TIG Welding mild steel

February 14, 2021

Before you get started welding, you need to set up your machine and work area to tackle the material you’re about to weld.

Machine and Torch Settings

Tungsten and Amperage Selection

I like to use 1.5% Lanthanated (Gold tip) for DC TIG and 0.8% Zirconiated (White tip) for AC, but many people like to use 2% Lanthanated (Blue), because it allows you to weld most things and you can just buy the one tungsten. You can also check out our Selecting a Tungsten for TIG article for more detailed information.

As a general rule, tungsten diameter should be approximately half the size of the material to be welded.

As far as amperage goes, there is probably a range of settings printed on the side of your machine, but as a general guide the amperage range is related to both the thickness of the work piece and the thickness of the material to be welded.

A higher amperage means things will happen more quickly, but a lower amperage is not always better either – lower amperages means it takes longer for the work piece to heat but the heat affected zone (HAZ) is much larger because the arc is putting lots of heat into the entire piece. Amperage is just one of those things like cooking – sometimes it’s more about the feel rather than the exact ingredient weight or baking time.

Imperial MeasurementMetric MeasurementElectrode Negative
(Most Common!)
Electrode Positive
(Specialist use Only!)
.040″1.0 mm40 – 8010 – 20
1/16” (.062” and .060”)1.6 mm60 – 10015 – 30
3/32” (.093”)2.4 mm80 – 15020 – 35
1/8” (.125”)3.2 mm120 – 22035 – 50
5/32” (.156”)4.0 mm160 – 31050 – 70
3/16” (.187”)4.8 mm275 – 45070 – 90
Tungsten sizes and suggested amperage range

Gas Flow Rate

‘Tradition’ dictates that the gas flow rate in CFM is approximately double the cup size that is used. But there are more factors than just cup size that will determine the flow rate. How far you want to stick the tungsten out of the end of the cup as well as gas lens vs regular collet body will change the required flow rate. Stick the tungsten further out and you will need more gas. A gas lens will provide better, more even coverage so you might be able to reduce the flow rate. I’d recommend a gas lens setup unless there are access issues with the torch and you need a smaller torch.

Here’s some suggested settings to start:

Cup SizeMinimum Gas Flow
CFH / LPM
Average Gas Flow
CFH / LPM
Max Gas Flow
CFH/LPM
#54.5 / 2.55.5 / 36.5 / 3.2
#66.5 / 3.28 / 49.5 / 4.5
#78.5 / 411 / 513 / 6
#811.5 / 5.515 / 717 / 8
#1017.5 / 8.522 / 10.525 / 12
#1225 / 1230 / 1435 / 16.5
Suggested argon flow rates

Filler Rod

Filler rod for mild steel is ER70S-2. Don’t use coat hanger wire, get some proper filler rod!

Machine Polarity

Remember that DC TIG welding mild steel is generally straight polarity – the electrode (held by the torch) is negative. Which naturally means that you have a positive earth. If you try to start an arc and find that the tungsten is melting, you probably have your polarity reversed! This is because about 70% of the heat gets put into the tungsten rather than the work piece.

There is, however a benefit to reversing the polarity and that is is you’re welding very thin sheet metal. You don’t want to put too much heat into the work in this scenario so reversing the polarity is beneficial.

Other Considerations

Keep your work area clean and your tungsten sharp. Click for some tungsten sharpening tips

Put on all your safety gear. Make sure you’re wearing gauntlets and a long sleeve shirt/jumper or you will get badly burned! Welding puts out strong UV light and you will get a bad sunburn. It’s also very easy to forget and pick up a piece of steel that’s still very hot – even though it looks cool.

Ready to Weld

Ok and now we’re ready. To start, hover the tungsten above the work at around 1/8″ and don’t let the tungsten touch the work/ Have an angle of no more than about 15 degrees from the Hold a length of filler rod into your other hand – usually torch goes in the right hand and filler rod in the left, but this may be reversed if your left handed.

Start the arc and wait for the puddle to form. It should only take a few seconds – if it’s taking longer, you should turn up the amperage slightly. If you have a machine with a foot pedal, you can also set the amperage a little higher and use maximum amps to start, then back off a little as you’re welding so you don’t make the work piece too hot.

Once the puddle has formed, start to slowly move the puddle by “pushing” it. How fast should you push it? Well have a look at a good demonstration in this youtube video:

Remember!

  • Too fast and you won’t form a nice bead and you will lack penetration
  • Too slow and you will put too much heat into the work and the beat and heat affected zone will be too large
  • Too much angle and you won’t get enough heat into the material, your bead will lack penetration and you may get porosity in the weld
  • Too far from the work (increasing arc length) will provide a wide, flat bead and potentially introduce contaminates or porosity

The next step is to start adding filler wire. As you push the puddle along the intended path of the weld, start to dip the filler rod into the leading edge of the weld puddle. Note I said dip the rod into the puddle, don’t let the rod vaporize in the arc or touch it to the tungsten (which you will contaminate). You should be moving at about the rate of one dip per second.

And remember not to dip the tungsten into the puddle! Doing so will contaminate the tungsten and you will have to stop and re-sharpen it.

Again, another youtube demonstration is here:

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