The only concrete experience I have was testing out a mold at our local hackerspace. It was supposed to be an exercise for myself on surface modeling by creating a simplified puffin bird totem. But since there was a concrete workshop happening during that time I decided to 3d print a small mold and test casting it. Which turned out better then I expected hence the fdm printer.
This is by the way the result of this topic Smooth transition of surface problem - #18 by 2DCube