Can anyone tell me anything about bending tube ? 1

[Jamaz17]

Hey,

I am designing a machine to bend a rectangle tube with .125 wall 1 1/2 x 3 mild stell. The bend I have to make is 5 degrees with the bend on the long face. Can anyone think of any problems I might have doing this, or which method of bending might be more suitable? I have done a few test bends using a simple press and no mandrel and the tube in caving in on the inside of the radius. Does anyone have any ideas or has anyone built a bender before. Thanks for the help as benders are new to me.

James

 

[dik]

It depends on the radius of curvature and the tube walls will likely distort. I have tables, but not at the office.

Dik

 

[rb1957]

how structural is this ? ... possibly heating the outside 1/2 (with a blow torch) would reduce the load to bend the tube ... but it would ruin the heat treat

 

[metengr]

You need to use a mandrel on the tube ID surface to provide some support on the tube wall during tube bending. Another option is to fill the tube with sand and bend.

 

[MikeHalloran]

Round tube can be bent with external support and only crushed a little.

For rectangular tube, you can:
- Control the buckle location with external support, and allow it to happen.
- Bend it over a punch so you control the shape of the buckle.
- Support the inside while bending.
- Stretch the entire tube while bending- some inside support may still be required.
- Support the outside and pressurize the inside while bending.

Go to some new car and truck dealers and crawl around under the vehicles, looking up. You will find a lot of bent tubes, many with intentional wrinkles.

Get yourself a subscription to the Tube & Pipe Journal.

http://www.magazines.com/ncom/mag?mid=7069

Mike Halloran
Pembroke Pines, FL, USA

 

[R1100S]

Old school trick is to pack with sand before bending. Even better trick is to fill with lead, bend, and melt the lead back out.

What sort of radius are we talking, and is this one bend or thousands. If we're talking thousands, how about a mandrel system.

 

[pennpoint]

I don't know about lead. But there are products that are sold specifically for this with low melting points, wax for one. Sand is great for a one time, low cost method. You haven't stated the radius at which you want to make the 5 degree bend. Did I miss it?. The smaller the radius the worst the negative effect on the tube. Practice on a piece of scrap to see the effects on the tube. Having .125 wall will be a chore with out some mechanical leverage. You may find that you'll have to cut (3 sides), bend then and weld in a patch. I do not recommend heating the tube as that brings ALL the metal at the localized point to yield and the bend will flatten, concave and thin out and you will not be able to control it.

Best Regards

pennpoint

 

[Jamaz17]

Thanks for all the info guys. I guess I should say this is a production part for an automotive application. The bend radius is about 8 inches. I'd love to be able to pack with sand or something but I don't think that will go well with a production application. I had one question for Mike, what did you mean by bending over a punch to control the buckle ?

 

[arto]

Don't use lead - use cerrosafe or a similar low melting point alloy:

http://www.cerrometal.com/lowmelt.html

tips for using:

http://www.brownells.com/aspx/NS/GunTech/NewsletterArchive.aspx?p=0&t=2&i=609

[gunsmiths us it for chamber casting]

 

[smcadman]

8" is a pretty tight radius since you are bending it the hard way (3" face). Go to

http://www.toolsforbending.com/literature.asp

and download the "tube and pipe bending manual". (hint, just enter an "x" or anything for the name and contact number to download it). Look on page 6 or 7 for crush bending and see if that would work for you.

Flores

 

[Hydroformer]

Your best solution... contract the job to me

*Without data, you're just another person with an opinion.*

Hydroformer

 

[Jamaz17]

Thanks for the link smcadman. lol and Hydroformer i wish that was an option.

 

[MikeHalloran]

What I meant by bending over a punch was ... go look at some lawn furniture, and see how round tube is bent to a tight radius, over what is clearly a punch, giving a roughly I-beam cross section (the easy way) to the tube at the middle of the bend.

You might contract hydroformer to assist you in selecting a hydroforming machine to buy, or in designing one if you insist on homebrewing.





Mike Halloran
Pembroke Pines, FL, USA