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 | Why Six Sigma? | |
| Quality makes us strong | |
| Steps to 6 sigma quality | |
| Words of Wisdom about Quality | |
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Quality makes us strong
In the past, conventional wisdom said that high levels of quality cost more in the long run than poorer quality, raising the price you had to ask for your product and making you less competitive. Balancing quality with cost was thought to be the key to economic survival.
Cost of Poor Quality in Motorola before Six Sigma Initiative
(Performance 2s ; COPQ 20-40% of Revenue), and after Six Sigma Implementation
(Performance capability 6s ; COPQ about 1% of Revenue).
The surprising discovery of companies which initially developed Six Sigma, or world-class, quality is that the best quality does not cost more. It actually costs less. The reason for this is something called cost-of-quality. Cost-of-quality is actually the cost of deviating from quality-paying for things like rework, scrap and warranty claims. Making things right the first time-even if it takes more effort to get to that level of performance-actually costs much less than creating then finding and fixing defects.
Overall Yield vs. Sigma Level
(Distribution Shifted +/- 1.5s)
| Number of parts or steps | 4s | 6s |
| 1 | 99.379 % | 99.99966 % |
| 10 | 93.96 | 99.9966 |
| 20 | 88.29 | 99.9932 |
| 100 | 53.64 | 99.966 |
| 300 | 15.43 | 99.898 |
| 400 | 8.28 | 99.864 |
| 500 | 4.44 | 99.830 |
| 700 | 1.28 | 99.762 |
| 800 | 0.69 | 99.729 |
| 1200 | 0.06 | 99.593 |
| 2000 | - | 96.656 |
Since defects are cumulative, as more parts or more operations are added, the chance of producing a defective product goes up. With process drift as a factor, if the number of parts or process steps exceeds 1200, four-sigma processes are virtually incapable of making one good product. On the other hand, a Six Sigma process with 1200 parts or steps would still be producing a yield of 99.593% good products.
Not only would the four-sigma producer have to spend much time and money finding and fixing defects before prod-ucts could be shipped, but since inspection cannot find all the defects, she would also have to fix problems after they got to the customer. The Six Sigma producer, on the other hand, would be able to concentrate on only a handful of defects to further improve the process.
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