## [SOLVED] Wrong sheet metal unfold dimensions?

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Fra88
Posts: 17
Joined: Fri Mar 09, 2018 8:27 pm

### [SOLVED] Wrong sheet metal unfold dimensions?

Hello, I'm making some tests with the module sheet metal.
I made a simple bend with this parameters:

- sheet metal thickness= 1mm
- bend configuration: 90° bend with Kfactor=0,5
other dimension are summarized on picture and FC file attached.
When I use the unfold command, I obtain a sheet metal long 198,356mm but, making some math calculation, the lenght should be equal to:
L1+L2+(T+Kf*T)*pi/4=98+98+(1+0,5*1)*pi/4=197,178mm
where L1 and L2 are the lenght of the straight plates, T=thikness, Kf=neutral factor, pi=3,14...

I don't understand where is the error.
Is there any configuration that I have to tune?

Attachments: FC file, picture with dimensions.
Best regards.
Attachments
bend test.FCStd bend dimensions.png (5.89 KiB) Viewed 500 times
Last edited by Fra88 on Thu Oct 17, 2019 7:38 pm, edited 1 time in total.
Fra88
Posts: 17
Joined: Fri Mar 09, 2018 8:27 pm

### Re: Wrong sheet metal unfold dimensions?

Sorry there is a mistak in the formula.
The correct one is:

L1+L2+(Ri+Kf*T)*pi/4=98+98+(1+0,5*1)*pi/4=197,178mm
where L1 and L2 are the lenght of the straight plates, T=thikness, Kf=neutral factor, pi=3,14..., Ri=internal bend radius
chrisb
Posts: 25145
Joined: Tue Mar 17, 2015 9:14 am

### Re: Wrong sheet metal unfold dimensions?

I have a different formula which uses pi/2 and not pi/4.
Fra88
Posts: 17
Joined: Fri Mar 09, 2018 8:27 pm

### Re: Wrong sheet metal unfold dimensions?

Yes you are right!!!
Sorry for my big mistake  chrisb
Posts: 25145
Joined: Tue Mar 17, 2015 9:14 am

### Re: [SOLVED] Wrong sheet metal unfold dimensions?

There is another error in your formula. According to my book the formula is for an angle of 90° (or less):

L1+L2+(Ri+Kf*T/2)*pi/2=98+98+(1+0.5*1/2)*math.pi/2 = 197.963

which is exactly what SheetMetal WB delivers. Besides that, according to my book th K factor should be 0.6 for a ratio radius/thickness of 1
Fra88
Posts: 17
Joined: Fri Mar 09, 2018 8:27 pm

### Re: [SOLVED] Wrong sheet metal unfold dimensions?

I think that dipend on the definition of Kf. In "my" formula Is defined as the ratio between neutral axes position taken from internal bend (t) and tickness: Kf=t/T.
I have found this definition in the file attached (i'm sorry It is in italian language). In this file neutral factor Is indicated with "e".
Attachments
2009-10-28-CALCOLO_SVILUPPO_LAMIERA.pdf
Fra88
Posts: 17
Joined: Fri Mar 09, 2018 8:27 pm

### Re: [SOLVED] Wrong sheet metal unfold dimensions?

Look at Page 7, picture 8.
chrisb
Posts: 25145
Joined: Tue Mar 17, 2015 9:14 am

### Re: [SOLVED] Wrong sheet metal unfold dimensions?

I'm afraid that with that formula you cannot use the same K factor as used in SheetMetal (or in my formula).