Understanding the fundamental differences between AC and DC welding is paramount for welders seeking optimal performance in diverse applications. In this article, we'll delve into the core distinctions of AC vs DC welding, exploring their respective strengths, weaknesses, and applications.
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In the world of welding, the choice between Alternating Current (AC) and Direct Current (DC) holds significant implications for welding processes. Each current type provides distinct advantages and limitations, influencing factors such as weld penetration, electrode consumption, and overall efficiency.
Understanding the fundamental differences between AC and DC welding is paramount for welders seeking optimal performance in diverse applications. In this article, we'll delve into the core distinctions of AC vs DC welding, exploring their respective strengths, weaknesses, and applications.
AC TIG Welding on Aluminum
Photo by @weldaii (TikTok)
Basic Electricity In Welding
Electrical arc processes use electricity to form and maintain an arc. A Welding machine (or power supply) serves as the power source in welding processes. These machines provide the electrical energy needed to create an arc, which makes the heat required to melt the metals.
The arc in welding is formed once you close the electrical circuit between the positive and negative sides of the cycle. On one side, you have your electrode or welding torch; on the other, you have the ground. Once the electrode touches the base metal, the circuit is closed, and the arc is formed.
The current you use during the welding can be either alternating (AC) or direct (DC) current. Each current flows differently, which results in a different penetration, cleaning action, or electrode consumption, so choosing AC or DC can make or break your welding project. That's why, further in the text, we'll explain the effects more thoroughly.
Source:
https://www.electronicsforu.com/technology-trends/learn-electronics/difference-between-ac-and-dc
Direct Current In Welding
Direct Current (DC) is an electric current that flows consistently in a single direction. It is characterized by a constant voltage polarity, meaning the positive and negative terminals remain fixed. Due to the continuous flow, the DC welding process produces a stable arc and consistent welding results.
In welding, the direct current flows consistently between positive and negative polarity. However, there is a polarity in DC welding, which will now affect the direction of electron flow. Electrons flow from the negative to the positive polarity, so depending on the terminal of your torch and ground, you can get either Direct Current Electrode Negative (DCEN) or Direct Current Electrode Positive (DCEP) polarity.
Direct Current Electrode Negative Polarity (DCEN)
In the DC negative, DCEN, or straight polarity, your torch is connected to the negative side of the terminal. In contrast, the ground or earth clamp is connected to the positive terminal of the welding machine. As the electrons flow from the negative to the positive side of the cycle or from the electrode into the base metal, 2/3 of the heat is focused on the plate, while 1/3 of the heat is focused onto the electrode.
Source:
https://www.weldinginfo.org/welding-technology/dcen-and-dcep-polarities/
As a result, DCEN welding polarity produces good penetration, stable arc, and consistent results with less spatter or electrode consumption. This makes negative polarity preferred by many welding processes, but that's not always true. The polarity has a different impact on each method, but we'll discuss it later.
Direct Current Electrode Positive Polarity (DCEP)
In the DC positive, DCEP, or reverse polarity, the electrode (torch) is connected to a positive polarity, while the ground is connected to the negative side of the terminal. Due to electron flow, 2/3 of the heat is concentrated into the electrode, while 1/3 of the heat is focused on the base metal.
Source:
https://www.weldinginfo.org/welding-technology/dcen-and-dcep-polarities/
As more heat is focused onto the electrode, the penetration is lower, but the electrode consumption is higher. This is desired when you need higher welding speed, higher deposition rates, and less heat in the base plate. Meanwhile, higher consumption can shorten the electrode life and create more spatter and lack of penetration.
The biggest advantage of DCEP is the cleaning action. As the electrons flow from the base plate into the electrode, they remove the oxide layer that forms on the material surface as it is exposed to atmospheric contamination. Additionally, it can help with dirt, rust, or other contaminants on the surface.
Pros and Cons of DC Welding
Pros of DC welding:
- Deeper penetration: Direct current promotes deep penetration into the base metal, making it suitable for welding thicker materials.
