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Sheet metal K Factor

Question asked by R. Vignesh on Sep 1, 2012
Latest reply on Nov 29, 2012 by Julio Cesar Silva

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Dear All,

The formula for K-Factor is t/T

where t=distance from neutral axis,T=Thickness of Sheet Metal.

Can anyone tell me how do we generally locate our neural axis. Its not always neccessary that our neural axis lies at the middle of the sheet.

I know it depends upon the material also. Say the material is HR (Hot Rolled) or CRCA ( Cold Rolled Closely Annealed),or SS (Stainless Steel)

Still any specific formula or method where in i can know where my neutral axis lies means at what distance does ot lie from ends.

Thanks & Regards,

R.Vignesh

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9 Replies

Kelvin Lamport Sep 1, 2012 11:18 AM
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I've not had chance to watch it yet, but see if this helps;
https://forum.solidworks.com/thread/59375?tstart=0
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Anna Wood Sep 1, 2012 1:42 PM
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There are no magic formulas. Deciding on what k-factor/BD/BA to use comes from experience with bending metal.

I would talk to your suppliers who will be manufacturing your parts and ask them for recommendations on k-factors.

If you are bending metal in house you can do testing to generate the k-factors/BD/BA that your material, equipment and processes will need.

http://www.ciri.org.nz/bendworks/

The SME Die Design Handbook is an excellent reference. http://sme.org/ProductDetail.aspx?id=14330&terms=die%20design%20handbook

Cheers,

Anna
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- R. Vignesh @ Anna Wood on Sep 2, 2012 12:51 AM
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  Dear Anna,
  
  Actually the suppliers had given us a step assembly file and an Auto CAd drawing for each part.
  The Auto CAD drawing contains the actual blank size of each part.
  If we import the step file and develop it in Solidworks it comes out around 0.7 mm less.
  we asked what K-Factor or Y-Factor has been taken into consideration,but the people who gave us the drawing didn't knew or it was confidential to be disclosed i don't know.
  
  So if we know the sheet thickness,bend angle and bend radius can we calculate the exact K-Factor.
  
  The bend works will be useful if there is only one bend,what if i have multiple bends with different bend angles and bend radius.
  
  Kindly help me on this.
  
  Regards,
  R.Vignesh
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Steven Smith Sep 2, 2012 3:53 AM
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The K-Factor should be set at 0.44
To ensure the correct development length, the material thickness and internal bend radius shoud be the same.
(eg, if the material thickness is 1.2mm then the internal bend radii shoud be set to 1.2mm)
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- R. Vignesh @ Steven Smith on Sep 2, 2012 5:50 AM
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  Dear Mr Smith,
  
  Can you please explain me how you came to conclusion that K factor must be 0.44, any specific reason behind that...
  I tried that too but i am not getting the exact blank size..
  If i put K factor as 0.44 , variation is more...
  The sheet thickness is 2.5mm.
  I am maintaining the bend radius as 2.5mm .
  
  Thanks & regards,
  
  R.Vignesh
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  - Bernie Daraz @ R. Vignesh on Sep 2, 2012 8:05 AM
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    Anna is correct in stating that your own K factor will need to be developed through testing. I have been working in precision sheet metal for 40 years, no one K factor will work everywhere. It may work here and there as demonstrated by Steven Smith.
    
    We used to use .42 for many years. But that was converted to bend deductions to make it easier for the guys on the brakes. The majority of them could recognize a .086 bend deduction in 16 ga steel as a coin bend. When .092 appeared on the router, it was an air bend.
    
    Yet, I'm a bit confused. If you know: "I tried that too but i am not getting the exact blank size.." If you know what the exact blank size needs to be you shouldn't have any problem with a blank developed within SolidWorks. You may not be using the correct methods for your workflow or production process.
    
    Without a model or even knowing what angle or material it is or whether you're air or coin bending it would be very hard to give specific advice. For me, if the bends were 90 degrees and the dimensions were outside to outside I would use a bend deduction of .179. That equates to a K factor of .46. Better yet, ask your brake guy what you should use as a bend deduction. He (or she) should know what he needs to make the part come out right. As an added benefit, it will be easier to bend when it's correct.
    
    My advice would be try a K factor of .46 or even the bend deduction (.179) in your model. Then flatten it and dimensionally inspect the features. If they match "your exact blank size" you should be good to go. If they don't I would guess there's something being missed.
    
    Again, without a model it's hard for us too!
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    - R. Vignesh @ Bernie Daraz on Sep 2, 2012 10:33 AM
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      Dear All,
      
      Thanks alot for your suggestions and advices.
      
      Regards,
      R.Vignesh
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Jerry Steiger Sep 2, 2012 11:50 PM
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R. Vignesh,

Listen to Anna and Bernie, as they know lots about sheet metal. (Not to slam you Steven, but there are a lot of posts in this forum discussing the utility of different K factors for different situations and materials, so I am pretty sure that you are just lucky that one value has worked for you.)

There was a post within the last week or two that included the simple mathematical relations between K factor, Bend Allowance, and Bend Deduction. (It wasn't one of the ones that shows up right now in the "More Like This" box.) Try searching on those three phrases.

Jerry Steiger
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- Julio Cesar Silva @ Jerry Steiger on Nov 29, 2012 6:46 PM
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  I am having a bad time working on my bends, to give me a proper developed flat. for 8mm I ended with 8mm internal radii and k factor 0.3
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Sheet metal K Factor

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