Slope Up/Down - Slope Up is where the Tig Welder starts the welding arc at a very low current, then smoothly brings the welding power up to the level set by the operator. Some Tig Welders have a pre set Slope Up time that cannot be adjusted, some have manual control that allow different Slope Up times to be set. Slope down works in the same way but at the end of the weld. When the torch trigger is released, the Tig Welder will fade the power down, instead of stopping it suddenly. Stopping a Tig Welder arc suddenly can cause the centre of the weld to sink (known as "Cratering"), sometimes even to the extent that a pin hole appears. Fading the Tig Welders arc allows the weld pool to solidify more slowly to avoid Cratering.
Pre/Post Welding Gas Flow - As the name suggests, Pre Welding Gas Flow is where the Tig Welder turns on the gas before the arc. This ensures a good welding gas shield. Post welding Gas Flow is where the Tig Welder keeps the welding gas flowing after the arc has extinguished. This is important as it prevents the hot tungsten Tig welding electrode from oxidising as it cools.
Pulse Welding - A Tig Welder with Pulse control allows the operator to weld very thin material with a little more control. The principle is that the Tig Welder emits a burst of higher power to achieve penetration, followed by a burst of lower power to prevent blow through. Pulse welding can also be used to achieve penetration on thicker material whilst at the same time, limiting weld size. Pulse welding is a relatively new addition to the Tig Welder and most professional operators still choose not to use it.
AC Frequency Control - An AC/DC Tig Welder may have AC Frequency Control. The frequency is the speed at which the polarity of the Tig Welding Torch switches from positive to negative and is measured in Hz (Switches per second). A Tig Welder with fixed frequency usually switches at around 70 - 100Hz. A Tig Welder with variable frequency control will typically have a range of around 50 - 250Hz. The effect the frequency has is to "focus" the Tig Welding arc, in the same way you would focus a torch beam. The higher the frequency, the more focused the welding arc. Higher frequency would normally be used to gain greater penetration on thick aluminium, repairing a crack in a casting for example, while lower frequency would be used on thinner sheet aluminium where the heat of the welding arc needs to be spread more to avoid blow through.
Tungsten Tig Electrodes
Two key types of Tungsten Tig Welding Electrode are available, Thoriated (red tip) for DC Tig Welding applications and Zirconiated (white tip) for AC Tig Welding applications. When a Tig Welder is in AC welding mode, the welding arc will cause the tungsten to "ball" at the end. The diameter of this ball should not exceed the diameter of the tungsten; if it does a larger tungsten should be used. When a Tig Welder is in DC welding mode, the tungsten should be ground to a point. This point should be as sharp as possible with the grinding lines running from the point, down the length, NEVER around the point.
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