Another newbie, advice RE: galvanised car body

[Error404]

Hi, i'm new to the forum, and to welding. I just bought a Clark 151TE, for general use mostly working on cars and general littel bits of fabrication.
The main reason i picked up a MIG now is that i'm restoring an old audi coupe quattro and wanted to seam weld the chassis for extra torsional strength.

I read the tutorials on here (bvery useful) and I practiced quite a bit on overlap joints with 0.8mm steel and after a while was getting pretty decent penetration and reasonably tidy welds - this was on lowest power setting and just over 5 (1- 10 scale on the knob) on the wire speed.
As soon as I went onto the car however, I couldn't get any decent penetration and the weld was building up on the surface and looking very snotty. As I was welding too, it was spitting badly. I know the panels on the car were galvanised from the factory, and I have wire brushed and gently grinded the joints back to bare metal, but it made no real difference - still spitting badly and not gettting decent penetration. I tried to weld slower and make the wled pool bigger but it just built up on the surface.

I went back to the 0.8 steel I was practising on and could weld ok again.

So I tried upping the power onto the second setting from bottom to get better penetration on the car body welds but it just started to blow away the top sheet on the overlap joint.

Have any of you experenced folk got any suggestions?

 

[rtbcomp]

Is there any wind blowing the shielding gas away?

 

[malcolm]

Sounds like the heat of the weld is drawing paint, seam sealant, or even galv out of the seam which is vaporising and displacing the shielding gas. Welding over existing seams is a pain at the best of times - for most cars paint and rust in the seam can cause that sort of trouble.

Cleaning as much much out from the seam as possible using a knife might help. Shotblasting the seam would be better. Could be worth trying a little more gas flow to see if that helps.

Another thought moving from practice sheets to a car is position - if you are welding a vertical seam a little extra wire speed might make things easier to control, but won't help with the sizzling.

Edit> Are you welding inside? As rtbcomp suggested the slightest breeze can cause similar problems.

 

[Error404]

Cheers for the advice

Welding indoors in the garage, so no breeze to worry about - gas wouldn't go at any higher flow, but i'm only on the crappy valve and little disposable gas bottles that came with it. I'm only using pure CO2 not an argon CO2 mix - from reading up a bit on the forum it sounds like the mixed gas might also help a little?
I'm going to try and get a proper regular and gas cylinder i think, as i've already used the two bottles of gas I had at £7odd a pop.

I've already tried to clean the seams up as best i can with a wire brush attachment on the drill, they look like nice shiney bare metal, but i guess stuff could be coming out of the seam as you suggest.

I'll try and get some pics if i can

I think some more trial and error (once i get some more gas )

 

[Error404]

A couple of pics:

The seams look like this at the moment:

and the welds look like this:

 

[malcolm]

Thanks for posting the photos - that clarifies things a lot. The seam looks very clean. The black smoke residue above the welds is likely from the paint beside the seam. In the photo of the weld the paint looks like iot gets quite close to the join. MIG likes things to be really clean.

It does look like you are minimal on gas. Disposable canister regulators are like that even when set on max. You might want a bit more flow. A proper regulator that measures flow rate attached to a bottle that dispenses gas for more than a few minutes would help a lot.

What kind of mask are you using? I notice the weld isn't in a straight line. I can't manage steady MIG with one hand so a full face mask would be the minimum. Autodarkening ones are handy.

I'd aim to create a puddle of molten metal and keep it going. You might find the on-off technique handy to let it cool a little and then keep it going again once it's cooled for a second, and would allow a higher power setting.

 

[Error404]

Thanks Malcolm - very helpful

Whats the best way to get the gas in a proper cannister etc? Do you need to go to BOC or the like? Are the regulators on ebay for £20 or so any good?

I'm using a full face mask - autodarkening one is another thing on the shopping list.

Looking forward to having another crack at it - its frustrating but still a good way to spend a sunday

 

[malcolm]

I much prefer the twin gauge regulators as the second gauge estimates flow rate. The alternative is to use a peashooter on the end of the torch to work out flow rate.

For cheaper gas than BOC or AP try the gas price spreadsheet and the gas supplier list

Work out which gas bottle you will get first - most are standard Argon/CO2 fittings but there are oddities around.

 

[Error404]

ok so i opened an account with BOC as my future brother in law's company are agents for them, so made life easy. Got some Argolight and a decent regulator - made life loads easier and now seem to be getting more reasonable penetration.
I've been doing small spot welds about 10-15mm apart, then coming back to fill in the gaps, trying not to get too much heat into the panels. Here's a pic:

Can anyone comment on the strength of this technic compared to say, welding an inch on, inch off for seam welding car chassis?

I also thoguht i could weld the same from the other side of the panel joins where accessible to add strength?

Thanks
Alex