Tungsten Inert Gas (TIG) welding is a popular technique for joining thin metal sheets, as it offers precise control, clean results, and minimal distortion. However, TIG welding sheet metal is not as easy as it sounds, and it requires some skill and practice to master. In this article, Megmeet Welding Technology will show you how to TIG sheet metal for a perfect weld, covering the basics of tungsten selection, filler metal, settings, metal prep, tack welding, and troubleshooting.
I. Tungsten Selection and Prep
The first thing you need to consider is the type and size of the tungsten electrode you will use for TIG welding sheet metal. The tungsten electrode is the part that creates the arc and transfers the current to the metal. There are different types of tungsten electrodes, such as lanthanated, ceriated, and thoriated, each with its own advantages and disadvantages. For mild steel and stainless steel, we recommend using gold-tipped lanthanated tungsten, as it has good arc stability, low erosion, and can handle a wide range of currents.
The size of the tungsten electrode depends on the thickness of the sheet metal and the amperage you will use. Generally, the thinner the metal, the smaller the tungsten. For example, for 1mm sheet metal, you can use 1.6mm tungsten, while for 3mm sheet metal, you can use 2.4mm tungsten. A smaller tungsten allows you to use lower amps and move slower, which reduces the heat input and the risk of burn-through. However, sometimes it may be better to use larger tungsten, higher amps, and faster travel speed, as this can also keep the heat input low by melting the metal faster and avoiding lingering in one spot. You need to find the right balance between speed and heat for your application.
Before you start welding, you need to prepare the tungsten electrode by grinding it to a sharp point. This helps to focus the arc and the puddle and to keep the heat-affected zone (HAZ) narrow. You should grind the tungsten lengthwise on a grinding wheel, not crosswise, to avoid contamination and arc wandering. If you are welding aluminum, you need to use a balled or flattened tip instead of a pointed one, as this creates a wider arc and better cleaning action.
II. Filler Metal
The next thing you need to choose is the filler metal you will use to join the sheet metal. The filler metal is the rod or wire that you feed into the weld pool to fill the gap and add strength. The filler metal should match the base metal in composition and thickness, or be slightly thinner. For example, if you are welding mild steel sheet metal, you can use ER70S-2 or ER70S-6 filler rods, which are commonly used for mild steel TIG welding. The diameter of the filler rod should be smaller than the thickness of the sheet metal, or equal at most. For example, for 1mm sheet metal, you can use a 0.8mm or 1mm filler rod, while for 3mm sheet metal, you can use a 1.6mm or 2.4mm filler rod. A thinner filler rod melts faster and easier and creates a smaller bead, which is desirable for sheet metal welding.
Sometimes, you may not need to use any filler metal at all, especially if you are welding very thin sheet metal, such as 0.5mm or less. In this case, you can use a technique called autogenous welding, where you fuse the edges of the sheet metal together without adding any filler. This can produce a very clean and smooth weld, but it requires a lot of skill and precision, as you need to maintain a very tight gap and a very consistent arc length.
III. Settings
Once you have selected your tungsten and filler metal, you need to adjust the settings on your TIG welder. The most important settings are the amperage, the polarity, and the gas flow. The amperage is the amount of current that flows through the tungsten and the metal, and it determines the heat input and the penetration of the weld. The polarity is the direction of the current flow, and it affects the arc characteristics and the cleaning action. The gas flow is the rate of the shielding gas that protects the tungsten and the weld pool from oxidation and contamination.
The amperage you need depends on the thickness of the sheet metal and the size of the tungsten. Generally, the thinner the metal, the lower the amperage. For example, for 1mm sheet metal, you can use around 40 to 60 amps, while for 3mm sheet metal, you can use around 80 to 120 amps. You can use a chart or a calculator to find the recommended amperage for your application, or you can experiment with different settings until you find the optimal one. You should start with a lower amperage and increase it gradually until you get a stable arc and a smooth puddle. You should avoid using too much amperage, as this can cause excessive heat input, warping, and burn-through.
