Gas Tungsten Arc Welding
Definition
Gas tungsten arc welding is an arc welding process that utilizes a non-consumable tungsten electrode (but it does not mean that the electrode will go on to infinity, it will still deplete). The tungsten electrode has the ability to withstand very high temperatures, even those of the welding arc. This process can be done with or without a filler metal.
Process
Gas tungsten arc welding or GTAW can also be called as TIG (Tungsten Inert Gas) welding is a process noted for its excellent quality welds and absence of spatter (because of the absence of slag).
This is a manual process where excellent hand and eye coordination of the welder is required. With a filler metal, a greater skill level of the welder is required. The filler metals used in GMAW and its designation is also the same that can be used for GTAW, the only difference is that in this process the filler metals are in the form of cut-outs not meters long of wire fed to the gun.
GTAW makes use of an external shielding gas source (typically inert) which flows out of the nozzle surrounding the tungsten electrode. Because of this, flux or flux coating will not be needed (since the process is making use of tungsten electrode), the deposited weld bead is very clean and slag removal is non-existent in this process.
Technique
The following technique used in GTAW is illustrated below. This is taken from the Welding Handbook Vol.2 8th edition. This is the reason why welder skill for this process has a higher learning curve than other process. Greater hand-eye coordination is needed especially when using filler metals.
Electrical Characteristics
The electrode polarity in GTAW just like any other welding process matters because this determines if the heat input will be on the workpiece or in the electrode.
GTAW is somehow opposite of SMAW in terms of polarity and heat input. As can be observed, DCEN for GTAW has more heat input in the workpiece while DCEN in SMAW heats the electrode more. This translates to a deeper but narrower penetration for DCEN in GTAW.
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Electrode Classification
The selection of electrode, current and shielding gas depends on the type of metal being joined and its thickness.
As you can observe GTAW can be used to weld aluminum, the electrical setting just needs to be AC, electrode must be pure tungsten and shielding gas must be argon or argon-helium.
Common Defects
There are common defects associated with GTAW, the most common and almost exclusively in GTAW is tungsten inclusion. The film showing the discontinuity is below.
Tungsten contamination is caused by the electrode melting and alloying with base metal. One solution is that use lesser current or larger electrode or use thoriated electrode or use a copper striker plate. A technique can also be employed by the welder to avoid the tungsten out of the molten pool.
Advantages and Disadvantages
Like any welding processes, GTAW pose advantages and disadvantages:
Advantages:
Disadvantages:
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