What is Tig welding? Tungsten Inert Gas welding

What is A Tig Welding?

Tungsten inert gas (TIG) welding (also gas tungsten arc welding (GTAW) or, more archaically, heli arc, which was used for early applications that employed helium as the shielding gas) is a welding technique that establishes an arc between a workpiece and a non-consumable tungsten electrode.

The TIG process provides a shielding gas to protect both the electrode and weld area; filler metal can be supplied, but is not necessary.

The use of a non-consumable electrode is what differentiates TIG welding from other forms of welding, which, in general there will be a source, filler material, and a shield, where each is relevant for the overall process.

TIG welding is similar to oxyacetylene welding in the manner that it requires the ability to manage the torch with one hand and the filler rod with the other. TIG welding requires additional coordination, since many machines use a foot pedal to control the amperage.

As a method similar to MIG welding, TIG welding may often be described as a clean welding method (this is due to shielding gas and the fact that no flux is required and that there is no slag that needs to be removed).

Safety

Since TIG welding is such a clean process, some of the welders may choose to work without gloves or choose to wear short sleeves. This is highly discouraged.

TIG is an arc welding process and produces UV light at even higher levels than other arc welding processes. In other processes, smoke or fumes are produced as a byproduct, which helps to filter out UV rays.

In contrast, the TIG process does not filter these rays and leaves the operator completely vulnerable to skin burns. Therefore, it is crucial that all exposed skin is covered to ensure you are not open to UV damage.

When it comes to eye protection, a minimum filter shade of #10 is required. If using an auto darkening helmet, check to make sure it is rated for a TIG process, as some of the lower end models do not consider TIG welding an approved process.

Equipment

The basics of TIG welding tools include a constant current welder, a cable and torch, a work lead and clamp, an electrode, and an inert gas cylinder with regulator and flow meter. Other optional items may include remote amperage controls and a water cooled torch. 

Withdrawal of the midrange shielded metal arc welding machine to provide the current is possible when using, however the dedicated, good quality TIG welding machine has many advantages.

The dedicated TIG welding machine can supply current in AC or DC and usually has an optional high-frequency output for arc initiation without contact as well as an option for a remote control and/or solenoid for use in conjunction with the shielding gas. 

Combining AC current with high frequency output is very useful when welding aluminum and will provide strong good results.

New inverter based TIG welding machines have appeared with better current control and are becoming very affordable, so even home or hobbyist workshops may have them if they want to.

Torch & cables.

The TIG torch is designed to hold the electrode firmly while also directing the shielding gas needed to weld. It can come in either air cooled or water-cooled versions, depending on the specific amperage strength needed for the job.

The main parts of the torch include the cup (or nozzle), collet body, collet, end cap, and torch body. The collet and collet body hold the electrode tightly and create a reliable electrical connection needed to successfully create the welding arc.

Electrodes are generally made with diameters of either 1/16″, 3/32″, or 1/8″. The collet and collet body must match the diameter of the electrode in order to properly fit in the collet. We don’t want any unwanted arcing to occur in the collet!

The cup, or nozzle, is used to direct the shielding gas that protects the electrode, weld puddle, and filler metal from oxygen, or the air in the surrounding atmosphere so that the weld stays clean and of high quality.

Air-cooled torches typically work well with anything under 200 amps. Anything more than that is usually accomplished through water-cooled torches that help manage heat.

Nozzles control the amount of shielding gas flow over and around the weld pool, while also controlling the area that is shielded with its coverage area based on size in diameters from around 1/4″ – 3/4″.

Smaller nozzles offer less coverage while larger nozzles allow extension of the shielded area. There is also a difference in length. Short or extra long. Typically, thicker nozzles will be more expensive, but there is also a price difference in the different materials and performance levels.

From lower amperage work a nozzle made from between 90% – 95% alumina oxide is a typically preferred choice for cost. However, its ability to withstand thermal shock is lower, and at higher amperages they may deteriorate, crack, or even break off.

Lava nozzles are considerably more expensive than alumina oxide, but are generally better at avoiding crack at medium amperage. However, it does have a variable wall thickness internally and even with shielding gas they may not exhibit appropriate coverage of gas.

Lastly, it would be helpful to have a few tools to go along with TIG welding such as welpers, locking pliers, or a stainless-steel-wire brush.

Tig Welding Gas

Argon

Argon, as a fairly inert gas, will not react with any element or compound. Argon is about 1.4 times heavier than air as well.

These inert qualities, along with other physical properties, allow argon to serve as an excellent barrier from atmospheric contaminants. So it is used widely as a protective cover gas. The low ionization potential allows for reliable arc initiation, and stable arc conditions during the weld.

Helium

Helium is an effective shielding gas because it has high thermal and heat conductivity and also allows for a greater degree of ionization with a higher heat input.

