Avoiding a manufacturing traffic jam

When do more cars travel on the highway, before or during rush hour?  It’s rush hour, right? Well, it depends on how you interpret the question. During rush hour, plenty of cars flood the highway at once, but they all take more time to get where they’re going. In fact, there’s a good chance that many people sitting in traffic will be late. Before rush hour, however, the highway traffic is somewhat below capacity, but the highway actually allows more people to get to where they’re going on time.

Say someone places a counter at one mile marker, then another counter several miles down the road. In the middle of the day--say, between 2 and 3 p.m.--the counter would tick off plenty of cars. But between 5 and 6 p.m. the counters would actually tick off fewer cars, because of course all the cars would be slowly inching forward. So now imagine two scenarios: a horrific, 24- hour rush hour, and another where highway traffic is at three-quarters capacity. Which scenario would involve more cars? The answer is three-quarters capacity.



This comes from Prof. Rajan Suri, founder of the Center for Quick Response Manufacturing at the University of Wisconsin. The center’s improvement methodology focuses on reducing lead-time using a counterintuitive approach--by reducing capacity levels.

The method only is counterintuitive, Suri said, when using traditional manufacturing thinking, where capacity utilization rules. As the saying goes, if a machine isn’t running it’s not making money. As Suri explained, this isn't the case. Machines don’t make money. Finished products do. Suri’s approach instead considers time as an essential element in determining how much a shop can produce. Flooding the floor with work is analogous to having constant rush-hour traffic.

The quick response manufacturing (QRM) methodology is more comprehensive than this, of course, and we’ll be covering it in an upcoming print edition of The FABRICATOR. But one major element is the fact that, if you’re trying to fabricate products as quickly as possible, producing at full capacity is a dangerous proposition, like a highway that’s stop-and-go. Running full out doesn’t allow for unforeseen variability, be it a late order change, rework, or a machine breakdown. Add a few more cars, and nobody moves; the same thing can happen with a shop floor flooded with work. If it takes forever and a day for a shop to ship parts, the plant doesn’t make money, because as that WIP sits there, the costs just add up.

In manufacturing, if a machine isn’t running then, well, nothing bad may be happening. The machines don’t “make” money, after all. Neither does work in process. Finished products, on the other hand, do. So perhaps this would be a better axiom: If parts aren’t moving, the plant isn’t making money.