A friend and I designed this bumper in AutoCAD/SolidWorks and I finally got around to getting it cut by a plasma CNC guy near my house. He's supposed to drop off the steel tomorrow and I want to get it started as soon as possible. Any advice on keeping everything square (I have welding magnets) and avoiding warpage? From what I can tell by the research I've done the best thing to do is tack it all together and then weld in relatively short beads alternating around the bumper to keep it straight. It's all 3/16" steel for what that's worth.

Here's my foam core mockup because I wasn't sure if I could trust SolidWorks' "unfold model" function:



And here's what the CAD model looks like:

 

3/16s? you should upgrade to 1/4 inch if you still have time

 

None of the commercially available bumpers I see are 1/4". It's not even a winch bumper so that seems excessive. It already weighs 50 lbs as pictured.

 

Looks like a solid design! Can't wait to see the final product.

1/4" is only necessary for the mounting brackets so that they're stronger. Other than that, 3/16's is perfect. Talk to anybody who builds bumpers - winch or not - and they'll tell you the same. 1/4" will make it WAY too heavy. Mine's 3/16's and still weighs 72lbs without a winch on it yet.

 

3/16" will be fine but you should add some shackle mounts that are welded to the front and back of the plate and to the mounting plates

which brings up the question of how are you mounting it
i hope your planing on using more then the 3 stock bolt locations

 

I have tie in brackets that you can see in my cut file:



They will also be 3/16" because my calculations have the bracket strength at 13,000 lbs (in tension) per side. I'll probably put some d ring mounts on it, but I haven't ordered those yet.

 

personally i would have the tie in brackets made from 1/4" but other then that all looks good nice design nice cad work ill be watching for the final product

 

I've noticed people make them thicker, but I haven't really seen pics of frame tie-ins broken from recovery. It seems kind of impossible given the weight of the XJ and, say, an 8k to 10k winch.

 

Better to be safe than sorry though. I highly recommend going 1/4" for the mounting brackets. If your ordering d-ring tabs, how do you plan to mount them? Simply welding them to the front surface doesn't give much strength. You're better off incorporating them into the bumper by having them welding along side the mounting brackets and extending through the front of the bumper, which would mean cutting into the front of your bumper if it's already being shipped.Recovery and mounting are 2 areas you DO NOT want to skimp on.

 

A 3/16" tie-in bracket would have 4.0"x0.188" of effective cross section. That's 0.75 square inches of A36 hot rolled which has a yield strength of 36,000 PSI. Ultimate strength of that steel is 55,000+ psi. So each frame tie-in would be rated at 27,000 lbs yield or 41,250 lbs ultimate strength.

I'm not looking to skimp on anything, but most D-ring shackles that I've seen are 7/8" shank which are rated under 10,000 lbs even in double shear.

But I do agree that the D-ring mount is important. My frame tie-in goes to the face of my bumper where it has a full section internal brace. If a D-ring mount was welded on at that point I'm guessing the weak point would be the two fillet welds on the D-ring mount. People seem to use those weld on D-ring mounts all the time without an issue so I'm not too worried about it.

I am, however, interested in seeing some failure pictures so I can get an idea of where bumpers/D-rings/mounts/tie in brackets have failed on XJs.

 

The issue with 3/16's for the mounts isn't straight forward pulling. It's pulling from an angle, especially sideways - sometimes, that's your only way. It's just a good idea to go stronger on the mounts. For the d shackles themselves, get a good set of 3/4" ones rated at about 10k each. And the tabs need to be welded to the mounting brackets. Plain and simple. I don't have pictures, but I have seen bumpers pulled away from the body, destroying the uni-body frame and I've see the d-shackle tabs that are just surface welded to a bumper snap off. It's incredibly dangerous.

 

I could see pulling it from the side bending your unibody rails no matter how thick your frame tie in is. I'm not sure I'd want to pull an XJ too hard from the side.

I'm definitely interested in seeing a bumper with, say, a 4" base d-ring tab ripped off. It seems like it would be a liability issue for all the vendors selling those tabs. I have a problem intentionally designing certain parts of a system to be 8x stronger than other parts.

 

The whole purpose on the 1/4" thick mounting isnt just the actual bumper mounting, its the unibody as well as the bolts mounting to your unibody. anyway, that topic has been beaten, 1/4" for good safety measures, or 3/16" for general strength. Up to you.

As for the mounting tabs for the D-rings, they need to go through the bumper and welded not only inside, but on the outside as well. The reason why they get ripped off, can probably be contributed to a number of things... 1. Their actual welding (laying of the bead) sucked 2. lack of prep time or 3. lack of design placement 4. or all the above. If the welding is done correctly with the right design the metal around the weld will give before the actual weld will.

So you are right, if you do place the tab ontop of your design there is a good chance it will rip off, due to the weld not being strong enough. Which in itself is a huge safety issue. I would highly recommend cutting hole just big enough in the face of the bumper for those tabs and do a double weld both inside and outside. Reason being, yes the metal may be good for 50,000lb or whatever, but if your ever stuck, and need a hard yank, that force is extremely great even if it is a split second. This is where metal and parts start to fail. Thats the reason, why people go with 1/4". More force will be needed to bend the 1/4"+unibody then the 3/16". And the double welds will increase the weld to metal surface area and increase the strength.

Anyway end of my little 2 cents

 

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if you just want more strength but same size metal. double them up. that would give you 3/8s and you wouldnt have extra cost of 1/4 metal