square tube forming 1

[southfab]

i am forming square tubing out of 5/16" mild steel sheets. i can get the basic shape of the tubing but i can not get the tube to close at the top because of springback. i need to calculate the force required to clamp the tube shut to be able to weld the two flanges at the top together, any ideas

 

[BillPSU]

Can you use standard size square tubing?

What size do you need? How long and what tolerances, size, straightness and twist?

 

[MikeHalloran]

You can buy square and rectangular steel tubing ready to use, in that wall, in a good range of sizes.

If you insist on bending it yourself, you will find it's much easier to fixture and weld if you put the seam at a corner, not in the middle of a face.




Mike Halloran
Pembroke Pines, FL, USA

 

[southfab]

the dimmensions of the tubing are length=100", width=3", height=7.87", with a thickness of 5/16". i have tried to buy square tubing with these dimmensions but i cannot find any.

 

[Kapitan]

If a stock size is not available you could weld together two lengths of 4" x 3" rectangular hollow section, which is easily sourced, this would give 8" x 3" - only an 1/8" over, which means just 1/16" machined off each side locally, where required.

Another advantage is that it is a symmetrical weld case, less likely to distort than only one weld line.

 

[smcadman]

5/16" plate? You may want to make a u-channel and cap the top instead. You will double the weld length, but your overall-width and quality would be more consistent. Use a vortec cold air gun to reduce distortion from the added weld.

Flores

 

[griffengm]

southfab,
When this type tube is made in a mill, it is usually rollformed and welded with rollers pressing in on each side. Seems like one could simulate this process on the lengths you want. Proper cooling is going to be the key to not winding up with a horseshoe.
Making two channels and welding from both sides might be less problematic even though you will have twice the weld as pointed out by smcadman.
As to force required, I could probably do it with five four- inch c-clamps.

 

[ornerynorsk]

If you use enough of the stuff (truckload qty) just have a real tube mill make it for you. They can make any size for a tooling charge, and it will be made right, with certs.

 

[BillPSU]

I had rolling tooling made for 5 3/8" x 7" x 3/8" 80,000 yield rectangular tube. Depending on which mill you go to the weld seam can either be on the short or long side. The minimum mill run quantities are quite high. The material was used with 8" x 6" x 1/4" wall tubing for A-frame outriggers for aerial device and digger derricks trucks.

At the time the only way to make this tube was to direct rollform the rectangular shape and weld. The mill I used originally was Bock Tube which was bought out by Bull Moose.

Previously the tubes with 5/16" 100,000 yield manufactured using (2) C-channels which were welded together. The channels were overbent to about 95 degrees and the weld was lower than the exterior of the tube.

 

[smcadman]

If you make the channel 7 7/8" wide with the flanges 2 11/16" tall and then cap it with a flat plate 7 5/16" wide, you can simply lay the plate on top and full-corner weld it. This will make welding, grinding, and finishing easier than butt welding 2 channels together.

l             l
l             l  (2 11/16" tall)
l             l
---------------
 (7 7/8" wide)

It is typically easier to grind a corner smooth than 2 faces welded together. Also, if you weld 2 channels together, you may have to bevel the edges before welding to get better penetration if you have to grind the faces smooth afterward. Bevelling the edges adds another step and adds extra time to produce.

Flores

 

[MadMango]

Probably better to weld two angles together instead of a c-channel and plate. All that heat on one side will create a lot of warping.

[green]"Art without engineering is dreaming; Engineering without art is calculating."[/green]
Steven K. Roberts, Technomad
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[BillPSU]

Two angles welded together have loading problems if the part is seeing twist. The welds will see high stresses. Using two C-channel allows you to put the weld on the neutral axis of the tube.