Welding copper flexible busbars using a diffusion welding machine requires precise control of temperature, pressure, and time to ensure high conductivity, flexibility, and mechanical strength. Below is a step-by-step guide optimized for industrial production:
1. Material Preparation
- Surface Cleaning:
Degrease with acetone or alcohol.
Remove oxides via chemical etching (e.g., 10% H₂SO₄) or plasma cleaning.
Critical: Achieve Ra < 0.2µm surface roughness.
- Cutting/Shaping:
Shear or laser-cut busbars to size (ensure burr-free edges).
2. Machine Setup (HAIFEI Example)
| Parameter | Value Range (Copper Busbars) | Notes |
|---|---|---|
| Temperature | 400–600°C | Below Cu's melting point (1,085°C) |
| Pressure | 20–50 MPa | Higher pressure = faster diffusion |
| Time | 1–10 minutes | Depends on thickness (e.g., 1mm vs. 5mm) |
| Atmosphere | Vacuum (10⁻³ mbar) or H₂/N₂ gas | Prevents oxidation |
3. Welding Process
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Step 1: Loading
Stack busbars with overlapping joints (typical overlap = 2× thickness).
Align using ceramic alignment pins to prevent slippage.
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Step 2: Heating & Pressing
Ramp-up Phase: Heat to 300°C at 5°C/min → apply 5 MPa pre-pressure to ensure contact.
Diffusion Phase:
Reach target temp (e.g., 500°C).
Apply full pressure (e.g., 30 MPa) → hold for 20–30 mins.
Key: Atoms diffuse across the interface → grain boundaries vanish.
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Step 3: Cooling
Slow cool at 3–5°C/min under reduced pressure (5 MPa) → prevents warping.
4. Quality Validation
- Conductivity Test:Measure resistance across joint → target < 1.1× base material resistance.
- Mechanical Test:
Peel strength: >80% of Cu's tensile strength (e.g., >210 MPa for C11000).
Flex Test: Survives 10,000+ bends (for flexible busbars).
- Microstructure Check:SEM/EDS confirms continuous grain growth across the joint.
5. Industrial Optimization Tips
- For Thin Busbars (0.1–1mm):
- Use pulsed pressure (e.g., 10 MPa → 30 MPa cycles) to avoid deformation.
- For High Throughput:
- HAIFEI machines with multi-stack fixtures weld 10–20 busbars per cycle.
- Dissimilar Joining (Cu-Al):
- Insert Ni interlayer (0.01mm) → blocks brittle CuAl₂ formation.
Why Diffusion Welding Beats Alternatives
| Method | Issues | Diffusion Welding Advantage |
|---|---|---|
| Laser Welding | HAZ reduces conductivity | No melting → 100% IACS conductivity |
| Brazing | Flux residues corrode over time | Flux-free, clean joint |
| Mechanical Clamps | High contact resistance | Metallurgical bond = lower resistance |
Final Output
A diffusion-welded copper busbar joint will:
✅ Carry 1000+ amps without hotspots (vs. 600A for bolted joints).
✅ Survive vibration/shock in EVs/robotics.
✅ Outlast 20+ years in grid/power applications.
By tightly controlling parameters, diffusion welding produces lighter, stronger, and more reliable busbars than any conventional method. 🚀
