Hello again Tom, I should have paid more attention to your stated parameters, my bad, hence my comment about the tungsten diameter. I do have a few more thoughts for your consideration. When you folks set-up your testing pieces how are you preparing them? How long between the time that they are set-up and the time you are attempting to weld them? Are you using shop air at any point to do any sort of blow off or are you using any air tools that have the porting that points towards the point of contact for the tool, I ask that question due to possible oily contamination from the compressor unit or other inline items that process the shops air. Have you thoroughly cleaned the backside edge of the bevels where they contact the backing strip as well as the backing strip face, ie., acetone, etc.
     Now to the actual set-up on your torch. You may want to consider trying a few things with regard to tungsten end-prep, grind it at between 20 and 30 degrees and blunt the end off at roughly 1/16" or slightly more, if it isn't blunted off enough it will likely round off with the application of amperage. Next try using a larger cup, I believe you may be having coverage issues with regard to the puddle and the end of the rod as it is being added to the puddle and withdrawn. Try a 5/8" cup instead and set the extension to around 1/4" to 5/16". By using the larger cup with more extension you will create a larger gas shielding envelope and possibly avoid rod contamination when the rod is moved in and out of the puddle. If the operator is using a lay-wire technique, meaning that he/she is not dipping the rod in and out of the puddle, but instead is just simply feeding it in continously, you may want to avoid this as this could prevent proper cleaning action of the weld area by the arc. Also consider setting your balance control a bit further away yet from the penetration side of the control. Pay attention to the cleanliness of the filler rod as well, if necessary wipe it down with acetone prior to using and make sure that the operators are using clean gloves.
     Tom, I would like to stress here that I am not trying to be condescending in any manner. If you are already aware of all of this please forgive me for bringing it up, however if you are possibly like me I forget sometimes to take a very methodical step-by-step approach on problems and some of those missed steps come back to bite me. Best regards, Allan

Tom,

I've been watching this thread develop with interest.

If you have in house RT you could do some control checks.

I am Assuming you are mixing your own gasses with a gas mixer.

Run RT and visual on Bead on plate surfacing welds (side by side) with  your straight argon and both your "Known Good" and suspect helium. The visual alone may be enlightening!

A larger cup is ok, but I don't see anything particularly wrong with your set-up as stated... A gas lens is ok too as long as you inspect the screen constantly!

As far a flow rate goes, I don't see a big problem with what your currently using. Helium is much less dense and generally requires a much higher flow rate vs argon anyhow. With the mix ratio your using I just dont see a red flag here.

Those "black spots" really smell like a gas issue to me. But there can be other causes.  Assuming your surface prep is sound (which I do) A contaminated tungsten can cause similar problems...  Aluminum tends to "run up" the tungsten when the electrode touches the work or filler.. So if an operater stops to clean up after a dip, but neglects to remove 100% of the bad stuff that climbs up the tungsten (up to 1/2 inch in high current ops) this can be an issue.  Doubtful in your case, but still possible.

Just walk out to the shop floor when everybody is on break, remove the tungstens from the torchs and inspect it's full length... This may tell you something about what really goes on on the shop floor day in and day out.