Amperage is a critical setting in TIG welding because the amperage control teh heat of the welding arc. Using too much amperage can cause the weld puddle to boil. Using too little amperage can create a weak welding arc causing the weld puddle to not wet out correct.
You must select the correct amperage for the metal being welded and the thickness of that metal. The tungsten electrode is used to create a welding arc. The size of the tungsten electrode are dependent upon the amperage that is to be used.
How to Choose Amperage and Tungsten for TIG Welding
Using a tungsten electrode that is too small for the amperage will cause the tungsten electrode to melt into the weld. Using a tungsten electrode that is too large for the amperage will create a wide welding arc and weld bead. The size of the tungsten electrode should match the thickness of the metal being welded and the amperage setting of the welding machine.
The color bands on the tungsten electrode indicate the types of alloy of the tungsten electrode. Pure tungsten that is green in color is used for welding aluminum as this type of tungsten perform well with the cleaning action of the alternating current needed for welding aluminum. Red thoriated tungsten is used for welding steel as this type of tungsten will maintain its point during the welding process with the direct current used for welding steel.
Grey ceriated and gold lanthanated tungsten is also used in welding as these type of tungsten electrode are non-radioactive and perform well with both alternating and direct current. The tungsten alloy should match the metal being welded for stability of the welding arc and longevity of the tungsten electrode. The settings for amperage for TIG welding will generally follow the rule of one amp for every thousandths of an inch of thickness of the metal being welded.
However, the amount of heat that is required to weld different metals will differ due to the way that each metal conducts heat. For instance, mild steel will require a specific amount of heat to weld. However, stainless steel will require less heat as it is more prone to warping.
Aluminum will require more amp to conduct enough heat to the weld area as aluminum conducts heat quick. Metals like titanium will require the welder to use lower amps and provide full gas shielding as the metal is more reactive and will discolor if exposed to oxygen. Using a foot pedal for TIG welding will allow the welder to adjust the amperage while welding.
Using a foot pedal will allow for increased amperage to assist penetration of the weld and decrease in amperage to prevent blow-through of the weld. When welding aluminum, the welder will need to use alternating current with a balance and frequency setting. The balance controls the ratio of cleaning action to penetration and need to be adjusted to provide enough cleaning action to remove oxide from the aluminum metal.
The frequency of the alternating current will control the width of the welding arc. Using higher frequency will allow for a tighter welding arc for thin sheets of aluminum metal. Additionally, pre-flow and post-flow of gases will be required.
Pre-flow will purge the air from the welding area prior to starting the welding arc. Post-flow will protect the weld and the tungsten electrode after the welding arc end. Insufficient post flow will cause the weld to oxidize.
Stainless steel pipe welds require the use of back purging to maintain the quality of the weld. Back purging will introduce argon gas into the weld to maintain the oxygen levels to 50 parts per million or less. Using too much oxygen during the welding process will result in sugaring of the weld where the weld area will take on a blue or black color.
A successful weld will be a silver color. Additionally, high frequency arc starting will be used to start the welding arc without allowing the tungsten electrode to contact the metal being welded. Using high frequency starting will keep the tungsten electrode free of metal oxidation.
