Is DC welding easier than AC?

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While AC/DC might make most reminisce about a certain era of rock music &#; I know I listened to plenty of the band&#;s music on KSHE 95 in St. Louis &#; to welders it means polarity. Stick welding is polarity driven. Direct current (DC) is used on most stick welding applications. Alternating current (AC) is typically only used as a second option.

DC stick welding offers advantages over AC when welding steel, including smoother and more stable arcs, easier starts, fewer arc outages, less spatter and easier vertical up and overhead welding. DC positive polarity provides a high level of penetration into the steel. DC negative polarity results in less penetration but a higher deposition rate. It is sometimes used, for example, on thin sheet metal in an attempt to prevent burn-through.

&#;Because AC polarity is half DC positive and half DC negative, it is right in the middle,&#; says Kevin A. Beardsley, application engineer, The Lincoln Electric Co. &#;You can choose AC if you don&#;t want to go DC negative because you don&#;t want that much penetration.&#;

Beardsley emphasizes AC is almost always a secondary choice. Most welders don&#;t bother changing polarity because their other jobs run on DC positive.

When in need

There are, however, a few situations where AC polarity is used. The obvious one is when the only available power supply has AC output only. This is typical with low-cost, entry-level welding machines, such as the &#;buzz box&#; welder.

&#;Also, there are some specific technical problems associated with using DC polarity, and number one is arc blow,&#; says Eric Stewart, pipewelding technologist at Lincoln. &#;When welding, that arc has a shape and the welder wants to direct that arc into the joint to get full penetration. When there is arc blow, that arc is blowing to one side or the other.&#;

An effective fix to arc blow problems, therefore, is switching to AC instead of DC polarity. The arc blow can be caused by magnetism in the material being welded or can be induced by the arc&#;s current.

&#;You can magnetize with current flowing through, so where you put your grounds and things like that can impact arc blow. The arc is going to wander,&#; Stewart says, also mentioning that another possible cause can be an external source, such as windy conditions.

Because AC alternates between positive and negative polarity, it enables magnetized parts to be welded.

&#;If you were welding in a box and pushing toward the intersection where the vertical line comes down, the two horizontals meet into a corner,&#; Stewart says. &#;The magnetic forces in relation to joint geometry actually at that point create a turbulent puddle and that will result in a tremendous amount of spatter.&#;

When in use

One specific industry for AC stick welding is in shipbuilding, particularly when welding into a corner and arc blow becomes a problem. Another area is maintenance and repair.

&#;Those are the guys that will use AC stick welding more than anyone as a primary option,&#; Beardsley says. &#;Maintenance and repair welding requires work on machines that are magnetized. Also, maintenance and repair work can involve a lot of rusty weld areas, where you don&#;t want high penetration.&#;

A switch to AC polarity requires a power supply and electrode both designed to run AC. Again, because any production type of process is probably going to be DC, &#;if you want an AC capability, you have to specify that,&#; Beardsley says. AC/DC power supplies are available but on the higher end models.

Which stick?

With many electrodes, the arc tends to frequently extinguish on AC polarity. At the instant of the switch, the arc actually goes out and then has to re-establish itself. Electrodes are available with specific elements in their coating that operate on AC polarity to keep the arc ignited.

The welding rods have a high cellulose potassium-type coating. These rods can be used with AC and DC polarity for all-position welding. They work especially well for welding rusty, dirty or older metal or making repairs outside where it&#;s windy. The rods are the AC version of the popular welding rods for DC. The have a high cellulose sodium-type coating, can penetrate deeply and are used for many applications in the field.

Both are fast-freeze rods, meaning the weld puddle changes from liquid to solid rapidly, and are used primarily by pipefitters and pipe welders. Sizes vary, but 1.8 in. to 5/32 in. are prominent. Other AC welding rods include , and .

The rods are all-position AC or DC polarity for welding new, clean sheet metal applications because they penetrate less but don&#;t burn through the metal.

The welding rods are used for pipe welding and structural steel welding and repair welding. This low-hydrogen, usually DC, all-position electrode can also be used with AC, which not many welders may know. The provides a good bead appearance and smooth, strong welds. It also works on higher strength steels.

