FMEA_失效模式与影响分析

1、FMEA （失效模式与影响分析）FMEA （失效模式与影响分析）Failure Mode and Effects Analysis潜在失效模式与后果分析在设计和制造产品时，通常有三道控制缺陷的防线：避免或消除故障起因、预先确定或检测故障、减少故障的影响和后FMEA正是帮助我们从 第一道防线就将缺陷消灭在摇篮之中的有效工具。FMEA是一种可靠性设计的重要方法。它实际上是MA（故障模式分析）和FEA（故障影响分析）的组合。它对各种可能的风险进行评价、分析， 以便在现有技术的基础上消除这些风险或将这些风险减小到可接受的水平。及时性是成功实FMEA的最重要因素之一，它是一个事前的行为， 而不是“事后的

2、行为。为达到最佳效益，FMEA必须在故障模式被纳入产品之前进行。FMEA实际是一组系列化的活动，其过程包括：找出产础程中潜在的故障模式；根据相应的评价体系对找出的潜在故障模式进行风险量化评估； 列出故障起因机理，寻找预防或改进措施。由于产品故障可能与设计、制造过程、使用、承包商共应商以及服务有关，因此FMEA又细分为设计FMEA、过程FMEA、使用FMEA和服务F MEA四类。其中设计FMEA和过程FMEA最为常用。设计FMEA（也记为d-FMEA）应在一个设计概念形成之时或之前开始，并且在产品开发各阶段中，当设计有变化或得到其他信息时及时不断地修 改，并在图样加工完成之前结束。其评价与分析的

3、对象是最终的产品以及每个与之相关的系统、子系统和零部件。需要注意的d-FMEA在体现 设计意图的同时还应保证制造或装配能够实现设计意图。因此，虽然MEA不是靠过程控制来克服设计中的缺陷，但其可以考虑制造装配过程中 技术的/客观的限制，从而为过程控制提供了良好的基础。进行-FMEA有助于：设计要求与设计方案的相互权衡；制造与装配要求的最初设计；提高在设计/开发过程中考虑潜在故障模式及其对系统和产品影响的可能性；为制定全面、有效的设计试验计划和开发项目提供更多的信息；建立一套改进设计和开发试验的优先控制系统；为将来分析研究现场情况、评价设计的更改以及开发更先进的设计提供参考。过程FMEA（也记为p

4、-FMEA）应在生产工装准备之前、在过程可行性分析阶段或之前开始，而且要考虑从单个零件到总成的所有制造过程。其评 价与分析的对象是所有新的部件过程、更改过的部件过程及应用或环境有变化的原有部件过程。需要注意的是，虽然p-FMEA不是靠改变产品设 计来克服过程缺陷，但它要考虑与计划的装配过程有关的产品设计特性参数，以便最大限度地保证产品满足用户的要求和期望。p-FMEA 一般包括下述内容：确定与产品相关的过程潜在故障模式；评价故障对用户的潜在影响；确定潜在制造或装配过程的故障起因，确定减少故障发生或找出故障条件的过程控制变量；编制潜在故障模式分级表，建立纠正措施的优选体系； 将制造或装配过程文件

5、化。FMEA技术的应用发展十分迅速。50年代初，美国第一次将FMEA思想用于一种战斗机操作系统的设计分析，到玉0年代中期，FMEA技术正式用于航天工业（Apollo计划）。1976年，美国国防部颁布了FMEA的军用标准，但仅限于设计方面。70年代末，FMEA技术开始进入汽车工业和 医疗设备工业。80年代初，进入微电子工业。80年代中期，汽车工业开始应用过程FMEA确认其制造过程。到了1988年，美国联邦航空局发布咨 询通报要求所有航空系统的设计及分析都必须使用MEA 1991年，ISO-9000推荐使用FMEA提高产品和过程的设计。1994年，FMEA又成为QS-9000的认证要求。目前，FM

6、EA已在工程实践中形成了一套科学而完整的分析方法。FMEA可以描述为一组系统化的活动，其目的是认可并评价产品/过程中的潜在失效以及该失效的后果确定能够消除或减少潜在失效发生机会的措施将全部过程形成文件无论是产品设计或者是过程设计，FMEA所关注的主要是策划和设计的过程，但随着其使用的场合不同又有不同的区分见的FMEA类别有：DFMEA:设计 FMEAPFMEA :过程 FMEAEFMEA:设备 FMEASFMEA:体系 FMEA在进行FMEA时有三种基本的情形，每一种都有其不同的范围或关注焦点情形1:新设计，新技术或新过程FMEA的范围是全部设计，技术或过程情形2:对现有设计或过程的修改假设对

