Reliability is a critical factor in product development and lifecycle management, especially for energy-related products (ErPs). Ensuring a high level of reliability can significantly reduce the environmental impact, lower production costs, and enhance customer satisfaction. This blog provides a comprehensive overview of how to calculate the reliability of your products based on the guidelines outlined in EN 45552:2020.
Understanding Reliability
Reliability is defined as the probability that a product will perform its intended function without failure under specified conditions for a given period. Unlike durability, which is concerned with the total expected lifespan of a product, reliability focuses on the probability of failure-free performance within a specified timeframe.
Key Concepts
- Reliability: The likelihood that a product will function as required under defined conditions without experiencing any failure.
- Failure Modes: The specific ways in which a product can fail to perform its intended function.
- Failure Mechanisms: The underlying causes of failure, such as material fatigue or environmental stress.
- Failure Sites: The specific parts or components of the product where failures are likely to occur.
Framework for Assessing Reliability
The assessment of reliability involves several key steps, which are detailed below:
1. Define the Product
First, clearly define the product or product group, including its primary, secondary, and tertiary functions. This functional analysis helps identify all the critical components and systems within the product that must be evaluated for reliability.
2. Environmental and Operating Conditions
Next, determine the environmental and operating conditions under which the product is expected to function. These conditions include factors such as temperature, humidity, mechanical stress, and electrical loads. Understanding these conditions is crucial for simulating real-world scenarios in reliability testing.
3. Additional Information
Gather additional information from various sources, such as field data, manufacturer constraints, regulations, stress analysis, and failure mode and effect analysis (FMEA). This data helps build a comprehensive picture of the potential reliability issues and the likely failure mechanisms.
4. Conduct Reliability Analysis
Perform a reliability analysis by linking functions to failure modes, failure sites, and failure mechanisms. This involves conducting an FMEA or similar analysis to identify and rank the most likely failures. The analysis should result in a list of failure sites and mechanisms ranked by their likelihood.
5. Select and Apply Reliability Assessment Methods
Choose appropriate methods for assessing the reliability of the product. These methods may include:
- Physical Testing: Testing the product under controlled conditions to observe its performance and identify failure points.
- Accelerated Life Testing (ALT): Subjecting the product to elevated stress levels to induce failures more quickly than under normal conditions. This helps estimate the product's lifespan and failure rates in a shorter time.
- Statistical Analysis: Using statistical models to analyze test data and predict the reliability of the product.
6. Document the Assessment
Finally, document the entire assessment process, including the input data, assumptions, analysis methods, and results. This documentation is essential for ensuring transparency and providing a basis for future reliability improvements.
Example: Reliability Assessment of an Electronic Device
Let's consider an example of assessing the reliability of an electronic control device in a car:
- Define the Product: The electronic control device is defined as a critical component responsible for managing the car's engine performance.
- Environmental and Operating Conditions: The device is expected to operate in a range of temperatures from -20°C to 85°C, with exposure to vibration and humidity.
- Additional Information: Field data indicates that previous versions of the device had a failure rate of 10% within three years due to component fatigue.
- Conduct Reliability Analysis: An FMEA identifies the main failure modes, such as solder joint fatigue and capacitor failure. These are ranked by their likelihood.
- Select and Apply Reliability Assessment Methods: Accelerated life testing is performed at elevated temperatures to induce failures quickly. Statistical analysis of the test data predicts a mean time to failure (MTTF) of 5 years under normal operating conditions.
- Document the Assessment: The results, including failure modes, test conditions, and predicted MTTF, are documented for future reference and improvement.
For more detailed guidance, refer to the full text of EN 45552:2020 and related standards such as EN 45554:2020 for repair, reuse, and upgrade assessments, and EN 62308 for reliability assessment methods.
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