I'm not sure where to ask about this...
I don't like the idea that an expensive die (dye?) can only make one shape for injection molding...
So, here's an idea...
Imagine an air hockey table, with the small holes on the surface of the table where the air goes through, instead of air, it is the melted foam filling the bay or general shape... more than likely a rectangle or square.
Above this table is an ultrasound-phased-array-gird (possibly not even phased) and this can create 3D shapes that the foam will run into, I am referring to a technology called "tactic or tactyle feedback" where a person can interact with a button hands-free via ultrasound and imaging. The ultrasound creates a pressure difference where a person feels that they are holding onto something solid.
Taking that idea, I believe you could 3D print injection-foam molded parts layer by layer and any shape using the variable ultrasound technology.
Thoughts?
I don't know how long it takes for the foam to get hard... and I think immediately this idea is flawed, especially the part about being "layered"