Dirty edges of welds

[wg1983]

Hello. I'm new here. I'm currently restoring an Austin Mini. The body is in very good condition so I don't have too much welding to do. It's about 0.9mm steel. I've been butt welding a few patches in after practising a bit. I'm doing this by cutting the patch to size, tacking it in, and then gradually filling in around the join with spots, eventually overlapping them. It's mainly going well. The only real problem I'm having, is that I am often left with 'dirty' edges around the welds.

It's difficult to describe what I mean and it's not easy to take photos of shiny metal. If anything, the photo makes it look worse than it probably is. In case it's not clear to see, imagine a painted wall, where you have used filler to fill a wide, shallow hole where a plasterboard nail has pushed a piece of plaster out. The filler is been sanded flat and flush with the surrounding surface, but there is a little gap between the filler and the wall surface. That's what I'm getting around my welds. In the gap, it doesn't look like clean, shiny metal (but that may be just because it's in shadow). It looks like there is an outward-facing conical void in the metal, with an inward-facing, ill-fitting conical 'filler' piece of weld in the hole, with a gap that seems to extend towards the point of the cone, but for an unknown depth. I would like this to not happen, so that I can send it flush and have it look like one continuous piece of metal.

I clean off about 5mm of metal around the patch, and I clean all of the patch before putting it in. I also clean the back and make sure there is no paint on it (apart from weld-through primer in some cases). What am I getting wrong?

https://www.pinterest.com/pin/1151654935981484162/

 

[Jack Ryan]

If I have the correct image:

There is a lack of fusion (no wetting) around the weld. Perhaps it is still dirty, too much gap, or cold.

Jack

 

[tigdlo]

If I have the correct image:

View attachment 533312

There is a lack of fusion (no wetting) around the weld. Perhaps it is still dirty, too much gap, or cold.

Jack

That photo doesn't definitely show lack of fusion, assuming it's a plug weld it could have full fusion on the edge of the sub 1mm sheet. It looks like a typical mig weld on thin sheet bodywork for other types of welds too, lots of filler to get full penetration, this often pulls the sheet creating a slight low spot around the weld, this is highlighted when grinding the weld flat to the panel. I see people gring further which only thins the sheet around the weld and creates a larger low spot.

A wire wheel on a grinder or phosphoric acid before keying with an abrasive will get it ready for paint, scotch pads are better than paper and sponge type abrasives are better for gettign into smaller low spots.

To get proper help you really need to post a few good photos of your welds along with the details of your welder and settings you have. Have you set up the welder on practice pieces first? This needs to be done in the same position as on the car to get them right.

 

[Jack Ryan]

That photo doesn't definitely show lack of fusion, assuming it's a plug weld it could have full fusion on the edge of the sub 1mm sheet. It looks like a typical mig weld on thin sheet bodywork for other types of welds too, lots of filler to get full penetration, this often pulls the sheet creating a slight low spot around the weld, this is highlighted when grinding the weld flat to the panel. I see people gring further which only thins the sheet around the weld and creates a larger low spot.

A wire wheel on a grinder or phosphoric acid before keying with an abrasive will get it ready for paint, scotch pads are better than paper and sponge type abrasives are better for gettign into smaller low spots.

To get proper help you really need to post a few good photos of your welds along with the details of your welder and settings you have. Have you set up the welder on practice pieces first? This needs to be done in the same position as on the car to get them right.

Why would you assume it is a plug weld when stitching of a butt weld was described?

Even if it were a plug weld, there is no wetting at the edges.

Jack

 

[tigdlo]

Why would you assume it is a plug weld when stitching of a butt weld was described?

The photo shows what looks more like a plug weld, I replied to you, you showed that photo. I then expanded say you would often see something similar on other welds too.

Even if it were a plug weld, there is no wetting at the edges.

The profile of a mig weld on thin car bodywork can be a high convex weld even when there is full penetration and wetting at the toes. The slight dip at the toes and the profile of the weld makes it look like there is no wetting. We need more photos of OPs welds front and back to help.

Here are the plug welds I tested a couple of weeks ago, a few different hole sizes and welder settings 45degree overhead to match the car. Even the weld I didn't finish because it was way too cold gave full penetration and fusion on the edge of the 1mm sheet even though it looks like there is no wetting at the toe. If I were to grind any of these welds level to the surface of the sheet there would be a visible ring around the weld highlighting the lows, grinding that out will thin the sheet and weaken it.

 

[wg1983]

Thank you for your replies so far. Sorry if my analogy to filler on a wall has confused things. I was trying to describe what the end result looks like, as it's not easy to photograph. Yes, you have the right picture. I didn't know how to make the picture appear directly in my post, but now I see I clicked 'media' instead of 'insert image'. In any case, in the next day or so, I will take some photos of my whole process and post them so that you can see what I'm doing.

 

[Fazerruss]

It looks like low areas around the weld caused by distortion from the welding process. This is unavoidable on thin guage steel. To get it to blend in seamlessly you will need to plannish the weld area with a hammer and dolly. This will raise up the low spots so it can be very lightly sanded with a DA orbital sander. There are still a few areas that need filler wire. The best weld process the the quality of finish you want is either TIG or OxyAccetylene.
It's a very time consuming process. Welding is the easy part, the real work is bringing the panel back to shape.
I do a lot of bike tin work that is re chrome plated afterwards so I don't have the luxury of using car body filler. The welds need to be seamless.