How to Weld Copper – Methodologies and Tips
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Copper is perhaps one of the most widely used materials in metal fabrication, whose provenance can be traced back to 3500 BC. It is a non-ferrous and soft metal that can be easily shaped, cut, bent, and joined with other metals with different welding methods. It has unique traits such as thermal and electrical conductivity as well as high corrosion resistance, making the metal ideal to weld with.
You can join copper and most copper alloys using soldering, brazing, and different welding processes. However, the specific process will largely depend on whether you are welding pure copper or a copper alloy. If working with an alloy, its elements and factors, such as filler material, will influence the welding method you can use.
Unfortunately, copper’s unique characteristics also make welding it a challenging endeavor. Not everyone will be able to make reliable weld joints. You must use specific methods and take extra precautions. Luckily for you, our how-to-guide will equip you with all the necessary information required for the different processes of welding copper.
This article will address the reasons why welding copper is different from other metals, the various methods of welding copper, and general tips to ensure that you can work with copper without any difficulty.
Why Welding Copper is Difficult
- When copper is heated, it experiences high chemical reactions, which will likely form an oxide-resistant film on its surface. If the oxides spread into the seam, they can create cracks in your weld.
- Due to the high thermal conductivity of copper, you must use a large current welder. Otherwise, the fast dissipation of heat will create defects in your joint.
- Copper welding creates a high thermal expansion coefficient on the welded joint. This can make the copper joint deformed and can easily crack or warp while cooling the metal.
- Molten copper can easily get saturated with hydrogen, which creates pores on the surface of the metal. Also, when hydrogen combines with oxygen, the oxidation process creates a layer on the copper’s surface, which makes the welding process harder.
- When you rapidly heat and cool copper, the welding joints tend to become brittle.
- Copper has high fluidity when it melts, which makes creating vertical welds and ceiling joints very challenging.
- The melting point of copper and its alloys is highly variable. It is about 1,000°F lower than the melting point of carbon steel. In addition, copper doesn’t display the same heat colors as seen when welding steel.
Different Methods of Joining Copper and Its Alloys
Since pure copper is too ductile to create a reliable joint, you must add small quantities of other elements to the various copper alloys. This will deoxidize the metal, reduce corrosion resistance, and improve machinability. There are several processes for joining copper and over 300 alloys that are commercially available. These include soldering, brazing, and welding.
This is one of the earliest methods of joining metals. The process involves heating filler materials which are usually in the form of a wire. In the molten form, it can then fill the joints. Soft soldering is the most common and simplest process you can use to repair small metal items. This method is also used by plumbers to repair and join copper fittings and copper pipes.
A simple blowtorch with an ideal flux or a cheap soldering iron is the main equipment used in soft soldering.
Hard soldering, on the other hand, involves heating the filler materials to a much higher temperature to ensure that the joints are stronger than other soldered joints. The filler materials are also different and usually contain silver. Hence, the name silver brazing.
This technique is like soldering but with one major difference. Brazing requires much higher temperatures. With the same filler materials (a brazing rod or a wire), you can braze copper and its alloys. However, the joints need to be close fitting so that the capillary action can draw the filler material between the two pieces of copper.
Despite the need for higher temperatures than those required for soldering, the base metal should not be heated to a molten state. Brazing is extensively used for plumbing and can join different types of metal with different thicknesses.
This process, more accurately referred to as arc welding, is perhaps the most utilized method of joining metals. Welding incorporates different techniques to create strong and reliable metal joints.
Mostly, the processes that utilize shielding gasses are preferred. However, shielded metal arc welding (SMAW), also known as the manual metal arc (MMA), is used in welding copper in situations that are not critical.
This method is suitable for a variety of copper thicknesses. It is also a useful method because the covered electrodes for copper welding using SMAW are readily available in a wide range of standard sizes.
The shielding gasses normally used for welding copper and copper alloys are argon, helium, or a combination of the two. These gasses are used for gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), or plasma arc welding (PAW). Mostly argon is preferred when manually welding copper or its alloys with relatively low thermal conductivity or a thickness less than 3.3 millimeters. A mixture of helium and argon is recommended for the manual welding of thicker pieces of copper and machine-welding thinner pieces of copper. The combination is also great for copper with high thermal conductivity.
How to Weld Copper
1. TIG Welding
Also known as Gas Tungsten Arc Welding (GTAW), this process can similarly weld copper to most arc welding methods. This involves the use of an electric arc to heat and melt the filler materials and the copper pieces.
When the weld pool created begins to cool and solidify, it is protected from atmospheric conditions by introducing a shielding gas to the pool. Helium and argon are the most used gasses in TIG welding copper. While this method may be like most arc welding processes, it does not direct the electric arc to copper using consumable electrodes.
