Welding Input - Chevelle Tech
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post #1 of 17 (permalink) Old May 14th, 19, 12:27 PM Thread Starter
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Drew
 
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Welding Input

I'm learning to MIG weld, for the most part it's sheet metal, anywhere from 18-20ga. I'm using gas and have a Millermatic 180. I have read several articles by Brian Martin and typically what he writes makes sense, easy to read/comprehend, at least for me.
I was practicing with some 18ga last night and it's some of my best group of welds, going with information from Brian's articles.

My question now is, when getting to the edge of the seam, is it common to blow through the metal? (Pic2) I had what I thought were some nice dots along the seam and then when I got close to the edge, blew a hole. Any suggestions on avoiding without re-adjusting the welder for that one spot?
The last pic is the backside.


Also, why are there little holes in the top of my weld dots? They aren't through the weld, just on top. Any concerns with that?
Thanks for the input.
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post #2 of 17 (permalink) Old May 14th, 19, 2:08 PM
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Re: Welding Input

Your welds look pretty good. Definitely better than mine when I first started. I blow thru the ends a lot as well, so I am interested to see what others have to say. As far as the little dot on the middle of the weld, that's perfectly normal in my opinion. Try lowering your wire speed just a touch, and maybe a notch up on the amperage. As I practice, I realize that you want to be REALLY hot but SHORT. Just little zaps. Thanks for the post, looking forward to other answers. Thanks!
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post #3 of 17 (permalink) Old May 14th, 19, 10:02 PM
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Re: Welding Input

I though Drew's welds looked pretty good too, but not having welded much sheet metal, I didn't want to be the first one to say so.
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post #4 of 17 (permalink) Old May 14th, 19, 10:27 PM
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Re: Welding Input

If there is one thing you take away from this is, DO NOT I REPEAT DO NOT cool the weld via water or air. It will make the metal shrink more therefor making your weld damage worse and also harden the metal, allow the panel to cool naturally under its own power.

What does the backsides of the weld look like? You want visible and feel able penetration on the backside without over doing it.

I would also try turning the wire speed down just a tad and turn the heat up.

A hotter weld is indeed a better weld for sheet metal. A quick hot weld will introduce less heat into the panel then a slower cooler weld because of time. Because you spend more time on the panel with a cooler weld it allows the heat to spread over a greater amount of the metal.

You should weld in quick hot fast tack welds. Make a tack then move several inches or whatever down the seem. Once you hit the end, wait allow the panel to cool BY ITS OWN DON'T FORCE IT. Now take a grinder and knock off the high protruding weld just to the point of flush. Now place your next tack weld over the previous weld by say 25%.

You grind the tack weld almost flush because without doing so, your new tack weld is trying to burn through not only that old tack weld but also the base metal.

You can place a piece of copper under the panel at the end to help soak up the heat to prevent blow through. But try starting the weld at the edge then working away from the edge. It blows through at the edge because the heat is built at the edge and has no where to go. When you start at the edge there is no heat build up yet.

Try pulling or pushing the torch, you might find one technique works better for you.
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post #5 of 17 (permalink) Old May 15th, 19, 1:04 AM
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Re: Welding Input

is your miller 180 an auto set?and if so do you have it on auto?
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post #6 of 17 (permalink) Old May 15th, 19, 9:16 AM Thread Starter
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Drew
 
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Re: Welding Input

Eric,
The backside is the last pic I have in my initial post. Too much metal or look about right?

My process was what you are stating, I tacked a spot then moved about an inch or so away and tacked it again. Cooling time was however long it took to trim the wire, adjust for stick out and lower my helmet. I didn't cool any of the welds other than time between tacks. After each pass of tacks, I went back and ground them down, not perfectly flat but to a point they were a fairly flat surface. I might have the next tack a bit more than 25% coverage of the previous tack, not sure, but I know I don't have any pin holes on the seam, something I've had issues with before.
After welding these together, the pieces I welded do have a noticeable curve in them.

