Plastics, rubber, and metal components are almost always produced by a forming process — injection molding, compression molding, die casting, or stamping — and each of those processes fails in recognizable, repeatable ways. A flash line on a molded part, a burr on a stamped edge, or a crack in a casting shows up in roughly the same place, on roughly the same part, every time it happens.
That repeatability is exactly what makes these components well suited to automated inspection — once a system is tuned to a defect signature, it stays consistent across every part on the line, unlike a human inspector’s attention over an 8-hour shift.