Hello, I used Surface Fill to fill a hole of a solid body. Then, used Thicken to turn that filled surface into another solid body. When I 3D printed it, it showed a boundary mark of the filled surface both in the slicer and in the actual printed part. How to hide such boundary without pro-processing of the printed part?  

I went back to SolidWorks and tried to use Combine-Add. However, SolidWorks gave me a "Rebuild Errors. Unable to create single body that is the sum of the input bodies.".