how to spot tig imperfections?

Date 04-04-2008 17:20

Most of the answers to your question lie in whatever code you're welding to. We need specifics; code, material, filler type, joint type, current, amperage, electrode size, even gas type and flow rate.

Basically, a "poor" weld and a "bad" weld are the same thing; a weld which contains reject able defects. The definition of what is and is not acceptable is provided in the acceptance standards of the code. Some defects are not allowable under any circumstances, such as cracks and lack of fusion. Others, such as porosity and undercut may be allowable if they fit within a certain measurable range of size and/or length. My basic rule of thumb when welding is: if I don't like the way it looks, I'm not presenting it for inspection.

As far as the filler size and electrode size go, well this is going to be dictated mostly by your material type and current. A basic rule is if your filler is melting before it gets to the leading edge of the puddle, then go a size larger. If it is not being completely consumed by the puddle, go a size smaller. In your case, I would reexamine the current you're using and the technique you're using to apply the filler. If you push the filler into the puddle too aggressively, you'll end up with a small bit which is not thoroughly melted at the rear of the puddle, or it will cool the puddle sufficiently to cause a lack of fusion or poor penetration. Likewise, if the current is too low, you will have a difficult time melting the filler into the puddle completely.

Hope that helps a little. I'm sure some of these 4 and 5 diamond guys will add some to it. But we do need to know the code you're working with to be more specific. Good luck!

By 4130wraith Date 04-04-2008 18:20

Thanks for the response, I really appreciate it, and it was helpful. I'm not sure what you mean be code? where do I find a code list? I'm welding 4130 .035 tubes notched a various angles, er70s filler 16th or 32nd, 16th cer. tung. electrode, argon at 15-20 with the machine at 75 amps and welding at about half that. Now and then I get a little black glass like bead usually at the end of my weld and sometimes various color difference's. I clean the tubes with pink stuff and hot water then all joints with acetone.

By rlitman (***)

Date 04-04-2008 19:48

That little black glass, is just that, glass.
Its actually composed of the silicon which is included in the er70s rod, to help its wetting action (as well as a deoxidizer).
It is essentially, slag, that isn't actually harmful, and doesn't come off easily, since its made of glass (kind of like an enamel).
I know, slag without flux, whoda thunk it. Anyway, you won't get this with TIG in stainless.
You can leave it on, but you should remove it if you're going to weld over the area. Its a pain to remove, but tends to chip off in small pieces. Brushing and solvents won't really help, but a pointy chipping hammer, or needle scaler (which I often use, but which beats the crap out of a pretty surface), will work fine.

BTW, er70s-2 has less silicon (but more of other deoxidizers) than er70s-6, so will leave behind less glass.

By 4130wraith Date 04-04-2008 20:01

Thanks, So it's not something I'm doing or need to worry about.

By rlitman (***)

Date 04-04-2008 20:49

Glass, probably not, so long as its smooth. If it looks like the surface of the moon, its porosity (bad).
One crater at the end of your weld, means you took your foot off the pedal too fast. As the puddle cools, it contracts, and leaves a crater (same reason why castings leave extra metal in the sprue). You may need to overfill by one extra drop of filler, as you start to lift off the pedal, and watch it contract back to level when solid.
If you're working with clean tubing, with the mill scale sanded off, and no oils on the surface, you won't get porosity. Mild steel is really cooperative.
Funky colors, could mean problem with your shielding gas (probably bad), or a lack of postflow (not as bad on mild steel, but still not ideal).
You need to keep the torch in place, until the postflow stops. Maybe need to adjust your postflow timer, or check for argon leaks.
What do you mean by the 1/16" filler being hard to get uniform? Don't expect a perfectly smooth surface. A stack of dimes is ideal.
A picture's worth 1000 words.

BTW, it sounds like you're using a foot pedal.
80 amps might be a higher setting than you want. I normally set my max current only a little higher than the numbers by the book (not double).
So, with .035", say, 45A might work best. With pedal control, you want to set your max current to the highest you will need for that weld.
Basically, you can then choose to put your foot down, and cruise along, and also have the finest control over current.

By 4130wraith Date 04-05-2008 02:20

Thanks, I played with it some tonight, great advice holding the pedal alittle longer at the end. I've been running higher amps because some of the tubes and plates vary if thickness. But I think I'll adjust the machine more because the lower amps were easier to control.

By rlitman (***)

Date 04-05-2008 04:53

General rule of thumb is 1A per thousandth thickness in mild steel. Less for stainless (its got lower thermal conductivity), more for aluminum (higher conductivity, and A/C has lower heat transfer). The cardboard miller slide calculators are a great place to get started.
Then, just set your maximum current for the thickest part.