Bending Square Hollow Section

[MozamPete]

I've been experimenting with bending square hollow section for a small project but not having much luck. I welded a nice radius and a couple of stops to some plate as a jig, heated the section and tried to bend it (like I would do for a solid bar) but it just pinched and buckled on the sides.
I was planning to use them as the 'shelves' (I'm sure there is a proper word but can't think of it) for a steel stock rack and just wanting to put a small kick in the end to stop any round section rolling off, maybe 30 degrees for the last 50mm. Section was 20mm x 20mm, 2mm wall.
I could just weld them on at a angle but I would prefer them to be horizontal with a turn up at the end if possible. I figure I'm going to have to go for a more elaborate jig, something with a radiused channel to support the sides of the section (should be easy enough to turn up on the lathe) and maybe a moving guide to bend it around like a proper pipe/tube bender.

Has anyone here done this and/or have any plans/photos of simple benders that have used for square tube?
Is hot bending the way I should go or would I be better to try cold bending them?
Any suggestions/comments appreciated.

 

[great white]

I would suggest you sand pack and then attempt the bend.

Make sure the sand is DRY if you try heat on a sand packed tube. Withe both ends capped and any steam produced inside it can become rather......exciting.

 

[GSWayne]

One technique to prevent collapse when bending tubing is to fill it with a low melting temperature metal allow like Cerrobend before bending. http://www.ebay.com/sch/i.html?_fro...C0.H0.Xcerrobend.TRS0&_nkw=cerrobend&_sacat=0

 

[Ulma Doctor]

maybe a little off topic, but the idea may help.
the chevrolet corvette used hydro-formed frames constructed from aluminum rectangular tube.
the tube is essentially filled with liquid to a predetermined volume and capped off.
then it's formed into shape with a hydraulic bender array.

with a little experimentation, you may be able to emulate the idea.
keep in mind that you'll need some air void inside the tubing when filling with liquid to allow for bending.
if you try to bend a tube that is completely full, it may burst as an unintended consequence .

 

[joshua43214]

For shallow bends, you need to bend it around a curved form. Heat the outside so that it will stretch. Not sure if you will reach 30 degrees, but I have done this with both square and round tube. If it is buckling, it is because the inner arc is not supported, and the outer arc is not hot enough.
You might need to fill the tube with sand to get that much bend.
Heat is the key, use a rose bud and acetylene.

Really much simpler to just notch, bend and weld.

 

[RJSakowski]

If you look at 90º bends in square tubing the tubing is purposely crimped at the bend .
This would be very difficult to accomplish without proper dies. If I were attempting the bend I would heat the inside of the bend to a red heat and start the bend. The walls will thicken locally as the bend progresses. By careful heating and bending, possibly with a little hammer work, you may be able to get your desired result. Just cold bending around a form will stretch the outside of the bend, thinning that area and possibly tearing it in the process.

If I were doing this, I would probably weld rather than trying to bend. If an outside radius was desired my pre-weld form would look something like the shape below. The solid lines are the cut tubing prior to bending and the dashed lines show the orientation after the bend. Proper chamfering would be done prior to the bend.

 

[BobSchu]

If what you are looking for is a small radius to keep your round stock on the rack use a variant of the above suggestion. Just make a number of wedge cuts close together at the point you want the bend. Bend to the proper radius and weld back together.

Another idea for your purpose is to avoid the troublesome bending altogether and simply weld a flat plate across the end of the shelf long enough to protrude above the bar far enough to hold your round stock from rolling off. A couple inches of plate exposed above the surface of the shelf would hold some pretty large pipe.

Bob

 

[george wilson]

I'd go with the Cerrobend. You could use lead I suppose. Just needs higher heat to get it out.

 

[janvanruth]

Have a look at the foldable beach chairs made out of bent square stock.
The bends are made while the inner side of the material in the bend is pushed into the hollow.
Nice round bends and strong at that too.

 

[extropic]

Band saw out a 30° V notch leaving one wall.
Bend to close the notch.
Weld to suit (two good tacks would probably be good enough).