Gas Tungsten Arc Welding (GTAW) is also known as Tungsten Inert Gas (TIG).TIG welding is used widely in the industry as the TIG welding is suitable to weld any kinds of metals and structures.
Besides carbon metal, TIG welding I also used for welding aluminium, alloy aluminium, stainless steel, and other kinds of alloy metal.TIG welding used tungsten electrodes as the heat source while argon gas, helium, or the mixture of both, is used as shielding gas.
In TIG welding, electric arcs happened when the electricity current is flowed to the tungsten electrodes.The distance between the end part of the tungsten electrode and the surface of the metalwork will cause an electron flow.This electron flow will then create an arc and high heat that will melt the metal.
TIG welding is done within a controlled atmosphere controlled using the electrode tungsten that functions in creating the arc in order to melt the metal.High frequency direct current or alternative current is used for the purpose of enabling the arc to be created continuously and in stable form without the electrodes touching the surface of the metal.
The arc is lit by pushing the switch located at the handle of the fire blowpipe.Filler rods need to be fed and filled into the melting crater as additional metal. While welding, the inert gas released from the gas cylinder through the blowpipe functions as the shield to protect the melting crater from the atmosphere air trapped in it.
Commonly, the TIG welding machine can provide either direct current or alternative current to the welding electrode.The choice of TIG welding machine type depends on the characteristics of welding needed. There is some metal than can be weld using alternative current while there are some that need direct current in order to do the welding in a better way.
Direct Current TIG Welding Machine (AC)
• Open Circuit Volt (OCV) on the welding machine must not be less than 100 volts. Open circuit volt means the welding machine has been turned on but no welding tasks is being done.
• Ratio of heat dispersion while welding is ½ of heat on the tungsten electrode and ½ on the metalwork (refer to diagram).
• Starting the arc with high frequency and volt will generate high level of heat without touching the end part of the electrode and the metalwork. This situation can prevent from the end part of the electrode from being damaged.
• Water-cooling system.
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Alternative and Direct Current MixTIG Welding Machine (AC/DC)
•This welding machine uses alternative current (AC) and puts out direct current (DC).
•Uses the water-cooling or air-cooling system. The choice of cooling system depends on the manufacturer and the requirements of the welding tasks that needed to be done.
•The rectifier is used to change between AC to DC
This type of machine can be set into two polar
- Direct Polar
- Alternative Polar
Direct Polar (DCEN or DCSP)
1.Direct polar circuit shows the electrode part as negative, due to being connected to the negative source while the metalwork is connected to the positive source.
2.Electron flow is from the electrode to the metalwork causes the metalwork heats quickly.
3.Direct polar is very suitable for welding using small diameter electrodes.
4.The types of metal suitable for welding are the ones with high melting point such as carbon metal, stainless steel and copper.
Alternative Polar(DCEP or DCRP)
1.Alternative current circuit shows the electrode part is positive due to being attached on the positive source while the metalwork is attached to the negative source.
2.Electron flow is from the metalwork to the electrode, which cause the focus point of the heat more onto the electrode’s end.
3.Alternative polar creates the ratio of 2/3 heat on the tungsten electrode while 1/3 on the metalwork.
4.This situation makes it more suitable for using wide diameter electrodes, which functions is to prevent the end of the tungsten electrodes from melting too fast.
5.The types of metal suitable for this kind of welding are stainless steel and magnesium.
6.Welding with alternative polar will produce wider melting area but shallower thrust point due to the usage of wider diameter electrode and lower current. The heat will also focus more at the end part of the electrode.
The electrode is made of pure tungsten or alloy tungsten, because of their high melting points. Aside from that, alloy tungsten electrodes contain 1% – 3% thorium or zirconium and able to increase electron flow and its capability. Commonly, tungsten electrodes are provided in three sizes that are diameter of 1.5mm, 2mm, and 3mm.
The types of tungsten electrode are:
(i) Pure Tungsten Electrode
(ii) Alloy tungsten electrode: (photograph: electrode tungsten)
The choice of electrode diameter is factored on the choice of the strength of the current used, type and thickness of the metal that will be welded.To produce high quality welding, the shape of the electrode’s end must be correct.
Generally, when using direct current, the suitable electrode’s end isthe one that is sharpened.For alternative current, it is more suitable using the one that is more rounded.
Filler rods are used to strengthen the attachment between the welding by embedding the molten filler rod into the melting crater.The shape is the same as the oxyacetylene welding filler rod. In general use, the choice of filler rod’s diameter must be the same with the thickness of the material unless it is metal (photo).
Sharpening the end of a thicker tungsten electrode must be done through several welding runs. Its physic must be the same with the metal that wanted to be weld so that the welding results will be of high quality.
The common inert gases that are used as shielding gas are argon, helium, or the mixture of both. Argon is more widely used as it is cheaper compared to helium.
Argon is also 1.4 times heavier than atmospheric pressure while helium gas is 0.1 times heavier than argon but still lighter than air. Argon’s characteristic of being heavier causes it to shield the welding area easier compared to helium.
Other characteristics of Argon:
•Argon can cover the welding are better due to its characteristics which is heavier than the atmospheric air.
•No fog that could deter the welder’s view.
•Acts as a cleaning agent when welding aluminium or magnesium when using alternative current.
•Easier to start the arc and the production of arc is more smooth and quiet compared to helium.
•Arc control is easier and stable when welding in vertical position or on top of the head. If the speed of the welding is the same, the heat effectiveness zone is also smaller.
Helium is often used as shielding gas when welding at high speed such as welding bigger components, welding using robots or welding metal that have high melting point.Arc volts’ produced when using helium is higher while low current can be used in order to generate arcs with the same level of power with what should be no apparent reduction of volts.The mixture of argon and helium is used when welding metal that requires higher level of heat.
Benefits of TIG Welding
Among the benefits of TIG welding are:
1.The attachment of the welding is stronger as it can go across oxidation better and finer.
2.The shielding gas makes it easier to start and control the arcs with more stability.
3.Less occurrences of air being trapped (pores), less pollution of impure materials, and no impurities trapped within the attachment.
4.The attachment is cleaner, no arc sparks and no impurities in attachment.
5.Shielding gas are not foggy and less smoke occur, making it easier for welders to see and control the welding area well.
6.The welding process is faster and suitable for welding in any positions. Welding products are smoother and do not need any refining processed.
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