Copper, a non-ferrous and malleable metal, has been used in metal fabrication since 3500 BC due to its versatility. It can be easily shaped, cut, bent, and joined with other metals using various welding methods. Its exceptional thermal and electrical conductivity, along with its high corrosion resistance, make it an ideal metal for welding.
Soldering, brazing, and different welding techniques can be used to join copper and most copper alloys. However, the specific method depends on whether you’re welding pure copper or a copper alloy. Factors such as filler material and the alloy’s composition will affect the welding method used.
However, welding copper can be a challenging task due to its unique properties. Achieving reliable weld joints requires specific methods and precautions. Fortunately, our comprehensive guide will provide you with all the necessary information for welding copper using various techniques.
In this article, we will discuss the unique challenges of welding copper and its alloys, the various methods of welding copper, and general tips for successfully working with copper.
Challenges of Welding Copper
Welding copper presents several challenges due to its unique properties, such as:
When heated, copper forms an oxide-resistant film on its surface, which can lead to cracks in the weld if it spreads into the seam.
Copper’s high thermal conductivity requires a large current welder to prevent defects in the joint caused by rapid heat dissipation.
Copper’s high thermal expansion coefficient can cause the joint to deform, crack, or warp when cooled.
Molten copper readily absorbs hydrogen, which creates pores and makes the welding process harder due to the oxidation of the metal’s surface.
Rapid heating and cooling of copper can result in brittle weld joints.
Copper’s high fluidity when melted makes it difficult to create vertical welds and ceiling joints.
Copper and its alloys have a highly variable melting point, about 1,000°F lower than carbon steel, and do not display the same heat colors as seen when welding steel.
To successfully weld copper, it’s crucial to understand these unique challenges and take appropriate measures to mitigate them.
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Joining Copper and Its Alloys: Various Methods
Pure copper is too ductile to create a reliable joint, hence the need to add small quantities of other elements to create copper alloys. This deoxidizes the metal, reduces corrosion resistance, and improves machinability. With over 300 commercially available alloys, several processes can be used to join copper, including soldering, brazing, and welding.
- Soldering
One of the earliest methods of joining metals, soldering involves heating filler materials, usually in the form of a wire, to molten form, which then fills the joints. Soft soldering is the simplest and most common method used to repair small metal items and by plumbers to join copper fittings and pipes. The main equipment required for soft soldering is a simple blowtorch with an ideal flux or a cheap soldering iron.
Hard soldering, on the other hand, requires heating the filler materials to a much higher temperature to create stronger joints than other soldered joints. The filler materials are different and typically contain silver, hence the name silver brazing.
2. Brazing
Brazing is similar to soldering but requires much higher temperatures. Using a brazing rod or wire, you can join copper and its alloys together, but the joints must be close-fitting so that capillary action can draw the filler material between the pieces of copper. Unlike soldering, the base metal should not be heated to a molten state during brazing. This method is commonly used in plumbing and can join different types of metal with varying thicknesses.
3. Welding
Arc welding is one of the most commonly used methods of joining metals. Various techniques are used to create strong and dependable metal joints. Shielding gas processes are often preferred, with argon, helium, or a combination of the two gases being used for gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), or plasma arc welding (PAW). When manually welding copper or its alloys with low thermal conductivity or a thickness of fewer than 3.3 millimeters, argon is the preferred gas. A combination of helium and argon is recommended for thicker pieces of copper and machine-welding thinner pieces of copper, as well as copper with high thermal conductivity. Shielded metal arc welding (SMAW), also known as the manual metal arc (MMA), is used for welding copper in non-critical situations and is suitable for a variety of copper thicknesses. Covered electrodes for copper welding with SMAW are available in a wide range of standard sizes, making it a useful method.
How to Weld Copper
1. Gas Tungsten Arc Welding (GTAW) or TIG Welding
TIG welding is a popular method of joining copper and its alloys that uses an electric arc to heat and melt the copper pieces and filler materials. Unlike other arc welding processes, TIG welding does not use consumable electrodes to direct the electric arc onto copper. Instead, it employs non-consumable electrodes to create a joint between the copper pieces, with or without filler materials.
