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首页 机械工程英语第二版翻译

机械工程英语第二版翻译.doc

机械工程英语第二版翻译

紧紧相依心连心
2017-10-07 0人阅读 举报 0 0 暂无简介

简介:本文档为《机械工程英语第二版翻译doc》,可适用于工程科技领域

机械工程英语第二版翻译UnitTypesofMaterials材料的类型MaterialsmaybegroupedinseveralwaysScientistsoftenclassifymaterialsbytheirstate:solid,liquid,orgasTheyalsoseparatethemintoorganic(onceliving)andinorganic(neverliving)materials材料可以按多种方法分类。科学家常根据状态将材料分为:固体、液体或气体。他们也把材料分为有机材料(曾经有生命的)和无机材料(从未有生命的)。Forindustrialpurposes,materialsaredividedintoengineeringmaterialsornonengineeringmaterialsEngineeringmaterialsarethoseusedinmanufactureandbecomepartsofproducts就工业效用而言材料被分为工程材料和非工程材料。那些用于加工制造并成为产品组成部分的就是工程材料。Nonengineeringmaterialsarethechemicals,fuels,lubricants,andothermaterialsusedinthemanufacturingprocess,whichdonotbecomepartoftheproduct非工程材料则是化学品、燃料、润滑剂以及其它用于加工制造过程但不成为产品组成部分的材料。Engineeringmaterialsmaybefurthersubdividedinto:MetalCeramicsCompositePolymers,etc工程材料还能进一步细分为:金属材料陶瓷材料复合材料聚合材料等等。MetalsandMetalAlloys金属和金属合金MetalsareelementsthatgenerallyhavegoodelectricalandthermalconductivityManymetalshavehighstrength,highstiffness,andhavegoodductility金属就是通常具有良好导电性和导热性的元素。许多金属具有高强度、高硬度以及良好的延展性。Somemetals,suchasironshavecooledsufficientlythemoldhalvesareopenedatthemoldpartingplaneandthepartsejectedbyaknockoutsystemdropintoareceivingbinbelow模具被紧紧地夹住以抵抗注塑压力并在热塑性塑料的融化温度以下很好地冷却。当模腔内的零件充分冷却剖分模在模具分模面处打开推出系统将零件推出落入下面的接收容器内。Thissummarizestheoverallcycle,butleavesoutmuchvitaldetailthatisnecessaryforunderstandingtheprocessHowever,withthisintroduction,itispossibletounderstandtheadvantagesanddisadvantagesoftheprocess这概述了整个循环但省略了许多对理解此工艺所必需的很重要细节。然而通过本介绍了解这种工艺的优缺点仍是可能的。EffectsofProcessVariablesonOrientation加工变量对方向性的影响Ininjectionmolding,anyvariationinprocessingthatkeepsthemoldingresinhotthroughoutfillingallowsincreasedrelaxationand,therefore,decreasedorientationSomeofthestepsthatcanbetakentoreduceorientationareasfollows在注塑成型时整个填料过程始终保持成型树脂高温的任何加工变化都会增加松弛作用而减少方向性。下面是可以用于减少方向性的若干措施。Fasterinjection(uptoapoint):lesscoolingduringfilling,henceathinnerinitialfrozenlayer,lowerviscosityduetoshearthinningbetterflowtocornersandlesscrystallinityallfavorlowersubsurfaceorientationTheprimaryeffectisthatthegatewillfreezemorequicklyAtthatpoint,orientationstopsandrelaxationstarts较快注塑(到点):在填料过程中冷却较少因此初始固化层较薄由于剪应变稀少而粘性较低能较好地流到角落结晶度较小所有这些促成表面下的方向性也较低。主要效果是闸道将较快固化。这样使得方向性停止产生而松弛作用开始增加。Highermeltandmoldtemperatures:lowermeltviscosity,easierfilling,andgreaterrelaxationfavorreducedorientationReducedpackingtimeandpressure:overpackinginhibitsrelaxationprocesses较高的融化和成型温度:融化粘性较低更容易填充较大松弛作用促成方向性减少。