How to avoid distortion welding aluminum bumper

Tue, 31 Aug 2021 09:44:25 GMT

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This is the factory aluminum bumper on a Porsche 912, and I’m modifying it to look like the RS bumper in the last pic.My plan is to weld in a sheet of 1/8” 5052 plate to fill this gap, and hammer it smooth.Question is how should I weld it so I don’t warp the bumper, i.e. how do I minimize distortion of the bumper.The bumper itself is about 1/4” thick.I was thinking cutting a single crescent shaped sheet in the shape of the gap and welding that in.Or would I be better off with a bunch of pie cuts and welding those?The gap itself is about 2” wide, so the strip will be about 3” wide.I was thinking about bolting the bumper to a large piece of box section while welding.Sent from my iPhone using Tapatalk Pro
Reply:Best way to avoid warping is to avoid welding. Otherwise cut a full length filler piece, shape it, tack it in and weld it in stages, allowing it to cool in between welds. Bolt it down as much as you can.
Reply:I found this to be interesting...……………..https://www.tinmantech.com/articles/...damaged-parts/
Reply:Standard methods are pre-stretch (stretch the material so it becomes the right length when it shrinks)pre-bend (so when it shrinks it becomes the shape you want)fixate (so it can't move freely during welding and cooling)minimize heat inputLast edited by Pete.S.; 01-15-2019 at 10:41 AM.
Reply:English wheel to finalize.
Replyo it in three pieces (using patterns from tag board, the light flexible cardboard used to back framed artwork) that set inside a bit of the opening. Tack every couple of inches, then Bondo to finish. I don't see how from the pix that you would bolt it back on, though?
Reply:Originally Posted by YofishDo it in three pieces (using patterns from tag board, the light flexible cardboard used to back framed artwork) that set inside a bit of the opening. Tack every couple of inches, then Bondo to finish. I don't see how from the pix that you would bolt it back on, though?
Reply:OK I get the way you are gonna mount, but I would still suggest to piece it and bondo to get a pleasant shape/profile which one can work to get a beautiful appearance.You're NEVER going to get that effect by hammering 1/8" material not to mention all the bug holes and differences in the plane from welding. One can chase that monster till jeezus comes for breakfast. Also, it's likely that the geometry of the aperture is not what you think it is, i.e., in that a simple rectangular band that will neatly fill the space. Ya know, world class welded AL sailing hulls are usually faired with Bondo, an easy to apply and fair material - the auto body man's best friend, too!
Reply:I’ve hand hammered a number of things before, made a few custom motorcycle fenders and a gas tank, and metal finished them, with just a tree stump and leather bag and hammers.I’m by no means an expert metal shaper, but I’ve shaped a few things. Also shaped a repair piece with a lot of compound curves for the lower BMW 2002 wheel well. This bumper fill strip will however certainly the longest piece I’ve ever worked though.I’m certainly not an expert in shaping metal but I know the basics of stretching and shrinking, and shaping. I’m sure I’ll probably have to skim coat it in bondo but I’m trying to keep it to a bare minimum.Sent from my iPhone using Tapatalk Pro
Reply:The good news for you is that aluminum distorts much less than steel when welded... so... get it done and post pictures of the process!
Reply:Are you doing the inset turn signals too?  I think single crescent would do it i think. I think 0.080 inch would be enough.  It will help keep the heat input down.  If you are doing the inset turn signals I'd form those first because once you weld it to the bumper you'll lose access for any hammer and dolly work.  In fact I'd all the shaping before welding and put the lap weld near the corners so you can blend those after welding.  I'd suggest a test bead somewhere on bumper to make sure you can weld on it.  If it's really 1/4 inch thick it might be cast, castings can be tricky to weld on.  If it's really that thick it won't move much during welding with the shape it has now.  The other place you might post this is allmetalshaping.com  There's a ton of experienced coach builders there that may have tackled something like this.
Reply:Originally Posted by sand_man_redAre you doing the inset turn signals too?  I think single crescent would do it i think. I think 0.080 inch would be enough.  It will help keep the heat input down.  If you are doing the inset turn signals I'd form those first because once you weld it to the bumper you'll lose access for any hammer and dolly work.  In fact I'd all the shaping before welding and put the lap weld near the corners so you can blend those after welding.  I'd suggest a test bead somewhere on bumper to make sure you can weld on it.  If it's really 1/4 inch thick it might be cast, castings can be tricky to weld on.  If it's really that thick it won't move much during welding with the shape it has now.  The other place you might post this is allmetalshaping.com  There's a ton of experienced coach builders there that may have tackled something like this.
Reply:Originally Posted by Andy SomogyiThanks, I’m keeping the turn signals in the bumper, but I’m going to cover up the outer part with a welded in patch so the turn signal looks just like the one in the finished blue bumper. Mine is pretty close to this now, only have just the outer hole to patch. This will be just a single 2.5 x 6 inch rectangular patch.That’s a really interesting idea with the lap weld, do you mean a lap weld as opposed to a butt weld in like in this pic. Yeah, I think I could do that, it would involve a lot of shaping as the bumper itself is about 5/16 or 3/8” thick. The lap weld would certainly be stronger. I’ll have to look into that and see if I can shape a bend like that. I don’t have a bead roller so might be kind of a challenge.Sent from my iPhone using Tapatalk Pro
Reply:All I want to see is the result, whatever you do. Too many fly-by's here. "How do I do this?" Then, adios!!!
Reply:This is what I meant by a lap weld on the corner.  You'll have to find the area on the corner where the weld blends nicely into the curves of the bumper.  Any way you do it I'd do all my shaping before welding because once it's welded on you can't get a dolly on the backside to support it.