General about the TIG Welding

Tig Welders and Tig Welding
In TIG Welding (Tungsten Inert Gas Welding), the Tig Welder strikes an arc between a tungsten Tig welding electrode and the workpiece. A separate Tig welding filler wire can be added to the weld pool as necessary. The weld pool is protected from oxidisation by pouring an inert welding gas (usually Argon) over the weld pool; this welding gas is usually turned on and off by the Tig Welder. Tig welding is fairly easy to learn and is probably the most versatile of the arc welding processes - the down side is that it is slow and a good quality Tig Welder can be expensive.

Tig Welders fall into two basic categories, a DC Output Welding Current Tig Welder can be used for most applications including the Tig Welding of Steel, Stainless Steel and Copper. A Tig Welder with AC and DC Output Welding Current can also be used for Tig Welding Aluminium and Aluminium Alloys. An AC/DC Tig Welder is essential for welding aluminium, however, these Tig Welders are significantly more expensive than a DC only Tig Welders.

DC Output Tig Welder Sub Types
DC output Tig Welders fall into 3 basic types, which are based on how the Welding Arc is initiated:

Scratch Start Tig Welder - this is the least expensive and most basic form of Tig Welder equipment and relies on the tungsten Tig welding electrode being touched down onto the job then lifted off to form a welding arc (much the same as MMA welding). Such a Tig Welder is, in fact, an Arc Welding Inverter with a Scratch Start Tig Welding Torch added. The limitation of such a Tig Welder is that the tungsten Tig welding electrode will try to stick to the workpiece when it is touched down and the Tig welders torch is permanently live. The Welders  would only suggest this type of Tig Welding equipment to customers who primarily want to arc weld, but may occasionally want to do some basic DC Tig Welding.

Lift Tig Welder - THis is the next stage up from a Scratch Start Tig Welder. The Tungsten still has to be touched down and lifted off to form an arc, but clever electronics in the machine keep the power output to a minimum to minimise the risk of the Tungsten sticking to the workpiece, full power is only delivered when the tungstan is lifted off and an arc formed. Some Lift Tig Welders have non live torches, some do not. Of those with a non live torch, some will have a manual gas valve, some will have an automatic gas valve. Because of these potential variations it is important to carefully check the specification and operation of machines so you know exactly what you are getting for your money.

High Frequency Start Tig Welder - this type of Tig Welder uses a burst of high frequency (HF) to establish the welding arc. This is easier and more precise than a Scratch start or Lift Tig Welder, as the tungsten Tig electrode does not have to be touched down. An HF start Tig Welder will usually have additional useful features such as Slope Down and Post Gas Flow. HF start machines are standard in industry and so can usually be considered as professional Tig Welders.

Tig Welder Control Features

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.