View Full Version : Fold and weld fabrication with 5/16" steel.

05-31-2013, 03:22 AM
I've built several things out of 1/8", 3/16" and 1/4" steel by laying out the patterns, making interrupted cuts with the plasma torch, folding along the interrupted cuts, and welding the joints. Some of the assemblies required 90-degree folds. I haven't had any problems with the joiner tabs breaking when folded......Until now.

I'm building a rectangular hopper out of 5/16" mild steel plate. It will have a flat bottom and four sloping sides with a vertical band around the top. The cut lines are laid out on a sheet that's six feet wide and eight feet long. There are eight fold lines with interrupted cuts where I left 3/8" tabs about 16" apart. Two folds need to be 60 degrees, two need to be 30 degrees, and the rest need to be 45 degrees. I've got the sheet positioned on a support under what will be the bottom of the hopper, and I plan to bend the sides down so I can tack the corner joints, then make the other bends to form the band around the top.

I also laid out and cut some smaller parts that need 90-degree folds on another sheet. When I tried to fold the first one, the joiner tabs broke at about 45-degrees of bend. That doesn't bode well for folding up the larger assembly.

What's the best way to keep the joiner tabs from breaking as they're being bent?

I know I could just cut the parts loose, but then I'd have to figure out a way to hold them in position to tack them together. They're pretty heavy, and I don't have much good help available right now.

Paul Alciatore
05-31-2013, 03:38 AM
Could you use an angle grinder to cut about half way through the tabs? That would/could make them thinner and less likely to break.

Jaakko Fagerlund
05-31-2013, 04:10 AM
Sounds like a too tight radius for bending that thick. Either grind it thinner or bend with a larger radius

05-31-2013, 09:14 AM
Heat it before you bend it!


05-31-2013, 09:24 AM
Hang it over the edge of a table and clamp one side to the table. Then heat all the tabs with a torch and let gravity bend it for you. You migh need to hang some weight on the outboard end. Be ready to hold it in position when it reaches the angle you wish. You could have some blocks of the right height to use as a stop. You don't need "red Hot", just enough heat that it bends under its own weight.

05-31-2013, 06:56 PM
Some of the fold lines are over six feet long with five tabs, so it's going to be hard to heat them all at the same time.

Grinding will leave small grooves across the top surface of the tabs being bent. I've seen a lot of cases where stress risers like that cause welds to fail in bend tests, so I'm a little hesitant to try that.

What do you think about making about 30 degrees of the bend, and then putting a small weld next to each joiner tab? The weld would be at the bottom of the V formed by the bending. The fresh weld metal might hold for the rest of the bend even if the original tabs break. Any chance that would work?

05-31-2013, 07:05 PM
You want to grind the tabs on the side your bending to, you are welding the inside aren't you?

05-31-2013, 07:53 PM
Ahh, yes. Grinding the tabs on the inside of the bend makes more sense.

As for the welding, I was planning on chain welding the outside of the V-shaped openings along the fold lines and joints. There's no reason to weld the inside. The finished hopper doesn't need to be smooth on the inside or leakproof.

05-31-2013, 08:16 PM
If the tabs are not too long you can play with the heat on all of them. If you have weight on the outboard ends and the heat get close it will slowley make your bend. I beleive the temp is only close to 800F maybe less. Definitly not in the "red heat " category. With just the tabs to heat it should go easy.

05-31-2013, 11:44 PM
I'd build myself a "roof" shape w appropriate angles and stops out of wood (2x4 ?) and use that as a "buck" as well as a support for said sheet for the flat bottom and sloping sides portion. Sorry but actually what I would do would be to cut the parts completely loose and then place them on the previously mentioned shape. My gut feeling is a problem in the making with trying to control the bend of the tabs with such a large/heavy sheet.

The way I am reading the OP plan you would have tabs at the bottom edge where the sides would slope but also at the top of those sides for the vertical band and, given the way my projects usually "go", this could get complicated IF those tabs don't all fold exactly correct...its usually on the last corner and given size/thickness/weight getting the last bit aligned could be tough (it would be for me for sure)

Paul Alciatore
05-31-2013, 11:52 PM
Bending the tabs should produce some pretty good stress risers on it's own. If they are thinner, the stress level should be less I would think. And I guess I was figuring you would weld over where you grind.

Some of the fold lines are over six feet long with five tabs, so it's going to be hard to heat them all at the same time.

Grinding will leave small grooves across the top surface of the tabs being bent. I've seen a lot of cases where stress risers like that cause welds to fail in bend tests, so I'm a little hesitant to try that.

What do you think about making about 30 degrees of the bend, and then putting a small weld next to each joiner tab? The weld would be at the bottom of the V formed by the bending. The fresh weld metal might hold for the rest of the bend even if the original tabs break. Any chance that would work?

