I'm thinking of making some parts from 3/2.5 or 6/4 titanium alloys and the welds will be load bearing.

I've been reading until my brain can't take anymore. I understand all the complexities like solvent washes, chlorine free gloves, alpha and beta phases, crystal structures, dislocations, holes, cottrell atmospheres, hall-petch effects, embrittlement and so on, ad infinitum.

The material never really goes over 5mm, but some pieces are only 1 or 2mm thick. I can't afford to have the these pieces of material distort, as I can't machine material away from such thin pieces, which means pulsed welding may be helpful.

I only need DC for the titanium, but may end up working with aluminium or magnesium and I want the welder for my own purposes too, so I'll probably go for an AC/DC set.

I seem to have a couple of choices from the different manufacturers that all lie in a similar price range and output current;

ESAB Caddytig 2200i (This is only available in Europe)
Miller Dynasty 200 DX (or syncrowave?)
Thermal Arc AM 200
Lincoln Precision / Intervec
Kemppi MasterTig
Murex Transtig

If you've owned or used one, or know someone who has, let me know what you think. I've used a Thermal Arc DC set before and it was a really nice machine, but I've not tried any of the others and I was using the set for stick welding regular steel, which is somewhat less demanding.

I've also considered the plasma welder from Thermal Arc, but I'm not sure about that given how little I've read about people actually using the process.

I could also use some advice on the following;

Are there any rules of thumb for selecting a waveform? Not important for titanium I know
And similarly, are there any tricks you use to choose pulse parameters?

The latter seems a lot like guess work when I've seen people using it in videos. But I expect there must be someone out there who's worked out a pattern of setting their welding up to tune the pulse width and frequency to an optimum.

Finally, is anyone aware of a UK or European body that will certify welds? If not, is there anyway to get certified with the AWS in the UK?