Manual for Life Cost Based FMEA
some failure types are “worse” than others, but give no quantitative indication of their relative effects.
Cost as a measure of failure
To resolve the ambiguity of measuring detection difficulty and the irrational logic of multiplying 3 ordinal indices, a new methodology was created to overcome these shortcomings, Life Cost-Based FMEA. Life Cost-Based FMEA measures failure/risk in terms of monetary cost. Cost is a universal parameter that can be easily related to severity by engineers and others. Thus, failure cost can be estimated using the following simplest form:
Expected Failure Cost = ∑
p: Probability of a particular failure occurring c: Monetary cost associated with that particular failure n: Total number of failure scenarios
Formation of team
FMEA is most effective when there are inputs into it from all concerned disciplines of the product development team. However, FMEA is a long process and can become tedious and won’t be effective if too many people participate. An ideal team should have 3 to 4 people from: design, manufacturing, and service departments if possible. Depending on how complex the system is, the entire process can take anywhere from one to four weeks working full time. Thus, it is important to agree to the time commitment before starting the analysis else, anxious managers might stop the procedure before it is completed.
Failure Mode and Effects Analysis (FMEA)
Failure Mode and Effects Analysis (FMEA) is used to assist in identifying potential failure modes early in the process of design. Traditional FMEA measures risk using the Risk Priority Number (RPN). The FMEA worksheet consists of a table that will be filled in by the FMEA team; it lists the causes and effects of potential failure modes which are known by the team of engineers. These failure modes are organized around functions or the “Voice of the Customer” (VOC) (see Table 1). The following section describes the elements of the spreadsheet used for listing identified failure scenarios in a device.
Table 1 Components of a FMEA Worksheet
Function or Requirement
Potential Failure Modes
Causes of Failure
Effect of Failure
R P N
Actions Recommended to Reduce RPN
Responsibility and Target Completion Date
FMEA MANUAL By S. Rhee and C.M. Spencer