Page 257 - Lean six sigma demystified

Chapter 7 Redu C ing Va R iation with Six Sigm a 235

was at work early, I could also leave earlier in the afternoon and beat the
evening rush.

Hint Spend more time reducing common causes than firefighting special causes.

Similarly, the temperature and humidity in a manufacturing plant can affect
the product (Fig. 7-1). Staffing can affect throughput; illness, absenteeism, tar-
diness, and vacation can all affect lead times.
All kinds of things can cause variation. Lockheed’s SR-71 Blackbird spy plane
used Burbank city water to rinse the plane’s welds. They discovered that rust
developed more rapidly on welds at certain times of the year. The manufacturer
traced the cause of variation back to the algae that bloom in the city’s water
supply in the spring and summer. Afterward, they used special filtration to
clean the water and prevent rust.
Some sources of variation are short term, such as machine settings, while
others are long term such as wear. To reduce variation in your product or
service, you will want to focus on the common causes of variation.

Measurement Materials Process/methods

Gage Hardness Maintenance
Measurement Density Lubrication
process Replacement of
worn parts

Problem statement

Variation
Temperature Feeding material Clearances
Humidity Centering Wear

Power supply Setup Tools
Strength
Wear
Environment People Machines

Ishikawa Fishbone Diagram
Cause Effect Analysis
FIgure 7-1 • Root causes of variation.