I think pulling the torch, when I don't tack, gets me better results.

I'll adjust the settings a bit and see how that goes and try a few pieces working from the edge and then toward the middle. Right now, if I can keep getting welds like I posted, I'll be happy.

My welder is an auto-set but I haven't used the auto function yet.
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post #7 of 17 (permalink) Old May 15th, 19, 9:30 AM
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Re: Welding Input

Learning...

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post #8 of 17 (permalink) Old May 15th, 19, 10:20 PM
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Re: Welding Input

Quote:
Originally Posted by Droff View Post
Eric,
The backside is the last pic I have in my initial post. Too much metal or look about right?

For a beginner welder, great job!
But with that said, if you were to hand that example into say an Icar certification test, it would fail.


To me, it appears you have excess penetration on the backside, but the killer is that you still have areas that are not fully welded on the back. You can clearly see the root gap.


I still say turn the wire speed down a touch but turn the heat up.
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post #9 of 17 (permalink) Old May 15th, 19, 11:30 PM
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Re: Welding Input

Quote:
Originally Posted by Droff View Post
Eric,
The backside is the last pic I have in my initial post. Too much metal or look about right?

For a beginner welder, great job!
But with that said, if you were to hand that example into say an Icar certification test, it would fail.
A properly welded joint seem is stronger then the surrounding parent metal and when destructive tested the weld will remain intact while the parent metal will tear.

To me, it appears you have excess penetration on the backside, but the killer is that you still have areas that are not fully welded on the back. You can clearly see the root gap.

I still say turn the wire speed down a touch but turn the heat up. Try when you make your welds, stand your gun perpendicular to the metal, then angle the gun back at the weld at about 60 degrees so the nozzle is pointing at the old weld. This will tend to push the heat and weld back into the previous weld

When welding thin gauge metal, you should strive for NO too as little as small gap as possible. A gap is harder to weld, shrinks the panel more, if one can't get 100% penetration on 18-20 gauge metal with no gap then you need more practice.

The curve you see is from weld distortion. Just like the shrinking disc on how it shrinks metal via heat, welding does the same thing. The localized heated metal is trapped by cooler much stronger surrounding metal and as it cools it has no where to go but collapse into itself making it thicker.

The ONLY way to correct that weld distortion is to reverse it. Shrinking caused the distortion so stretching is what will correct it.

Currently working on How to videos and replacement sheetmetal panels

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1970 chevelle SS455 not a typo its a BUICK BABY
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post #10 of 17 (permalink) Old May 16th, 19, 12:01 AM
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Re: Welding Input

While the I-CAR Steel Welding Qualification Test does not include this type of weld, the basic criteria can still apply.

There is too much penetration. Turning down the wire will reduce the heat and reduce the amount of material deposited. All the wire you are burning has to go somewhere, with a lot of heat gravity pulls it thru to the back. This could be the reason for the sinking on the front also. All you need is "evidence of penetration", a small bump that is more than just a heat mark. It takes only a small bump to pass the destructive weld test, any more penetration is not stronger, it only adds more heat which can weaken the metal.

When I conduct the test I examine almost all the welds with a magnifying glass, partially due to my older eyes but also to be sure the welds are correct. With pictures I cant see what your root gap is, play around with it to see what you like. Making it closer will kill some penetration. 0 to 1 metal thicknesses is recommended. I like them tight but you have to clamp good to keep them from climbing.

Clip the ball on the end of the wire EVERY time before you start a weld. If you are using .023 wire and have a ball on the end you are trying to melt larger wire at the start of the weld. This will cause cold starts which may be the cause of your lack of penetration as you start overlapping previous overpenetrated welds.


As mentioned gun angle can make a difference on penetration as can distance. Think of the wire as trying to push heat thru the metal and change your angle to where the heat is needed. I lay the gun down more at the end to reduce burn out buy directing more heat towards the previous weld bead instead of down thru the metal. The weld bead will take the heat better than an edge will.