Helium can be used when heat input is to be increased and to reduce the amount of oxidizing elements going into a molten bead, as in the case of welding aluminum and magnesium.

Gas Flow Rate

Gas flow rates during welding can vary tremendously from a minimum of 10 CFH to over 60 CFH, and must consider many aspects of the weld, which include the welding current, torch size, the shielding gas, the position of the weld and the surrounding work area.

In general, the more current being used, the larger the nozzle, and subsequently, the flow rate will be. Although using a water cooled TIG torch does not always need to happen unless the current goes above 150 amps.

A water-cooled TIG torch can keep heat from building up, smaller tungsten can be used, and help reduce as much weld operator fatigue as possible.

Important factors also need to be addressed, like gas density, and the minimum flow rates required to effectively shield the weld.

Argon is approximately 1.4 times denser than air and is approximately ten times heavier than helium, therefore higher flow rates are needed, such as horizontal and vertical, while arc welding, otherwise the quality of the arc weld can be compromised.

Helium is also approximately ten times less dense than argon and therefore better to use in the overhead position because it will rise and form effective shielding.

When using helium, and helium enhanced gas blends while arc welding flat, the gas flow must be increased compared with argon. In fact, it may be 50% more or greater flow to achieve the same overall quality in the weld.

Tig Welding Rod (Electrodes)

Choosing the right tungsten electrode is the first very important step in TIG welding, with six different types that are routinely used. The preparation of the electrode tip is also important to confine the welding electrode tip, which may affect the welding results.

These tungsten electrode types include pure tungsten, 2% thoriated, 2% ceriated, 1.5% lanthanated, zirconiated, and rare earth. Each of these types has typically three different types of tips: balled, pointed, or truncated.

Tungsten is a rare metal and is critical to TIG electrodes because the tungsten hardens and resists extremely high temperatures, allowing for the current from the welding machine to be transferred efficiently from the electrode tip to the welding arc. Among metals, tungsten has the highest melting point, which is 3,410 degrees Celsius.

These non-consumable electrodes, which can be made of pure tungsten or tungsten alloys with rare-earth metals and oxides, are available in numerous sizes and lengths.

Which electrode to choose primarily depends on the type and thickness of the base material, and if the welding process uses AC or DC welding current.

The preparation of balled, pointed, or truncated tips is also very important to produce proper welding results. To help properly identify electrodes, the tips are colored coded, which helps prevent confusion among the different electrode types.

Preparing The Electrode

Prior to use, either the cut end of the electrode can be ground to a point or melted to form a ball. This is accomplished by either grinding the tip to a point or chemically sharpening it. As a general guideline, the electrodes are supplied as 7-inch lengths.

An electrode can be scores with a file or cut off wheel and than snap in half, thus increasing the number of usable points. Although tungsten electrodes are very hard, they are brittle, making it easy to break one if you hold each end with pliers and snap it over something sharp, such as the edge of a table.

Since tungsten electrodes are indistinguishable in appearance and feel, the electrode should be separated by type. The color coded markings will fade with usage or may be rejected if the electrode tips are ground.

Therefore, it is recommended that sometimes prevent mistaken identity by using containers that are clearly labelled for each type of electrode.

The two critical factors when sharpening electrodes are the choice of grinding wheel and the direction of the grind. A hard, fine-grit grinding wheel should only be used for tungsten.

If the wheel has residual metal particles from grinding aluminum or steel, those contaminants can be picked up by the tungsten and can cause erratic arc stability and poor weld quality.

Because tungsten is a very hard material, it generates a lot of heat when ground. The electrode tip should have the grinding marks running lengthwise along the tip, not crosswise or circular.

When the tungsten electrode is ground along the length of the tungsten, electron flow is concentrated towards the tip of the electrode.

Grinding the electrode in a circular motion causes the arc to become unfocused, and the arc may travel sideways from the tungsten electrode and not from the tip of the electrode.

Tungsten may also be sharpened chemically by dipping a hot tungsten rod in an appropriate chemical. The taper on the tungsten tip should preferably be two three times the diameter of the tungsten.

How To Set Up a Tig Machine?

Dedicated TIG machines, such as this one, have many advanced features. The basic setup, however, is the same.

• The positive and negative output connectors allow the torch and work clamp to be connected.
• The gas outlet is set up to connect with the torch gas hose.
• The remote-control socket accepts a foot or finger controlled device, which gives the welder control of the current during the process for more accuracy.
• The operating mode selector switch gives the user the option of using high frequency start or scratch start.
• The process mode button or reset switch is used to select between alternating current (AC) or direct current (DC) type of welding current.
• The AC balance control, which uses the settings button and the encoder knob, allows the user to change the AC power to be either more positive or more negative. This change affects the cleaning action and amount of penetration. Standard for AC power is set to be 50%, but newer machines offer to go as high as 90% in either direction for adjustment.
• The start current control changes the current needed to start the arc.
• The welding current adjustment helps define the range of operating current, and the foot or finger control varies amount of current within range.
• Slope downtime reduces the arc power gradually to the arc without torching it off, so the melt crater can fill and slow the flow down before the arc stops.
• The gas post-flow control sets the length of time the shielding gas will flow after the arc has stopped.

