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Howaredatumfeaturebonustolerancestypicallyappliedingauging?在检测中基准特征的盈余公差是如何应用的?
Attributeor"hardgauges,"iftheyaredesignedtoverifyconformanceofallfeaturessimultaneouslythat"declarethesamedatumfeaturesinthesameorderwiththesamedatumandtolerancemodifiers"physicallyapplythedatumfeaturebonustoleranceproperly.Bonustolerancesfromdatumfeaturesareappliedsimultaneouslytoallrelatedfeaturesbecausethedatumshiftisaccomplishedphysicallyto"fit"thepartonthegauge.Thatsaid,manyofthehardgaugesaredesignedtoverifyacollectionoffunctionallyrelatedfeatures,whichmayormaynotincludeeveryidenticallyreferencedfeaturespecification.The"
rincipleofsimultaneity"inthedimensioningandtolerancingstandardestablishestheconstraintbutitcanhowever,berevokediftheindividualfeatureshavethewords"SEPARATEREQUIREMENT"attachedtothefeaturecontrolframe.
属性或硬检具,如果对于所有注明有相同的顺序,具有相同的公差修正符号的相同基准特征他们用于同时验证特征的一致性,按照规律响应地应用基准特征盈余公差.源于基准特征的盈余公差会同时应用到所有相关的特征上,由于实际上把零件与检具相配合时就,产生了基准偏移.那也就是说许多硬检具是用于验证相关特征的综合作用,是否会包含每个同样地参考特征要求.尺寸公差标准内的同时性要求建立了限制但是如果单个特征带有与公差控制框相连的”单独要求”时,它就不起作用了.
Mostvariablesdatagaugingdevicesaredesignedtorestrictmovementofdatumfeaturestostabilizethemeasurementofrelatedfeatures.Consequentlythe"bonustolerance"attributabletodatumfeaturesizeisnotconsidered."Bonustolerances"forbothfeaturesanddatumsaretypicallyignoredwithsimplevariablesdatagaugingdevices.Furthermore,thedatagatheredfromthesedevicesiscommonlyusedtomonitorandcontrolprocessesstatisticallyand,asstatedearlier,thetraditionalcalculationsoftheindices"Ppk,Cpk"thatreflectconformancetospecificationdonotaccommodateavariabletolerances.
大部分可变数据检测设备用于限制基准特征的移动以便固定相关特征的测量.所以就不需要考虑由基准特征尺寸产生的盈余公差.对特征和基准的盈余公差会单一可变数据检测设备.而且从这些设备采集到的数据通常用于监控和统计控制工艺.如前面提到的如包括Ppk,Cpk的传统计算反映符合不适应可变公差的规范
Theonlyvariablesdatagagingdevicesthatdoaddress"bonustolerances"aresoftwaredrivendevices.Theseinclude,coordinatemeasuringmachines,visualcomparatorsandothertoolswithintegrateddataanalysis.Thesoftwaretypicallyincludesoptionstoenableordisabletheapplicationof"bonustolerances"intheanalysis.Whilemostofthesoftwareroutinescorrectlyapplytheindividualfeature"bonustolerance"tothefeatureitself,the"bonustolerance"derivedfromthedatumfeatureiscommonlyappliedindependentlyratherthancollectivelytoallrelatedfeatures.Applyingthedatumfeaturebonustolerancecorrectlywouldrequireaniterativeapproachtoshifttheoriginofmeasurementafteracquiringthemeasuredresultsfromallrelatedfeatures.Sincethemeasurementprocessisgenerallyaccomplishedandreportedsequentiallyfew,ifanyprogrammers-operatorsapplydatumfeature"bonustolerances"correctly.Whenitisappliedindependentlytoindividualfeaturesitisworsethannotapplyingitatallbecauseitpermitstoleranceincreasesbeyondthespecification.Aswiththesimplevariablesdatagaugingdevicesthetraditionalstatisticalevaluationsof"Ppk,Cpk"demandaconstanttolerancesoeveniftheresultsfromproperlyappliedbonustolerancesdemonstratethattheresultsarewithinspecification,thestatisticalevaluationwillstrip-awaybonustolerancesandyielddifferentresults.