It will be tough to weld coupons and not get some distortion. Each weld is putting in the same amount of heat as it would on a big panel but on a big panel you have more area to absorb/dissipate the heat. Distortion is not scored on the test as long as it does not affect fit-up.
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post #11 of 17 (permalink) Old May 16th, 19, 1:42 PM Thread Starter
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Re: Welding Input

I adjusted the heat up and wire speed down, I’m not positive but it looks like my welds were a bit flatter. Penetration may be a bit less heavy as well but hard for me to actually tell. I did not grind any of them, just wanted to see how the metal took the added heat, which it looks like it went pretty well.
I can’t describe the sound well but when the result looks like a good tack, the sound was a consistent buzz or zap. Not frying bacon.

Again, I’m using a MillerMatic 180 so I have the wire speed a bit under “50” and the heat up to the low side of 16ga. Gas is running around 20-22 CFH. The wire lead is around 3/8” to ½” out and tip is usually around a 45 degree angle to the seam so I can see the seam. I don’t have solid consistency on tip position but I’m fairly close.

I’m trimming the wire before every tack weld which is tedious but very helpful, cuts down on variables.
Notice the perpendicular seam with the crappy looking welds. I did not have a tight fit there with at most I’d say 1/32” gap. With the same settings I kept blowing holes in the metal, couldn’t get to a point where I got it resolved but I’m guessing maybe go with less heat as there is a gap? If I can’t weld a gap like that, I’m going to have issues as I don’t think I’ll be able to get every piece cut perfect with no space.

Thanks.
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post #12 of 17 (permalink) Old May 16th, 19, 1:44 PM Thread Starter
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Re: Welding Input

The pics with the older looking metal is what I’m actually going to be working on, I need to replace a section of the core support under the battery tray. It’s thicker material, somewhere in the 16-18ga range (I think). I wanted to do a few test spots with the old piece and the new replacement piece. I got it cleaned up with a spot blaster as it’s pretty pitted. I adjusted up the heat and got a few decent looking welds but the penetration looks kind of sketchy. Is that due to heat or wire speed or rough metal condition?

It was very noticeable that I did not get any kind of zap or buzz sound on any of those welds, it was mostly just a hissing sound. Again, only guessing but I’m thinking the older, pitted metal is the cause of the sound.
Any tips or input on welding the older stuff is appreciated as well.
Thanks.
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post #13 of 17 (permalink) Old May 16th, 19, 1:58 PM
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Re: Welding Input

The ground clamp may be suspect in some of what I read. Also, as was noted earlier and in my limited experience, the use of a copper backing plate may help prevent the blowouts.

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post #14 of 17 (permalink) Old May 21st, 19, 6:11 PM
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Re: Welding Input

I would learn to weld on good clean metal first. Get the welder set up and practice and practice. A beginner learning to weld on pitted metal is foolish, you simply have no idea what you are doing and now you throw an extra variable in mix.

If you are welding are the weld sounds like bacon frying your welds are gonna look like sh!t It should be making a nice constant ZZZZZZZZZZ.

What size or diameter is your wire, 23 or 30? For 18-20 gauge metal wire size 23 is preferred less heat required to melt that smaller wire.

Your welds on that pitted metal look like crap because you are welding a good clean piece of .047 thick steel to a pitted piece of metal that now might range from .047 to .020.
IMO age has nothing to do with it, its all because of the varying degrees of metal thickness on one side of the weld joint.

Go to a hardware store buy a 2 ft long section of 3/4 copper tube. Cut into various lengths, then smash flat with hammer. Clamp copper to backside.

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post #15 of 17 (permalink) Old May 22nd, 19, 9:38 AM
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Re: Welding Input

Might try a bottle of 75/25 Ar/Co2 gas, works very well with carbon steel.
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