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There may be a few secrets in this factory or that factory but the bottom line is it's plastic injection molding. Lots of examples on YouTube.
Somewhere on the web there's the Ripley's segment which shows some molding within the Discraft plant. Ed's ashes were added to the mix and molded...wacky enough to get on TV. I think there's a youtube posting of this piece, perhaps its elsewhere. As others have pointed out, its just injection molding. I know the production folks are sensitive to the fancier stamping/printing technology. No secret on that, either. Its all on the web if you google the right terms.