Page 282 - Six Sigma Demystified

262 Six SigMa DemystifieD

Interpretation

The RPN will range from 1 to 1,000, with larger numbers representing higher
risks. Failure modes with higher RPNs should be given priority. Some organiza-
tions use threshold values, above which preventive action must be taken. For
example, the organization may require improvement for any RPN exceeding
120.
Reducing the RPN requires a reduction in the severity, occurrence, and/or
detection levels associated with the failure mode. Generally:

• Reducing severity level requires a change to the design of the product or
process. For example, if the process involves a manufactured part, it may
be possible to alter the design of the part so that the stated failure mode
is no longer a serious problem for the customer.
• Reducing detection level increases cost with no improvement to quality.
In order to reduce the detection level, we must improve the detection
rate. We might add process steps to inspect product, to approve product,
or (as in the example) to double-check a previous process step. None of
these activities adds value to the customer, and each is a “hidden factory”
sources of waste to the organization.
• Reducing the occurrence level is often the best approach because reduc-
ing severity can be costly (or impossible) and reducing the detection level
is only a costly short-term solution. Reducing the occurrence level re-
quires a reduction in process errors, which reduces cost.

5 S

5S is a lean tool that originates from the Japanese words used to create organi-
zation and cleanliness in the workplace [Seiri (organization), Sieton (tidiness),
Seiso (purity), Seiketsu (cleanliness), and Shitsuke (discipline)]. The traditional
five S’s have been translated into the following five English words (Revelle,
2000):
1. Sort: Eliminate whatever is not needed.
2. Straighten: Organize whatever remains.

3. Shine: Clean the work area.
4. Standardize: Schedule regular cleaning and maintenance.
5. Sustain: Make 5S a way of life.