Critical welds in Ti - machines, waveforms, codes

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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 200Lincoln Precision / IntervecKemppi MasterTig Murex TranstigIf 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 knowAnd 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?
Reply:A quick google search turned up the following, which should contain at least some relevant information on European Welding Standards:http://www.gowelding.com/wp/quals.htmI skimmed through the webpage, and it appears that most standards deal with structural and pressure vessel welding applications.  I did see some mention of Titanium, so you might find some of the standards relevant.  Most of the documentation appears to be ISO, so it should be readily available over the internet.In regards to pulsing parameters, in my limited experience, and for manual welding, they seem to be largely a matter of personal preference.  Since travel speed, arc length, and torch angles all play a role in heat input, pulse parameters much reflect the weldor's tendencies and habits.  This is just my opinion, of course...Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:Originally Posted by A_DAB_will_doA quick google search turned up the following, which should contain at least some relevant information on European Welding Standards:http://www.gowelding.com/wp/quals.htmI skimmed through the webpage, and it appears that most standards deal with structural and pressure vessel welding applications.  I did see some mention of Titanium, so you might find some of the standards relevant.  Most of the documentation appears to be ISO, so it should be readily available over the internet.In regards to pulsing parameters, in my limited experience, and for manual welding, they seem to be largely a matter of personal preference.  Since travel speed, arc length, and torch angles all play a role in heat input, pulse parameters much reflect the weldor's tendencies and habits.  This is just my opinion, of course...
Reply:The dynasty is a really nice little powerhouse. It has user friendly menus for setting up pulse and wave shaping capabilities. I think you'd fine that you like it. --Gol'
Reply:Hey John, a couple of other manufacturers i would add to the list of candidates...EWMFroniusLike the ESAB and Kemppi both these offer more than 200A output from single phase. I've had an invertec v205t for over 7 years, never missed a beat. Very stable arc at low amps, even stiffer with a high frequency pulse. I've used the transtig briefly, nice arc but i didn't get enough time on it to really put it through it's paces. Personally i would try and get demos on as many different machines from your list as you can.Can't really comment on PAW except to say that with higher running costs (gas mixs, two gas flows before you add purges etc) i wouldn't consider it unless you do enough specialised work to really justify itAC waveforms... squarewave offers many benefits over sinewave. Some are 'more' square than others. Arc's a bit harsher but the only drawback is increased noise as far as i'm concerned- especially with the AC frequency cranked upSome of these sets also offer a 'triangular waveform'. The brief time spent at 'peak' makes it more suitable for low amp AC welding. It's noticably different but IMO doesn't make a massive improvement- mine stays on squarewave 99% of the timeAt the end of day, weld quality is down to the operator not the machine. AC waveforms/adjustable frequencies make some jobs easier/fasterPulse parameters... much is down to preference, many people use it as a 'crutch'- a slow pulse to time filler additions and produce the 'dimes' . To set it up properly you would work with an 'average' amperage and a pulse ratio (2:1, 3:1 being fairly common) i.e. 40A peak, 20A background, 50% 'peak time' would be 30A average, 2:1 ratio. Pulse frequency would depend on travel speed- each 'peak' creates a spot weld, frequency needs to be set to allow sufficient overlap. For repetitive/production work it's worth spending the time to optimise things. Everything i do is typically 'one off'. I favour a very high pulse frequency (>100Hz) and ratios above 3:1 on the occasions i use it- a slower pulse tires my eyes quickly, it's barely noticable at high frequencies- just a stiffer constricted arc and higher travel speeds. I never use it on AC but then the invertec is limited to low AC pulse frequencies (as are many machines). Apparently a high frequency AC pulse can help 'float' immpurities to the edges of the weld pool but i've not had the chance to try it. 'gowelding' is indeed a good site.Last edited by hotrodder; 04-11-2008 at 04:57 PM.
Reply:Only in a limited sense, say for example, in a horizontal fillet weld, the torch angle chosen would control whether or not more heat was directed at the flat or vertical side of the joint. Originally Posted by Go1lum(ExIx60)/Travel Speed. Were does torch angle fit into that equation to play a role in heat input.
Reply:I'm not an expert at all... But the place I work for does alot of structural Ti work.All of our stuff is done with T/A 185's  and 300's (same as the AM 200) Everything done in a vac chamber of course.I like to party!