A Comparative Study of LINEX, INLF and RINLF Loss Functions on Risk Assessment

• Main Authors: Wei-cheng Lu, 盧為丞
• Other Authors: Jeh-Nan Pan
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/07312307353366674213

碩士 === 國立成功大學 === 統計學系碩博士班 === 97 === Traditionally, engineers perform process capability indices to analyze the performance of key quality characteristics. Since the quadratic loss function proposed by Taguchi, the quality loss concept has been shifted from “defined by specification limits” to “defined by user”. Engineers should highlight the seriousness of the quality problem through cost/lost estimation, so the senior managers can handle and monitor the process quality precisely. The risk of process can be regarded as expected value of loss or an average loss. Therefore, practitioners can utilize the method of quantitative risk assessment linking the expected loss of failure and process capability indices to evaluate the likelihood and consequence of their processes. The research establishes the relationship between various process capability indices, such as Cp, Cpk and Cpm, and three types of expected losses including INLF, RINLF and RLINEX under normal assumption for both unilateral and bilateral specifications. This approach gives decision-makers a concrete tool since the likelihood and consequence resulting from the failure of a manufacturing or environmental system can be evaluated simultaneously. The result suggest that if the acceptable range(in which no quality loss incurred) within the neighborhood of target value is 0.5 times or more of half of the specification width, RINLF is the most appropriate loss function in assessing manufacturing and environmental risks since it can better describe the actual loss of a process. If the acceptable range is below 0.18 times or smaller of half of the specification width, then RLINEX would be better. Finally, several summary tables listing various process capability indices and their expected losses as well as the corresponding failure rates have also been established. Hopefully, the summary tables can provide a useful reference for quality practitioners in conducting risk assessment.