Using PFMEA to Recognize Opportunities for Layered Process Audits

Does your organization use process failure modes and effects analysis (PFMEA) on a routine basis to identify potential failures in product design, manufacturing or assembly processes? If so, this practice could do double duty by also serving as an effective technique for identifying at-risk processes on which to focus your layered process audits (LPAs).

A Closer Look at the PFMEA Method

For those unfamiliar with the PFMEA method, the American Society for Quality defines failure modes as the ways, or modes, in which something could potentially fail. Failures are any errors or defects, especially those that impact the customer, and they can be either potential or actual failures. Next, the term “effects analysis” refers to studying the consequences of those failures. Developed in the 1940s by the U.S. military, PFMEA was later refined by the aerospace and automotive industries. Ideally, PFMEA begins during the conceptual stages of design and then moves through the entire life of the product.

Calculating Risk Priorities

Failures identified in a PFMEA exercise are typically ranked or prioritized by:

• seriousness of their consequences (Severity)
• how frequently they happen (Occurrence)
• how easily they can be discovered (Detection)

To calculate a risk priority number for a failure, take the product of the estimates of severity, occurrence, and detection (S x O x D). In general, higher risk priority numbers indicate more serious consequences, such as a complete product redesign or a parts recall. The risk priority number provides a means of ranking failure modes in the order of their relative importance.

The goal of a PFMEA exercise is to assess risk and prioritize an appropriate course of action. With a standard PFMEA system, engineers can quickly decide which failure risk to tackle first.

Using PFMEAs to Strengthen Your LPA System

Use PFMEA results as a guideline for where to start implementing layered process audits within your plant. For example, your LPA checklist could include specific questions that require the auditor to verify that controls are in place for PFMEA items with the highest risk priority numbers. Paying close attention to your greatest potential risks is a smart business practice that will pay dividends by increasing overall quality in your organization.

A well-designed LPA checklist based on PFMEA helps bring together multiple layers of management onto the shop floor, which promotes an organization-wide culture of quality. By utilizing randomized audit scheduling, employees from various levels across the plant are working together, which provides the benefit of extending the culture horizontally as well as vertically.

In addition to the results of PFMEA, other ideas for focusing on risk to improve your LPAs could include information gathered from:

• Customer complaints
• First-time through data, such as scrap reports
• Results of quality system audits, such as ISO 9001, ISO/TS 16949, or AS9100

When LPAs are conducted daily and are completed by all layers of management, it’s more likely that process errors will be found early. If your LPA checksheet questions are well developed and risks are carefully identified through robust methods such as PFMEA, your LPAs will proactively minimize process variation. The result will be evident in process, product and financial metrics, such as first-time quality, parts per million defects, control charts, productivity measures, overall equipment effectiveness, as well as scrap and rework cost.

Isn’t it time for your organization to get more from PFMEA? If so, consider using this method to improve your LPA system.