Technical Welding cracked fenders opinion

Is it better to weld just the crack up or cut out and weld in a wider patch?
Metal fatigue at the crack?

 

What you working on? Photos will help a bunch.

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If the metal has weakened to the extent that a crack has appeared due to metal fatigue that basically means if you try to weld it you'll be trying to weld fatigued metal. You may get a good weld but the next cracks will appear along the side of your weld run as the metal is still brittle and made even more so by the heat of the welding. Take the time to cut out the fatigued area and weld a new patch in recommend using tig welding not mig if its an older fender. Do it once do it right no need to go back and redo it afterwards painful if the panel has been painted.

 

I was always told if it's got a tear in it, to drill a hole at the end of the crack, then weld it up from both sides. I suppose it would depend on where the crack is too and the condition of the surrounding metal. If it's an area that's prone to fatigue I don't think you just want to weld on top and grind it flush again.

 

I spent about 25 hours on these 4 fenders welding up the cracks and cutting out bad spots because we wanted to stay with steel fenders. I cut out the cracks and formed the metal to replace a larger area. Then painted it like this.

 

Remember, if it split to come apart it also stretched. You can't just close the tear and weld it up. You need to correct the shape also in the repair. If this is an opening with a Wire in it you need to remove the complete wire and replace it with one continuous piece.
The Wizzard

 

Yea, I was just wondering in theory, I usually (depending on length/location) cut out and form a patch. I thought maybe I was making more work for myself by doing it that way....

 

I crashed the car that is my avatar. I took the right rear fender which was torn and bent to several people with English wheels and tried to get them to either form a new one or help work out the bad spots. No one would touch it. So I cut the fender in 5 pieces and finished each piece and then welded it back together. The front clip was fibergl*** so we just gl***ed it back together.

 

I glued a metal rod around the inner edge of the fenders on the avatar car after replacing cracked and damaged areas.

 

If you weld it peen the snot out of it.

 

I did the same only I spot welded mine in.

 

It seems possible that the HAZ region of the weld would soften, resembling the prior cold worked matl surrounding it. Fenders were low carbon Stl.