10.12  From prototype to production

Two cases where the printed part is not the whole story. In the first, printing is only the prototype: the part will be injection moulded, and some of our courses design it for the mould from the start and then adapt the same design for the printer. Draft angles, uniform wall thickness, ribs, bosses and snap fits are moulding rules; orientation, overhangs and layer direction are printing rules; some of them agree (uniform walls, crush ribs, which printing borrowed from moulding) and some conflict (draft, thin ribs, a part that must be split to print). We show how to design a part that is right for the mould and still printable, and what a printed prototype can tell us about the moulded part: its fit and its function, but not its strength, which differs in magnitude and in direction. In the second case printing is the production process, as in a print farm. Then the rules shift to throughput and yield: a small bed contact and mouse ears for easy removal, orientation for the plate, functional integration against the cost of reprinting a large part to repair a small feature, and shadow lines that hide the seams between parts.