...how about the issue of the robots having a known decrease in final product? I guess the theory is they can put the bolt in precisely the right spot, but if this panel is juuuuust a hair off then a human eye can make a little tweak here or there and present a better end product. I have zero manufacturing experience though but I could see that being the case.
Having worked in a machine shop, I can tell you that the human eye is often an inadequate measuring instrument. That's why we have measuring devices such as micrometers. If the tolerance is that important, then the automated line should use a laser scanner to ensure a hair-fine positioning.
The real limit to automation on auto assembly lines back in the 1980s*, for example GM's failed Saturn line, was that the "robots" back then were not flexible enough. They were too limited and could not easily be repositioned, repurposed, or reprogrammed to perform a different task. The Saturn manufacturing lines were ultimately abandoned because they could not be used for anything other than building the one exact model year of the car model they were set up to build. Contrariwise, many or most auto assembly lines can make more than one model, and many variants on those models. In a documentary examining the failure of Saturn, it was pointed out that in Japan, machines and automation were (at that time) being used more to assist humans on auto assembly lines, rather than vice versa. Humans are much more flexible, and can usually be "reprogrammed" with just a few hours of training for another job on the line.
*You were talking about automation in the 1990s, but I'm going to talk about what I know at least a bit about rather than what I know almost nothing about.
As Domenick says, things are different today. Robotic arms are much more flexible, much more versatile, and much more easily repurposed and/or reprogrammed, than they were just a few decades ago. Of course humans are still much more flexible and versatile than robots for nearly all tasks, but the cost of human labor generally keeps increasing, while the cost of robotic "labor" keeps going down.
Furthermore, Elon Musk is right about the speed of assembly line work. The eye-blurring speed at which many assembly line machines move on the "How It's Made" series is often amazing. There's simply no way that human workers could ever match that speed. So, the
potential for much greater throughput is there, if human workers are removed from the assembly line and all replaced by robots. Musk is certainly right about that. But very clearly, putting that theory into practice is proving to be much more difficult than he anticipated. That doesn't surprise me at all. If substantially increasing throughput by using near-100% automation on an auto assembly line was that easy, then it would already be a widespread practice.
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