Abstract
This study demonstrates the application of parametric accelerated life testing (ALT) as a procedure to identify design deficiencies and correct them in generating a reliable quantitative (RQ) specification. It includes: (1) a system BX lifetime that X% of a product population fails with a parametric ALT scheme, (2) fatigue design, (3) ALTs with alternations, and (4) judgement as to whether the design(s) secures the desired BX lifetime. A (generalized) life–stress model through the linear transport process and a sample size formulation are suggested. A pneumatic cylinder in a machine tool was used as a case study. The cylinder was failing in a flexible manufacturing system. To reproduce the failure and modify the design, a parametric ALT was performed. At the first ALT, the metal seal made of nickel-iron alloy (36% Ni) partially cracked and chipped and had a crisp metal sound. It was modified by changing the seal from a metal to a polymer (silicone rubber). At the second ALT, the piston seal leaked due to seal hardening and wear. The failure modes of the silicone seal in the laboratory tests were similar to those returned from the field. For the third ALT, the seal material was changed from silicone rubber to (thermoset) polyurethane. There were no concerns during the third ALT and the lifetime of the pneumatic cylinder was shown to have a B1 life of 10 years.
Highlights
Because of competitive requirements in the market, mechanical systems must be designed to have good performance and high reliability
A pneumatic cylinder is a mechanical component that can be utilized in an automatic assembly line in a flexible manufacturing system
To ensure a product does not fail in the field, flawed components need to be identified and redesigned using a testing methodology such as parametric accelerated life testing (ALT), which can produce reliability quantitative (RQ) specifications before the system is introduced into the market [4,5]
Summary
Because of competitive requirements in the market, mechanical systems must be designed to have good performance and high reliability. To ensure a product does not fail in the field, flawed components need to be identified and redesigned using a testing methodology such as parametric ALT, which can produce reliability quantitative (RQ) specifications before the system is introduced into the market [4,5] Material faults, such as extremely small voids and contacts when subjected to repeated loads, may begin to fail because of fatigue. The ALT combined with the reliability block diagram was investigated as another method [8] It included a test plan for the system, identifying failure mechanics such as fatigue, and using a sample size equation, accelerated loads, etc. A pneumatic cylinder in a machine tool subjected to repeated pressure loading is used to illustrate this methodology
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