Let's POLCA: Manufacturing strategy synchronizes a Wisconsin company's wild work flow
In foodservice, the concept "first-in, first-out" is a standard method for dealing with everything from inventory to meal orders. In manufacturing, its peer is "just-in-time," a system that relies on Kanban materials request cards to balance production and ensure bins of the proper parts arrive in time for the next step.
But for businesses that make custom products, such as Rockwell Automation Packaged Control Products (PCP) Division, an approach that centers around an existing inventory of standard components loses its effectiveness.
On an order-to-order basis, the Richland Center business manufactures electrical boxes that drive large systems in industrial settings. Commonly called motor-control centers, the 21-square-foot modular-steel cabinets contain motor starters, variable-speed motor drives, programmable controllers and other electrical equipment.
With just a day or two of lead time, one department in the plant builds cabinets on demand for each of seven assembly cells that then add electrical components. However, job priority shifts, workloads and part availability all affect the time it takes workers in the assembly cells to finish their orders, says Scott Gilson, shop floor control manager at PCP.
And as a result, work in progress at the plant was out of sync, leaving some assembly cells with a cabinet surplus while other cells waited for more. "It was sort of a best guess on when they were going to need those cabinets in the final assembly cells," he says.
To find a solution, he turned to the Center for Quick Response Manufacturing (QRM), which generally works with companies that produce high-variability, high-mix custom products to help cut lead times in all phases of manufacturing.
Through the center, a team of manufacturing systems engineering students helped the plant implement POLCA (Paired-cell Overlapping Loops of Cards with Authorization). Quick Response Manufacturing, a book by Professor and CQRM Director Rajan Suri, details the POLCA strategy, which center investigators have refined and implemented at several Midwest manufacturers.
Each POLCA card represents one unit, and a cell or department receives a set number of cards that workers use to signal when capacity is available. At PCP, when all of the cards are attached to cabinets, the cell will not receive more cabinets until it has finished the work it has. "The cards are pretty much a line in the sand that says, 'Here's how much you get, and that's it,'" says Gilson.
The cards in this case actually are large color-coded, numbered magnetic rectangles that "stick" to each cabinet. "Where POLCA really helps us out is that each cell has only a limited number of cards for these cabinets," he says. "So once they use up all their cards, the signal to the cabinet department is that a certain cell can't take any more work, even though the dispatch list may say the next job on the list is for that cell."
Instead, the cabinet department now skips work for "full" cells, completes work in progress for other cells and returns to the skipped work when it receives more POLCA cards from those cells.
"Although the Kanban system also employs cards, those cards signal replenishment of specific inventory items, while the POLCA cards are combined with the dispatch list to enable production of the plant's customized products," says Suri.
Under this new system, the company has reduced work in process by 15 percent and cycle time by about 20 percent. But an even greater benefit, says Gilson, is more breathing room on the shop floor. "These empty cabinets aren't just sitting there doing nothing," he says.
When the project began, PCP was unfamiliar with POLCA, he says. Members of the student team visited the plant weekly and helped analyze the departments' throughputs, capacities and organization. They worked with Gilson to plan how many POLCA cards each loop would need and how workers at each assembly stage would deal with them. Together, they also conducted training sessions for everyone in the company and performed live simulations before the company actually implemented the system. "We wouldn't have been able to do it without the students," says Gilson.
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