undercutting

[Dave B]

I have occasional problems with udercutting. This time it's .134 wall mild steel tubing, TIG, electrode neg, 120 amps, 1/16 2 percent thoriated electrode, 19 cfm pure argon, 70S-6 filler rod.
These are similar conditions to previous times when this problem has ocurred. I have tried moving slower/ faster, higher/lower amps. The only thing that seems to help at all is a slight weave, but it's not totally eliminating it. Can anyone help!

[fordracer80]

do you get the mill scale off ? if you dont it will undercut

[Dave B]

This is clean DOM tubing, no scale to speak of, or do I need to clean it anyway?

[Dan]

What diameter of filler rod are you using? You should always clean the basemetal to shiny bright metal. On square or rectangular tubing I use an abrasive recondtioning pad on my 4 1/2" angle grinder. Basically there like a scotch bright pad. For round tubing I just use emery cloth.

By the way can someone tell me what DOM tubing is anyway.

[Dave B]

Thanks to both of you Fordracer & Dan. I'll try that today. Dan, I've tried 1/16 and 3/32 filler. I've only run into this a few times, But when I do I usually only wire brush. I'll try working a little more. Thanks again

[Mike Sherman]

Dan, DOM - Drawn over Mandrel. Undercutting is often associated with excessive heat, inadequate amount of filler metal and excessive travel speeds, plus what you have already been told.

[Dan]

Are you using a machine with remote current control so that you can vary the current or are you using a machine with a fixed output? Im wondering if this undercutting is occurring as the basemetal becomes hotter and you start loosing control of the puddle.

[Dan]

Originally posted by Mike Sherman
Dan, DOM - Drawn over Mandrel. Undercutting is often associated with excessive heat, inadequate amount of filler metal and excessive travel speeds, plus what you have already been told.

Mike thanks for answering my question. I alway just knew DOM tube as being called seamless tube.

[dysfunction]

The blackness of the tubing is oil from the drawing process. I emory cloth the areas around the joints then clean them with acetone. Course 90% of the time the tubings covered with residue white lithium grease spray from lubing it for bending.

[Guest]

Arron, undercut is a groove adjacent to the weld bead, which makes a weak point. I have found that the most often it is caused by a dirty tungsten. also too slow a feed rate with the filler metal. Mild steel is famous for that.

I have always wanted to see the DOM process...it must be facinating

[Arbo]

Darn Rocky,

I thought you were old enough to have seen it all

[Dave B]

Thanks Fordracer, Dan, and Mike. I went in today and really cleaned the base metal with scotch brite--- beautiful, I can weld again. The tubing looked so clean and bright that I mistakenly thought wire brushing was enough, the scotch brite really works well. Thanks again