减少挤压时间和压力:过度挤压会抑制松弛过程。Reducedgatesize:largergatestakelongertofreezeoffandpermitincreasedorientation减小闸道尺寸:闸道越大则固化时间越长并会使方向性增加。ExcessivelyhighinjectionspeedcancausehighsurfaceorientationandincreasesusceptibilitytostresscrackingForexample,moldingsthataretobeelectroplated,andwillbesubjecttoacidsolutionsduringplating,mustbemadeusingveryslowinjectionspeedstominimizesurfaceorientation过高的注塑速度会引起较高的表面方向性及增加应力破裂的敏感性。例如要电镀的注塑件在电镀时会经受酸溶液必须采用很低的注塑速度制造以使表面方向性最小化。Ontheotherhand,thetransversemotioncomponentofthemeltfrontinmostmoldingscancausetransversesubsurfaceorientationsuperimposedontheprimaryorientation,givingadesirablebiaxialorientationeffect另一方面大多数注塑件的融化前部横向运动部分能导致在主要方向性上有层理的表面下横向方向性产生需要的双轴方向性效应。OrientationcanbeseriouslyincreasedbyobstructionstoflowduringfillingofthecavityFlowaroundanobstructioncausesadecreaseinmeltfrontspeedandleadstohighlocalviscosityandreducedrelaxationThisisalsolikelytooccurneartheendofthefillingphaseifgatingisinadequate在填充模腔时流动受到阻碍会极大地增加方向性。围绕障碍物流动使融化前部的速度下降并产生较高的局部粘性而减少松弛作用。如果闸道不适当这也很可能发生在接近填充结束阶段。Themoldermustrecognizethedangersofexcessivefillspeed,insufficientinjectionpressure,excessivemelttemperature,andinadequatepackingThesedangersareweighedagainsttheopposingeffectsonorientationdiscussedabove注塑工必须认识过快填充速度、不足注塑压力、过高融化温度和不充分挤压的危害性。这些危害性要与上述方向性的反向效应相权衡。ThickerpartsdelaycoolingandincreaserelaxationtimeandtendtoresultinlowerorientationThickerpartsalsotendtowarplessTherefore,aminimumwallthicknesscanbeestablishedbyexperienceforvariousshapes,materials,andprocesscombinations较厚零件会延迟冷却并且增加松弛时间趋向于导致较低的方向性。较厚零件也有助于减少翘曲。因此对各种形状、材料和工艺组合能通过经验来确定最小壁厚。Lowermolecularweightandbroadermolecularweightdistributioninthermoplasticsfavorlowerorientationandreducedinternalstressinmoldings在热塑性塑料中较小的分子量以及较宽泛的分子量分布促成方向性减少同时降低注塑件中的内应力。Theskinthicknessratioisaffectedbyprocessvariablesinthesamewayasonewouldpredictfortheorientationthatis,itdecreasesasthemeltormoldtemperaturesandcavitypressureincreasesTensilestrengthandstiffnessincreaseasskinthicknessratioincreasesMicroscopicexaminationthusprovidesanotherwayofstudyingtheprocessefficiently外壳厚度比受加工变量影响的方式与方向性预测一样也就是它能随融化或成型温度及模腔压力的增加而减少。拉伸强度和硬度随外壳厚度比增加而增加。因而显微镜检查提供了有效研究该工艺的另一方法。Advantages优点HighproductionratesForexample,aCDdiskcanbeproducedwitha~scycleinhighmeltflowindexPC高生产率:例如一张CD盘在高融体流动指数生产控制中只需~s一个循环就能生产出来。RelativelylowlaborcontentOneoperatorcanfrequentlytakecareoftwoormoremachines,particularlythemoldingsareunloadedautomaticallyontoconveyors相对较少的工作内容:一个操作者经常可以照看两台以上机械尤其是当成品能自动卸到输送机上时。