BODY WORK COMING BACK AFTER 6 MONTHS

J

JC Daniel

Promoted Users
I did some wheel arch patch panels on my friends truck in February and all the body work looked really good when the truck left the shop but now I can see all the weld seams showing back up, It is like all the filler and 2k shrunk right into the seam? What did I do wrong or what did I not do right?
 
I won't be able to get pictures for a while, I used Chroma lite filler over the repair after covering with spi epoxy.
 
I don't have anywhere near the experience with metal work as many on here, but I have seen your same problem many times. I have found that almost every time the problem starts at the bottom with the weld. My guess is improper weld penetration. After grinding your welds flush, the metal is thinner where the seam is, and after some heating and cooling cycles, the seam cracks. No matter what you put on top of it, it will rear it's ugly head. Just my theory, and waiting to hear what the real metal men^^^ say.
 
I start welding tacks in center and then move a quarter of the way across and tack again and I coll each tack with air, I continue to tack until all tacks are connected and I grind down and then move on to finish work. I use 75/25 gas mix and .025 solid wire. I can not believe this happened but it did so I have to be better on future work. I am a perfectionist and I can not have any of my work to look that way, I will probably get it back this winter and redo it. I did check the panels and they are very tight with no movement. How can I keep the seam from cracking?
 
In the future don't cool the tack welds. Let them cool naturally. That could be one reason they are cracking. All cooling a tack does is cause it to shrink more. You end up with more distortion. Either that or you didn't get good penetration, then ground most of the weld off (oops I see Texas beat me to it:)) Especially when tacking/spotting you need to turn up the heat and wire speed. Was this a butt weld or a lap weld?
 
Did you seal the back of your welds? If you didn’t and there is any porosity it will get ugly pretty fast imho.

Don
 
Some guys are not holding the trigger to get a fully penetrated spot, that makes for a higher bead, then grinding/sanding some of the metal away with the bead, leaving a thin weld seam which will crack.
I don't personally do it, but there is something to be said for MP&C's method of grinding each spot.
 
I could not get to the back side of my welds, What method is used to "seal" the backside of the weld? Yes it is a Ghost line all the way around the repair. I can't get pictures for a good while as he is not close enough to me, I can pick up on some of my troubles by what you guys are telling me. I use a Lincoln 135 and set temp on A or B and wire speed on 2.5 or 3, I think that I am not getting good penetration and my wire speed is too slow. I want you guys to know that I really appreciate any help and advice you can give, I only do about 5-10 jobs a year so I need any help possible. I wish one of you guys lived near Beckley, WV so I could visit your shop?
 
#870 filler adhesive . polyester shrinks bad especially the lightweight fillers . vpa is hard and shrinks very little .
mig welders lie. if you have a lot of weld to grind off it likely did not penetrate . a good spot weld is right before it blows a hole in it.
 

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One thing I have learned from real metal men on here is if you blow holes, turn the wire speed up instead of turning the heat down. Short, high temp tacks work much better than longer, built up tacks. My patches look so much better now than a few years ago by following advice on here:). Try welding 2 pieces of sheetmetal together with your settings, then look at the back side. The weld should look very similar. If there is still a line on the back side, turn the heat up. If you start blowing holes, turn the wire speed up. I think you will find your settings need to be higher than what you are using now. I know I did.
 
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For butt welds the better fit you have the easier it will be to tack/spot together. You need to have good fit to turn up your heat and speed. If you have big gaps it won't work. Sometimes you end up with gaps, in that case turn down your heat and speed concentrate on bridging the two pieces then start tacking off that bridge.
 
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