For many people, AC/DC gets them reminiscing about a certain era of rock music, but for welders it means polarity. Welding involves creating an electric arc between an electrode and the metal that is being welded. However, for creating the best welds, it’s important to use the proper power supply, which can be either alternating current (AC) or direct current (DC). The strength and quality of the weld depend on using the right electrode and the right polarity. So if you’re confused about when to use which, below is some information to help you understand what is the difference between AC and DC welding.
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AC vs DC Welding
Electricity flows in two ways: either in an alternating or direct current. It’s the movement of electrons through a conductor. The difference between AC and DC polarity is in the way these electrons move.
DC currents have the electrons flowing in a steady single direction. It has constant polarity, which can be either positive or negative.
DC is often used in low voltage devices, such as cell phone batteries and remote controls.
DC polarity is used in most welding applications. It produces a smoother welding output compared to AC. It creates a more stable arc, easier welding and less spatter. You can also either use DC negative for faster deposition rates when welding thin sheet metal or use DC positive for more penetration into the steel.
Applications Of DC Welding:
- It’s used in most stick welding applications.
- Overhead and vertical welding.
- Stainless steel TIG welding.
- When welding thinner metals.
- Single carbon brazing.
Drawbacks Of DC Welding:
- Can’t fix arc blow.
- DC currents usually require an internal transformer for switching the current, which makes DC welders more expensive.
- It’s doesn’t work well for welding aluminum as it can’t produce the necessary high-intensity heat.
In AC, the flow of electrons keeps switching directions, going back and forth. It can change its polarity 120 times per second. Every time the polarity goes from DC negative to DC positive, the output for a split second has zero amperage. This no output moment results in that the arc tends to wander or extinguish. To overcome this problem, look for electrodes specifically designed for AC welding. They have special coating that keeps the arc ignited. However, the arc will still have more fluctuation and flutter than on DC polarity.
Alternating current helps to transmit electricity over large distances. So you can typically find this current used in high voltage devices, such as household outlets and appliances.
AC is usually a secondary choice in welding. However, there are a few instances where AC would be preferred. First of all, you can use it if it’s the only power supply available. For example, low cost, entry-level machines sometimes offer only AC power.
Secondly, switching to AC can help to fix arc blow problems, which means that the arc starts wandering or blows out of the joint. The cause of arc blow can be magnetism of the metal you’re welding or the arc’s current. The alternating current between positive and negative polarity enables a steadier arc when welding magnetic parts. Arc blow problems can also have external causes, such as windy conditions.
Applications Of AC Welding:
- TIG welding aluminum since AC supports welding at a higher temperature. Aluminum also has a tenacious oxide film on the surface and when AC switches to electrode positive, it helps to remove the oxide and clean the surface.
- In shipbuilding when you need deeper penetration of plate metals.
- When welding materials that have a magnetized field.
Drawbacks Of AC Welding:
- The quality of the weld is usually not as smooth as with DC welding.
- It also creates more spatter.
- The arc is more difficult to handle and it’s not as reliable as when DC welding.
Which Electrode To Use?
For DC welding, look for electrode 6010. It’s intended for direct current use only. It has a high cellulose sodium-type coating. It provides better penetration and has many applications in the field.
When welding on AC polarity the arc tends to go out and then needs to re-establish itself. So for AC welding, use electrodes that have specific elements in their coating, which will help to keep the arc ignited. AC welding rods include 6011, 6013, 7018 and 7024.
- The 6011 has high cellulose potassium-type coating. It can be used for all-position welding. They also work well on rusty and dirty metal, as well as when welding outside in windy conditions.
- The 6013 rods are used for welding clean sheet metal. They provide less penetration and prevent burning through the metal.
- The 7018 rods are usually used for DC welding, but can also be used with AC. They provide a good bead a strong welds.
- The 7024 rods can be used at high current levels. They run well on AC for flat and horizontal welds. These rods are also used for general fabrication when a higher deposition rate is required.
AC and DC welding can be used for accomplishing different tasks. In most cases, DC welding is more advantageous over AC welding. However, in certain cases, AC will also be a better choice. Keep in mind that in order to achieve proper penetration, a good bead and a strong weld, it’s important to choose the right current and polarity, as well as the right electrode.