Staging area manages flexible workflow
Vertical-lift storage systems, stack-racking, and modular drawers at Mannesmann-Rexroth team up to organize subcomponent flow for high efficiency and throughput.
By Staff -- Modern Materials Handling, 1/1/1998
Manufacturing truly has to be flexible at the Mannesmann-Rexroth plant in Lexington, Ky. The company makes a wide variety of cylinders and the average lot size is 1.8 cylinders per order. "Customer demand is such that we must run lots of one efficiently," says Larry Tackett, vice president of manufacturing.Rexroth has found ways to manage all the work orders flowing to assembly operations, however, so that the plant is far more sophisticated than any job shop ever was. The company achieved its most dramatic results by creating a staging area where subcomponents are gathered prior to routing to assembly by conveyor. With "storage" equipment turned into staging systems, throughput has increased while both inventories and operating expenses have decreased.
With other improvements and new equipment, Rexroth has changed its plant from a tangle of chaotic workflows and confusion into a smoothly running, purposeful manufacturing system.
Characterized by complexity
Manufacture of Rexroth's hydraulic and pneumatic cylinders is characterized by complex products, small quantities, and short lead times. The cylinders range in size from 1.5 in. to 14 in. in diameter. They may be standard (catalog products) or special (customized products).
Production workers in a plant such as Rexroth's can become overwhelmed by the constant decision making: "Which order should I run first?" "Where is that tote?" "What's holding up assembly?" "What happened to order number 10968?" Manufacturing systems like this one are notoriously complex and difficult to manage profitably.
Manufacturing engineers and managers met with materials handling experts and asked how to remove constraints in the plant, however. Staging of work orders seemed like the best place to start.
Replacing search and pull
Previously, "staging"-such as it was-involved stacks of plastic totes scattered about the plant on carts and on the floor. Production workers had to remember the location of hundreds of work order totes. Whenever one worker moved a tote, another worker had to search for it. Time and effort were wasted searching for totes and pulling them out from under other totes.
The keys to changing this situation and achieving success came in distinguishing between pre-production and production and in providing a simple yet computerized system for managing work order totes. Then the orderliness created by the staging station soon spread to other departments, encouraging greater efficiencies in picking parts and in assembly, the workflows preceding and following the staging area, respectively.
The company designated some 1,200 sq ft of floor space as a staging area and specified installation of two double-wide vertical-lift storage systems (powerdrawer from Stanley Storage Systems) for staging work orders. The systems were put into the existing facility by expanding up-taking advantage of unused vertical space. Software in the two double-wide systems interfaces with a factory-floor computer system.
Computers are useful for tracking vital information-inventories, work orders, and material flows- but this information needs to reach and be used on the plant floor. Otherwise, constant, hands-on management and expediting of work orders is the rule.
The first step upon receipt of a work order at staging is to scan the bar code of the work order into a computer which then automatically searches for a vacant location in a vertical-lift unit. From that point on, the work order number is synonymous with the work order tote location in the vertical-lift unit.
When the work order is called up on the computer or the bar code of the work order is scanned, the computer automatically finds the tote. The staff does not have to keep track of the tote location. Assigning a location to a work order can be done with a few clicks of a mouse.
The software program provided with the vertical-lift units allows the user to add, store, or pull totes from the system. When a work order comes in, a tote must be added. The menu allows some choice over the tote location selection. For example, the user can toggle between zone 1 and zone 2, which correspond to the two vertical-lift units; and he can toggle between large and small tote size, and several tote heights which correspond to drawer heights.
According to shop floor scheduler Rick Bridges, staging in a vertical-lift unit saves a lot of time. "At first, I thought it would slow things down, but that hasn't been the case. It helps tremendously. It's quicker than I thought and it eliminates human error.
"There's no chance of calling up the wrong tote because there are no numbers to enter; the computer finds the totes when the bar code of the work order is scanned. We don't have to constantly look up locations. That frees up our attention for more important things," he adds.
"Staging is orderly because there is a single delivery point and everything is in the same area. The system has been a real asset in coordinating parts," Bridges declares.
With this means of staging, the vertical-lift system locates all work order totes in one place. A work order bar code is scanned and within seconds the tote is delivered to a single point-of-use. As a result, the vertical-lift is now the center of activity in the staging area.
When all parts are ready, an operator slides a work order tote from a vertical-lift unit onto a mobile cart. Then he rolls the cart over to a conveyor, and slides the tote off the cart onto the conveyor for delivery to the assembly area.
(Once the tote is removed from the staging station, the "pull" command is used to wipe out that work order from the memory of the computer, making the location available for incoming work orders.)
With staging more efficiently run, it wasn't long before production planning moved their desks into this area. Computers and printers are nearby, allowing for close cooperation between planning and production.
Flanking the staging area on one side are storage areas, including modular drawer cabinets and a stack-racking system, and, on the other side, the assembly area. This arrangement has proved flexible enough for many small runs of assemblies that contain hundreds of components.
Stack-racking provides heavy-duty storage for large and heavy components. As configured for Rexroth, the racking has four rows, and each row has 11 bays with an average of 12 pallets per bay, or a total of 528 pallets.
A captive-mast "forklift" in the racking is used to pull out the pallets. An advantage of this stack-racking system is that each pallet can hold up to 2,000 lb and each pallet position is vertically adjustable, so there is no wasted space storing low-profile components.
A benchmark facility
Mannesmann-Rexroth has transformed its plant into a smoothly running facility against which others might want to benchmark. Well-planned staging and storage systems and highly trained staff operating them now facilitate manufacturing the company's small runs of custom products quickly, run after run.
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