Instead, TIG welding utilizes non-consumable electrodes to create a joint between copper pieces with or without filler materials. While filler materials can be used as electrodes in many arc welding processes, you need a separate filler wire in TIG welding copper. Also, this method does not necessarily require filler materials.
TIG welding can join copper and alloys up to 16 millimeters in thickness. The filler material should have the same composition as the base metal. Argon is the best shielding gas for welding copper that has a thickness of 1.6 millimeters. If the metal pieces are thicker, a combination of helium and argon is better for shielding the weld pool. This is because the mixture has a deeper perforation at the same welding current. The mixture is mixed in the 25% argon to 75% helium ratio.
TIG welding can join copper and its alloys using a semi-automatic or manual argon-arc method. A strong weld is created by a direct current polarity. The ideal value of the current is determined on the basis that each 0.04 millimeters metal thickness requires 100A. This value is adjustable depending on the metal’s composition. When TIG welding, ensure that the flow rate does not exceed 0.25 gallons per minute.
2. MIG Welding
Also known as Gas Metal Arc Welding (GMAW), this process has similar characteristics to SMAW. It uses an electrode as the filler material. However, unlike SMAW that uses a series of short rods as the consumable electrode, MIG automatically feeds a continuous wire to the welding torch at a seed specified by the user. Also, one can adjust the settings for feeding the shielding gas.
When MIG welding copper and its alloys, experts recommend using Ecru copper electrodes. Alternatively, you can use Aufhauser deoxidized copper. This metal is a great filler material because it has a 985-purity level. The thickness of the metal will determine the gases used in MIG welding copper pieces. Mostly, argon is used as a shielding gas for metals up to 6 millimeters. If thicker, a mixture of argon and helium is better for shielding the weld.
To optimize your work, ensure that you have a gas flow rate of 40 gallons per hour for the copper thickness of up to 0.4 inches. If your workpieces are thicker, the gas flow rate should be 53 gallons per hour. Also, the diameter of the filler material should be at least 60% the thickness of your metal but not more than 0.3 inches wide.
When MIG welding copper, ensure that your flame is positioned perpendicular to the joint. Also, ensure that the wire is melted before the base metal. To prevent deformities on your weld, your work should be continuous.
For a successful joint, heating will not be necessary if the pieces are thinner than 0.2 inches. However, you will need to heat the materials to 482 degrees Fahrenheit for thicker pieces. Proceed to anneal at 932 degrees Fahrenheit, then quickly cool your metal with water.
General Tips for Welding Copper
Due to the dangerous nature of welding copper, safety should be paramount. Ensure that you take all the necessary precautions to protect yourself and your welding equipment. This involves the use of welding helmets, jackets, goggles, boots, and gloves as well as cleaning your workspace.
Also, since welding copper will produce dangerous fumes, ensure that you work in a well-ventilated environment. You can also use a smoke extractor gun to reduce the fumes in your workshop.
Choose the Correct Filler Material
The best way to make your weld strong and durable is to ensure that the weld metal is significantly stronger than the base metal. For instance, if your copper alloy has at least 70% of copper in it, use 30-70 nickel-copper for filler material. The nickel will make the weld metal stronger than the base metal.
Clear All Contaminants
Generally, grease, oil, and paints can destroy your weld if left on the surface of your metal. Make sure that you remove all contaminants before welding. You can use a wire brush or a piece of cloth to clear off any debris from your metal.
Use Correct Copper Welding Procedure
As you may have gathered, copper welding is dissimilar to steel welding. So, make sure you prepare your equipment properly while paying attention to the different metal thicknesses. A square butt prep is ideal for metals less than 3 millimeters thick, while beveled prep is better for thicker metals.
Position Your Weld Correctly
You can weld copper in different welding positions. However, welding down-hand is best suited for copper and its alloys. It makes it easier to perform a successful weld. Also, it’s best to position your pieces in a way that will allow you to weld down-hand to create a successful weld.
Copper is a popular metal in metal fabrication because of its unique chemical and physical properties. It has a higher resistance to corrosion, thermal conductivity, and electrical conductivity with applications in various industries.
Unfortunately, it is one of the most difficult metals to weld. You must use different procedures to weld it. Understanding how to properly handle copper will ensure that you are safe and able to fuse the metal pieces successfully. Ensure that you have a basic understanding of the type of copper alloy you are welding as well as the material thickness so that you can choose the correct procedure.
The commonly used methods of successfully welding copper are TIG, MIG, and plasma welding. However, before attempting an actual welding project, try out your skills on disposable or smaller metals.
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