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The difference between welding AC and DC

I

Welding Arc Stability

AC Welding: The stability of AC arc is relatively poor. The direction of the alternating current changes periodically, and the arc will extinguish and re-ignite when the current crosses zero. This causes the arc to easily flicker and be intermittent.

Example: When using AC power for welding during SMAW, the welder can clearly feel that the arc is not as stable as DC, and this instability will affect the shape and size of the molten pool, making the welding process more difficult to control.

DC Welding: DC arc has good stability. Because the direction of the DC current is constant, there will be no current zero crossing, so the arc combustion is more stable. Especially for some welding processes that require high arc stability, such as gas shielded welding (such as argon arc welding), the use of DC power supply can obtain a stable arc, which is conducive to accurately controlling the welding pool, thereby improving the welding quality.

Example: When welding thin plate materials, a stable DC arc can avoid burn-through and better control the shape of the weld.

II

Welding Polarity (for DC Welding)

1. Positive Connection

The workpiece is connected to the positive electrode, and the welding gun is connected to the negative electrode. This connection method is suitable for welding thick workpieces. Because during positive connection, the workpiece is connected to the positive electrode, and the heat is mainly concentrated on the workpiece. According to Joule’s law, when the current is the same, because the positive electrode generates more heat, it can quickly melt thicker workpiece materials.

Example: When welding thick steel plates, using direct current connection can melt the steel plates faster and improve welding efficiency.

2. Reverse Connection

The workpiece is connected to the negative electrode and the welding gun is connected to the positive electrode. Suitable for welding thin workpieces and non-ferrous metals. When the workpiece is connected to the negative electrode, electrons flow from the negative electrode (workpiece) to the positive electrode (welding gun). At this time, most of the heat is concentrated on the electrode of the welding gun, and the heating of the workpiece is relatively gentle. For thin workpieces, this connection method can prevent burn-through due to overheating. When welding non-ferrous metals such as aluminum and magnesium, reverse connection can also use the cathode crushing effect to remove the oxide film on the surface of the workpiece and improve the welding quality.

Example: When welding aluminum alloy thin plates, DC reverse connection can effectively avoid burn-through, and can clean the oxide film on the surface of the aluminum alloy to ensure good bonding of the weld.

III

Cost and Complexity of Welding Equipment

AC Welding Equipment

Relatively simple structure and low cost. The AC power supply has a relatively simple structure and does not require complex rectifier devices.

Example: Common AC manual arc welding machines are relatively cheap and have low maintenance costs. This makes AC welding equipment widely used in some situations where the welding quality requirements are not particularly high and the budget is limited, such as the welding of some simple steel structural parts.

DC Welding Equipment

More complex structure and higher cost. Since AC power needs to be converted into DC power, complex electronic components such as rectifiers are often included.

Example: DC argon arc welding equipment is more expensive than AC argon arc welding equipment, and its maintenance requires professional technicians because once the internal electronic components fail, repairs are relatively complicated. However, its high-performance welding quality makes it widely used in high-end manufacturing fields such as aerospace and automobile manufacturing.

VI

Applicable Range of Welding Materials

AC Welding: AC welding has certain advantages for welding some magnetic materials. Because alternating current can overcome the magnetic deflection phenomenon of magnetic materials.

Example: When welding some magnetic alloy steel, AC welding can reduce the arc deflection caused by the magnetic field and make the weld more uniform. At the same time, AC welding is also suitable for the welding of ferrous and non-ferrous metals that do not require high welding speed and relatively moderate quality requirements.

DC Welding: DC welding has a wider application range, especially for welding with high quality requirements. It can be used to weld various ferrous metals (such as carbon steel, alloy steel) and non-ferrous metals (such as copper, aluminum, titanium, etc.). For some active metals, such as titanium, DC welding can effectively prevent metal oxidation and ensure welding quality under appropriate protective gas.

Example: In the aerospace field, titanium alloy parts are usually welded using DC welding methods to ensure the strength and corrosion resistance of the weld.

Post time: Jun-18-2026

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