Gas Ratio in TIG Welding

Hello vscid,

When I had a shop, and if the quality of the weld was not good, one of the things we looked at among others is the mix.

These gases are inert, creating a shield for your weld. Do not know what or how this effects the material or type of material being welded since these gases are inert, but when we were welding we had a tri mix, being helium, argon and CO2. This we had good results. We were welding Stainless Steel 304, 304? and 316 ,316L.

And when I wrote up the weld procedure, the gas types are specified.

This may not help much, I'll be looking to see if any other colleague can elaborate farther.

Do u knw the ratio of that tri mix

I'll have to look, A guess is 80%, 17.5% and 2.5% Helium, Argon and Co2.

This is from memory, I'll verify it

Hi Phoenix911,

I confess up front that I know very little about welding, but I am wondering whether the mixture ratio in the gases has to do with the thermal conductance properties of the gases as well as the inert properties.

aqua doc,

I am not an expert either but also physical properties of the gases also plays a big part. Where Helium is lighter, or even the type of welding you are doing, whether purge or back gases if your doing process piping and such. I am watching these posts to pick up some good information on the reasons.

When I went through the U S Navy Class A welding school, we used Helium. It is much cleaner and gives a better weld. However Helium is much more expensive than Argon. So the different mixes were developed to cut down on the cost of the shielding gas. I use strictly Argon as my welding doesn't have to pass certification. If you are getting into exotic alloys, contact your local welding supplier for information. However, get several opinions as not every salesman knows the requirements for some alloys. A couple of good contacts would be Lincoln or Miller. They are the best in the welding business.

Yes it does depend on the material yard. (thats why here are so many blends.) Lincolon and miller are also the biggest players.

Before any decision is made on gas mix and type you must know #1 alloy you are welding #2 Filler metal you are welding with.

70/30 Ar/He Would be used when welding thick sections or alloys with a high thermal conductivity or relatively high melting temperature. At all currents levels, for equivalent arc lengths, the arc voltage obtained with Helium is appreciably higher than with Argon. Since heat in the arc is roughly measured by the product of current and voltage (arc power), Helium offers more available heat than Argon. Helium is lighter than argon and will require a higher rate of flow for proper sheilding.

Helium offers the advantage of deeper penetration. The arc force with helium is sufficient to displace the molten weld pool with very short arcs. It is also very effective for at high welding speeds used in tube mills. However, helium is very sensitive for bead profile and difficult to control during long arcs which are needed for feeding filler wires.

Helium has another disadvantage. It is lighter than air and will not provide effective shielding during TIG welding. To be effective, its flow rates should be twice as high as argon's for acceptable gas stream during welding. It is also ineffective to large an extent during drafts and is difficult to ionize, necessitating higher voltages to support the arc. It is also unstable with AC and cleaning action does not occur.

Argon is denser than air, effectively shields the weld during positional welding. It is also permits fairly long arcs at lower voltage and well suitable to weld with additions of filler metals and with AC. Though helium was used initial days of TIG welding, argon has replaced it as it is available commercially and cheaper and used wherever required.

Hence, to get the best of both, Helium is mixed with Argon to get combined benefits of cathode cleaning and deeper penetration, particularly in manual welding of Aluminum. The common ratios are 75 + 25 and 70 + 30 for helium and argon.

Trust above info. will be of help to you.

Straight argon is for tig welding and mig welding aluminum and the argon/carbon dioxide mix is for mig welding steel (per a friend of mine who works for Airgas Corp). Helium is used (as others have noted) for some of its special properties, but mainly where cost is not an objection point.