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Current & Pressure Adjustment Methods for Insufficient Penetration When Welding Thick Workpieces with MF Spot Welders
Aug 04,2026
When welding thick steel, thick stainless steel and heavy hardware structural parts with medium frequency spot welders, defects such shallow penetration, incomplete fusion, interlayer cold joints and insufficient tensile strength often occur. Thin plate welding focuses on rapid heating and cooling to prevent deformation and burn-through, while thick plate welding requires heat accumulation and stable temperature for deep fusion. Thick plates dissipate heat quickly, making it hard to concentrate heat at the bonding surface. Simply increasing current delivers limited improvement and easily causes spatter, overburning and brittle weld nuggets.
I Core Causes of Insufficient Penetration on Thick Plates
1.Fast heat dissipation of thick plates: heat diffuses outward rapidly and only forms superficial micro-fusion instead of deep penetration.
2.Excessive welding pressure: tight fitting reduces contact resistance and heat generation; molten metal is flattened to create thin nuggets with shallow penetration.
3.Too short welding time: heat only heats the surface layer without penetrating inward, resulting in superficial fake fusion and internal incomplete welding.
4.High rigidity and poor flatness of thick plates; insufficient pre-pressure leaves tiny gaps that scatter heat and shift nuggets, preventing full compact fusion.
II Typical Defective Appearance
Weld spots look normal with little spatter or discoloration, but cross-section reveals small, shallow nuggets. Welds peel easily under load and white unfused lines exist between layers. Parameters have narrow adjustment tolerance: higher current leads to spatter & deep indentation, lower current results in weak joints.
III Current Adjustment Techniques
1.Prioritize extending welding time: follow the rule "extend time first, then raise current". Longer heating allows heat to penetrate gradually and build full nuggets with fewer voids and looseness.
2.Segmented preheating welding: low current preheating flattens gaps and stabilizes contact resistance to reduce arcing and spatter, followed by standard main current for layered heat penetration and deeper fusion.
3.Stepwise mild current increase: raise current slightly only when time is sufficient and no spatter occurs to compensate heat loss, avoiding surface overburn from sharp current jumps and ensuring uniform fusion.
4.Optimize slow cooling process: add slow cooling after welding to slow molten pool solidification, reduce internal cracks and looseness for denser, more stable nugget crystallization.
IV Pressure Adjustment Techniques
Thick plates cannot adopt the high-pressure logic for thin plates; moderate stable pressure enables normal nugget growth.
1.Appropriately reduce welding pressure: set pressure just enough for gap-free fitting to retain proper contact resistance for steady heat generation, preventing flattened molten pools and limited penetration.
2.Extend pre-pressure time: adequate pre-pressure flattens thick plates and eliminates micro interlayer gaps for even heating, reducing cold joints and nugget shift.
3.Lengthen post-weld hold time: thick molten pools cool slowly; holding pressure shapes welds to offset cooling shrinkage stress, preventing collapse and cracking and maintaining full nuggets.
V Auxiliary Optimized Processes
1.Grind and clean electrodes regularly to guarantee flat, aligned end faces with even pressure & conductivity, avoiding insufficient penetration and oversize indentation from uneven pressure.
2.Remove oil, rust and oxide layers on welding areas before welding to keep clean surfaces for concentrated heat penetration.
3.Avoid rapid continuous spot welding; set proper intervals for sufficient heat accumulation and consistent penetration depth.
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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