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Pentamet
Posts: 9
Registered: ‎02-02-2013
Message 1 of 15 (416 Views)
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Unfolding question

416 Views, 14 Replies
02-12-2013 04:23 AM

Hello,

 

I have drawn a cylinder, with inside diameter 1028mm, wall thickness 5mm. We usually have calculated unfolded part length like this: outside dim. 1038mm - 5mm (wall thickness) = 1032 x 3,14 = 3240mm. Now when i unfold in inventor I get for the length 3215,35mm. It is quite far from the result we usually would have received.

 

Unfolded part will be rolled to cylinder. What parameters should be overlooked when making unfolded parts for plate rolling?

 

BR,

Marko

Valued Mentor
mpatchus
Posts: 451
Registered: ‎10-22-2008
Message 2 of 15 (395 Views)

Re: Unfolding question

02-12-2013 06:08 AM in reply to: Pentamet

Check your sheet metal setting.  I get 3243.380 mm unrolled.

unfold.JPG

Mike Patchus

Inventor 2012 SP3 ~ Vault Pro 2013
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*Expert Elite*
Curtis_Waguespack
Posts: 2,802
Registered: ‎03-08-2006
Message 3 of 15 (369 Views)

Re: Unfolding question

02-12-2013 06:43 AM in reply to: Pentamet

Hi Pentamet,

You can use a bit of a trick to set up the Contour Roll tool to allow you to specify the Developed Length for rolled cylinders. In order to specify the developed length you need to have a small flange, otherwise you will not get the Unroll Method options.

 

First set up your sketch with an extra little flange:

 

Autodesk Inventor Developed Length Trick1.png

Then you can set the Unroll Method to Developed Length:

Autodesk Inventor Developed Length Trick1.png

 

 

 

Then create a work plane to define the actual height of the cylinder and use the Split tool to cut the extra flange off.

 

Autodesk Inventor Developed Length Trick3.png

 

 Attached is a sample file that you can look at as well.

 

I hope this helps.
Best of luck to you in all of your Inventor pursuits,
Curtis
http://inventortrenches.blogspot.com

 

 



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Distinguished Contributor
ljandueza
Posts: 106
Registered: ‎11-03-2005
Message 4 of 15 (363 Views)

Re: Unfolding question

02-12-2013 06:49 AM in reply to: Pentamet

Hi Marko,

 

You should pay attention to the unfold method you are using on your design.

You have basically three methods: Kfactor, Bend Table, and Unfold Equation.

 

At first try to adjust the Kfactor, until you get the desire value (that I assume is the one you get in real fabrication) and then create a template.

 

You should be very carefull because when you are bending and folding sheet metal you have some factors involved like the thickness, material and the bending machine.

 

 

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@ljandueza
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Mark.Downes
Posts: 109
Registered: ‎11-18-2010
Message 5 of 15 (353 Views)

Re: Unfolding question

02-12-2013 06:56 AM in reply to: Pentamet

Hi,

 

As the sheet development is not "rectangular" the flat pattern will be different to a stock calculation for development.

(150mm off-set centers)

 

A stock rolled development would be (as previously mentioned) 3243.4mm

or 4 x 810.845 = 3243.38mm (excel spread sheet - see captures)

 

Using inventors k factor of 0.44 you would expect a development length of 3216.9mm

 

hope this helps

Cheers

 

Mark

Inventor 2013

 

Capture2.JPG

Capture1.JPG

*Expert Elite*
JDMather
Posts: 26,256
Registered: ‎04-20-2006
Message 6 of 15 (336 Views)

Re: Unfolding question

02-12-2013 07:27 AM in reply to: Pentamet

Pentamet wrote:

 1038mm - 5mm (wall thickness) = 1032 x 3,14 = 3240mm.


 

bend calc.png

You are calculating the neutral circle in the bent part without allowance for bend stretching in the flat.

As shown in the formula posted by Mark
When you bend material it stretches on the outside of the bend and compresses on the inside of the bend.
The neutral plane (no stretching, no bending) is often (usually? allways?) not in the center of the material thickness.
The Bend Allowance is a function of the Material, Thickness, Bend Radius and the Bend Angle (and perhaps direction of grain in the material).
You have about 70 bends (I lost count) that are stretching the material.
Oops, I didn't need to count - Inventor Bent Table tells me 72 bends. That is a lot of bends to allow for stretching.
You need to find an appropriate technique for calculating this stretching (k-factor, bend allowance table...).
See your Machinery's Handbook section on Bend Allowance.
Please mark this response as "Accept as Solution" if it answers your question.
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Active Member
Pentamet
Posts: 9
Registered: ‎02-02-2013
Message 7 of 15 (325 Views)

Re: Unfolding question

02-12-2013 07:36 AM in reply to: Pentamet

Unfortunately machine is ancient and documentation is not available anymore. We have successfully managed to use so far formula: outside diameter - thickness of the material x 3,14, for the materials we most commonly use. I will test other options.

Active Member
Pentamet
Posts: 9
Registered: ‎02-02-2013
Message 8 of 15 (323 Views)

Re: Unfolding question

02-12-2013 07:38 AM in reply to: JDMather

Additionally this will not be done with press brake, it will be rolled, so not 70 or more bends in part! Even if I put kfactor to 1, it gives me ca. 3230mm

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mrattray
Posts: 2,470
Registered: ‎09-13-2011
Message 9 of 15 (305 Views)

Re: Unfolding question

02-12-2013 07:56 AM in reply to: Pentamet

Well there's your poblem. You modeled this part as a press brake part, not a roll formed part.

 

Capture.JPG

Mike (not Matt) Rattray

Active Member
Pentamet
Posts: 9
Registered: ‎02-02-2013
Message 10 of 15 (263 Views)

Re: Unfolding question

02-13-2013 03:22 AM in reply to: mrattray

Should I use then loft contour?

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