1、FMEA （失效模式與影響分析）FMEA （失效模式與影響分析）Failure Mode and Effects Analysis潛在失效模式與后果分析在設計和制造產品時，通常有三道控制缺陷的防線：避免或消除故障起因、預先確定或檢測故障、減少故障的影響和后FMEA正是幫助我們從 第一道防線就將缺陷消滅在搖籃之中的有效工具。FMEA是一種可靠性設計的重要方法。它實際上是MA（故障模式分析）和FEA（故障影響分析）的組合。它對各種可能的風險進行評價、分析， 以便在現有技術的基礎上消除這些風險或將這些風險減小到可接受的水平。及時性是成功實FMEA的最重要因素之一，它是一個事前的行為， 而不是“事后的

2、行為。為達到最佳效益，FMEA必須在故障模式被納入產品之前進行。FMEA實際是一組系列化的活動，其過程包括：找出產礎程中潛在的故障模式；根據相應的評價體系對找出的潛在故障模式進行風險量化評估； 列出故障起因機理，尋找預防或改進措施。由于產品故障可能與設計、制造過程、使用、承包商共應商以及服務有關，因此FMEA又細分為設計FMEA、過程FMEA、使用FMEA和服務F MEA四類。其中設計FMEA和過程FMEA最為常用。設計FMEA（也記為d-FMEA）應在一個設計概念形成之時或之前開始，并且在產品開發各階段中，當設計有變化或得到其他信息時及時不斷地修 改，并在圖樣加工完成之前結束。其評價與分析的

3、對象是最終的產品以及每個與之相關的系統、子系統和零部件。需要注意的d-FMEA在體現 設計意圖的同時還應保證制造或裝配能夠實現設計意圖。因此，雖然MEA不是靠過程控制來克服設計中的缺陷，但其可以考慮制造裝配過程中 技術的/客觀的限制，從而為過程控制提供了良好的基礎。進行-FMEA有助于：設計要求與設計方案的相互權衡；制造與裝配要求的最初設計；提高在設計/開發過程中考慮潛在故障模式及其對系統和產品影響的可能性；為制定全面、有效的設計試驗計劃和開發項目提供更多的信息；建立一套改進設計和開發試驗的優先控制系統；為將來分析研究現場情況、評價設計的更改以及開發更先進的設計提供參考。過程FMEA（也記為p

4、-FMEA）應在生產工裝準備之前、在過程可行性分析階段或之前開始，而且要考慮從單個零件到總成的所有制造過程。其評 價與分析的對象是所有新的部件過程、更改過的部件過程及應用或環境有變化的原有部件過程。需要注意的是，雖然p-FMEA不是靠改變產品設 計來克服過程缺陷，但它要考慮與計劃的裝配過程有關的產品設計特性參數，以便最大限度地保證產品滿足用戶的要求和期望。p-FMEA 一般包括下述內容：確定與產品相關的過程潛在故障模式；評價故障對用戶的潛在影響；確定潛在制造或裝配過程的故障起因，確定減少故障發生或找出故障條件的過程控制變量；編制潛在故障模式分級表，建立糾正措施的優選體系； 將制造或裝配過程文件

5、化。FMEA技術的應用發展十分迅速。50年代初，美國第一次將FMEA思想用于一種戰斗機操作系統的設計分析，到玉0年代中期，FMEA技術正式用于航天工業（Apollo計劃）。1976年，美國國防部頒布了FMEA的軍用標準，但僅限于設計方面。70年代末，FMEA技術開始進入汽車工業和 醫療設備工業。80年代初，進入微電子工業。80年代中期，汽車工業開始應用過程FMEA確認其制造過程。到了1988年，美國聯邦航空局發布咨 詢通報要求所有航空系統的設計及分析都必須使用MEA 1991年，ISO-9000推薦使用FMEA提高產品和過程的設計。1994年，FMEA又成為QS-9000的認證要求。目前，FM

6、EA已在工程實踐中形成了一套科學而完整的分析方法。FMEA可以描述為一組系統化的活動，其目的是認可并評價產品/過程中的潛在失效以及該失效的后果確定能夠消除或減少潛在失效發生機會的措施將全部過程形成文件無論是產品設計或者是過程設計，FMEA所關注的主要是策劃和設計的過程，但隨著其使用的場合不同又有不同的區分見的FMEA類別有：DFMEA:設計 FMEAPFMEA :過程 FMEAEFMEA:設備 FMEASFMEA:體系 FMEA在進行FMEA時有三種基本的情形，每一種都有其不同的范圍或關注焦點情形1:新設計，新技術或新過程FMEA的范圍是全部設計，技術或過程情形2:對現有設計或過程的修改假設對