PartsrequirelittleornofinishingForexample,flashcanbeminimizedandmoldscanbearrangedtoautomaticallyseparaterunnersandgatesfromthepartitselfVerycomplexshapescanbeformedAdvancesinmoldtoolingarelargelyresponsible零件几乎不需要修整:例如飞边可以最小化并且模具能被设计成自动将浇道和闸道从零件本身分离。非常复杂的形状也能成型:模具的进步很大程度上是可靠的。Flexibilityofdesign(finishes,colors,inserts,materials)MorethanonematerialcanbemoldedthroughcoinjectionFoamcorematerialswithsolidskinsareefficientlyproducedThermosettingplasticsandfiberreinforcedshapesareinjectionmolded设计的灵活性(光洁度、颜色、插入物、材料):通过复合注塑可以成型多于一种材料。可以高效地生产带有固体外壳的泡沫型芯材料。热硬化性塑料和纤维加强形状都可以注塑成型。MinimumscraplossRunners,gates,andscrapcanusuallyberegroundRecycledthermoplasticscanbeinjectionmolded废料损失最小化:浇道、闸道和废料通常可以重新研磨。循环热塑性塑料可以注塑成型。ClosetolerancesareobtainableModernmicroprocessorcontrols,fittedtoprecisionmolds,andelaboratehydraulics,facilitatetolerancesintherangeondimensionsandweights(butnotwithoutahighlevelofoperationalskillsinconstantattendance)能得到接近的公差:现代微处理器控制、合适的精密模具和精心制作的液压设备使得尺寸和重量的公差保持在的范围内(但不是没有在持续照看时的高水平操作技能)。Makesbestuseoftheuniqueattributesofpolymers,suchasflowability,lightweight,transparency,andcorrosionresistanceThisisevidentfromthenumberandvarietyofmoldedplasticproductsineverydayuse充分利用聚合物诸如流动能力、重量轻、透明和耐腐蚀等独特属性:从日常使用成型塑料产品的数量和种类就能明显看到。DisadvantagesandProblems缺点和问题HighinvestmentinequipmentandtoolsrequireshighproductionvolumesLackofexpertiseandgoodpreventivemaintenancecancausehighstartupandrunningcosts较高的设备和模具投资需要较高生产量才合算。缺少专门技术和良好的预防性维修会导致较高的启动和运行成本。QualityissometimesdifficulttodetermineimmediatelyForexample,postmoldwarpagemayrenderpartsunusablebecauseofdimensionalchangesthatarenotcompletedforweeksormonthsaftermolding质量有时难以马上确定。例如成型后的翘曲会导致零件不能用因为在成型后几星期甚至几个月尺寸变化都不能完成。AttentionisrequiredonmanydetailsrequiringawidevarietyofskillsandcrossdisciplinaryknowledgePartdesignsometimesisnotwellsuitedtoefficientmolding对许多需要广泛多样性技能和交叉学科知识的细节必须加以注意。零件设计有时不能很好地适应有效率的成型。Leadtimeformolddesign,moldmanufactureanddebuggingtrialsissometimesverylong模具设计、模具制造和调试试验这些先导工作有时要花费很长时间。UnitTheimportanceofmachiningprocessescanbeemphasisedbythefactthateveryproductweuseinourdailylifehasundergonethisprocesseitherdirectlyorindirectly()InUSA,morethan$billionsarespentannuallyonmachiningandrelatedoperations机加工过程的重要性可通过日常生活使用的每件产品都直接或间接经历这一过程的事实来强调。()在美国每年花在机加工及其相关作业上的费用都多于千亿美元。()Alargemajority(above)ofallthemachinetoolsusedinthemanufacturingindustryhaveundergonemetalcutting()AnestimateshowedthatabouttoofallthemetalproducedinUSAwasconvertedintochips()用于制造业的全部机床中的大多数(多于)都经历过金属切削。()有估计显示美国生产的所有金属中约到转变成了切屑。ThesefactsshowtheimportanceofmetalcuttingingeneralmanufacturingItisthereforeimportanttounderstandthemetalcuttingprocessinordertomakethebestuseofit这些事实说明了金属切削在常规制造中的重要性。