What am I doing wrong?

[Mags]

Hi all, I'm in the middle of repairing the passenger door on my '72 VW Camper, I've been welding on a bottom panel that replaces about a third of the door frame before replacing the skin, its been going OK other than less than perfect fit of the new panels but when I inspected some plug welds I had made they haven't actually attached the new panel to the original inner frame/strengthener rails which is a much heavier gauge material. The Plug welds look good but they just don't seem to have stuck to the material underneath, I'm assuming that I might not be getting a good earth on the original frame, would this make sense?
I also had a few issues with the arc not starting where I had used weld through Zinc primer, so again, could this just be earth problems?
I've played around with settings on my Mig, but at a medium setting (4 out of 6 on a SIP 180 amp MIG) I can easily blow holes in the thinner material when trying to plug weld. I've found on a lower setting (2 or 3)I can get much better results on the butt welds with what I think is good penetration but some of the plug welds just aren't working for me.

Sorry, don't have pic's but I'll get some if its needed.

Cheers

Mags

 

[malcolm]

I used to get the same thing with plug welds. The trick is to arc against the rear sheet without letting the arc touch the front sheet. When it's built up nicely just circle the torch around the blob to bond to the front sheet. Otherwise no heat gets into the rear sheet and you get a cold weld or no weld at all.

The size of hole is important - any less than 6mm and stray arc will stop you getting to the rear sheet, but anything more than 8mm is a pain to fill on thin sheet.

Also It's possible to up the heat a bit. Two sheets of 1mm clamped tightly together will be 2mm thick, so the power setting should be higher than you would use for 1mm.

 

[Mags]

Thank,' I've been using 5mm holes as I read somewhere this was good and the joggler/punch seems to make ~5mm holes, I'll drill out the bad ones and try again with a slightly bigger hole.

Cheers
Mark

 

[Rusty]

Plug welds take a bit of practice to do right , you need to concentrate on getting a good weld on the rear sheet then gradually join to the front sheet in a circular motion ( try upping the power to )

 

[Stunter]

I used to get the same thing with plug welds. The trick is to arc against the rear sheet without letting the arc touch the front sheet. When it's built up nicely just circle the torch around the blob to bond to the front sheet. Otherwise no heat gets into the rear sheet and you get a cold weld or no weld at all.

The size of hole is important - any less than 6mm and stray arc will stop you getting to the rear sheet, but anything more than 8mm is a pain to fill on thin sheet.

Also It's possible to up the heat a bit. Two sheets of 1mm clamped tightly together will be 2mm thick, so the power setting should be higher than you would use for 1mm.

good advice - i've used this method a lot of times thanks to your tutorial's. I used to try and weld where the metals joined inside the hole, almost like doing a round butt weld if you see what i mean.....did this to some tubing when i extended some legs on a seat for the back of my van as i couldn't weld right at the top of the tubing as i would melt the vinyl.

It also works well using the same technique to weld nuts onto threaded bar to make your own bolts

thanks Malcolm

 

[Rich.C]

I also had a few issues with the arc not starting where I had used weld through Zinc primer, so again, could this just be earth problems?

I've found it better to remove the primer at least from the centre of the hole. Gives you a better arc on starting the weld.

 

[..DAZ..]

http://www.mig-welding.co.uk/plug-weld.htm

have a look above, I found it pretty useful as I had neve done plug welds before

cheers
daz

 

[Tino]

I know it says weld through primer but you will always get better results with clean material.

 

[Mags]

Thanks all, much more sucessful this time round, I used a bigger hole, turned up the power and made sure I had a good clean earth on the heavier material, got a nice plug weld that doesn't appear to be shifting now. I was trying to clean out the primer from the hole before but leads me onto another question, I'll have a search first and then post int he right forum if I can't find the answer.

Mags

 

[zardoz]

there is such a beast known as a "plug weld pliers" or similar name. I have heard of it being used to good effect when people have been having difficulties.

 

[chrisg3103]

ooo they look like a good idea! nice lump of copper on the back to stop you blowing through, get a good bit of heat in there. could make some out of a bashed in bit of copper pipe and an old pair of mole grips