How To Weld Copper – A Technical Guide

How to Weld Copper

Copper welding is not hard. The heat required for this type of welding is approximately twice that required for steel of similar thickness. Copper has a high thermal conductivity. To offset this heat loss, a tip one or two sizes larger than that required for steel is recommended.

When welding large sections of heavy thicknesses, supplementary heating is advisable. This process produces a weld that is less porous.

Copper may be welded with a slightly oxidizing flame because the molten metal is protected by the oxide which is formed by the flame. If a flux is used to protect the molten metal, the flame should be neutral. Oxygen-free copper (deoxidized copper rod) should be used rather than oxygen-bearing copper for gas-welded assemblies. The rod should be of the same composition as the base metal.

What is Copper?

Copper is a soft, non-ferrous metal that can be easily bent, cut, shaped, and joined using several welding processes. While it is often used to make decorative household and architectural items, it is an excellent conductor of electricity and heat, and so is widely used in the electrical industry, while copper pipe, valves, and other fittings are commonly used for plumbing.

Since it is ductile and highly malleable, copper is also used as the major element in hundreds of different alloys, including brass, bronze, and nickel copper. The most common alloying elements used for copper alloys are aluminum, nickel, zinc, tin, and silicon.

Because pure copper is too ductile to be successfully machined, small quantities of other elements are added to the various alloys to improve machinability, as well as to deoxidize the metal, make it more resistant to corrosion, improve its mechanical properties, and improve its response to heat treatments. In all, there are more than 300 copper alloys available commercially.

The Different Methods for Welding Copper

Copper can be welded via several methods. However, we’re only going to discuss the most common techniques in this article about teaching how to weld copper. These include Gas Metal Arc Welding (GMAW), Gas Tungsten Arc Welding (GTAW), and Manual Metal Arc Welding (MMAW). Following is an explanation of each.

Gas Metal Arc Welding (GMAW)

Also called MIG welding, Gas Metal Arc Welding (GMAW) follows the SMAW system for welding. This means that the filler material used in this welding technique is an electrode.

However, there is a difference between the two methods; while a series of short rods are used by SMAW as the consumable electrode, the GMAW method automatically feeds a continuous ‘wire’ to the welding torch at a speed defined by the user. Additionally, there is a regulated setting for feeding the shielding gas.

When using the GMAW method to weld copper, it is recommended that you use ERCu copper electrodes. The use of Aufhauser Deoxidized Copper is also recommended; this is a copper alloy or filler material with a 985 purity.

The thickness of the copper section that you need to weld will determine the gas mixture needed. Generally, argon is used for thicknesses up to 6mm. For thickness that exceeds this, a mixture of helium and argon is used. In the GMAW method for welding copper, you need to deposit the filler metal with narrow weave or stringer beads; this can be done using spray transfer.

Gas Tungsten Arc Welding (GTAW)

Also called TIG welding, Gas Tungsten Arc Welding (GTAW) welds copper in a way similar to most arc welding processes; this means that GTAW involves the use of an electric arc for heating and melting both the copper piece and the filler material.

As the molted weld pool cools and solidifies, it is protected from atmospheric effects by introducing a shielding gas such as argon or helium at the torch’s tip. While GTAW is similar to many arc welding processes, it does not weld like arc welding methods that pass the electric arc to the copper being welded using consumable electrodes.

Instead, GTAW uses a non-consumable electrode to create a weld joint between the workpieces; it can do this with or without filler material. Also, in many other arc welding methods, the filler material is used as the electrode carrying the electric arc to the copper being weld.

However, separate filler wire is used in the Gas Tungsten Arc Welding method. Also, it isn’t at all necessary to introduce a filler material while the GTAW method is used to weld copper.

The GTAW methods can successfully weld copper pieces with a thickness of up to 16mm. The filler wired recommended for this method is any metal having a composition similar to the base metal. Argon shielding gas is preferred for copper sections with a thickness of up to 1.6mm. For workpieces that exceed this level of thickness, a mixture of helium and argon is used.

When compared to argon, a mixture of helium and argon allows higher travel speeds and deeper perforation at a similar welding current. To provide the copper piece being weld with helium’s good perforation characteristics together with argon’s arc stability properties, the mixture commonly used is 25%Ar/75% He. Lastly, forehand welding is recommended when performing this method on a piece of copper with a narrow weave or stringer beads.

Manual Metal Arc Welding (MMAW)

This method is mainly used to perform repair or maintenance welding on copper and copper alloys. The filler material recommended for this is method is the ECuSn-C electrode. Another recommendation is using a Direct Current electrode positive (DC+) with a stringer bead technique. When this filler material is used, the MMAW method can help in the following:

  • Welding copper to other metals
  • Small repair of thin copper pieces
  • Weld joints with restricted access

These are the three most common methods used to weld copper. Now that you have basic information on each method, you can pick a technique/method that is most suited to your needs and the job being performed. However, regardless of the method you choose to weld copper, you need to follow some basic steps to produce an effective weld. We discuss these steps in the next section.

The Key Steps in Welding Copper

When welding copper on your own, you need to know the critical steps involved in effectively welding copper. There are 11 steps involved in DIY copper welding. By performing these steps in the following order, you will be able to produce an extremely durable copper weld.

