Design Evaluation

When design parameters are fixed then, approximate estimates of reliability requirements should also be, deduced. With the start of formal design phase, the reliability professional should provide guidance and judgment about the reliability requirements. Data on the reliability of proposed components and the implications for product reliability should be documented for the team at each design refinement after thorough analysis of the reliability requirements allocated to subcomponents focusing on every potential failure and establish cost-effective ways of preventing them.

Four types of evaluation are

• Environmental stress screening – Product is exposed to the most severe design environmental stresses and accelerated life testing may be used as per requirement so, as to identify weak components.
• Reliability development/growth tests – They are a series of tests conducted periodically from design through production phases to demonstrate the impact of corrective actions on reliability.
• Reliability qualification tests (or reliability demonstration tests) – They are conducted on a sample from production to determine whether production units meet reliability requirements so, as to serve as a basis for production approval.
• Production reliability acceptance tests – It is a periodic test during production to determine whether the output continues to meet reliability requirements.

The two general approaches to failure prevention are fault tolerance and fault avoidance. A fault-tolerant approach requires design of redundant systems so that a fault does not result in a failure for example dual master cylinders in an automotive braking system. The fault-avoidance approach requires designing the product with components that are sufficiently reliable to guarantee the minimum product reliability for example, it is accomplished by using heavier structural pieces, or more reliable components. The customer’s lifecycle cost for the product can be minimized by establishing optimum reliability levels and implementing systems for obtaining them.

Reliability engineers should provide the design team with data from testing of the final version of the product, validating that the design meets the reliability requirements during design review.

Alternative manufacturing processes and parameters should be studied for their impact on reliability in order to meet or exceed design requirements during preproduction. A testing program should be established to verify that production output meets reliability requirements during actual release of the product for production.

A system for follow-up should also be implemented to study any failures, in-house or in the field, post-production and is usually done by failure reporting, analysis, and corrective action system (FRACAS). Thorough documented of design requirements, help assure customer satisfaction.