Problem: Burn back with Miller push pull pulsed MIG

[herynkc]

I am running an XR aluma pro plus gun alongside a D-74 Mpa plus wirefeeder. The powersource is an XMT 350 Mpa. I am getting pretty much immediate burn back when welding aluminum in pulsed MIG (I have tried both synergic and non synergic options with no noticeable difference). I basically can weld for 3/8” of length until the wire melts back onto my contact tip. It does weld better in NON pulsed MIG but still eventually burns back. My set up on the steel half welds with no issues in short circuit or spray (this is a dual wire feeder.)

I have tried a range of wirefeed speeds (350 to 550 IPM with .035 wire). I have tried both 4043 and 5356 wire and neither makes a difference. I’m using straight argon at 25-30 cfh. I’m maintaining about a 15 degree torch angle with a pushing motion. I tried adjusting the run-in to x.50 (which is 50% set wirefeed speed?). The material is all 1/8” wall 6061, I’ve tried to weld many different joints in flat position (fillet, open and closed butt, and simply just on top of flat plate).

I’m burning tips left and right and don’t know what I should do to rectify this. There must be some machine parameter that is off or out of sync? I’ve looked over the liners, u groove rollers, and feeder guides - everything seems to be feeding fine (until it burns back and birds nests). I’m going to call Miller tomorrow, but I wonder if someone out there knows of a solution that can save me some time? Many thanks in advance.

[shovelon]

That is odd. There must be a burn-back parameter hidden somewhere in your settings. Although desireable for steel welding, your alum wire melts much faster. You need to find that setting and adjust it to zero or better. But remember or write down the setting it is currently at for steel. I specifically purchased the optional panel for my MM200 to get the burn-back adjustability.

Also check the drag tension on your spool. They tend to continue to rotate after the arc is stopped but alum is 1/3rd the weight of steel so the tension may be too much and stopping the spool dead in it's tracks making the drive motor work very hard and making the wire burn back.

Good luck.

[shovelon]

I am not familliar with your power supply but check to see if any slope control is programmed in. Could be an area of concern.

[herynkc]

Thanks for your reply shovelon. I will keep your suggestions in mind.

So I called Miller technical support this afternoon and the guy pretty much instantly suggested that I use the AL specific contact tip. I was using a bernard T-035 instead of T-035AL.

"Because aluminum expands significantly when heated, the tip needs to be over-sized a few thousandths of an inch to accommodate for this." Supposedly the wire is getting lodged in the contact tip when the arc starts to heat up.
I have some AL tips on order so Ill let you know the results. To be honest, Im a bit skeptical this will solve the problem since the guy who sold me the gun was running AL through it with the standard T-035 tips without issue.

Back to running TIG on everything until the tips come in.