Another MIG question

[Argeo]

Ok, I started welding last night a 1X3" cut out from my front fender. The piece fit real well and then I welded into place. What I noticed was that if I put a light behind it, you can see probably 10 or so pin holes around where I welded. Is that ok considering that the area will be covered with a thin layer of bondo? I will also be POR-15ing from the back side. I tried welding more into these holes but the spaces are to small to get any of the weld wire in there. I cover up but when I sand they reappear which tells me the weld is not going into the hole but just covering on the surface where my grinder eventually sands off. Is this because I am going to fast or because I am using flux.



One other question, other than the flux being more messy than mig is it weaker also? Will gas mig flow better for reducing such small pin holes. I have the gas but I haven't hook up yet. I love making more work for myself.

Thanks,

David

[Allenk]

You can get some seam seal to use on the weld from the back side. This will fill the holes so moisture doesn't get to the bondo from the pinholes. Por also makes a metal patch that can fill the pinholes-I don't like it.

[Argeo]

Hi AllenK,

Thanks for the quick response. Would the POR stuff be a putty they sell for patching holes in metal. I thinK I may have some. The stuff I have came with two sticks of seperate putty type stuff that are mixed together and then used to fill holes.

I used this stuff to fill a hole in a panel last year before I stripped the whole car, it was a PITA to get out.

Is this the same stuff or is there a finer product?

Thanks,

David

[RickM]

Just build small pools of weld over the areas with pin holes. You're going to be grinding it anyway. You want to get good penetration with no burn through and little, if any, warpage. Experience will build quickly.

[Allenk]

The stuff is more a gel that air reacts. Personnally I like the epoxy seam seal.

[fuelie600]

David,

If you look at the back side of the weld, does it look like it fully penetrated the metal seam? It sounds like you might not have the welder set up quite right. (not sure - I don't use flux wire.) Do you have some scrap sheet metal to practice on?

You need to make sure you are getting the metal to the molten stage, and not just depositing melted wire on top of the sheetmetal. try turning your wire speed down and work to get that sizzling sound. Once you have it right, the pinholes will fill easily. (Slag from the flux might make this harder.)

As far as filling inferior welds, once the filling/coating material breaks down and lets air into the pin holes, the welds will rust from inside out. It's better to get them solid.

Fun huh?

Keep up the good work!

[RickM]

Argeo, If you have a digital camera now's the time to use it.

[jm529]

you need a size 23 wire for sheet metal with a co2/argon mix. the flux core is only good for thicker metals with a high amp welder.

since its all welded up already i would use a fiberglass type filler to fill up the pin holes before you use bondo. seam sealer and por15 will work on the back side (we use zero rust at my shop).

hope this helps.

[Argeo]

Thanks guys.

I do have some fiberglass filler incase I am unable to fill the holes.

I was told to use a 30 wire with the argon mix using 18 guage sheet metal.

The wire is definitely melting. Not sure why it is not filling. If it is popping the setting is to low, if to hot it will burn right through the metal. Is this all correct?

I will convert my welder over tonight to gas.

Thanks again,

Oh, I do need a digital camera.

David

[widebody911]

Nope, .030 is way too big.

The weld isn't filling because you're moving too fast. You need to learn how to (quickly) find the molten pool and work from that. It's difficult on thin metal.

How much of a gap did you leave between the two pieces? For sheet metal, a hacksaw blade width works well.