06-01-2013, 03:59 AM
Here's a question I just thought of.

When I make part of the bend, I'll be putting some stress in the tabs. Will heating the partially-bent tabs and allowing them to cool release that stress, so that I can continue bending without reaching the breaking point?

I realize it's an ambitious project and there are other ways to do it, but I really want to make this fold-and-weld idea work on thicker metal.

06-01-2013, 04:00 AM
Oops. DP.

06-01-2013, 04:13 AM
I believe that if you heat the partially bent tabs, they will then bend further without cracking.

My first thoughts on this was that you have probably hardened the tabs by the plasma cutting. Re-heating each tab and playing the torch to allow a much slower cooling of each tab would probably help resolve the problem.

Another thought was that since this is thicker material, the length of the tab vs the width of the plasma cut slots is now shorter. You don't want to widen the slots to make the tabs longer and thus more able to bend without cracking, but you could lengthen the tabs by plasma cutting a bit of a T at the ends of each slot. That will probably allow the bend to take place without cracking, but it might also leave the width of the slot wider than you'd like it after the bend is done. Could be worth an experiment.

I like the idea of angle grinding some material out of the inside of the tabs. That would tend to keep the edges closer together after they're bent, and it would leave a clean look on the outside. Again, I think an experiment would be in order.

06-01-2013, 06:29 AM
Just an uneducated guess, but bend to a little less than 45 degrees, then heat each tab to near red heat to anneal them. Even mild steel will work harden and CRS (cold rolled steel) will start out harder than HRS.

06-01-2013, 08:51 AM
+ what ulav8r said.

While it is possible to harden even mild steel if you cool it quickly enough, which is possible using a plasma cutter, the heat affected zone would necessarily be small as well.

Heating the hinges with a rosebud even one at a time would seem the next and simplest route to try.

Some thing else you could try is to cut the kerf adjacent to the hinge point a little wider. I suspect that what is happening is due to the thicker stock there is much more stress on the hinges than there would be on thinner stock. IE the ratio of the thickness of the stock to the kerf should be closer to unity.

I have used this method for bending, but perhaps as you get to thicker cross sections it might be easier to just 'jog' the cut and use the male and female areas created to interlock the two pieces to align them for welding.


06-01-2013, 10:55 AM
Heat the tabs to red heat to relieve the stress,then bend some more rinse repeat.

Maybe think about getting a couple 50ton air jacks and building a homebrew press brake.It would sure save a lot of welding:D

06-01-2013, 05:21 PM
That would take a pretty significant home brew press brake to bend 5/16 thick material of length.

I'm a relative newbie when it comes to welding, plasma cutting, etc, but isn't there a way you can blast a puddle of metal away- I'm thinking that it might be possible to thin the tabs by 'torching away' the excess metal, rather than removing it by a strictly mechanical means. Maybe using an angle grinder would still be the best way though-

I think that's the answer- thin the tabs from what will become the inside of the bends. When all is said and done, the tabs themselves won't be providing any of the strength of the assembly, so you could thin them down to 1/8 or even less, over a distance of about 1/4 inch. That should allow an easy but tight bend radius without breaking the tabs or distorting the sheet material around the tabs.

06-01-2013, 08:17 PM
For all the effort to cut out sections to create tabs, grinding to reduce the thickness of the tabs, bending and then welding, you might as well just cut two pieces and weld them at a 90. I think it would be faster than all the other monkeying around.

06-02-2013, 12:34 AM
...but I really want to make this fold-and-weld idea work on thicker metal.Just wondering why - aesthetic or an artsy feel ?
I personal like that "finger joint" look in wood working (not including the strength for wood working), bent around a corner would probably look pretty cool.

06-02-2013, 01:15 AM
Sounds like the slits are too narrow for the material thickness, the tabs are being ripped with a zipper crack, the break should be fibrous and stringy, if the plate was too hard then the fracture would look grainy, try a wider slit and see how it works, also try rotating the parts through 90. Or even 45 degrees, sometimes the r2 or r3 ductility is considerably better than r1, r1 being rolled direction r2 at 90 to rolling or across the rolling, and r3 is at 45 degrees to the rolling direction, these are the three directions that tensile tests are performed on plate at the mill test house also, you should be able to bend most steel
sheets without cracking unless it has been excessively temper rolled (cold rolled) which is fairly unlikley at that thickness as not many stockholders have straightening rolls to uncoil it even if the cold bill could roll and wind it, I for one would not trust the signore bands to hold a coil that thick of temper rolled steel, it would be a hell of a clock spring!

