In the late 1980's I worked for an enginering and machine tool company. One project was to build a continuous motion assembly machine to assemble somewhere around 180 spark plugs per minute for AC-Delco. The AC plant was somewhere near Dayton, Ohio.
The machine automatically assembled the plug, cut welded and bent the ground strap, set the gap, tested the product and seperated any rejects. One operator ran the machine and several people delivered parts to it. The machine had a PLC computer controler. Production and inspection data was displayed in real time, automatically collected and available as a print out. Quality and consistency were the emphasized. The machine had to meet specific Cpk capabilities before it could be accepted. This was all proven technology in the 1980's. The machine met its production and quality requirements by a good margine.
As US production moved overseas the machine tool company I used to work for was sold to a foreign company and US branch was eventually "disposed of" and closed due to a lack of work in the US. I have to wonder how the AC-Delco spark plug plant has faired.
I also have to wonder how the quality of the Chinese production compares to the US quality.