What if you could systematically prevent manufacturing failures from occurring? What if you could fix the highest-risk processes before they cause a problem? This is the promise of Process Failure Mode Effects Analysis (PFMEA).
The following article will describe this powerful analytical method and introduce you to Pro QC’s related suite of services.
What is PFMEA?
“Process Failure Mode Effects Analysis” is an analytical technique used by an organization’s business unit or cross-functional team to identify and evaluate the potential failure modes of a process and their associated causes.
In its most rigorous form, an FMEA is a summary of the team’s thoughts including an analysis of items that could go wrong based on experience as a process is developed.
- PFMEA provides a framework for identifying and prioritizing the action for the items having a risk factor to minimize the risk.
- PFMEA helps us to establish the impact of failure, the result is a living document detailing risk in a ranked, actionable manner.
To illustrate with a practical example, think of the many ways a ballpoint pen may fail:
- It may run out of ink.
- The roller point may get stuck in place.
- The ink may stop flowing.
- The tip may not project and retract
- The cap may not fit properly on the tip or end.
Each of these is called a failure mode and each one varies in severity, occurrence, and detectability
A PFMEA will identify each of these many potential failure modes, rank them in terms of impact, and identify ways to eliminate or reduce the risk. The pen might get a fatter ink well, a better fitting cap, or a reformulated ink to prevent crust and jams.
Apply this same logic to a highly complex manufacturing process, follow the PFMEA tool, and you will have identified and mitigated the highest-priority failure modes before they led to defects. For example,
Consider a stamping process that is intended to leave a hexagonal imprint in a plastic component. Among many other failure modes:
- The bit may be incorrect.
- It may wear out over time, leading to a drift in the dimensions of the hexagon.
- The bit may come loose and be stuck in the plastic. It may drift in disposition and stamp too high or too low.
- It may heat up during production and leave plastic strings behind.
A thorough PFMEA process will identify all these modes, decide on the highest risk ones, and systematically reduce those risks by modifying the process.
When to use PFMEA?
Performing a PFMEA is recommended under three conditions:
- Modification to an existing process
- Introduction of new technology, equipment, or process steps to the production
- Relocation of a process to a new facility
Advantages of PFMEA
Manufacturers across many industries can benefit from this analytical tool.
PFMEA’s main benefits
- Its preventive nature; instead of reacting to failures after the fact, such as by inspection or (more seriously) customer complaints, a cross-functional team can proactively address the system factors that lead to defects. Team members with close knowledge of the process can follow this tool to devise unexpected ways to error-proof the process and even make certain defects impossible. This results in reduced scrap rates, better safety, and a wider understanding and control of process variables.
- PFMEA is a risk-based process. The RPN displays semi-quantitatively which failure mode needs to be addressed first.
- PFMEA identifies the safety concerns of machine operators, highlights the customer impact of failure modes, and provides data to the design team on changes that may be needed in the design.
Quality Objectives of Process FMEA:
- PROCESS IMPROVEMENTS: The FMEA drives process improvements as the primary objective with an emphasis on error/mistake-proofing solutions.
- HIGH-RISK FAILURE MODES The FMEA addresses all high-risk failure modes, as identified by the FMEA team, with executable action plans all other failure modes are considered.
- CONTROL PLANS: The pre-launch and production control plans consider the failure modes from the process FMEA
- INTEGRATION: The FMEA is integrated and consistent with the process flow diagram and process control plan, the Process FMEA considers the Design FMEA, if available as part of its Analysis
- LESSONS LEARNED: The FMEA considers all major “lessons learned” (such as high warranty, campaigns, non-conforming, product, customer complaints, etc.) as input to failure mode identification.
- SPECIAL OR KEY CHARACTERISTICS: The FMEA Identifies appropriate key characteristic parameters as an input to the key characteristic selection process, if applicable.
- TIMING: The FMEA is completed during the “window of opportunity” where it could most efficiently impact the design of a product or process.
- TEAM: The right people participate as a part of the FMEA team throughout the analysis and are adequately trained in FMEA methods. As appropriate, a facilitator should be used.
