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A basic question

  1. Jan 5, 2015 #1
    Hi guys,

    New to the forums so if ive posted this in the wrong section I apoloise!

    Just a basic question on designing really,

    I'm currently designing a backplate to fit onto a rucksack for a project at college at the moment and I'm havig a bit of a brain fart.

    The backplate I'm designing is basically bent on the two ends 30 degrees down in flat stainless steel 2mm sheet (316). My question is that of I know the degrees in bending the sheet down and the thickness, is there any formulae I can use to work out what radius will be incurred on the inside of the bend? Apologies if this comes across vague, I can provide more information if required!

    I have worked this out via drawing it on autocad however it would be useful to do this by hand if possible.

    Many thanks!
    Brad
     
  2. jcsd
  3. Jan 5, 2015 #2

    Bystander

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    Are you using a sheet metal break? Bending it over your knee?
     
  4. Jan 5, 2015 #3
    I'll be using a friend who has a press break. I Understand that e can use different die's to achieve different radii however I just mean for design purposes. Is there a radius that will be given if I bend the metal at a certain degree or can I choose this myself dependant on the die he will have?

    I know this sounds like a really stupid question and to be honest Im kind of answering this myself. I'm just trying to clear this up.

    Cheers,
    Brad
     
  5. Jan 5, 2015 #4

    Bystander

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    Sheet metal design depends a lot on what you want the piece to do for you once you've finished forming, bending, drawing operations. I'm guessing you're trying to stiffen the sheet for your pack frame, and that means a short radius bend giving you a permanent deformation of the sheet. A very rough rule of thumb from growing up in a sheet metal shop is that any radius less than ~ 10 times the thickness (or some other minimum dimension) of the stock being bent will give you a permanent deformation.
     
  6. Jan 5, 2015 #5
    Ah brilliant. That answers my question.

    Thank you very much for the help!
     
  7. Jan 5, 2015 #6
    Sorry just to also clarify, if this is one ten times the thickness (as a rule of thumb), will the bend then be too weak for forces to be applied against the bend?
     
  8. Jan 5, 2015 #7

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    Depends on the material --- steels in annealed condition can be folded just like paper up to quarter to half inch thick sheet/bar; heavier than that, the outside radius of the bend will suffer tensile failure, cracking, tearing. If you've got a scrap of your 2 mm SS, you can have your buddy fold it, and you'll see the beginning of cracking on the outside radius (that's a "zero" radius inside bend, or just however sharp the knife on his break is).
    Don't try the final product first time around. Bend a few scrap pieces first to get the feel for what you can and can not get from a particular radius of bend.
     
  9. Jan 5, 2015 #8
    Many thanks Bystander.
     
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