To Ensure Quality, Connect PFMEA, Control Plans and Testing

To develop and manufacture new products, the automotive industry usually employs advanced product quality planning (APQP).

APQP is a structured framework to ensure the quality and reliability of a product from its conceptualization through its production and delivery. Integral to the product development process, APQP encompasses various phases, including planning, product design and development, process design and development, product and process validation, feedback, assessment, and corrective actions.

This methodology emphasizes early identification of potential issues, robust design practices, and rigorous testing to meet customer requirements and industry standards. By integrating quality planning into every stage of product development, APQP helps organizations minimize risks, reduce costs, and successfully launch high-quality products that meet or exceed customer expectations. This comprehensive approach fosters cross-functional collaboration and continuous improvement, enhancing product performance and customer satisfaction.

Understanding PFMEA

Process failure modes and effects analysis (PFMEA) is a systematic method for evaluating manufacturing processes. It is a vital tool in ensuring product quality and reliability. This tool helps prioritize which failure modes are of the highest risk and require the most attention to ensure product quality and reliability. By understanding and mitigating these risks, manufacturers can significantly reduce defects, improve customer satisfaction, and lower costs associated with rework and scrap.

PFMEA is an integral part of developing the assembly line. It focuses on the critical aspects during the production line setup, transitioning from prototype parts delivery to full-scale production. Just as design failure modes and effects analysis (DFMEA) does for product design, PFMEA ensures that the prototype parts from the assembly line meet quality expectations, thereby maturing the manufacturing processes.

While this article does not aim to provide an exhaustive guide on PFMEA, it does aim to demonstrate the interconnectedness of various elements in setting up manufacturing processes.

We begin by mapping out the manufacturing process and identifying each step. This includes detailing inputs, outputs and critical characteristics at every stage. For each step in the process, brainstorm all possible ways a failure could occur. These are the potential failure modes.

Next, we will rate each failure mode on a scale from 1 to 10 according to its severity, likelihood and detectability. This step involves understanding the impact of failures on quality, safety and performance. Failures will have a range of consequences (severity) and a probability of occurrence (likelihood). In addition, we want to assess the ability of our controls to detect the failure mode before it reaches the customer. The more detectable the failure, the lower the rating.

Finally, we calculate a risk priority number (RPN) for each failure mode by multiplying their severity, likelihood and detectability ratings. This number helps prioritize which failure modes need the most attention.

For example, one failure mode could be stripping a screw during assembly. We might rate the severity of this problem as 1, if it can easily be repaired. We might rate the probability of this problem occurring as 1, based on historical records and our well-trained employees. If we use a torque-controlled tool to install the screw, a stripped fastener would be relatively easy to detect, so we would rate detectability as 1.

The RPN for this failure mode would therefore be 1 (1 x 1 x 1). Given such a low RPN score, we would deem the proposed controls on this portion of the manufacturing line appropriate.

Develop and implement action plans to mitigate or eliminate the risks for high-priority failure modes. This might involve process changes (control plan changes), additional controls, or design modifications. Sometimes, we think we know, but we are not certain. That’s where production validation testing (PVT) comes in.

The PFMEA and the control plans are living documents that should be revisited regularly, especially when the process changes or new information about failures becomes available.

Understanding the Control Plan

It has been a long time since the days of setting up the assembly line after the product design was complete. These days, the assembly line is typically developed hand in hand with the product; ideally, we will use this assembly line to build our prototype products. This way, we learn about the product and things to help us set up the assembly line.

A control plan is a comprehensive document used in manufacturing to ensure that processes remain consistent and quality standards are met. It is a guideline for maintaining and controlling process and product quality by outlining the specific controls, checks and measures needed to monitor and manage each process step. The control plan is an essential part of the quality management system and is closely linked to tools like PFMEA.

A control plan consists of the following elements:

• Process steps: This is a detailed description of each process step or operation. This includes the specific tasks involved and their sequence.
• Process parameters: These are the key parameters that must be controlled to ensure the process operates within specified limits. These parameters are critical to the quality and consistency of the output.
• Control methods: These are the methods used to monitor and control the process parameters. This can include inspection, testing and measurement techniques.
• Measurement systems. These are the tools and equipment for measuring process parameters and product characteristics. These systems ensure that the data collected is accurate and reliable.
• Control limits: These are the upper and lower limits of the process parameters. Staying within these limits ensures the process remains stable and produces quality products.
• Frequency of monitoring: How often are the process parameters and product characteristics measured? How will they be measured? This can vary depending on the importance of the parameter and the stability of the process.
• Reaction plan: These are the actions to be taken if a process parameter or product characteristic goes out of control. This includes steps to bring the process back within limits and prevent recurrence.
• Responsibility: This is a list of the personnel responsible for monitoring, measuring and controlling the process. Clear assignment of responsibility ensures accountability and effective management of the control plan.
• Documentation and records: Keep records of all monitoring and control activities. This documentation is crucial for traceability, audits and continuous improvement.

Control plans are not a one-off event. They are developed while developing the assembly line and processes. Early assemblies from the line will often be used for product testing and exploration. This learning will aid in developing both the product and the line.

The first control plan you develop will be for prototype production. These parts are used during the development of new products or processes. The plan should focus on controlling and validating the early stages of development.

The pre-launch control plan is developed for the line before full-scale production begins. It ensures that the process can consistently produce quality products.

The production control plan is used during full-scale production. It maintains ongoing control of the process and ensures consistent product quality.

Connect the PFMEA with Control Plans

Connecting the three levels of control plans—prototype, pre-launch and production—with the PFMEA is a strategic approach to quality management in product development and manufacturing. Each control plan level is informed by the insights and priorities established through PFMEA, ensuring a systematic transition from concept to full-scale production and emphasizing risk management and quality control.

