Aircraft
If your engineer did not give you parameters for background current, pulses per second and % on time than he really isn't doing much engineering now is he?
Pulsation for manual GTA welding with filler wire addition is rarely beneficial. Pulsation can lower heat input in production lap welds with no filler, but technique, practice and a learning curve are all going to be variables to be considered.
Having said that, manual GTA welding of titanium is unique in that some folks still employ a technique for addition of filler, rather than dipping wire as you progress forward, welders often lay the wire down on the weld path with a slight pressure and move the torch over it. This technique is employed mainly because of the sticky nature of the tip of the titanium wire and the fear that poor dabbing technique may subject the hot wire tip to oxygen or nitrogen if it was to be pulled out of the Argon envelope. Furthermore, there is risk here as you may have already surmised, that with a technique of manually progressing over a stationary piece of welding wire, lack of fusion can be chronic problem until all heat and travel speed parameters are worked out.
Pulsation may lower heat input in an automated production run (GTA or Plasma with wire addition provided by a mechanized feeder on the high pulse). We employ this method quite often, but in manual GTA situations, what happens when the welder struggles to synchronize the wire additions to the pulse or has to wait in one spot for the heat to increase due to misalignment or other fitup irregularities?….. You got it, ……WAY more heat input than with a non-pulse set up.
What are we talking about in the way of joint geometry?
And material type…6AL4V?
Filler wire or no? If yes, how are you adding it?
Big production run, or custom work?
New material, or repair and rework?
Are heat sinks and restraining fixtures being employed?
If your engineer is insisting that you employ pulsation than HE MUST provide the data (process controls) your looking for.
You will find a table providing some parameters for (Automated) pulse GTA welding in the ASM Handbook Vol.6 page 194 figure 12. I suspect that while the current values may be of use that the pulsation times will have to be slowed to facilitate manual addition of filler if any is to be applied.
Tell us more and we will tell you more
Lawrence
here ya go
http://www.pro-fusiononline.com/welding/pulseparams.asp
I haven't used the above program so I can't speak to how close it will bring you to workable parameters, lemme know if you like how it works
Lawrence>> was a cracked 2in duct on a b757 trim air duct. So it was a butt joint, I have slept since then and several welds ago I think it was AMS4911, but don't hold me to that. Yes filler wire was used and I use the dipping method.
The engineer called for a very narrow HAZ, which I new was narrower than I normally produce. The engineer suggested the pulse method but had no idea how to set it up. The weld turned out fine and I could not believe that narrow of bead had that much penetration I was very impressed, I do not believe you could have done this without the pulse feature. I was using 10 PPS at 40% background and 50% peak time and this was a total guess on my part it just seemed to work good.
Firstly, I'm glad the repair worked out.
Repair welds in Titanium ducts present special challenges, the least of which is the need of a narrow heat effected zone.
In the world of Aircraft repair welding of Titanium components the need for cleanliness in surface and flaw prep overrides any requirement for narrow heat effected zone. By saying this I mean that BOTH sides of the flaw must be mechanically cleaned if possible and the crack routed to remove any possible trace of contamination. Welding over a crack (even a tight one) that has been exposed to carbon, Skydrol, Glycol in winter, or any other contaminant can render a titanium weld unsatisfactory by embrittlement, while that very same weld has perfect surface appearance and an apparent 100% X-ray quality
This admonishment is equally applicable to shielding and trailing gas coverage. Meaning, The amount of Oxygen or Nitrogen needed to foul a titanium weld is far less than the amount of Oxygen or Nitrogen needed to produce unsatisfactory color indications on the weld face or root. To make the point perfectly clear...Good color does not guarantee a good weld.]
EWI TWI and the Naval Joining Center are working diligently to come up with a more usable hardness testing criteria which may soon be helpful in field work and repair of Titanium components.
For now however, we must simply keep these factors in mind and apply the precepts as points of craftsmanship until new authoritative practices focused on titanium repairs are published.
I have visited the Boeing plant in Everett WA. where those ducts are produced. What an example of professionalism and cooperation between engineering and craftsmen on the shop floor they are! They have such good process control and communication that any discrepancy is immediately spotted and dealt with. By attention to detail over many manufacturing cycles they have removed most of the variables that cause us difficulty in the repair venue. What an exciting topic this is, but if I blab on further I might give away proprietary info.
Forum
