grille pattern with round enclosure

Hello,

I'm trying to model a grille as shown on the left side of the added picture, but Creo 2.0 gives me the one on the right side.

Any ideas on how to make this happen?

This is a sheet metal part, because the plate is curved. If it were just a solid a would add an extra extrude to fill the excess, but that doesn't work in sheet metal.

Thanks,

Robbie.