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13-Aquamarine

## Help writing a relation for a bend

I cant' figure out the correct equation to drive the wing outside diameter and wing inside diameter for this part.
(I will attach the part file)

Image 1 - This is the part bent. The part wings should be fitting into the vertical surface walls.

Image 2 - Just for a visual reference.

Image 3 - View showing that the bent wing is falling outside of the inside and outside radius. (It should be inside of them)

Image 4 - View showing the sketch and relations driving the part.

I'm open to other methods as long as I can flatten it and that the flat pattern drawing will let me place dimensions on the arcs.

Thank you for your help

5 REPLIES 5
18-Opal
(To:SYNDAKIT)

Here is a model that has the wings constrained as specified. In order to get this the bend lines need to be normal to the radial surface of both surfaces making the ID and OD. This was built with no relations, it was all done with geometry constraints. This is a quick hack to get the geometry to regenerate for reference.

13-Aquamarine
(To:tbraxton)

Thank you Tbraxtn.

That is a really clever method.

That model get's me really close to what I'm trying to achieve. There is one other hurdle I need to get over though, and that's the dimensioning part. When I go to dimension the flat pattern,  I would like to be able to pull a radial dimension for the wings; although because of the geometry this may not be possible.

And that brings me back to the relations. I thought that if I started with a sketch that uses radius dimensions for the wings and was controlled by relations, that then when I did the flat pattern I would be able to pull radius dimensions again.

If I'm unable to figure out a way to get the relations to work, I might just have to fake the radius dimension by creating a sketch that's constrained to the spline of the flat pattern at three points; the two ends and a mid point:

What are your thoughts?

Thank you for helping me out.

18-Opal
(To:SYNDAKIT)

The wing curved edges are not constant radius so there is no single radius dimension for these curves. If you observe the equation (or shape) of the curve created by the intersection of a plane and a cylinder which is in the context of your design then you will see the nature of the curve. It is an ellipse so you can define it in the flat pattern with the major and minor axis along with the conic parameter.

Consider the intersection of a plane at angle of 45 degrees relative to the base of a right cylinder (the wings) and you will see that it is an ellipse that is the result of the intersection. You can derive the parametric equation of the ellipse analytically and use that in relations to define the flat pattern if desired. In the interest of expediency I would sketch the ellipse on the plane of unbending such that you have access to the dimensions of the ellipse for the drawing. Make sure to use the conic parameter for an ellipse when sketching in Creo.

13-Aquamarine
(To:tbraxton)

Tbraxton,

Thank you for the quick reply.

I'm following what you're saying but I'm not sure how to derive the equation from the ellipse.

I think this may be a bit past my current understanding.

Here is what I found on conic parameters.

Would you be able to help me out with this?

18-Opal
(To:SYNDAKIT)

The method I am suggesting does not involve a conic surface. I am proposing to use a sketched ellipse. Refer to geometry resources on the web or a text book for the parametric equations of conics in a plane.

Creo has an ellipse predefined in the sketcher pallet that you can use. If memory serves me, this library ellipse uses a rho value equal to the sqrt(2)-1.  This should work for the purpose of resolving your specific case. If you do not want to derive the equations then you can work this out graphically in the creo sketcher with proper constraints placed on the ellipse sketch relative to your wing geometry.

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