- Stable arc: single direction flow produces a more stable arc compared to AC
- Reduced spatter: DC welding tends to produce less spatter than AC welding, creating cleaner welds with less time spent on post-weld cleaning
- Arc is easy to start: precise control during the start.
- Stable results in overhead and vertical applications: DC welding is often preferred for vertical and overhead welding applications due to its better control and stability.
- Suitable for most electrodes: Most electrode types, such as low hydrogen electrodes, work more effectively with DC, ensuring high-quality welds.
Stick welding with E7018 low hydrogen electrodes
Photo by @weldingandstuff (TikTok)
Cons of DC Welding:
- Limited material compatibility: DC welding is not suitable for all metals, especially the ones with an oxide layer, such as aluminum
- Electrode wear: Electrodes in DC welding tend to wear more quickly than in AC welding, leading to more frequent changes and potential downtime.
- Not suitable for thinner materials: high penetration of DC is not suitable when joining thinner metals
DCEN VS. DCEP VS. AC Penetration Comparison
- Less efficient for long-distance transmission: DC is less efficient than AC for long-distance power transmission, limiting its use in applications requiring power distribution over significant distances.
Alternating Current (AC) Welding
An alternating Current (AC) is an electric current that periodically changes direction, oscillating back and forth. Unlike DC, which flows steadily in one direction, AC reverses its flow at regular intervals. The oscillation intervals are known as a frequency measured in hertz (Hz). 1 Hz means the current alternates between the positive and negative sides once in a second.
Source:
https://www.sunpower-uk.com/glossary/alternating-current/
AC current is standard electricity in both US and European homes. However, the US home outlets provide 110-120V AC power with a 60Hz frequency, while European homes utilize 220-240V with a 50Hz frequency. The role of welding machines is to either use this electricity from the outlet or transform it into the DC.
So, how does the alternating current affect welding? As you weld, your current jumps from the positive to the negative terminal, producing a good balance between penetration and cleaning action. The negative polarity has the penetration, while the cleaning action occurs while the current is in the positive cycle. This makes AC welding advantageous in many applications, but this oscillation doesn't always have the best effect on the arc stability, so we'll explain the impact on the welding processes further.
Pros And Cons of AC Welding
Pros of AC welding:
- Suitable for exotic metals: AC welding is more versatile when welding specific and exotic metals such as aluminum and specific alloys.
- Good performance on rusty or dirty metals: AC welding is practical on surfaces with rust, scale, or contaminants, as the alternating current helps break through surface impurities.
- Reduced Electrode Wear: Electrodes typically wear less in AC welding, leading to longer electrode life and reduced downtime for replacements.
- Suitable for Thin Materials: AC welding is often preferred for thin materials as it provides good control over heat input, minimizing the risk of burn-through.
AC TIG Welding for thin Aluminum
Photo by @vanthefabricator (TikTok)
- Effective for magnetic materials: AC welding is suitable for welding magnetic materials, as the constantly changing current helps avoid arc blow associated with DC welding.
Cons of AC Welding:
- Poor arc stability: AC welding tends to create a less stable arc compared to DC, making it unsuitable for new welders
- Limited penetration: Achieving deep penetration can be more challenging with AC, which makes it less suitable for thick metals
- Increased spatter: AC welding often produces more spatter than DC welding, leading to increased time spent cleaning
Spatter of AC Stick Welding
Source:
- Not great for all electrode types: AC welding is not the preferred choice when using specific electrode types, so make sure you check the manufacturer's recommendations.
- Less efficient for certain processes: In some specific welding processes, such as TIG welding, AC may be less efficient compared to DC, affecting the overall welding performance.
Ac VS DC In Welding
Now that you understand the base differences between DC and AC, it is time to explain their effects on the welding process and help you choose the right one for your welding projects and further applications. AC and DC welding will affect welding arc and overall welding performances differently.
AC vs DCEN vs DCEP Stick Welding Effect Comparison
Source:
So let's see which one is the best for your Stick, MIG, TIG, or Flux-cored arc welding.
