<<< Back to Index
This Month's Article >>>

FMEA Corner 
This Month's Theme is Using Process FMEAs to Improve Process Control Plans
Next month's theme will be FMEA effectiveness surveys

Every month in FMEA Corner, join Carl Carlson, a noted expert in the field of FMEAs and facilitation, as he addresses a different FMEA theme (based on his book Effective FMEAs) and also answers your questions.

Questions and answers are a great way to learn about FMEAs, for both experienced and less experienced FMEA practitioners. Please feel free to ask any question about any aspect of FMEAs. Send your questions to Carl.Carlson@EffectiveFMEAs.com, and your contact information will be kept anonymous. All questions will be answered, even if they are not featured in the FMEA Corner.

 

 

 


What is a Process Control Plan?

A Process Control Plan (PCP) is a "summary description" of the methods used in the manufacturing environment to minimize variation and control product and process characteristics in order to ensure capability and stability of the manufacturing process. It is a structured approach for the design, selection and implementation of control methods, and reactions to problems with the manufacturing and assembly operations when they do occur.

What is the relationship between Process FMEA and PCP?

Process FMEA is an input to the Process Control Plan. Typically, the causes from the Process FMEA become process characteristics in the PCP and the Process Controls from the Process FMEA become control methods in the PCP. There are other inputs to the PCP, including Process Flow Diagram.

How do Process FMEAs improve PCPs?

The Process FMEA is a key contributor to the effectiveness of the Process Control Plan. This linkage between the PFMEA and the PCP goes two ways:

The Process FMEA team includes representation from the manufacturing controls area, in order to ensure that the team considers all needed input from process controls as part of the analysis.

When the Process FMEA team identifies failure modes and associated causes that are not currently detected or controlled in PCPs or associated procedures, the PCP and procedures can be updated and improved, so all failure modes of concern are detected and controlled during manufacturing or assembly. Any changes to PCPs or procedures should be included in the Process FMEA recommended actions.

Why enter PCP improvements in the Recommended Actions column of the FMEA?

As covered in a previous FMEA Corner, the short answer is that everything that the FMEA team believes needs to be done different from what is already planned or in place should go in the Recommended Actions column of the FMEA. The reason for this is that the entries in the Recommended Actions column have additional information to facilitate execution of the task that is recommended, such as the person who is responsible for the execution of the task, the target date when the task should be completed and other project management information.

What does a PCP look like?

The following is a fictitious and simplified example of a Process Control Plan for wheel-spoke installation for the front wheels of a bicycle, excerpted from Chapter 6, Figure 6.33 of the Effective FMEAs book. The “Process Controls” from the Process FMEA are transferred to the “Control Method” column of the PCP, and causes from the Process FMEA identify process characteristics in the PCP. The process controls team fills out the rest of the PCP. Note, in this example, in addition to transferring the process controls to the PCP, the “Recommended Actions” from the Process FMEA that are related to process improvements are also added to the PCP. The columns of the PCP are easily configurable in the Xfmea software.

Process Control Plan

How is Process FMEA synchronized to PCP in Xfmea?

In Xfmea, it is easy to synchronize the Process FMEA to the PCP. The best time to do this is when the Process FMEA is completed up through Recommended Actions. That way both current process controls, as well as improvements that are recommended to the PCP (from the Recommended Actions column), can be included. The resulting PCP will need to be reviewed and updated to ensure it reflects input from the process control team, including sample sizes, etc.

Choose Analyses > Add Control Plan. The Process FMEA will be synced to the PCP.*

[Note: in the following image, one failure mode of the fictitious Process FMEA is excerpted in order to illustrate the synchronization of PFMEA to PCP in Xfmea.]

PFMEA and Control Plan in Xfmea

The process control team can enter the remaining information into the PCP.

Summary

One of the objectives of Process FMEA is to improve the Process Control Plan. Following the suggestions in this article will help Process FMEA teams accomplish this purpose.

* In this example, the operation description in the PCP comes from the function in the PFMEA. Xfmea can be configured to bring in the operation description from the system hierarchy, from the function in the PFMEA or from the Operation Description column in the Process Flow Diagram worksheet.

!FMEA Tip of the Month

The Design FMEA can identify Key Product Characteristics (KPCs). KPCs are inputs to the Process FMEA, and require follow up in the Process Control Plan. They usually have their own approval process.