- DOCUMENTATION: The FMEA document is filled out “by the book” including “actions taken” and new RPN values
- TIME USAGE: Effective and efficient time spent by the FMEA team with a value-based result. This assumes recommended actions are identified as required and actions are Implemented.
Steps of PFMEA
PFMEA follows these general steps, with modifications for industry and type of process:
- Describe the name and functions of the process.
In this step team members will write up the general process features they are working with for shared understanding and good documentation.
- Describe all requirements (and measurements involved) for the process function.
To properly describe a failure, analysts need to know the desired state against which a failure is defined. Each requirement in a manufacturing process must be measurable so that failures are identified on a quantitative basis.
- Identify each failure mode
This process may involve brainstorming and should always include experts with close and thorough knowledge of the process. Failure modes will be pinpointed and may be described and categorized with terms such as full, partial, intermittent, and unintentional.
- Effects of failure
Document the potential effects of the failure. For example, a medical device used at home such as a covid test may give a false positive or a false negative. Always note whether the customer affected is internal or external to the company.
- Potential Causes / Mechanisms of Failure
Analysts define causes for each failure, using tools such as a fishbone diagram to work backward. A potential failure mode of a machine may be traced to numerous causes including software, training, age, drift, etc.
- Current process controls
For each failure mode, identify current process controls that address this failure mode. Process controls might include tests, inspections and error-proofing that detect the failure, contain it, or prevent it from occurring at all.
- Rank severity 1-10
A process failure of low severity may result in production delays. A higher-severity failure might result in a large amount of scrapped material or unsafe or halted production. Severity is one of three factors that feed into the risk priority number.
- Occurrence Ranking
Occurrence is the second of three factors used in calculating the risk score and indicates the likelihood of the failure. Estimating the likelihood of a known or surmised failure is difficult. Some approaches include using data from similar technology, trial runs or the lack of data itself. The likelihood may be expressed as failures per units produced or with qualitative language such as “infrequent,” “occasional,” or “almost never.” This ranking should be given a score for each failure mode so that it can feed into the risk priority number (explained below).
- Detection/Detectability Rankings
Detection/detectability refers to how likely a failure mode is to be discovered during the process. For example, visual inspection software may scan 100% of the output of a manufacturing station and be assigned a moderate detectability rating. A machine that error-proofs against this failure mode, making a discrepant part impossible, will be assigned a better detection score. Visual inspection by the human eye of high numbers of parts will have a poorer detection score. Detectability is the third of three scores that determine the risk priority number.
- Risk Priority Number (RPN)
The RPN is the product of the scores for severity, occurrence and detectability. This allows the ranking of failure modes by overall risk. In general, the failure mode with the highest RPN should be addressed first and other failure modes prioritized thereafter. There are no established RPN cutoffs for taking action on a failure mode.
- Recommended Actions
Completing recommended actions is the target of this whole PFMEA exercise. An action should be understandable and actionable to an assignee outside the PFMEA team. Ideally, it is addressed toward a factor in the RPN, such as reducing failure mode severity or increasing failure mode detectability in a process.
- Responsibility and Target Completion Date
Assign who does what by when using solid project management practices.
- Actions Taken and Completion Date
Document the completed actions and refer to tests and reports that demonstrate improved scores.
- Re-Rank RPN
Feed the new severity, likelihood and detectability scores into the RPN to calculate each new failure mode risk. If the actions were effective, each failure mode’s risk is reduced, and the highest-risk failure modes have been mitigated.
Pro QC is a Global Quality Assurance provider. We help improve manufacturing quality performance with tailor-made solutions.
The PFMEA is a powerful tool and involves much more than filling out a spreadsheet. Done right, it leads to breakthrough reductions in risk for a new or modified process. Each PFMEA is different, and each one is the result of a hands-on project team using proven tools.
Based on your needs, we will partner with you in the PFMEA, with the outcome of driving down defects and delays and establishing a framework for effective process control and product quality.
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