06-02-2013, 03:55 AM
The steel I'm working with is half of an eight-foot by twelve-foot sheet. Four of the fold lines (two that get bent 60 degrees and two that get bent 30 degrees) are parallel to the roll direction, and four (all get bent 45 degrees) are perpendicular to it. The tabs that broke on the smaller part were on a fold line that was perpendicular to the roll direction.

IIRC, the fracture surface on the tabs that broke were shiny and smooth near the outside of the bend and grainy near the inside.

I'll take some pictures Monday.

I recall seeing impression-stamped info in several places on the sheet. I haven't seen that on the mild steel we buy. I suppose it's possible this donated stuff is something other than mild steel.

06-02-2013, 06:39 AM
I recall seeing impression-stamped info in several places on the sheet. I haven't seen that on the mild steel we buy. I suppose it's possible this donated stuff is something other than mild steel.

Try some simple spark testing with a direct compairson against mild steel.
You might think of mild steel as 'typical steel' but thats only because its great for general fab and is so forgiving its common.
Many alloys don't like to (cold) bend, others can't be (properly/easily) welded, etc.

06-02-2013, 10:27 AM
It's interesting, you may well have a sheet of something like a wear steel, hardox 600 or something for bucket making, plant repair, I find that the high carbon manganese work hardening steels do crack in the way you describe, and it's very directional as you point out, I go for sticking things at odd angles with hot rolled plate, seems to help with fabrication and I get less distortion than when I work in a tidy fashion with the plate, that may be just my imagination but try it for yourself, my last instructor at a skill centre hated my random cutting plan as he reckoned it was way wasteful but I did find that things fitted better, didn't twist up so bad as one piece of steel works against the other so everything seems to balance out, when I work with the plate I find the distortion to be cumulative, this is purely my theory but try it you may be surprised.
Hope you sort it!

06-02-2013, 10:38 AM
Is there any nomenclature on the plate that could ID it?

06-02-2013, 03:36 PM
Hmm- if you're willing to plasma cut the gaps already, why not just finger joint it- all you'd be doing is staggering the cut line. No bending required- just fit it, set the angle, weld. You won't need hundreds of inch wide fingers- six inches wide or even longer would be fine. The fit will be better, and the structure will be stronger. You would stagger the cut line by the thickness of the material, so the fingers nest together without overhanging or falling short.

Dovetailing would be a bit much though:)

06-03-2013, 12:22 PM
Here's the marking on the steel:


The 6' by 8' sheet with most of the cuts made:


And the fracture of the first trial bend:


06-03-2013, 12:28 PM
Heating the tabs between small bends worked great, and only one tab broke early in the process. Here's the hopper after the first set of bends with the corner clamped for welding:


And here it is with the rest of the bends made and the corners tacked:


After it's completed, it's going to replace this relic:


I'm REALLY happy with the way it turned out!! It was well worth the extra time and effort to get everything to fit together so well.

06-03-2013, 03:05 PM
Some of the fold lines are over six feet long with five tabs, so it's going to be hard to heat them all at the same time.

I see its a little late now, but in retrospect could you have 12 half foot long tabs rather than a single six foot long tab?

06-04-2013, 01:26 AM
Turns out to be a pressure vessel grade, propane tanks and that kind of stuff, it should have bent cold but looking at the fracture it was a brittle fracture probably due to the cooling rate of the HAZ either side, if you have an off cut you could try a 90 degree bend test in the vise it should take it with a BFH cold, I have shoved that grade in a pressbrake no problem (16mm thick) but since finishing work last week I shan't be doing that again........ever, although forever is a long time!
Nice looking shop too

06-04-2013, 04:21 PM
I got the legs attached, and the table is now upright.


From this viewpoint, you can see the top edges of the hopper lined up pretty well.


Too bad the diagonal measurements across the corners at the top are 1/4" different. I couldn't check that while it was upside down, so we'll just have to live with it. :)

I still need to add some 2x2 angle stiffeners around the bottom of the sloped sides before I cut the bottom out. Then I'll add some crosspieces so support the cutting grate assembly.

06-04-2013, 05:27 PM
I was wondering early on in this thread about this folding idea BUT in viewing the near finished project the process is certainly growing on me. Thanks much for posting.

I am a bit curious as I don't own a plasma cutter, how wide is the kerf and can you control the width? [Reading some of the previous responses, I could see how being able to cut a wider or very narrow kerf could come in handy...]

06-04-2013, 07:50 PM
Ahhh...grade 70,no wonder you were having some trouble,that stuff can be brittle.Had to weld some last year for a overhead spreader bar.Heated rods,preaheated joints and ultrasonic inspection,touchy stuff.

Very nice job on the bruning table.Will the new top have replaceable slats in it?

