burn through?

[jackfrost]

I have a Millermatic 140 Autoset turned all the way down, and I'm still burning through when putting new panels in (butt welded). the welder claims it'll do 24 ga., but this is 20 ga., and I'm still having problems. I'm not trying to do a continuous bead, just like 1/4" at a time.

is there something I can do to make it cooler? less wire speed? move the torch farther away? would those heat absorption pastes help? I have no problem with warping.


thanks.

[69stang]

Not familliar with the Miller but I have a Hobart 140 and I have no problems. You might try increasing wirespeed so you're moving the heat away quicker.

[dhutton]

I'm no expert but I think you should only be doing a quick spot tack, not trying to put down a bead even if it is only 1/4 inch.

How big is the gap between the two pieces?

Is your gas flow rate high enough? How far are you holding the tip from the metal?

[jackfrost]

even on tacks it burns through.

the gaps are usually pretty small, like less than 1mm.

flow rate I think is about 15 lpm, and i normally hold the torch as close to the metal as I can get.

i think maybe I just need more patience, and let the metal cool down between each tack.

thanks for the thoughts.

[dhutton]

You should space your tacks a couple of inches apart and work your way around. Then you start again.

[Mathius]

Just because your welder's prints say it'll do 24 gauge, doesn't mean it's SETUP to do 24 gauge. What size wire are you running? You should be running .025 or .023 wire. Even then I would only stick in 1" sections and jump around. Are you butt welding? Anytime you weld on the edge of the metal you're risking burn through and your settings need to be a bit lower than if you were running a bead in the center of the piece, or else you need to just tack. Are you running MIG or Flux core? Flux core burns hotter than a regular MIG weld. Your technique can sometimes cause burn through although if you can't even tack then I'm guessing that's not the case. But running a weave for example is going to put more heat into the piece than just running a straight bead.

Mathius

[oestek]

And you're right... let the panel cool between tacks.. it can take some time, but watch your heat affected zone around the tacks.. you want it as small as possible.

[jackfrost]

.023 solid wire w/ 75% Argon/ 25% CO2. butt welding.

thanks.

[Kokamo]

If you are having burn thru problems, and the machine is turned all the way down, and you have the smallest wire, I would say the next step would be to go strait C02 gas. The argon in your mix makes for a hotter burn.

But I would agree with a few post above....jump around with spot welds. Remember the more you weld in one spot, the more likely you are to warp your metal.

~Joe

[Simbad68]

When you prep the panels, did you use 2" or 3" disk? It's easy to cut to far in the panel and thin it out.
What pressure are your gauges set at now? You might try adjusting the gas pressure (Higher). I have a mm251 and I have to run higher gas pressures on thinner metal.
I have a roof panel if you want some pratice metal to try to get your welder set up.

[jackfrost]

I think the issue is grinding the welds down. I do pretty well doing the first tacking in, then I grind down the weld and fix any holes, and thats when it burns through, so apparently I'm grinding down too much, although I was trying to be careful.

so how do you get smooth welds without grinding away too much metal?

[Mathius]

I think the issue is grinding the welds down. I do pretty well doing the first tacking in, then I grind down the weld and fix any holes, and thats when it burns through, so apparently I'm grinding down too much, although I was trying to be careful.

so how do you get smooth welds without grinding away too much metal?

Switch to a less aggressive technique or disk. Switch to a flap disk instead of a grinding disk. Or use a cut-off wheel and grind with the edge of the disk. Apply less pressure? Really you don't want to be using a grinding wheel on a car other than to knock down the high spots, then you should finish with a sanding disk of some sort, whether it be a flap disk or a roloc, or whatever.

Also, I would suggest you get good at filling in holes. Poor panel fitment can cause the necessity of having to bridge rather large gaps, so that hole-filling skill will come in handy. Also helps with large plug welds.

Mathius

[Damn True]

I'd also suggest using a copper plate to back your welds.

[dhutton]

I think the issue is grinding the welds down.
so how do you get smooth welds without grinding away too much metal?

Take most of the weld down with one of those thin 3" cutoff wheels. The small size lets you only knock down the top of the weld without touching the surround sheet metal. Then you can finish it with a flap disc.