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

[JoshStratton]

Hey all, and probably Matt since he seems to be the forum guru on this subject and may reply

I looked for a thread like this but didnt see one. I am guessing it fell off the board if one ever existed.

I am planning on doing some body work on my car. I have a small MIG welder that seems to do a decent job on thick stuff up to 1/4 inch.



I practiced with my welder by creating a body cart.




Now that I am about ready to work with sheetmetal, I wanna make sure I don't create a brittle mess of welds and I know that sheetmetal is a whole new animal from what I worked with previously. I will make sure my butts (hehe) are tight (hehe again), but I am not quite sure how to do the finishing welds after spotting every 6 inches or so.

I think I saw Matt mention in another post that with a MIG, you wanna find you setting and then pull the trigger on one spot for 2 or 3 seconds.

Instead of laying a bead when finishing thicker stuff, do you just create a series of spot welds all the way down the seam?

Would anyone have any pics of what the welds would look like before grinding them all off?

Also, what kind of penetration are you looking for with sheetmetal?

Should the weld go through the entire panel, or just 3/4 of it?

I am sure I will have more questions after getting some answers but I thought I would start with these.

[Travis B]

the method you are reffering to is called stich welding.....Get your peice tacked in good. Then go around the area slowly putting a series of tack welds back top back to back......(slightly overlap the previous tack weld) is the best way to describe it. I usuall to 1/2 to 3/4 of an in and move to a different area on the panel and work my way around! As far as penetration goes you shouldn't be able to see a gap on the back side of the panel. You want to be sure after you metal finish the area that it will have enought structure to hold it's self! hope that wasn't to confusing

[JoshStratton]

Thanks for the info! When you say you shouldnt be able to see the gap on the backside, should you be able to see the 2 pieces butted together or should the weld cover that as well (full penetration)?

With the slight overlap of 1/2 to 3/4's, are you saying that you put one spot down, then another on top of it before moving to a different place? I like that idea. Originally I was going to do that but was worried about warping. So, I decided I was going to just spot every 6 inches, then go around again and overlap the original spots one time. Then go around again, until they all connect. My biggest fear with this is that the weld would harden, and then the next time around I would just be piling it on the original spot instead of getting penetration.

If warpage shouldnt be a problem, I will do it your way. Cool beans.

Now here is another question. With my body cart, I wasnt too worried about how the welds looked. Do I need to actually dip this wire in the weld for sheetmetal, or should I let it burn off without touching? I think with a MIG it has to touch to get the ground, but I wasnt too sure.

[Matt@RFR]

Hey Josh. Yeah, welding bodywork is completely different than structural stuff.

To quickly answer one of your questions, no, structural MIG does not include individual spot welds, ever. That's just begging for a failure of one kind or another. I attached the only picture I have of one of my MIG welds. It's 1/8" mild steel.

To give you a real world example of how much spot welding would be frowned upon in the world of structural steel (bridges, buildings, etc.), anywhere a weld stops, the end of the weld must be ground down to the base metal before another weld is begun. And in multi-pass welds, starts/stops are staggered so they aren't in the same area.

,,,but I am not quite sure how to do the finishing welds after spotting every 6 inches or so.

Well, puting a tack every 6 inches is a good start. Then tack the joint every 3 inches. Then every 1 1/2". Then every 3/4", etc., etc..

Concerning the physical technique, once again we're talking about something that's pretty personal. It depends on your voltage/wire speed/wire size/stick out/gas coverage/metal cleanliness, as well as how well you can actually see what's going on in the roughly 1/2 second that the arc is on. I think most guys find that just pulling the trigger and holding the gun still works fine for them.

Penetration on 16-20ga and thinner should be complete, but for bodywork, I'm thinking it's not really required. Also, I'm not even sure the body guys completely weld the seems. You may want to check on that.

[JoshStratton]

Oh! In regards to preperation:

With the body cart, I grinded down the edges of the connecting pieces to create a gap when they were butted together. I then layed a bead in the grinded area to get a solid connection, then I did the looping )))) motion to finish it and get full connection. What would be the method of preperation for sheet metal? It is too thin to grind down this way, I would think. It sounds like the method would just be a series of spots instead of the bead and ))) method.

Hey Josh. Yeah, welding bodywork is completely different than structural stuff.

