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This paper presents a practical reliability development and improvement approach that can be applied early to a design or process in order to help meet and exceed customer requirements and achieve customer satisfaction. The particular procedure involves proper coordination of product/process reliability growth management, design of experiments, and failure investigation which help to evaluate design or process FMEA (Failure Mode, Effects Analysis) prioritized effects and customer requirements before verification.

Reliability growth test management is a feasible method for identifying failure modes, implementing design changes and monitoring reliability progress on an on-going basis during the early phases of a product development program. Implementation of this particular process will provide very useful information on concept selection, product/process reliability, and cost effectiveness without exorbitant time, money and engineering effort being spent on the development of failure suspect parts. Recent experience with the testing of automotive components has led to a practical method for efficiently organizing, initiating, and monitoring a reliability growth test process under a competitive automobile environment. Analysis techniques to be presented address product/process design concerns and validation testing issues by providing 1) timely reliability growth progress, 2) practice tests leading up to validation, and 3) confidence limits with test time.

This paper discusses an analytical technique for computing the failure rate of steel springs used in automotive part applications. Preliminary computations may be performed and used to predict spring failure rates quickly at a very early stage of a product development cycle and to establish program reliability impact before commitment. The analytical method is essentially a combination of various existing procedures that are logically sequenced to compute a spring probability of failure under various operational conditions. Fatigue life of a mechanical component can be computed from its S-N curve. For steels, the S-N curve can be approximated by formulae which describe the fatigue life as a function of its endurance limit and its alternating stress. Most springs in service are preloaded and the actual stress fluctuates about a mean level. In order to compute an equivalent alternating stress with zero mean, an analytical method based on the Goodman Diagram is used.

This paper will focus on the process, as used at AC Rochester, of performing reliability analyses early in the design phase of automotive component development and the integration of specific techniques and methods. This methodology forms an effective tool that achieves the identification of component failure modes and mechanisms with greater confidence than any single technique and provides for the simple and direct communication of the results. In addition, our experience shows that this process provides the maximum preventive impact on the product during the design phase, thus yielding demonstrably improved reliability characteristics on the production part. Specifically, a four-step up-front analysis process can facilitate the usefulness of various analytical techniques to the identification of product reliability problems.