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Shrink Fit / Pull Force

Question asked by Tyler King on Mar 25, 2009
Latest reply on Apr 8, 2009 by Richard Obrien
I am really new at the COSMOSWorks thing and have never had formal training. Regardless, I am trying desperately to use COSMOSWorks to validate the design of a plastic knob insert. I am running SW SP05. The 2 key things I am trying to accomplish are:

1. Verify that the forces from the crush ribs and flaps in the X and Y direction=0. This is critical for the knob to remain concentric to the potentiometer shaft.
-I have tried to fix the outside of the knob and the flat surface of the pot shaft and add shrink fit contact sets. I then ran the analysis and tried to see if the stress on the shaft was equal, which would indicate equal forces form the ribs/flaps. This almost seemed to work, but the stresses on the flat side of the shaft never seemed right. And I'm not sure this is the best way to accomplish this. Is there another way to do this? Perhaps withe the correct restraints I could find the displacement and measure the distance from the axis or the knob insert and pot shaft.

2. Determine the proper interference to acheive a pull force of ~5 kg
-I likewise am using the shrink fit contact sets and have tried adding a force to the bottom of the knob. Although this doesn't tell me anything but that the knob does in fact slide off! I have tried listing the result force>contact/friction force and selecting the faces that I used in the shrink fit contact set, but the value for the friction force is extreemly high. Not to mention it is really annoying to use this tool because it is not a standard result that is saved, maybe I'm using it wrong.

I am also aware that ABS may not fall under the criteria of a linear elastic material, but I also cannot find how to run a non-linear study as shown in the help file. Is it part of COSMOSWorks or another tool? For what I'm doing this may be an acceptable assumption..? As of now, no one here has gone through this trouble and the knobs end up needing to be tweaked to get the concentricity and pull force correct, often with a compromise. I hope to get this working, my paper calculations have a lot of assumptions and only get me so close. Any help would be greatly appreciated!

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