planishing mig welds

[tech69]

I'm welding just one side and although the penetration is good from the outside the weld is just a tad smaller on the inside of the part and this leaves an occasional area where you can see the line between pieces welded together. It's good penetration, it just doesn't completely cover that line. Off the top of my head I'm thinking, grind it down good enough to planish but leave some meat on it to file smooth after planishing, and if there's an occasional line on the backside that I need to weld, I should grind down the weld a little for better penetration and then zap it and carry on. Do you guys think this is a good idea to just weld where I need to on the backside or should I first grind down the backside and do a whole new set of tacks there, then grind front and back?

In regards to mig, is there a risk of cracking the metal when plannishing a mig weld area that has already been filed smooth?

Sorry for all the questions. Just trying to learn as much as I can.

[gerry miller]

Henry, I've done both sides on some stuff with that line. I think it is because I didn't get enough penetration. If there is not enough penetration it will crack when you try to planish it. Ask me how I know.
Gerry in Colorado

[Marty Comstock]

Turn the machine up a notch or three, and spend less time on the trigger. you'll have less wire buildup to grind off. Grind all of your weld before you hammer or stretch your HAZ. Nothing wrong with welding both sides, just doubles your labor. The weld will crack like any other process, if you make a bad weld or grind too much and all over the place making the panel thin.

[tech69]

well I can't go any higher on amperage but I can turn down the wire speed a tad. I'll get closer too. The penetration seems decent but is just a hair smaller than the outside, which leaves an occasional line, but if I bring my tacks closer up top to correct the bottom than it won't penetrate as well into the metal up top... so yeah, you're totally right. I need to dial in my settings a little better. Thanks for that.

[tech69]

Thanks for the advice, Marty. I made some adjustments and am happy with the results. Originally I was at about 50 wire speed and 4 voltage. Now I'm at 37 wire speed and 4 voltage. Still the same problem with the line showing where the panels meet but it's only in a few spots and now that the welds are lower I can just tack the line shut from the backside without even having to grind anything down, so it's working out great!

[jhnarial]

What size wire?

[lots2learn]

Its a common misconception with MIG that voltage is amperage. Wire speed is actually the amperage. Voltage controls the arc length and changes with different gases also.

[Marty Comstock]

Wire speed is wirespeed. MIG is a CV power supply where the voltage is constantly controlled and kept at a constant rate, but can change with how much wire stickout is utilized. Amperage is the draw of the short circuit happening at the point of contact, supplied by the pressure, voltage. True, without ample wire speed, you'll have no arc to draw amperage. But to call wire speed a direct relation to amperage, I am not so sure I would say it that way.

Here is a good explanation.

http://www.lincolnelectric.com/en-us...ge-output.aspx

Either way, turn up the energy input knob.

[MP&C]

Looking at your picture above, the weld appears to have good fusion to the parent metal, so it looks like you have plenty of heat. If you are not getting enough weld proud on the back side to eliminate the seam, try more wire feed. You shouldn't have to weld from both sides to get sufficient weld penetration.. That's just adding more shrinking effects. Fine tune your machine settings and technique to get it done from the one side.

[jag2be]

Greg, your correct.

With almost al the conventional Mig/mag welders the wire speed button is also changing the amps settings.the big one is changing the voltage setting .