AC vs DC Welding | Explained

Introduction

AC and DC welding is arc welding techniques that employ different currents to create an electric arc. An electric arc is formed between an electrode and the metal being welded in this sort of welding. The electric arc generates heat, which fuses the metals together.

To generate the arc, a power supply is necessary, which can be either alternating current (AC) or direct current (DC) (DC). The polarity of the electrical current that flows through the electrode is determined by the power source (AC or DC). The power source used has an effect on the weld generated.

The strength and quality of your weld are affected by the polarity of your electrodes. The two types of current flow are also known as ‘electrode negative’ and ‘electrode positive,’ and are commonly referred to as straight or reverse.’ The DC polarity is constant, whereas the AC polarity flows in one direction for half of the time and the other, reverse, way for the other half of the time.

AC vs. DC Welding Differences Summarized

The chart below was produced as a quick reference to help you understand the differences between AC and DC welding.

Continue reading to learn more about the distinctions.

ACDC
Weld SpatterMoreLess
Arc StabilityWorseBetter
Filler Metal Deposition RatesModerateHigh
PenetrationModerateHigh
Voltage Drops Using Long LeadsNoYes
Arc Blow Occurs When Welding Magnetized MetalNoYes
Welds Ferrous Metal Like SteelSMAW onlyAll arc welding processes
Welds AluminumAC TIGDC MIGLow
TIG Welding Equipment CostHighLow
Stick Welding Equipment CostLowMedium to High

What is DC Welding?

DC is an abbreviation for direct current, which flows in only one direction. Because the electric circuit must be continuous for electricity to flow, we finish the circuit with a ground clamp and an electrode holder or a TIG/MIG torch. The electrical circuit is completed when the arc leaps between the electrode and the metal with the ground clamp attached.

Because of the metal’s electrical resistance, the electrode and metal heat up to the melting point. However, using the incorrect polarity dramatically lowers weld quality.

As a result, your ground clamp and electrode must be properly connected to the power supply (welding machine). Depending on the welded metal and electrode selection, each welding procedure necessitates a different polarity.

The ground clamp is negative while the electrode is positive in the direct current electrode positive (“DCEP”).
The electrode receives around 70% of the heat and 30% of the work.

The ground clamp is positive while the electrode is negative in the direct current electrode negative (“DCEN”).
The electrode receives around 30% of the heat and 70% of the work.

Electrons are always moving from the negative to the positive pole. Electrons move from the workpiece to the electrode if the electrode is positive, and vice versa if the electrode is negative.

You might believe that the DCEN polarity is the best for welding since the heat is focused on the workpiece.
That must be beneficial for penetration.

Right?

This is often true, but not always.
Later in the article, we’ll go into the required polarity and why stick welding requires the opposite polarity as TIG welding.

Pros

  • A smoother welding output than with AC
  • A more stable arc
  • Less spatter
  • DC negative offers faster deposition rates when welding thin sheet metals
  • DC positive provides greater penetration into the welded metal

Cons

  • DC welding is unable to fix arc blow problems
  • Equipment is more expensive as DC currents require an internal transformer to switch the current

Applications

DC welding is great for combining thinner metals and is utilized in most stick welding applications, including – steel TIG welding.
This welding technique is also suitable for overhead and vertical applications.

What is AC Welding?

Alternating current reverses the current direction numerous times every second. Standard US house outlets deliver 110-120V AC electricity at 60Hz, whereas European countries utilize 220-240V at 50Hz.

As a result, the polarity of your available power is reversed 50-60 times each second. The same is true when welding with an AC power supply. Many times per second, the electrode holder/MIG/TIG torch and the ground clamp will flip polarity.

However, don’t get the AC input and welding machine output frequencies mixed up. Unlike older welders, which could only give the output frequency from the wall outlet (input frequency), contemporary welders allow you to change the output frequency. Some equipment can produce frequencies of up to 500Hz!

Pros

  • The alternating current between positive polarity and negative polarity allows for a steadier arc for welding magnetic parts
  • Fixes problems with arc blow
  • Enables effective aluminum welding
  • AC welding machines are cheaper than DC equipment

Cons

  • More spatter
  • Weld quality is not as smooth as with DC welding
  • Less reliable and therefore more difficult to handle than DC welding

Applications

When converted to AC positive, it also aids in the removal of oxide from the metal surface, making it appropriate for welding aluminum.

AC welding is also commonly employed in shipbuilding, particularly for seam welds, because it allows for a larger current setting than DC welding. AC welding also provides quick fills and is commonly utilized for down-hand heavy plate welds.

