AC & DC Welding: What are they and How is it Different

Last Updated on May 2022

Introduction

Every welder needs a source of power to achieve the perfect weld. Power enables the flow of electrons to connect with the material that is being welded. This source of power exists in two forms: AC and DC.

AC stands for Alternating Current, while DC stands for Direct Current. These terms define how power or electricity flow through a conductor. The difference in how electrons move or the polarity of electrons is the key difference between AC and DC.

A high-level definition is that Direct Current flows in one direction while Alternating Current switches direction. Some factors must be considered before making a decision on which source of power you would like to use. Consider things like the type of weld needed, type of material that will be used, understand the advantages and disadvantages of each type of current.

To help you make the right choice, we have analyzed DC versus AC power by looking at what they are pros and cons for each and their various applications when welding.

AC & DC Welding Explained

Direct Current (DC)

Electric currents in DC flow in a single and stable direction. This kind of flow means that its polarity is constant and can be classified as either positive or negative.

When welding, a negative polarity produces less heat, melts at a quicker pace, and has higher degrees of deposition compared to positive polarity. On the other hand, you can expect much deeper penetration rates when dealing with positive polarity (also known as reverse polarity). Due to these qualities, DC negative is best for thin welding material while DC positive for heavier ones.

DC is the most commonly used option during welding. It is best suited for applications with low voltage like remote controls, flashlights, and cell phone batteries.

Where is DC welding applicable?

  • In most of the stick welding applications
  • On thinner sheet metal because negative electrode DC produce less heat that helps to prevent burn up
  • During overhead or vertical welding.
  • Where there is a build-up of heavy deposits
  • In single carbon brazing.
  • All stainless steel TIG welding
  • Hard facing.
  • In tap cutting.

Pros of DC Welding

  • It results in a smoother weld
  • The constant linear direction of its current ensures there is minimal spatter
  • It is reliable and more comfortable to work with because it maintains a stable arc compared to AC
  • It is relatively cheaper to acquire and use the equipment required
  • There are fewer outages when DC welding
  • Most suitable for thinner metals
  • It allows for more relaxed overhead and vertical up welding.
  • DC positive polarity provides deeper penetration rates into the steel being welded.
  • DC is applicable on a broader variety of welding projects compared to its AC counterpart

Cons of DC Welding

  • It is almost impossible to prevent arc blows with DC welding – this means that the arc gets pushed to a side that the welder does not necessarily intend. A welder usually aims to direct an arc into a joint to get full penetration, and these efforts are thwarted when an arc blow occurs. Causes of arc blows include the arcs current, magnetic material, and even wind.
  • It can be a costly affair – if there is a need to switch currents from AC to DC, there will be need to install an internal transformer because typically, electrical grids do not supply DC electrodes.
  • DC welding generally utilizes low heat; therefore, it is not useful for welding aluminum, which demands high-intensity heat.

Alternating current (AC)

Electric currents in AC do not flow in one direction. Here, the electrons change direction and reverse back and forth. While DC is known to have constant polarity, AC has been proven to alter polarity up to 120 times per second.

The alternating current that bounces between positive and negative polarity is advantageous in that it facilitates a more stable arc primarily when welding magnetic material.

AC is useful where you need to transmit electricity over large diameters. It is a less utilized power compared to DC. It is most suitable for applications with high voltages such as household appliances and other powerful equipment both in homes or work environments.

Despite being the number two choice to DC, there are situations that AC is preferable. These conditions include where you are dealing with low-cost equipment that only utilizes AC power or when AC is the only power available.

Where is AC welding applicable?

  • TIG welding aluminum with high frequency, because the current supports welding at high heat temperatures. The ease of electric current switches in AC is useful for cleaning oxide off aluminum surfaces (once it converts to electrode positive)
  • Repair and maintenance – especially of machines which are mostly old and rusty and some have magnetized fields
  • Shipping industry – used to weld seams when building ships. This is useful because AC welding will easily achieve deeper penetration of the metal plates.
  • Unlike DC, AC welding supports welding of materials that have a magnetized field without losing the arc direction that could lead to arc blowing.
  • AC supports rare weld types such as Down hand heavy plate and fast fill.

Pros of AC Welding

  • Works well on magnetic material – the switching of current back and forth supports the welding of magnetized material with zero to minimal challenges
  • It is affordable because there is no need to install an internal transformer
  • Suitable for use in aluminum which has been cited as the most challenging material to weld
  • Has high portability rate
  • Achieves a deeper weld penetration

Cons of AC Welding

  • Results in more spatter
  • The finish is not as smooth as DC welded material
  • The flow of current back and forth makes it difficult to handle the arc

Conclusion

DC welding is mostly preferred over AC welding because it can be applied on a wider variety of welding applications. However, both are uniquely useful, so it is upon you as the welder to clearly define and understand your specific welding needs, then pick the option that will help you achieve the perfect weld.

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