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Segmented Pressure Holding Technology for Uniform Internal Fusion of Thick Copper Busbars in Polymer Diffusion Welding
Aug 08,2026
Polymer diffusion welding realizes solder-free bonding for thick copper bars & large cross-section copper parts, delivering products with excellent conductivity and high structural strength. A common defect during production: smooth exterior but loose internal lamination, discontinuous central fusion, leading to insufficient tensile force and unstable electrical conduction.
I Main Causes of Uneven Internal Fusion of Thick Busbars
Thick copper has completely different welding characteristics from thin sheets: thin copper transfers heat and forms joints quickly, while thick material suffers delayed heat & pressure penetration. Heat only penetrates slowly from surface to core, causing low central temperature and superficial-only fusion. Thick rigid bars with multi-layer stacked gaps cannot be fully compacted in short holding time; residual air blocks atomic diffusion and creates loose interiors. Deep metal diffusion requires long-term pressure maintenance; short holding only bonds the surface. Rapid pressure relief & cooling after welding creates inconsistent internal/external shrinkage and hidden interlayer gaps.
II Disadvantages of Blindly Extending Single-Stage Pressure Holding
Simply lengthening holding time without segmented control cannot solve inner cold joints, and brings extra defects: long high-temperature holding softens copper and coarsens crystal grains, causing deformation & poor flatness; graphite molds accelerate oxidation and abrasion under prolonged heat & pressure.
III Optimized Three-Stage Pressure Holding Process for Thick Copper Busbars
1 Preheating Stabilization Stage
Thick copper cannot be processed under direct high temp & pressure, which seals surface air and traps voids inside. Adopt low temp low pressure with extended preheating duration to transfer heat slowly to core, narrow internal-external temperature difference, gradually squeeze tiny interlayer gaps and exhaust air for deep fusion preparation.
2 Constant Temperature Diffusion Stage
Critical step to eliminate internal loose fusion. After stabilizing temperature & pressure, extend holding time proportionally according to bus thickness. Thicker & more stacked layers require longer holding. Stable thermal environment enables full atomic penetration to eliminate dotted & layered cold joints and achieve uniform internal & external fusion.
3 Cooling Shaping Stage
Maintain constant pressure while cooling slowly after fusion completion to realize synchronous shrinkage of the whole workpiece, avoiding surface rapid contraction and core thermal rebound that form micro gaps, locking compact internal fusion structure and hidden delamination.
IV Optimized Pressure Holding Delay Parameters
1 Rational Temperature Matching
No need to raise temperature sharply for longer holding; adopt medium steady temperature. High-speed high-temperature welding easily burns the surface while core remains unwelded. Stable mild heat allows deep penetration without copper embrittlement or deformation.
2 Gradient Segmented Pressure
Three-stage pressure: low-pressure leveling → medium-pressure diffusion → constant-pressure shaping. Avoid pressure fluctuation or mid relief to guarantee uniform stress across thick workpieces.
3 Flat & Accurate Molds
Uneven graphite tips or non-parallel upper/lower molds cause partial poor fusion even with extended holding. Grind and calibrate mold parallelism regularly for full tight contact of whole workpieces.
4 Thorough Pre-Welding Surface Cleaning
Oil, rust and dust block atomic diffusion and result in poor interlayer bonding. Grind and clean contact surfaces before welding to expose pure metal for superior diffusion fusion.
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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