Friday, June 29, 2007

Toyota Way Fieldbook (Part 3)

In a previous post, I discussed the "continuous improvement spiral" from The Toyota Way Fieldbook, and went into the first step, "stability." In this post, I'll go into the second step, "create flow."

Once processes are stabilized through implementation of the 6S's and elimination of big wastes and obstacles (machinery breakdowns, employee problems, poor quality, disorganization, shortages, etc.), we can look at creating flow.

What is flow? Flow is the ideal of how an order should move from process A to process B. Flow is trying to avoid having an order stored in a rack (inventory), stopped for rework (defects), or delayed because of any of the other 7 wastes.

Why is flow a positive thing? When work flows across processes, orders get to the customer quicker and at lower cost. This is the most tangible result. Another deeper and more valuable reason to have process flow is that it brings problems to the surface. When there is no buffer between processes, any little problem has the potential to shut down the process and eventually the entire production line. This is a great motivator to identify problems and solve them before they bite you in the butt. There's a reason why Toyota refers to TPS as the Thinking Production System; you have to use your head to keep the line rolling.

How do you create flow? First, make sure that you've properly stabilized the processes that are to be linked. If the cycle times of the processes can't make Takt time, then they aren't ready for flow. If they're truly ready, then go about linking the processes together. When doing this, the rule is to "flow where you can, pull where you must." Aligning processes side-by-side in a cellular flow is the ideal, but if that's currently not feasible, install a pull system.

What is a pull system? A pull system is just an agreement on how a downstream process is to notify an upstream process of when they need more of something. Upstream only produces when signaled by downstream. Many variants of pull systems exist: supermarket pull (stock parts, use kanban to signal for replenishment), sequenced pull (pull from a sequenced feeder), and FIFO sequenced flow (just like flow, but with a small buffer). The key is to constantly reduce the buffers and ultimately approach one-piece flow.

Once processes are connected via one-piece flow and pull systems, problems will be surfaced. These problems must be addressed and eliminated through the use of problem-solving skills. When these problems are removed, the processes will be left in a much better condition. The newly improved processes will be more reliable, more efficient, and much flexible. With the extreme variety that we have in our product offering, these are all necessities.

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