【正文】 / testing may occur at the subject operation or at subsequent operation(s) that can detect the subject failure mode. Process Control Examples Typical Process Documents ? SPC records ? Visual aides ? Work instructions ? Inspection instructions/records ? Equipment operating instructions ? Training records ? Traceability records Remended Actions ? Corrective Action should be first directed at the highest concerns as rank ordered by RPN. ? The intent of any remended action is to reduce the occurrence, severity and/or detection rankings. ? If no actions are remended for a specific cause, then this should be indicated. ? Only a design revision can bring about a reduction in the severity ranking. ? To reduce the probability of occurrence, process and/or specification revisions are required. ? To increase the probability of detection, process control and/or inspection changes are required. Improving detection controls is typically costly. The emphasis should be placed on preventing, rather than detecting, defects. ? Faulttree analysis is a deductive process Especially useful for Analyzing failures, when the causes of failures have not been identified ? Reliability engineering Tool Motor Failure The Role and Function of FTA Motor Failure Fault Tree Symbols ? The Ellipse The top event, the ellipse, contains the description of the systemlevel fault or undesired event. This symbol appears at the head or top of the tree and is included only once in any tree. The input to the ellipse is from a logic gate. ? The Rectangle The fault event, the rectangle, contains a brief description of a lowerlevel fault. This description should be short without being vague. Fault events appear throughout the tree and have both their input and output from a logic gate. ? Logic Gates Logic Gate inputs and outputs, except for the Inhibit Gate, which is addressed below, have similar connections. The output from a logic gate is to any fault event block or to a Transfer Out function. The input is from any fault event block or from a Transfer In function. The AND Gate is the logic gate in which the output occurs only if all inputs exist. The OR Gate is the logic gate in which the output occurs only if one or more of the input events occur. Fault Tree Fundamentals 1. Defining the Undesired Event(s) (Major Fault(s)) a. The undesired event is most often the fault which, upon occurrence, results in plete failure of the system, the failure of a backup system, degradation, or an undetected failure. This is considered catastrophic failure. The major fault is a failure which causes loss of availability through the degradation or system shutdown and/or poses a safety hazard to operators and/or maintenance personnel. The undesired event, however, may be an unusual failure at a subsystem level, the root cause of which is unknown. Any observable event may be chosen as the “ undesired event” . The analyst must recognize that the FTA will not identify failures unrelated to the chosen event. b. To define the undesired event, the normal system operation and environment must be known in order to allow the analysis to show the undesired event as a failure. When defining the undesired event, care must be taken to prevent the range of the faults from being too broad. For example, “ Failure to plete trip” , for an automobile, is not specific enough to allow for ease of analysis. This is because failure could vary from an air conditioning fault, which caused disfort, to loss of engine power, which caused loss of mobility. Both faults could be considered failure。 ：是 可能 發(fā)生的缺陷，是潛在的，不一定是已有發(fā)生的。 4. 思考：想一下，為什么？？ 練習(xí) 2 . 對(duì)產(chǎn)品的特殊特性有影響的過(guò)程 先標(biāo)出來(lái)，這些過(guò)程應(yīng)當(dāng)優(yōu)先評(píng)估。 。 一般是組長(zhǎng) 怎樣做 PFMEA？ . 定義所涉及的 產(chǎn)品的特殊特性 ： 。 D最小為 1， 最大是10。 怎樣用 FMEA評(píng)估過(guò)程的風(fēng)險(xiǎn)？ 1. 失效模式的發(fā)生頻率 （ O） O（發(fā)生頻率）來(lái)表示產(chǎn)品的缺陷的可能性。 RPN越大，被評(píng)估過(guò)程的風(fēng)險(xiǎn)越大。 Characteristics I Characteristics II Characteristics III Characteristics IV Characteristics V 怎樣用 FMEA評(píng)估過(guò)程的風(fēng)險(xiǎn)？ 1. 什么是失效模式 （缺陷）。如 “ ?”， “ ?”等。應(yīng)在量產(chǎn)的方案確定之前或量產(chǎn)批準(zhǔn)前。用于評(píng)估設(shè)計(jì)的失效風(fēng)險(xiǎn) ?PFMEA 從設(shè)計(jì)開發(fā)完成開始到產(chǎn)品的試產(chǎn)前。 ? ISO 9001 預(yù)防行動(dòng)的要求 . FMEA是一個(gè)很好的持續(xù)改進(jìn)的工具來(lái)符合這個(gè)條款的要求。根據(jù)失效模式的風(fēng)險(xiǎn)和所采取的行動(dòng)來(lái)消滅和減少發(fā)生的幾率。 ? 提供一個(gè)方法用來(lái)分析制程并持續(xù)改進(jìn)。 ? ISO14000 可以用來(lái)評(píng)估有害物質(zhì)的風(fēng)險(xiǎn)。用于評(píng)估制造過(guò)程的失效風(fēng)險(xiǎn)。 概念設(shè)計(jì) 設(shè)計(jì) 設(shè)計(jì)完成 試生產(chǎn) 產(chǎn)品和過(guò)程批準(zhǔn) 量產(chǎn)開始 PFMEA DFMEA SFMEA 三種 FMEA之間的關(guān)系 SFMEA PFMEA DFMEA 失效模式 后果 原因 來(lái)自 SFMEA中的問(wèn)題的原因 來(lái)自 SFMEA有著更好定義的中的后果 對(duì)設(shè)計(jì)失效的新的根本原因 來(lái)自 DFMEA中的問(wèn)題的原因 與 DFMEA相同的后果 對(duì)過(guò)程失效