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How to Improve Fusion Effect for Copper Braided Wire & Terminals Prone to End Cracking & Falling Off in Polymer Diffusion Welding
Aug 08,2026
Polymer diffusion welding is ideal for integrated welding of copper braided wire and terminals, delivering finished products with excellent electrical conductivity and high toughness. During mass production, common defects include microcracks, fraying, delamination, detachment and fracture under vibration at wire ends. Improper pressure may crush copper wires or cause insufficient compaction; unsuitable temperature leads to brittle cracking or cold solder joints. Poor end quality mainly stems from uneven fusion, stress concentration, thermal cycling shock and surface contamination blocking atomic diffusion.
I Core Causes of Cracking, Delamination & Detachment
Copper braided wire features soft multi-strand structure while terminals are rigid; the combination of soft and hard materials is difficult to achieve full intermetallic fusion. Gaps and oxide films exist between strands, resulting in pseudo-bonding where only the surface fuses and inner layers remain unwelded. The wire end acts as the transition zone between soft and hard sections; inconsistent shrinkage during cooling generates stress cracks. Mismatched temperature & holding time causes incomplete fusion. Rapid cooling creates invisible microcracks. Oil, rust and dirt on welding surfaces block atomic diffusion and form weak fusion zones.
II Typical Defect Phenomena
Tiny cracks and loose broken filaments at terminals; braided strips peel apart easily by hand; insufficient tensile strength leading to fracture at welding roots; unstable fusion after continuous production and easy falling under vibration.
III Process Optimization Schemes
1 Adopt Three-Stage Welding Process
Abandon one-step rapid heating, holding and quenching.
1.Low-temperature low-pressure pre-compression: flatten copper strands and expel air between wires to eliminate internal voids;
2.Constant temperature & constant pressure holding: enable full interpenetration and fusion between copper strands and terminals;
3.Slow cooling & pressure relief: release welding stress, boost end toughness and reduce microcracks.
2 Rational Matching of Pressure Parameters
Pressure shall only compact gaps and assist diffusion; excessive high pressure is forbidden. Maintain stable moderate pressure throughout the whole process to eliminate interlayer cold joints & delamination, meanwhile prevent copper wire crushing and terminal brittle cracking.
3 Moderate & Stable Welding Temperature
Too low temperature results in loose fusion and low strength; overheating embrittles copper strands and triggers cracking. Use moderate temperature with sufficient constant-temperature duration to realize dense fusion via steady heat penetration while retaining original ductility of copper wires and reducing brittle defects.
4 Pre-Wire Trimming & Cleaning
Arrange braided wire ends before welding to ensure neat strands without loose or warped filaments. Remove oil, dust and oxide layers on welding areas to guarantee clean surfaces for uniform fusion.
5 Optimize Molds to Eliminate Stress Concentration
Grind and clean graphite molds regularly to keep flat surfaces free of carbon deposits and grooves. Place workpieces at the center during welding to avoid unilateral stress and tearing caused by offset positioning.
6 Standard Slow Cooling Procedure
Forbid rapid demolding, air blast cooling or contact with cold tables. Allow natural cooling inside molds until fully cooled before inspection, to realize synchronous internal & external shrinkage and avoid hidden microcracks induced by thermal shock.
7 Control Raw Materials & Workpieces
Select flat, clean, undeformed braided wires and terminals. Straighten warped workpieces before welding for tight contact, reducing uneven fusion and stress cracking from the source
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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