#1. Ensure Safety

When looking to weld copper on your own, the first thing that you need to do is ensure your safety. No matter what metal you’re welding, you need to take proper precautions before you start welding. Failure to do so can put you at the risk of injury.

So, what are the possible precautions you can take before you start welding copper? You need to put on safety gear, ensure there’s no flammable item around you, and work in a clean area or area free from foreign materials.

Taking safety precautions is especially important when welding copper; this is because copper is an extremely good conductor of electricity and you can get an electric shock if you handle the metal with bare hands.

In addition to the risk of an electric shock, welding copper can expose you to toxic gases. So, you shouldn’t stop at leather gloves and safety garments to ensure your safety when welding copper. Instead, you should include a respirator mask and eye protection in your safety gear as well.

#2. Prepare the Surface

Surface preparation for welding copper means keeping the weld area free of grease, oil, paint, dirt, and other foreign particles before you start to weld. Why do you need to keep the weld area free of these particles? Because the weld can crack if they get mixed in with the metal. Additionally, they may contain harmful chemicals such as sulfur, phosphorus, and lead.

In addition to the weld area, you should clean the copper as well before you start to weld. How can you clean the weld area and the copper? With a bronze wire brush and an appropriate cleaning agent. First wire brush with then de-grease using the cleaning agent. Also, make sure to remove the oxide film that forms during welding with a wire brush after depositing each weld run.

#3. Pre-Heating

Why is it important to preheat copper before you can start welding? Because this metal has high thermal conductivity. This is especially important if the thickness of the copper metal is more than 0.01 inches. You should preheat all segments that needed to be welded uniformly.

Since copper can conduct heat rapidly from the weld joint into the base metal surrounding it, a high preheat is required to weld the thick copper sections. The temperature will depend on the metal’s thickness and can range between 50° to 752° F.

However, if you’re welding copper alloy, then you can skip this section because the thermal diffusivity, in this case, is much lower compared to copper. In case you are welding copper and not copper alloy, you need to select the appropriate preheat for your application. You must pay special attention to the copper being welder, it’s base metal thickness, the welding process, and even the weldment’s overall mass.

In addition to the above, another important thing to do is restrict the heat to a localized area as much as you can; this will help you to ensure that not too much of the material is in a temperature range that leads to a loss in ductility.

Moreover, you should maintain the preheat temperature until the joint has been welded. After you start to weld, the heat of the preheated copper starts to dissipate, and this lowers the risk of cracking.

#4. Considering Joint Design

Another important step in welding copper effectively is a joint design consideration. What does this entail? Firstly, you need to consider the distance between the joints. Ideally, you should control this distance to within certain tolerances based on the parent metal and the brazing alloy used. However, the optimum gap for joints is between 0.04 and 0.20mm.

Another important consideration here is a joint overlap. The ideal joint overlap will be at least three times thicker than the thinnest part that you need to join. You should try to use as little material as possible since this will help you to achieve the desired strength.

#5. Adjust the Flame

If you want to produce an effective copper weld, then you must adjust the flame appropriately. The best thing to do here would be to use a neutral flame. What does a neutral flame mean? A neutral flame is a flame adjusted to allow the same amounts of acetylene and oxygen to mix at the same rate. Another critical thing to do here is clearly define the white inner cone and ensure 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 right filler material is one of the most critical steps in welding copper effectively. Choosing the right filler material helps in welding a copper piece that is stronger than the base metal. The best or most suitable filler material for welding copper will depend on the metal’s resistance to corrosion, how much strength you require in the joint, the operating temperature, and the costs involved.

For the best results, you should choose a filler metal with Silicon (Si) or Manganese (Mn) content acting as a deoxidant. This is regardless of whether you’re using the GMAW, the GTAW, or MMAW method for welding copper.

When it comes to filler materials for welding copper, the most recommended and commonly used materials are ErCu and ErCuSi-A. The former facilitates fluidity as it contains both Si and Mn with Tin (Sn). On the other hand, you should go for ErCuSi-A filler material if you want to weld P-oxidized copper; it is also a good option for welding hard-pitch copper that contains both Si and MN as deoxidants.

Copper Soldering

Soldering, which is one of the earliest methods used to join metal, involves heating filler metal (in the form of a filler wire) so that it melts and fills joints. Soft soldering is the simplest process, and the one commonly used in and around the home to repair small metal items. It is also the method used by plumbers to join and repair the copper pipes and copper fittings.

You can use an inexpensive soldering iron or a blowtorch with a suitable flux for soft soldering. Hard soldering involves heating the filler materials to a much higher temperature, so the joint will be a lot stronger than other soldered joints.

The filler material is different and usually contains silver, so the technique is often referred to as silver brazing. However, true brazing is executed at an even higher temperature.

Copper Brazing

Brazing is essentially a technique similar to soldering, and it utilizes the same sort of filler material (wire or a brazing rod) used for soldering. Joints need to be very closefitting so that capillary action can draw the filler metal between the pieces of copper being joined.

Even though temperatures used must be considerably higher than those required for soldering, the base metal mustn’t be heated to the melting point.

Used extensively for plumbing work, brazing may also be used to join different types of metal as well as metal workpieces that are of different thicknesses.