The Challenges of Welding Copper

Copper is used in a wide range of applications because it’s malleable and a great conductor of both electricity and heat. Its thermal conductivity is approximately 385.0 W/m-K and its melting point is 1,984°F / 1,085°C.

Copper is highly reflective of laser light, especially infrared lasers. Therefore, it takes a large amount of power to cause copper to couple. However, as its temperature rises so does its ability to absorb heat, and at its melting point, copper becomes highly absorptive and the chances of blow-outs and spattering drastically increase. Due to copper’s high thermal conductivity it is very easy to deform and damage a part by applying too much heat. Ways of avoiding this include using lasers with shorter wavelengths or of particular colors (green) as well as careful ramping of the laser power intensity.

A consistent weld seam requires the melt pool to be smooth and even as it solidifies. Copper, however, has a low viscosity melt pool – much lower than steel or aluminum – and is prone to rippling and movement. Copper also solidifies quickly, resulting in weld seams with an irregular morphology compared to other materials, such as steel, and poor filling of the weld gap. With copper, the laser itself causes waves and streams in the melt pool, which in turn cause turbulence throughout. At EB Industries we develop copper welds with a long, oval shaped melt pool such that turbulence diminishes in the rear of the pool before solidification. This is difficult to achieve and requires precise control of heat and feed speeds.

Copper weld seams are typically soft compared to the base material because copper is non-allotropic and phase transformations do not occur. Molten copper solidifies with a coarse microstructure that can be crack prone. The problem worsens depending on the amount of oxygen in the copper. Copper oxides can react with hydrogen to produce steam, which can cause intercrystalline cracking. Using oxygen-free copper (OFC) or oxygen-free high thermal conductivity copper (OFHC) can mitigate cracking. Careful use of cover gases and control of the weld environment can also help to mitigate cracking and increase the quality of the weld.