Inventor 2018 Sheet Metal Plate Cylinder Unfold Flat Pattern Gap - K-Factor

[Anonymous]

Hello,

I am sort of new to Inventor, my question pertains to the fold and unfold plate function. I have a very simple cylinder 30" outside diameter 3/4" thick cylinder that I have modeled and I have ripped it with a 1/16" gap. When I unfold this plate, the length of plate that I am getting is 91.54". Now I know that if I go to the middle center line of that plate while it is rolled it gives me 29.25" diameter, when you multiply this by PI that gives you 91.89159" of circumference. I know you rip it a .0625" gap it will take some length off the circumference but 91.89159-91.54=.351585! That is almost a 3/8" gap. Can someone explain this to me? Again, sorry in advanced if this seems like a newbie question!

kelly.young has edited your subject line for clarity: Plate fold and unfold question

[JDMather]

Bend Allowance

When you bend metal plate it stretches on outside of bend radius and compresses on inside.

The neutral plane  -  no stretching or compression is not in the middle of the plate thickness. 

[swalton · Accepted solution]

I think the issue is the stretching of the metal as it is formed from flat to round.  Your model is setup to use a K-factor to define the stretch.  There is a good discussion here: http://sheetmetal.me/formulas-and-functions/k-factor/  

If you modify the k-factor to .5, your flat pattern comes out at 91.827".  Add 0.062 for the rip gap, and I get 91.889.  That is within .003 in from your hand calc.  I suspect the difference is that I did not stretch the gap dimension by the k-factor. 

The workflow is to model the part at the finished size and shape.  Inventor will use the K-factor setting to calculate the size of the flat pattern that will produce the finished size and shape.  Do you have some existing designs that you produce?  If so, model one up and adjust the k-factor until Inventor's flat pattern matches the known-good design.

If not, you will need to run some sample pieces to verify that the flat pattern is being calculated correctly.  Make sure that your test pieces are run on the production tooling on the final material.  Minor changes in tooling radius, die width, grain direction, thickness, etc can affect the results.

Take a look at http://help.autodesk.com/view/INVNTOR/2018/ENU/?guid=GUID-D1EBE010-86D3-49CC-88B3-522F9A0CCA3B

[johnsonshiue · Accepted solution]

Hi! This has something to do with the K-factor. The default K-factor is 0.44, which means that the neutral cylinder is 44% thickness from the inner face. The neutral cylinder is where the unfolded/unrolled length equals to folded/rolled length.

For your case, you want to change K-factor = 1. Go to Manage -> Styles Editor -> Sheet Metal Unfold -> Default_KFactor and change the K-factor value to 1. By doing so, you are making the outer cylindrical face as the neutral cylinder. If you want the inner face to become neutral, you can change the K-factor to 0.

If the part was created by Contour Roll, there should be a way to assign Unroll method in Contour Roll dialog. That workflow seems to be broken. I need to follow up with the project team to find out how we can fix it.

Many thanks!

[kelly.young · Accepted solution]

Hello @Anonymous it sounds like they gave you quite a bit of info regarding the K-factor.

For the initial question, I would look at drawing this differently:

• Sketch your Diameter circle.
• Extrude as a Surface for Height.
• Create a Sketch on the vertical origin plane defining the radius of your sphere.
• Extrude the arc line as Surface at Diameter distance both ways. 
• 3d Model > Surface > Trim Surface.
• Thicken to generate the sheet metal Thickness.

This will give you much better control for the Flat Pattern. 

See attached part. 

Hope that helps!

Please select the Accept as Solution button if a post solves your issue or answers your question.

[Anonymous]

Thanks for the help guys! Lot of great information.