The document discusses process capability (Cp) and process capability index (Cpk). It defines Cp as the ratio of the specifications given by the customer (VOC) to the actual process parameters (VOP). Mathematically, Cp is equal to (USL-LSL) divided by 6σ, where USL and LSL are the upper and lower specification limits and σ is the standard deviation. It provides examples calculating Cp for different processes based on their standard deviation and specification limits. A Cp greater than 1 indicates an acceptable process, while greater than 2 indicates a highly acceptable process.

1. Navneet Dwivedi
PGDM-Operations and Supply Chain

2.  Part1: Process Capability (Cp)
 Part2: Process Capability Index (Cpk)
 Part3: Six Sigma Derivation
 Part4: Implementation of Six Sigma Project

3. What is Process Capability (Cp)??
◦ It is the ability of process to produce output as per
the given specification.
◦ It can also be defined as the ratio of voice of
customer(VOC) to voice of process(VOP)
where,
VOC represents the specifications given by customer
VOP represents the actual process parameters

4. mathematically
Cp = ( 𝑉𝑂𝐶
𝑉𝑂𝑃)
or Cp =
𝑈𝑆𝐿−𝐿𝑆𝐿
6𝜎
 where “ 𝜎" is the standard deviation of the process.
 This can be clarified in better way in pictorial representation
as follows.

5. LCL UCL
VOC
VOP
−2𝜎 −𝜎−3𝜎 +1𝜎 +2𝜎 +3𝜎
𝜎

6.  How can we say a process as 2𝝈/3𝝈/6𝝈 ? ?
 When to do Process Capability Study ??
 Lets consider few example and calculate their Cp value
48
𝜎
Case 1:
UCL: 48 mm
LCL: 42 mm
SD: 1.2 mm
42
46.2 47.4 48.641.4 42.6 43.8
𝐶𝑝 =
48 − 42
6 ∗ 1.2
=
6
7.2
= 0.833 < 1
Undesirable

7. 48
𝜎
42
46.0 47.0 48.0
Case 2:
UCL: 48 mm
LCL: 42 mm
SD: 1.0 mm
𝐶𝑝 =
48 − 42
6 ∗ 1.0
=
6
6
=1
Acceptable
43.0 44.042.0

8. UCL
𝜎
LCL
46.0 47.0 48.0
Case 2:
UCL: 48 mm
LCL: 42 mm
SD: 0.5 mm
𝐶𝑝 =
48 − 42
6 ∗ 0.5
=
6
3
=2
Highly
Acceptable
43.0 44.042.0

9. UCLLCL
6𝜎
2𝜎
Cp =
𝑈𝑆𝐿−𝐿𝑆𝐿
6𝜎

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