Pre welding Checklist

• If using a water-cooled torch, check for leaks.
• Check all cables for wear and damage.
• Clean and fit up parts to be welded.

Striking An Arc

If you do not have a high frequency option, you must physically strike the arc, or scratch start it. To scratch start the arc, you will need to put the cup against the workpiece at a very sharp angle. Move the tip so it makes contact with the surface briefly, then quickly angle it away to establish the arc.

Once the arc is established, lift the cup away from the workpiece and adjust to the slope of correct torch angle. Remember that a high frequency system will allow the arc to jump the gap without contact from the electrode to the workpiece.

How To Tig Weld?

Step 1: First, set the machine according to the manufacturer’s settings for the material to be welded. Turn on the welding unit and the water pump, if you are using one. Then connect the work clamp to the workpiece or work table.

Lower your helmet, turn on the foot pedal or finger control if you have that option, and for non-high frequency equipment, touch the tungsten to the base metal and slowly drag the tungsten lightly to create a sufficient arc.

If your welder has a high frequency starting function (recommended), the scratch start method is not necessary, thus skipped.

Then, complete a tack weld at both ends of the joint. Depending on the materials and setup, you may be able to fuse the pieces together, filling with the torch only. Otherwise, a filler rod will need to be added (to secure tack welds) or the torch made to the ideal temperature to make the tack welds secure.

Step 2: If you are right-handed, for example, begin welding from the right to the left. Hold the torch at a 15-degree angle to the right of center. The filler rod is in your left hand, and you will want to ensure you are in a comfortable position to control both rod and torch throughout the weld.

Step 3: After the puddle has formed, carefully gamble the tip of the filler rod into the center of the puddle. Hold the rod low to where it is not in the way of shielding gas. Ensure the filler rod is out of the puddle, but not so far out that it is away from or should not touch the puddle surface. Continue travelling left, dipping the molten puddle and fusing material.

Step 4: As you get close to the end of the weld, keep in mind that you may need to adjust your travel speed as the accumulated heat causes the molten puddle to develop faster than at the starting point. This may require slowing travel speed, or adjusting the torch to a shallower angle (less heat on base metal) for a more finished and controlled weld puddle.

Post welding Sequence:

• Turn off the cylinder valve.
• Purge gas from the gas line.
• Turn off the flow meter or gauge.
• Turn off the machine.
• Coil hoses and cables off the floor.

TIG Welding Troubleshooting

Filler metal for TIG is supplied in rod form usually from 1/16 to 3/16 in diameter, and a number of different alloys are available including aluminum; chromium and chromium nickel; copper; nickel and its alloys; magnesium; titanium; and zirconium alloys.

Each of these different filler metals is an alloy with composition specified to yield particular welds on specific base metals.

Filler metals for TIG welding are in general very similar to those used with oxyfuel welding, the main difference being the carbon steel rods for TIG welding are not copper coated, whereas carbon steel rods for oxyfuel welding are copper coated.

Becoming proficient in TIG welding takes practice, and identifying problem welds is an important step.

• In Weld A, it is clearly demonstrating too much heat input and you should be increasing your travel speed or lowering your amperage.
• Weld B shows that it is not getting enough heat input, and the weld is barely resting on the top of the base metal with a lack of penetration. Easiest options to remedy the situation is lower the travel speed or increase the amperage.
• Weld C was simply too fast; indicating that you need to travel at a consistent controlled speed!
• Weld D: This was a good weld with consistent ripples, proper penetration, and moderate crown, meaning this is good overall quality.

TIG Welding Problem

Weld Looks Porous or Sooty

Solutions:

• Make sure the shielding gas is on and is the correct type.
• Make sure the shielding gas cylinder is not empty.
• Eliminate drafts.
• Make sure the base metal is totally dry.
• Clean base metal thoroughly.
• Increase gas flow rate.

Base Metal Distorts

Solutions:

• Tack weld parts before welding.
• Clamp parts down to the rigid surface.
• Scatter welds to diminish heat buildup.

Unstable Arc

Solutions:

• Adjust the electrode to the work angle.
• Clean base metal thoroughly.
• Clean electrode.
• Connect the work clamp to a workpiece.
• Bring the arc closer to work.

Electrode Is Rapidly Consumed.

Solutions:

• Make sure polarity and current settings are correct.
• Increase electrode size.
• Increase gas flow.
• Decrease current.
• Increase gas post-flow time.
• Use proper shielding gas.

A well done TIG welding on aluminum has even ripples and good penetration. This sample weld shows two passes to create a fillet weld on 1 ⁄4″ stock.

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