TIG welding polarity is an important factor that affects the success of any welding. Polarity refers to the direction of electric current and its effects on a weld. With TIG welding, there are two main types of polarities: Direct Current Electrode Negative (DCEN) and Alternating Current (AC). The negative torch is used for TIG welding mild steel, stainless steel, copper, and titanium, while AC is typically used for aluminum and magnesium.
What is Tig Welding Polarity?
Tig welding, also known as Gas Tungsten Arc Welding (GTAW), is a versatile and precise welding process used to join a wide range of metals. Polarity, in the context of Tig welding, refers to the direction of current flow between the welding torch and the workpiece. The two primary polarities used in Tig welding are Direct Current Electrode Negative (DCEN) and AC/DC but NEVER Direct Current Electrode Positive (DCEP).
Direct Current Electrode Negative Polarity (DCEN)
In direct current (DC) polarity, the electrode is connected to the negative ( – ) side of the welding power source and the metal workpiece is connected to the positive ( + ) side. This type of polarity creates a stable arc with 70% of the heat concentrated on the tip of the material being welded. It is the preferred choice for ferrous metals like steel and stainless steel, as it produces a deep penetration weld.
DCEN polarity, also referred to as straight polarity or electrode negative, involves the flow of electrons from the tungsten electrode to the workpiece. In this configuration, the tungsten electrode serves as the negative terminal, while the workpiece acts as the positive terminal. DCEN polarity is commonly used for welding non-ferrous metals, such as aluminum, magnesium, and copper.
Positive Polarity For GTAW
During TIG welding, the negative torch or TIG torch is never on the positive polarity terminal of the power supply. This is because negative polarity is best for certain types of weld metal like mild steel, stainless steel, copper, and titanium. However, the welding machine, specifically AC/DC TIG welding machines, switches the current multiple times a second measured in hertz. This characteristic comes into play when dealing with aluminum or magnesium, as the swift current shift aids in oxide cleaning action and prevents shallow penetration, which could lead to weak joints.
Alternating Current Polarity
Alternating current (AC) polarity is the opposite of DC polarity, with the electrode connected to the negative (-) side of the power source and the metal workpiece connected to the positive terminal (+) side. This type of polarity produces a more shallow penetration weld, but it is beneficial when welding aluminum and magnesium due to the oxide layer that forms on these metals. AC polarity helps by the positive electrodes flowing from the workpiece to the electrode displacing the oxide layer.
Understanding the Effects of Polarity
The choice of polarity in Tig welding has a significant impact on the welding process and the resulting weld quality. Let’s explore the effects of each polarity in detail:
1. DCEN GTAW Polarity Effects
- Increased heat at the workpiece: DCEN polarity concentrates heat at the workpiece, leading to improved penetration depth.
- Narrower arc cone: DCEN polarity produces a narrower and more focused arc cone, enabling precise control over the welding process.
- Lower tungsten consumption: Due to reduced tungsten erosion, AC/DC polarity results in lower electrode consumption, leading to cost savings.
2. AC/DC TIG Welding Polarity Effects
- Enhanced oxide cleaning action for aluminum welding: The electron flow from the tungsten electrode to the workpiece creates a cleaning effect, removing impurities and oxides from the weld metal surface.
- Tungsten selection: The AC/DC polarity switching limits the types of tungsten electrodes for aluminum.
- Wider arc cone: AC/DC polarity creates a wider arc cone, suitable for wider cleaning action giving increased productivity from cleaner quality welds.
- Higher electrode wear: DCEP polarity accelerates tungsten erosion, leading to increased electrode consumption and the need for more frequent electrode sharpening or replacements.
- Insufficient fusion can occur if there’s an overemphasis on AC balance on the positive side during TIG welding. This imbalance can lead to a reduction in the heat focused from less direct current on the workpiece, resulting in inadequate proper penetration and potentially weaker welds.
Choosing the Right Polarity for Your TIG Welding Project
When determining the polarity for your Tig welding project, several factors come into play. Consider the following guidelines to select the appropriate polarity:
- Material Type: Determine whether the base metal is ferrous or non-ferrous. Ferrous metals generally require DCEn polarity, while non-ferrous metals benefit from DCEP polarity.
- Welding Process: Assess the specific welding process requirements, considering factors such as heat input, deeper weld penetration, and desired weld appearance.
- Electrode Selection: Different tungsten electrode types have varying characteristics and performance under different polarities. Consult our non-consumable electrodes recommendation for optimal polarity usage to extend tungsten electrode life.
Using Reverse Polarity For TIG
TIG welding, the electrode should never be connected to the positive terminal (also referred to as reverse polarity or Direct Current Electrode Positive (DCEP)). When you use positive polarity (DCEP), more heat gets focused on the tungsten electrode itself. This can cause the tungsten to heat up and wear down faster. This is known as Thermonic emission.
Thermionic emission is like a process where electrons escape from a metal. This happens when the metal gets really hot, in this case, from the electricity used during welding. The electricity creates a lot of heat (like when a wire gets hot if too much electricity goes through it), and this heat gives energy to the electrons in the metal. If they get enough energy, they can break free from the metal. This energy needed to set them free is what we call the work function.
“Work function” is a scientific term. It’s used in physics to describe the minimum amount of energy that is required to remove an electron from a metal surface. This term is particularly important in understanding phenomena like the photoelectric effect and thermionic emission. It’s like the “energy price” an electron has to pay to escape from the metal.
Effects of Polarity In Welding Applications
The choice of polarity has an effect on the overall quality of the weld, as well as the rate at which the weld is completed. DC polarity produces a higher concentration of heat than AC polarity, allowing for deeper penetration. AC polarity provides a shallow wider weld profile but an increased cleanliness of the weld area.
Which Polarity Is Most Widely Used In TIG Welding Conclusion
Understanding and appropriately selecting the correct polarity in TIG welding is vital to achieving high-quality welds. Polarity refers to the direction of electric current between the welding torch and the workpiece, significantly affecting the welding process, rate, and overall weld quality. In TIG welding, the two primary polarities are Direct Current Electrode Negative (DCEN) and Alternating Current (AC). DCEN, commonly used for welding ferrous and non-ferrous metals, focuses heat on the workpiece for deep penetration. On the other hand, AC polarity, mainly used for aluminum and magnesium, helps remove oxides due to its swift current shift and cleaning action.
It’s crucial to remember that in TIG welding, the electrode should never be connected to the positive terminal, a setup known as reverse polarity or Direct Current Electrode Positive (DCEP). Such a configuration can lead to quicker tungsten wear and weaker welds due to thermionic emission, where more heat gets focused on the tungsten electrode, causing it to heat up and wear down faster.
Furthermore, keep in mind that an overemphasis on the positive side in AC balance can cause insufficient fusion due to less direct current, resulting in inadequate penetration and potentially weaker welds. Therefore, it’s essential to understand the material type, welding process requirements, and electrode selection when determining the correct polarity for your TIG welding project.
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