The Process FMEA can identify Key Control Characteristics (KCCs). Similar to KPCs, they require follow up in the Process Control Plan.
When the Design FMEA team identifies and communicates KPCs to the Process FMEA team, this is one of the linkages between Design and Process FMEAs.

?Something I’ve always wanted to know about FMEAs
The important thing is not to stop questioning. - Albert Einstein

A reader submitted the following question to Carl Carlson. To submit your own question about any aspect of FMEA theory or application, e-mail Carl at Carl.Carlson@EffectiveFMEAs.com.

With pleasure, I attended some of your presentations and tutorials during ARS events in EU over the last decade. Further, your book is helping me to organize FMEA procedures and strategies very well.

Thanks for your contribution to the world on the FMEA aspects and the "Best Practice" way of working!

Reading the ReliaSoft HotWire 178, I again realized that there is one aspect in your FMEA book, and also in the HotWire report, that is not getting much attention. And yes, there are certainly more aspects, but I noticed this one now. It concerns the proposed test duration and sample-size of the test added (or proposed) during the FMEA sessions.

Some comments and questions about this are:

1. The proposed tests should be based on the understanding of the failure mechanism (might be the Cause in the FMEA?), thus a certain understanding of the Physics of Failure MODEL behind the mode/mechanism.

2. The FMEA test proposals would need statistical support on the duration, length, acceleration factors (AF), related AF models, Confidence levels, type of testing (Zero-failure testing or test to failure?) etc.

3. How should we deal with a bundle of different tests or different AF’s that are executed by one’s own company or suppliers? 

Carl: Thank you for your kind words about the book.

Your comments and questions are very thoughtful. I’ll reply to each one of them below.

1. This is true. Ideally, proposed tests are based on an understanding of the underlying failure mechanism. Note, failure mechanism and cause of failure are not the same. This is explained in Chapter 6, pages 129 to 133. Where possible, understanding the Physics of Failure model is useful. Reference "Failure Modes, Mechanisms, and Effects Analysis (FMMEA)," which is discussed in Chapter 15, pages 356 to 358.

2. This is generally true, although the specific test content and statistical requirements need careful attention. There is considerable literature written about test development. I’ll provide a few articles that help explain the concepts.

Determining the Right Sample Size for Your Test: Theory and Application:
http://www.ReliaSoft.com/pubs/2015_RAMS_right_sample_size.pdf

Life Data Analysis:
http://www.weibull.com/basics/lifedata.htm

Quantitative Accelerated Life Testing Data Analysis:
http://www.weibull.com/basics/accelerated.htm

A Blueprint for Implementing a Comprehensive Reliability Engineering Program:
http://www.weibull.com/Articles/RelIntro/Reliability_Testing.htm

3. Each test requires its own set of parameters and planning. If the individual tests are developed with correct assumptions and techniques, they can be executed using Design Verification Plan & Report. An example follows:
http://www.ReliaSoft.com/pubs/xfmea_dvpr.pdf


About the Author

Carl S. CarlsonCarl S. Carlson is a consultant and instructor in the areas of FMEA, reliability program planning and other reliability engineering disciplines. He has 30 years of experience in reliability testing, engineering and management positions, and is currently supporting clients of ReliaSoft Corporation with reliability and FMEA training and consulting. Previous to ReliaSoft, he worked at General Motors, most recently senior manager for the Advanced Reliability Group. His responsibilities included FMEAs for North American operations, developing and implementing advanced reliability methods and managing teams of reliability engineers. Previous to General Motors, he worked as a Research and Development Engineer for Litton Systems, Inertial Navigation Division. Mr. Carlson co-chaired the cross-industry team that developed the commercial FMEA standard (SAE J1739, 2002 version), participated in the development of SAE JA 1000/1 Reliability Program Standard Implementation Guide, served for five years as Vice Chair for the SAE's G-11 Reliability Division and was a four-year member of the Reliability and Maintainability Symposium (RAMS) Advisory Board. He holds a B.S. in Mechanical Engineering from the University of Michigan and completed the 2-course Reliability Engineering sequence from the University of Maryland's Masters in Reliability Engineering program. He is a Senior Member of ASQ and a Certified Reliability Engineer.

Effective FMEAsMaterial for the FMEA tips, problems and solutions is excerpted from the book Effective FMEAs, published by John Wiley & Sons, ©2012. Information about the book Effective FMEAs, along with useful FMEA aids, links and checklists can be found on www.effectivefmeas.com.