Butt welding thin sheet?

[San Migweld]

I need let in some new metal on a car body floor (16swg) which needs to be seen from both sides so I want to butt weld? My intention is to mig both sides on the lowest setting and grind back with a flexible disc.

Is there a better way or would this method be ok please?

 

[Premiershipman]

If its thin sheet, dpending on your lowest amp output for your welder you could try the 'stitch' technique or 'stop/start' technique where you do multiple spot welds in a continuous line as this gives a small time for the metal to cool slightly before the next spot weld.

 

[Sean]

If its the floor, welding from the inside so gravity is working with you will be the easiest.

Batting a few bits of plumbing copper pipe flat and placing it under the work means that you can up the power a bit and get good fusion

polished up with flap wheel and you wont need to weld from underside, where you'll probably end up in a mess anyway.

Sean

 

[Drains]

Weld from above, but when you set up the job , leave a gap - about 1mm - at the joint. your 16g is easy to work, but depending on the thickness of the steel you're joining to, which is probably less than 16g, you may need to use the thin metal technique or bias the heat towards the 16g and wash over to the parent metal. You won't need lots of power if you leave a small gap but you'll still get full penetration and fusion if you do it properly. You'll just have to give the underside a gentle going over with a flap disc.

Use enough tacks to keep the sheet held in place firmly and stop the gap closing up as you weld, ideally doing the tacks from below so they don't affect the welds.

Welding on the lowest setting is not the way to approach the problem. If you close the gap up tight and weld on a low setting, when you grind the weld back there will be no weld left and the joint will break. Use the right setting and the right joint preparation, whatever they are.

 

[San Migweld]

Many thanks guys for all of your sound advice!

 

[Randall977]

Did a bit of butt for my car restoration welding using the thin metal technique...I think it looks okay. The original part is on the left - it's a brake servo housing.