“I didn’t fail the test, I just found 100 ways to do it wrong.” Benjamin Franklin
Properly done, Design FMEAs should improve product designs and test plans. This article describes how DFMEAs can be used to improve testing and analysis, which are embodied in the Design Verification Plan (DVP).
What is a Design Verification Plan?
A Design Verification Plan (DVP) documents the strategy that will be used to verify and ensure that a product or system meets its design specifications and other requirements. Each of the product requirements are listed in the DVP along with the physical test or analytical method that will determine if the requirement is met.
What is the relationship between Design FMEA and DVP?
The System or Design FMEA is a key contributor to the effectiveness of the Design Verification Plan. The linkage between the FMEA and the DVP plan goes two ways. In the first, the FMEA team includes representation from the testing department, in order to ensure that the team considers all needed input from testing as part of the analysis. In the second, the FMEA team ensures that the Design Verification Plan is impacted in a positive way by the results of the FMEA.
How do FMEAs improve DVPs?
Specifically, when the FMEA team identifies failure modes and associated causes that are not currently well detected in test plans or procedures, the test plans and procedures should be updated and improved so all failure modes / causes of concern are detected during testing. Any changes to test procedures or test plans should be identified as FMEA recommended actions.
Here is an example DFMEA on a bicycle hand brake subsystem
Can you identify the Recommended Actions that improve the test plan for the hand brake?
Why enter DVP improvements in the Recommended Actions column of the FMEA?
The short answer is 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 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 DVP look like?
The following is a fictitious and simplified example of a Design Verification Plan for Hand Brake Subsystem, excerpted from chapter 6, Figure 6.32 of the book Effective FMEAs. The “Design Controls” from the Design FMEA are transferred to the “Test/Specification Method” column of the Design Verification Plan. The test/verification team fills out the rest of the DVP. Note, in this example, in addition to transferring the design controls to the DVP, the Design FMEA recommended actions that are related to test improvements are also added to the DVP.
Can you identify the Hand Brake Test/Specification Methods that are improved based on the corresponding Hand Brake DFMEA?
Some FMEA practitioners enter suggested tests in the Recommended Actions of the Design FMEA. This is not a good practice. The best practice is to recommend modification to the DVP. For example, if the Design FMEA team wishes to add a new cable strength test, the recommended action in the FMEA would be, “add cable strength test to DVP.” If the FMEA team enters “conduct cable strength test” to the FMEA Recommended Actions, both the FMEA and the DVP will be tracking the accomplishment of the cable strength test, which is double tracking.
What risk factors drive changes to the DVP?
In general, when the current design controls (such as specific tests) do not adequately detect a higher risk failure mode / cause, the FMEA team should recommend additions or modifications to the DVP in order to improve the detection capability of the failure mode / cause.
One of the objectives of Design FMEA is to improve the Design Verification Plan. Following the suggestions in this article will help FMEA teams accomplish this purpose.
Since FMEA is a living document, I always thought that reviewing of it should be as simple as possible. If the FMEA document is maintained only in a paper form, is it permissible to update this document without saving copies of last version? Or should we have a story of changes? What is the way it is usually done?
The policy for maintaining FMEA records is up to each company, and should be well thought out. Since FMEAs are legal documents, the policy for updating and retaining FMEAs should be consistent with company legal guidelines. Most companies maintain records of FMEA versions once the original FMEA has been completed through Recommended Actions and Actions Taken. Each subsequent FMEA version has its own unique identification number. This provides a record of changes without adding unduly to the burden of maintaining records.
Properly done, Process FMEAs should improve process designs and process control plans. This article describes how PFMEAs can be used to improve manufacturing and assembly processes.