In the Prototype phase, PFMEA is critical for identifying potential failure modes that could affect the product and the production process at this early stage. Since prototypes are primarily about testing design assumptions and process capabilities, PFMEA helps pinpoint where failures are most likely to occur, their potential impact, and their detectability.

The prototype control plan then uses this information to focus on these critical areas. It includes specific checks, tests and inspections designed to validate the reliability of the design and the effectiveness of proposed manufacturing processes against the identified risks. Controls at this stage are often stringent, but flexible, allowing for rapid response to the findings.

As the product moves into the pre-launch phase, the PFMEA is updated with data gathered from the prototype phase. This updated analysis provides a refined view of potential risks more representative of real production conditions.

The pre-launch control plan incorporates these insights to establish more defined control measures and process validations. It ensures that all systems, from tooling to operator training, can consistently produce the product to specifications. This control plan bridges the experimental nature of prototypes and the rigors of full production, focusing on scalability and process stability.

By the time full-scale production begins, PFMEA has provided a comprehensive risk assessment throughout the development process, including insights gained during pre-launch. The production control plan is the most detailed and stringent, designed to ensure continuous monitoring and control of the manufacturing process.

It systematically applies controls to critical process points identified by the PFMEA, employing tools such as statistical process control, regular audits and ongoing process verification. This plan aims to maintain quality and process consistency, reduce variability, and consistently ensure that the product meets customer requirements.

Across all phases, the dynamic updating of the PFMEA as new data becomes available ensures that the control plans are relevant and practical. This structured approach mitigates risks and enhances product reliability and manufacturing efficiency by closely aligning the risk management efforts with operational controls throughout the product life cycle.

Development Testing

The development team will need parts to learn about what matters in the product. Sometimes, these parts will be built entirely from prototyping equipment and processes. Ideally, our prototype parts will have some connection to the assembly line and its growth in capability. Admittedly, the first products produced may be largely off prototyping processes and tools. Each of these testing phases will also evaluate the production processes defined by the control plan.

Engineering testing is used to understand the product’s operating space. Developers and customers will use these early mock-ups and parts to evaluate the proposed design concept. These parts can be geometric attributes or performance evaluations. They are often only partially from a formal assembly line, for example, a pick-and-place machine for the PCB with an enclosure from a 3D printer. Ideally, the parts used will not have any manufacturing-induced defects. The objective is to find design problems and not have to sort out what has resulted from poor manufacturing. Manufacturing failures take time to understand, which takes away time from design vetting.

Next comes design validation testing. To solidify the proposed design, we will have a few prototype parts that are increasingly sophisticated and capable. Specifically, incremental features, feature refinement and the ability to endure the expected and anticipated physical environment. As these parts increase in competency, the testing will become more rigorous and include stressful environmental exposure.

Production validation testing (PVT) is the final phase before full-scale production. It involves rigorous testing of the production process and product to validate that all systems are functioning correctly and that the product meets all specified requirements.

PVT ensures the following:

• Validation of production process: Confirming that manufacturing can produce products that meet quality standards.
• Verification of control plan effectiveness: Ensuring that the controls defined in the control plan effectively maintain process stability and product quality.
• Identification of remaining issues: Detect any last-minute issues not identified in earlier phases and ensure they are resolved before full-scale production.

PVT provides a final check to ensure that the insights from PFMEA and the measures outlined in the control plan are effectively implemented and that the process is ready for consistent, high-quality production.

Integrating PFMEA, Control Plan and PVT

By integrating PFMEA, the control plan and testing, manufacturers can create a robust quality management system that ensures process reliability, reduces failure risk, and delivers consistent product quality. This integrated approach promotes a proactive culture of continuous improvement and risk management.

PFMEA to control plan: Use the findings from the PFMEA to develop the control plan. The control plan addresses the high-priority risks identified in the PFMEA by implementing specific controls and monitoring activities.

Control plan implementation: Implement the control plan during the initial production runs. This involves training personnel, setting up measurement systems, and establishing control limits and reaction plans.

PVT phase: Conduct testing to evaluate and improve the competency of the production process and ensure that the control plan is working as intended. Any discrepancies found during testing are used to update the control plan and make necessary adjustments to the process.

After PVT and product launch, monitor the process and use the control plan as a living document. Regularly review and update the PFMEA and control plan based on production data, feedback, and any process or product design changes.

Real-World Example

I once worked on a project to develop a new vehicle instrument cluster, as well as the cluster’s assembly line. During the PFMEA, one of the failure modes that was uncovered and prioritized was the bubbling of the overlay due to repeated heat on the light guide. This bubbling would ultimately impede the movement of the pointer. A pressure-sensitive adhesive was used to bond the overlay to the light guide. A press applied even pressure to ensure the overlay bonded to the light guide.

The PFMEA evoked the possibility of bubbling. To assess this perceived failure mode, the assembly was subjected to long-term thermal cycling as part of the PVT. At the end of the test, an evaluation was performed, and we found that adhesion of the overlay to the light guide was, indeed, compromised. Subsequently, the overlay process was changed to include a weighted wheel rolled over the overlay, ensuring a better adhesion to the light guide.

As a recap, the pre-launch control plan described the actions to affix the overlay to the light guide on the assembly line. The line produced assemblies at the expected rate, which were then used for PVT. Analysis of the assemblies indicated that the manufacturing process was not likely to produce the desired results. The control plan, work instructions, and tools for this process step were altered to remove the failure mode.

Editor’s note: The author of numerous books on project management, Jon has held engineering and management positions at Volvo Trucks, PACCAR and other companies. Email Jon at jon.quigley@valuetransform.com