To protect the weld pool from atmospheric conditions during cooling and solidification, a shielding gas such as helium or argon is introduced. Argon is the ideal shielding gas for welding copper with a thickness of 1.6 millimeters, while a mixture of 25% argon and 75% helium is recommended for thicker copper pieces, as it has a deeper penetration at the same welding current.
TIG welding can join copper and its alloys up to 16 millimeters in thickness. The filler material used must have the same composition as the base metal. A strong weld is created by a direct current polarity, with the ideal current value determined by the metal’s composition. The flow rate should not exceed 0.25 gallons per minute.
TIG welding can be performed using a semi-automatic or manual argon-arc method.
2. Gas Metal Arc Welding (GMAW) or MIG Welding
MIG welding, also known as Gas Metal Arc Welding (GMAW), is similar to SMAW in many ways. It involves using an electrode as the filler material. However, unlike SMAW, which uses short rods, MIG automatically feeds a continuous wire to the welding torch at a user-specified speed. The user can also adjust the settings for feeding the shielding gas.
When welding copper and its alloys using MIG, experts recommend using Ecru copper electrodes or Aufhauser deoxidized copper as filler material. The latter is a great choice because of its 985 purity level. The gases used for shielding the weld will depend on the thickness of the metal. Argon is commonly used for metals up to 6 millimeters thick, while a mixture of argon and helium is preferred for thicker metals.
To optimize your work, ensure that you have a gas flow rate of 40 gallons per hour for copper thicknesses up to 0.4 inches. For thicker workpieces, the gas flow rate should be 53 gallons per hour. The diameter of the filler material should be at least 60% of the thickness of your metal, but not more than 0.3 inches wide.
When MIG welding copper, position your flame perpendicular to the joint and ensure that the wire is melted before the base metal. To prevent deformities on your weld, make sure your work is continuous.
If the pieces are thinner than 0.2 inches, you won’t need to heat them for a successful joint. However, for thicker pieces, you will need to heat the materials to 482 degrees Fahrenheit. Anneal at 932 degrees Fahrenheit, then quickly cool your metal with water to prevent deformities on your weld.
Tips for Welding Copper
Prioritize Safety
Welding copper can be dangerous, so safety should always be your top priority. Make sure you take all necessary precautions to safeguard yourself and your welding equipment. This includes wearing welding helmets, jackets, goggles, boots, and gloves and keeping your workspace clean. To reduce harmful fumes in your workshop, ensure proper ventilation or consider using a smoke extractor gun.
Select the Correct Filler Material
To make your weld strong and durable, ensure that the weld metal is significantly stronger than the base metal. For copper alloys with at least 70% copper, use 30-70 nickel copper for filler material, as the nickel will strengthen the weld metal.
Eliminate All Contaminants
Grease, oil, and paint can ruin your weld if left on the metal surface. Thoroughly remove any contaminants before welding using a wire brush or a piece of cloth.
Follow the Correct Copper Welding Procedure
Copper welding is different from steel welding, so make sure your equipment is properly prepared, paying attention to the metal thickness. For metals, less than 3 millimeters thick, a square butt prep is ideal, while a beveled prep is better for thicker metals.
Position Your Weld Correctly
Weld copper in different positions, but down-hand welding is ideal for copper and its alloys. It is easier to achieve a successful weld when working in this position. Additionally, position your metal pieces to allow for down-hand welding to create a successful weld.
Final Thoughts
Copper is a popular metal in metal fabrication due to its unique chemical and physical properties. It has high resistance to corrosion, thermal conductivity, and electrical conductivity, with applications in various industries. However, welding copper is challenging and requires different procedures than other metals. Ensure you have a basic understanding of the copper alloy you are welding and its thickness to select the correct procedure. TIG, MIG, and plasma welding are commonly used methods for successfully welding copper. Practice your skills on disposable or smaller metals before attempting an actual welding project.
