For the first time in more than 20 years, U.
S. automakers are questioning a pillar of manufacturing: The practice of bringing parts to assembly lines right before they're used.
So called just-in-time deliveries have helped automakers save billions and run their factories more efficiently. But the approach also relies on an almost perfect supply chain. And twice in the last year, the system's weak links have been exposed.
An earthquake last March knocked out many Japanese parts makers, resulting in factory shutdowns and model shortages around the world. And last month, an explosion at a German chemical plant cut off supplies of a resin essential in car fuel lines. Without those parts, assembly lines could slow or grind to a halt within weeks, causing shortages of cars on dealer lots later this year.