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Traditional welding of copper can be tricky because its high thermal conductivity causes it to radiate heat away from the weld much faster than steel, for example. As a result, high energy and heat levels are required in order to fully melt the two workpieces and create a solid weld.
Copper Welding Techniques
The high thermal conductivity and expansion rate of copper and alloys such as brass also can cause warping and distortion of welds more easily than steel. To prevent this, the workpieces may need preheating. Use of clamping and fixtures, welding in a proper sequence, and making tack welds spaced closer together can also help.
Some alloying metals in copper, such as aluminum, react with oxygen to create oxide films on the surface. These must be removed before welding, along with any shop dirt or other contaminants from the surfaces to avoid entrapping them in the weld. These particles tend to vaporize in the high welding heat, leaving voids and causing porosity.
To prevent this, inspect and clean the work pieces and the weldment before and after each stage of tacking and welding. Only use grind wheels and wire brushes which have been used on stainless steel or copper/copper nickel, but never on carbon steel, to prevent contamination with carbon particles.
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Copper is mainly alloyed with tin, zinc, aluminum, silicon, and nickel, along with small amounts of other elements. Brass is a copper-zinc alloy and bronze is copper alloyed with either tin, aluminum or silicon.
Copper-nickel alloys are another common combination, with either 90/10 (90% copper to 10% nickel) or 70/30 (70% copper to 30% nickel). For this material, there’s no worry about creating heat affected zones, which could alter the metal’s characteristics.
The exact makeup of each copper alloy will dictate its physical properties, such as melting temperature, which in turn affect its welding characteristics. For example, welding copper nickel alloy is actually easier than welding copper, because its lower thermal conductivity doesn’t require pre-heating.
Welding Process
According to the Copper Development Association, both MIG, or gas tungsten arc welding (GTAW) and TIG, or gas tungsten arc welding (GTAW), are good choices for welding all types of copper and copper alloys.
Shielded metal arc welding (SMAW), or stick welding, can be used with certain copper alloys, such as aluminum bronze, silicon bronze, and copper nickel.
The gas shielding is important to prevent oxides forming during the welding process, which could lead to porosity. Be sure to keep the filler metal within the protection of the gas shield to prevent oxidation.
The same tungsten electrodes that would be used for TIG welding steel are used for copper.
Prevent Welding Effects
Incomplete fusion of the weld can happen due to the metals’ high thermal conductivity. Pre-heat these alloys, including brass containing less than 20% zinc, before welding.
Certain copper alloys, including copper nickel, are susceptible to hot cracking, once the weld has cooled. To prevent this, clean the surface of the workpieces thoroughly to remove even small amounts of contaminants. Slow the cooling rate by minimizing the amount of added heat. Other copper alloys containing low aluminum content should be preheated to reduce the risk of cracking.
Choice of Gas
Argon gas can be used when welding thicker copper materials or alloys with lower thermal conductivity, such as copper nickel. However, most copper and copper alloy welding should be performed with helium or helium mixed with argon, to provide higher heat input to the work pieces.
Industrial Metal Supply carries all your copper welding needs, including welders, welding supplies and several shapes and sizes of copper, brass and bronze.
