Page 642 - Design for Six Sigma a Roadmap for Product Development

Tolerance Design 595

Cost

Quality loss cost

External repair cost
A 0

Internal repair cost
A
y

T – 0 T – T + T + 0
Figure 16.9 Quality loss cost versus repair costs.

If the internal repair cost is A at producer tolerance , by letting the
repair cost equal to quality loss, then

A 0 2
A
2
0
Therefore

0
(16.32)
0

A 0 /A
Example 16.12. Bacteria Count in a Meat Item Clearly the bacteria
count y in a portion of meat is a smaller-the-better requirement. Assume
that if the bacteria count in a meat pack is more than 8000, then the per-
son who eats the meat will get sick. Suppose that the average cost of med-
ical treatment and lost pay is equal to $500. If the meat is determined to
exceed the limit within the meat-packing plant, the meat will be discarded,
and the cost will be $3.00. We can suggest the internal inspection limit for
bacteria count to be

0 8000 8000
620
A 0 500/3 12.9

A

In other words, the meat-packing factory will inspect the meat packs, and if
the pack contains more than 620 bacteria count, the meat will be discarded.
The safety factor is 12.9.