How to Weld Copper
Welding copper is not difficult. The heat needed to weld copper is twice as hot as welding steel of the same thickness. Copper has a high thermal conductivity. The recommendation is to use a tip one or two sizes larger than is needed for steel to offset this loss of heat.
If the weld is heavy and a large section is being welded, heat pre-heat should be used in supplemental heating. This gives a weld with less porosity.
Copper can be welded with a slight oxidizing flame since the oxide that the flame forms protects the molten metal. If a flux is used to protect the molten metal, the flame should be neutral.
Gas welding assemblies should use oxygen-free copper bodies (deoxidized copper rod). The rod’s composition should be the same as the base metal.
What is Copper?
Copper is a soft, non-ferrous metal that can be easily bent, cut, shaped, and joined using a number of welding processes.
While copper has been historically used for decorative household and architectural items, it is a good conductor of electricity and heat, and is used widely in the electrical industry; copper pipe, valves and the like are used for plumbing.
Because its ductile and very malleable, copper is also used as the primary component in hundreds of different alloys that include brass, bronze, and nickel copper. The most common alloying elements that are used in copper alloys include aluminum, nickel, zinc, tin, and silicon.
Pure copper is too ductile to be used successfully in machining, so small quantities of other elements are added to the various alloys to enhance machinability, de-oxidation of the metal, improve corrosion resistance, improve mechanical properties, and improve response to heat treatments. In total, there are more than 300 copper alloy variations that are commercially available.
The Different Methods for Welding Copper
There are a number of ways to weld copper. In this article on teaching how to weld copper, we will only address the most common methods of welding copper, which include: Gas Metal Arc Welding (GMAW), Gas Tungsten Arc Welding (GTAW), and Manual Metal Arc Welding (MMAW) and provide explanation for each.
Gas Metal Arc Welding (GMAW)
Also known as MIG welding, Gas Metal Arc Welding (GMAW) follows the same designator as the Shielded Metal Arc Welding (SMAW) system for welding in that the filler material used is an electrode.
There is a distinction to be made, however, while SMAW uses a series of short rods as the consumable electrode, GMAW utilizes a continuous ‘wire’ that is fed automatically to the welding torch at a user-defined speed. In addition, the shielding gas is fed at a regulated setting.
When using the GMAW method to weld copper, it is recommended that you use ERCu copper electrodes. It is also recommended that you use Aufhauser Deoxidized Copper. This is a copper alloy or filler material consisting of a 985 purity.
The thickness of the copper section that you have to weld will determine the gas mixture required. For thicknesses of 6mm and below, you typically use argon for the gas mixture.
For thicknesses over 6mm you would use a mixture of helium and argon. For the GMAW method of welding copper, you need to deposit the filler metal with narrow weave or stringer beads using the spray transfer.
Gas Tungsten Arc Welding (GTAW)
Gas Tungsten Arc Welding, also referred to as TIG welding, is a method of welding copper in a manner similar to most arc welding processes. This means that GTAW is another process that requires an electric arc to heat and melt not only the copper piece, but the filler material as well.
Just like when you weld steel using GTAW, the molten weld pool is protected from the atmosphere while it cools and solidifies by introducing shielding gas (either argon or helium) at the tip of the torch.
GTAW is very similar to other arc welding processes but unlike other arc welding processes, GTAW does not use consumable electrodes to carry the electric arc to the copper being welded.
GTAW does provide a weld joint to join two with or without filler material. In many other arc welding processes, the filler metal serves as the electrode and carries the electric arc to the copper being welded.
With GTAW, there is a separate filler wire that is the filler wire for the purpose of the GTAW method. Additionally, when welding copper using the GTAW process, again, you do not have to apply a filler material at all.
The GTAW processes can weld copper pieces with a maximum thickness of 16 mm. The filler wires recommended for this process are of the same composition as the base metal.
Argon shielding gas is recommended for copper pieces of a maximum thickness of 1.6 mm. When the thickness of workpieces is greater than 1.6 mm, a mixture of helium and argon is used.
Compared to argon, a mixture of argon and helium produces higher travel speeds and deeper penetrations at the same welding current.
