Typically, sand cast molds are created from a "male" pattern of the final part, slightly oversized to allow for shrinkage of the material. That pattern is split and half put on each side of a flat plate. The "mold" is created from 2 metal frames, called a cope and a drag, forming a perimeter that constrains the sand. One of those parts is placed over the pattern, filled with sand that is compressed to hold it in position (a binder is used to make the sand stick together) and vents and sprues cut for filling the motion metal. The pattern is flipped and the process repeated for the opposite side. The pattern is then removed and the cope and drag are assembled (the assembly now called a flask if my memory hasn't failed). Then the casting occurs, after which the flask is separated and sand removed from the final part, with sprues, runners and vents cut off.
Now-what you said makes sense and fits with what I think has been written about the process, using 3d printing to form the sand-cast molds, eliminating the need for the pattern. Such a process would allow for much more complex parts, since draft and a straight direction of pull to remove the pattern aren't needed. Not to mention eliminating the entire pattern making process. What exactly that 3d printing process would look like IDK. Some form of selective laser sintering perhaps, melting a binder in the sand? Still need to be able to remove the excess material from the mold cavity. Perhaps a form of FDM....but I would think a high percentage of sand would be very abrasive of the tooling.
And now that I wrote this I realize it belongs in engineering discussions. Sry.
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