Process Failure Modes and Effects Analysis (PFMEA) tables can be a powerful tool to identify potential failures in a process, and to prioritize which failures should be improved first. However, the effort required to complete a PFMEA can take many hours, which costs money.
Based on our experiences with PFMEAs, here are a list of tips and tricks for making them more effective and efficient. We will break the information into three categories: Forms and Templates, Efficiency, and Effectiveness.
Forms and Templates
- Break out the process control column from the detection control column. Sometimes they are contained in the same column, and the teams often focus too much on the detection and forget to talk about prevention activities in place. We would recommend having the columns in this order: Cause of failure mode, process controls, occurrence score, detection controls, then detection score.
- Create a new column for Severity x Occurrence ranking, to identify internal rework cost issues (high impact and it happens frequently, regardless if we detect the failure in-house). Typically, teams rank risks by RPN only, but that is only assessing the risk of external customer escapes.
- Consider adding another category for cause category, based on the fishbone diagram (Machines/tools/equipment, Methods/Processes, People/Personnel, Materials, Environment, etc). The PFMEA team can summarize the type of causes, and that information can be summarized and reported to identify systemic or higher level issues. If machines is the highest category, then the team should identify a project to look at machine preventative maintenance or equipment calibration updates.
Efficiency (complete PFMEA faster with fewer people)
- “The more; the merrier” is not a good approach for conducting a PFMEA. Instead of having a larger team involved in the event just in case certain team members might be needed, invite only the core team, and have others as “experts on call”. When the team runs into an issue, highlight the cell by color to identify who needs to answer the question. Then bring in each expert as needed, and review the questions for them all at once.
- Before the PFMEA session begins, enter the failure mode and process steps into the form, so the team doesn’t waste time watching the facilitator fill it out on the screen. Where do you get the failure modes? One suggestion is to schedule time with the team to brainstorm these failures using sticky notes and a whiteboard, then between meetings, enter them into the form.
- Don’t let the team get hung up on one point differences in scores. Instead, consider flipping a coin, have someone make the tie-breaker decision, vote using majority rules with the team members, or always select the highest score (round up).
|Speaking of failure modes, this coin flip controversy cost Pittsburgh the game.|
- Before diving too deep into the exercise, scope the overall effort ahead of time. Consider evaluating Key Characteristics, Critical to Quality (CTQ) or Most Important Requirements (MIRs) only, instead of trying to assess every requirement. The idea is to start with the most important risks, so the biggest risks get identified as early as possible. Often times, the teams start to dwindle over time, so address the biggest issues when the momentum and excitement is highest. Another way to minimize the size of the FMEA is to focus on elements or requirements that are NUD’s (new, unique or difficult), instead of spending time filling out the form on things that team has been successful with already, and would be considered low risk.
- Start with listing all the failure modes, then group the failure modes together and score them all. This helps align the team with the proper severity score. Next, list all the detection controls and detection scores (that align with the failure modes). Next, brainstorm the causes of the failure modes, then list the process controls and then score the occurrences (to help align the occurrence scores).
- Keep sessions between 2-4 hours long. Over 4 hours can be tough for the team members to keep attention. Less than 2 hours is inefficient, since it takes some time to get setup and calibrated, and requires scheduling many more sessions, which increases the chance of people not attending.
- To keep the team from digging deep into solutions during the scoring, add notes and ideas into the Improvement Actions column, so the team can move on to the next item.
- Keep track of attendance and hours for each PFMEA session, so actual costs can be captured. There is often overestimates of PFMEA cost, so this data will help dispel myths. Ideally, your company will begin to create estimates for how must each PFMEA will cost based on size and magnitude of the effort.
Effectiveness (Identify more potential failures and causes, and make analysis more complete)
- Bring in the physical product, forms, software (view on screen), etc that is being discussed, so the team can physically see the process. If possible, perform the PFMEA right in the process area, so observations and questions can be answered quickly by the right people.
- Align the failure modes with defect categories in your quality system, and align your process steps with process step names in your business system or documentation.
- Fill out as much detail as possible into each column, such as document and reference numbers. Often times, what was written down was a summary of the discussion, and teams struggle to remember what the statements mean when the read it days later, and it helps others not involved in the sessions to understand what was discussed.
|We prefer this level of detail, not just “friction” or “excess weight”|
- After actions are implemented, in order to reduce occurrence scores, there must be a process control (training, fixture, mistake proof device, procedure change, etc) implemented. To reduce detection scores, there must be an inspection or test implemented.
- Spend time calibrating the team on the scoring tables at the beginning of each PFMEA session (especially the first session). Don’t speed through this process, or you will struggle to keep the team aligned.
- Provide scoring handouts for each team member, or post the scoring on the wall. Allow extra time to go through the first couple lines slowly with the team.
- A regular review of the PFMEA should be setup as a recurring meeting (suggest monthly or quarterly), to force the teams to get together and update the PFMEA.
- Don’t use a cut-off RPN score criteria for actions, instead work on the top risks only. Teams can be biased in their scoring when trying to stay below a value (such as 150 or 100) that require actions. Some processes may have many actions over that threshold, but the team cannot address all of them at once. However, AS 9100 requires that the criteria for how the team decides to take action should be defined on the PFMEA. We would recommend taking action on the top 5 RPNs, regardless of score.
- Customize the PFMEA ranking tables to align with your business, to minimize scoring differences between teams. Especially if conducting a PFMEA in a service or transactional process, or an industry other than manufacturing (where PFMEAs were developed, and most scoring tables were designed for).
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