DC vs AC welding is differentiated based on the welder type. Remember AC or DC is not a welding process, but it is a welding power source (welder) characteristic. The output electric current type supply determines the type of welding power.
This means that a welding power source can be used for either:
- AC Welding or
- DC Welding.
DC vs AC Welding
DC welding is the most common type of welding. It is used for most metals and alloys. DC welds are made with a constant current, which means that the metal is heated evenly. DC welding is more efficient and produces a higher quality weld.
| DC Welding | AC Welding | |
|---|---|---|
| Welding Penetration | Medium | High |
| Welding Spatters | Less | More |
| Arc Stability | Very Good | Poor |
| Weld Deposition Rate | High | Medium |
| Oxide Cleaning Action | Poor | Excellent |
| Non-ferrous welding | Fair | Very good |
| Welder Cost | High | Low |
| Control of weld penetration | Possible | Not possible |
| Arc Blow control | No | Yes |
| Power source versatility | Yes (can be used for TIG, Stick, MIG) | Limited |
AC welding is used for aluminum and other non-ferrous metals. AC welding is where the current alternates between positive and negative.
DC welding is most commonly used for welding ferrous metals. The advantages of DC welding are that it produces a more stable arc, less spatter, and better penetration.
What is DC Welding?
In direct current (DC) welding, the electrode and workpiece are connected to the negative or positive terminals, thus creating an electrical circuit.
The arrangement of these connection types determines the polarity for DC welding and has the following two types:
- Direct Current Electrode Positive- DCEP (also called Reverse Polarity).
- Direct Current Electrode Negative-DCEN (also called Straight Polarity).
Advantages of DC Welding
DC welding is used in Stick welding, MIG welding, and TIG welding. Advantages of DC welding include a more stable arc, less spatter, better weld penetration, and easier starts.
DC welding is advantageous because it provides a more stable arc than alternating current (AC). This is due to the fact that the electrons flow in one direction only in DC welding. As a result, there is less spatter and better weld penetration.
In addition, DC welds are easier to start because the arc can be ignited with a lower voltage than AC.
DC Welding has a constant level of welding current during welding. This provides a constant overall welding heat input and thus gives higher welding penetration compared to AC Welding for the same welding current value.
What is AC Welding?
When welding with AC power, the welder does not have to worry about polarity as the machine will automatically change it for you. During welding, current navigate from positive to negative and vice-versa in AC welding.
In the below figure, you can notice that the current cycle changes from negative to positive during welding and the electrons flow in both directions.
Due to the change in the current level, the overall welding heat input is lower in AC welding compared to DC welding.
Advantages of AC Welding
The advantages of AC welding are many, but most notable is the cathodic cleaning action it provides.
Read my article on how Cathodic Cleaning action works in TIG Welding.
This means that it can clean the oxide layer automatically, which is ideal for welding aluminum and magnesium.
Additionally, AC welding is good for non-ferrous material welding, as it produces less heat and thus lessens the risk of warping or melting the material.
