simulation model not recognized

Hey there,

I met a problem in my extruder simulation. I designed the components in AutoCAD Inventor and imported them as “.obj” or “.stl” files in blender 2.78c, but the screw in the first picture is not recognized during the simulation process. The rigid body particles fall through the blade of the screw, but not through the other components (the configurations are the same). Does anyone know where the problem is and how to solve it?

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