Normally you leave fillets to the very end of a model, but in this case we need to add some fillets now or the next step will not work out for us. This is also a good time to take a look at FilletXpert. When you select the fillet option on your feature tab you will have the option to create Manual fillets or use FilletXpert. One of the great benefits of filletXpert is that it allows you to select one edge, and then you are given options for other edges like it. So in this case we need to fillet 8 vertical edges inside the fan body. When you select one edge a pop up next to the cursor will give you the available options which will highlight on the model. You can see them in pink. While 8 edges doesnt seem like a lot, this can be extremely helpful in many different ways. Add a 10mm fillet to the 8 vertical edges.
Now start a new sketch on the Top Plane. This time draw a circle at the origin with diameter 72mm. This circle will represent the inside of the fan.
Exit the sketch and go to the Surfaces tab and select Extruded Surface. We want this to be 10mm tall and use the Mid Plane direction option.
We are going to make a combination of surfaces and knit them together to form a solid for this piece. Before we make any more parts find the Offset Surface button and create an offset surface with distance 0 of the inner faces of the fan body.
After this surface is created, expand the Surface Bodies folder in your Feature Tree and Hide it. The reason we hide it is because for these next surfaces we want to make sure we select the edge of the solid body. In this specific case it wouldnt make a difference but there are times when the offset surface may not exactly match and could potentially cause issues. When possible use original geometry and not a copy for things like this.
Now we want to do a Lofted Surface. Your first profile is the upper edge of the extrude surface we created.
Next you will need to Right click and use the Selection Manager. In the selection manager pop up box you need to make sure "select group" is active. This is the icon with 3 cursors. Then proceed to select the top edge as shown.
Once you have select the entire edge OK the dialog box and you should see a preview. An important note here is the location of the Green endpoints on the profile. These are free to be drug around the model. You want to be sure they line up or the loft produced will be twisted.
After you OK the loft you should see a nice surface blending from our solid body down to the extruded surface.