Your Reliability Engineering Professional Development Site
A common and poor technique to gather field data is to count the number of returns by week or month. This can provide a graph showing the number of returns over time.
It hides information you need to understand your field failures.
Let’s take a look at a way to gather the same field failure data and retain the critical information necessary for time to failure analysis. [Read more…]
In the article, Hypothesis Tests for Proportion, the comparison is between a given value and the sample. In this case, let’s compare two populations. We take a sample which provides a proportion representing each population and determines if the populations are different from each other based on the two samples.
The exact solution uses the Binomial distribution, yet when np and 1 – np are greater than 5, then we can use a normal approximation for the test statistic and critical value. [Read more…]
Fielded products fail day by day. Customers report these failures generally seeking a way to remedy this issue. Gathering the reported or returned products or confirmed failures is common practice.
Depending on the product a simple replacement or exchange may suffice. For other products, repair or a refund may be appropriate.
In general, and not always, when a product fails in the hands of a customer, the organization designing, manufacturing and distributing the product learns of the failure. [Read more…]
In the previous article, What is Reliability Optimization, we defined the concept. One of the elements of optimization is identifying which elements of a system to focus improvement efforts on.
Simply improving every element of a design may provide an overall improvement of reliability performance.
Given constraints such as time or funding, selecting the specific few elements that would provide the most improvement is key. [Read more…]
On occasion, you and the team sit down to review the design.
The idea is to check the design for any issues with the combined wisdom of the people involved. Or, it may be a status update for the entire team providing a focus on the most important issues and action items.
The review may involve all departments, such as marketing, operations, supplier management, and the design team.
It may involve just you and the electrical engineer in a private meeting. In either case, it is a review and a chance to illuminate salient reliability issues and form a consensus on the appropriate action. [Read more…]
Delivering the best reliability performance within the various constraints imposed.
Without constraints such as budget, time to market, customer expectation, product functional capabilities, and product weight, you certainly could design and deliver a highly reliable product.
There always are constraints.
In the Oliver Wendall Holmes poem, The One Hoss Shay, the deacon procures the strongest oak, the supplest leather, and the best of best materials. Cost was not a constraint. And the shay lasted 100 years to the day.
If the technology permits there may be stronger or more durable components available for a price, yet cost is often a limiting factor. [Read more…]
A plan is a guide or roadmap for intended action.
A reliability plan is also a collection of specific tasks and milestones and enhanced with a rationale to allow the entire team fully understand their role accomplishing the reliability objectives.
The plan is a way to achieve the desired business objectives. Meaning the product is reliable enough to meet customer expectations, minimize warranty expenses, and garner market acceptance. The plan is just a plan, it is the accomplishment of the tasks, the decision which improves the design, the signals monitored that stabilize the supply chain and assembly process, that make the difference.
A plan without action is not worth the effort. [Read more…]
In some circumstances, it is desirable to ensure the system continues to operate even if there is an internal failure. An aircraft navigation system should be able to operate even if an internal dc-dc regulator fails, for example.
Not everything within some systems benefits by being fault tolerant.
For example, a failure of a cabin reading light over a passenger seat is not critical to the safe operation of the aircraft, thus is likely not created to be fault tolerant. One criterion to determine what should be fault tolerant is the criticality of the function the system provides.
This also applies to specific subsystems within a system allowing some elements to be created fault tolerant and others within the system not. [Read more…]
Do you have one in your organization? Is it used regularly?
If not, your organization’s products are likely not as reliable as they should be. You are shipping products that are not as robust nor reliable as your customers deserve.
Derating and Safety Factors, defined earlier, provide a means to select components or create design features that have sufficient margin to accommodate variation in use and strength over time.
So why are these tools routinely ignored or given only fleeting attention? [Read more…]
Fault tolerance is a system that is reliant to the failure of elements within the system. It also may be called a fail safe design.
A fault tolerant system may continue to operate just fine, after one of the power supplies fails, for example. Or it may operate in a reduced or degraded state.
Other systems may have a ‘limp home’ condition, allowing the system to save critical data or allowing you to drive to a safe place to change a flat tire. [Read more…]
Key Performance Indicators (KPIs) are measurable values related to essential business objectives.
A KPI provides a means to monitor the performance of a specific function.
In larger organizations, with sales & marketing, research & development, operations, supply chain and other teams working to bring products to market, each department has a specific role. [Read more…]
Concurrent engineering is a common approach that pairs the development of the product design and it’s supporting manufacturing processes through the development process.
Design engineers may require the creation of new manufacturing processes to achieve specific material properties, component performance, or mechanical, electrical or software tolerances. [Read more…]
A product or system’s actual reliability performance is a function of the design, assembly, and use.
Decisions made during design predominately create the inherent reliability capability performance.
The selected components, manufacturing, transportation and installation all can add variability and errors to the product, often reducing the actual reliability performance.
The use conditions and maintenance add another layer of variability, again reducing reliability capability. [Read more…]
Next week is RAMS – the Reliability and Maintainability Symposium. A multitrack 3.5-day conference with classes, tutorials, paper sessions, a small trade show, plus many of you – peers, colleagues, and friends in the reliability world.
The conference is hosted by 9 professional societies and organized by a group of about 50 or so volunteers from those societies (I was an active member of the RAMS management committee for many years). [Read more…]
System engineering is a superset of the other engineering fields (mechanical, civil, electrical, software, etc.) as the system engineers work to bring all the various elements of a system together into a final and cohesive whole. [Read more…]