New Welding Thread ?'s for beginners...MIG

[parsonsj]

Josh,

Yes ... that's how I do it.

One other thing to keep in mind about warpage: it is caused by heat from welding, but is also caused by the metal getting pulled in place. If you have a gap between the pieces of metal when you start welding, the molten puddle between them will shrink as it solidifies. That stress causes warping. That's why you want to get even spaced tacks all the way around and progressively close it so that the metal pieces don't move (as much) from the solidifying puddle.

jp

[Matt@RFR]

Key:

...so that the metal pieces don't move (as much) from the solidifying puddle.

For terminology, please see the attached drawing. It represents a section view of a fillet weld, also called inside corner weld.

Undercutting would happen, most likely, at the toe of the vertical leg of a fillet weld. It's when some of the base metal is pulled or washed into the weld, leaving a step at the toe of the weld. It's caused by lots of things...too hot, too fast, too shaky, etc.

Are the stringers the welds that go north-south in the pic? That is what I used on my cart before laying the circles (well, more like bloby puddles) on top of them.

The very same.

What you're talking about is a root pass, and a cover pass. You would probably have been fine running that in one pass, as long as you moved ahead and buried the arc in the root before filling up the rest of the joint, but it's hard to say without seeing your weld prep.

(EDIT): On that drawing, the 'fusion' arrow should be pointing at where the toe meets the base metal. I also wanted to mention that welds are sized by the length of the shortest leg, NOT the throat.

A good rule to live by is the weld should be as big (leg length) as the base metal is thick (thinnest member).

[Camaro Zach]

you can butt each tack up against one another but unless you get each tack right ontop of the other and get alot of heat on it you wont get 100% penetration inbetween each tack. here are some pics of what im talking about.

[JoshStratton]

you can butt each tack up against one another but unless you get each tack right ontop of the other and get alot of heat on it you wont get 100% penetration inbetween each tack. here are some pics of what im talking about.

Zach,

Thanks for the examples. I have actually been able to get a few sheetmetal welds to look like those! woohoo! I think my biggest issue is how I apply them to what I am doing and where to put them.

Am I seeing these correctly?

On the first pic, it looks like you bent the metal down and tacked the end so it would stick. That second pic looks like you did the rest of the tacking on the underside. Did you also lay a weld on the other side (which appears to be the outside of the piece)? What kind of weld did you lay down on the outside if you did weld that side? In that last pic, is that what it looked like when it was all grinded down and finished?

[Camaro Zach]

Zach,

Thanks for the examples. I have actually been able to get a few sheetmetal welds to look like those! woohoo! I think my biggest issue is how I apply them to what I am doing and where to put them.

Am I seeing these correctly?

On the first pic, it looks like you bent the metal down and tacked the end so it would stick. That second pic looks like you did the rest of the tacking on the underside. Did you also lay a weld on the other side (which appears to be the outside of the piece)? What kind of weld did you lay down on the outside if you did weld that side? In that last pic, is that what it looked like when it was all grinded down and finished?

the pics got thrown out of order when i posted them. But the first pic shows an outside corner weld. basically i just cut all the way down the piece but left that 1/4 or 3/8" at the end to hold the 2 pieces together when i bent them, then i tacked the other side so the pieces wouldnt spread apart. The second pic shows the uneven penetration on the corner weld and the butt joint. the third pic shows the top of the butt weld before it was finished. and the last pic shows what they look like ground down (although i didnt finish the butt joint because someone needed the extension cord)

[JoshStratton]

Josh,
That's why you want to get even spaced tacks all the way around and progressively close it so that the metal pieces don't move (as much) from the solidifying puddle.

jp

Oh boy. Now that is something I would have never thought of. No wonder body shop guys make 50+ bucks an hour.

A good rule to live by is the weld should be as big (leg length) as the base metal is thick (thinnest member).

This rule would not work for sheetmetal, would it?....god I hope not. Something like 18 gauge would be pretty hard for me to do.

After seeing your definitions, I totally realize how ugly my welds are. They are too wide and have a lot of undercutting. Is this something that could possibly lead to a dangerous situation? I plan on using my cart so I can get under it and work. I had the whole car on it, minus the front sub, at one point. It has only gotten MUCH lighter since.

[Matt@RFR]

This rule would not work for sheetmetal, would it?....god I hope not. Something like 18 gauge would be pretty hard for me to do.

After seeing your definitions, I totally realize how ugly my welds are. They are too wide and have a lot of undercutting. Is this something that could possibly lead to a dangerous situation? I plan on using my cart so I can get under it and work. I had the whole car on it, minus the front sub, at one point. It has only gotten MUCH lighter since.

No, that rule of thumb pertains to any joint besides a butt joint. Butt welds don't have legs, so you're left judging the weld "size" solely by penetration.

There's two downsides to undercutting. 1) It creates a stress riser. Stress risers usually only fail when under cyclic loading/vibration. 2) At the deepest part of the undercut, if you can picture this, the metal is thinner there. So basically, if the weldment is over engineered with material selection, it will probably be fine.

I'll leave the decision up to you, as to whether it's safe or not. Too much liability involved for anyone but you to make that call.

John, that's a tough question to answer, since it depends so much on the end use of the weldment, and how it was engineered (additional gusseting, supporting elements of the weldment, etc.). But, generally speaking, my quickie drawing depicts good penetration.

You can test your own welds: Section the weld, polish to a semi-shine or so, and etch it with muratic acid, or equivelant. That will show you exactly what's in my drawing.