CuSi3 brazing – also frequently referred to as MIG brazing – is a specialised joining process mainly used in bodywork and thin sheet metal applications.
In contrast to MIG/MAG welding or TIG welding, the base material is not melted, but is joined using a copper-silicon brazing alloy.
However, in order for CuSi3 to be processed correctly, the welding machine, accessories and settings must meet certain requirements.
What exactly is CuSi3 brazing?
CuSi3 brazing is a brazing process that is usually carried out in practice using a MIG welding machine. The filler material CuSi3 consists of a copper-silicon alloy (about 97% copper and 3% silicon) and melts at a significantly lower temperature than steel. In contrast to conventional welding, the base material is not melted during CuSi3 brazing. Instead, only the filler wire, which acts as the brazing alloy, is melted. This liquid alloy wets the surface of the components, flows into the joint gap and joins the workpieces by adhesion and metallic bonding. After cooling, a solid, clean brazed joint is formed. Due to the lower heat input, the material structure, coatings – such as zinc – and component shape are largely preserved, making CuSi3 brazing particularly suitable for galvanised sheets, thin sheet metals and bodywork applications.
- Special hard soldering process.
- Simple and fast like MIG-MAG.
- Ideal for galvanised sheet metal.
Difference between welding and CuSi3 brazing
| Conventional MIG welding | CuSi3 brazing |
| Base material melts | Base material remains solid |
| High heat input | Very low heat input |
| Risk of distortion | hardly any distortion |
| Zinc burns off | Zinc largely preserved |
| High strength | Sufficient for non-load-bearing joints |
CuSi3 brazing is not used for load-bearing constructions, but for precise, heat-sensitive applications.
Suitable and unsuitable applications
Particularly suitable for:
Galvanised steels
Thin sheets (under approx. 2 mm)
Bodywork and repair work
Advantages:
Very low heat input
Hardly any zinc burn-off
Good gap bridging
Clean, visually high-quality seams
Not suitable for:
Highly stressed or load-bearing weld seams
Thick components with structural function
CuSi3 brazed joints are not designed for load-bearing constructions.
Requirements for the welding machine
Adjustable low current range
CuSi3 has a comparatively low melting point (approx. 960 °C).
Therefore, a sensitively adjustable current range is crucial.
Typical working range: approx. 30–120 A
Stable regulation at low currents is absolutely necessary
Machines with poor low current performance are unsuitable
Stable arc characteristics
A steady, low-spatter arc is required for clean brazed joints.
The following are advantageous:
Inverter technology
Very stable short arc operation
MIG brazing or brazing characteristics (if available)
An unstable arc quickly leads to uneven seams and poor wetting.
Precise wire feed
CuSi3 wire is significantly softer than steel wire.
A consistent wire feed is therefore particularly important.
Recommended:
Four-roll feed or very precisely adjusted two-roll feed
U-groove rollers or specially suitable feed rollers
As little friction as possible in the torch hose
immediately leads to process instability.
Torch and wear part requirements
Wire diameter
Typical wire diameters for CuSi3 brazing:
0.8 mm → standard for bodywork and thin sheets
1.0 mm → higher deposition rate, somewhat more robust
The welding machine must reliably support the respective wire diameter.
Contact tip and wire liner
Oversize contact tip recommended
(e.g. 1.0 mm contact tip for 0.8 mm CuSi3 wire)
→ Compensates for thermal expansion of the wireWire liner made of plastic / Teflon
→ Reduces friction and prevents wire jams
Shielding gas – essential requirement
Pure CO₂ is unsuitable for CuSi3.
Recommended:
Argon 100% (standard)
Optional: Argon + 1–3% CO₂ or O₂
(depending on the machine and desired arc characteristics)
Gas flow rate:
approx. 8–12 l/min, depending on torch, gas nozzle and environment
Machine settings – guideline values
The exact values depend on sheet thickness, wire diameter and machine.
Typical tendencies:
Voltage: lower than for steel welding
Wire feed: consistent, rather moderate
Inductance: rather high → softer arc
Pulse function (if available): advantageous, but not strictly necessary
Summary – Requirements for CuSi3 brazing
A suitable welding machine should:
Be MIG-capable
Enable stable low current operation
Provide consistent wire feed
Be able to operate with argon-shielding gas
- Ideally have fine manual adjustment options or a MIG brazing characteristic
Notes:
Also see our article: CuSi3 brazing with the RED MIG 210 SYN (not recommended)
If you are unsure whether your RED welding machine is suitable for CuSi3 brazing or which settings are recommended, please contact us via the contact form. We are happy to support you with selection and setup.
Do you also want to learn about the other welding processes?
Here are the respective articles: