How to create separate mid-surfaces from a assembly

Hi to All,

I have an assembly and, for each part, I want to create its own mid surface. The goal is to affect shell thickness properties for each mid surface (which is subdivided).

When I create mid surface for each component, all created mid surfaces are grouped on a same entity named 'Middle Surface'. This is not what I want, since it is difficult to correctly affect properties on a subdivided mid surface. I rather want for each part, each own mid surfaced labelled 'Middle Surface 1',  'Middle Surface 2',...

Could anyone help me for this problem?

Thank you.

Nice day.