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HYPERLINK”http://www。cnshu。cn/"FromPeterSmid,CNCProgrammingHandbook:AComprehensiveGuidetoPracticalCNCProgramming,SecondEdition,IndustrialPress,Inc.200MadisonAvenue,NewYork,2003.CHAPTER6:PROGRAMMINGPLANNINGThedevelopmentofanyCNCprogrambeginswithaverycarefullyplannedprocess。Suchaprocessstartswiththeengineeringdrawingoftherequiredpart.Beforethepartismachined,severalstepshavetoconsideredandcarefullyevaluat(yī)ed。Themoreeffortisputintotheplanningstageoftheprogram,thebetterresultsmaybeexpectedattheend.STEPSINPROGRAMPLANNINGThestepsrequiredinprogramplanningaredecidedbythenatureofthework.Thereisnoformulaforallthejobs,butsomebasicstepsshouldbeconsidered:*Initialinformation/Machinetoolsfeatures*Partcomplexity*Manualprogramming/computerizedprogramming*Typicalprogrammingprocedure*Partdrawing/Engineeringdat(yī)a*Methodssheet/Materialsspecifications*Machiningsequence*Toolingselection*Partsetup*Technologicaldecisions*Worksketchandcalculat(yī)ions*QualityconsiderationsinCNCprogrammingThestepsinthelistaresuggestionsonlyaguideline.Theyarequiteflexibleandshouldalwaysbeadaptedforeachjobandtothespecificconditionsofthework.INITIALINFORMATIONMostdrawingsdefineonlytheshapeandsizeofthecompletedpartandnormallydonotspecifydataabouttheinitialblankmaterial。Forprogramming,agoodknowledgeofthematerialisanessentialstart-mainlyintermsofitssize,type,shape,condition,hardness,etc。Thedrawingandmaterialdataaretheprimaryinformationaboutthepart.Atthispoint,CNCprogramcanbeplanned.Theobjectiveofsuchaplanistousetheinitialinformationandestablishthemostefficientmethodofmachining,withallrelatedconsiderat(yī)ion–mainlypartaccuracy,productivity,safetyandconvenience.Theinitialpartinformat(yī)ionisnotlimitedtothedrawingandthemat(yī)erialdat(yī)a,italsoincludesconditionsnotcoveredinthedrawing,suchaspro-andpost-machining,grindingallowances,assemblyfeatures,requirementsforhardening,nextmachinesetup,andothers。Collectingallthisinformationprovidesenoughmat(yī)erialtostartplanningtheCNCprogram.MACHINETOOLSFEATURESNoamountofinitialinformationisusefuliftheCNCmachineisnotsuitableforthejob。Duringprogramplanning,programmerconcentrat(yī)esonaparticularmachinetool,usingaparticularCNCsystem.Eachparthastobesetupinafixture,theCNCmachinehastobelargeenoughtohandlethesizeofthepart,thepartshouldnotbeheavierthanthemaximumweightallowed.Thecontrolsystemmustbecapabletoprovidetheneededtoolpat(yī)h,andsoon。Inthemostcases,theCNCequipmentisalreadyavailableintheshop.VeryfewcompaniesgoandbuyanewCNCmachinejusttosuitaparticularjob。Suchcasesareratherrareandhappenoniftheymakeeconomicsense.*MachineTypeandSizeThemostimportantconsiderat(yī)ionsinprogramplanningarethetypeandthesizeoftheCNCmachine,particularlyitsworkspaceorworkarea.Otherfeatures,equallyimportant,arethemachinepowerrating,spindlespeedandfeedraterange,numberoftoolstations,toolchangingsystem,availableaccessories,etc.Typically,smallCNCmachineshavehigherspindlespeedsandlowerpowerrating,largemachineshavelowerspindlespeedsavailable,buttheirpowerratingishigher。