Ac VS DC In Stick Welding
Stick welding is one of the few processes that can successfully utilize AC and DC polarity, including DCEP and DCEN. However, DC Arc welding takes part in most Stick welding applications as it provides easier starts, fewer arc outages and sticking less spatter/better-looking welds, easier vertical up and overhead welding, and many consider it is easier to learn how to weld.
The constant polarity flow of DC Stick provides smoother welding output, a more stable arc and better weld quality compared to AC. As we noted, DC arc welding can be carried out at both DCEP and DCEN, and you'll have to check the electrode compatibility.
In Stick welding, DCEP produces 10% higher penetration compared to DCEN, even though the polarity is reversed. As the electrons flow toward the electrode, the focused heat helps melt the electrode, which is then transferred back into the joint, actually leading to higher penetration. Meanwhile, DCEN is used when welding thinner metals due to lower penetration.
AC Arc Welding
Even though Stick benefits most from DC welders, there is a specific weld defect that occurs at DC Stick welding, known as arc blow. Arc blow is a weld defect in which the arc doesn't follow the shortest path between the electrode and joint. The arc wonders, causing it to be highly unstable and hard to control. This issue can be solved by switching to alternating current or AC Stick welding.
AC Stick welding will help you with arc blow, but typically, this current is not recommended. As the current alternates, it can create a highly unstable arc that can extinguish or stick to the base metal. Therefore, welders only recommend AC with stick welding when dealing with arc blow.
Source:
AC VS DC In TIG Welding
TIG welding is one of the most complex welding methods, and when it comes to current, it can use both AC and DC. Welding common steels, such as mild steel, stainless steel, and carbon steel, is done at DC while welding aluminum or magnesium requires AC.
DC TIG Welding Process on Steel
Photo by @vanthefabricator (TikTok)
As a hobbyist, you are likely to use DC TIG welding for your everyday work and DIY projects that involve steel. Unlike Stick, TIG welding is highly impacted by polarity since a tungsten electrode is not consumable, and it can be damaged by high heat. As a result, most welding jobs on steel will require DCEN polarity. DCEP provides lower heat input, which is suitable for thin sheet metal but can cause excessive electrode damage, which is why it is rarely used. Welders found a way to control the heat in TIG using advanced features such as pulse.
DC TIG equipment is typically cheap, but remember that buying a DC-only TIG welder will limit you only to steel welding. We recommend
YesWelder TIG205P DC TIG welder if your projects involve welding steel.
YesWelder TIG205P DC TIG welder
AC TIG Welding
Welders use AC polarity when TIG welding aluminum or other metals that form an oxide layer on the surface. AC in TIG welding provides a perfect balance between heat and cleaning action, which is crucial when TIG welding aluminum. Once the current jumps to DCEN, it provides enough heat to melt and fuse pieces, but aluminum can get pierced due to high heat. That's when DCEP kicks in, as it reduces the heat and removes the oxide layer from the surface.
AC TIG Welding Aluminum
Photo by @vanthefabricator (TikTok)
As a result, AC became a must-have for any TIG welder that regularly deals with aluminum. That's why manufacturers perfected these machines, so now you can adjust the balance or time spent in one or other polarity. That's why DC/AC welders are pricy, but if you are looking for a capable but reasonably priced machine, check out the
YesWelder TIG200P AC/DC welder.
YesWelder TIG200P AC/DC welder
AC VS DC In MIG Welding
MIG welding is one of the most straightforward welding methods that is easy to learn. With the low price of the MIG welders such as
YesWelder MIG 205 DS, it became a foundation for any new welder or a beginner who's getting into the world of welding. One of the reasons MIG is considered easy is the fact it only uses DC current.
YesWelder MIG-205DS-B
The MIG welding process is done at DC, and similar to Stick, it uses a DCEP polarity. Like with Stick/Arc, the heat focused into the electrode helps in melting the wire, which is then sprayed into the welding joint. The heat is transferred through droplets of molten filler metal, which increases the penetration and yields higher deposition rates, which is suitable when you need to get the job done quickly.
