These are the basics of how to tig weld titanium...
The 3 C's of tig welding titanium are...
clean the metal, clean the filler metal, use clean gloves and shield any area that will get red hot with argon.
It helps to know some things that can go wrong with titanium because these mistakes can scrap a part and parts made from titanium are usually ver expensive.
Titanium can display a finish or sheen that resembles stainless steel or inconel and if you weld titanium with any other filler rod than a titanium filler rod then guess what? you will start hearing "tink!! tink!! tink!!" and that is the bead letting you know its cracking and that your day just got worse.
When a filler metal like stainless steel or nickel alloy mixes with titanium it creates brittle intermetallic compounds that are brittle like glass.
Now the entire bead will need to be removed and might just scrap a part.
Think about someone asking you to weld an exhaust component and to you it looks like stainless and maybe you have seen a bunch of stainless exhaust parts that look just like this one.
But actually it is .032" thick titanium.
Its a one inch long exhaust crack and you weld with it using a stainless filler rod with a bead about 3/16" wide....The entire bead plus a little extra will need to be ground out and now you have a 1/4" wide gap to fill on .032" thick titanium...Not Good!
The same thing can happen just by accident if you leave other filler metals on your work table while tig welding titanium.
So best practice is to clean your work area and remove any filler metal other than your titanium filler metal from your table.
The best way to identify titanium is with a spark test using a sanding disc.
Pick an area where a few grinding marks wont compromise the part and use a sanding disc around 120 grit and apply just enough pressure to make sparks. Titanium sparks are almost white and much brighter than any steel sparks.
Titanium is what is known as a reactive metal.
It reacts with elements like oxygen, nitrogen, and hydrogen in the air when its molten or even red hot and forms brittle compounds and also a brittle oxide layer known as alpha case.
Not purging the back side of a full penetration stainless weld is bad enough but a stainless unpurged weld might actually last a while for some applications .
.. But not purging the back side of a full penetration titanium weld is horrible and the weld wont hold up very long for any application where the weld is stressed even a little bit.
Using a standard small cup for tig welding titanium just wont do.
You risk contamination of the molten puddle and at the very least, excess discoloration which for most welding codes is cause for rejection.
In a fixture with chill blocks a jazzy 10 cup can work but on jobs where chill bars are not possible, something like a furick BBW is the ticket to provide a large blanket of argon shielding and a silver weld.
The first 2 mistakes are much worse than this one.
But not cleaning titanium before welding usually will result in porosity.
so if the weld will be subject to x ray testing, not cleaning it will almost always fail an x ray test.
Mike Zanconato shares purging tips, along with tips for pulse settings and more on titanium bike frames