《机械专业英语》课件第6章

Unit6TEXTLEARNTOSPEAKNEWWORDSANDEXPRESSIONSNOTESEXERCISES

READINGMATERIALPROFESSIONALWORDSANDPHRASES TheDesignofJigsandFixtures

Holdingdevicesmaybeclassifiedasjigsorfixtures.Ajigisawork-piecelocatingandholdingdevicewhichpositionsandguidesorcontrolsacuttingtool.Afixtureisawork-piecelocatingandholdingdeviceusedwithmachinetools,inspection,weldingandassembly.Itdoesnotcontrolthepositionofthetoolorinstrumentwhichisbeingused.Inmanyinstancesgaugeblocksmaybeprovidedforsettingthedepthorpositionofthecuttingtool.TEXTFig.6-1Drillingjig

Thedesignerapproachesthedesignprojectbyfirstbecomingfullyawareofallcriticaldimensionsandsurfaces.Ifpossible,heshouldalsoknowhowthepartfitsintothemainassembly.Onceheisfamiliarwiththespecialfunctionalrequirementsanddimensions,hecollectsthedatawhichmayhaveaneffectonhisdesign.Datasuchastypeofmaterial,physicalproperties,weight,andthecharacteristicsoftherawmaterial.Otherinformationwhichcouldaffectthetypeoffixturetobebuiltistheproductionquantities,lotsizes,etc.

Nextthedesignerdetermineswhetherfixturesalreadyintheplantcanbealteredandusedforhisjob.Hemustalsoconsiderthepossibilityandadvisabilityofusingstandardholdingdevicessuchasvises,parallelsandclamps.

Onceitisdecidedthataseriesofoperationsaretobedonewithnewlydesignedfixtures,thedesignercombinesasmanyoperationsintoonefixtureaspossible.Fig.6-2Millingfixture LEARNTOSPEAKMr.Zhang: Goodmorning,Mr.Cheng.Mr.Cheng: Goodmorning,Mr.Zhang.Mr.Zhang: Whatareyoudoing?Mr.Cheng: Iammachiningawork-piece.Mr.Zhang: What’sthis?Mr.Cheng: Itisafixture.Mr.Zhang: Whatcanitdo?Mr.Cheng: Wecanuseittolocateandholdthework-piecewhenitismachined.Mr.Zhang: Isthefixtureonlybeusedtomachine?Mr.Cheng: No.Infacttherearemanykindsoffixtureandtheycanalsobeusedforinspection,weldingandassembly.Mr.Zhang: Whatareitsadvantages?Mr.Cheng: Wecanimprovetheproductprecisionandreducetimeassumptionoflocatingthework-piece.Mr.Zhang: It’sverykindofyoutotellmeaboutthese.Mr.Cheng: That’sallright.classifiedas 分为locatingandholdingdevice定位和夹紧装置gaugeblock 量块criticaldimension 重要尺寸physicalproperty 物理性能rawmaterial 原材料

NOTES1．Holdingdevicesmaybeclassifiedasjigsorfixtures.夹持装置可以分为钻模和夹具。

beclassifiedas 分为

像这类后面用as引出的补语的动词还有：

characterize…as 表示……的特征为

consider…as 认为……是

define…as 把……定义为

describe…as 把……描绘成

regard…as 认为……是

use…as 把……用作2．Thedesignerapproachesthedesignprojectbyfirstbecomingfullyawareofallcriticaldimensionsandsurfaces.设计师首先通过全面了解零件的关键尺寸和表面来决定设计方案。

becomeawareof发觉，了解

“firstbecomingfullyawareofallcriticaldimensionsandsurfaces”这一V-ing短语与“by”一起构成介词短语，修饰谓语动词，表示方法、手段。3．Datasuchastypeofmaterial,physicalproperties,weight,andthecharacteristicsoftherawmaterial.像材料的类型、物理性能、重量以及原材料的特性等。

这一部分虽然以大写字母开始，以句号结束，但不是句子，而是前面句中data的同位语，作进一步的说明。

4．Nextthedesignerdetermineswhetherfixturesalreadyintheplantcanbealteredandusedforhisjob.接着，设计师确定厂里已有的夹具是否能改动一下，以供使用。