因此了解金属切削过程以充分利用它是重要的。Anumberofattemptshavebeenmadeinunderstandingthemetalcuttingprocessandusingthisknowledgetohelpimprovemanufacturingoperationswhichinvolvedmetalcutting在了解金属切削过程并运用这些知识帮助改善与金属切削有关的制造作业方面已经做了许多努力。AtypicalcuttingtoolinsimplifiedformisshowninFigTheimportantfeaturestobeobservedarefollows典型切削刀具的简化形式如图所示。要注意的重要特征如下。RakeangleItistheanglebetweenthefaceofthetoolcalledtherakefaceandthenormaltothemachiningdirectionHighertherakeangle,betteristhecuttingandlessarethecuttingforces,increasingtherakeanglereducesthemetalbackupavailableatthetoolrakeface前角:它是被称为前倾面的刀具面与垂直机加工方向的夹角。前角越大则切削越好且切削力越小增加前角可以减少刀具前倾面上产生的金属阻塞。ThisreducesthestrengthofthetooltipaswellastheheatdissipationthroughthetoolThus,thereisamaximumlimittotherakeangleandthisisgenerallyoftheorderofforhighspeedsteeltoolscuttingmildsteelItispossibletohaverakeanglesatzeroornegative但这会和减少通过刀具散发的热量一样减少刀尖强度。因此前角有一最大限制用高速钢刀具切削低碳钢通常为。前角取零度或负值也是可能的。ClearanceangleThisistheanglebetweenthemachinedsurfaceandtheundersideofthetoolcalledtheflankfaceTheclearanceangleisprovidedsuchthatthetoolwillnotrubthemachinedsurfacethusspoilingthesurfaceandincreasingthecuttingforcesAverylargeclearanceanglereducesthestrengthofthetooltip,andhencenormallyanangleoftheorderof~isused后角:这是机加工面与被称为后侧面的刀具底面夹角。后角使刀具不产生会损坏机加工面的摩擦和增加切削力。很大的后角会削弱刀尖的强度因此一般采用~的后角。Theconditionswhichhaveanimportantinfluenceonmetalcuttingareworkmaterial,cuttingtoolmaterial,cuttingtoolgeometry,cuttingspeed,feedrate,depthofcutandcuttingfluidused对金属切削有重要影响的条件有工件材料、刀具材料、刀具几何形状、切削速度、进给率、切削深度和所用的切削液。Thecuttingspeed,v,isthespeedwithwhichthecuttingtoolmovesthroughtheworkmaterialThisisgenerallyexpressedinmetrespersecond(ms)切削速度v指切削刀具经过工件材料的移动速度。通常用米每秒(ms)表示。Feedrate,f,maybedefinedasthesmallrelativemovementpercycle(perrevolutionorperstroke)ofthecuttingtoolinadirectionusuallynormaltothecuttingspeeddirectionDepthofcut,d,isthenormaldistancebetweentheunmachinedsurfaceandthemachinedsurface进给率f可定义为每循环(每转或每行程)切削刀具在通常为垂直于切削速度方向的次要相对运动。切削深度d是未加工面与已加工面之间的垂直距离。ChipFormation切屑的形成MetalcuttingprocessisaverycomplexprocessFigshowsthebasicmaterialremovaloperationschematically金属切削过程是一个很复杂的过程。图用图的形式显示了基本材料去除作业。Themetalinfrontofthetoolrakefacegetsimmediatelycompressed,firstelasticallyandthenplasticallyThiszoneistraditionallycalledshearzoneinviewoffactthatthematerialinthefinalformwouldberemovedbyshearfromtheparentmetal在刀具前倾面前的金属直接受到压缩首先弹性变形然后塑性变形。考虑到最终形状中的材料是通过剪切从母体金属去除的此区域传统上称为剪切区。