*ControlSystemThecontrolsystemistheheartofaCNCmachine。Beingfamiliarwithallthestandardandoptionalfeaturesavailableonthecontrolisamust.Thisknowledgeallowstheuseofavarietyofadvancedprogrammingmethods,suchasthemachiningcycles,subprograms,macrosandothertimesavingfeaturesofamodernCNCsystem.AprogrammerdoesnothavetophysicallyrunaCNCmachine.Yet,theprogramswillbecomebetterandmorecreativewithgoodunderstandingofthemachineanditscontrolsystem。Programdevelopmentreflectsprogrammer’sknowledgeoftheCNCmachineoperat(yī)ion.Oneofthemainconcernsinprogramplanningshouldbetheoperator’sperceptionoftheprogram。Toalargedegree,suchaperceptionisquitesubjective,inthesensethatdifferentoperat(yī)orswillexpresstheirpersonalpreferences.Ontheotherhand,everyoperat(yī)orappreciatesanerr-free,concise,well-documentedandprofessionallypreparedpartprogram,consistentlyandoneafteranother。Apoorlydesignedprogramisdislikedbyanyoperator,regardlessofpersonalpreferences.PARTCOMPLEXITYAtthetimethedrawing,materialandtheavailableCNCequipmentareevaluated,thecomplexityoftheprogrammingtaskbecomesmuchclearer.Howdifficultistoprogramthepartmanually?Whatarethecapabilitiesofthemachines?Whatarethecosts?Manyquestionshavetobeansweredbeforestartingtheprogram。SimpleprogrammingjobsmaybeassignedtoalessexperiencedprogrammeroftheCNCoperator.Itmakessensefromthemanagementperspectiveanditisalsoagoodwaytogainexperience.Difficultorcomplexjobswillbenefitfromacomputerizedprogrammingsystem.TechnologiessuchasComputerAidedDesign(CAD)andComputerAidedManufacturing(CAM)havebeenastrongpartofthemanufacturingprocessformanyyears。ThecostofaCAD/CAMsystemisonlyafractionofwhatitusedtobeonlyafewyearsago.Evensmallshopsnowfindthatthebenefitsofferedbymoderntechnologyaretoosignificanttobeignored.Severalprogrammingsystemsareavailablevariouscomputersandcanhandleanyjob。Foratypicalmachineshop,aWindowsbasedprogrammingsoftwarecanbeverybeneficial.AtypicalexampleofthiskindofapplicationistheverypopularandpowerfulMasterCAM,formCNCSoftware,Inc.Tolland.CT。Thereareseveralothers.MANUALPROGRAMMINGManualprogramming(withoutacomputer)hasthemostcommonmethodofpreparingapartprogramformanyyears。ThelatestCNCcontrolsmakemanualprogrammingmucheasierthaneverbeforebyusingfixedorrepetitivemachiningcycles,variabletypeprogramming,graphictoolmotionsimulat(yī)ion,standardmathematicalinputandothertimesavingfeatures.Inmanualprogramming,allcalculationsaredonebyhand–withtheaidofapocketcalculator–nocomputerprogrammingisused。ProgrammeddatacanbetransferredtotheCNCmachineviaacable,usinganinexpensivedesktoporalaptopcomputer.Thisprocessisfasterandmorereliablethanothermethods.Shortprogramscanalsobeenteredmanually,bykeyboardentry,directlyatthemachine.Apunchedtapeusedtobethepopularmediaofthepastbuthasvirtuallydisappearedfrommachineshops.