The polarity you need depends on the type of metal you are welding. For mild steel and stainless steel, you should use direct current electrode negative (DCEN), which means that the current flows from the tungsten to the metal. This creates a narrow and deep penetration and concentrates most of the heat on the metal, not the tungsten. For aluminum, you should use alternating current (AC), which means that the current alternates between positive and negative. This creates a wider and shallower penetration and balances the heat between the tungsten and the metal. It also provides a cleaning action that removes the oxide layer from the aluminum surface.
The gas flow you need depends on the size of the tungsten and the nozzle, and the welding environment. Generally, you should use a flow rate that is sufficient to create a protective gas shield around the tungsten and the weld pool, but not too high to cause turbulence and gas waste. For example, for a 1.6mm tungsten and a 6mm nozzle, you can use around 8 to 10 liters per minute (lpm) of gas flow, while for a 2.4mm tungsten and an 8mm nozzle, you can use around 10 to 12 lpm of gas flow. You should also consider the wind and the ventilation in your welding area, and adjust the gas flow accordingly. You should use a higher gas flow if there is a lot of wind or air movement, and a lower gas flow if there is none.
The type of gas you need depends on the type of metal you are welding. For mild steel and stainless steel, you should use pure argon, which is the most common shielding gas for TIG welding. Argon provides good arc stability, penetration, and weld quality. For aluminum, you should use a mixture of argon and helium, which enhances the heat input and the cleaning action. A common ratio is 75% argon and 25% helium, but you can vary the percentage depending on your preference.
IV. Metal Prep
Before you start welding, you need to prepare the sheet metal by cleaning it and fitting it. Cleaning the sheet metal is essential to remove any dirt, oil, grease, rust, paint, or other contaminants that can affect the weld quality and cause porosity, cracks, or inclusions. You can use a wire brush, a grinder, a solvent, or a degreaser to clean the sheet metal, depending on the type and level of contamination. You should also clean the filler rod if it is dirty or oxidized.
Fitting the sheet metal is important to ensure a tight and consistent gap between the edges that you want to weld. You can use clamps, magnets, or jigs to hold the sheet metal in place and align it properly. You should also use a backing bar or a copper plate behind the sheet metal to support it and prevent it from sagging or blowing through. The gap between the sheet metal edges should be as small as possible, ideally zero, or up to 0.5mm at most. A larger gap can cause the arc to wander, the filler to drip, or the weld to be weak.
V. Tack Welding
Before you weld the entire joint, you should make some tack welds along the sheet metal edges to secure them and prevent them from moving or warping. Tack welds are small and intermittent welds that act like temporary fasteners. To make a tack weld, you need to strike an arc, add some filler, and extinguish the arc quickly. You should space the tack welds evenly along the joint, about 10 to 15 cm apart, depending on the length of the joint. You should also alternate the tack welds on both sides of the joint, to balance the heat and the stress. You should avoid making too many or too large tack welds, as this can cause excessive heat input, distortion, or cracking.
VI. Welding
After you have made the tack welds, you can proceed to weld the entire joint. To weld sheet metal, you need to use a technique called pulsing, which involves varying the amperage between a high and a low value. Pulsing helps to control the heat input and the penetration, and to create a uniform and smooth weld bead.
To use the pulsing technique, you need to set your TIG welder to a pulsing mode and adjust the peak and background amperage, the pulse frequency, and the pulse duty cycle. The peak amperage is the high current value that melts the metal and creates the weld pool. The background amperage is the low current value that maintains the arc and cools the weld pool. The pulse frequency is the number of times the current switches between the peak and the background values per second. The pulse duty cycle is the percentage of time the current stays at the peak value within each pulse cycle.