To combine the good penetration characteristics of helium, as well as the overall stability characteristics of argon, the most commonly used mix is 25%Ar/75%He. Finally, GTAW on copper workpieces which require stringer beads or narrow weave, prehand welding is preferred.
Manual Metal Arc Welding (MMAW)
This process is used mainly for repair and maintenance welding of copper and its alloys. The recommended filler material for this application is the ECuSn-C electrode. Another suggested, is use Direct Current electrode positive (DC+) with the stringer bead technique, when using this filler material, the MMAW process is capable of doing the following:
- Weld copper to other metals
- Small repairs of thin copper
- Welding joints with limited access
These are the 3 most common processes used in welding copper, now that you know basic information on these processes you can apply integrating a technique/process that is best suited for your needs and the job at hand.
Having said this there are some basic steps that you will need to follow, to achieve a good weld, no matter what the process you have chosen to weld copper. The following section will discuss these basic steps.
The Key Steps in Welding Copper
If you’re going to weld copper on your own, you need to be aware of the essential steps involved in successfully welding copper. There are 11 steps to do-it-yourself copper welding. By completing these steps in order, you will achieve a copper weld that will be extremely durable.
#1. Ensure Safety
If you are going to weld your own copper, the first thing that you need to do is establish your safety. Since the welding process involves very intense heat, safety is paramount.
Regardless of the type of metal getting welded, it is your job to make sure you have established proper safety procedures prior to welding. Without proper safety procedures, you could injure yourself.
So what some proper safety measures to take before welding copper? First things first, you need to wear safety gear, ensure there are no flammable items around you, and you should be welding in a clean or clear area that is free from foreign materials associated with welding.
The precautions associated with copper welding are incredibly important since copper is one of the best conductors of electricity, and you will be able to easily shock yourself while handling copper with bare hands.
In addition to the electric shock concept, one must keep in mind that welding copper might cause exposure to toxic gases. Therefore, you should not stop at leather gloves and safety garments when you are welding copper. You should go as far as including a respirator mask and protective eye gear to your safety gear as well.
#2. Prepare the Surface
Surface preparation for welding copper involves keeping the weld area clean of grease, oil, paint, dirt, and other contaminants before welding. Why keep these contaminants away from the weld area?
Because if these contaminants get intermixed with the metal, the weld can crack. They may even have aggressive solvents containing harmful elements such as sulfur, phosphorus and lead.
In addition to the weld area, it would also be best to clean up the copper as well before you proceed to welding. How do you clean up the weld area and the copper? With a bronze wire brush an cleaning agent.
First wire brush and clean with the cleaning solvent. Also, after depositing a weld run also be sure to remove the oxide film that forms during welding with a wire brush .
#3. Pre-Heating
Preheating copper before welding is paramount. What is the reason for that? This is due this metal’s extremely high thermal conductivity, especially if the thickness of the copper metal is more than 0.01 inches. You should preheat all sections of copper that need to be welded evenly.
Due to copper conducting heat extremely well the heat from the weld joint travels so quickly that a high preheat is required when welding thick sections of copper. The preheat will vary based on the thickness of the metal and can be anywhere from 50° to 752° F.
However, if you are welding copper alloy, you can proceed past this section, as it has significantly lower thermal diffusivity than the copper. If you are welding copper and not copper alloy, then choose a preheat temperature range suitable for your application.
You must consider the copper be welded, the thickness of the base metal, the welding process, and even the total mass of the weldment.
In conjunction with this, it is equally important to limit the heat to as small of an area as possible, as this will help ensure that not too much of the material gets to a temperature at which ductility can be lost.
In addition, there have include staying at your chosen preheat until the joint is fully welded. Once you start welding, the heat in the preheated copper will begin to dissipate, which has the effect of lowering possible cracking.
#4. Considering Joint Design
Another critical champion of successful copper welding is joint design consideration. What does this mean? First, you need to consider the distance between the joints.
Ideally, you want to control this distance to some tolerance based on the parent metal and brazing alloy (considerably thicker if using a soldering process). However, an acceptable gap (for joints) would be between 0.04 and 0.20mm.
Another critical consideration here is joint overlap. The minimum overlap should be at least three times the thickness of the smallest section you are trying to join. You should attempt to use as little material as possible as this will help provide adequate strength.
