PFMEA – Identify and Manage Process Risks
Posted on January 27th, 2012 in Blogging | No Comments »
Process Failure Modes and Effects Analysis (PFMEA) is a systematic approach for identifying quality risks inside a manufacturing or transactional process. During a PFMEA session, a team of process and product experts evaluates each step in the process and assigns values to three risk factors (outlined below) – Severity, Occurrence, and Detection. These three values, typically ranked on a scale of one to ten, are multiplied to obtain a Risk Priority Number (RPN) for each process step.
Process steps and their associated risks are typically completed on an PFMEA spreadsheet and then sorted in descending order of RPN, at which point the team begins brainstorming countermeasures for the top process risks.
Severity, Occurrence, and Detection Definitions
The above three factors, when multiplied together, make up the RPN value for each process step. All factors are rated on a 1-10 scale, with 10 being the worst-case scenario.
Severity is the effect that a given defect has on the customer.
Occurrence is the likelihood that the defect will happen in the first place.
Detection is the likelihood that the defect will be detected by the process or system before it actually reaches the customer.
Three Important Factors in Creating a PFMEA
- Ensure that a process flow diagram (PFD) exists and is up to date. The process steps in the PFMEA should match those in the PFD for easy cross-reference.
- Recommendation: build the PFMEA in a series of four-hour sessions – the team’s productivity will tend to drop off in longer sessions, and it’s important to keep a positive level of energy through the meeting so the attendees will be motivated for the next session.
- The PFMEA team should consist of both process and product experts. The process experts will help mostly with the Occurrence and Detection scores, and the product experts will help with the Severity scores, which are based on each potential failure’s affect on the customer.
Countermeasures and Follow-Up
The right-hand portion of the PFMEA form is dedicated to countermeasures that are planned to offset high RPN values. Most organizations will select a “cutoff” RPN value in the 100 to 200 range, where any RPN values above those levels must be addressed with countermeasures.
Lastly, the PFMEA should be maintained over time, as more information becomes available and the Severity, Occurrence, and Detection can be fine-tuned based on real experience.
PFMEA and Six Sigma
PFMEA is also used in the Analyze phase of Six Sigma. Countermeasures frequently include error proofing steps that make the creation of a defect impossible. These countermeasures are then monitored in the Control phase to ensure that they remain in place over the long run.
If you are interested in developing a prevention mindset in your company, then start applying PFMEA’s to your processes – this is a proven tool that is well worth the investment.
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