Making o-rings flexible in assemblies

[TomD.inPDX]

A quick flexibility and family table application for an o-ring.

Certainly not exceptionally comprehensive but easy to use if you must show multiple states of an o-ring on a drawing.

The challenge here was to make a rectangular shape round with flexible components.  A revolve section sketch will not allow lines to go to zero length like some features allow.  The second best choice was to add a round to a rectangular profile.

For this instance is an o-ring that has a defined groove of .125 x .093.  The o-ring's free state sectional diameter is .125.

A perimeter value in a sketch is used to confirm, but not utilize the value of the resulting radii when the o-ring is squished.  The required level of accuracy here is purely up to the user.  In this case, I chose that the perimeter remains constant.

note: relations cannot be used with dimensions applied to flexible component tables.

The o-ring model was created in the squished state.  This is purely a matter of choice as both affected dimensions are overwritten at the assembly level with family tables.

What makes this work is the ability to make a square profile fully round with the round feature.

Let me know if you have any questions.

Enjoy.

Video Link : 4185

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[BrentDrysdale]

Hi Tom,

Love that you share what you learn/know with our community.

I have dealt with this before but in a different way.  Not at my Creo computer right now and not even sure I could find it but in case it is of use it went like this:

• Make a sketch of your O-Ring cross-section using four conics.  I used plenty of construction lines in the sketch to "box" the O-Ring shape and constraints etc.  I use a RHO value of 0.414 as an approximation of a radius and the "box" dimensions plus other RHO values to make sharper or flatter curves for the shape you want to distort to.
• Make a Fill using this sketch and you will be able to get the area of this surface.  Lets you distort the O-Ring and check that the area is the same as the uncompressed version.  Never got to making an analysis feature for this nor did I look at using BMX to optimise but I think that more work could be done in this area.
• Now make a revolved feature as you show.

This overcomes the problem having a zero length segment while still giving a high level of control.  You can do a simple compression such as clamping and you can simulate pressure distortion but only to the point of squaring a corner and not extruding a corner out into a gap as can happen.

Hope this helps.

Regards, Brent

[TomD.inPDX]

Thanks Brent.  I do this so I can find these tips later for myself Its a gray matter thing...

Good tip on using the conics.  I have had to calculate deformation in relation to area rather than perimeter.  I couldn't find a clean way to manage this either.  A graph function (evalgraph) in the sketch relations comes to mind.  That would reduce the 2 dimensions to 1 in the family table.  Or better, use distance between the two surfaces.  For applications more critical, it would be worth the extra effort to map a few points for a graph feature.

Now where did I put that document regarding evalgraph....