Why and How to Spot Weld With TIG Welder


Spot welding is quick and easy and creates a strong join. It doesn’t use any flux or filler metal, so there is no need to grind excess slag when finished, and there is no dangerous open flame. There are some situations, however, when using a spot welder isn’t practical. In certain instances, a TIG welder can be used to spot weld instead. In some cases, it may even be more effective than other options.

Why and how to spot weld with a TIG welder? If you are not able to access both sides of the point to the spot-welded, or if the metal being joined is particularly thin or cannot handle high amperage, you may be able to use a TIG welder instead. Attach the work lead (often referred to as the ground cable) to the less accessible piece of metal, clamp the joining piece in place firmly, position the tungsten electrode of the TIG welder and operate the foot pedal to strike the welding arc.

To understand when it is possible to use a TIG welder to spot weld, we first need to know how both spot welding and TIG welding work, and the advantages and disadvantages of each.

How Spot Welding Works

Spot welding is a subset of electrical resistance welding in which contacting metal surface points are joined by the heat obtained from resistance to an electric current. The workpieces, which are typically sheets between 0.5 and 3 mm (0.020 and 0.118 in) thick, are pinched between two shaped copper electrodes.

A large current is passed through the electrodes very quickly, usually between 10 and 100 milliseconds. This heats the metal of the workpieces because they have more resistance than the copper electrodes. The workpieces melt, and when they cool, they have been joined at this point. This process only occurs at the point between the electrodes, preventing excessive heating of the remainder of the sheets.

The amount of energy applied varies depending on many factors, including the properties of the type or types of metals being welded, the thickness of the workpieces, and the type of electrodes used. Using too little energy will not melt the metal fully, resulting in a weak weld. Using too much power, however, will melt too much of the workpieces, resulting in ejected molten material and a hole in the spot of the intended weld.

Spot welding is typically used to join two sheets of sheet metal, welded wire mesh or wire mesh, or any combination thereof. Spot welding is usually not used for thicker stock because the heat dissipates into the surrounding material more easily.

On a large scale, spot welding is used extensively in automobile manufacturing, where automated machines can produce as many as 200 spot welds in 6 seconds. On the other end of the spectrum, spot welding is also used in orthodontics to resize molar bands. It’s also used in the production of batteries.

Advantages of Spot Welding

There are many advantages of spot welding that make it the preferred method of joining in many situations.

  • It’s quick. The application of current lasts only a matter of milliseconds. Because the heat is localized to one spot, the material can be repositioned for more welds quickly, especially if you leave space between welds and double back after they’ve cooled.
  • It’s easy. Spot welding can be performed without special skill, so it is easy to automate. Once the correct time and amperage have been determined, a robot can repeat the process ad infinitum.
  • It can join many types of metals and can join different types of metal to each other.
  • It can join multiple sheets at the same time.

Disadvantages of Spot Welding

Spot welding does have some disadvantages, which is why it is not always the best option.

  • It can only create localized joins, which may not be as strong as other types of welding.
  • It can be challenging to join oddly shaped pieces of metal. Because the current melts the metal between the copper electrodes, you must be able to reach both sides of the sheets to position the electrodes.

Some of these disadvantages can be resolved by using a TIG welder instead of a spot welder. To understand how to let’s look at how a TIG welder works.

How TIG Welding Works

Tungsten inert gas (TIG) welding is also known as gas tungsten arc welding (GTAW). Non-Consumable tungsten is used because it has the highest melting temperature among pure metals, at 3,422 °C (6,192 °F), and therefore doesn’t contaminate the weld by introducing traces of the electrode’s element. The purity of the weld is so dependent on the absence of contamination that if the tungsten electrode ever touches the weld puddle, it must be reshaped (preferably in a grinder used only for grinding tungsten) before the next weld.

The weld area is further protected from oxidation or other atmospheric contamination by an inert shielding gas. The type of inert gas used varies depending on the type of material being welded, joint design, and desired final weld appearance. Typically argon is used because it helps prevent defects due to a varying arc length. In heliarc welding, helium is used as the inert shielding gas to increase the weld penetration in a joint, increase the welding speed, and to weld metals with high heat conductivity, such as copper and aluminum.

