Copper is a soft and malleable metal with high thermal and electrical conductivity. Copper finds its application in many areas, and different welding processes can weld it.
This article concentrates on welding copper, different welding processes that can weld copper, and the problems faced when welding copper.
How to weld copper?
Copper, a metal with high thermal conductivity, needs higher welding heat input. GTAW/TIG (Tungsten inert gas) welding and GMAW/MIG (Metal inert gas) welding usually are preferred for welding copper. You can also use MMA (manual metal arc) welding, but the weld quality will be inferior compared to TIG and MIG welding processes. The reason is TIG and MIG can provide better shielding to the molten weld pool. SMAW or MMA welding is useful for works that are not critical or maintenance works or works at outdoor locations where TIG & MIG are not suitable.
Selecting the proper filler wire for MIG/TIG or electrode for SMAW is essential for effective welding and making the weld bead stronger than the workpiece (base) metal. Use a filler wire or electrode containing silicon or manganese to act as a de-oxidant for welding copper.
The most commonly recommended filler wires are ErCu and ErCuSi-A. ErCu has silicon, manganese, and tin to enable fluidity. ErCuSi-A is suitable for welding copper that contains silicon and manganese in the form of de-oxidants.
Selecting a suitable shielding gas is also crucial for welding copper. The preferred shielding gas for welding copper is argon or helium or a mixture of argon and helium gas. If you need a faster weld, go for helium as the shielding gas. Helium enables a higher heat level than argon (at the same welding current) and improves weld quality. Choose a suitable welding technique based on the specifications of welding.
The weld joint designs used for copper welding should be wider than the steel weld joints, which helps better penetration and fusion.
Preparation for welding copper
Use a dedicated stainless steel brush and a cleaning agent to clean the copper workpiece surface to remove oil, paint, dirt, and other contaminants. Reserve this brush for copper welding only.
Preheat the welding area of the copper workpieces to a temperature of 50º F to 750º F (depending on the base metal thickness). Copper has excellent thermal conductivity, and part of the welding heat dissipates. Preheating the copper workpiece helps welding with low amperage.
Wear the complete welding gear and take care of your safety.
MIG weld copper
You can use the following wire electrodes for welding copper by MIG welding.
ERCU is a deoxidized type of copper alloy filler wire. It can deliver thick, good-quality weld deposits with base metal qualities like good electrical conductivity. This wire electrode can be used for MIG and TIG welding processes. This filler wire can also be used for welding deoxidized copper with mild steel, and the resulting joints have good strength.
The chemical composition of this filler wire is copper minimum of 98%, aluminum 0.01%, 0.5% manganese, 0.5 to 1% tin, and other elements. Its liquidus temperature is 1050º C (temperature above this will turn copper into liquid).
Aufhauser deoxidized copper welding electrodes and filler wires are made from deoxidized copper wire and can give you good sound welding. The weld bead is free of welding defects like porosity and has a good tensile strength (equivalent to popular commercial copper). The workpiece metal may have to be preheated up to 700º C (1292º F).
The composition of this filler wire or electrode is copper 98% or more, manganese 0.1%, aluminum 0.1%, silicon 0.1%, iron 0.2%, lead 0.02%, and other metals are zinc, nickel, tin, and phosphorous.
Most of the filler wires used in MIG welding are designed to work with reverse polarity (DCEP direct current electrode positive).
Shielding gas: The composition of the shielding gas depends on the thickness of copper workpieces. Argon is the inert gas used for copper up to a thickness of 6 mm (1/4ʺ), and a mixture of argon and helium is preferred for welding workpieces of thickness more than 6 mm.
When MIG welding copper, you can use the technique of depositing the weld metal with a narrow weave (4 to 6 times the wire diameter) or stringer beads (narrow and straight weld bead).
GTAW/TIG welding for copper
TIG welding is similar to MIG but not the same. Both MIG and TIG welding use inert gas for shielding the molten weld pool, but TIG welding uses a non-consumable tungsten electrode to strike the arc, and a filler wire fed manually (not auto-feed as in MIG). TIG welding may not need a filler wire for welding thin copper.
You can use TIG welding to weld copper workpieces of thickness up to 16 mm (5/8ʺ). You can use a filler wire that has a composition similar to the base or workpiece metal (the filler wire suggested for MIG welding can be used). Argon is the preferred shielding gas for welding copper workpieces up to a thickness of 1.6 mm, and for thicknesses, more than 1.6 mm, a mixture of argon and helium (argon 25% and helium 75%) is recommended.