Next(本句中用作adv.)有两种用法：

(1) adj.其次的，下(一个的)。例如：

Thework-pieceismovedtothenextstation.工件送到下一个工位。

(2) adv.其次，然后。例如：

Nexttheholeisreamed.然后铰孔。

5．Hemustalsoconsiderthepossibilityandadvisabilityofusingstandardholdingdevicessuchasvises,parallelsandclamps.他还必须考虑是否可能或值得利用虎钳、平行垫铁和压板等标准夹持装置。

这里的“parallel”是名词，意为“平行垫铁”。“clamp”也是名词，意为“压板”、“夹钳”。EXERCISES1．PutthefollowingintoChinese:(1) Jigsandfixtures(2) Markout(3) Atrialwork-piece(4) Interchangeable(5) Erroraccumulate(6) Thecuttingforce(7) Thedegreeoffreedom(8) Thethreemutuallyperpendicular(9) Thenecessityofmakingprecisionjigs(10) Positionthework-piecewithrespectthemachinemovement

2．Readthetextcarefullyandanswerthefollowingquestions:

(1) Whatisajig?

(2) Whatisthedifferencebetweenthejigsandfixtures?

(3) Whythework-piecemustbemarkedoutbeforemachinestart?

(4) Canyousaysomeadvantagesofjigsandfixtures?Givesomeexamples.

(5) Whatisthedegreeoffreedom?

3．TranslatethefollowingEnglishintoChinese:

Jigsareworkholderswhicharedesignedtohold,locateandsupportawork-piecewhileguidingthecuttingtoolthroughoutitscuttingcycle.Fixturesandjigsarealikebecausetheybotharedevicestoensurethatthework-pieceiscorrectlylocatedandclamped.Buttherestillaresomedifferencesbetweenthem.Unlikejigs,fixturesdonotguidethecuttingtool,butrather,provideameanstoreferenceandalignthecuttingtooltothework-piece.Forthemostpart,fixturesaredesignedtowithstandmuchgreaterstressedandtoolforcesthanjigs,andarealwayssecurelyclampedtothemachine.READINGMATERIAL

IntroductiontoMachineDesign

Machinedesignistheapplicationofscienceandtechnologytodeviseneworimprovedproductsforthepurposeofsatisfyinghumanneeds.Itisavastfieldofengineeringtechnologywhichnotonlyconcernsitselfwiththeoriginalconceptionoftheproductintermsofitssize,shapeandconstructiondetails,butalsoconsidersthevariousfactorsinvolvedinthemanufacture,marketinganduseoftheproduct.

Peoplewhoperformthevariousfunctionsofmachinedesignaretypicallycalleddesigners,ordesignengineers.Machinedesignisbasicallyacreativeactivity.However,inadditiontobeinginnovative,adesignengineermustalsohaveasolidbackgroundintheareasofmechanicaldrawing,kinematics,dynamics,materialsengineering,strengthofmaterialsandmanufacturingprocesses.

Asstatedpreviously,thepurposeofmachinedesignistoproduceaproduct,whichwillserveaneedforman.Inventions,discoveriesandscientificknowledgebythemselvesdonotnecessarilybenefitpeople;onlywhentheyareincorporatedintoadesignedproductwillabenefitbederived.Itshouldberecognized,thereforethatahumanneedmustbeidentifiedbeforeaparticularproductisdesigned.

Machinedesignshouldbeconsideredtobeanopportunitytouseinnovativetalentstoenvisionadesignofaproduct,toanalyzethesystemandthenmakesoundjudgmentsonhowtheproductistobemanufactured.Itisimportanttounderstandthefundamentalsofengineeringratherthanmemorizemerefactsandequations.Therearenofactsorequationswhichalonecanbeusedtoprovideallthecorrectdecisionsrequiredtoproduceagooddesign.Ontheotherhand,anycalculationsmademustbedonewiththeutmostcareandprecision.Forexample,ifadecimalpointismispla