Types of PFEMAs

There are two basic types of PFEMAs in the industry. The difference between them relates to interpretation of the “P” in PFEMA. The use of “Potential” typically refers to a product, and the use of “Process” relates to a manufacturing method or service. CNC shops would typically use the Process FEMA.

Styles of PFEMAs - Generic vs Specific

Many companies making a process-based PFEMA will create a generic document. This generic document will cover all the risks and mitigations for all the processes that a company is responsible for in the manufacturing of a product.

Some customers do not like the generic PFEMA, so a part-specific PFEMA may be requested. This will be a subset of the generic PFEMA and will be a more controlled change record since it is a document tied to the control plan and validation process. At Protomatic we do both, but favor the generic because it is always up to date.

RPN - Risk Priority Number: Various Scoring Systems and Weighting Systems

There are many systems utilized, but the most common is a 10-point system. This creates a maximum point count of 10 for “severity,” 10 for “occurrence,” and 10 for “detection.”

A higher number for severity means there is more of an impact on the product performance if the potential failure mode goes wrong. A higher number for occurrence means that the situation typically occurs more often. For example, if 1 of 100 pieces has a paint flaw, it would have a higher occurrence number than if only 1 per million has a paint flaw. The detection number is related to the accuracy of the measurement technique. Visual or subjective methods may have a higher detection number, versus a CMM measurement. This creates a maximum score of 10x10x10=1000. Each potential failure mode is scored, and depending on value, a mitigation action is determined. This 10-point system is the most common system for the transportation industry.

For medical applications, Protomatic uses a system with 5-point scoring, creating a maximum of 125. The severity ranking, occurrence ranking, and detection ranking are based on our business, which involves low-volume batch sizes. Although we produce batch sizes from 1- 150,000 pieces per year, our average batch size is relatively low. Keep in mind, sometimes the RPN system is defined by the industry served and should be consulted prior to implementation.