.Adjust welding sequence: For multiple nuts, adopt diagonal skip welding to disperse heat. Reserve cooling intervals to avoid batch burn-through caused by continuous heat accumulation.
6.Complete pre-weld cleaning: Remove oil, dust and scale from welding spots; lightly polish severely oxidized areas to guarantee clean welding interfaces and uniform resistance, eliminating local overheating.
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Wuxi HAIFEI Intelligent Equipment Co., Ltd.
Wuxi HAIFEI Welding Equipment Co., Ltd.
Add: 28 Shuiyun Road, Yuecheng, Jiangyin, Jiangsu Province, China. (Postal Code: 214404)
Mobile: +86 18915302352
Email: wushijie@jshaifei.com