7、现有设计或过程已有FMEA）.FMEA的范围应集中于对设计或过程的修改，由于修改可能产生的相互影响以 及现场和历史情况情形3:将现有的设计或过程用于新的环境场所或应用（假设对现有设计或过程已有FMEA）.FMEA的范围是新环境或场所对现有设计或过程的影响FMEA- 8D流程的介绍QS9000、ISO/TS16949, ISO9001、TL9000、ISO14001、OHSAS18001等管理体系中都有涉及到预防措施；依据“ISO9001： 2000质量管理体系一基础和术语”的定义，“预防措施，是指“为消除潜在不合格或其他潜在不期望情况的原因所采取的措施或者简单地定义为：采取预防措施是为了防 止

8、发生。在企业实际的管理体系运作中，虽然都会去编制一份有关预防措施，的形成文件的程序，但真正可以达到预见性地发现较全面的潜在问题通常存在 较大难度，也即：这样作业的可操作性不强；取而代之的主要是纠正措施；但“纠正措施与预防措施的确是两个不同的概念，“纠正措施是为 了防止同样的问题再次出现所采取的措施。为能有效地实施预防措施，使可能存在的潜在问题无法出现，需要一个从识别问题到控制潜在影响的管理系统，对于这一点，各企业都可能制定 各自不同的方法以对应，这些方法也许都是适用的；但这里所要介绍的是一种行之有效且便于操作的制定和实施防措施的方法，即：美国三大 车厂（戴姆勒克莱斯特、福特、通用）制定的潜在失

9、效模式及后果分析，或简称为FMEA。FMEA于2002年推出第三版本，该第三版本较第二版本更具备简便的可操作性FMEA在汽车零组件生产行业已被广泛的应用，同时这也是美国 三大车厂对所属供应商的强制性要求之一。FMEA事实上就是一套严密的预防措施之识别、控制、提高的管理过程;其不仅可在汽车零组件行业可予使用，也可应用于任何期望能严格控制 潜在问题出现的行业，尤其是产品（或服务）质量的好坏可能会极大影响到顾客利益的领域；因此MEA能在QS9000及ISO/TS16949一类的汽 车业质量管理体系中运用，其同样可应用于其他管理体系之中，而且同样可以在企业内部形成一种严密的防措施系统。执行FMEA，其

10、实并不困难，它是一种分析技术，即：在一张包括诸多要求的表单上进行分析并加以控制和应用便可达成的过程控制；美国三大车厂在潜在失效模式及后果分析一书中已有明确给定了这种表单的格式；该表单包含了如下主要内容：（1）“功能要求，：填写出被分析过程（或工序）的简单说明；（2）“潜在失效模式：记录可能会出现的问题点；（3）“潜在失效后果，：列出上述问题点可能会引发的不良影响；（4）“严重度，：对上述问题点的不良影响进行评价并赋予分值（得分10分），分值愈高则影响愈严重；（5）“潜在失效起因或机理：该潜在问题点可能出现的原因或产生机理分析；（6）“频度”：上述“起因或机理出现的几率大小（得分110分），分值

11、愈高则出现机会愈大；（7）“现行控制，：列出目前本企业对这一潜在问题点所运用的控制方法；（8）“探测度，：在采用，现行控制，的方法来控制时，该潜在问题可以被检查出来的难易程序（得分110分），得分愈高则愈难以被检出；（9）“风险顺序数，：将上述严重度”、“频度，、“探测度”得分相乘所得出的结果；该数值愈大则这一潜在问题愈严重，愈应及时采颠防措施，；（10）“建议措施，：列出对风险顺序数，较高之潜在问题点所制定的预防措施，以防止其发生；（11）“责任及目标完成日期，：写出实施上述预防措施，的计划案；（12）“措施结果，：对上述，预防措施，计划案之实施状况的确认。从上述内容项目不难看出这已经包含了

12、处理预防措施，之识别、控制所需的全部基本要求。由于FMEA是一种“预防措施，其必然是一种事先的行动；如果把MEA当作事情发生以后再执行处置的动作，其将无法达到MEA的真实效果， 亦将把这一 FMEA演变成“纠正措施，。汽车行业产品由于存在人身安全风险及车辆召回等危机，不得不严格执彳预防措施，其最有效的、最全面的方式也就是运府MEA。对于其他行业（或其他管理体系）在执行预防措施时，如果采用FMEA，同样将会极大降低失败的机会，事实上这亦商防措施，的最终目的。当然对于其他行业（或其他管理体系）而言，不一定完全按照美国三大车厂给定爵重度、“频度及“探测度之评价标准进行评分，完全可以视本企业之实际情况

13、设定一系列类似的评价标准以执行对策作业，且在具体操作手法上也可根据实情采用适合于自身的方式，只要能达到更有效地识 别、控制潜在问题的发生即可。总之，认识、了解FMEA，并予以持续采用，将会极大地强化企业的预防措施效果，使，错误”、“失败，出现的可能性达到最小。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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38、WiT也 p jTl2214FL1 海比ceWlOCrftiflip.日.&两 1血1普庄沁 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