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Unlike steel, titanium, and most other metals that are TIG welded with Direct Current Electrode Negative (DCEN), aluminium is usually TIG welded with Alternating Current (AC). The AC waveform consists of an Electrode Positive (EP) and an Electrode Negative (EN) portion. The EP portion of the AC waveform helps to remove the aluminum oxide layer on the aluminium alloy, thereby ensuring a high-quality and clean weld. The EN portion helps with penetration of the base metal.
Traditional AC TIG machines were made with transformer technology and produced a sine wave waveform at a frequency of 50Hz/60Hz, depending on the line current the welding machine was connected to. Sine waves produce a very smooth welding arc and is the traditional welding arc for aluminium welding.
With the advancement of technology, welding manufacturers incorporated inverter technology into the welding machine. This meant that welding manufacturers were now able to modify the traditional sine wave to produce different AC waveforms for different TIG welding applications.
The first modified AC waveform was the square wave. Compared to the sine wave, the square wave transfers considerably more heat into the metal. In addition, the square wave also allows for instantaneous switching between the EN and EP portion of the AC waveform. As a result of these two differences, the welding arc produced by the AC square wave “feels” different as compared to the sine wave, and also allows for much faster travel speeds.
The first AC square wave waveform had a symmetrical shape. The amplitude of the current in the EN and EP portion was the same, and the amount of time spent in the EN and EP portion of the cycle was also similar.
As welding technology grew more sophisticated, welding manufacturers found a way to produce asymmetric AC square wave waveforms. This meant that welders could independently adjust the amplitude and the balance of the EN and EP portion of the AC waveform. Having precise control of these parameters allows the welder to optimize the TIG welding arc for specific applications. For example, if the application requires the welder to build up a surface, increasing the EP portion of the AC cycle can help result in a broad weld with shallow penetration. Alternatively, if a welder is already operating at the upper limit of the welding machine, the welder can consider increasing the amount of time spent in the EN portion of the AC cycle to increase penetration.
The default AC waveform for most of the Miller Electric TIG welding machines is the soft square wave. This is a unique blend of both the sine wave and square wave. Soft square wave provides good puddle control and arc stability and is ideal for most welding applications.
Lastly, the triangular AC waveform is also made possible by inverter technology. Triangular AC waveform is ideal for welding of very thin materials, as the minimal heat input during welding helps to reduce chances of distortion.
For all of the AC waveforms mentioned above, a welder can change the balance between the EN and EP portion of the AC cycle. However, for most aluminium welding applications, a 75% EN, 25% EP, soft square wave will be a good starting point. If you have any further questions, feel free to reach out to us at sgoffice@millerwelds.com