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Spring back force

  1. Aug 13, 2012 #1
    Hi all,
    I want to know if there is any formula for calculating spring back force for flat sheet.

    what i am trying to achieve:
    I am trying to bend a 3.5mm thick 1200(w)x1800(L) mm sheet into a shape of hollow cylinder.
    If one end of sheet is fixed i want to calculate how much force is required to hold/press the other end adjacent to fixed edge.
    Neglect weight of strip

    Material : steel 55mpa

  2. jcsd
  3. Aug 14, 2012 #2

    Simon Bridge

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    That is rather complicated - when you bend a sheet into a circle and let go, it generally does not spring back to flat, but holds some of it's cylindrical shape depending on it's material properties. i.e. you'll exceed the elastic limit.

    So you need to know about plasticity as well as elasticity for your sheet.

    You'll also find it is easier to hold the inner edges together than to hold the two ends flat just by pulling on it.
  4. Aug 14, 2012 #3
    Thanks for reply mate,
    With regard to my problem i just want to calculate how much force is required to keep sheet in cylindrical shape, not too much worried what profile it take once we remove the force.

  5. Aug 15, 2012 #4

    Simon Bridge

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    You misunderstand - it is difficult to calculate because you are exceeding the elastic limit, otherwise it is just an extreme torsion spring. The force is whatever it takes to close the last inch or so.

    This is something you determine empirically - which means you won't know until you do it. I'd guess will be close to the spring back force of a small compression on a steel tube with the final dimensions so you want to bank on more than that.

    But, if the initial bending put the ends slightly past each other, it would relax back to the shape you want but for 3.4mm mismatch (it's actually bent in a slight spiral) and that's just a small torsion-spring problem and you get a decent circular cross-section to the finished tube.

    If the initial bending puts the ends smack-on, it'd relax back 2-5cm or so unless it's really good steel. Then, if you draw the edges close to weld them, you'll end up with a slight tear-drop cross-section.

    Are you trying to figure if you have a machine capable of the force? Or if the weld (or whatever is to hold the ends together) will hold?
  6. Aug 15, 2012 #5
    Hi Simon ,
    Thanks again mate.
    I do agree with all the comments made in previous reply. It is bit difficult to calculate, well i will continue on some way to figure out how can we calculate this.

    We want to calculate for machine capablity. It a roller pussing against the tail end of coil to keep the last flap of the coil on the curvature of the coil.

    Thanks Again
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