squashing tubing into an ellipse

[amorrison]

If a thin walled metal round tube is squashed along its entire length will the final yielded shape be an ellipse (new "diameter/smaller axis" limited to no less than 0.75D)?

 

[carnage1]

my experience has been that it is sorta an ellipse but you end up with a pair of flats on the long sides. could you pull it through a die or would slightly flat be OK?

Luck is a difficult thing to verify and therefore should be tested often. - Me

 

[IRstuff]

Depends on the metal material, I would think, but it would be highly unlikely to result in a true ellipse. The compression sides will will flatten, but the major axis might actually fold.

TTFN

FAQ731-376

 

[CorBlimeyLimey]

Depends how it is 'squashed'.
Feed it through shaped rollers or use shaped dies in a press.

Chances are you will end up with an oval more than a true ellipse.

 

[GregLocock]

I am 100% sure that it will not form a true ellipse, unless you use a die to form it.

The reason is that 4 or 6 plastic hinges will form a mechanism and prevent the rest of the metal from yielding.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[tbuelna]

If you need a true elliptical cross section, hydroform the tube to that shape. Squashing a round tube (assuming you're using flat plates to do the "squashing") will simply yield flat sides with somewhat rounded ends.

There are also some oval cross section tubes available from sources like this:

http://www.burnsstainless.com/OvalTubing/ovaltubing.html

Good luck.

 

[ajack1]

As others have said if you need a true ellipse either hydroform the tube or extrude it, if you need something better but not a true ellipse use a form tool with a shaped punch and die, this will limit the “outside” dimensions but not the “inside” or for a very basic oval shape form between two plate plates.

Depending on the tube size just sticking a small sample length in a vice should give you a good idea what you are likely to get with flat forming, capping and filling the tube with sand will give a better result on a shaped form tool. If it is seemed tube the placement of the weld will have a fairly major impact.

As with so many things in engineering small increases in accuracy result in large increases in cost, how accurate does it need to be?

 

[chicopee]

Must the tube be trully elliptical or can you get something less perfect?

 

[jmw]

Curious to know why you need an elliptical tube?
I know some tube density meters have an "elliptical"/"oval"/"flattened" tube which is nominally 1" bore.
The reasons? it gives the tube a preferred bending moment when it is vibrated and it is to minimise the pressure effects on the resonant frequency...


JMW

http://www.ViscoAnalyser.com

 

[unclesyd]

There used to be local shop that made elliptical tubing from round. They're gone now but they used a machine that had vertical rollers such as this one. I recall correctly they had 3 rolls in operation and made two passes to form the correct elliptical shape.

http://www.boschertusa.com/bendopc300.html