Six sigma & levels of sigma processes

1. FICCI CE
Six Sigma

2. Accurate and Precision
Six Sigma can be best explained
by using the analogy of a rifle firing
at a target.
Six Sigma in simple terms

3. Accuracy and precision
With the center of the target taken to be the true
value of the characteristic being measured and
by the rifle shots representing the measured
values, there are four combinations of accuracy
and precision as depicted in the following slides.

4. Inaccurate and imprecise

5. Accurate and imprecise

6. Precise but inaccurate

7. Accurate and precise

8. Objectives of Six Sigma
As observed from the Picturization in the preceding slides, the objective of
moving towards world class manufacturing a is to continuously achieve
greater consistency of the processes by aiming for higher levels of accuracy
& precision

9. FICCI CE
Sigma in statistical terms
Standard deviation is also referred to as the Greek letter sigma in
quality management literature. Consequently process variation
can be described by how many sigmas ( i.e how many multiples of
standard deviation or SD ) fit within the specification limits.The
higher this number, the better is the quality and vice versa.
Sigma is a statistical measure of the quality consistency
for a particular process / product.

10. FICCI CE
Sigma process
From a sigma process we come to know that at what distance,
in terms of the standard deviation, the specification limits are
placed from the target value.

11. FICCI CE
Move beyond 3 sigma
Until a few years back all statistical process controls were
designed on the basis of 3 sigma limits. It is only in the recent
years that this concept has been challenged and the
organizations have started looking for quality levels beyond 3
Sigma.

12. FICCI CE
3 Sigma process
LSL
USL
Mean=8
SD = 2
- 3 SD + 3 SD
23456789 1210 16151413111
Note : LSL is Lower specification limit and USL is Upper specification limit.

13. FICCI CE
4 Sigma process
2 3456789 1210 16151413111
LSL
USL
Mean=8
SD = 1.33
- 4 SD + 4 SD

14. FICCI CE
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LSL
USL
Mean=8
SD = 1.07
- 5 SD + 5 SD
5 Sigma process

15. FICCI CE
LSL
USL
Mean=8
SD = 1
- 6 SD + 6 SD
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6 Sigma process

16. FICCI CE
Precision
Lesser the standard deviation of the process, more precise or
consistent is the process

17. FICCI CE
3 Sigma Vs 6 Sigma
The goal of Six Sigma program is to reduce the variation in every
process to such an extent that the spread of 12 sigmas i.e. 6 Sigmas
on either side of the mean fits within the process specifications. The
figure on next slide shows what this looks like.

18. FICCI CE
23456789 1210 16151413111
LSL
USL
6 Sigma curve
3 Sigma curve
3 Sigma Vs 6 Sigma
In a 3 sigma process the values are widely spread along the center line,
showing the higher variation of the process. Whereas in a 6 Sigma
process, the values are closer to the center line showing
less variation in the process.

19. FICCI CE
3 Sigma Vs 6 Sigma
The comparison on the previous slide also shows a process in which the process
spread of Six Sigmas (ie. 3 Sigmas on either side just fits within the specifications). In
this case one must be extremely careful to ensure that the process average never
slips off the target, otherwise the curve will shift and non-conforming items will
increase. With Six Sigma requirement the process mean can shift by as much as 1.5
sigma before the likelihood of non-conforming items is increased. Even if the process
mean does shift off center by as much as 1.5 sigma, only 3.4 non-conforming items
per million parts should result.

20. FICCI CE
Amount of process shift allowed
23456789 1210 16151413111
LSL
USL
SD = 1
1.5 SD 1.5 SD

21. FICCI CE
Sigma levels and defect rate
Quality level % Quality Defective PPM*

3 Sigma 99.73 66807
4 Sigma 99.9937 6210
5 Sigma 99.999943 233
6 Sigma 99.9999998 3.4

*Parts Per Million

22. FICCI CE
Sigma levels & Cost of quality
SigmaDefect rate(PPM)Cost of qualityCompetitive level
3.4 <10%
233 10-15%
6210 15-20%
66807 20-30%
308537 30-40%
6,90000
>40%
World
Class
Industry
Average
Non
Competitive
6
5
4
3
2
1

23. FICCI CE