Navneet DwivediPGDM-Operations and Supply Chain

Process Capability

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

Agenda

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 customerVOP represents the actual process parameters

mathematically Cp = (

or Cp = where “ is the standard deviation of the process.

This can be clarified in better way in pictorial representation as follows.

LCL UCLVOC

VOP

−2𝜎 −𝜎−3𝜎 +1𝜎 +2𝜎 +3𝜎

𝜎

How can we say a process as 2/3/6 When to do Process Capability Study ?? Lets consider few example and calculate their Cp value

48

𝜎

Case 1:

UCL: 48 mmLCL: 42 mmSD: 1.2 mm

4246.2 47.4 48.641.4 42.6 43.8

𝐶𝑝=48−426∗1.2

Undesirable

48

𝜎

4246.0 47.0 48.0

Case 2:

UCL: 48 mmLCL: 42 mmSD: 1.0 mm

𝐶𝑝=48−426∗1.0

1

Acceptable

43.0 44.042.0

UCL

𝜎

LCL46.0 47.0 48.0

Case 2:

UCL: 48 mmLCL: 42 mmSD: 0.5 mm

𝐶𝑝=48−426∗0.5

2

HighlyAcceptable

43.0 44.042.0

Quick Overview

UCLLCL

6𝜎2𝜎

Cp =

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