只有提供盈余公差的可变数据检测设备是有软件驱动的.这些包括,CMM,可视对比器和其它的具有整合数据分析的工具.在分析中软件包括是否应用盈余公差的选项.大多数软件路径能正确给特征自己应用单独特征的盈余公差,从基准特征中得到的盈余公差是分别应用到所有的相关特征而不是同时.在从所有相关特征取得测量结果后,正确应用的基准特征盈余公差会需要一个反复的过程去移动测量原点.由于测量工艺一般很少是按顺序完成并报告,如果有程序员正确地应用数据功能“盈余公差”。当它被单独应用到独立的特征时,比不应用到所有的特征更差，因为它允许公差超出规定。与简单可变数据测量设备相比,“Ppk，Cpk”的传统统计评估需要一个固定的公差,这样即使从应用适当的盈余公差中得到的结果表明该结果符合规范，统计评价将去处盈余公差,产生不同的结果。
ShouldthemanufacturingprocessorgaugingconstraintsdrivetheselectionoftheDatumandFeatureToleranceModifiers?No!Productdesignsshoulddescribefeaturetolerancesaccordingtotheirconstraintsforfitandfunctionsothattheproductwillperformasintendedandultimatelyprovidevaluetothecustomer.GeometricDimensioningandTolerancingprovidesthetooltoconveythoseboundariesandconstraintsandifdepictedproperlywilldescribeonlyfitandfunctionnotmanufacturingorgaugingconstraints.Whenthedesignisdetailedassuchmanufacturersarefreetoreplicatebestpracticeswithouttriggeringdesignchanges.Theyhavethelibertytoemployinnovativeandreliableprocessestomanufactureproducts.Whenthedesigncodifiesaparticularmanufacturingorgaugingstrategyitfrustratesalternativestrategiesandoftencompromisesthefunctionaldefinitioninfavorofconcessionstoresidentassumptions.
生产工艺或测量限制应该规定基准和特征公差修正符的选择么?不!产品设计应该根据配合和功能的限制来描述特征公差,以便产品按照预想方案工作,最终给客户提供价值.GD&T提供一个传达边界和约束的工具,如果合适的描述仅仅是描述了配合和功能而不是制造和检测限制.当设计制定详细的生产或检测方案,那么它就会破坏了其它可能的选择并且常常
Recentbreakthroughsinstatisticalmethodstoapplybonustolerancestoprocesscapabilityevaluationsraisenewissues.Whiletheirdiscoverymaybebeneficialformanufacturingbecauseitpermitsthemtousemoreofthespecifiedtolerancetodemonstrateprocesscapability,itmayalsobealiabilitytothecustomerifthedatumandtolerancemodifierswerechosenfornonfunctionalpurposes.Sincethe(M)modifierispreferredtoenable"hardgauging"orchosenbecausethetolerancepertainstoa"featureofsize,"asstatedearlier,itislikelythatsomespecificationsmayhavenonfunctionalmodifiers.Sincemoststatisticalevaluationsignorethebonus,manufacturingispenalizedstatisticallyinreportingcapabilityevaluations.Iftheadditionaltoleranceisnowappliedandhere-to-foreincapableormarginalprocessperformancesarevalidatedthenthecustomerisultimatelyaffected.
统计方法上,应用到工艺能力评估上的盈余公差的方法取得的突破带来了新的问题.然而他们的发现可能对生产带来益处,因为它对于表现工艺能力时可以使用更多的规定公差.对于非功能性的目的是否采用基准和公差修正符客户也有责任.由于M修正符更倾向或选择硬检具,因为公差适合尺寸特征,如前面所描述一些规定可能具有非功能性的修正符,由于大多数统计评估忽略盈余,在报告能力评估时,生产会在统计学上受到惩罚.如果现在应用额外的公差并且接受了无用的或边界工艺性能那么客户最终会受到影响.
Howshoulddatumandfeaturetolerancemodifiers(M),(L),&(S)beappliedtoproductdesigns?Datumandfeaturetolerancemodifierdesignationsgreatlyinfluencehowtheboundariesoffeaturetoleranceareinterpreted,howsizecontributestogeometrictolerances,andhowgagingormeasurementisperformed.Theproductdesignercanchoosethecorrectmodifierbyansweringthesimplequestion:"Howdoessizeaffectthefunctionalrelationshipbetweenfeatures?"Iffitandfunctionistheprimarydriverthentheproductcanorwillbeevaluatedaccordingtoitsfunctionalconstraintsultimatelybenefitingtheconsumer.Therearemanycompetingjustificationsforchoosingthesemodifiersbutnoneareasimportantasfunction.
基准和特征公差修正符应该怎样应用到产品设计中呢?基准和特征公差修正符的指定极大地影响了如何解释特征公差边界,如何对几何公差产生影响以及检具或测量的性能如何.通过回答以下问题,产品设计者就能选择正确的修正符”尺寸是怎样影响特征间的功能关系?”如果配合和功能是主要驱动者,那么根据它的功能限制产品能或可以被评估极大地有益于客户.对于选择这些修正符存在许多激烈的正当理由,但是没有什么比功能性更重要的了. |
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发表于 2010-11-29 21:26:23
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