Performing "puff and stuff" with a moon buggy
Pulled along by chain-on-edge conveyor within the plant floor, a moon buggy (bottom) holds two axle/suspension assemblies. Overhead power-and-free conveyor with carrier unit (top) brings body down for assembly by worker team (cover photo).
By Staff -- Modern Materials Handling, 6/1/1999
Chrysler and other automakers for years have used what they call moon buggies. Essentially, a moon buggy is a towed platform with 2 lift devices aboard it (photo). Chain-on-edge conveyor in the plant floor tows the buggy.The buggies' lift devices assist workers in performing a "puff and stuff" step in assembly. Plant compressed air provides a "puff" of air raising a lift holding either a front or rear axle/suspension assembly. Then line workers "stuff" the heavy axle unit into place.
At DaimlerChrysler's Jefferson North plant, 35 moon buggies help produce '99 Jeep Grand Cherokees. These buggies are the latest version of the platform (Kuka) with new lift technology (Handling Specialty). This upgraded version further enhances the ergonomics of inserting axle units-weighing up to 400 lb each-into the SUV underbody.
The upgraded buggies, explains Kuka project manager Rick Eberling, feature an hydraulic, four-point scissors lift system to help position axles. An automatic air charge unit powers the lift by driving an air motor, which then controls hydraulics. In contrast, older buggies had an air-over-oil lift system based on a center post cylinder, which raised axles.
More "maintenance friendly," the scissors lifts on Jeep's newer moon buggies also provide greater stability and more true positioning capability than the older, air-over-oil cylinder units, says Eberling.
Here's how the axle unit assembly step now works: A buggy, like the one shown here (or the one with workers aboard on this month's cover) moves around a loop. The buggies travel at a speed of 25 ft/minute.
Aboard a buggy, a front or rear axle unit is placed on top of each of two lifts. (The lift is underneath the bellows which covers it to safeguard workers from the lift's scissor mechanism.)
Overhead power-and-free conveyor, meanwhile, brings vehicle bodies held in carriers down from above to match up with their corresponding front or rear axles on a buggy moving below the carrier, and in synchronization with it.
Workers hop aboard a buggy. Within a travel distance of about 60 ft, workers will raise each of the two axle units into place. The work team compresses each axle unit against the underbody framing just enough for a loose secure of all fasteners.
Three workers will insert the front axle, then two workers will position the rear axle. The worker team can complete these steps for up to 72 vehicles per hour.
To limit the potential for downtime at this assembly step, Jefferson North has 37 moon buggies, with 35 on line and 2 spares. Workers can pull a buggy off line "in 2 minutes or less," says Eberling. This "pit crew" then can replace a buggy needing maintenance or repair with a spare in about the same time period.
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