The work lead (often referred to as the ground cable) is attached to the workpiece or the metal surface that the workpiece is on. One hand holds the electric torch. The torch contains the tungsten electrode protruding about 1/8th of an inch from a ceramic cup through which an inert gas is blown. The torch must be held close enough to the workpiece to ensure that the arc is small and contained within the inert gas, but not so close that the electrode ever touches the workpiece or weld puddle. You can tell if this has happened because it will result in a different sound and color.

The other hand holds filler metal, which the welder feeds into the weld area as needed. Typically this metal is used to bond two workpieces together, though, in autogenous welds, such as spot welding, no filler metal is used.

When the torch and filler metal are in place, the arc is struck by engaging the TIG welder with a foot pedal. Once the maximum amperage has been set, the foot pedal can be used to initiate and reduce the amperage and resulting heat gradually. This soft starting and soft stopping prevent temperature shocking of the metal, which can be important when welding certain metals such as alloy steels used in auto racing. Thermal shock can result in brittle welds.

When the arc is struck, the torch is first moved in a small circle to create a weld puddle. Then the torch is tilted back 10 to 15 degrees from vertical and moved along the seem, with filler metal added to the front end of the weld pool as needed. The filler metal is removed from the weld puddle whenever the torch advances but is not removed from the cone of inert gas to avoid contamination and oxidation. Again, the tungsten electrode must be kept about 1.5–3 mm (0.06–0.12 in) from the workpiece at all times.

Advantages of TIG Welding

TIG welding is a very specific process that offers several advantages.

  • It uses less amperage than other methods. The low amperage used makes it ideal for joining metals that are very thin or cannot handle high amperage.
  • It is versatile. Just about every variable in the TIG welding process can be altered to accommodate welding different metals for different purposes.
  • The torch is small, making it capable of welding in difficult positions.
  • High-quality welds are produced because the inert gas and tungsten electrode prevent oxidation and other types of contamination.

Disadvantages of TIG Welding

Of course, these benefits come at a cost. TIG welding also has some disadvantages.

  • It’s hard to learn. There are so many variables that many hobby welders are too intimidated even to try TIG welding.
  • It’s slow compared to other methods.

Now that we have an understanding of how to spot welding and TIG welders work, we can see how a TIG welder can overcome some of the disadvantages of a spot welder.

Why You Should Spot Weld With a TIG Welder

Though the processes of spot welding and TIG welding seem drastically different, they share enough commonalities that a TIG welder can indeed be used to produce spot welds. Namely, both processes use an electric arc instead of an open flame to melt metal to create a join. Knowing this, we can use the advantages of a TIG welder to overcome the limitations of a spot welder.

Issues of Access

The biggest reason to use a TIG welder instead of a spot welder is if you don’t have access to both sides of the workpieces. A spot welder requires the workpieces to be pinched between the two copper electrodes at the point of the weld.

If you cannot reach the backside of one of the workpieces, however, you can attach your ground cable to that piece and use the TIG torch to spot weld the other piece to it.

Material Can’t Handle High Amperage

Another reason to use a TIG welder to spot weld is if the material cannot handle high amperage. If the metal is exceptionally thin or has a low melting point, most welding methods will burn a hole through the material instead of creating a weld. The variability of a TIG welder allows for the joining of metals to fragile for other processes.

For example, it is difficult to spot weld copper with a spot welder because of the copper electrodes of the spot welder heat at a similar rate as the copper workpieces. The tungsten electrode of a TIG welder, on the other hand, has a much higher electrical resistance and melting temperature, making spot welding copper sheets possible.

This is especially true of metals subject to thermal shock. The control allowed by the TIG welder’s foot pedal, which can slowly increase and decrease the amperage (and therefore heat) applied to the weld, is necessary on such metals to prevent reducing their strength at extreme temperatures.

Weld Quality

Likewise, if the quality of the weld must be high, a TIG welder is the only method that uses a cone of inert gas to protect the weld from oxidation and other atmospheric contamination, keeping the weld pure.

