Wednesday, December 21, 2011

Making a model of negative space in ProE/Creo

Need a model of the negative space inside an assembly model that you're developing? Here's a way. Note that only parts in contact with the inner surface are included in the negative; detached parts will not show up in the negative space. Also on occasion you will need to click the green check mark to finish out a command.

- Make a new part model, and make an associative shrink wrap in it: Click Insert > Shared Data > Shrinkwrap and then select or open model from which geometry will be copied. Define placement and then select Auto collect all solid surfaces in list next to Subset. Click the Options panel and check "solidify geometry". Options I did not use: Click Subset to select contributing geometry and click OK. Click the Options panel to fill contours.

- Make a new, stand-alone assembly. This one will only be used for creating the negative space. Insert the shrinkwrap model with "default" placement. Create and insert a new part model, I will call it "negative", with "default" placement.
- From inside the new assembly, right-click and "activate" the "negative" model.
- Now to select the internal surfaces with a little secret ProE magic:

  • Click the shrinkwrap model once, then hover over it again. You will now be in "surface select" mode.
  • Reject (right-click) the surface until an internal surface is highlighted, then click it. 
  • Hold down shift, and select another internal surface, then let go of the shift key. Now all of the internal surfaces should be highlighted.

- Copy (ctrl-c) and paste (ctrl-v). This should paste the surfaces into the "negative" model, since it was active.
- Hide the shrinkwrap model (click it, hold down right-mouse, and select "hide")
- Inspect the "negative" model for missing surfaces. I found that one surface was left out. If so, remember which one is missing, unhide the shrinkwrap, then select, copy, and paste the missing surface.
- Now open the "negative" model, select the surface objects, and in the top menu, click Edit>Merge.
- Select the "merge" object, and click Edit>Solidify.

And there you have it, a negative space model. If you modify the original assembly that it is created from, you will need to open the shrinkwrap model, select and right-click the shrinkwrap object, and select "update shrinkwrap". Next time the "negative" model regenerates, the mods should appear in it.

Now you can insert the "negative" model into your original model with default placement if you like, but word of caution: suppress the "negative" part before updating the shrinkwrap. If you do not, the "negative" will fail, because it is caught in an impossible self-referential loop of doom.

Enjoy!

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