MIG Weld Penetration

[knots43]

What constitutes good penetration using a MIG welder. I have two Millermatic welders. The older is a Millermatic 35 in which I run .035 wire, the newer is a Millermatic 185 in which I run .023 wire. Is the following an accurate definition of penetration ? Additions/Corrections, expansions please ?

On a practical level the penetration is complete if the weld is uniformly fused with no void areas at the weld root or within the weld interfaced area.

[diamondback]

what your describing is good fusion.

a definition for good penetration is like saying quality work. It is all based on what your using for a standard. For automotive they say 20% of the base metal thickness. For rail car connectors they like to see more than 3/8" penetration, neither one is served by the other.

In general welding data discusses the weld and it's faying surface as your discussing without making a definitive statement that "X" is good penetration. The proof of it lies with you, what can you prove to be good. The codes and specifications are all over that but to say one penetration depth is good while another isn't, well it just isn't done. It would be to limiting in the scope of what a welder might be able to do.

To say in general what you said about the penetration is complete if the weld is uniformly fused is like saying the salad dressing is good so we should be able to water ski. They just don't address the same thing, one is penetration and one is fusion. When that gets worked out then we can discuss dilution.

[knots43]

Thank you DIAMONDBACK.

[Sberry]

Penetration is mostly a function of joint design, some joints need none, some 100%. 1st is fusion, on first pass fusion all along the fillet and on second washing a pass over and melting completely to the first. Second pic, more penetration with gap on 1/4 with no bevel, 3rd pic a demonstration of simply melting almost all the way thru a 1/4 fillet and stacking weld and molten metal back in joint. Might not be pretty with such magnification but no doubt melted in.

[Sberry]

Whoops, those were not Mig. Penetration. ,,,, And I think the 6010 Hob up pic describes some dilution Diamondback talks about,, ha.

[Sandy]

This is where some investigation on each individuals part is warranted. You have know what you and your machine in combination are getting as far as fusion is concerned. Some cutting and etching is generally the only easy way to get in tune with your own welding results.

Beyond joint prep, regardless of the depth of V that is cut or bevel put on or even gap left, the depth of fusion needs to be more than laminar, ie., glued on. This is where using too small of equipment or too low of settings can be deceiving. One can put two 1/2 inch plates in a T configuration, pour in a 1/2 inch fillet, get good apparent fusion yet experiance lamellar tearing under high stresses. Seems like Fusion is a big word and can be anywhere from glued on to burned through.

[aametalmaster]

Do youself a favor and put .030 wire on that MM35 it will weld much nicer...Bob

[diamondback]

I think there may need to be some definitions to terms for this thread.
1. Faying surface: the surface of a member that is in contact with another member, that is about to be joined. Let's call it the weld preparation area, where the weld will be made.
2. Penetration: the depth of the weld beyond the prepared surface of the base metal.
3. Dilution: the ratio of weld metal and base metal at any given point in the weldment. (the dilution will vary with distance from the center line of the weld).
4. Fusion: the turough and complete mixing between the two edges of the base metal to be joined or between the base metal and the filler metal added during welding.

I hope this helps to decifer what I said before.

[nedster]

Great thread with some good info. Question: When setting up a MIG to weld 1/4" mild steel, can you run a stringer on a solid plate (not a joint) of the same material and determine if the machine settings are correct? Specifically if the penetration is correct? If so, how much penetration should you expect to see?

[diamondback]

from the top of the weld you will never tell what the penetration is like. You have to cut and etch if you dont have an ultrasound or xray.

That being said there are some indicators that will help you think that your in the right range. Bead profile and appearance will give you a sense of security although sometimes a false sense if you have done your due diligence in testing parameters. Look for a smooth transition at the weld toes and a weld face that is consistent to get the wire feed speed and voltage balanced for MIG. For stick and TIG your looking for a similar appearance but your control is different due to the CC set up.

At the end of the day the only way to know what the penetration is for a give voltage and current in a joint is to run a PQR and prove what you think your doing is right.

[Ls2cam]

Good information..