7、現有設計或過程已有FMEA）.FMEA的范圍應集中于對設計或過程的修改，由于修改可能產生的相互影響以 及現場和歷史情況情形3:將現有的設計或過程用于新的環境場所或應用（假設對現有設計或過程已有FMEA）.FMEA的范圍是新環境或場所對現有設計或過程的影響FMEA- 8D流程的介紹QS9000、ISO/TS16949, ISO9001、TL9000、ISO14001、OHSAS18001等管理體系中都有涉及到預防措施；依據“ISO9001： 2000質量管理體系一基礎和術語”的定義，“預防措施，是指“為消除潛在不合格或其他潛在不期望情況的原因所采取的措施或者簡單地定義為：采取預防措施是為了防 止

8、發生。在企業實際的管理體系運作中，雖然都會去編制一份有關預防措施，的形成文件的程序，但真正可以達到預見性地發現較全面的潛在問題通常存在 較大難度，也即：這樣作業的可操作性不強；取而代之的主要是糾正措施；但“糾正措施與預防措施的確是兩個不同的概念，“糾正措施是為 了防止同樣的問題再次出現所采取的措施。為能有效地實施預防措施，使可能存在的潛在問題無法出現，需要一個從識別問題到控制潛在影響的管理系統，對于這一點，各企業都可能制定 各自不同的方法以對應，這些方法也許都是適用的；但這里所要介紹的是一種行之有效且便于操作的制定和實施防措施的方法，即：美國三大 車廠（戴姆勒克萊斯特、福特、通用）制定的潛在失

9、效模式及后果分析，或簡稱為FMEA。FMEA于2002年推出第三版本，該第三版本較第二版本更具備簡便的可操作性FMEA在汽車零組件生產行業已被廣泛的應用，同時這也是美國 三大車廠對所屬供應商的強制性要求之一。FMEA事實上就是一套嚴密的預防措施之識別、控制、提高的管理過程;其不僅可在汽車零組件行業可予使用，也可應用于任何期望能嚴格控制 潛在問題出現的行業，尤其是產品（或服務）質量的好壞可能會極大影響到顧客利益的領域；因此MEA能在QS9000及ISO/TS16949一類的汽 車業質量管理體系中運用，其同樣可應用于其他管理體系之中，而且同樣可以在企業內部形成一種嚴密的防措施系統。執行FMEA，其

10、實并不困難，它是一種分析技術，即：在一張包括諸多要求的表單上進行分析并加以控制和應用便可達成的過程控制；美國三大車廠在潛在失效模式及后果分析一書中已有明確給定了這種表單的格式；該表單包含了如下主要內容：（1）“功能要求，：填寫出被分析過程（或工序）的簡單說明；（2）“潛在失效模式：記錄可能會出現的問題點；（3）“潛在失效后果，：列出上述問題點可能會引發的不良影響；（4）“嚴重度，：對上述問題點的不良影響進行評價并賦予分值（得分10分），分值愈高則影響愈嚴重；（5）“潛在失效起因或機理：該潛在問題點可能出現的原因或產生機理分析；（6）“頻度”：上述“起因或機理出現的幾率大小（得分110分），分值

11、愈高則出現機會愈大；（7）“現行控制，：列出目前本企業對這一潛在問題點所運用的控制方法；（8）“探測度，：在采用，現行控制，的方法來控制時，該潛在問題可以被檢查出來的難易程序（得分110分），得分愈高則愈難以被檢出；（9）“風險順序數，：將上述嚴重度”、“頻度，、“探測度”得分相乘所得出的結果；該數值愈大則這一潛在問題愈嚴重，愈應及時采顛防措施，；（10）“建議措施，：列出對風險順序數，較高之潛在問題點所制定的預防措施，以防止其發生；（11）“責任及目標完成日期，：寫出實施上述預防措施，的計劃案；（12）“措施結果，：對上述，預防措施，計劃案之實施狀況的確認。從上述內容項目不難看出這已經包含了