*DisadvantagesTherearesomedisadvantagesassociatedwithmanualprogramming。PerhapsthemostcommonisthelengthoftimerequiredtoactuallydevelopafullyfunctioningCNCprogram.Themanualcalculat(yī)ion,verificationandotherrelatedactivitiesinmanualprogrammingareverytimeconsuming.Otherdisadvantages,alsoveryhighonthelist,arealargepercentageoferrors,alackoftoolpathverificat(yī)ion,thedifficultyismakingchangestoaprogram,andmanyothers。*AdvantagesOnthepositiveside,manualpartprogrammingdoeshavequiteafewunmatchedqualities.Manualprogrammingissointensethat(yī)itrequiresthetotalinvolvementoftheCNCprogrammerandyetoffersvirtuallyunlimitedfreedominthedevelopmentoftheprogramstructure。Programmingmanuallydoeshavesomedisadvantages,butitteachesatightdisciplineandorganizationinprogramdevelopment.Itforcestheprogrammertounderstandprogrammingtechniquestothelastdetail.Infact,manyusefulskilllearnedinmanualprogrammingaredirectlyappliedtoCAD/CAMprogramming.Programmerhastoknowwhatishappeningatalltimesandwhyitishappening.Veryimportantisthein—depthunderstandingofeverydetailduringtheprogramdevelopment.Contrarytomanybeliefs,at(yī)horoughknowledgeofmanualprogrammingmethodsisabsolutelyessentialforefficientmanagementofCAD/CAMprogramming.CAD/CAMANDCNCTheneedforimportantimprovedefficiencyandaccuracyinCNCprogramminghasbeenthemajorreasonfordevelopmentofavarietyofmethodsthatuseacomputertopreparepartprograms。ComputerassistedCNCprogramminghasbeenaroundformanyyears。First,intheformoflanguagebasedprogramming,suchasAPT?orCompactⅡ?.Sincethelate1970's,CAD/CAMhasplayedasignificantrolebyaddingthevisualaspecttotheprogrammingprocess。TheacronymCAD/CAMmeansComputerAidedDesignandComputerAidedManufacturing。Thefirstthreeletters(CAD)covertheareaofengineeringdesignanddrafting。Thesecondthreeletters(CAM),coverstheareaofcomputerizemanufacturing,whereCNCprogrammingisonlyasmallpart.ThewholesubjectofCAD/CAMcoversmuchmorethanjustdesign,draftingandprogramming.ItisapartofmoderntechnologyalsoknownasCIM–ComputerIntegrat(yī)edManufacturing.Intheareaofnumericalcontrol,computershaveplayedamajorroleforalongtime.Machinecontrolshavebecomemoresophisticated,incorporatingthelat(yī)esttechniquesofdataprocessing,storage,toolpathgraphics,machiningcycles,etc。Programscannowbepreparedwiththeuseofinexpensivecomputers,usinggraphicalinterface。Costisnolongeranissue;evensmallmachineshopscanaffordaprogrammingsysteminhouse.Thesesystemsarealsopopularbecauseoftheirflexibility.Atypicalcomputerizedprogrammingsystemdoesnothavetobededicatedonlytoprogramming–allrelatedtasks,oftendonebytheprogrammer,canbeimplementedonthesamecomputer,forexample,cuttingtoolinventorymanagement,databaseofpartprograms,materialinformationsheet,setupsheetsandtoolingsheets,etc.ThesamecomputercouldalsobeusedforuploadinganddownloadingCNCprograms.