There are three types of Gas Shielded Arc Welding Process; TIG welding (Tungsten Inert Gas Welding), Metal Inert Gas Welding (MIG) and Dual Shielded Flux Core Arc Welding (FCAW). In dual-shield mode of FCAW welding, an additional supply of gas is provided along with the self-shielding of core flux, due to which FCAW is also listed in gas shielded arc processes.
What is TIG Welding?
TIG stands for Tungsten Inert Gas, the Working principle of which is based on the production of arc using a high melting and non-consumable tungsten electrode. The process is referred to as (TAGS) tungsten arc gas-shielded and also known by other names like; argon arc welding, gas tungsten arc welding, etc. Normally a Gas Shielding is employed to protect the weld from atmospheric contamination. These gases are transparent so the weld puddle is visible to a welder. Some other distinct features of TIG process are
- No flux is used and there is no fear of corrosion due to flux entrapment.
- No slagging and that contributes to the elimination of post-weld cleaning.
- Since there is no spark and fumes, that is why sound weld with the perfect definition is made.
TIG Welding Techniques
TIG is applied in both welding of ferrous and non-ferrous metals with the wide range of thickness not above 8mm. Both alternating (AC) and direct (DC) current supplies are employed with the current range of 15 to 350 amps. With the use of small diameter electrodes and suitable current range, the process is applied in both repair work and new manufacturing. Although it is comparatively slower than other arc processes but produces high-quality welds with the perfect definition in aluminum, carbon steel and stainless steel family. DC source is used for welding of stainless steel, carbon steel, nickel, and copper alloys. On the other hand, AC is suitable for the welding of Aluminum and its alloys.
Equipment for TIG welding
B. Additional Features
1. Water Cooling System
Welding with high amperage means cooling is required. A water cooling system is installed in which water is circulated through the torch to keep it cool. Older systems were connected with the additional cooling system but nowadays it is installed inside the modified equipment. The water flow is controlled either by foot pedal or torch.
2. DC Suppression
In Aluminum and magnesium alloys welding, formation of surface oxide is a major concern. In Aluminum welding, as the arc is formed between the tungsten and aluminum (dissimilar metals) chances are that AC would be converted into DC mode. So a DC suppressor is used to prevent the conversion of AC to DC.
This feature put the arc to be extinguished when delay shielding is required for cooling purposes. In this way, it not only protects weld but also provides means of safety to the welder. This process is also controlled by torch and foot pedal.
Tungsten is a high melting point metal which is about 3000 degree Celsius. In TIG process pure tungsten with its best thermal and electrical conductivity is used. Nowadays alloyed tungsten with 1-2% thorium and zirconium is employed for better arc stability and improved electrode life. Two types of alloyed tungsten electrodes are; a thorated electrode for DC mode and zirconated for AC mode. It is also noticeable that electrode diameter depends on current polarity.
D. Gas Nozzles
These nozzles are of high-temperature ceramic materials to bear high welding temperature. As it is stated above some nozzles are equipped with water cool system. Only the right choice of nozzle size gives better protection of weldment, pool and filler material. Various shapes of nozzles are available for different kinds of jobs. Small size nozzles are also available for confined areas. Long shapes are available for deep groove joints.
E. Gas Lens
Gas lens is provided to prevent the turbulence of gas flow. Poor gas flow may not give good shielding service and that is why gas lens is used to provide consistent and smooth gas flow to shield the weld puddle. With the help of gas lens, electrode extension can also be achieved for the access of complicated areas.
How to TIG Weld?
1. Arc Initiation
Arc initiation by touching the electrode with a base metal can cause serious problems of contamination and may lead to arc un-stability. Tungsten inclusion as a result of electrode chipping, can cause localized hard spots in welding.
On the other hand, the transfer of base metal to tungsten electrode can also cause contamination and consequently un-stabilize the arc. For the electrode not to touch with a workpiece, a high-frequency spark is produced that causes some sort of ionization in the spark gap.
