Power-and-free conveyors help boost throughout
By Staff -- Modern Materials Handling, 9/15/1999
When Jeep management decided to boost production of the 1999 Jeep Grand Cherokee for a hungry SUV market, they included in the plan major changes to the '98 model. To meet the greater capacity and model redesign goals, Jeep added 847,000 sq ft to their Jefferson North Assembly Plant in Detroit, along with more than 10 miles of power-and-free and other types of conveyor.The new conveyor systems had to be installed and integrated with new process equipment. Completing changeover consumed over 400,000 man hours of work. The Jeep plant's trim shop changes alone required the services of more than 1,100 people working 24 hours per day, 7 days per week.
At present, the more than 10 miles of power-and-free conveyor equipment run through the two body shops and trim facility at the Detroit plant. Before any '99 Jeep Grand Cherokee starts recording miles on its odometer, it completes a ride of a day-and-a-half's duration over these power-and-free systems, as well as short stretches of powered roller, chain-on-edge, and flat-top conveyor systems.
There's a very good reason for making power-and-free technology the dominant conveyor type, says Mike Colburn, plant engineering manager: "We can buffer our processes more on the new line than we did on the old line with accumulation zones. The power-and-free system provides this capability for accumulation and storage. This design feature protects us from having excessive downtime. And it improves our throughput," says Colburn.
Transfers between overhead and inverted power-and-free systems are accomplished by means of equipment such as a high-lift transfer mechanism or by a fork transfer method.
The Jeep plant relies heavily upon JIT suppliers to deliver seats, fascia, and instrument panels to the trim shop.
Jefferson North assembles on an in-sequence basis, says materials manager, Frank LaSota. These parts are supplied not only just-in-time, but also in the build schedule or order sequence that they'll go to assembly to be matched to a specific vehicle by color, fabric, or other feature. EDI (electronic data interchange) transactions between plant and supplier ensure information on sequence is correctly communicated.
Seats, for example, arrive in the supplier's delivery truck as a slug to be unloaded automatically. The truck trailer's bed includes roller conveyor. Upon arrival, the truck driver "plugs into" the dock system to begin the unloading process. Seats on special pallets roll off the truck and into the plant.
Before a new, major launch of a model, an automaker goes through years of advance work and planning, as Colburn observes. One aim is not to affect prior production. Nor does the plant want to get off to a slow start on new assembly processes for a makeover.
Typically, however, an automaker has only a summertime plant shutdown period of several weeks to make the changes in process equipment and handling systems that go into a launch.
Instead, in switching over to '99 Grand Cherokee production, the company chose to build a new South Body Shop.
There, Jeep pilot operations for the redesigned '99 vehicle, or WJ model, could be conducted for some 7 months, prior to shutdown of production on the prior model.
"Working the pilot in the new body shop gave us a tremendous lead time on our WJ launch," says Colburn. "Our new process equipment systems and conveyors were all well tried out in advance of our three-week changeover period."
Methods for vehicle production and related materials handling procedures at this plant hardly are static. Continuous improvement is a goal, and one which involves hourly employees along with managers.
During the months of the countdown to the '99 launch as many as 120 hourly employees were involved at any one time with a corporate and vendor design team directed at problem solving - maintenance workers, millwrights, pipefitters, and others joined the group.
The company also continually simulates its operations on computer software to find ways to improve processes and materials handling. During the next plant shutdown, Colburn says, the findings from team suggestions and simulation will result in several changes to conveyor systems on the main line and at a door assembly step. Dearborn Mid-West Conveyor
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