Mig porosity out of nowhere?

[Rock Crawler]

Last night a buddy drops a grapple off that he tore the grapple up-stops off of the frame. So I take the stop brackets and take a 7" grinder and clean the old weld material off as well as the paint. Then I take the grinder and a 4" flapper and clean the mounting point of the grapple frame of old weld and paint. I have my gas on and start welding and all is good for a couple inches and then I see it.... boiling bubbles in the weld as I keep going. So I assume some paint is boiling below, I'll grind out the 5" weld to the base material, then try again. Same **** thing! I placed 8 welds, each one about 5" long. 6 of them were text book beautiful, 2 of them are half full of blow holes. Even after grinding down and trying again, they blew back out in the same areas.

I was down to shiny steel, flapped it all smooth, paint was off about 1/2" from any weld areas. What the heck am I missing? I've had these battles before, and I wonder if it is my lack of formal weld training. One thing that I am thinking is that this is 5/8" steel plate and I push my gas/heat forward with the MIG torch. Is the thicker metal still fluid and I have moved the shield ahead before it cooled causing atmosphere to attack before it goes solid?

I am starting to think that instead of pushing the gas for the mindset of pre-heating by pushing the kernel forward, maybe I am screwed up and I should be dragging the gas over the weld area behind me to keep blowing shield gas over it?

I am running a Thermal Arc (Thermal Dynamics) Fabricator 210 mig with 75/25 shielding gas. Gas tank was just refilled, it still has plenty of pressure.

I forgot to take pictures of the porosity, but I'm sure you've seen it. It looks like fast boiling water that was frozen instantly.... Swiss cheese. I attached a photo of a weld I placed last night that did not screw up. Frustration!

 

[4570Man]

I've only that problem welding dirty metal or when I'm out of shielding gas. It doesn't sound like that's the problem.

 

[yomax4]

Porosity is usually a gas issue but can be from contamination. Pop your drive rolls open and pull the gun trigger and hold the nozzle to your ear. If you hear and feel gas, Not a gas issue. I always recommend that people buy one of the cheap flow meters that goes on over the gun nozzle to read actual CFH at the tip. You may just have a bad o-ring on the power pin of your gun or worse case, A hole in the gun cable. Paint and grease are another culprit.

 

[flyerdan]

A couple of things come to mind, take off the nozzle and make sure you don't have any slag or deposits built up in a crescent shape that restricts the flow in one direction, and if your are welding outside or even inside with drafts, air currents can disrupt the shielding gas.
I used to weld a lot of galv, and the zinc would build up inside the nozzle pretty good. And I tired to run as low gas flow as practical, but when all the shop doors were open we would get some pretty good drafts at time that required a lot more flow to keep things pretty.

 

[Oldpath05]

"make sure you don't have any slag or deposits built up in a crescent shape that restricts the flow in one direction"<<<<<Yup, and also maybe........

Diffuser gas holes clean and or new diffuser, tip, barrel, Insert in barrel hasn't slipped towards top, O-rings on the gun where it inserts in the welder are good, mig gun lined up with gas inlet where it inserts in the welder, gas line is sealed tight so air is not being sucked in, Murphy's Law.

 

[rustyshakelford]

I got a bad batch of mig mix once and there was nothing that could be done to fix it other than swapping out the bottle. LWS admitted it was their screw up. They didn’t care I was shut down and had to drive two hrs round trip to swap it out but once I had the fresh bottle I was back in business again

Brett

 

[crazyal]

Make sure you're not cooking any of the grease from the joint close by. Just like smoke from burning paint smoke from other contaminates will also cause problems. With grease taking a lot less heat to cause problems it doesn't have to be close to turn to smoke or other fumes. Also make sure you don't have a breeze from a fan or something else blowing pushing your shielding gas away.

 

[sw99]

I had a similar experience the other day when my C25 was bumped to 30'ish. Backed it down to 25 and I was GTG again. Same thing, very clean metal and no other explanation that I could find.

 

[bdog]

Not sure if this was your problem but it doesn’t take much breeze to blow the shielding gas away. My mig welder is 20’ inside my shop and the shop only has doors on one end. I often have to shut the doors to keep the breeze away. When it happens there are certain positions or locations that are fine and out of the wind and others that get the porosity.

 

[dragoneggs]

Not sure if this was your problem but it doesn’t take much breeze to blow the shielding gas away. My mig welder is 20’ inside my shop and the shop only has doors on one end. I often have to shut the doors to keep the breeze away. When it happens there are certain positions or locations that are fine and out of the wind and others that get the porosity.

I'm slowly realizing that having the doors or window in my shop or fan going does make a difference. I didn't know it was so sensitive. Too bad because I want the ventilation for health reasons that I appreciate as I get older.