12、處理預防措施，之識別、控制所需的全部基本要求。由于FMEA是一種“預防措施，其必然是一種事先的行動；如果把MEA當作事情發生以后再執行處置的動作，其將無法達到MEA的真實效果， 亦將把這一 FMEA演變成“糾正措施，。汽車行業產品由于存在人身安全風險及車輛召回等危機，不得不嚴格執彳預防措施，其最有效的、最全面的方式也就是運府MEA。對于其他行業（或其他管理體系）在執行預防措施時，如果采用FMEA，同樣將會極大降低失敗的機會，事實上這亦商防措施，的最終目的。當然對于其他行業（或其他管理體系）而言，不一定完全按照美國三大車廠給定爵重度、“頻度及“探測度之評價標準進行評分，完全可以視本企業之實際情況

13、設定一系列類似的評價標準以執行對策作業，且在具體操作手法上也可根據實情采用適合于自身的方式，只要能達到更有效地識 別、控制潛在問題的發生即可。總之，認識、了解FMEA，并予以持續采用，將會極大地強化企業的預防措施效果，使，錯誤”、“失敗，出現的可能性達到最小。FAILURE MODES AND EFFECTS ANALYSIS (FMEA)Kenneth Crow DRM AssociatesIntroductionCustomers are placing increased demands on companies for high quality, reliable products.

14、The increasing capabilities and functionality of ma ny products are making it more difficult for manufacturers to maintain the quality and reliability. Traditionally, reliability has been achieved through extensive testing and use of techniques such as probabilistic reliability modeling. These are t

15、echniques done in the late stages of development. The challenge is to design in quality and reliability early in the development cycle.Failure Modes and Effects Analysis (FMEA) is methodology for analyzing potential reliability problems early in the development cycle where it is easier to take actio

16、ns to overcome these issues, thereby enhancing reliability through design. FMEA is used to identify potential failure modes, determine their effect on the operation of the product, and identify actions to mitigate the failures. A crucial step is anticipating what might go wrong with a product. While

17、 anticipating every failure mode is not possible, the development team should formulate as extensive a list of potential failure modes as possible.The early and consistent use of FMEAs in the design process allows the engineer to design out failures and produce reliable, safe, and customer pleasing

18、products. FMEAs also capture historical information for use in future product improvement.Types of FMEAsThere are several types of FMEAs, some are used much more often than others. FMEAs should always be done whenever failures would mean potential harm or injury to the user of the end item being des

19、igned. The types of FMEA are:System - focuses on global system functionsDesign - focuses on components and subsystemsProcess - focuses on manufacturing and assembly processesService - focuses on service functionsSoftware - focuses on software functionsFMEA UsageHistorically, engineers have done a go

20、od job of evaluating the functions and the form of products and processes in the design phase. They have not always done so well at designing in reliability and quality. Often the engineer uses safety factors as a way of making sure that the design will work and protected the user against product or

21、 process failure. As described in a recent article:A large safety factor does not necessarily translate into a reliable product. Instead, it often leads to an overdesigned product with reliability problems.Failure Analysis Beats Murpheys LawMechanical Engineering , September 1993FMEAs provide the en

22、gineer with a tool that can assist in providing reliable, safe, and customer pleasing products and processes. Since FMEA help the engineer identify potential product or process failures, they can use it to:Develop product or process requirements that minimize the likelihood of those failures.Evaluat

23、e the requirements obtained from the customer or other participants in the design process to ensure that those requirements do not introduce potential failures.Identify design characteristics that contribute to failures and design them out of the system or at least minimize the resulting effects.Dev

24、elop methods and procedures to develop and test the product/process to ensure that the failures have been successfully eliminated.Track and manage potential risks in the design. Tracking the risks contributes to the development of corporate memory and the success of future products as well.Ensure th

25、at any failures that could occur will not injure or seriously impact the customer of the product/process.Benefits of FMEAFMEA is designed to assist the engineer improve the quality and reliability of design. Properly used the FMEA provides the engineer several benefits. Among others, these benefits

26、include:Improve product/process reliability and qualityIncrease customer satisfactionEarly identification and elimination of potential product/process failure modesPrioritize product/process deficienciesCapture engineering/organization knowledgeEmphasizes problem preventionDocuments risk and actions

27、 taken to reduce riskProvide focus for improved testing and developmentMinimizes late changes and associated costCatalyst for teamwork and idea exchange between functionsFMEA TimingThe FMEA is a living document. Throughout the product development cycle change and updates are made to the product and

28、process. These changes can and often do introduce new failure modes. It is therefore important to review and/or update the FMEA when:A new product or process is being initiated (at the beginning of the cycle).Changes are made to the operating conditions the product or process is expected to function

29、 in.A change is made to either the product or process design. The product and process are inter-related. When the product design is changed the process is impacted and vice-versa.New regulations are instituted.Customer feedback indicates problems in the product or process.FMEA ProcedureThe process f

