Bend deduction and k factor questions and suggestion

Hi,
I keep getting this message after trying to unfold a tube with a cut down
it's side.

Sketch
Arc length 1108.78mm
chord Length 0.2mm
Radius 176.5
Angle 359.94

Base Flange
direction 1 = 420
sheet metal parameters T1 =2mm reverse direction
radius 174.5


sheet thickness 2mm
bend radius 174.5


Error Unfold1 The specified bend deduction value for the given radius and
thickness is invalid. Try using a different bend deduction value, or use a
different bend allowance type.

Now here is my theory, if Solidworks knows that the bend deduction value to
be invalid, then it must know what the valid range is!

So could it not be helpful and show what the valid range is instead?

k factor 0.9525 works and the tube unfolds.

Is there a way to work out the bend deduction from the k factor?

 

Do you understand what k-factor is?

 

K-factor is a ratio that represents the location of the neutral sheet (t),
with respect to the thickness (T) of the sheet metal part.

In other words K-factor = t/T.

But, our sheet metal department does not use the k-factor they use, bend
deduction.

So it would make sense to use bend deduction.

On a 90 degree bend this is easy to work-out, But I am having trouble with a
rolled tube in solidworks.

I know what the blank size is, I know what the bend deduction is, but I can
not get Solidworks to make the part, with that information. Hence my posting
here.

 

Generally when the inside radius is greater than or equal to twice the
material thickness, the neutral axis is half way through the material,
therefore k=.5.

I just tried it and it worked fine if using K factor. Flat length =1102.50.
And by creating the sheet metal part this way, you will find that it
recognizes the large radius and uses it as the bend radius. Do a RMB on
BaseBend1 and select Edit Feature to see that.

But if I then say that the bend deduction should be 6.282 because that's the
difference between the neutral axis length and the outside arc length, then
I end up with the same error you do. My guess is that BD will not work
properly with such a large radius relative to the material thickness.
Interesting, indeed.

WT

 

Good. Using K-factor, you can then calculate the unbent length of the
bend region. I believe this is what most call "bend deduction".

 

Never mind that. I was wrong. Turns out there is a good explanation
of bend deduction in the help.

Always used K-factor in the past.

 

Thank you for your replies,

As Wayne has found out, BD does not work as expected, in this case.

If nothing else it has proved that I was not having a bad day, Solidworks
was,lol

 

The K-factor is the placement of the centerline of the material in the
bends. (i.e. 0,30 means its 0,3 x material thickness meassured from
the inside of the bend in SolidWorks)
That factor is very dependent on the bending tools used.

You should have that in mind if you use different sub-suppliers
(different set of tools) for manufacturing

 

Thank you Ronni,

That's a useful bit of info to bear in mind.


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