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Before the advent of inverter-based RF Welder

Before the advent of inverter-based RF Welder, no one even thought about frequency control as a way to improve aluminum welding. The current that came from the wall was the same current that went into the weld—60 Hertz. Since then, countless manufacturers have sworn off 60 Hertz after seeing first hand the benefits of adjustable output frequency.

Before the advent of inverter-based TIG welders, no one even thought about frequency control as a way to improve aluminum welding. The current that came from the wall was the same current that went into the weld—60 Hertz. Since then, countless manufacturers have sworn off 60 Hertz after seeing first hand the benefits of adjustable output frequency.

In AC TIG welding, frequency refers to the number of times every second that the direction of the electrical current completes a full cycle, expressed in Hertz. Frequency is represented by a sine wave, which represents the current flow rising and falling as it reverses direction (see graphic below).

Direct current cannot be used with non-ferrous metals because of the oxide layer that forms on the surface of the base material. In Direct Current Electrode Negative (DCEN) TIG welding, the current flows from the tungsten electrode to the work surface and the positively charged argon gas ions flow from the work surface to the tungsten. DCEN works well for steel and other common types of ferrous metals, but the oxide layer that forms on non-ferrous metals such as aluminum and magnesium melts at a higher temperature than the base metal. Trying to weld with this process causes the base metal underneath the oxide layer to liquefy while the surface remains hard and impenetrable.

Direct Current Electrode Posititive (DCEP) solves the oxide problem because the current flows from the work piece to the tungsten, lifting the oxide off the material in the arc zone. DCEP alone provides the oxide cleaning action and very little penetration. Because the heat is being concentrated on the tungsten instead of the work piece, DCEP also causes the tungsten to ball up at the end.

Alternating Current, then, combines DCEN and DCEP to provide good heat penetration with cleaning action. Historically, though, Alternating Current has posed an obstacle to TIG welding because the arc would frequently extinguish itself as the current reached a zero point before reversing direction. Without any current passing between the tungsten and the base metal, the arc would simply go out.

Improvements in transformer-based TIG machines created the “squarewave,” which increased the amount of time the arc spent at full current flow in both DCEN and DCEP. Squarewave technology eliminated the tendency for the arc to extinguish when the current came to a halt as it reversed directions by making the transition very quickly. This greatly improved the stability of the arc and made squarewave technology the preferred method for TIG welding aluminum and other materials that form an oxide layer, such as magnesium. - See more at: http://www.davison-machinery.com

This was posted in Bdaily's Members' News section by davison-machinery .