Theactualseparationofthemetalstartsasayieldingorfracture,dependinguponthecuttingconditions,startingfromthecuttingtooltipThenthedeformedmetal(calledchip)flowsoverthetool(rake)face金属的实际分离始于屈服或断裂(视切削条件而定)从切削刀尖开始。然后变形金属(称为切屑)流过刀具(前倾)面。Ifthefrictionbetweenthetoolrakefaceandtheundersideofthechip(deformedmaterial)isconsiderable,thenthechipgetsfurtherdeformed,whichistermedassecondarydeformationThechipafterslidingoverthetoolrakefaceisliftedawayfromthetool,andtheresultantcurvatureofthechipistermedaschipcurl如果刀具前倾面与切屑(变形金属)底面之间的摩擦相当大那么切屑进一步变形这也叫做二次变形。滑过刀具前倾面的切屑被提升离开刀具切屑弯曲的结果被称为切屑卷。Plasticdeformationcanbecausedbyyielding,inwhichcasestrainedlayersofmaterialwouldgetdisplacedoverotherlayersalongtheslipplaneswhichcoincidewiththedirectionofmaximumshearstress屈服能导致塑性变形在这种情况下材料变形层沿着与最大剪应力方向一致的滑移面被其它层所取代。AchipisvariablebothinsizeandshapeinactualmanufacturingpracticeStudyofchipsisoneofthemostimportantthingsinmetalcuttingAswouldbeseenlater,themechanicsofmetalcuttingaregreatlydependentontheshapeandsizeofthechipsproduced在实际加工过程中切屑的尺寸和形状都是变化的。对切屑的研究是金属切削最重要的事情之一。如同后面将要看到的那样金属切削力学极大地依赖于所产生切屑的形状和尺寸。Chipformationinmetalcuttingcouldbebroadlycategorisedintothreetypes:(Fig)()Discontinuouschip()Continuouschip()ContinuouschipwithBUE(Builtupedge)金属切削中的切屑形成可以宽泛地分成三个类型(图):()间断切屑()连续切屑()带切屑瘤的连续切屑DiscontinuousChipThesegmentedchipseparatesintoshortpieces,whichmayormaynotadheretoeachotherSeveredistortionofthemetaloccursadjacenttotheface,resultinginacrackthatrunsaheadofthetool间断切屑:分段的切屑分散成小碎片既可能相互附着也可能不相互附着。在靠近切削面处发生金属的剧烈变形导致在运动刀具前方金属层产生裂缝。Eventually,theshearstressacrossthechipbecomesequaltotheshearstrengthofthematerial,resultinginfractureandseparationWiththistypeofchip,thereislittlerelativemovementofthechipalongthetoolface,Figa最后横过切屑的剪切应力与材料的剪切强度相等造成断裂和分离。生成这类切屑时切屑沿刀具面几乎没有相对运动见图a。ContinuouschipThecontinuouschipischaracterizedbyageneralflowoftheseparatedmetalalongthetoolfaceTheremaybesomecrackingofthechip,butinthiscaseitusuallydoesnotextendfarenoughtocausefracture连续切屑:连续的切屑一般具有分离金属沿刀具面流动的特征。切屑可能有一些破裂但在这种情况下切屑通常不会延长到足以引起断裂。ThischipisformedatthehighercuttingspeedswhenmachiningductilematerialsThereislittletendencyforthematerialtoadheretothetoolThecontinuouschipusuallyshowsagoodcuttingratioandtendstoproducetheoptimumsurfacefinish,butitmaybecomeanoperatinghazard,Figb这种切屑形成于用较高切削速度机加工有延展性的材料时。材料几乎没有粘附刀具的倾向。连续切屑通常具有良好的切削率和趋向于产生最适宜的表面光洁度但可能成为操作的危险之源见图b。ContinuouswithabuiltupedgeThischipshowstheexistenceofalocalized,highlydeformedzoneofmaterialattachedor“welded”onthetoolface带切屑瘤的连续切屑:这种切屑显示了粘合或“焊接”在刀具面上材料局部高度变形区的存在。