Soldagem de alumínio AC: você realmente conhece?

AC aluminum welding: do you really know it?

Aluminum welding is conducted using tungsten inert gas (TIG) welding, with alternating current (AC) as the power source. This is because aluminum is covered by a layer of aluminum oxide, making welding difficult. The melting point of the surface oxide layer is close to 2015°C, while the melting point of pure aluminum is only 650°C. This results in the fusion of the oxide layer and the pure aluminum beneath it, making subsequent welding impossible when the oxide layer is penetrated during welding.

Effective welding can only be achieved when the surface oxide layer is damaged or exposed. During AC TIG welding, the tungsten electrode continually switches between positive and negative polarity. When the electrode is positive, negative electrons move from the part to the electrode, causing the oxide layer to rupture. As the electrode becomes negative, electrons move from the electrode to the workpiece, generating heat and allowing the weld to penetrate.

Related reading: Aluminum alloy welding: method and material selection

Waveform is

The welding power source designed for direct current is equipped with an inverter that produces alternating current.

Many welding machines have several settings that allow you to adjust the AC conductance during positive and negative current conversion.

Users can choose from several half wave options.

Example: Current can flow in a positive range and then change to a negative range with equal intensity, forming a constant rectangular waveform.

With these settings applied, the oscillogram will be stable, but the intense noise generated during the welding process can disturb the welder, requiring the use of ear protectors.

A smooth sine waveform is also an option. However, this will reduce the noise level but will result in an unstable arc.

For most aluminum welding applications, the ideal choice is a combination of both waveforms. The negative current half wave is represented by a rectangular waveform with rounded corners, while the positive current half wave is sinusoidal.

The Vonnex welding system also offers a triangular waveform, which can be combined with other waveforms for a stable, high voltage arc. The welder can choose the most suitable configuration for each specific application.

Cap

When purchasing tungsten electrodes, the top of the electrode rod must be flat.

When using direct current, the tip of the tungsten electrode is typically cut into a sharp shape.

However, to maintain a stable arc, the top of the tungsten electrode tip must be shaped into a semicircular arc when working with alternating current, as this allows better control of the arc.

This semicircular electrode tip is commonly called the “cap”.

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