AC vs DC Welding - 5 reasons which one is right for your ...

Although DC welding is preferred, in some cases AC welding may provide a better solution. In this article, I’m going to open it up a bit and explain why it’s important for you to understand.

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If you're familiar with or working in the welding industry, you might have heard these terms: AC and DC. These refer to two types of current used in the welding process. Welding uses an electric arc to initiate the heat process needed to melt the metal. The aim is to produce a stable current flow with varying polarities depending on the material to be welded.

Understanding these two currents and their impact on welding machines and electrodes is crucial for making good welds. We need to explore AC vs DC welding and their differences.

The polarity of the current passing through the electrode of the machine determines whether it's AC or DC welding. The welding strength & quality depend on the electrode's polarity.

Neither DC nor AC is inherently superior. They have distinct characteristics, and the one you choose depends on various factors, discussed below to better understand the differences between DC and AC welding.

Analysis of AC welding

Alternating Current (AC) causes electrons to flow back and forth. These electrons switch directions at a speed of 120 times per second. AC is called alternating current because of its continuous change in direction.

In most scenarios, AC is considered inferior for welding, making DC the more natural choice. However, this isn't universally true, and it depends on many factors, which we'll discuss further.

Instances where AC welding is superior

AC welders are cheaper than DC welders, making them a natural choice for beginners based on price alone. In situations where only AC welders are available, they become the obvious choice.

Welding magnetic materials necessitates AC because it creates a steadier arc, significantly reducing arc blow, a common issue with DC welders.

AC welders are ideal for welding aluminum, which requires very high temperatures, producing a stable and high-temperature arc.

AC welding penetrates deeply into metal plates, making it suitable for applications like shipbuilding.

Shortcomings of AC welding

Despite its advantages, AC welding isn't always the first choice due to several drawbacks. The main issue is the continuous alternation of current direction. When the current changes direction, there's a moment with no amperage.

AC welders experience more arc fluctuation, making DC welders more accepted for their easier and cleaner welds.

AC welding generates more spatter, making it less suitable for overhead and vertical welding.

Advantages of AC welders

• AC machines are usually more affordable.

• Arc blow issues can be managed more easily.

• Ideal for aluminum welding.

• Best for magnetic field welding.

Disadvantages of AC welders

• AC welders don't produce smooth welds.

• More fluctuation compared to DC welding.

• Generates maximum spatter.

• The arc is challenging to control.

Analysis of DC welding

DC welding is more commonly used than AC welding and is considered superior. DC current flows continuously in one direction. The arc is constant and flawless.

This current type is used in batteries and low-voltage devices. Cars also utilize DC electricity.

Where DC welding is a choice

The arc in DC welding is stable, avoiding zero amperage moments found in AC welding. This stability allows for easier control of the arc, resulting in clean, smooth, and spatter-free welds.

DC welding produces less spatter and is a better choice for overhead and vertical welding compared to AC welding.

DC welding is ideal for beginners. It allows for attractive welds with minimal learning. As such, DC is the most common welding choice.

Shortcomings of DC welding

There are instances where DC welding may not be the best choice. Arc blow in DC welding is problematic for magnetic materials.

DC welding doesn’t reach the high temperatures of AC welding, making it unsuitable for aluminum.

While DC is generally preferred, the higher cost can make it challenging for beginners to choose over the less expensive AC welder.

Advantages of DC welding

• Very stable arc.

• Produces smooth welds.

• Minimal spatter.

• Easy to operate.

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Disadvantages of DC welding

• Expensive equipment.

• Arc blow issues.

• Not suitable for aluminum.

Is DC/AC welding superior?

Deciding which welding process is superior is complex. The reality is that each has its advantages depending on the situation.

The choice between AC and DC welding depends on the specific scenario. Each welding type may be better suited to particular conditions.

Aluminum Welding

AC welding is better when welding aluminum. AC welding achieves higher temperatures, essential for aluminum welding.

DC welders can't reach the same temperature, making them less suitable for aluminum welding.

Thin metals welding

The lower temperature of DC welding makes it suitable for thin metals, preventing them from blowing out as they might with AC welding.

Beginners or Novices

DC welding is easier to master and offers clean welds, making it ideal for novices. However, the higher cost of DC welders might push beginners towards more affordable AC welders.

Deep Penetration

Thick metal workpieces need deep penetration for firm adherence, making AC welding better for such tasks.

Vertical and Overhead Welding

DC welding is clean, non-messy, and produces minimal spatter. This makes DC welding ideal for vertical and overhead positions.

Magnetized Metals

For welding magnetized materials, AC is preferred due to the absence of arc blow, a common issue with DC welders.

Situations for DC Welding

• When affordability is not an issue.

• When smooth and clean welds are needed.

• Thin metals welding.

• Overhead and vertical welding.

• Novices with little welding experience.

Situations for AC Welding

• Limited budget.

• Weld's appearance isn't a concern.

• Deep penetration is required.

• Welding magnetized material.

• Welding aluminum.

See also: A Guide To Aluminum Welding Process, Understanding Aluminum Welding Process Compared With Steel Welding

Difference between DC and AC welding

DC Welding AC Welding

AC Welding

The initial cost is high. AC welding machines cost less than DC equipment.

All types of welding electrodes can be used. Bare electrodes can't be used. Only specially designed coated electrodes are applicable.

Maintenance costs are higher compared to AC welding. Maintenance costs are lower than in DC arc welding.

Compared to AC, the welding output is smoother. Weld quality isn't as smooth as DC welding.

Stable Arc Unstable arc

Heat distribution at the two poles differs (polarity). Heat distribution is uniform.

Arc blow is severe. Arc breakdown doesn't occur.

DC positive electrodes provide greater weld metal penetration. Less penetration into weld metal.

Less spatter. AC welding produces more spatter than DC welding.

Straight polarity can weld thinner metals better than AC. Not recommended for thinner metals.

More suitable for overhead and vertical welding. Better with flat-position welding.

The following table compares welding process electrical characteristics:

Inference

After comparing Alternating Current (AC) and Direct Current (DC) welding, we conclude that there is no definitive answer to which one is better. Each has its strengths and weaknesses. Depending on circumstances, each type can be superior. Therefore, mastering both methods is advisable. If forced to choose one, DC welding is generally preferable. It works on a wide range of metals, produces smooth welds with minimal spatter, and is easier to master. However, keep in mind that it is more expensive than an AC welder.

I, like many others, learned to weld with an old Lincoln cracker box (AC only machine). If you can learn to weld on AC, switching to DC is like a dream. DC gives a much smoother arc. Remember, on A/C current the arc tries to extinguish itself 120 times per second (60hz). That's one reason why it's hard to strike and maintain an arc when first beginning with A/C. As for spending extra money on a machine capable of DC, it's all relative. Lincoln makes an AC/DC cracker box that’s versatile for almost any around-the-house projects. Consider what you'll be welding and make the best financial decision. If you get a DC-capable machine, you won't regret it. It allows for a broader range of electrodes and makes welding easier. Plus, you can convert any DC stick welding machine to a scratch start Tig welder!

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