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I'm using a Lincoln Electric 140 mig welder with 75/25 shielding gas.

I'm having a problem when I tack weld. Instead of the weld building up, the sides build but the centre hollows out and leaves a tack weld that looks a crater instead of a small bump.

I've checked the instrutions for the welder and it's hooked up correctly for polarity. I've tried varying the gas flow rates with no success.

Has anyone had this problem....how to I fix it?

Any help would be appreciated.
 

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The more voltage you use, the quicker your wire will melt... you have to therefore adjust voltage within the range that your wire feed speed is set to.

When ever I don't get a consistent tack, I adjust up the voltage first.... I prefer to run on the hotter side in many applications. It makes for a flatter tack or bead, but then there is less grinding too. YOu can adjust too far, then you will need to bring the wire feed up. I had an instructor once ask me, does your weld look like you've just added metal on top, or does it look like you have added metal to the base weld pool. Adding to the weld pool is what your after.

You have to be careful to not run too hot, or you will introduce too much heat into thinner panels like the outside of your car. Adjust your settings. You may find that you need to stitch weld on your thinner panels, getting on and off the trigger quickly... this minimizes heat,

Good luck
Gil
 

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Who's wire are you using? I usually use Lincoln's but ran out the other day and went to a local place and bought an off brand. Now I'm having all kinds of weird welds....bubbles,etc. I've had issues before with off-brand wire.
Josh
 
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