Back in the mid 1970s I had a friend that worked at Kodak on the molds for Instamatic cameras. His job was to build up the wear areas in the molds so that they

Back in the mid 1970s I had a friend that worked at Kodak on the molds for Instamatic cameras. His job was to build up the wear areas in the molds so that they could be re-machined. I cannot recall the exact process, but it was some form of plasma spray welding. Only fractions of a mm, so that the process of re-machining was easy. The plastic they used was abrasive to the molds, and the bodies had to be quite precise to generate acceptable image quality. I forget how many cycles the molds could run before being swapped out, but it was only days, not weeks.