Oct. 23, 2020
Whenever tungsten inert gas welding is used for aluminum welding, ac will be used. The reason is that the surface of aluminum is covered with a layer of aluminum oxide, which makes the application of aluminum welding extremely difficult.The melting point of the surface oxide layer is close to 2015℃, while the melting point of pure aluminum is only 650℃.This means that when the oxide coating on the surface is welded through, the pure aluminum underneath is also melted, making it impossible to weld further.Welding is only effective if the surface oxide layer is damaged or exposed.
When welding with alternating current, tungsten electrodes continuously switch between positive and negative electrodes.When tungsten is extremely positive, negative electrons move from the workpiece to the tungsten electrode, and the oxide layer breaks in the process.After that, when tungsten is extremely negative, electrons move from the tungsten electrode to the surface of the workpiece, generating heat -- which is necessary for the weld to produce a depth of penetration.
The welding power supply suitable for direct current is equipped with an inverter that generates alternating current.Many welder systems have different Settings to set the alternating current conduction during the anode and cathode current conversion.The user can choose between different half-waves.
For example, current can flow now in the positive electrode region and then with the same intensity in the negative electrode region -- thus forming a constant rectangle on the waveform.Using these Settings, the waveform is very stable, but for welders, the noise can be so annoying that the welder has to wear earmuffs.A smooth sinusoidal waveform is certainly achievable.Although this reduces noise, it also causes arc instability.
In most aluminum welding applications, the combination of the two is the best choice. The negative half wave is a rounded rectangle, and the positive half wave is a sinusoidal pattern.When buying a tungsten electrode, the tip of the tungsten electrode bar is flat.In the case of direct current, the tungsten electrode tip is tapered.To keep the arc steady, however, the top of the tungsten electrode must be turned into a semi-circular arc so that the arc can be fully controlled.This semicircular electrode head is also known as the "cap".
