What's the Difference Between AC and DC Welding?

For most, the mention of AC/DC evokes memories of a certain rock band. For welders, it means comparing two different electric currents that are used during the welding process. There's just one question: What's the difference between AC and DC welding?

Comparing The Currents

During the welding process, an electric arc is produced between an electrode and the welded metal. It's vital to use the right power supply for that electric arc so you don't end up with a bad weld that has terrible quality. After all, a weld's quality and strength largely depend on utilizing the right polarity and the right electrode. 

This is where alternating current (AC) and direct current (DC) come into play.

Electricity flows in one of two ways: with an alternating current or a direct current. These result in electrons moving through a conductor, and the variance between AC and DC polarity comes down to one element: how the electrons move for each one.

AC welding

AC and DC welding exampleAs the 'alternating' part of its name suggests, AC continually switches the direction for electrons' flow. The electrons go back and forth, with the polarity changing up to 120 times per second. As it transmits electricity over big distances, AC is found in high voltage devices such as appliances and household outlets. 

When the polarity is going from negative to positive, the output features zero amperage for a split second. This is bad because the electric arc either wanders or extinguishes completely.

To avoid this from happening, you can search for electrodes crafted specifically for AC welding. These incorporate a special coating that ensures the arc remains ignited. Just keep in mind there will be more fluctuation and flutter with the arc compared to DC polarity. 

In welding, AC usually finds itself behind DC in the pecking order. Yet this doesn't mean there are no circumstances where AC is the preferred option. If it's the only available power supply, for instance, AC is there to help. Plus, thanks to its steady arc, AC can also assist with rectifying any arc blow issues.

Uses for AC welding

As AC promotes a higher temperature, aluminum is a more suitable material to work with on welding projects. For instance, aluminum features a tenacious oxide film on its surface – not ideal for welding. Yet when AC turns to electrode positive, that oxide film is removed, and the surface is clean. 

AC welding is also the recommended option when plate metals require a deeper penetration – such as in shipbuilding. Furthermore, AC is used if the welding materials feature a magnetized field.

The Disadvantages Of AC Welding

Even though it falls behind DC as the main option in welding, the aforementioned guide has established how useful AC is in certain situations. Nevertheless, it does suffer from a few notable drawbacks. These are: 

  • Not as smooth: When compared with DC welding, the weld's quality doesn't tend to match up in terms of smoothness. 
  • More splatter is produced: No welder wants to have to deal with splatter. Yet AC welding is susceptible to producing a significant amount of it, which means you could spend hours cleaning your work surface, floor, welding project, etc. – unless you make use of anti-splatter spray and other precautions.
  • Unreliable arc: Not only is the arc less reliable when compared to DC welding, but it's also trickier to handle.

DC Welding

So why is DC welding the more popular option over AC welding? Well its electrons all flow in a single, nice steady direction. There is no alternating. The polarity is constant, and it can be selected as either positive or negative. This is the main reason why DC tends to be utilized in devices with low voltage. This includes products such as remote controls and cell phone batteries. 

As the drawbacks of AC welding spotlighted, DC has several advantages over its counterpart. Due to producing an arc that is more stable, it ensures welding is an easier process overall. The welding output is smoother than AC, and less splatter is created. 

Another advantage in DC's favor is the optional use of its positive and negative polarity. When DC positive is used, it supplies more steel penetration when required. Due to the faster deposition rates it offers, DC negative is recommended when working with thin sheet metal.

Uses For DC Welding

Due to its positive points, DC welding is used in a wide variety of applications. For instance, it is utilized in the vast majority of stick welding applications. DC welding is also a suitable choice for the following: 

  • Stainless steel TIG welding
  • Single carbon brazing
  • Overhead and vertical welding 
  • When thinner metals are welded

The Disadvantages Of DC Welding

It's the favored option out of the two. It has a wealth of advantages. Yet despite all of this, DC welding does suffer from some notable drawbacks. It's true – although the damage caused by these disadvantages is minimal for the most part

  • Arc blow: The biggest technical problem relating to the use of DC welding is arc blow. When welding, the welder wants to direct the shaped arc into the joint to gain full penetration. Yet when arc blow happens, this arc is moving to either one side or the other. A fix for this is using AC polarity. 
  • More expensive equipment: An internal transformer is usually necessary for DC welding. This transformer allows the user to switch the current, yet this comes at a cost – literally.
  • Not ideal for aluminum: DC isn't the solution when attempting to produce high-intensity heat when welding. As a result, it falls behind AC welding as the best choice when working with aluminum.

In summary

As this guide has established, both AC and DC welding can be utilized to complete a multitude of tasks. In most cases, DC has the advantage over AC and is the more versatile of the two. However, it's important not to overlook AC as it is a better option for certain jobs. Ultimately, both AC and DC are required within the repertoire of any serious welder.

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