Tube Bending 1

[joao100]

I am working in a bending machine and having problems with stainless tube bending. It's a hydraulic machine, with a pressure die, a clamp die and a non lubricated plug mandrel. I worked with mild steel in this machine and the stainless tube is being a problem. If someone have experience with this kind of work, please give me some tips.

Thanks.

 

[hydrodude]

What kind of problems are you having with the tubing? crushing, splitting. What size tubing and how much are you trying to bend it

 

[strokersix]

Also, what stainless alloy, heat treat, cold work, and finish will be helpful.

 

[IFRs]

Welded or seamless?

 

[joao100]

The tube size is 1.75" OD x 2mm wall thickness, stainless 304, welded tube. The bend radius is about 120 mm, 100 degrees bend.

Something more, just ask.

Thanks.

 

[hydrodude]

I have never worked with tubing bending in a size that large but if you are having trouble with collapsing or kinking you might try an old trick we used to use when we didn't have a bender handy and that is filling the tubing with fine sand to keep from kinking it

 

[FourJawChuck]

Bending speed is critical with stainless since it work hardens. You also need approx 1 1/2 times the power to bend stainless as compared to carbon steel, if you are operating the bender close to it's capacity then your running out of power to complete the bend. You could try annealing between bend attempts or you could just get a larger bender with more power, bend speed is very important.

Also Cerabend or other low melting point allow is useful to fill the tube before bending, boil in water to remove the alloy after the bend is complete...no need to cap the ends with Cerabend.

 

[ornerynorsk]

That's relatively thin wall for that diameter. You need to make sure you have enough pressure in your clamp and follow dies to insure that it's not forcing them "open" when the bend starts. Also, you need to make sure the mandrel is adjusted properly to the centerline (is it a segmented or a solid mandrel?) I have also seen instances using stainless where a wiper die is needed to help the material hold shape as it is bent. Good luck.

 

[Philrock]

I have heard that in the making of brass musical instruments, the tubing is filled with water, then frozen before bending - then you bend the tube full of ice.

 

[aceshigh]

ok, im no prfessional in anything.I am in my first semsester of machine tool... so im sorry for being uneducated.. i bought a $100 hydraulic tube bender, i thought it would be relatively simple to bend some tubing to make a different bumper/brush guard for my truck, so the structral strength isnt a huge issue, its more for looks and keeping sticks from punching out a headlight. i havnt been able to bend one tube right yet. ive tried heating a little, heating allot, 1"dia and 2", different wall thicknesses. dont know if the tube was welded, pretty sure its mild steel, it was just all scrap metal to practice on but i dont know what to try anymore. it always kinks in the die. the bender i bought is this one

http://www.cumminstools.com/browse.cfm/4,486.html

i got it for wayy cheaper than listed.. but is this bender not meant to bend tubing thats going to be used for bumpers/ lightbar / brushguards? i was hoping to one day bend tubing for a rollcage and stuff that will require allot of structural strength.
i tried searching this forum already but i cant understand half of what you guys ar talking about. im pretty new to this whole fabricating thing.. so if you could suggest some methods for bending or point me to a thread where it explains it in dummy terms so i can understand.
oh and buying one of those big several thousand dollar benders isnt an option... right now. and im not about to pay someone to do something i am capable of learning.
thanks

 

[notnats]

Ah! aceshigh. What you have there is a pipe bender. The outside diameter of pipe is different to tube, so the tube won't be properly supported for bending. Also pipe usually has a heavier wall than tube and is less likely to kink anyhow. Tube benders usually have more sophisticated arrangements. Try going to a hardware store and looking at the tube benders they sell to plumbers for 1/2" copper tube and you will see what I mean. Imagine this sized up to 2" tube with hydraulic rams and you are looking at thousands of dollars. Try hydrodude's tip of filling it with sand, plugging the ends tight, heating red hot and forming it around a 4" pipe. This will work with practice, but is hardly a commercial proposition.

 

[JDana]

Anyone considering filling tubes with sand and plugging the ends, please use dry sand. You do not want a steam pressure vessel when heating.

Spreading the sand on some sheetmetal and heating with a torch from below works well.

 

[chicopee]

You have not stated the type of problem with your tube bending operation. Is the tube crushing where it is being clamp to the die? With a properly sized mandrel and die, the tube should not crimple at the point of tangency where the bend is being formed. Is the wall thickness tearing on the outside surface of the bend and if so annealing as mentioned above may be a solution or the radius of curvature may be too much. Please state your problem--