DC MIG Welding Process
Photo by @westernweldingacademy (TikTok)
MIG welding at DCEN polarity is not recommended, as it can create a highly inconsistent arc. Lack of heat on the wire will cause a lack of wire metal transfer and less penetration, leading to uneven beads and inconsistent arc. AC output in MIG will also show similar results and inconsistent arc, which is why it is rarely used.
AC VS DC In Flux-Cored Welding
Flux-cored arc welding uses a self-shielded wire similar to a Stick electrode but with a semi-automated welder with a wire feeder, like a MIG welder. You can run a self-shielded wire with the most common MIG welders at DC current or use dedicated DC equipment such as
YesWelder Flux135, but you will have to swap the polarity.
YesWelder Flux-135-PRO
Flux core welding is performed with DC output and negative polarity (DCEN) due to the physics of attraction and repulsion. As the electrons flow from the base metal into the electrode (DCEP), they can attract atmospheric gases and contaminate the core of the wire. Meanwhile, at DCEN, the electrons flow towards weld metal, so the contaminants are focused on the weld joint. However, as the flux layer melts, it grants protection to the weld bead, which makes FCAW widely used for outdoor repairs and on-field jobs.
FCAW Welding Process in Outdoor
Photo by @datboimiggz (TikTok)
AC VS DC Welding - Quick Comparison
| AC | DC |
| Weld penetration | Moderate | High |
| Weld spatter | Moderate to high | Low spatter producing smoother weld |
| Arc stability | It can create an inconsistent arc | Good stability |
| Cleaning action | Good | Poor |
| Filler Metal Deposition | Moderate to low | Average to high with DC+ |
| Arc Blow Risks | Low | Medium to high on magnetized parts |
| Performance on Steel | Not great besides SMAW | Excellent |
| Performance on Aluminum | Excellent with AC TIG | Only good with AC MIG |
| Equipment Cost: | High with TIG | Low |
Conclusion
The choice between Alternating Current (AC) and Direct Current (DC) welding hinges on specific project requirements. DC offers stable arcs, deeper penetration, and efficiency with certain electrodes, making it ideal for various applications.
However, AC's versatility in material compatibility, better performance on dirty surfaces, and cost-effectiveness make it a preferred option in different scenarios. That's why making a decision will ultimately rest on factors like material type, thickness, and desired welding outcomes. We hope our article helped you determine the differences and choose the best current for your future projects.
AC VS DC Welding Explained FAQ
1. How to choose DC or AC when TIG welding: AC VS DC In TIG Welding?
When choosing between DC and AC for TIG welding:
- DC Welding: Ideal for welding common steels (mild, stainless, carbon). Use DCEN polarity for most steel welding to prevent electrode damage. DCEP is used less frequently due to its lower heat input and potential for electrode damage. DC TIG welders are generally cheaper and suitable for hobbyists focusing on steel projects.
- AC Welding: Necessary for welding aluminum or magnesium due to the oxide layer these metals form. AC welding balances heat and cleaning action, preventing the aluminum from piercing while removing the oxide layer. AC/DC welders are more expensive but versatile for those regularly welding aluminum.
For hobbyists mainly working with steel, a DC TIG welder like the YesWelder TIG205P is recommended. For more versatility, especially with aluminum, an AC/DC TIG welder is essential.
2. What is DC (Direct Current) and AC (Alternating Current) in Welding?
DC (Direct Current): An electric current flowing consistently in one direction with constant voltage polarity, producing a stable arc for consistent welding results. It can use DCEN (electrons flow from torch to workpiece) or DCEP (electrons flow from workpiece to torch) polarity.
AC (Alternating Current): An electric current that periodically changes direction, oscillating back and forth at a frequency measured in hertz (Hz). AC is standard in household electricity, differing in voltage and frequency between regions (e.g., 110-120V at 60Hz in the US and 220-240V at 50Hz in Europe). Welding machines can use or convert AC to DC.
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