• Having site issues? Contact Dub@southernPolyurethanes.com

Flat Hood Weld Repair

#42
BTW. Does anyone know why some OEM spot welds are just that, spots, while others look more like a smear?
They did that all day long 5 days a week, with the spot welder suspended on a cable which went up to a pulley on a roller so they could move around. So going from one hood to the next the roller will want to keep going when he stops. He was also working at a fast pace, not trying for perfection.
Robots do a much better job today, and they work cheaper.
 
#44
Here is a photo of the completely exposed back side of the larger of the weld patches I put in the hood.
The spots where there is good penetration are probably the initial weld spots. They look good to me. Agreed?
The spots in between these are where I laid the next spot adjacent to the original welds. Obviously, the penetration was not as good.
And then there are the spots where I connected two previous spots and got very little penetration, if any.
I didn't know that you were supposed to grind down the spots as you go before connecting another spot to the previous one.
Will grinding the spot before connecting the next one alleviate the bad penetration issue? 004.JPG
I will be removing this patch and starting over.
BTW. I'm using a Tweco Fabricator 141i. Does anyone have experience with this machine and have any views on it? I liked my Handler 140 better but someone thought they needed it more than I did so they came and got it in the middle of the night :mad::mad::mad:
I've purchased a spoon and a crowned face hammer.
Any views on which to use ?

I know, lots of questions. Sorry.

Thanks
 
Last edited:
#46
Some. Mostly over the last few days.
I removed the old patches and installed the new ones after practicing and setting my machine up properly. 11-27-18.JPG
Not perfect but much better penetration. This photo is after some initial grinding then more spot welds.

Yesterday and today, I've been rough grinding, more plannishing and some off-dolly hammer work. I've still got more to do but I'm getting close.
The templates were made from the identical location on the other side of the hood.
003.JPG 004.JPG 005.JPG 006.JPG 007.JPG 008.JPG 009.JPG
Unfortunately, I found another rust through when I wire brushed the under side of the hood. It's about 1" up from the front lip of the hood. Glad I found it now, though.
 

Attachments

#47
With MIG I normally grind down the weld "dots" both front and back (after planishing) so they don't act as a heat sink for the next adjacent weld. Here's a video on grinding a plug weld, which is normally only done on the outside, but shows the process just the same.


 
Last edited:
#48
Well, I got to feeling a little big for my britches and decided to try out my new shrinking disc set. After I got the big patch all nice and pretty, at least in my eyes, I had a ridge that ran along the line shown. I figured that it was caused by shrinkage along the weld bead adjacent to the feature line of the hood. So, I said to my self, use the small shrinking disc and start working out the ridge so I used it on the dark rectangle, in the circle, along the feature line.

Im sure that I used the wrong technique because it seemed to stretch the metal, not shrink it so I tried using the disc on the back side and got a little of the "belly" out of the area. I worked on this area most of the day with hammer and dolly, treating it as if it were a ding. Got most of it out but still had the ridge to deal with.
This time I decided to use the 7" disc and try to use more of the surface of the disc rather than the edge like I had on the first attempt.
I worked with light pressure, not getting the metal to the point of discoloration and working in a broader area. Here, you can see the pattern left by the disc.
002.JPG
Everything seemed to be going well until this happend. A deluxe oil-can .
004.JPG
I'm confused. As I understand it, oil-canning is caused by too much metal for the surrounding metal. So it has to go some where and that causes the metal to bow out, creating the oil-can effect.
If I was shrinking the metal how could shrinking cause this?

Thanks in advance.
 

Attachments

#49
Well, I got to feeling a little big for my britches and decided to try out my new shrinking disc set. After I got the big patch all nice and pretty, at least in my eyes, I had a ridge that ran along the line shown. I figured that it was caused by shrinkage along the weld bead adjacent to the feature line of the hood. So, I said to my self, use the small shrinking disc and start working out the ridge so I used it on the dark rectangle, in the circle, along the feature line.

Im sure that I used the wrong technique because it seemed to stretch the metal, not shrink it so I tried using the disc on the back side and got a little of the "belly" out of the area. I worked on this area most of the day with hammer and dolly, treating it as if it were a ding. Got most of it out but still had the ridge to deal with.
This time I decided to use the 7" disc and try to use more of the surface of the disc rather than the edge like I had on the first attempt.
I worked with light pressure, not getting the metal to the point of discoloration and working in a broader area. Here, you can see the pattern left by the disc.
View attachment 6628
Everything seemed to be going well until this happend. A deluxe oil-can .
View attachment 6629
I'm confused. As I understand it, oil-canning is caused by too much metal for the surrounding metal. So it has to go some where and that causes the metal to bow out, creating the oil-can effect.
If I was shrinking the metal how could shrinking cause this?

Thanks in advance.
Any time you weld a patch the weld seam, as well as the surroundind heat effected zone (HAZ) will shrink as the metal cools. The method of controlling this is to planish (hammer on dolly) the weld and HAZ area in order to stretch the area back to it's origional size.

I generally grind, planish and work the weld area after every few tacks. This way the panel will stay in shape and the heat induced into the panel is the least it can be. Once the panel is allowed to get out of shape there are stresses on it that will travel clear accross the panel.

Shrinking the high spots created away from the repair area on a low crown panel rarely works because it does not remove the stress. It frequently complicates the repair because it allows the stressed area to travel and extend itself into other areas. The solution to a repair unfortunately is to remove the stress in the repair area, not attempting to repair the area stressed by the repair.

40 years ago in my biginning days :) I attempted to weld a 51 Chevy hood together and remove the center strip. I chased high spots accross the hood until it finally made a big noise and pulled a giant buckel into it. We live and learn. Hood one, John zero.

