"We made it share-alike as any of our project because we believe in the Open-Hardware comunity "
No you don't. You pay lip service to the idea of open source; but that is about all. Effectively this extruder is a dead end. There is no point for anyone else to pick it up and extend it any further.
"If you are planning to manufacture our extruder and sell it as if it was your work we're not as happy because we spent many days designing it. "
and how many thousands of person years worth of effort went into the open source tools you are using? Would you even be able to do all that you can do if others had of encumbered their work the way you are encumbering yours?
Open Source culture is not about control. It's about being grateful for what we have received and when given the opportunity, giving back.