how to setup for dcep tig welding aluminum

[craig]

i know the old heliarc was dcep and used helium. i've experimented using argon and actually got a bice bead. but only on flat material. any kind of lap joint would cause the arc to wander. did they use a balled end on the tungsten? it's kind of hard not too with all the heat in it. does the helium make the arc bigger or just hotter? little help from the old timers would be great.

[dseman]

Well, I can make some opening comments and then others can add (or is that pile on?).
DCEP welding of Al is best done with Argon and not Helium because the process is one of low penetration. DCEP provides a lot of cleaning action and the tip will become well balled. In fact you will probably have to go up 2 sizes over what you would normally use just to keep the tungsten from eroding. Best to use for 1/16" stock and less. Keep the 'ball' as small as possible, and a tight arc in order to reduce the arc wandering. DCEN welding of AL is best done with Helium because it it the gas which provides a 70% increase in arc voltage over the same arc in Argon. This extra heat is necessary to 'burn-off' the oxide that would normally be cleaned by the DCEP pulses in an AC waveform. This process provides a wider and deeper weld nugget and your travel speed will be about 2x that of AC or DCEP welding. It is best to use for > 1/8", though I do have welding data for smaller thicknesses when using an 0.040 tungsten.It is really important to clean the metal even better than you would for AC welding. Chemical cleaners, aluminum carbide cutters, SS wheels can all be used. You may need to alter your regular technique of dip, dip, dip with the filler as you inch the torch along. Keep the filler tip in contact with the metal and run the arc over the joint, consuming the filler in the process. This is easier to do since you will be traveling faster. Depending on the alloy, there may be some burnt magnesium (black stuff) on the side of the weld. This should brush off when it is still hot , but more difficult if allowed to cool. Post some pics if you want to give it a try.

-dseman

[craig]

thanks, thats some great info