While creating implementation layer, you might have got the screen to import the cases. If you made cases after creating all the framework app and impl app, then you could also import the case from the impl layer case design. When you right click on case type in designer studio you will get that option.
Even if there, it is not showing, then you could open your impl application design (application dropdown (impl application) -> definition. Navigate to case and data tab and add the framework case type.
Thanks much for your response.I don't see any option to import the casetypes from framework to implementation when i'm creating my implementation.I'm using 7.2.2, since we can't create FW,Impl at one go in this version first i created FW then extended implementations on top of that.The other option adding under cases and data tab of our implementation also didn't inherit the case types :( .