A mixture of argon and helium allows better weld travel speeds and weld penetration than argon (at the same welding current). The recommended welding is the forehand technique (filler wire before the welding gun).
Typically, welders recommend DCEN (direct current electrode negative) for TIG welding copper.
Stick weld copper
Manual metal arc welding (MMA) is usually used for maintenance works involving copper welding or outside work where MIG and TIG are not feasible.
The welding rod can be ECuSn-C, a phosphor bronze electrode with a chemical composition of 90% or more copper, Tin 7 to 9%, aluminum 0.01%, lead 0.02%, ferrous, phosphorous, etc. This electrode is perfect for joining copper with copper, copper with stainless steel, steel, and cast iron.
Direct current electrode positive (DCEP or reverse polarity) and stringer welding technique is used. Apart from maintenance work, MMA welding is useful for minor works and where accessibility of the work has constraints. Use a chipping hammer and steel brush to remove the slag.
The recommended weld position for MMAW is the flat position. TIG and MIG processes can be used for other weld positions.
Other welding processes for welding copper
You can weld copper with oxyacetylene flame, plasma arc welding and resistance welding can also be used.
Plasma arc welding
Plasma arc welding is good for welding copper alloys. Argon is ideal for manual welding of copper or copper alloy with a comparatively low thermal conductivity or when the thickness is less than 3 mm. Helium or a mixture of 75% helium and 25% argon is favored for auto welding of thin copper material or manual welding of higher thicknesses. The mixture of helium and argon can also be used for welding copper with high thermal conductivity.
Oxyacetylene flame welding
When welding copper with oxyacetylene flame, an oxidizing flame is preferred (the oxide formed in the flame protects the molten weld pool); however, if you apply flux to the welding area, a neutral flame is recommended. The filler wire used should have the same composition as the base metal. Use an optimum welding speed and keep the end of the filler wire/rod in the molten weld pool. Protect the molten weld pool with the outer flame of the torch.
Resistance welding
You can use resistance welding also for some welding applications for copper.
Tips for welding copper from experienced welders
When welding copper, you should be aware of some of copper’s physical and mechanical properties, like high thermal and electrical conductivity.
The coefficient of thermal expansion of copper is more compared to steel. Low melting point compared to steel (around 800º F less than steel), and the mechanical strength of copper is acquired mostly during cold working. Copper welding requires weld heat much more than steel welding (1.5 to 2 times).
You can use a backup material (carbon or thin metal) to weld copper to ensure even penetration. You must clean the weld bead with a stainless steel wire brush after every weld run to remove the oxide film formed.
Can you weld copper with flux core?
You can weld copper using the flux-cored arc welding process and a recommended flux core wire. However, the quality will be inferior to MIG and TIG welding. If you have an FCAW setup, it is recommended to use the option of MIG welding with a recommended filler wire and shielding gas (usually, you can use an FCAW machine for FCAW as well MIG welding). Flux core is a costlier process compared to SMAW or MMA welding.
Problems faced in welding copper
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- The properties of copper, like high thermal conductivity and thermal expansion, may result in weld distortions. Preheating can minimize weld distortion.
- The high thermal conductivity of copper partially dissipates the weld heat, which can lead to defective weld beads. To counter this, preheating copper workpieces is essential and means additional work.
- The molten weld pool can get oxidized, and you need to clean the weld bead with a stainless steel brush before going for the next run after each weld run.
- Copper oxides present in tough pitches (Electrolytic Tough Pitch or ETP) copper can cause brittleness of the heat-affected zone and porosity in the weld metal. You can overcome the weld porosity by using a filler wire with de-oxidants like aluminum, manganese, silicon, etc.
- Copper gets its mechanical strength due to the cold working on it, and welding copper reduces this mechanical strength in the heat-affected zone. This gains importance when the weld joint strength is essential.
- The tip used is larger than those used for steel (one or two sizes larger).
Conclusion
Copper has high thermal and electrical conductivity, making it an essential metal for various products. And many such products need copper to be joined with copper or other metals like aluminum. Hence, copper welding is vital for engineering industries. We hope the topics discussed in this article have helped you know a little more about welding copper.
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