Sometimes welders find themselves in tight spots switching between TIG welding and spot welding. In certain scenarios, it may be easier to be able to adjust the settings of the TIG welder to produce the spot welds instead of getting out, switching the TIG welder out for a spot welder, and repositioning before switching to spot welding.

How to Spot Weld With a TIG Welder

Several adjustments must be made to a TIG welder to switch from TIG welding to spot welding.

  1. Adjust the settings. The amperage, electrode material, and inert gas may need to be adjusted depending on the type of metal or metals that will be joined. You’ll want to run several tests on clean scrap metal to determine the correct settings before commencing with your main project.
  2. Attach the wok lead (ground cable) to one of the workpieces, either the larger piece or the least accessible piece.
  3. Clamp the workpieces together. To get a good join, the sheets of metal must be well connected. Any air or space between the sheets will result in a weaker bond. Spot welders accomplish this by pinching the workpieces between the two copper electrodes. When using a TIG welder, you’ll need to secure them in some other way. Eastwood sells a TIG spot welding kit that includes a clamp designed to leave room for a specially designed spot welding ceramic cup attachment for the TIG torch that holds the tungsten electrode at a proper distance and prevents it from coming in contact with the workpiece.
  4. Position the TIG torch so that the tungsten electrode is close, but not touching, the spot you want to weld.
  5. Activate the arc with the foot pedal, which will send a current from the tungsten electrode through the inert gas cone, and into the workpieces, heating and joining them at this spot.

Safety

TIG welding poses many risk factors. Welders need to protect themselves from electric currents, molten metal, extreme light and heat, UV rays, and toxic gases. Make sure you wear adequate protective gear.

  • Light and thin leather gloves – to protect from heat and electric shock
  • Long-sleeved shirts with high collar – to protect skin from sprayed molten metal
  • Opaque helmets with dark eye lenses and full head and neck coverage – to protect against UV damage. Because TIG welding does not produce smoke, the light produced during the weld is brighter and more intense than other welding methods.
  • Liquid crystal-type faceplate that self-darkens upon exposure to the bright light of the struck arc – to protect eyes from bright flashes and UV exposure. A welding helmet with a fixed tinted lens could also be used, but the self-darkening lens allows you to get the TIG torch in place with the shield down, reducing the chance of it coming out of place when you nod it into place.
  • Transparent welding curtains made of a polyvinyl chloride plastic film – to protect nearby coworkers from the UV rays produced during the electric arc.
  • Proper ventilation or gas masks – to protect from toxic gases. The arc of a TIG welder can break down surrounding air to form ozone and nitric oxides or break down cleaning and degreasing materials to form poisonous gases. Though ozone and nitric oxide levels are typically moderate, exposure duration, repeated exposure, and the quality and quantity of fume extraction can cause emphysema and edema of the lungs, which can lead to an early death.

It is always better to be safe than sorry.

How Thick Can You Spot Weld?

Spot welding is usually used to join sheets of metal less than 3 mm thick. If the workpieces are not the same width, they shouldn’t be more than a ratio of 3:1. Spot weld diameters can be adjusted by increasing or decreasing the width of the electrode, and range from 3 mm to 12.5 mm. The strength of the join depends on the number and width of the welds.

Conclusion

If you were to survey a large group of welders, most would say that you can’t or shouldn’t spot weld with a TIG welder. Perhaps this misconception comes from the fact that, in most cases, the fastest, easiest, and most efficient way is to use a spot welder. Because TIG welders are so intimidating, many welders opt to drill holes and do a rosette or plug weld with a MIG welder. But as we’ve seen, in certain cases, it may be possible, and in some cases preferable, to spot weld with a TIG welder.

Alexander Berk

A bit about myself: I am a certified international welding engineer (IWE) who worked in different welding projects for TIG, MIG, MAG, and Resistance Spot welding. Most recently as a Process Engineer for Laser and TIG welding processes. To address some of the questions I frequently got asked or was wondering myself during my job, I started this blog. It has become a bit of a pet project, as I want to learn more about the details about welding. I sincerely hope it will help you to improve your welding results as much as it did improve mine.

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