*IntegrationThekeywordintheacronymCIMis–integration.Itmeansputtingalltheelementsofmanufacturingtogetherandworkwiththemasasingleunitandmoreefficiently.Themainideabehindasuccessfulintegrat(yī)ionistoavoidduplication.OneofthemostimportantrulesofusingaCAD/CAMcomputersoftwareis:NeverDoAnythingTwice!WhenadrawingismadeinaCADsoftware(suchasAutoCAD),thendoneagaininaCAMsoftware(suchasMasterCAM),thereisaduplication.Duplicationbreedserrors.Inordertoavoidduplication,mostoftheCADsystemincorporateatransfermethodofthedesigntotheselectedCAMsystemtobeuseforCNCprogramming。TypicaltransfersareachievedthroughspecialDXForIGESfiles。TheDXFstandsforDataExchangeFilesorDrawingExchangeFiles,andtheIGESabbreviationisashortformofInitialGraphicsExchangeSpecificationfiles.OncethegeometryistransferredformtheCADsystemtotheCAMsystem,onlythetoolpathrelatedprocessisneeded.Usingapostprocessor(specialkindofformatter),thecomputersoftwarewillprepareapartprogram,readytobeloadeddirectlytotheCNCmachine.*FutureofManualProgrammingItmayseemthatthemanualprogrammingisonthedecline.Intermsofactualuse,thisisprobablytrue.However,itisnecessarytokeepinperspectivethatanycomputerizedtechnologyisbasedonthealreadywellestablishedmethodsofmanualprogramming.ManualprogrammingforCNCmachinesservesasthesourceofthenewtechnology–itistheveryelementaryconceptonwhichthecomputerizedprogrammingisbased.Thisknowledgebaseopensthedoorfordevelopmentofmorepowerfulhardwareandsoftwareapplications。Themanualprogrammingmaybeusesomewhatlessfrequentlytodayandeventuallywillbeusedevenless–butknowingitwell–reallyunderstandingit–isandalwayswillbethekeytocontrolthepowerofCAMsoftware.Evencomputerscannotdoeverything。TherearesomespecialprogrammingprojectsthataCAMsoftware,regardlessoftheprice,mayhandletoanabsolutesatisfaction。Ifthecontrolsystemcanhandleit,manualprogrammingisthewaytotheultimatecontroloversuchaproject,whenanyothermethodsmaynotbesuitable.Evenwithawellcustomizedandorganizedcomputerizedprogrammingsystem,howcanthegeneratedprogramoutputbeexactlyasintended?HowcantheCNCoperatorchangeanypartoftheprogramonthemachine,withoutknowingitsrulesandstructure?Successfuluseofcomputerizedprogrammingrequiresunderstandingofmanualprogrammingmethods.TYPICALPROGRAMMINGPROCEDUREPl(wèi)anningofaCNCprogramisnodifferentthananyotherplanning;itmustbeapproachedinalogicalandmethodicalway。Thefirstdecisionsrelatetowhattaskshavetobedoneandwhatgoalshavetobereached。Theotherdecisionsrelatetohowtoachievethesetgoalsinanefficientandsafemanner.Suchaprogressivemethodnotonlyisolatesindividualproblemsastheydevelop,italsoforcestheirsolutionbeforethenextstepcanbetaken。ThefollowingitemsformafairlycommonandlogicalsequenceoftasksdoneinCNCprogramming。Theitemsareonlyinasuggestedorder,offeredforfurtherevaluation。