Welding Tips and Tricks

I've heard that vertical down mig welding makes for pretty weak joints, with poor penetration, so I thought I'd give it a test:

I welded two 1/2" HRS plates together in a T joint, both sides vertical down. Then I laid the joint flat and clamped it to the table and started wailing with a two handed sledge hammer. The first 35 blows only bent the vertical plate and had no visible effect on the weld. The next 21 hits started to show a little crack at the toe of the start side of the weld in tension (all blows were from right to left). The 57th hit broke the weld.

I'm using a Hobart IM230, with 030 ER70s6, and C25. Settings were 9/85.

This seemed pretty strong to me, but then I'm not a veteran of too many hammer tests. Is this result pretty good and I worry too much, or is this a poor weld and I've set the bar too low?





So what do you guys think?

Welcome, Robbie,

There's truth behind the idea of greater penetration in a vertical-up mig. It's logical. When gravity keeps the puddle below your arc, you'll get more penetration in the root.

That said, a properly designed joint intended for vertical-down will perform well, as your hammer test showed.

If you'll look closely at the break, you'll see your simple tee-joint still has a sharp line where the parts meet. (Bevelling the tee piece would change this.) In a vetical-up, your arc spends a bit of time "in" this joint, fusing it. As impressive as your hammer test is (and I agree vertical-down is more than adequate for many applications), vertical-up done correctly willmake a stronger joint.

Repeat this test with the tee as a knife-edge, for full penetration from both sides, and you might prove "down" as equal to "up".

Steve S

I was going to say the same thing steve said took the words out of my mouth

I did both a vert up and down yesterday and then broke the weld in a press.
The down didn't peno anywhere near as much as the up,
But looked a lot prettier.

Your test is an excellent indication of the tensile strength of the weld metal, as the penetration of the base metal is not a consideration,

Mick

Mike, I understand that the tensile str of the weld material is a limiting factor in the overall strength of the joint... but I don't understand when you say that the penetration (or more importantly, the lack of penetration) is not a consideration. If there were no penetration, or perhaps extremely shallow penetration, wouldn't the joint have failed immediately, and the break would have been between the bead and the base metal?

The way I interpret it would suggest that the tensile strength of the bead-to-base metal interface is greater than the strength of the bead itself - which is supported by the observation that the bead remained stuck to the two pieces of base metal, but didn't stick to itself (broke down the middle).

Am I seeing this correctly, or missing something?

I guess my original question is, in the grand scheme of things, is 57 good, solid hits with a heavy hammer a good result for this joint? Does it indicate that the joint is strong, with the back side weld perhaps compensating for the lack of root penetration? How many hist does a test like this usually take to cause failure? I've seen some of Lanse/ChuckE2009's videos on YouTube where he breaks a single sided joint in 10 to 15 blows - is that more typical for a test like this?

Do it again but only weld one side.
Then do the hammer test so that it try's to open up the back on the weld, not the face.

RobbieKnobbie wrote:Mike, I understand that the tensile str of the weld material is a limiting factor in the overall strength of the joint... but I don't understand when you say that the penetration (or more importantly, the lack of penetration) is not a consideration. If there were no penetration, or perhaps extremely shallow penetration, wouldn't the joint have failed immediately, and the break would have been between the bead and the base metal?

The way I interpret it would suggest that the tensile strength of the bead-to-base metal interface is greater than the strength of the bead itself - which is supported by the observation that the bead remained stuck to the two pieces of base metal, but didn't stick to itself (broke down the middle).

Am I seeing this correctly, or missing something?

I guess my original question is, in the grand scheme of things, is 57 good, solid hits with a heavy hammer a good result for this joint? Does it indicate that the joint is strong, with the back side weld perhaps compensating for the lack of root penetration? How many hist does a test like this usually take to cause failure? I've seen some of Lanse/ChuckE2009's videos on YouTube where he breaks a single sided joint in 10 to 15 blows - is that more typical for a test like this?

The short form is, your bead tore where it did because of a lack of root penetration, not a lack of penetration in the weld interface. The absence of a true "root" in the weld left a sharp corner (the original fit of the tee), creating a "stress riser", or a concentration of forces, as you hammer on it. This is where the prep-work somes in to play, in properly designing a joint for it's particular service, whether welded up or down. Grind that Tee piece to a knife-edge, weld one side downhand, back-grind the other side, and weld it downhand, and try to break it again...

Steve S

And, yes, 57 good solid hits is a good recommendation for the joint you welded. Does that make it a "Heinz" joint?

Steve S

Hey,

What i was getting at was that when the root isnt fused 100%, what you have is, effectively, weld-gap-gap. So when you opened your can of whoop ass on it, all the force was on the weld metal. Yes it is fused to the plates, but not all tied together. Shows the strength of the deposited metal its self.

On a joint that has complete fusion through out, the weld will have more strength than the parent metal and with enough force, will actually tear the metal out around the weld zone, or in your case when both sides of the joint is welded, will simple tear the plate in half, at the top of the welds, leaving the weld intact.

Hope this isnt confusing you too much.

Mick