機(jī)械設(shè)計準(zhǔn)則外文翻譯

SomeRulesforMechanicalDesignDesigningstarswithaneed,realorimagined.Existingapparatusmayneedimprovementsindurability,efficiently,weight,speed,orcost.Newapparatusmaybeneededtoperformafunctionpreviouslydonebymen,suchascomputation,assembly,orservicing.Withtheobjectivewhollyorpartlydefined,thenextstopindesignistheconceptionofmechanismsandtheirarrangementsthatwillperformtheneededfunctions.Forthis,freehandsketchingisofgreatvalue,notonlyasarecordofone’sthoughtsandasanaidindiscussionwithothers,butparticularlyforcommunicationwithone’sownmind,asastimulantforcreativeideas.Whenthegeneralshapeandafewdimensionsoftheseveralcomponentsbecomeapparent,analysiscanbegininearnest.Theanalysiswillhaveasitsobjectivesatisfactoryorsuperiorperformance,plussafetyanddurabilitywithminimumweight,andacompetitivecost.Optimumproportionsanddimensionswillbesoughtforeachcriticallyloadedsection,togetherwithabalancebetweenthestrengthoftheseveralcomponents.Materialsandtheirtreatmentwillbechosen.Theseimportantobjectivescanbeattainedonlybyanalysisbasedupontheprinciplesofmechanics,suchasthoseofstaticsforreactionforcesandfortheoptimumutilizationoffriction;ofdynamicsofinertia,acceleration,andenergy;ofelasticityandstrengthofmaterialsforstressanddeflection;andoffluidmechanicsforlubricationandhydrodynamicdrives.Finally,adesignbaseduponfunctionandreliabilitywillbecompleted,andaprototypemaybebuilt.Ifitstestsaresatisfactory,andifthedeviceistobeproducedinquantity,theinitialdesignwillundergocertainmodificationsthatenableittobemanufacturedinquantityatalowercost.Duringsubsequentyearsofmanufactureandservice,thedesignislikelytoundergochangesasnewideasareconceivedorasfurtheranalysisbasedupontestsandexperienceindicatealterations.Salesappeal,customersatisfaction,andmanufacturecostareallrelatedtodesign,andabilityindesignisintimatelyinvolvedinthesuccessofanengineeringventure.Tostimulatecreativethought,thefollowingrulesaresuggestedforthedesigner.Applyingenuitytoutilizedesiredphysicalpropertiesandtocontrolundesiredones.Theperformancerequirementsofamachinearemetbyutilizinglawsofnatureorpropertiesofmatter(e.g.,flexibility,strength,gravity,inertia,buoyancy,centrifugalforce,principlesoftheleverandinclinedplane,friction,viscosity,fluidpressure,andthermalexpansion),alsothemanyelectrical,optical,thermal,andchemicalphenomena.However,whatmaybeusefulinoneapplicationmaybedetrimentalinthenext.Flexibilityisdesiredinvalvespringsbutnotinthevalvecamshaft;frictionisdesiredattheclutchfacebutnotintheclutchbearing.Ingenuityindesignshouldbeappliedtoutilizeandcontrolthephysicalpropertiesthataredesiredandtominimizethosethatarenotvideforfavorablestressdistributeandstiffnesswithminimumweight.Oncomponentssubjectedtofluctuatingstress,particularattentionisgiventoareductioninstressconcentration,andtoanincreaseofstrengthatfillets,threads,holes,andfits.Stressreductionaremadebymodificationinshape,andstrengtheningmaybedonebyprestressingtreatmentssuchassurfacerollingandshallowhardening.Hollowshaftsandtubing,andboxsectionsgiveafavorablestressdistribution,togetherwithstiffnessandminimumweight.Sufficientstiffnesstomaintainalignmentanduniformpressurebetweencontactingsurfacesshouldbeprovidedforcrank,cam,andgearshafts,andforenclosuresandframescontainingbearingsupports.Thestiffnessofshaftsandothercomponentsmustbesuitabletoavoidresonantvibrations.Usebasicequationstocalculateandoptimizedimensions.Thefundamentalequationsofmechanicsandtheothersciencesaretheacceptedbasesforcalculations.Theyaresometimesrearrangedinspecialformstofacilitatethedeterminationoroptimizationofdimensions,suchasthebeamandsurfacestressequationsfordetermininggear-toothsize.Factorsmaybeaddedtoafundamentalequationforconditionsnotanalyticallydeterminable,e.g.,onthinsteeltubes,anallowanceforcorrosionaddedtothethicknessbasedonpressure.Whenitisnecessarytoapplyafundamentalequationfortoshapes,materials,orconditionswhichonlyapproximatetheassumptionsforitsderivation,itisdoneinamannerwhichgivesresults”onthesafeside”.Insituationswheredataareincomplete,equationsofthesciencesmaybeusedasproportioningguidestoextendasatisfactorydesigntonewcapacities.choosematerialsforacombinationofproperties.Materialsshouldbechosenforacombinationofpertinentproperties,notonlyforstrengths,hardness,andweight,butsometimesforresistancetoimpact,corrosion,andloworhightemperatures.Costandfabricationpropertiesarefactors,suchasweldability,machinability,sensitivitytovariationinheat-treatingtemperatures,andrequiredcoating.selectcarefullybetweenstockandintegralcomponents.Apreviouslydevelopedcomponentsisfrequentlyselectedbyadesignerandhiscompanyfromthestocksofpartsmanufacturers,ifthecomponentmeettheperformanceandreliabilityrequirementsandisadaptablewithoutadditionaldevelopmentcoststotheparticularmachinebeingdesigned.However,itsselectionshouldbecarefullymadewithafullknowledgeofitsproperties,sincethereputationandliabilityofthecompanysufferifthereisafailureinanyoneofthemachine’sparts.Inothercasesthestrength,reliability,andcostrequirementsarebettermetifthedesignerofthemachinealsodesignsthecomponent,withtheparticularadvantageofcompactnessifitisdesignsintegralwithothercomponents,e.g.,gearstobeforgedinclustersorintegralwithashaft.Provideforaccuratelocationandnon-interferenceofpartsinassembly.Agooddesignprovidesforthecorrectlocatingofpartsandforeasyassemblyandrepair.Shouldersandpilotsurfacesgiveaccuratelocationwithoutmeasurementduringassembly.Shapescanbedesignedsothatpartscannotbeassembledbackwardsorinthewrongplace.Interferences,asbetweenscrewsintappedholes,andbetweenlinkagesmustbeforeseenandprevended.Inaccuratealignmentandpositioningbetweensuchassembliesmustbeavoided,orprovisionmustbemadetominimizeanyresultingdetrimentaldisplacementsandstresses.機(jī)械設(shè)計準(zhǔn)則設(shè)計時從實際或者假想的需要開始的。對于現(xiàn)有的設(shè)備可能需要在耐用性、效率、重量、速度或成本等方面做進(jìn)一些改進(jìn)工作；也可能需要新的設(shè)備完成以前由人來做的工作，如計算或裝配。當(dāng)目標(biāo)完全或部分被確定以后，下一個設(shè)計步驟是對能夠完成所需要功能的機(jī)構(gòu)及其布局進(jìn)行總體設(shè)計。對于此項工作，徒手畫的草圖是很有價值的，它不僅可以記錄下我們的想法，而且還有助于與別人進(jìn)行討論，特別是和自己的大腦進(jìn)行交流，從而促進(jìn)創(chuàng)新想法的產(chǎn)生。當(dāng)一些零件的大致形狀和幾個尺寸被確定后，就可以開始認(rèn)真的分析工作。分析工作的目的是要在重量最輕、成本最低的情況下，獲得令人滿意，即優(yōu)良的工作性能，并且還要安全耐用。對于每個關(guān)鍵承載截面，應(yīng)該尋求最佳的比例和尺寸，同時要對這幾個零件的受理進(jìn)行平衡。要對材料和處理方式進(jìn)行選擇。只有根據(jù)力學(xué)原理進(jìn)行分析才能達(dá)到這些重要目的。這些分析包括根據(jù)靜力學(xué)原理分析反作用力和充分利用摩擦力，根據(jù)動力學(xué)原理分析慣性、加速度和能量；根據(jù)彈性力學(xué)和材料力學(xué)分析應(yīng)力和變形；根據(jù)流體力學(xué)來分析潤滑和流體傳動。最后，完成基于功能要求和可靠性所進(jìn)行的設(shè)計，且要制作一臺樣機(jī)。如果試驗結(jié)果令人滿意，而且該裝置將要進(jìn)行批量生產(chǎn)，就應(yīng)該對最初提出的設(shè)計方案做一些修改，使其能以較低的成本進(jìn)行批量生產(chǎn)。在以后的制造和使用期內(nèi)，如果產(chǎn)生了新的想法或者根據(jù)試驗和經(jīng)驗所做的進(jìn)一步分析結(jié)果表明，可以有更好的替代方案，則很可能對原設(shè)計方案進(jìn)行修改。銷售吸引力、客戶的滿意程度和制造成本均與設(shè)計有關(guān)，而設(shè)計能力則與工程創(chuàng)新的實現(xiàn)是密切相關(guān)的。為激發(fā)創(chuàng)造性思維，建議設(shè)計人員遵循下列準(zhǔn)則。創(chuàng)造性地利用所需要的物理性能和控制不需要的物理性能?？梢岳米匀环▌t或物質(zhì)的性能（如柔性，強度，重力，慣性，浮力，離心力；杠桿原理和斜面原理，摩擦，粘性，流體壓力和熱膨脹）和許多電學(xué)，光學(xué)和化學(xué)現(xiàn)象來滿足一臺機(jī)器的設(shè)計要求。一種性能在某種場合下可能是有用的，而在另外一種場合下則可能是有害的。閥門的彈簧應(yīng)該有柔性，而閥門的凸輪軸就不需要柔性。離合器結(jié)合面上需要有摩擦，而離合器軸承卻不需要摩擦。設(shè)計時，需要創(chuàng)造性地利用和控制所要的物理性能，將不需要的物理性能減至最小。在重量最輕的情況下，提供合理的應(yīng)力分布和剛度。對于承受交變應(yīng)力的零件，應(yīng)該特別注意減輕應(yīng)力集中和提高圓角，螺紋和配合處得強度。改變零件的形狀，可以降低它所承受的應(yīng)力，對零件施加預(yù)應(yīng)力，如表面滾壓和淺表面硬化，均可使其得到強化。空心軸和空心管道，箱形截面能獲得有利的應(yīng)力分布，同時具有強度高而重量輕的特點。曲軸，凸輪軸以及含有軸承支座的外殼和構(gòu)架都應(yīng)有足夠的剛度以保證直線對中精度和接觸表面之間的壓力均勻分布。軸和其他零件須