Introduction to TIG welding
WHAT IS TIG WELDING?
Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, is an arc welding process that uses a tungsten electrode to produce the weld. The weld area (or pool) is protected from atmospheric contamination by a shielding gas (usually Argon), and a filler metal is normally used. A constant-current welding power supply produces energy which is conducted across the arc through a column of highly ionized gas and metal vapours known as a plasma.
The TIG process is most commonly used to weld thin sections of stainless steel and non-ferrous metals such as aluminium, magnesium, and copper alloys. The process grants the operator greater control over the weld than competing procedures such as shielded metal arc welding and gas metal arc welding, allowing for stronger, higher quality welds. However, TIG Welding is comparatively more complex and difficult to master, and furthermore, it is significantly slower than most other welding techniques.
HOW TIG WELDING WORKS?
TIG welding is often considered the most difficult of all the welding processes because the welder must maintain a short arc length, great care and skill are required to prevent contact between the electrode and the workpiece. TIG welding normally requires two hands, since most applications require that the welder manually feed a filler metal into the weld area with one hand while manipulating the welding torch in the other. However, some welds combining thin materials can be accomplished without filler metal; most notably edge, corner, and butt joints.
In higher quality machines an arc is created using a high frequency circuit (HF) to create spark. Lesser featured machines use the scratch-start method whereby the electrode needs to make contact with the workpiece in order to create an arc. This can cause contamination of the weld and the electrode.
WHAT ARE THE ADVANTAGES OF USING A TIG WELDER?
Engineers prefer TIG welding because of its low-hydrogen properties and the match of mechanical and chemical properties with the base material. While the aerospace industry is one of the primary users of TIG welding, the process is used in a number of other areas. Many industries use TIG for welding thin workpieces, especially nonferrous metals. It is used extensively in the manufacture of space vehicles, and is also frequently employed to weld small-diameter, thin-wall tubing such as those used in the bicycle industry. In addition, TIG is often used to make root or first pass welds for piping of various sizes. In maintenance and repair work, the process is commonly used to repair tools and dies, especially components made of aluminium and magnesium.
Because the weld metal is not transferred directly across the electric arc like most open arc welding processes, a vast assortment of welding filler metal is available to the welding engineer. In fact, no other welding process permits the welding of so many alloys in so many product configurations. Filler metal alloys, such as elemental aluminium and chromium, can be lost through the electric arc from volatilization. This loss does not occur with the TIG process. Because the resulting welds have the same chemical integrity as the original base metal or match the base metals more closely, TIG welds are highly resistant to corrosion and cracking over long time periods, TIG is the welding procedure of choice for critical welding operations like sealing spent nuclear fuel canisters before burial.
CHOOSING THE RIGHT ONE
The best way to decide which model is going to be right for you is to consider the thickness of metal you intend to weld and then the types of work you are going to be producing – this will determine the kind of features you will need to look for to ensure you can achieve what you set out to do. AC/DC welders will weld all steels and alloys whereas DC only welders will only weld steels. Realistically, you should insist on these features as they will give you the best all-round control over all kinds of welding work:
Pulse Welding
In the pulsed-current mode, the welding current rapidly alternates between two levels. The higher current state is known as the pulse current, while the lower current level is called the base current. During the period of pulse current, the weld area is heated and fusion occurs. Upon dropping to the base current, the weld area is allowed to cool and solidify. Pulse welding has a number of advantages, including lower heat input and consequently a reduction in distortion and warpage in thin workpieces. In addition, it allows for greater control of the weld pool, and can increase weld penetration, welding speed, and quality.
Slop Up/Slope Down
This feature essentially delivers a smooth current from base amps up to the amperage set by the operator at the start of the weld. Slope down is the same but in reverse. When the torch switch is released the power fades out instead of stopping suddenly. A sudden stop of the current can cause a condition known as cratering. Slope down will help eliminate this.
AC Squarewave Frequency
This feature allows for much greater control of the arc. By adjusting AC Squarewave the cone shape of the arc narrows – allowing for greater control of the weld pool, quicker travel speed and the ability to get into tight spaces by concentrating the arc width. Most TIG professionals would choose to have this on their machines. By increasing the frequency you can effectively ‘beat the heat transfer’ by moving along the weld faster. Too slow in any one area can cause a build up of heat in a localised area meaning that the work can start to deform and spoil. This feature will avoid this. It’s a fantastic feature for a beginner to learn with as. Our AC/DC TIG’s all have this feature built in to them.
AC Squarewave Balance
This feature allows the operator to adjust how much of the arc is set for cleaning or penetration of the weld material. Aluminium has an oxide coating and this has to be lifted (cleaning) off the surface of metal before it is penetrated to create weld pool. So if the machine is set to more cleaning, it will spend more time lifting of the oxide layer and give a cleaner end weld with less penetration (ideal if you are welding old contaminated materials. If you set the machine to more penetration, the machine spends less time cleaning and gives more penetration. Balance is normally set at middle 50%, turning down to 30% gives more cleaning and increasing above 50% gives more penetration.
See our range of TIG Welders here.
Learn more using our Free How to do TIG Welding Guide
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