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Unfolding question

14 REPLIES 14
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Message 1 of 15
Pentamet
3504 Views, 14 Replies

Unfolding question

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

14 REPLIES 14
Message 2 of 15
mpatchus
in reply to: Pentamet

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

unfold.JPG

Mike Patchus - Lancaster SC

Inventor 2025 Beta


Alienware m17, Intel(R) Core(TM) i9-10980HK CPU @ 2.40GHz 3.10 GHz, Win 11, 64gb RAM, NVIDIA GeForce RTX 2080 Super

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Message 3 of 15

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

 

 

Message 4 of 15
luis_andueza
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.

 

 

Luis José Andueza Castro
Ing. Mecánico - Consultor CAD/CAM/CAE/Data Management
www.dimcad3d.com | LinkedIn |

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Message 5 of 15
Mark.Downes
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

Cheers
Mark
Inventor 2018, 3DS Max 2018, Vault 2018
Message 6 of 15
JDMather
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.

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Autodesk AutoCAD 2013 Certified Professional
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Message 7 of 15
Pentamet
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.

Message 8 of 15
Pentamet
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

Message 9 of 15
mrattray
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

Message 10 of 15
Pentamet
in reply to: mrattray

Should I use then loft contour?

Message 11 of 15
Mark.Downes
in reply to: Pentamet

Hi,

 

If you loft the sections as a rolled part (as mattray shows) you should get your flat pattern development you need. I think your way of calculating the basic size got a bit lost in translation as your developing an ellipse not a circle.

 

Lay 2 of the same parts in an assembly align the axis and push the parts around each other, you will see a slight overlap as the ellipse cross at 90 degrees.

 

Hope this helps

 

Cheers

Mark

Inventor 2013

 

Capture.JPG

Cheers
Mark
Inventor 2018, 3DS Max 2018, Vault 2018
Message 12 of 15
Pentamet
in reply to: Mark.Downes

Hi Mark,

 

This is exactly what I want. But I cannot loftcountour to this shape. It just give me cylinder under angle, what should I do.

 

BR,

Marko

Message 13 of 15
Pentamet
in reply to: Mark.Downes

Attached current result!

Message 14 of 15
Mark.Downes
in reply to: Pentamet

Hi,

 

If you want to loft as per your first model.

Draw a center point arc instead of a circle. Loft as before, select “die-formed” button on the output selection menu.

 

I have a 10 degree gap in the center point arc. This is only for clarity, change this to a gap more suitable to what you need (ie 1, or 0.1 or 0.01 etc…)

 

Hope this helps

Cheers

Mark

Inventor 2013

 

Capture.JPG

Cheers
Mark
Inventor 2018, 3DS Max 2018, Vault 2018
Message 15 of 15
JDMather
in reply to: Pentamet

Check this example.

 


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Autodesk AutoCAD 2013 Certified Professional
Certified SolidWorks Professional


The CADWhisperer YouTube Channel


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