stl file can't be mesh in Netgen

I create a .stl file include two solid parts. I use the same nodes of interface between two solids. But Netgen can’t mesh the solid. It always shows inconsistent triangles. But if I seperately mesh the two parts, it works.

So how netgen mesh the composite solid? Or what’s the format of .stl file?
I can’t use .geo file because I think it can’t create a complex geometry which defined by an equation.
I put my .stl file in attached.
Thank you!

Attachment: PartialSphereWhole_2019-09-05.stl

sorry the stl mesher is only able to mesh single solids. You could use the step or igs format and our opencascade interface.

Thank you. But when I use FreeCAD to transfer .stl file to STEP or IGS format, Netgen only draw the surface mesh not volume. I don’t know why.

I put one of my STEP file in attached file.