FICCI CE

Variation Control

Variation is a basic phenomenon of nature. This effects all entities

including products and processes. Variation is found in all stages of

product life cycle including design & development, manufacturing, service

and supplier processes. Controlling process variation is a key to achieving

Six Sigma quality.

FICCI CE

Understanding & controlling variation

Variation is responsible for the difference between one unit of

product and another. It can also be defined as the difference

between specifications and customer requirements. Variation

is present in all processes. When it is present in one or more

characteristics of a product or process, it causes poor quality

and customer dissatisfaction.

FICCI CE

Understanding & controlling variation

Products and processes are expected to vary because no two

things are exactly alike. Differences result from material

characteristics, methods, people, machine and

environmental factors as depicted on the next slide.

FICCI CE

Variation

Methods •Procedures

•Policies

•Accounting

Material •Assemblies

•Components

•Suppliers

•Consumables

Environment •Noise level

•Humidity

•Temperature

•Lighting

Sources of variation

People •Training

•Experience

•Skill

•Attitude

Machine •Technology

•Variability

•Tooling

•Fixtures

Measurement •Counting

•Instruments

•Gauging

•Tests

FICCI CE

Causes of variation

Chance / Inherent Causes

They have the influence on

the output all the time.

Causes

Special / Assignable Causes

They influence the output

only once in a while.

FICCI CE

Chance / inherent causes of variation

Chance or inherent causes are sources of variation which are always

present because of small day-to-day variables. These causes are inherently

part of the process (or system) and affect everyone working in the

process. They are typically due to a large number of small random

sources of variation. Chance causes also contribute to the output

variability because they themselves vary.

FICCI CE

Chance / inherent causes of variation

Each chance/inherent cause typically contributes a small portion to the total

variation in process outputs. Inherent causes usually have a nonsystematic,

random appearance. Process or system variability is defined in terms

inherent causes because they are regular contributors. The variables

involved in inherent causes may change slightly from day to day, but this is

natural. They will always be present, and the best way to stay ahead of this

situation is to plan for it.

FICCI CE

Special / assignable causes

These are causes that do not occur naturally and are unusual. These types of

causes are not inherent part of the process (or system) all the time or do not

affect everyone but arise because of specific circumstances. Special causes

are sporadic contributors and are due to some specific circumstances.

Process or system variability is defined without them. Special causes can be

identified and efforts can be made to minimize their influence on the

process.