Process Failure Mode Effects Analysis (PFMEA)
Posted: 09/30/2010 12:00:00 AM EDT
A Process Failure Mode Effects Analysis (PFMEA) is a structured analytical tool used by an organization, business unit, or cross-functional team to identify and evaluate the potential failures of a process. PFMEA helps to establish the impact of the failure, and identify and prioritize the action items with the goal of alleviating risk. It is a living document that should be initiated prior to process of production and maintained through the life cycle of the product.
PFMEA evaluates each process step and assigns a score on a scale of 1 to 10 for the following variables:
- Severity — Assesses the impact of the failure mode (the error in the process), with 1 representing the least safety concern and 10 representing the most dangerous safety concern. In most cases, processes with severity scores exceeding 8 may require a fault tree analysis, which estimates the probability of the failure mode by breaking it down into further sub-elements.
- Occurrence — Assesses the chance of a failure happening, with 1 representing the lowest occurrence and 10 representing the highest occurrence. For example, a score of 1 may be assigned to a failure that happens once in every 5 years, while a score of 10 may be assigned to a failure that occurs once per hour, once per minute, etc.
- Detection — Assesses the chance of a failure being detected, with 1 representing the highest chance of detection and 10 representing the lowest chance of detection.
- RPN — Risk priority number = severity X occurrence X detection. By rule of thumb, any RPN value exceeding 80 requires a corrective action. The corrective action ideally leads to a lower RPN number.
How to Complete a Process FMEA
A simple explanation of how to complete a process FMEA follows below:
- Form a cross-functional team of process owners and operations support personnel with a team leader.
- Have the team leader define the scope, goals and timeline of completing the FMEA.
- As a group, complete a detailed process map.
- Transfer the process map for the steps of the FMEA process.
- Assign severity, occurrence and detection scores to each process step as a team.
- Based on the RPN value, identify required corrective actions for each process step.
- Complete a Responsible, Accountable, Consulted, and Informed (RACI) chart for the corrective actions.
- Have the team leader on a periodic basis track the corrective action and update the FMEA.
- Have the team leader also track process changes, design changes, and other critical discoveries that would qualify and update the FMEA.
- Ensure that the team leader schedules periodic meetings to review the FMEA (based on process performance, a quarterly review may be an option).
- FMEAs should never be filled out by only one person; it needs to be filled out by the team that owns the process. Buy-in from every team member is required to prevent the FMEA from becoming an afterthought.
- It is a good idea to spend the time to identify which process really needs an FMEA. Conducting too many FMEAs on non-critical processes will consume resources without returns.
- Once the decision is made to pursue an FMEA, it is critical to include people in the team who have extensive experience with the process and who can share historical data that will prove invaluable while assigning severity, occurrence, and detection scores. This step will help to provide a more accurate representation of the immediate to-dos and wish list items the team needs to complete from a risk standpoint to quality and the customer.
- It is extremely critical to spend time at the “gemba” or the actual spot where the process takes place, as it is useful to understand in detail each and every process and sub-process that will be part of the FMEA.
- As pre-work for the FMEA, it is wise to have the data for the field failures (failures of the product at a customer location) available with some preliminary analysis completed. Some items, like a Pareto chart highlighting what have been the failure modes for the field failures, can be powerful pieces of information that can add to the validity of the FMEA.
- A no brainer, any time there is a change to the process, spec, design, material, etc., the FMEA will need to be updated, and a new RPN value will need to be calculated.
- In my opinion, a fixed time interval for reviewing the FMEA of the process must be assigned, with the flexibility to revisit upon a change. This must be a mandatory part of the organization's engineering change management system.
I welcome all comments on this article.
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