Good luck with what you are trying to accomplish but I fear your trying to shrink the high spots away from the weld area are not the way you need to go.

John
 
#50
Thanks, John.
I did try plannishing the HAZ as well as the weld bead. I guess it wasn't enough.
Any idea what I can do to get myself out of this mess?

Donny
 
#51
That's a tough question Donny. I am skeptical to be honest. Without being able to see it, it is hard to say. At this point you have nothing to loose. In the future though, the key is to never let it get out of shape. Planish as you go to relieve the stress and keep it in shape. Removing the skin was probably your best decision. Trying to shrink the distorted areas was probably not. I have an old 3/4" steel welding table that makes a great third hand dolly. I can lay the panel on it upside down and planish from the backside



My thoughts are it would be just as quick to buy another hood even if you had to travel a couple hundred miles. A day trip with the wife on some nice back roads could be fun.

I hope I have not been too negative here. It certainly is not my intention to kick you while you are down. I have been in your shoes. You are doing one of the toughest repairs there is on that large low crowned hood.

John
 
Last edited:
#52
Thanks, John. Your comments are not negative at all and I appreciate all of the comments from more experienced craftsmen such as yourself.
I knew going in that that this might be a lost cause but I've learned a lot from it regardless of success or failure.

The owner of the car wants a driver, not a show car, so it's up to him but I'm going to keep beating on this hood just to see if I can get it into good enough shape.

That piece on the welding table looks great, by the way.

Cheers

Donny
 
#53
The only way we can get good spots with the mig is constantly opening up the butt area. When it shrinks from the last weld, keep cutting it open, trying to get the same size wheel or cutter as the wire you use, so you are actually starting in the middle of the part. You get some better penetration that way.

I also saw the one real good tech on the Kindigit show use an angle grinder with a flat aluminum wheel. He was using it to heat the panel and then quenching it to get it flat again. Has anyone ever seen one of those?
 
#54
There's only 5 rules to working sheet metal. You can:
1. Stretch it.
2. Shrink it.
3. Cut it.
4. Weld it.
5. When all else fails; cuss at it, cut it out and start over with rules 1-4.


When you welded in the patch, you SHRUNK it. When you hit it with the shrinking disc, it shrunk even more, thus becoming sunk or depressed. When you hit the back side with the shrinking disc, you shrunk it again. That is not an oil can, it is over shrunk and pulling the crown inward.

All welds shrink. Proper correction after welding is to STRETCH.
 
#55
So I went back out there and put on my thinking cap and came up with the brilliant thought, "work backwards". How orriginal of me. LOL
I planished the entire area that I used the shrinking disc on until I could push up from the bottom and have it hold the crowned shape.

Than I thought again>>>>What if the shrinking disc was acting more as a planishing disc, or a hammer off dolly than a shrinking disc. After all, all of the videos I've seen the user is working on a small crease or ding, or other small area. I was working on a large area.

Then I flipped the hood over and used the wheel on what were now the high spots on the back side and voila' it worked.

I would using this technique on several areas that needed to be stretched, not shrunk and it worked beautifully. The hood is not perfect. I've still got a slight ridge that runs across the portion of the hood that I've been working, but I can live with that.

So, I'm going to quit while I'm only a little behind and move on to prepping the structure for epoxy and then welding them back together.
Here's a pic of the same area against my pattern that I showed in my previous post.
 

Attachments

#56
The only way we can get good spots with the mig is constantly opening up the butt area. When it shrinks from the last weld, keep cutting it open, trying to get the same size wheel or cutter as the wire you use, so you are actually starting in the middle of the part. You get some better penetration that way.

I also saw the one real good tech on the Kindigit show use an angle grinder with a flat aluminum wheel. He was using it to heat the panel and then quenching it to get it flat again. Has anyone ever seen one of those?
If you properly planish the weld but not the surrounding material the butt gap will not close up. That is the key to knowing you are doing it correctly. If you have to cut open the gap, the panel is drawing on you and you are not successfully planishing the welds.

I am pleased you were able to save the panel grogetter. Good luck as you move forward.

John
 
#57
Thank you, John. Just another question, if you don't mind.
Why do you planish before grinding? Seems to me that if you did a rough grind on the spot, top and bottom, making flat surfaces, then planished, it would work better and be easier, too.
 
#58
Thank you, John. Just another question, if you don't mind.
Why do you planish before grinding? Seems to me that if you did a rough grind on the spot, top and bottom, making flat surfaces, then planished, it would work better and be easier, too.
You are correct. Generally the weld is planished after it is rough ground, being left slightly proud. If you weld your tacks really hot with very short bursts there will not be as much to grind and your penetration issues will deminish also.
 
#59
I hope no one thinks I am trying to steel your thread but this may clarify what I am trying to explain.

Here is a door skin I wheeled for a car I am building. It is very low crown and any shrinkage is going to pull distortion into the door. BTW, I intentionally placed the seam where it is to be sure I could get a dolly behind it.



As I began to tack it together, I started tacking at one end, tacking about every inch. from one side toward the other. By planishing each tack, I could see the butt gap ahead of me move together or apart depending on the amoumt of planishing. Also by working from one side toward the other you don't end up with access metal on one side or the other.



Next, continue building your tacks by stacking them on each other planishing as you go so the panel N E V E R looses it's shape. By doing it this way, you will end up with maybe 30 gaps to fill at the end. If you keep tacking between tacks instead of connecting then, you will end up with 80 or so gaps tp fill and it will become much more difficult at the end.

You can see here how I have been able to maintain the crown.



Here is the final project. There is no body filler on it yet. Just 3 coats of SPI epoxy. The amount of filler will be minimal.



I hope this helps explain the process I am trying to describe.
John
 
Top