Tungsten copper (CuW) is not one material but a family. The two ratios that dominate resistance welding are W/Cu 75/25 and W/Cu 70/30 — and choosing between them wrongly shows up on your line as either electrodes that glaze and mushroom, or welds that run hot and stick. This guide explains what each ratio actually delivers and how to match it to your process.
What the numbers mean
The ratio is by weight. More tungsten means a stiffer, harder, more refractory structure; more copper means more current-carrying capacity and better heat extraction. There is no “better” alloy — there is only the right trade-off for your weld schedule.
| Property (typical) | W/Cu 75/25 | W/Cu 70/30 |
|---|---|---|
| Density | ≈ 15.2 g/cm³ | ≈ 14.5 g/cm³ |
| Hardness | 85–95 HRB | 80–90 HRB |
| Electrical conductivity | ≥ 38% IACS | ≥ 42% IACS |
| Softening temperature | ~900 °C | ~900 °C |
| RWMA class | Class 11 | Class 10 |
Values above are typical for infiltration-sintered material. Certified test reports per ASTM B702 are available on request. The 5% tungsten difference is worth about 5% in weight for the same section — run your dimensions through the electrode weight calculator if the part is large enough for handling to matter.
Where W75Cu25 wins
The extra 5% tungsten raises hardness and, more importantly for wheels, resistance to face deformation under high electrode force. Choose 75/25 when:
- Seam welding wheels run long campaigns — the harder face holds its profile between dressings, keeping the weld seam width consistent. See our W75Cu25 electrode wheels.
- Spot welding high-strength or coated steels, where contact pressure is high and face growth is the main failure mode.
- Flash and upset welding dies, where the electrode must resist punching into the hot upset.
The penalty is resistivity: the same current schedule runs hotter in the electrode and cooler in the workpiece. If your weld window is narrow on heat input, 75/25 may force you into a higher-current schedule.
Where W70Cu30 wins
The extra 3% copper buys conductivity and a slightly faster heat escape. Choose 70/30 when:
- Projection welding of fasteners, nuts and brackets — high current density through small projections favours the more conductive face.
- Welding galvanized or otherwise coated sheet, where a cooler electrode face reduces coating pickup and sticking.
- High-duty automated lines where the electrode takes continuous current and heat extraction matters more than the last few points of hardness. Our W70Cu30 electrode wheels are the usual pick for can-making and tube-mill lines.
The practical selection heuristic
If you are replacing an existing electrode, match the alloy that is in the drawing — weld schedules are tuned to it. If you are specifying from scratch:
- Start with 70/30 if the part is coated, thin, or current-hungry.
- Move to 75/25 when face wear, seam width drift, or mushrooming — not heat — is what limits electrode life.
- If you cannot run a full trial, buy a sample set of both; sample quantities are small and lead time is short.
Machinability and supply
Both ratios are infiltrated and machined in the same way: turning, milling, drilling, and thread cutting all behave like a hard bronze. This is why fully custom shapes — threaded studs, bore-fitted wheels, stepped profiles — are practical with a 10–14 day lead time on standard shapes. Rods, blocks and threaded electrodes are available in both ratios from our rods and blocks page.
Common questions
Can I mix ratios on the same line? Yes. Many automotive cells run 75/25 on the seam wheels and 70/30 on the stationary tips. What matters is that each station’s schedule matches its alloy.
Is there a hardness problem welding with 70/30? No — but expect more frequent dressing under the same force. The trade is dress frequency against heat input.
Do you supply other ratios? We deliberately concentrate on W75Cu25 and W70Cu30 so that both are stock items with short lead times. Higher-tungsten grades are a different supply chain entirely and are not part of our catalogue.
Get a quote
Send us your drawing or a photo of the worn electrode, plus alloy preference if you have one — request a quote and we will reply within 24 hours with a firm price, valid 7 days.