The welding current continues to flow due to this ionized spark gap. This feature also contributes to enhancement of electrode lifespan. Listed below are the arc initiation methods that are normally being employed in modern equipment.
a. Scratch Start
In this method, the electrode is brought down to the workpiece and gently scratched to initiate the arc. As it is stated above that a slight contact can cause the problem of contamination. This method is applied only in those applications where contamination is less and no serious problems of weld are generated.
b. Lift Up
In this method, the electrode is brought down to make contact with the workpiece at the initial point of welding. Torch switch is pressed that creates contact and still no current is produced. When the electrode is lifted up making a gap, the current continues to flow and rapidly increases to the pre-set value. This rapid increase in current is referred to as popular term slope up.
c. Slope Up
Slope up is a rapid rise of welding current to preset current by switching the power on. By the use of switch, a welder can set the time required for the rise of current to the selected amperage. This feature offers less contamination and reduces the danger of burning thin sheets at the initial stage of welding.
d. Slope Down
Slope down is a gradual decrease of welding current to zero. It is referred to as the time taken to decrease the current until the arc is extinguished. Well, this feature is used to fill the crater (weld imperfection) at the end of the weld. Normally this function is operated with the help of torch switch and foot pedal.
2. Electrode Grinding
Electrode grinding is one of the major concern in achieving consistent performance. Electrodes are ground according to the application (joint). There are two ways for electrode grinding; machine grinding and manual grinding. Machine grinding results in consistent grinding. However, care must be taken while manual grinding.
3. Electrode Shape
a. Electrode is usually ground to required vertex angle. For DC mode the electrode is ground to a length of 1-3 times the diameter of the electrode.
b. For AC usage the side of electrode end is ground to 45 degrees, remaining the front side to be flat. This gives the spherical shape.
4. Electrode Installation
Well, this one is simple. The electrode is installed in the torch and held tightly with the help of grippers knows as sockets. They can grip and hold the electrodes of various diameters.
TIG Welding in Stainless Steel
The most common metal on which TIG operation is applied is stainless steel. However, in aluminum, magnesium and copper alloys, this process also has proven best.
GTAW’s compatibility is better with the industrial application as compared to other processes. As a result, the welds usually have higher strength and quality.
The complexity sometimes hinders the unskilled labor. It’s a slow process. In all stainless steel types, almost 10.5 % chromium is maintained. It’s the chromium which gives the shine to the metal.
The chromium helps the stainless steel to resist the corrosion and rusting. So from automotive to aerospace industry; TIG welding is preferred for chromium contained materials.
The welding of stainless is complex while at the same time; TIG welding is itself a difficult operation to perform. The presence of this dual challenge requires excellent expertise and command on the operation.
American Welding Society’s codes and process are available to abide by in GTAW.
The basic thing to tackle during the TIG welding of stainless is the heat. The rule for this is; there has to be 1 amp of current for every thousandth inch of material thickness.
Sometimes, the selection of inert gas depends on the economic factor while in special case; the environment and the chromium content in metal decides the gas.
Some Important TIG Welding Tips
Speed of the Process:
The speed has to be up and steady. If the speed disrupts, the current intensity will be disturbed and the whole weld strength would become questionable.
It also recommended using the gas lens in torch. Through the layered screen, it distributes the gas more uniformly and with less turbulence.
Keep in check the size the parameters of the filler metal before the operation as the diameter of the filler rod should be less the filler metal. You must also be well informed about the chemical proportion in base metal and filler rod, as the chemical compatibility is an essential factor for the bonding and soundness of weld.
Importance of Position:
While working on the difficult angles, keep yourself at a stable position with the effective safety system. The control of foots and arms affects the process greatly. The weld uniformity might get changed in the absence of the stable working condition.
These are some of the key elements to keep in mind during a TIG operation on Stainless Steel. Do you have more views about it? please share your experience with us. Stay Blessed!