The settings you need for pulsing depend on the thickness of the sheet metal and your preference. Generally, you should use a peak amperage that is slightly higher than the normal amperage for the sheet metal thickness and a background amperage that is about 20% to 30% of the peak amperage. For example, for 1mm sheet metal, you can use a peak amperage of 50 amps and a background amperage of 10 amps, while for 3mm sheet metal, you can use a peak amperage of 100 amps and a background amperage of 20 amps. You should use a pulse frequency that is comfortable for your hand movement and eye coordination. A higher pulse frequency can create a smoother and finer weld bead, but it can also be harder to follow and control. A lower pulse frequency can create a more distinct and rippled weld bead, but it can also be easier to follow and control. A common range for pulse frequency is between 1 and 10 pulses per second, but you can go higher or lower depending on your application. You should use a pulse duty cycle that is suitable for the heat input and the penetration you want. A higher pulse duty cycle means that the current stays longer at the peak value, which increases the heat input and the penetration, but also the risk of burn-through. A lower pulse duty cycle means that the current stays longer at the background value, which reduces the heat input and the penetration, but also the risk of burn-through. A common range for the pulse duty cycle is between 30% and 70%, but you can vary it depending on your application.
To start welding, you need to strike an arc by touching the tungsten to the sheet metal and lifting it quickly, or by using a high-frequency start if your welder has one. You should hold the torch at a 70° to 80° angle to the sheet metal, and keep the tungsten about 1mm to 2mm away from the metal. You should also hold the filler rod at a 15° to 20° angle to the sheet metal, and keep it about 5mm to 10mm away from the metal. You should feed the filler rod into the weld pool only when the current is at the peak value, and withdraw it when the current is at the background value. You should move the torch along the joint at a steady and consistent speed, following the rhythm of the pulses. You should also move the torch slightly from side to side, to create a wider and stronger weld bead.
VII. Troubleshooting
TIG welding sheet metal can be challenging, and you may encounter some problems along the way. Here are some common issues and how to fix them:
Burn-through: This happens when the heat input is too high, and the metal melts through, creating a hole. To prevent this, you should use a lower amperage, a smaller tungsten, a thinner filler rod, a faster travel speed, or a lower pulse duty cycle. You should also use a backing bar or a copper plate to support the sheet metal and dissipate the heat. If you already have a hole, you can try to fill it by using a higher amperage, a larger tungsten, a thicker filler rod, a slower travel speed, or a higher pulse duty cycle. You should also use a smaller gap and a tighter fit between the sheet metal edges.
Warping: This happens when the sheet metal bends or twists due to the uneven heating and cooling of the metal. To prevent this, you should use a lower amperage, a smaller tungsten, a thinner filler rod, a faster travel speed, or a lower pulse duty cycle. You should also use clamps, magnets, or jigs to hold the sheet metal in place and align it properly. You should also alternate the welds on both sides of the joint, to balance the heat and the stress. You should also let the sheet metal cool down gradually, and avoid quenching it with water or air. If you already have warping, you can try to straighten it by using a hammer, a press, or a torch.
Porosity: This happens when the weld pool contains gas bubbles that solidify and create holes. To prevent this, you should use a clean sheet metal and filler rod, and remove any dirt, oil, grease, rust, paint, or other contaminants. You should also use a sufficient gas flow and a suitable gas type, and avoid any wind or air movement in your welding area. You should also use a smooth and steady arc, and avoid any arc breaks or restarts. If you already have porosity, you can try to grind it out and re-weld it, or use a filler rod with a higher deoxidizing content.
Cracking: This happens when the weld metal or the HAZ develops cracks due to the rapid cooling and contraction of the metal. To prevent this, you should use a lower amperage, a smaller tungsten, a thinner filler rod, a faster travel speed, or a lower pulse duty cycle. You should also use a filler metal that matches the base metal in composition and thickness, or has a lower coefficient of thermal expansion. You should also preheat and postheat the sheet metal, if necessary, to reduce the temperature difference and the stress. You should also let the sheet metal cool down gradually, and avoid quenching it with water or air. If you already have cracking, you can try to grind it out and re-weld it, or use a filler rod with a higher ductility or a lower carbon content.
VIII. Conclusion
TIG welding sheet metal is a skill that requires practice and patience, but it can produce excellent results if done correctly. By following the tips and tricks we have shared in this article, you can learn how to TIG sheet metal for a perfect weld. Remember to choose the right tungsten, filler metal, and settings, to prepare the sheet metal properly, use the pulsing technique, and to troubleshoot any problems you may encounter. We hope you found this article helpful and informative, and we wish you good luck with your TIG welding projects.
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