Select the appropriate gas to use. When using GMAW (gas metal arc welding), argon gas is appropriate for copper sections 6 mm or less in thickness, while helium-argon mixtures are appropriate for thicker pieces of copper. When using GTAW (gas tungsten arc welding), argon shielding gas is preferable for sections up to 1.6 mm in thickness, and helium-argon mixtures are appropriate for thicker sections.
Obtain a copper alloy, to serve as filler metal, with similar physical properties to those of the copper being welded. Alloys with similar properties will help you obtain the strongest possible welds. The filler metal should be in the form of small stringer beads, which will help you maintain control over the welding puddle.
Clean the surface of the copper. Use a bronze brush to remove surface oxides and a degreaser to remove greases and oils from the surface.
Provide shielding gas on the root side of the metal (the side opposite the welding). This will help prevent the weld from becoming contaminated with oxidation and pits.
Use wider joints than those used for steel. Due to copper's relatively high heat conductivity, wider joints are required to achieve an adequate fusion and penetration of the weld.
Maintain control over the welding puddle and avoid burn-through by moving the welding tool at a high travel speed.