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Welding Current and Polarity
Outsiders sometimes underestimate the amount of skill and knowledge needed to be a successful professional welder. While you don’t need to be a scientist to work in welding jobs, you do need to have a solid understanding of the basic scientific concepts at work in welding equipment and processes. Not sure if you have what it takes? Let’s run down the basics on a fundamental part of welding science: current and polarity.
Welding School: What is the Meaning of Current and Polarity?
Welding equipment is labeled as either AC or DC. AC stands for Alternating Current, and DC stands for Direct Current. These terms refer to the current flowing through the machine. Electrical circuits have positive or negative poles, which is called polarity.
DC means that the electrical current flows in only one direction. AC means that the current is constantly switching the direction it flows, back and forth, over a hundred times per second.
DC results in constant polarity. AC, on the other hand, changes polarity as the direction of the current switches back and forth.
Why Does Polarity Matter in Welding Jobs?
Polarity matters because it has a direct impact on the strength and quality of your weld. Using the wrong polarity means more spatter and less control.
But which polarity is right and which polarity is wrong? Let’s talk about polarity types.
Types of Polarity in Welding
- DC straight polarity – This happens when the plates are positive and the electrode is negative. More heat is generated at the electrode and less is generated at the base plate. This can result in defects like lack of penetration, poor fusion, and high reinforcement (unnecessary extra metal beyond what’s needed to fill a joint.)
- DC reverse polarity – This happens with a positive electrode and negative plates. In this case, more heat is generated at the base plate versus the electrode – the reverse of DC straight polarity. This helps with faster welding and has less chance of causing defects. It’s best for thinner metals but might not be great for thicker ones or those with high melting points. There may be a lot of reinforcement needed, and it can shorten electrode life.
- AC polarity – This happens when an AC power source is used, causing reverse and straight polarity to rapidly switch back and forth, 50-60 times each second. As a result, it blends the characteristics of straight and reverse polarity.
The Right Polarity for the Job
As you might be starting to see, there is no single answer to the question of which polarity is “right.” You have to consider things like the thickness of the material and its melting point. Different polarities work better for different materials. DC welding is good for steel and stainless steel welding and is very stable. AC welding is popular for welding magnetized materials. The right choice of polarity also depends on whether you’re doing stick welding, MIG welding, TIG welding, or flux core welding. (Don’t know what those terms mean? Poke around our blog some more.)
Learn the Science of Welding Success at ETI
El welding program at ETI School of Skilled Trades will give you the foundational scientific and technical knowledge and hands-on skill you need to flourish in a career as a professional welder. All classes are taught by experienced instructors, and you’ll be able to practice in our 13,000 square foot welding lab with modern industry equipment. The proof of our program’s quality is our 20-year relationship with local Chicago-area employers who keep coming back to hire ETI graduates. Enroll today!
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