Actually,analysisofphotomicrographsshowsthatthisbuiltupedgeisheldinplacebythestaticfrictionforceuntilitbecomessolargethattheexternalforcesactingonitcauseittodislodge,withsomeofitremainingonthemachinedsurfaceandtherestpassingoffonthebacksideofthechip,Figc实际上对显微照片的分析显示这种切屑瘤受到静摩擦力抑制直至它变得大到作用在它上面的外力使其移动一些留在机加工表面上而另一些延伸到切屑的背面见图c。ShearZone剪切区TherearebasicallytwoschoolsofthoughtintheanalysisofthemetalremovalprocessOneschoolofthoughtisthatthedeformationzoneisverythinandplanarasshowninFigaTheotherschoolthinksthattheactualdeformationzoneisathickonewithafanshapeasshowninFigb在对金属去除过程的分析中主要存在两种思想学派。一种思想学派认为变形区如图a所示那样非常薄而平坦。另一学派则认为真实变形区象图b所示那样为一厚的带有扇形的区域。Thoughthefirstmodel(Figa)isconvenientfromthepointofanalysis,physicallyitisimpossibletoexistThisisbecauseforthetransitionfromundeformedmaterialtodeformtotakeplacealongathinplane,theaccelerationacrosstheplanehastobeinfinity虽然第一种模型(图a)从分析的角度看是方便的但实际上是不可能存在的。这是由于未变形的材料沿着剪切面发生变形而且越过剪切面的加速度无穷大。Similarlythestressgradientacrosstheshearplanehastobeverylargetobepractical同样在实际运用中越过剪切面的应力梯度必须很大才行。Inthesecondmodel(Figb)bymakingtheshearzoneoveraregion,thetransitionsinvelocitiesandshearstressescouldberealisticallyaccountedfor在第二种模型(图b)中让剪力区分布于一个范围速度和剪应力的转变能说明得更符合实际。Theanglemadebytheshearplanewiththecuttingspeedvector,ΦisaveryimportantparameterinmetalcuttingHighertheshearanglebetteristhecuttingperformanceFromaviewoftheFiga,itcanbeobservedthatahigherrakeanglesgiverisetohighershearangles由剪切面和切削速度矢量形成的角度Φ在金属切削中是一个十分重要的参数。剪切角越大切削作业越好。从图a观察可以看到较大的前角能增大剪切角。CuttingToolMaterials切削刀具材料VariouscuttingtoolmaterialshavebeenusedintheindustryfordifferentapplicationsAnumberofdevelopmentshaveoccurredinthecurrentcentury在工业中为了不同的应用可以使用各种各样的切削刀具材料。在最近的百年里产生了许多进展。AlargevarietyofcuttingtoolmaterialshasbeendevelopedtocatertothevarietyofmaterialsusedintheseprogrammesBeforewediscussthepropertiesofthesematerials,letuslookattheimportantcharacteristicsexpectedofacuttingtoolmaterial多种切削刀具材料被开发出来以满足这些方案中使用材料的多样性。讨论这些材料性能之前先看一下作为切削刀具材料应具备哪些重要特性。Higherhardnessthanthatoftheworkpiecematerialbeingmachined,sothatitcanpenetrateintotheworkmaterialHothardness,whichistheabilityofthematerialtoretainitshardnessatelevatedtemperaturesinviewofthehightemperaturesexistinginthecuttingzone硬度要比被切削工件材料高这样它才能进入工件材料。热硬度即材料由于存在于切削区的高温而升温时仍能保持其硬度的能力。WearresistanceThechiptoolandchipworkinterfacesareexposedtosuchsevereconditionsthatadhesiveandabrasionwearisverycommonThecuttingtoolmaterialshouldthereforehavehighabrasionresistancetoimprovetheeffectivelifeofthetool耐磨性切屑刀具与切屑工件的接触界面处于如此严酷的状态粘附和磨损是很普遍的。因此切削刀具材料应具有高耐磨性以提高刀具的有效寿命。