Saturn Uses New Assembly Process
Plant tries foam casting, flexible production
SPRING HILL, TENN. — AFTER an eight-year wait, American motorists are finally going to get a good look at the car General Motors Corporation has promised will revolutionize the auto industry. Saturn, GM's first new passenger car division in half a century, was designed to develop a line of subcompacts rivaling Japan's best in terms of quality, cost, and manufacturability.
It will take months to determine whether the $3 billion project will pass muster with demanding consumers. But even now, one thing is clear: in terms of manufacturing, Saturn has taken some revolutionary steps.
Saturn is designed to be a flexible carmaker, able to react quickly to shifts in market demand. To do this, the 4 million-square-foot Spring Hill plant relies on several critical concepts such as ``just-in-time'' production, a method borrowed from the Japanese.
Rather than warehousing weeks worth of parts, the entire Saturn complex could be called a giant loading dock. Trucks carrying parts from suppliers unload their cargo right where it is needed along the assembly lines.
And Saturn uses a sophisticated computer system to tell suppliers what parts are needed each day and when to deliver them. That goes for in-house components, too. There's only a two-hour ``float'' of transmissions and engines, each for a specific customer's order. Customers choose base or performance versions of the 1.9 liter engine, and manual or automatic transmissions.
``We can swing our production from 25 to 75 percent of either manual or automatic transmissions,'' says Bill May, director of transmission manufacturing.
That switch would be instant. Though the two transmission types share no common parts, the surfaces are functionally identical, so they can be built on the same line with much of the same equipment. A traditional transmission plant would have cost 60 percent more and used 74 percent more space, Mr. May says.
Perhaps the most striking manufacturing innovation is also found in the powertrain plant, a concept pioneered by Saturn known as lost foam casting.
Here, polystyrene molds are made of six critical parts, including the engine block, crankshaft, and transmission casing. The mold is then buried in sand. A shot of molten aluminum or iron is poured into the mold, which instantly vaporizes. When the molten metal cools, a perfect duplicate remains. Final castings can be more complex than with conventional casting. And they can incorporate parts, such as an alternator bracket, that would otherwise have to be bolted on.
The Saturn work force also benefits from some of the new concepts. On a traditional assembly line, workers perform the same task over and over once or twice a minute. At Spring Hill, worker teams get up to six minutes to perform a variety of jobs.
To ease the burden, much of the work is done while riding a ``skillet,'' which carries the team along with the car so they don't have to walk and work at the same time. This not only improves productivity and quality, but also reduces boredom among workers, says Dave Kauppila, chief engineer of vehicle systems.
With so many new concepts introduced at once, results may not live up to expectations. But Saturn hopes it will set a new pace in quality and cost.