To quickly answer one of your questions, no, structural MIG does not include individual spot welds, ever. That's just begging for a failure of one kind or another. I attached the only picture I have of one of my MIG welds. It's 1/8" mild steel.

Penetration on 16-20ga and thinner should be complete, but for bodywork, I'm thinking it's not really required. Also, I'm not even sure the body guys completely weld the seems. You may want to check on that.

Thanks Matt. In that pic, have those been grind down? My welds are kind of piled up. I am pretty sure I got good penetration, but I think I didnt go fast enough and they were piling up.

Is that just a matter of slowing down the wire speed? I had my heat just about as high as I could get it. It is a small 110 welder. It isnt a Lincoln, but it looks like one. I cannot remember what brand. hmm....

[Matt@RFR]

It sounds like the method would just be a series of spots instead of the bead and ))) method.

Correct.

In that pic, have those been grind down? My welds are kind of piled up. I am pretty sure I got good penetration, but I think I didnt go fast enough and they were piling up.

No, the picture I posted is of an untouched weld. No grinding, no wire brushing, no nothing. The only time I grind welds is if something has to fit flush where a convex weld is.

A weld that sits too high is either too cold, or too slow. Yes, if you travel too slowly, the incoming filler will just pile ontop of the filler that's allready been deposited, resulting in no further penetration. It's a very dangerous habit to get into. If travel speed is too slow, then the arc never sees the root of the joint, which, again, results in fusion, but no penetration.

[Travis B]

Matt-

is that a continuous weld in the pic?

[Matt@RFR]

Yessir.

[Travis B]

WOW! very nice

just out of curiousity do you push or pull your welds?

[Matt@RFR]

Thank ya. Mostly I push, but it depends on the circumstances. Usually that boils down to how lazy I am that day versus required aesthetics. Generally, I keep things to within 15º or so of 90º, so there isn't much change.

[JoshStratton]

How big is that piece in the picture?

[Matt@RFR]

That is the long side of 1 1/2" x 2 1/2" x .120 rect tubing, the triangular parts are 1/8" thick, long leg is roughly 6".

[Travis B]

I am still trying to come up with how you got the nice dime looking pattern. I feel like I can weld pretty good mig and tig...at least I think I can.

What kind of mig do you have was it on any kind of special setting or.....am I not as good as I think I am..lol!

[Matt@RFR]

I have a Miller 251. No special settings, just a good solid setting for the material thickness, and a steady hand. A big part of it is being completely relaxed. I can carry on an in-depth conversation while welding.

I'm pretty sure I did that weld using a push/pull technique, as opposed to doing circles. Who knows, I change the way I weld every day. I get bored easily.

[Travis B]

regarding your comment about circles and other methods.....I usually try and make a solid pass no circles, no hesitations or anything like that! And my welds come out nice and smooth good penetration basically a nice consistent uniformed sized weld! But they don't have the nice "droppin dimes"look that yours in the pic has????

now i'm gonna loose sleep...thanks a lot! lol

[Matt@RFR]

Well, if you look at that picture again, there's two welds like you're describing. Those are called stringers.

There's nothing wrong with that technique, IF you move fast enough, don't get any undercutting, and still end up with the correct size weld. For those reasons, I usually stay away from stringers on fillet welds. It can be hard to get the weld size you want and still keep your travel speed up. Plus, using a pattern like a weave, circles or push/pull, it's easier to make a good looking weld on those really shaky days, or in akward positions.

[JoshStratton]

If you dont mind, there are a few terms in there that I would like to add to my metal glossery.

What do you mean by undercutting? Is that the same as blow-through?
What is a fillet weld?
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.

[parsonsj]

On my body work welds I do the tack weld thing until the tacks are 3/4" to 1" apart. Then I run a set of stitch welds from one tack to the next. Pull trigger, release, move, pull trigger ... in about 1-2 second periods. You'll get a rhythm that lets the new spot melt into the old one with an over-penetrated weld which is perfect for grinding smooth for bodywork. Be sure and move around to reduce the warping.

Also, watch it when grinding the weld ... that heat can also warp panels.

jp

[Travis B]

that is what I was trying to explain...well put john

[JoshStratton]

Ahhh I get it now! So you don't spot all the way around next to each other? Do kind of what Matt was saying at 6" then 3" then 1.5" then .75" then lay a stitch to close them?

Thanks guys. I will give this some practice. If it doesnt work, I will try and post some pics to get some feedback.