Defining a proper product reliability goal is a critical step in ensuring that a product meets customer expectations and performs adequately throughout its intended lifespan. This also involves a careful balance between the required level of reliability and the associated costs and complexities of achieving that reliability.
Here’s how to approach this:
Testing Time and Design Complexity
The level of reliability required for a product will directly influence the amount of testing time and the complexity of the design process. More stringent reliability goals typically necessitate longer testing periods and more sophisticated design approaches.
- Assess Reliability Requirements: Determine the level of reliability needed based on the product’s intended use, customer expectations, and competitive benchmarks.
As example: Let’s consider a company that designs and manufactures electric cars.
Intended Use: The car is intended for daily commuting and long-distance travel. Therefore, the reliability requirements would include a high Mean Time Between Failures (MTBF), indicating that the car can operate for a long time without breaking down. The car should also have a high availability, meaning it should be operational and ready for use whenever the customer needs it.
Customer Expectations: Customers expect the car to be reliable and safe. They would not tolerate frequent breakdowns or failures, especially during long-distance travel. The car should also have features like autopilot, which should work flawlessly. If the car fails to meet these expectations, customers might switch to a competitor.
Competitive Benchmarks: The company needs to benchmark its reliability standards against those of its competitors. If a competitor’s car has an MTBF of 100,000 hours, the company should aim for an MTBF that is at least as high, if not higher. The company can use methods like surveys, interviews, and focus groups to gather data on competitors’ reliability standards.
- Estimate Testing Time: Calculate the time required for thorough testing, including development, validation, and accelerated life testing to simulate long-term use in a shorter time frame.
It is derived from the reliability function of the Weibull distribution and the binomial distribution for zero failures. The formula is:
$$ \displaystyle \frac{t}{t_{0}}=\left(\frac{N\cdot\textrm{ln}R}{\textrm{ln}\left(1-CL\right)}\right)^{\frac{1}{\beta}} $$where:
$- t -$ is the test duration,
$- t_{0} -$ is the target time,
$- N-$ is the sample size,
$- R-$ is the reliability,
$- CI-$ is the confidence interval, and
$- \bets -$ is the shape parameter of the Weibull distribution.
Given that the shape parameter (beta) is 1.2, no failures are allowed, and the reliability requirement is R90C90 with a target time of 100,000 hours, you can substitute these values into the formula to calculate the test duration. However, the sample size (N) is not given in your question, so you would need to determine this value first.
- Design for Reliability (DfR): Implement DfR practices early in the design phase to anticipate and mitigate potential failure modes.
The DFMEA process is a critical tool in the DfR methodology, helping to detect potential failures impacting reliability or safety before they occur. By identifying and mitigating these risks early in the design process, DFMEA can help to significantly reduce the costs and impacts of unreliability.
DFMEA defining failure modes by Pareto low 20% of failure modes are lead to 80% of total product failures.
Complexity vs. Cost: Evaluate the trade-offs between increased design complexity and the costs involved, including the potential need for more advanced materials or technologies.
Alignment with Warranty and Financial Support
The reliability goal should align with the warranty period and the financial resources the company is willing to allocate for warranty support and potential failure remediation.
- Warranty Analysis: Define the warranty period and understand the implications for reliability goals. The reliability target should ensure that failures are minimized within this period to reduce warranty claims.
- Financial Planning: Consider the financial impact of the reliability goal, including the costs of additional testing, potential warranty claims, and the investment in quality and reliability improvements.
- Risk Management: Analyze the risks associated with not meeting the reliability goal, such as increased warranty costs, customer dissatisfaction, and potential damage to the company’s reputation.
To define a proper product reliability goal, you must consider the required testing time and design complexity to achieve the desired reliability level. This goal must be well-aligned with the warranty period and the financial resources available for warranty support. Balancing these factors will help ensure that the product meets both customer expectations and the company’s financial objectives.
Leave a Reply