ToughnessEventhoughthetoolishard,itshouldhaveenoughtoughnesstowithstandtheimpactloadsthatcomeinthebeginningofcutorforcefluctuationsduetoimperfectionsintheworkmaterialThisrequirementisgoingtobemoreusefulfortheinterruptedcutting,egmilling韧性虽然刀具是坚硬的但也应有足够的韧性以经受住冲击载荷这些载荷来自于切削的开始或由于工件材料的缺陷而产生的作用力波动。这个要求对如铣削之类的间断切削更有用。LowfrictionThecoefficientoffrictionbetweenthechipandtoolshouldbelowThiswouldallowforlowerwearratesandbetterchipflow低摩擦系数切屑与刀具间的摩擦系数应当较低。这会使磨损率较小及切屑流动更好。ThermalcharacteristicsSincealotofheatisgeneratedatthecuttingzone,thetoolmaterialshouldhavehigherthermalconductivitytodissipatethisheatintheshortesttime,otherwisethetooltemperaturewouldbecomehigh,reducingitslife热特性因为大量的热产生在切削区刀具材料应当具有较高的热传导性以在最短的时间内散发热量否则刀具温度会升高寿命会减少。AllthesecharacteristicsmaynotbefoundinasingletoolmaterialImprovedtoolmaterialshavebeengivingabettercuttingperformance所有这些特性不可能存在于单一刀具材料中。改进的刀具材料已经被赋予较好的切削性能。SurfaceFinish表面光洁度Machiningoperationsareutilizedinviewofthebettersurfacefinishthatcouldbeachievedbyitcomparedtoothermanufacturingoperations由于机加工能获得比其它制造作业更好的表面光洁度所以机加工作业具有实用价值。ThusitisimportanttoknowwhatwouldbetheeffectivesurfacefinishthatcanbeachievedinamachiningoperationThesurfacefinishinagivenmachiningoperationisaresultoftwofactors:因而了解能在机加工作业中获得怎样的实际表面光洁度是重要的。给定机加工作业中的表面光洁度是两个因素共同作用的结果:()theidealsurfacefinish,whichisaresultofthegeometryofthemanufacturingprocesswhichcanbedeterminedbyconsideringthegeometryofthemachiningoperation,and()thenaturalcomponent,whichisaresultofanumberofuncontrollablefactorsinmachining,whichisdifficulttopredict理想的表面光洁度是通过考虑机加工作业的几何体系所决定的制造工艺几何学的结果和自然要素即在机加工中一些难以预测的不可控因素作用的结果。IdealSurfaceFinishinTurningTheactualturningtoolusedwouldhaveanoseradiusinplaceofthesharptoolpoint,whichmodifiesthesurfacegeometryasshowninFigaIfthefeedrateisverysmall,asisnormalinfinishturning,thesurfaceisproducedpurelybythenoseradiusaloneasshowninFig车削中的理想表面光洁度实际使用的车削刀具有一个刀尖半径取代锋利刀尖它将表面几何形状加工为如图a所示。如果进给率很小象精车中很正常的那样工件表面则完全是由刀尖半径单独产生的如图所示。ForthecaseinFig,thesurfaceroughnessvalueistobeRa=f(R)Where:RaisthesurfaceroughnessvalueRisthenoseradiusfisthefeedrate对图这种情况表面粗糙度值为Ra=f(R)式中:Ra是表面粗糙度值R是刀尖半径f是进给率TheaboveareessentiallygeometricfactorsandthevaluesrepresentanidealsituationTheactualsurfacefinishobtaineddependstoagreatextentuponanumberoffactorssuchas:上述基本为几何要素其值代表了理想情况。而实际获得的表面光洁度很大程度上还取决于下列一些因素:()thecuttingprocessparameter,speed,feedanddepthofcut()thegeometryofthecuttingtool()applicationofcuttingfluid()workandtoolmaterialcharacteristics()rigidityofthemachinetoolandtheconsequentvibrations()切削工艺参数、速度、进给和切削深度()切削刀具的几何形状()切削液的运用()工件和刀具的材料特性()机床的刚度及其伴随发生的振动ThemajorinfluenceonsurfacefinishisexertedbythefeedrateandcuttingspeedAsthefeeddecreases,fromtheaboveequations,wecanseethattheroughnessindexdecreases对表面光洁度产生主要影响的是进给率和切削速度。