Question

Suppose that the buyer has set specifications for the part. The specifications require that the diameter fall in the range covered by 34 ± 1.5. Calculate the process capability (Cp), process capability index (Cpk) and the sigma level of the process

Sample		R
1	34.5	3
2	34.2	4
3	31.6	4
4	31.5	4
5	35	5
6	34.1	6
7	32.6	4
8	33.8	3
9	34.8	7
10	33.6	8
11	31.9	3
12	36.6	9
13	35.4	8
14	34	6
15	37.1	5
16	34.9	7
17	33.5	4
18	31.7	3
19	34	8
20	35.1	4
21	33.7	2
22	32.8	1
23	33.5	3
24	34.2	2

Answer 1

We can see that the upper specification and lower specification limits are as follows

mean of the sample ==33.9

the standard deviation of the sample is = =1.4

the capability index(cp) = = 0.357

the process capability index(cpK) =

=minimum(0.38,0.33)

= 0.33

to calculate thensigma level we use the formula where we see USL or LSL which one is closer to the mean

here LSL is closer to the mean as their difference is lower than USL.

the sigma level= = 1

the sigma level here is 1