30、or conducting an FMEA is straightforward. The basic steps are outlined below.Describe the product/process and its function. An understanding of the product or process under consideration is important to have clearly articulated. This understanding simplifies the process of analysis by helping the en

31、gineer identify those product/process uses that fall within the intended function and which ones fall outside. It is important to consider both intentional and unintentional uses since product failure often ends in litigation, which can be costly and time consuming.Create a Block Diagram of the prod

32、uct or process. A block diagram of the product/process should be developed. This diagram shows major components or process steps as blocks connected together by lines that indicate how the components or steps are related. The diagram shows the logical relationships of components and establishes a st

33、ructure around which the FMEA can be developed. Establish a Coding System to identify system elements. The block diagram should always be included with the FMEA form.Complete the header on the FMEA Form worksheet: Product/System, Subsys./Assy., Component, Design Lead, Prepared By, Date, Revision (le

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37、GrrtrB ig04C3 shcr!fPR-33 S2JQA 阪V ZO GD.沖睥/昌加 F Lg cmeItB Dvn2勺1247PR知A YWE7ih。昌任就的迫閂 hllWHl1 Oil 心AjIdK-i i臼 HM很 網n21124C5 :Per2PR-23 $216M PrtK： 20.&日.HaE 10H5/92Hil7Ki?bnb皿 pfin21124CW or庶 nmorl2PR-EJ5伸串ZQA PTOG RB.lvwel iQnM-J昌由Iwl eUE n?n2q1Z4科 E3PR-Ki忘曲E224Qm庇皿 3.0B. HDwAli L：1 5/：CLUdEd I亡 G

38、WiT也 p jTl2214FL1 海比ceWlOCrftiflip.日.&兩 1血1普莊沁 dSJ k :f 巾 p?nEl4卜LWt-心史2W】00% S5PTidHMlGGErB 濡rm2tJ64o2ISD4221gDUse the diagram prepared above to begin listing items or functions. If items are components, list them in a logical manner under their subsystem/assembly based on the block diagram.Identif

39、y Failure Modes. A failure mode is defined as the manner in which a component, subsystem, system, process, etc. could potentially fail to meet the design intent.Examples of potential failure modes include:CorrosionHydrogen embrittlementElectrical Short or OpenTorque FatigueDeformationCrackingA failu

40、re mode in one component can serve as the cause of a failure mode in another component. Each failure should be listed in technical terms. Failure modes should be listed for function of each component or process step. At this point the failure mode should be identified whether or not the failure is l

41、ikely to occur. Looking at similar products or processes and the failures that have been documented for them is an excellent starting point.Describe the effects of those failure modes. For each failure mode identified the engineer should determine what the ultimate effect will be. A failure effect i

42、s defined as the result of a failure mode on the function of the product/process as perceived by the customer. They should be described in terms of what the customer might see or experience should the identified failure mode occur. Keep in mind the internal as well as the external customer. Examples

43、 of failure effects include:Injury to the userInoperability of the product or processImproper appearance of the product or processOdorsDegraded performanceNoiseEstablish a numerical ranking for the severity of the effect. A common industry standard scale uses 1 to represent no effect and 10 to indic

44、ate very severe with failure affecting system operation and safety without warning. The intent of the ranking is to help the analyst determine whether a failure would be a minor nuisance or a catastrophic occurrence to the customer. This enables the engineer to prioritize the failures and address th

45、e real big issues first.Identify the causes for each failure mode. A failure cause is defined as a design weakness that may result in a failure. The potential causes for each failure mode should be identified and documented. The causes should be listed in technical terms and not in terms of symptoms

46、. Examples of potential causes include:Improper torque appliedImproper operating conditionsContaminationErroneous algorithmsImproper alignmentExcessive loadingExcessive voltageEnter the Probability factor. A numerical weight should be assigned to each cause that indicates how likely that cause is (p

47、robability of the cause occuring). A common industry standard scale uses 1 to represent not likely and 10 to indicate inevitable.Identify Current Controls (design or process). Current Controls (design or process) are the mechanisms that prevent the cause of the failure mode from occurring or which d

48、etect the failure before it reaches the Customer. The engineer should now identify testing, analysis, monitoring, and other techniques that can or have been used on the same or similar products/processes to detect failures. Each of these controls should be assessed to determine how well it is expected to identify or detect failure modes. After a new product or process has been in use previously undetected or unidentified failur