Identifying Design Inherent Failure Modes with An Accelerated Method
The FMVT® process is an accelerated method
of identifying design inherent failure modes. This case study was
conducted in order to demonstrate the amount and type of information
that can be gained from testing the ECG unit on an FMVT® machine in a
short amount of time.
In this case study, the FMVT® process produced four failure modes - two hard and two soft.
Testing Time
The testing time to conduct an FMVT® can be expressed in three parts: preparation, testing and post analysis.
Preparation
The preparation required to run an FMVT® is as follows:
1. Identification of stress sources.
2. Determination of operational checks.
3. Fixture and instrumentation construction.
4. Staging.
Typically the preparation stage takes around two weeks to complete. Steps 1, 2 and 3 can be completed before the prototype is available.
Testing
Conducting an FMVT® typically takes one to two days. The test is
intense and requires the participation of a testing engineer, a failure
analyst and a design responsible engineer. This testing time is
significantly shorter than comparable, traditional durability tests.
Post Analysis
The post analysis is conducted to follow up on any failure modes whose
root cause was not determined during the day of test. A thorough
tear-down of the module is also conducted.
Post analysis typically takes two weeks.
Preparation
This section details the preparations made for the testing.
Sample Selection
The samples were selected and supplied by the client. Three samples
were provided with one sample tested for this particular test.
Operational Checks
To check the operation of the ECG, the unit was visually inspected
throughout the testing. The operation of the unit was checked by
conducting an ECG (pressing the ECG button) and power up/down tests.
The unit's display was also monitored for any errors or power status
changes (battery vs. AC).
Fixturing
The fixture held one ECG unit on a flat surface attached to three pod
heads. The ECG unit was fastened to the surface through the three
threaded inserts in the bottom side of the ECG unit. These stripped out
during the test and the ECG unit was then strapped down to the flat
surface.
Staging
During setup the sample tested was verified for functionality. The unit
was found to be in good working order, completed its self check
properly and printed an ECG properly.
Testing
Throughout the FMVT® procedure every event is recorded on the Event
Tracking Log in the "FMVT® ECG check sheets" Excel spread sheet (see Flow Chart).
Failure Analysis
Detailed failure analysis is key to making the FMVT® process effective.
With a traditional reliability test, the test results would be given to
a reliability engineer for statistical analysis. With FMVT®, a body of
statistical data is not generated for the reliability engineer to
analyze. However, a group of failure modes is generated for the failure
analyst to examine and determine the root cause. The final results of
an FMVT® are the root cause of the failures and their ranking. Section
4 detailed the ranking while this section will detail the failure
analysis and root cause determination.
Documentation
At each step of testing, the ECG unit was operated to evaluate performance.
Conclusion
The FMVT® Machine, with a broad frequency range, was able to activate
both mechanical and electrical related failure modes in the ECG unit
test sample. Conventional "Air Hammer" vibration machines typically
produce a higher frequency range, activating only electronic related
failure modes.
By producing a broader spectrum of electro/mechanical failures, the FMVT® Machine provides more information to the design engineers, expediting the redesign process.
For more information on FMVT®contact Entela (Grand Rapids, MI) at (616) 247-0515 or via its website at www.entela.com.
