cracking welds :(

[robwizard]

Basically I bought a MIG off this forum and ran it with the gasless wire that came with it just to practice and then upgraded to a pub gas bottle once I became more confident.

I bought it to do car bodywork amongst other things and everything is going well, I'm getting done what I need to butttttttt.. the problem I seem to continually have is the welds cracking when I'm grinding them off!!

I think maybe I need to turn the power up so the weld penetrates the metal more? but then it burns holes.. should I be quicker with the stop start technique?

I'm not great at describing and I have no pictures but if anyone can advise me that would be awesome!

Cheers

 

[keith19]

Just a midnight thought, Rob, is that pure CO2 you are using from the pub? Some CO2 bottles have a CO2/N2 mix, which makes them pretty useless for welding. Nitrogen is good for making tiny bubbles...

If your gasless welds were good, and your methods of cleaning and technique are the same, then it sounds like the gas needs checking out.

 

[robwizard]

Yeah the gas is defo Co2..

When I was practicing with the gasless wire It was mostly on thicker stuff.. I didn't notice the cracking because I wasn't grinding the welds down as flush as I am on the car panels if that makes sense?

It's like if I were to make a patch I put it in, put a couple of tacks down and make sure it is all fitted up nice, then weld it in. Then go back to any bits where I have blown through, everytime lol, and patch them up. Then I get the grinder out, with a flap disk, then start grinding the welds flush. And that is when they usually crack!

 

[pulltopark]

Just a thought u hAve changed the polarity

 

[robwizard]

yep polarity is changed for the gas wire

 

[rikrobson]

Are the weld beads thenselves cracking or is there not enough penetration and when you grinding down the bead you are seeing the original gap in the two bits of parent metal?

 

[backpurge]

As Rik says above you need to confirm whether they actually are cracks or lack of penetration

 

[Drains]

It's most likely you've no pen, the weld is sitting on top, then you're grinding it off. Either up the volts and travel speed, up the volts and use the thin metal technique, or leave a prep- eg a gap, between your pieces to be welded. The gap can be small and you might even need to turn your volts down, but the weld will penetrate easier, and you should get less finishing to do.

 

[Stereophoney]

or are they gaps between the welds ? are you using the stitching technique leaving cold spots ?

 

[TechnicAl]

If they are straight line cracks they arent cracks they are lack of penetration. Proper cracks follow the line of least resistance which is invariably wavy.

 

[robwizard]

Lack of penetration it would seem then!

Thanks alot I will get on sorting it out asap

Cheers