Mig weld penetration.

[Jeelock]

I’m trying to get something clear in my head. Mig weld penetration. I’ve researched a lot of places online on this subject and found both, real pictures and drawn diagrams. What is kinda confusing can best be described by a cross section of a joint. Especially one that has been etched with acid. On some of the pictures it shows the weld easing into the parent metals. On some it looks like the etching follows only the lines of the weld. Top and bottom. I’ve read articles and read from forums and some say that is still good penetration even if it doesn’t ‘melt’ into the parent metals. I. Sorry but what in the heck am I missing? In my feeble mind it should run into the parent metals, or there’s no ‘penetration’. Yet I’ve seen many that didn’t. Just followed the lines of the weld.
This is just one of those things I want to understand. The theory I guess.
(Dimwitted question coming) .......
is there something going on at what I’m calling the ‘lines’ of where the weld meets the parent metals that I don’t understand? Most of y’all know already MOST of my stuff is hobby stuff. But sometimes and more and more often, I get into something that needs to be structurally sound.
i haven’t let anything go that I wasn’t confident in.
But I guess I just want to understand more of the theory of penetration. Also i see people looking at some of the pics and can pretty much ‘read them’ as to what was going on in the puddle. Besides wanting to understand that better, I also think it’s pretty cool.
I’m posting a picture of a T joint cross section that I used a rust remover to etch with, instead of that particular acid. ( can find all kinds of junk online. Lol)
It’s 3/16” hot roll pcs properly prepped and tacked. Then one pass down each side with the HH140.
On this I was running very close to the door chart settings although I’ve posted a few times about having to run only 70-80% recommended wfs. I backed down just a tad on another pc to minimize spatter. Also my travel speed was faster than my usual. Obviously probably closer to where it should be.
One pass down each side, weaving up to down pattern.
Pic is below. Tell me what y’all see in this. Does good penetration need what I THINK I’m looking at? And if so can you still have good penetration when the etch follow just the ‘lines’
Hope to heck I’m making sense. And this isn’t the greatest picture. But just what I could come up with.
Throwing myself to the wolves here. And as always thanks In Advance.

[MAC702]

And naturally the pic didn't work.

[Jeelock]

And naturally the pic didn't work.

Mac. Can’t see the pic? I see it but it may be because it was posted from this device. Let me try again.

[Jeelock]

Won’t let me add again on original post. Going to see if I can add to this new post.

[MAC702]

That worked! I'll defer to my betters on analyzing it. I might have time to peruse it later.

[Jeelock]

Thanks Mac. It’s good to know I’m not the only one that can see it. Lol.

[Jeelock]

And I’ll throw these in. Pics of the two welds. And yes, I had been watching some guys stacking dimes vids earlier that day. Lol.

[lars66]

What diameter wire are you using? Narrow up your bead to about 3/8" wide and concetrate the heat more on the bottom plate. C-25 gas?

[Jeelock]

Hello Lars. I’m using .03” wire and yes sir C25.
Looking back at the pic i can see why you say to heat more in the bottom. I appreciate your input.

[Jeelock]

Ok. Been hopping around again reading some info. I just left a fabrication site where there was an article on this subject. It stated that Fusion and NOT Penetration was the most important factor. Pretty much said that the amount of fusion from toe to root was what determined the strength and not the ‘depth of penetration’
and another site pretty much said the same. And had a diagram showing the areas of Fusion not being that deep yet it was a strong weld.

I may be overthinking all this. When I ran across all the acid etching stuff, by accident I might add, it kinda got my attention. In ‘my little welding world’ which hasn’t existed that long, I guess the look of the weld and in some instances if the BFH didn’t break it. Well it was a good strong weld. Lol.

And to be honest, in my narrow mind, I guess I thought it was just a glob of the parent metals and wire all melted together.
Now it seems it’s a bit more techy than that?

In the acid etch tests to me Fusion and Penetration are the same thing?? According to some stuff I’ve looked at it apparently isn’t?? What’s going on in that area that some refer to as Fusion and some as Depth of Penetration.
So far I ain’t ‘got it’. (Sorry. Lol.)

Is this just one of those things that folks have different opinions on? I can see what’s going on of course. And as Lars pointed out, I needed more heat in the bottom. I can see a ‘lack of penetration’ there.

What’s confusing is some of the more techy sites state that as long as you have a ‘length’ of good Fusion from toe to root, a lack of Depth of Penetration does not necessarily make it a weak weld.

Im just curious what magic is happening there if that’s true.

[MAC702]

It also depends greatly on what you are welding together. Some things are engineered and NEED the full strength that a weld can get under the sizes and parameters under which it is done. Some things are going to be plenty strong for whatever it is they have to do if they even get remotely stuck together. Some things are welded just to make them airtight, and relatively no strength is even needed in the weld.

[Jeelock]

Thanks Mac. So if I’m understanding correctly, UNLESS I’m welding something say with engineered specs on a print, a good rule of thumb for somebody like me would be, check something every once in awhile and build my skills from what I’m seeing and hone them from that? Eventually I’ll be more comfortable after looking at a few to see what the heck I’m Actually laying down?

I can see this as a good tool used like that.
Not gonna worry about the debates over this I’ve been reading.

So ‘in general’ and for most things a little penetration, fusion or whatever is gonna be fine? Unless it’s specified on a drawing? Which ain’t likely gonna be happening to me because after all those years before retirement, trust me, I ain’t gonna stress over a micron, strength, tolerance or anything else like that again and hope I never see a blueprint again.

Or to rephrase, my ‘yard art’ and horseshoe cowboys, Indians and soldier figures ain’t gonna mysteriously fall apart one day cause it AINT a glob of melted parent metal and welding wire that I kinda had in mind?

I try to keep a good attitude and keep this fun for me because it’s exactly what it is. A hobby. But at the same time I think it wise to understand these things because if I’m ever asked to repair Billy Bubbas trailer hitch I want to be confident in it. My wife says I’m OCD. I say after what.... like 43 years or so in precision machining, last 14 years or so in engineering, I just want to know certain things. Understand things.

I think I ‘Got It.’ (Sorry. Couldn’t help it )

Thanks. Mac!

[Dale M.]

For "Hobby/Home" work trying to define, analyze weld penetration by scientific method's is probably beyond the scope of home welder.... I find the visual studying the weld bead and it appears to have bonded to both parent metals and and I do a bend/torture test my welds are "good enough" for projects at hand, But then I watch where the arc is flowing from wire to metal being fused, ensuring it bridges acceptably and running my heat where I am always on verge of burning through,...

ITs ok to understand the "penetration/fusion" concept by studying scientific methods, but in practicality, for me at least its will the "bond" be good and hold as desired.... I have no illusion that my welds are really safe for operations where human life may be in danger or high stresses like in trailer towing where the stresses are continual and varied.... But I have yet to have my welds fail; from poor fusion/penetration....

Dale

[Jeelock]

Thanx Dale. I’m just one of those ‘gotta understand it’ kind of people.
appreciate your input!

[Jeelock]

Dale, also I’m not thinking or intending analyzing everything. It’s just when I ran across this stuff it sort of messed up my thinking about what was going on in there. I really was kinda imagining a glob of metals all melted together. Seems that’s not what’s happening ??
the bead is only from the welding wire. ‘Fusing’ to the parent metals?? Do I understand that correct?
And thanks again.