ac dc tig welderAn AC DC TIG Welder (the full name is alternating current / direct current tungsten inert gas welder), also known as an AC DC GTA welder (alternating current / direct current gas tungsten arc welder), is a set of devices that use a non-consumable tungsten electrode to produce the weld. The torch can be either manual or automatic in operation and is either air-cooled or water-cooled. A shielding gas (commonly argon) is used to protect the area being welded from contamination by atmospheric gases such as nitrogen and oxygen, which can make the weld ineffective. Filler metals are commonly used as in other types of welding, except for autogenous welds that do not require them. The constant-current power supply produces energy across the arc via the state of matter called plasma (simply defined as a gas whose particles are ionized). The process itself is an outgrowth of arc welding.

Alternating current means that the flow of electric current changes direction, from negative to positive; while direct current means that the flow is in only one direction. This is important, since those two currents are suited for different types of metals to be welded.

The DC-only TIG welder, which is usually small-range and has average amperage of 130 amps is meant for steel, nickel, and titanium and comes with two preferred polarities – a negatively charged electrode (DCEN or straight polarity) or a positively charged electrode (DCEP or reverse polarity).

The AC DC TIG Welder, which is in the middle and large ranges and can have 160-250 amps for the middle range and up to 650 amps for the large range combines the power of both DC properties and is meant for aluminum and magnesium, though steel can also be applicable. There is really no set rule for currents and their respective metals, but there are things to keep in mind. Oxides must be removed regardless of source metal(s) using the AC wave’s reverse polarity, creating a cathodic etch and a wide, shallow weld; and the electrode must not overheat from the AC wave’s straight polarity for the resultant deep and narrow weld to be solid and pore-free.

This can be simplified as “cleaning versus penetration”. The combined currents in the AC/DC welder, which is manifested in a feature called slope control, provide a happy balance between the two opposing particulars and can be adjusted. This welder, therefore, is versatile and can be used in bonding dissimilar metals, which is prevalent in repair work. When melding dissimilar metals, it is important not to melt excessive base materials, and a welder’s setting of 7 gives a balanced weld while maintaining versatility. And with wrong slope control, rectification (failure of the arc to reignite as the polarity switches from straight to reverse and thus AC is converted to DC) will ruin the weld.

With all those complexities and more involved in TIG welding in general (in fact, it is the most difficult and one of the most expensive of all the welding processes used in industry), great skill and proper protection must be inculcated, lest risks to the skin and eyes from ultraviolet radiation and exposure to dangerous gases harm the operator. In fact, those who aim to enter this profession must first be certified by the American Welding Society or the American Society of Mechanical Engineers. Defective welds arise from too little or too much heat input; as well as improper positioning of the welding torch, improper amount of current used, and insufficient gas shielding.

The complications involved nevertheless yield the strongest bonds yet. With TIG welding, the resultant bond is concentrated, clean, and does not affect the base metal(s) too much; there are no sparks or spatter generated (and thus little smoke is produced); and there is greater control involved since the settings from the power source are highly adjustable and a foot control provides additional accuracy and precision. It is the preferred welding method in the production of aircraft since its inception in the 1920’s, and Linde Air Products (now L-Tec) codified the standards after the Second World War (the third term for TIG welding, heliarc welding, was a trademark by Linde).

All the things associated with an AC DC TIG Welder may be too much to bear for a first-time welding operator, but this complication serves a greater purpose: the strongest bonds ever made in metalworking.