What is the current volume break point on protoype vs. real parts?
Hopefully it is much higher than when I retired >10 yr ago.
It greatly depends on a number of factors - material, required production rate, what exact CNC/3D printer/other rapid prototyping gear you have, and the design of the product.
There are current mainstream production cars (not exotics, one offs, limited production or prototype cars) today that use parts made by various forms of 3D printing, so in some cases, prototyping *is* production, in the hundreds of thousands of units per year range. It’s still far cheaper to make simple shapes like a plastic promotional keyfob or a slab panel of plastic through injection molding and such, but for complex multipart shapes, it is slowly becoming cheaper to just make one big 3D printed part. Metal parts are lagging a bit in additive manufacture because the 3D printing of metal is still a relatively expensive process and often requires significant hand finishing - but CNC machining from billet has gotten far cheaper over time and has led to cheaper die and mold costs as well as cheaper metal parts.