minimising distortion when mig welding thin steel

[optima21]

here's my way of doing this, on a doorskin and welding in a new bottom edge from 0.9mm zintec. When Mig welding thin sections I prefer not to have a gap between the sections and to get them touching if possible. I'll start off by welding a few tacks along the length. the tacks will shrink when cooling so the gap may need to be adjusted with some hammer and dolly work.

and do a few more tacks, the panel alignment can still be adjusted at this stage.

when you think you have enough tack, grind most of the tack, but leave enough so you can see where they are, this also shows how close the gap is.

then start to to join the tacks with ovelaping tacks to reduce the heat input, and leave a few inches between the tacks.

then go back and do a few more, this will reduce the heat input to reduce the distortion

\

and the same again

and again

and when youve completed it you can grind the welds back

and the end result, I dont think its too bad, and could be improved with a bit of dolly work.

 

[nickk]

Good technique,polo Mk1 ?

 

[striker]

Good technique. I've not done much car stuff for a long time...I also blasted with compressed air after each tack.

 

[JOEPRO]

Nice work thanks for sharing

 

[optima21]

Good technique,polo Mk1 ?

close its a mk2f polo

Good technique. I've not done much car stuff for a long time...I also blasted with compressed air after each tack.

Ive tried that in the past, but I need 3 hands to use a compressed airline too ..... one day someone will make a mig torch with a foot operated airline

the main thing is to keep the heat input low, to reduce the amount of metal expansion which causes the distortion. best thing it to try different techniques and stick with which works for us best

 

[steveo3002]

clean work

those polo doors are a weird construction eh

 

[Memmeddu]

I know the tack and hammer smack technic .
You put a tack then you put a bodywork tassel behind and hit with an hammer

 

[bainzy]

I tried your method yesterday @optima21 on a floor pan lip I need to extend and like it a lot, thanks for sharing. Previously I was filling the entire length with just small tacks but it's hard to get sufficient penetration the entire length, even if you grind back a few times.

I was able to use a thick copper bar behind mine and get away with bursts of weld about 1 inch long for the second step. End result was good penetration the entire length of the weld with no obvious distortion beyond the seam itself.

 

[GRW]

I'm a not-great occasional self-taught mig user, & most of my thin panel welding has been on my yr 2000 rusting LDV Convoy Camper (RIP Nov 2022).
The LDV was actually a good vehicle to learn on, cos it was so fugly that my poor welding & plating finish wasn't really an issue aesthetically

The thin (like 0.7mm) sheet on the LDV meant "tack & move" was all that worked without blowing through and/or lots of distortion.
I also saw "Bad Chad" on YouTube using the method adding in the compressed air cooling ..... but not tried that myself (yet) due to most of the panel welding taking place on my driveway.

Hopefully one day my weld repairs will be as neat as the OP's Polo door repair

 

[mrgoodwelds]

Turn your gas lil higher than normal and try to almost weld in strait line at a low speed and low heat using like aluminum or other metal that dosent stick to the weld afterward clamped or just against the two pieces tightly on the opposite side you are welding, this helps if you burn through, the trick is to get metal as flat so when you weld its alomost a straight line or the ol' push and pull method the aluminum is there to give the weld support so you don't have the weld causing the metal to sag or twist basically you want to make your weld as even as possible almost like it was 2d instead 3d because the weight of the bead is a huge factor with thin metals

 

[mrgoodwelds]

How fast your Pushing the wire into the weld is how to adjust the thickness/penatraion of weld its tricky but possible