[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?

Postby Fra88 » Thu Oct 17, 2019 4:41 pm

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

- sheet metal thickness= 1mm
- internal bend radius= 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
(15.74 KiB) Downloaded 15 times
bend dimensions.png
bend dimensions.png (5.89 KiB) Viewed 515 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?

Postby Fra88 » Thu Oct 17, 2019 6:23 pm

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: 25890
Joined: Tue Mar 17, 2015 9:14 am

Re: Wrong sheet metal unfold dimensions?

Postby chrisb » Thu Oct 17, 2019 7:24 pm

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?

Postby Fra88 » Thu Oct 17, 2019 7:37 pm

Dear chrisb, thank you for your reply.
Yes you are right!!!
Sorry for my big mistake :oops: :oops:
chrisb
Posts: 25890
Joined: Tue Mar 17, 2015 9:14 am

Re: [SOLVED] Wrong sheet metal unfold dimensions?

Postby chrisb » Thu Oct 17, 2019 7:44 pm

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?

Postby Fra88 » Thu Oct 17, 2019 8:08 pm

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
(631.55 KiB) Downloaded 18 times
Fra88
Posts: 17
Joined: Fri Mar 09, 2018 8:27 pm

Re: [SOLVED] Wrong sheet metal unfold dimensions?

Postby Fra88 » Thu Oct 17, 2019 8:16 pm

Look at Page 7, picture 8.
chrisb
Posts: 25890
Joined: Tue Mar 17, 2015 9:14 am

Re: [SOLVED] Wrong sheet metal unfold dimensions?

Postby chrisb » Thu Oct 17, 2019 10:47 pm

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