06-04-2013, 10:50 PM
Is this a water filled table?, looks nice

06-04-2013, 11:44 PM
The kerf is about 1/8", and it nearly closes up as the bends are made. There's not much I can do to control the width when cutting by hand. If I go slow, the kerf will get a little wider, but the slag buildup on the far side will be horrible. You can program the kerf width on our CNC plasma cutter, but I've never seen it done.

Trying to hold the four heavy pieces in odd positions for welding would have been much more difficult IMHO. I seriously doubt it would have turned out as well that way.

The instructor was really skeptical about me using the fold-and-weld method on something this size, but he's really pleased with the results.

I got the preliminary plans yesterday for the pan that fits under the burn table to catch the drops and slag. It's got a platform that the forklift tines fit into, and the pan itself is hinged to the platform so it can be dumped easily. More fun.

06-05-2013, 07:59 AM
under the burn table to catch the ... slag

So _that's_ what you're building. I thought this was the worlds biggest coolest BBQ grill. No not going for laughs, seriously. All you'd need to make it a giant bbq grill would be two sets of grates/grids instead of just one set. It also vaguely resembles one a nearby kids summer camp has (of course, all it took to resemble was its huge, its steel, its rectangular, its got a grid, there's no bottom or top, so ...) (edited to add, and I was hungry when I first read this thread...)

Don't get me wrong, its cool and looks like a great project. But maybe you could make a second shell, this one with two shelves of grates, or better yet angle iron around the edges to hold commercial size COTS cast iron grates, weld the whole works to an appropriate rated trailer, and get invited to approximately every backyard party in your whole county, which sounds like a summer of fun. Or the worlds largest tailgating party.

06-05-2013, 06:43 PM
HaHa. We just got a 250-gallon tank (code name: Big Stinky) that's going to be a smoker/grill combination on a trailer, but that's a project for another thread.

My first project for tomorrow is getting an eight-by-twelve (that's feet, btw) sheet of 5/16" plate cut into manageable pieces, so I can make the catch pan assembly for the burn table. I used up the last of the first sheet making the supports for the grate.

06-06-2013, 05:21 PM
I added the crosspieces that will support the grates.



We're going to order 3/8" x 4" flat bar for the grates. The work surface will be an inch higher than the edges of the table to reduce the chances of burning through the upper edges.

06-06-2013, 05:38 PM
Nice looking fab work.

06-06-2013, 11:47 PM
We do this all the time in the fab trade. We call them field bends.
I prefer to torch cut the stiches...they seem to leave the hinge part softer.
You normally only need three or four short hinges. Most guys use too many and leave them too long.
On thicker steel...I just nick the inside of the (short) hinge with the torch so they bend easier.

06-07-2013, 12:17 AM
Thanks, sasquatch.

We have an old O/A rail torch with portable rails, but I went with the plasma because it's so much easier to set up and use. I had over fifty feet of cutting to do with dozens of "non-edge" start points for the stitches. What took several hours with the plasma would have taken days with the rail torch, and I'm sure the accuracy of the cuts (crucial for something like this) wouldn't have been as good.

Heating the tabs worked very nicely. It seemed to "reset" the steel each time so I could get another twenty degrees of bend with only moderate force.

You're right about the length of the tabs. I tried to make them all 3/8", but some ended up being only 1/4". They were strong enough and much easier to heat and bend.

06-12-2013, 05:50 PM
I got the catch bin for the new burn box almost finished today. It's made of 5/16" plate, but I used conventional fabrication because most of the joints were 90 degrees and the pieces were light enough to handle without help.



The bin tilts 90 degrees for dumping the contents on our scrap trailer.


There's a piano hinge on the bottom positioned so the bin dumps on it's own when the latch on the back is released.

06-12-2013, 11:33 PM
It's a nice job, much cleaner than the floor I used last!

06-14-2013, 10:19 PM
Sorry to backtrack a bit...those angle stiffeners on the bottom...is the idea that the angle stiffens the edges much more efficiently than say another flat piece would...?

Curious as while I learn to weld I want to absorb as much theory as I can...makes perfect sense, just I would not have thought about such a detail and it could be significant...all four sides? Or is the short side stiff enough on its own...

06-15-2013, 01:02 AM
The angles welded to the plate form a closed section that is a little more rigid than a flat strip would be. It's much less likely to get damaged when handling the box with a forklift, and it won't be a place for stuff to collect. Most of the angle was salvaged from something in the scrap pile.

I added some stops to the sliding release handle on the catch box. They're U-shaped pieces that also keep the handle pointing up.

I'm planning on adding some pieces of chain hanging down on one side so I can tell when the catch box is in the proper location.