Welding Copper and Alloys
Copper has a very high thermal conductivity and a high coefficient of expansion. High heat inputs are required for fusion welding and these in turn can cause distortion problems. Copper is also susceptible to hot cracking so restraint needs to be avoided. Tough pitched copper contains oxygen, which can cause severe hot cracking when using MIG and TIG welding processes. The oxygen also causes porosity if gas welded by a process called "gassing". Oxygen free copper was developed to overcome this problem. The phosphorus deoxidised grades have the better weldability and are the most common grade for applications where electrical conductivity is not important. Pre-heat (200-210°C) is recommended for thicknesses above 5mm and lagging the workpiece to contain the heat may also be beneficial. Helium rich mixtures such as Alushield Universal and Heavy can be used to increase the heat input. The cupro nickels are more easily welded and seldom require pre-heating. They have lower thermal conductivity and do not tend to crack. Most brasses are also readily weldable by either MIG or TIG but there can be a problem due to zinc fume being produced. This makes the weld difficult to see and can be harmful to the welder.
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