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Problems Caused by Mismatched Pressure During Projection Welding of Flange Nuts with Capacitor Discharge Spot Welders
Jul 20,2026
Projection welding of flange nuts is widely adopted in auto mass production. Capacitor discharge spot welders feature low heat impact and high efficiency, ideal for mass nut welding. Weld quality primarily depends on welding pressure; mismatched pressure leads to various defects even after energy adjustment.
I Core Principle of Flange Nut Projection Welding Pressure
Flange nut projection welding consists of three stages: compaction & lamination, discharge fusion, cooling & shaping. Welding pressure eliminates interlayer gaps, equalizes force and current distribution and stabilizes nugget formation. Capacitor welders deliver instantaneous energy and are extremely sensitive to tiny pressure deviations.
II Defects from Insufficient Pressure
1.Cold joints & insufficient torque: incomplete projection fusion only forms superficial adhesion; nuts loosen under vibration and fall off.
2.Arcing & dark welds: gaps between parts create discharge sparks, pits and poor surface finish.
3.Skewed nuts: inadequate clamping force fails to fix nuts, leading offset holes and assembly failure.
4.Uneven fusion & unstable batch quality: inconsistent force across multiple projections creates mixed cold joints.
5.Easy weld oxidation: trapped air accelerates high-temperature oxidation and reduces conductivity & mechanical strength.
III Defects from Excessive Pressure
1.Over-squeezed molten metal creates plate indentations, bulges and flatness out of tolerance, scrapping workpieces.
2.Excessive pressure crushes and flattens nut welding projections, destroying projection welding structure.
3.Flange edge cracking & microcracks under heavy compression; threads deform causing jamming, slipping and loose bolts.
4.Forced extrusion of molten metal creates hollow incomplete fusion inside nuggets.
5.Deep indentations and scratches on workpieces from high electrode pressure.
IV Composite Defects from Unstable / Uneven Pressure
1.Skewed nuts causing assembly jamming and unusable parts.
2.Wildly fluctuating weld strength and unstable batch performance.
3.Frequent arcing & spatter accelerating electrode adhesion and wear.
4.Severe residual stress from uneven heat & force distribution leading to plate warpage post-weld.
V Quick On-Site Judgment of Abnormal Pressure
1.Low pressure: spattered dark nuggets, loose nuts, insufficient torque, partial cold joints.
2.Excessive pressure: plate collapse, deformed flanges, thread jamming, deep indentations.
3.Unstable pressure: skewed nuts, single-side dark welds, single-side cold joints, inconsistent batch quality.
VI Pressure Matching Optimization Solutions
1.Activate pre-pressure & constant pressure functions to discharge only after full compaction; avoid gap welding and pressure fluctuation from air supply instability.
2.Apply light pressure for thin plates, moderate pressure for thick plates; use medium-low pressure uniformly for nut projection welding, avoid extreme pressure values.
3.Adopt buffered slow contact clamping to eliminate instantaneous pressure shock and prevent nut shift & plate deformation.
4.Maintain holding pressure briefly after welding to release residual stress and reduce cold joints & distortion.
5.Grind, straighten and replace worn electrodes regularly to guarantee flat, parallel coaxial end faces and unilateral offset pressure.
6.Use dedicated nut positioning jigs; add backing plates under thin sheets to evenly distribute force across all welding projections and prevent plate collapse.
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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