Managing Variability by Stopping the Line to Fix Problems
The virtues of stopping to fix problems are well known. In a supply chain, that method might not work the best. In the seat example above, it is not possible to stop the line to fix the problem each time a defective seat is noticed. Doing so will take too long and be too costly. Does that mean one gives up the principle? What exactly is the logic behind stopping to fix the problem? There are two concerns: (1) The link between cause and effect becomes attenuated the longer the corrective action is postponed. (Try an exercise in recall: go back and read the first hundred pages in this book; then try to recall what exactly you were reading prior to revisiting those 100 pages.) (2) Unless production or supply is halted, the problem is never given the priority it requires for a permanent solution to be found. The latter issue is more subtle. It is possible to record problems so that the information is not completely lost, which addresses the first concern. But how would one design a supply chain that focuses attention on the special causes that need to be addressed? How should causes of root problems be uncovered and eliminated permanently?
Watanabe provides an example of how to do so in a supply chain. Soon after he took over as president of the company, several quality problems arose. Engineers were instructed to find the root cause. The investigators found that the problems were due to either design defects or insufficient lead time. They decided to experiment thoroughly and test a large number of prototypes. In response, Watanabe states, “I will not allow the same problems to recur.” He halted several projects just as workers do when they stop production.
When we visited the Toyota plant in Kentucky, we were told of another instance where this seemingly bullheaded persistence of eliminating defects prevailed. The problem was with the canopy of the Solara convertible; the first canopies delivered to Toyota had many quality defects. The supplier of the canopies had moved close to the plant and set up a facility to supply exclusively to Toyota. The root cause required several changes to the management style and practices of the supplier. A senior manager at the plant was told to work with the supplier exclusively until all root causes were eliminated. The manager worked for several months at the supplier plant before returning to Toyota.
Managers usually seem perplexed when we discuss the idea of finding permanent cures. In response, we tell them to find the most important cause for problems and address it. That effort requires a combination of the prioritization method (i.e., customer first, suppliers and dealers second, and factory last) as well as tools to uncover the systematic issues that need addressing. Moreover, it requires halting production once a threshold limit is exceeded, thus signaling a special case. The three have to be used in combination. The Toyota Way document provides guidance as “Focus on Concrete Proof/Exhaustive Due Diligence: Actions are undertaken only after thorough study and testing to determine what must be done.”