By Gary Cone
One Quality school of thought suggests opportunities are counted using a definition that includes only those things that are tested or inspected. However, by placing the emphasis on what is tested and inspected, this definition promotes the idea of more test and more inspection as a method of improving the sigma level. This would seem contrary to the objective of trying to make our processes more efficient.
The best manufacturers in the world do very little test and inspection. Why? They don't need to. The best manufacturers in the world also have test or inspection time limited by the line flow. So now in order to embrace Six Sigma, these companies would have to add test and add inspection? I don't think so.
What is wrong with the focus on test and inspection for counting opportunities?
- The focus is on non-value added activities.
- The more we are sure of our quality, the less we will test and inspect potentially worsening the sigma level. At its extreme the denominator of the DPMO equation is 0, which means we have an undefined sigma level.
- We could disrupt the flow of work trying to comply with this definition.None of this sounds right, does it?
Is it opportunity for defects or opportunity to do things right?
At the detail level of a process, one useful tool for determining failures and defects is called a Failure Modes and Effects Analysis (FMEA). FMEA is a tool that helps identify every possible failure mode of a process or product to determine its effect on other sub-items and on the required function of the product or process. The number of ways a product could have a defect is large and could approach infinity especially if you start considering handling, misprocessing, etc.
For an alternative perspective, let's look at the objectives of Lean Enterprise. According to the principles of lean, processes should use the least amount of resources needed to transform a good or service into something the customer wants. I would argue that the definition of a defect in this context is any use of resource over the minimal required to do the job. So spending ten extra seconds at a station is a defect. Handling something twice when once will do is a defect. Having a queue of parts when no queue is necessary is a defect. You get the picture.
Another aspect of the Lean Enterprise theory is the idea that there should be synergy between of all of the goals of the organization. Lean Enterprise is trying to minimize non-value added activities. So there is a whole category of things that cannot be viewed as opportunities if we are seeking synergy. This would include test, inspection, transport, storage, and rework (including all of those rework steps we think of as process). What we are left with, if we expect Lean Enterprise and Six Sigma to be viewed as complementary (they are - right?), are value added activities - a focus on the opportunity to do things right, not the things that can go wrong.
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