Preheat advice requested

[BukitCase]

Built this bending jig for use on my 20 ton press - all flat bar is 3/4 x 3, long dimension is 12", gap between uprights is 1/16" wider than the 1.5" male plunger plus two thicknesses of 1/2" x 3" bar stock -

The intent is to bend a couple of U-shaped 3" x 6" pieces of 1/2" mild steel by pushing them down between the two uprights.

It's only lightly tacked at present, and it's EXACTLY the size and shape I want it to be - hopefully when I'm done it won't explode when I try to cram a piece of 3" wide 1/2" flat bar into it

I'll be welding it out with my mm252 and .035 Lincoln L56 wire, C25 gas.

Question - would you preheat it (and if so, how hot) and weld it out hot then let it air cool, do small stitches and let cool between, fill the gap between left and right sides with solid bar stock and clamp in a vise and just go for it, or ??!?

I know it's tempting to voice opinions based on conjecture, but I'd prefer experience since I don't want to build another one of these just to get it right - it will only be used for sure on two un-even legged U-shaped pieces which will be the upper "hooks" of a quick-attach system for my Case 580's FEL. I want to be able to switch from bucket to grapple to hydraulic flail to forks to brush bucket without taking the whole day.

Thanks for any useful advice... Steve

 

[mikehaugen]

I don't think preheating is necessary. Even if you welded like crap, I don't think a 20 ton press could break that in the way you want to use it. I would be more worried about spring back, but I assume you have have thought about that and have a plan for dealing with it.

With a properly designed and welded piece, the welded part should never be the weak point, it should be as strong or stronger than the rest of the steel. I don't think that is what you are looking for here, nor do I think it is necessary. My vote says weld away, just make sure you get decent penetration. I personally would stick weld it with 6010 followed by 7018, but that's because I don't have a mig welder.

For disclosure I don't have experience building a "u-shaped bending jig" but have built and seen enough to be confident.

 

[Shield Arc]

Are you planning on welding all the way around? If so, these two welds right here will bend the bottom plate. You need to think about a strong back under the bottom plate. Or pre-bend before welding.

 

[DXN1EL]

Mr. Shrink!!!!

 

[mikehaugen]

Are you planning on welding all the way around? If so, these two welds right here will bend the bottom plate. You need to think about a strong back under the bottom plate. Or pre-bend before welding.

Yes, shieldarc is correct. I apologize, when I first read your post I was taking it as you were asking about preheating for weld-penetration purposes.

Heating to prevent/fix warpage is definitely an art. Your stitch method may work but I will not comment further. Good luck.

 

[kencunningham]

It looks to me that you really only need to weld up the gussetts, that should keep the warpage to a bare minumum. Let us know how it turns out. Im wondering if the upright section of the jig will spread apart when you try to push in the flat bar.

 

[BukitCase]

Guys, thanks for the help - Sorry, I was up kinda late (even for me) and didn't explain myself as thoroughly (and endlessly ) as usual -

Shield, I did NOT intend to weld across the long piece for just the reasons you stated - I may, however, weld across the INSIDE of that (other side of the two places you indicated) if you think it would be necessary to keep them from wanting to bow during the push.

I have plenty more of the 3/4x3 FB so a strongback wouldn't be a problem. Also, if the bottom DOES bow inward, I can easily straighten it by supporting the two ends on press plates (scrap pieces of FB between gussets) and nudging it til I'm back to original 2-9/16" between uprights.

I'm also in doubt that I can get the U bend STARTED with supports that close together - if not, may need to break out the rosebud to warm up the center of the proposed bend.

I'm aware of springback - I'm pretty sure that, once the push is done, I'll be left with a U-shaped piece stuck between the uprights - I assume I'll be turning the entire jig on its side and pushing the "U" out the side while standing "somewhere else" - I've replaced the original 20t bottle jack with the air/hydraulic version, so if necessary I could be outside the shop to actuate it.

Also in that vein, once the bend is (hopefully) made, I may need to turn the "U" piece on its side and nudge it tighter - the only real requirement is that both pieces are very close to the same, and that the bottom of the "U" will support a 1.5" dia. loader pin with minimal slop. The upper part of the "U" will be a bit wider for easy insertion.

There are several threads on QA setups, mostly for Kubota or JD, but I didn't bookmark 'em - apologies to whoever I "borrowed' this pic from, but this is what I'm going for - just "upsized" to fit my 580 Case. Also, channel/square tubing won't work for my dimensions, so all pieces will be 1/2" FB welded in an "offset H beam" (one of the two channels in the "H" narrower than the other)

Once the "U" pieces are done, I'll use them for a pattern to cut the 1/2" FB pieces out, then weld in the "U" (see pic, thanks to whoever posted this (feel free to claim it, I only know it's NOT mine and I'm very grateful for it)

Hope that clears a few things up, feel free to critique my plan... Steve

 

[BukitCase]

Ken, thanks for that - I think (hope) that the down pressure required to bend that 1/2" FB will prevent that, at least during the push - at least, "that's my story and I'm stickin' to it" ... Steve

To clarify, I intend (at this time) to weld both sides of the gussets, both horizontal and vertical - insides are NOT beveled, will be fillet welded. Anything else is still up for debate based on more experienced wisdom than mine

 

[Shield Arc]

Me personally I would weld all the way around. Before making those welds on the vertical plates I would put say 1/8-inch or 1/4-inch round stock under the center of the plate and clamp the ends down. This will put a slight bow in the plate. After you make the welds let it cool completely to the touch before removing the clamps.

 

[Shield Arc]

Here is the weld sequence I would use. Make sure you make the opposite weld each time. And don't be in any big hurry while doing this.

If the vertical plates do bow towards each other you can heat a line on the bottom of the plate to heat shrink it back to planned shape.