Risk Discovery Analysis in Xfmea 5
One of the most important tasks during a Design for
Reliability (DFR) process is to perform Design FMEAs for
critical systems, subsystems and components. Although it
is ideal to be able to perform FMEAs for all items, few,
if any, organizations can afford the time and effort
it takes to do everything in a linear fashion.
One of the quality characteristics of successful
FMEAs is that the team focuses on high-risk items first.
This enables the team to place the highest priority on
issues that are really
important to address, and leave lower-risk items for
later, or even ignore items that the team does not think
are worth putting any further effort into investigating.
Various methods (such as a preliminary risk assessment
or change point analysis) can be used to choose which
analyses will be performed and at what level of detail.
How can these concepts be set up into a systematic
process? Furthermore, how can ReliaSoft's
Xfmea 5
software assist with initial risk
discovery so that users can employ a common platform that
contains both risk prioritization and the actual FMEA
analyses? In this article, we will present the new Risk
Discovery analysis functionality in Xfmea 5 and explain how it can
help an FMEA team achieve the aforementioned objectives.
Preliminary Risk Assessment or Change Point Analysis
Let’s review the reasons for conducting an FMEA. It
is a methodology designed to help an organization:
- Identify and fully understand potential failure
modes for a product or process.
- Assess the risk associated with those failure
modes and prioritize issues for corrective action.
- Identify and carry out corrective actions to
address the most serious concerns.
The assessment of risk is key to streamlining the
process. A good FMEA is done as early as possible in a
design cycle (in the case of product development) and
identifies the high-risk areas quickly. Then the risks are
addressed by identifying and executing recommended
actions.
Different methods can be used for the initial risk
discovery activity. Some organizations might perform a
preliminary risk assessment in which the analysts
evaluate each assembly or component with respect to a
list of relevant factors in order to determine (yes/no)
whether it poses sufficient risk to warrant further
analysis. In other cases, the organization might use a
predefined set of rating scales to assign a score to
each factor and then use the overall scores to rank and
prioritize the assemblies/components for further
analysis.
For example, in a DFR process, the fundamental
question that teams are asking when designing a new
product is, "What has changed?" or "How much of the new
product is new and how much has been modified?" Expert opinion
is used to assess:
- How much (if at all) the existing
components were modified.
- Whether the proposed application (stress) of the
existing components poses new reliability risks.
- Exactly what was changed.
- The current knowledge (or assumptions)
concerning the new components in terms of their
reliability.
The formal approach to this methodology is called
"change point analysis" and a "change point" can be:
- Change in the design.
- Change in the manufacturer.
- Change in the supplier, supplier design or
process.
- Change in the usage environment.
- Change in the system — interface points.
- Change in the system — upstream and downstream
parts.
- Change in the specification.
- Change in the performance requirements.
- Any other change that can affect reliability.
The fundamental concept behind focusing on what
changed is that if a proven design is unchanged, there
will be no new reliability/quality problems. The
majority of problems lie where changes have occurred.
So, if enough attention is paid to the changes and the
changes are managed through a systematic process, the
design process will be robust and will yield significantly
fewer unforeseen problems and surprises.
Utilizing the Risk Discovery Analysis Feature in Xfmea 5
Let’s examine the new Risk Discovery analysis feature in Xfmea 5 through
a fictional
example. Suppose that a technology company is developing a new
complex product. It is a multi-function printer that
prints, copies, scans and has several other features,
such as scan to e-mail, document management, etc.
Figure 1 shows the system
hierarchy, with some subsystems fully expanded down to
the component level and others collapsed at the
subsystem level.
Figure 1: Multi-Function
Printer System Hierarchy
As a best practice, the team first conducts an FMEA at the
top (system) level in order to address any
potential problems related to
interactions and interfaces. Starting the analysis at lower levels
has been proven to be a practice that can lead to
omission of interactions between subsystems. In most
complex systems, interactions will account for more than
50% of the total failure modes that the system will
experience. In such cases, it is essential to start with
a top-down approach.
Once the top (system) level
FMEA has been completed, the next question that the FMEA
team faces is which subsystems and components to focus
on. This is where the Risk Discovery
feature in Xfmea 5 is used.
The team adds a Risk Discovery analysis for each of the
main subsystems of the product: the printing system, the
copying system, the scanning system and the document
management system. Xfmea supports two
configurable methods for this type of analysis: a set of
yes/no questions (where a yes answer indicates that the
assembly/component poses a risk that warrants more
detailed analysis) or a set of predefined rating scales
(which can be used to calculate an overall rating for
each assembly/component). For this example, we will
assume that the organization has selected to use the
Questions tab with the sample questions that are shipped
by default with the software. These questions address the
issues that would typically be considered with a change point analysis
approach (new technology, new application, historical
problems, supplier capability), together with other
relevant issues (safety,
regulatory requirements and mission criticality).
When the team uses the questions to discuss each
subsystem, they determine that the highest risk
assemblies are the printing system followed by the
document management system. The copying and scanning
systems are highly leveraged from previous designs and
as a result they were graded lower in terms of risk. The
two assemblies that will receive subsystem level FMEA
are marked by selecting the "Mark item for more detailed
analysis" check box and they are then highlighted
in the system configuration display. Now the team has a clear path of
where to focus their FMEA efforts first. Figure 2 shows
the analysis for the printing system and Figure 3 shows
the system configuration with two subsystems highlighted
for more detailed analysis.
Figure 2: Risk Discovery
Questions for the Printing System
Figure 3: System Hierarchy
with Two Subsystems Highlighted for More Detailed
Analysis
Although it will not be discussed in this article, it
should be noted that the team has the option to do more Risk Discovery
analyses, even at the component level inside the
printing system, in order to prioritize component level
FMEAs.
Customization of the Risk Discovery Questions and
Ratings
As mentioned before, the risk discovery questions and
ratings in Xfmea are fully customizable in order
to serve specific organizational needs. This allows the
tool to serve a wide variety of industries. As an
example, Figure 4 shows a partial view of the customized risk
discovery rating scales that were developed by an
organization that builds and manages oil
refineries.
Figure 4: Customized Risk
Discovery Rating Scales for a Company that Builds Oil
Refineries
Conclusion
Methodologies such as preliminary risk assessment and
change point analysis can provide a powerful tool to quickly direct an FMEA team's efforts toward the
high-risk areas in a design or process. The new Risk Discovery analysis
feature in
Xfmea 5 can be configured to fit a variety of
different methods and allows the organization to
integrate the initial risk discovery analysis results
with the FMEAs that are performed on the items with the
highest priority.
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