The welding rods, commonly referred to as Jet Rod, run well on AC. They are a good general-purpose rod with a high deposition rate for flat and horizontal welds and are typically used to make large welds. They have a heavy iron powder content. The rods are used for general fabrication, including deep grooves and big ships where a high-deposition rate is required.

Both the and rods are also known as &#;drag rod,&#; where the end burns off slightly inside the flux coating, allowing the welder to drag the rod along the joint. The heavy slag should just peel off leaving a smooth weld.

The Lincoln Electric Co.

Mention AC/DC to most people, and they will immediately think of a popular Australian hard-rock band. On the other hand, welding professionals recognize it as polarity, referring to the negative and positive poles formed in the electrical circuit as soon as you turn on a welding machine.

What makes polarity so important in welding? Choosing the correct polarity can ensure the strength and quality of the weld, while the wrong one can cause poor penetration, excessive spatter, and less control of the welding arc.

Welding professionals often talk about the pros and cons of AC vs. DC welding. The primary difference is polarity: AC (alternating current) welding alternates rapidly between DC negative and DC positive, while DC (direct current) uses a straight polarity current to supply electricity to the electrode. Which of these you choose will depend on specific factors, so here&#;s what you should know:

AC welding definition

AC welding means you are using an alternating current in the welding process. The alternating current reverses its direction many times per second. For instance, a 60-hertz current will alter its polarity 120 times per second. Since the magnetic field and current reverse direction, it allows for a steadier arc on magnetic parts.

DC welding definition

DC welding employs a direct current with constant polarity flow in one direction. The current can be positive or negative, with positive polarity flowing from the welder to the workpiece to the electrode and back to the welder. The current flows from the welder to the electrode to the workpiece and then back to the welder with negative polarity. Electrode positive welding offers deeper penetration, while electrode negative provides faster deposition rates.

AC welding vs. DC welding

Even though DC welding is preferred for most welding applications, AC welding works well in some specific applications. TIG welding aluminum, welding magnetized metals, downhand welding on heavy plates, with fast-fill electrodes, and welding where the only electrical outlets are 110 volts all lend themselves to AC welding. Unlike DC welding, arc blow is far less noticeable when welding with AC.

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On the other hand, direct current maintains a constant and stable arc and is more reliable than AC. It typically produces a smoother weld with less spatter because of the continuous direction of the current. DC also welds thinner materials better than AC, working best with stick welding, stainless steel TIG welding, and vertical or overhead welding.

Electrode negative vs. electrode positive

As mentioned earlier, the DC current can be positive or negative. But how does that affect the welding process?

Sometimes called straight polarity, electrode-negative polarity is preferred for most welding jobs. It produces a hotter arc and faster electrode melting, allowing operators to be more productive and lay down a bead faster. Straight polarity DC will almost always be a welder&#;s first choice unless a specific need for something else comes up.

Electrode-positive polarity, also referred to as reverse polarity, generates deeper penetration. Even though it is slower than straight polarity, it is usually the choice for welding thick material. The advantage of reverse polarity becomes evident when working with metal more than half an inch thick.

AC welding vs. DC welding: summing things up

AC Welding

DC Welding

Polarity

Alternating polarity

A single polarity that could be positive or negative

Applications

Magnetized metals, aluminum, heavy plates

Stainless steel, overhead, vertical, and thinner plate welding (Most applications)

Weld strength

Weaker with more spatter

Stronger and smoother

Arc blow

Fixes arc blow issues

Can cause arc blow

Arc stability

Arc can be hard to work with

Stable arc

Welding machines

Less expensive, portable

More expensive and heavier

The answer is: it depends on your situation. While DC welding will probably be your first choice, each type of welding has some distinct advantages in specific circumstances. If you&#;re starting your welding career, DC welding is easier to work with and results in cleaner welds. However, DC welding machines are typically more expensive than AC, prompting beginners to lean toward the more affordable welders.

Since each has its strengths and weaknesses, you might be better served with a welding machine that can do both!

Thanks for reading.

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