Magnetized materials are one of the most common applications of AC welding. This makes it useful for machine repair.

The Differences Between AC & DC Welding

The primary distinction is evident. The polarity of an AC output is switched, and the current constantly flows back and forth, but the polarity of a DC output is uniform, and the current flows in one direction.

AC is unsuitable for the majority of welding applications. Every time the polarity changes, the arc is quenched and rekindled. As a result, while stick welding, AC creates arc instability and does not enhance MIG or FCAW welding processes.

Let’s look at the distinctions between AC and DC welding in terms of procedure…

AC vs. DC Stick Welding (SMAW)

The original stick welders, sometimes known as buzz boxes, used alternating current (AC). The buzz box got its name from the device’s polarity-switching function, which made it sound like a bumblebee.

While these AC welders did the job, the arc was not as steady as with DC output power sources. As a result, stick welding is mostly done with DC machines.

However, polarity selection is critical in achieving quality SMAW welds. Even when the current is focused on the stick welding electrode, DCEP delivers the best penetration.

I realize that sounds counterintuitive. But consider the following…

The heat is focused on the electrode, causing it to melt, and the liquid droplet at the rod’s tip is driven into the welded metal, causing it to penetrate deep into the weld joint.

As a result, during stick welding, DCEP is the most usually used polarity. DCEN, on the other hand, has applications. When welding thin material or executing surfacing welds, for example, maximal penetration is not required.

For welding mild and stainless steel, there are dozens of SMAW electrodes available. Some work with all polarities, while others prefer AC, DCEN, or DCEP. It is determined by the composition of the flux coating.

AC vs. DC TIG Welding (GTAW)

TIG welding employs either DC or AC output depending on the welded substance. Mild steel, stainless steel, and carbon steel are typically welded using direct current (DC), whereas aluminum and magnesium require an alternating current (AC) output.

DC TIG

The polarity of standard DC TIG welding is the inverse of stick welding. Because the current and heat are focused on the welded metal, DCEN is the preferred polarity.

DCEP concentrates too much heat on the tungsten electrode, resulting in tungsten erosion and electrode tip melting. If you need to ball up the tungsten tip quickly, you can use DCEP. Aside from that, DCEP is rarely utilized for TIG welding.

AC TIG

When exposed to air, aluminum forms an oxide coating on its surface, and this oxide layer melts at a greater temperature (3200o+F) than the pure aluminum beneath it (1200oF). To successfully weld aluminum, the oxide layer must be removed prior to welding.

However, eliminating this layer is impossible, especially because it forms shortly after you clean it. After cleaning, a tiny oxide film forms in less than a second, and these oxides cause weld contamination.

Fortunately, the DCEP TIG welding polarity easily dissolves this aluminum oxide residue. The aluminum oxide on the surface is broken up and burned away as electrons from the workpiece (the negative pole) arc onto the tungsten electrode (the positive pole).

However, DCEP has low penetration, and the electrode diameter must be big to prevent the tungsten electrode from burning.

As a result, once the DCEP cleans the surface, DCEN plays an important role in reaching the aluminum beneath the oxides. By switching the polarity multiple times per second, AC TIG uses both electrode positive and electrode negative.

If the welder controls allow the user to choose the frequency, the TIG AC welding frequency can be preset at 50-60Hz or range from 20 to 500Hz.

Where are AC and DC Welding Used?

When TIG welding aluminum or if the welded metal is magnetic, AC welding is the best option. For everything else, DC welding is preferred.

However, we created the table below as a quick reference graphic.

Common DC Welding ApplicationsCommon AC Welding Applications
DC TIG, Stick, MIG, and Flux-cored processesAC TIG and Stick welding processes only
Welds mild steel, stainless steel, cast iron, titanium, copper, brass, bronze, nickel, and many other metalsSMAW: low carbon steel, stainless steel. AC TIG: aluminum and magnesium
Non-magnetized metalsNon-magnetized and magnetized metal
Welding near the power sourceWelding far away from the power source

Wrapping It

Except for metal, DC output is a preferable alternative for welding. However, many applications necessitate the use of an AC output as well. As a result, skilled welders prefer to have both alternatives available.

Some high-quality TIG/Stick multi-process welding equipment have AC and DC outputs for both processes, not only TIG.

At first, the DC polarities can be perplexing. However, with practice, you will remember the distinctions between DCEN and DCEP and it will become second nature.

Leave a Comment