The Goal

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the average setup and process times for each type of part, and I'm able to calculate when each batch should clear the bottleneck. Because we're only dealing with one work center, with much less dependency, we can average the statistical fluctuations and get a better degree of accuracy."

Ralph went on to say that he knows from observation it takes about two weeks, plus or minus a day or two, for material to reach the bottlenecks from the first operations.

"So by adding two weeks to the setup and process times of what's in queue at the bottleneck," said Ralph, "I know how long it will take until the bottleneck is actually working on material we release. And as each batch leaves the bottleneck, we can update our information and calculate a date when Stacey should release more red-tag material."

Jonah looked at Ralph and said, "that's excellent!"

"Ralph," I said, "that's terrific. How accurate do you really think we can be with this?"

"I'd say we'd be accurate to within plus or minus a day," he said. "So if we keep, say, a three-day stock of work-in-process in front of each bottleneck, we should be safe."

Everyone was telling Ralph how impressed they were when Jonah said, "But, in fact, Ralph, you can do much more than that with the same information."

"Like what?" asked Ralph.

Jonah said, "You can also attack the inventory problems in front of assembly."

"You mean we not only can do something about excess in- ventory on the bottleneck parts, but on the non-bottleneck parts as well?" I asked.

"Exactly," said Jonah.

But Ralph said, "Sorry, folks, I'm not sure how I'd do that."

Then Jonah explained it to him-and all of us. If Ralph can determine a schedule for releasing red-tag materials based on the bottlenecks, he can also determine a schedule for final assembly. Once he knows when the bottleneck parts will reach final assem- bly, he can calculate backwards and determine the release of the non-bottleneck materials along each of their routes. In this way, the bottlenecks will be determining the release of all the materials in the plant.

I said, "You know, that's going to produce the same effect as