#5. Adjust the Flame
To create a proper copper weld, you will need to use the correct flame. Ideally, this would include using a neutral flame.
What is a neutral flame? Essentially, a neutral flame is a flame that combines equal proportions of oxygen and acetylene together at the same rate. Another important part would be to clearly define the white inner cone and to make sure there is no haze.
#6. Remove the Flux
You must remove the residue in one of the following ways if the flux has been used:
- Brushing with wire and steaming
- Brushing with wire and using hot water to rinse
- Diluting in hot caustic soda dip
If you fail to completely remove the flux, then this may lead to the weakening and even failure of the joint.
Choose Filler Material
Choosing the correct filler material is one of the key steps to effectively welding copper. Choosing the proper filler material leads to welding a copper piece that is stronger than the base material.
The best or most suitable filler material for welding copper will depend on the metal’s corrosion resistance, the strength you require in the joint, the operating temperature, and costs.
For optimal results, you should use a filler metal with Silicon (Si) or Manganese (Mn) content acting as a deoxidant. This is true whether you use either of the GMAW, GTAW, or MMAW methods for welding copper.
In terms of filler materials for welding copper, the typical and usually recommended filler materials are ErCu and ErCuSi-A. The filler metal ErCu allows for fluidity as it has Si and Mn with Tin (Sn).
Go with ErCuSi-A filler metal if you want to weld P-oxidized copper or hard-pitch copper that have both Si and Mn as deoxidants.
Copper Soldering
Soldering, which is one of the oldest techniques for permanently joining metals, involves melting filler metal (in the form of a filler wire) by heating it until it is liquid, and that liquid fills the joint.
Soft soldering is the easiest form of soldering and is the technique typically used in and around the home for the repair of small items of metal. It is also a technique that plumbers use to join and repair copper pipes and copper fittings.
Soft soldering can be done with a cheap soldering iron or a blow torch with suitable flux. Hard soldering is able to heat the filler materials to a much higher temperature; thus, the joint should be noticeably stronger than a soft-soldered joint.
The filler material is different, and usually contains silver, so this technique is sometimes referred to as silver brazing. True brazing is done at an even higher temperature.
Copper Brazing
Brazing is basically a technique very similar to soldering, which uses essentially the same filler material (wire or brazing rod) for soldering. Joints must be very closefitting so that capillary action can draw the filler metal in between the two pieces of copper being joined.
Even though the temperatures have to be much higher than soldering, the base metal must not be heated to its melting point.
Brazing is used extensively for plumbing work. Brazing may also be used to join dissimilar metals and to join metal workpieces of varying thickness.
FAQs
Can copper be welded?
Copper and Copper alloys are important engineering materials because of their good electrical and thermal conductivity, corrosion resistance, metal-to-metal wear resistance and distinctive aesthetic appearance. Copper and most copper alloys can be joined by welding, brazing, and soldering.
Why is welding copper difficult?
In addition, copper has a very high thermal and electrical conductivity and a low melting point, making it very tricky to weld. “Free-Machining” copper alloys containing tellurium and selenium shouldn’t be welded because they are very susceptible to cracking. But most other copper alloys are weldable.
What gas is used to weld copper?
For sections up to 1.6mm thick Argon shielding gas is preferred, while helium mixes are preferred for welding sections over 1.6mm thick.
How do you weld two pieces of copper together?
You can TIG weld up to about 1/2 in. thick copper, but you’ll need to significantly preheat the part before welding such high thicknesses (about 650°F). MIG welding works better for high thickness copper, but the TIG process has the advantage of precision and narrow heat affected zone (HAZ).
Can you weld copper with a stick welder?
Stick welding, also known as Shielded Metal Arc Welding (SMAW) or Manual Metal Arc Welding (MMA), is not commonly used for welding copper due to its high heat input and potential for cracking. However, it can be used for thicker copper sections or in situations where TIG or MIG welding is not feasible.
Can I weld copper with a MIG welder?
You can use a MIG welder and gun to essentially braze the materials together. Using MIG equipment and silicon bronze welding wire makes joining copper an easier, more repeatable quality process.