Mig advice sought

[Tim novice]

hi, please see attached pics. These are the inside of the Centre tunnel of a vw beetle where my son has welded on a new frame head ( where the front axle assembly bolts on, so needs to be strong). We are both new to welding , he being 16, and so used a progressive tack around the joint. The metal is approx 2mm thick.
The penetration looks ok to me, but I have no idea what I am talking about!
I wondered if I could seek a wiser and more experienced comment and suggestions as what to do if the weld is deemed poor and liable to failure. The outside has been ground back and primed so I have not posted a pick of this.
Than you

 

[Tim novice]

Oh dear. The pic is of the inside so to grind it back we will need to cut it off, grind and then re-weld.

 

[gordon stephenson]

Get some 2mm metal, and practice doing continuous welds. and then practice some more,

 

[cumbriasteve]

Some pointers for the future:

I can't really see much evidence of cleaning of the area prior to welding, something like a flap wheel should be used to get it as clean as possible.

The tacks look as though your son thought he had to use the thin metal technique, as mentioned if the joints were tight you should manage that with a continuous weld on 2mm.

Going back to the thin metal technique if you ever really need to use it, the tacks/short runs should be joined, that is you progress by starting each new tack on the back of the last one, leaving gaps between no matter how small can be an MOT fail on certain parts of a vehicle bodywork/chassis.

There could be an off chance of running a hot weld along those tacks and penetrating through ok but it's probably a skill level your son is not yet at and that same decent skill level would be required to know if it had been a success.

 

[Cobbler]

There are several members on here from Gloucester, you may be able to get some advice from someone local.

 

[malcolm]

A stop start weld isn't ideal for 2mm thickness (a continuous weld would have been better), but the welding in the photos doesn't look that bad to me. There is a bit to the left of the second photo which doesn't have quite enough penetration, but the rest looks way better than the average I saw while looking up the repair on VW forums. I'll stick my neck out and say it looks fine to me and I wouldn't re-do it.

I'm assuming it is penetration we are looking at in the photo not the side the weld was done from.

From the WV forums the repair section itself looks a bit frightening. There seems to be a repair piece that includes the end of the tunnel and the corresponding bit of floor which is butt welded in place a bit like a cut and shut. That is poor practice. It is much better to stagger the joints. It would be better to repair the tunnel and then replace the complete floor panel to avoid a clean weld line all the way across the chassis. That stands however good a welder you are.

 

[Spark plug]

Could you post some pics of the other side and of the bigger picture, this may help point you on the best route forward.

As said it should be no probloem seam welding 2mm, it's only when you get sub 1mm ware the real thin metal probloems start to develop.

 

[Tim novice]

Thanks for the comments and advice.
Malcolm, you are correct when you surmise that the pics are of the penetration. He tried a bit of seam welding first, but was not penetrating. We ground that flat and did the stop start after and kept sliding my phone inside to check that they were penetrating.
The frame head is a bit frightening but the floor of the frame head is a seperate component even when new, although the tunnel obviously was continuous. The tunnel bit is set back about 60mm from the floor section so there is a little stagger. The most frightening bit is that the centre tunnel is the only real load bearing bit of the whole chassi, the floor pans are relatively floppy until screwed on to the cill ( even the new ones!).
See pics of welded area after flattening.

 

[Spark plug]

Are you useing gasless mig?

 

[Tim novice]

No. Argon mix with .8 wire. The welder is an old sealy supamig 150.

 

[trewjohn2001]

For structural parts like that I put in a backing plate of 1.5mm steel - wide enough to plug weld first either side of the join. I leave a leave a slight gap between the panels to be joined and then run a continuous bead. That way you can bite into the backing plate and the panels and not worry about burning through and your not just relying on a butt weld for strength. It will never look factory finish but should be stronger than the original panel at that point.


I have seen a lot worse than you have done. Are you using a grinding disc or flap wheel on the welds?

 

[Tim novice]

A flap wheel disk, I saw a post on here from a chap who did a realy complex shape, welded it, used the flap disk so perfectly is needed virtually no filler. It all looked so easy .
The butt strap idea is a very good one, we may well cut it off and try that.

 

[trewjohn2001]

Even the flap discs can be a bit aggressive for sheet metal. I use a black and decker power file as its very easy just to run over the top of the weld to smooth it off and take away any spatter before painting without taking any base metal with it.

I think in a structural area like that it's ok to leave the weld proud and not worry about it being invisible. It will be covered by carpet.

 

[malcolm]

Flap discs are the best, but I prefer to just grind just the weld and not the surrounding metal - no point thinning what is there. Looks reasonable enough - other Beetles will fall in half before yours. If you are worried then a diamond shaped bit of steel plug welded across the joint at the top maybe 3 inches wide and 6 inches long would add a safety margin for unplanned crashes. The floor will hold the bottom.

How is the square gap at the bottom of the tunnel treated? Is there a box section welded to it?