从上述公式可以看到随着进给的减少粗糙度指标会降低。Similarlyasthecuttingspeedincreases,wehavebettersurfacefinishThuswhilemakingachoiceofcuttingprocessparametersforfinish,itisdesirabletohavehighcuttingspeedandsmallfeedrates同样随着切削速度的增大能得到较好表面光洁度。因此在为光洁度而选择切削工艺参数时采用较高的切削速度和较小的进给率是适当的。CuttingFluids切削液Thefunctionsofcuttingfluids(whichareoftenerroneouslycalledcoolants)are:TocoolthetoolandworkpieceToreducethefriction切削液(经常误称为冷却液)的功能如下:冷却刀具和工件减少摩擦ToprotecttheworkagainstrustingToimprovethesurfacefinishTopreventtheformationofbuiltupedgeTowashawaythechipsfromthecuttingzone保护工件不生锈改善表面光洁度防止切屑瘤的形成从切削区冲掉切屑However,theprimefunctionofacuttingfluidinametalcuttingoperationistocontrolthetotalheatThiscanbedonebydissipatingtheheatgeneratedaswellasreducingitThemechanismsbywhichacuttingfluidperformsthesefunctionsare:coolingactionandlubricatingaction然而在金属切削作业中切削液的主要功能是控制总热量。这可通过既散发又减少所产生的热量来达到。切削液实现这些功能的机理是:冷却作用和润滑作用。CoolingactionOriginallyitwasassumedthatcuttingfluidimprovesthecuttingperformancebyitscoolingpropertiesaloneThatiswhythenamecoolantwasgiventoit冷却作用:最初设想切削液仅仅是通过冷却特性来改善切削作业。这也是它曾被称为冷却液的原因。Sincemostofthetoolwearmechanismsarethermallyactivated,coolingthechiptoolinterfacehelpsinretainingtheoriginalpropertiesofthetoolandhenceprolongsitslife由于大多数刀具的磨损机理都是由热引起的冷却切屑刀具接触界面有助于保持刀具的原有特性从而延长其使用寿命。However,areductioninthetemperatureoftheworkpiecemayundercertainconditionsincreasetheshearflowstressoftheworkpiece,therebydecreasingtoollifeIthasbeenshownthroughanumberofinvestigationsthatcoolinginfactisoneofthemajorfactorsinimprovingthecuttingperformance可是工件温度的降低在特定条件下会增加工件的剪切流动应力从而降低刀具寿命。通过一些研究已经表明实际上冷却只是改善切削作业的主要因素之一。LubricatingactionThebestimprovementincuttingperformancecanbeachievedbythelubricatingactionsincethisreducestheheatgenerated,thusreducingtheenergyinputtothemetalcuttingoperation润滑作用:切削作业的最大改善可通过润滑作用来达到由于它减少了热量的产生因而减少了金属切削作业的能量输入。However,ifthecuttingfluidistobeeffective,itmustreachthechiptoolinterfaceButitisnoteasytovisualizehowitisaccomplishedinthecaseofacontinuousturningwithasinglepointturningtool,speciallywhenthechiptoolcontactpressureisashighasMPa可是如果要使切削液起作用就必须让它到达切屑刀具接触界面。但如何在采用单尖刀具连续车削的场合尤其是切屑刀具接触压力高达MPa时实现并非易事。MerchantthoughtthatminuteasperitiesexistedatthechiptoolinterfaceandthefluidwasdrawnintotheinterfacebythecapillaryactionoftheinterlockingnetworkofthesesurfaceasperitiesMerchant认为:在切屑与刀具接触界面上存在微小的粗粒切削液通过这些表面的微小粗粒组成连锁的网络的毛细管被吸入到切屑与刀具的接触界面上
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机械工程英语第二版翻译

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