Thisordermaybechangedtoreflectspecialconditionsorworkinghabits.Someitemsmaybemissingorredundant:Studyofinitialinformat(yī)ion(drawingandmethods)Materialstock(blank)evaluationMachinetoolspecificationsControlsystemfeaturesSequenceofmachiningoperationsToolingselectionandarrangementofcuttingtoolsSetofthepartTechnologicaldata(speed,feedrates,etc.)Determinationofthetoolpat(yī)hWo(hù)rkingsketchesandmathematicalcalculationsProgramwritingandpreparationfortransfertoCNCProgramtestinganddebuggingProgramdocumentationThereisonlyonegoalinCNCprogramplanningandthatisthecompletionofallinstructionsintheformofaprogramthatwillresultinanerror-free,safeandefficientCNCmachining.Thesuggestedproceduresmayrequiresomechanges–forexample,shouldthetoolingbeselectedbeforeorafterthepartsetupisdetermined?Canthemanualpartprogrammingmethodsbeusedefficiently?Canthemanualpartprogrammingmethodsbeusedefficiently?Aretheworkingsketchesnecessary?Donotbeafraidtomodifyanysocalledidealprocedure–eithertemporarily,foragivenjob,orpermanently,toreflectaparticularCNCprogrammingstyle.Remember,therearenoidealprocedures.第六章:制定編程計(jì)劃編寫任何CNC程序都必須經(jīng)過周密計(jì)劃后開始.這個過程的起點(diǎn)就是所需工件的工程圖。在實(shí)施工件加工之前一些步驟必須仔細(xì)考慮和評估。在程序的計(jì)劃階段付出的努力越多,最后預(yù)期的結(jié)果可能就越好.制定編程計(jì)劃的步驟具體采用哪些步驟要根據(jù)實(shí)際的工作條件而定,沒有國定的程式.但還是有一些基本的步驟可供參考:初始信息、機(jī)床的加工特性工件的復(fù)雜程度手工編程、電腦編程典型的編程工藝工件圖紙、工程數(shù)據(jù)處理表、材料規(guī)格加工工序刀具選擇工件的夾裝技術(shù)要求工程草圖和計(jì)算編程要達(dá)到的質(zhì)量要求這些建議只是提供了一點(diǎn)基本的方向。具體的應(yīng)用變化很多,必須根據(jù)對應(yīng)的加工和工作特定的條件靈活的調(diào)整.初始信息大多數(shù)工程圖只是定義了零件的形狀和尺寸,一般不標(biāo)明最初毛坯料的數(shù)據(jù)。對于編程來說,基本的起點(diǎn)是對原材料的掌握,諸如尺寸、形狀、硬度、加工性能等等。對于工件來說最主要的信息就是工程圖和原材料數(shù)據(jù),在這基礎(chǔ)上程序才得于建立。這個計(jì)劃的目的就是利用最初的信息去建立最高效的加工方法,要考慮到所有的相關(guān)事項(xiàng)—-主要是工件的精度、生產(chǎn)率、安全性和方便性。最初的工件信息并不限于零件圖的材料信息,它還包括一些沒有涵蓋在零件圖中的內(nèi)容,比如前加工和后加工、磨削余量、裝配特點(diǎn)、硬化要求、下一步加工準(zhǔn)備以及其他信息.收集所有的信息給開始給CNC編程制定計(jì)劃供了充足的材料.機(jī)床加工特性如果CNC不能適合某個作業(yè)的話再多的初始信息也沒有用.在計(jì)劃編程階段程序員精力都集中在特定的CNC系統(tǒng)相應(yīng)的機(jī)床刀具上。所有的工件都必須在固定在夾具上,CNC機(jī)床的加工極限要大于工件尺寸,工件的重量不能超出容許的范圍.控制系統(tǒng)必須可以提供所需的走刀路線,諸如此類.在通常的情況下,CNC設(shè)備已經(jīng)在工廠設(shè)置好了,很少有公司為了適應(yīng)某個特殊的作業(yè)而購置新的CNC機(jī)床,這種情況非常罕見,除非這樣做符合經(jīng)濟(jì)意義.機(jī)床的型號和尺寸給編程制定計(jì)劃時最重要的考慮是機(jī)床的型號和尺寸,尤其是它的加工空間或是加工區(qū)域.其它特性也非常重要諸如機(jī)床的功率等級、主軸速度和進(jìn)給范圍、刀庫的數(shù)量、換刀系統(tǒng)、配件等等。通常小型CNC主軸轉(zhuǎn)速高功率小,而大型機(jī)床功率等級高主軸轉(zhuǎn)速則偏低??刂葡到y(tǒng)控制系統(tǒng)是CNC機(jī)床的心臟。必須熟悉所有控制器的標(biāo)準(zhǔn)功能和可選功能。有了這些知識,就可以使用各種高級編程方法,比如加工循環(huán)、子程序、宏和現(xiàn)代CNC系統(tǒng)其它節(jié)約時間的功能.盡管編程人員不必實(shí)際操作CNC機(jī)床,然而熟悉機(jī)床及其控制系統(tǒng)有助于使編程更合理更具有創(chuàng)造性。程序反映出了編程員對CNC機(jī)床運(yùn)行知識的理解程度.在編制計(jì)劃時有一點(diǎn)也很重要,那就是機(jī)床操作人員對程序的看法。在很大程度上,他們的觀點(diǎn)相當(dāng)?shù)闹饔^,不同的操作員個人的偏好不同。但另一方面,每個作業(yè)員都喜歡沒有錯誤、簡練、文檔完備以及專業(yè)的零件加工程序。排除個人偏好,沒有人喜歡一個設(shè)計(jì)有缺陷的程序。零件復(fù)雜程度對工件圖、材料和可用的CNC設(shè)備進(jìn)行評估之后,編程工作的復(fù)雜程度就變得十分清楚.在開始編程之前還要考慮清楚零件手工編程的難度有多大?機(jī)床是否適合?成本是多少?簡單的編程任務(wù)可以分配給初具經(jīng)驗(yàn)的程序員或者是操作員。這是符合管理理念的,也可以幫助他們獲得經(jīng)驗(yàn).困難或復(fù)雜的作業(yè)得益于計(jì)算機(jī)編程系統(tǒng).計(jì)算機(jī)輔助設(shè)計(jì)(CAD)、計(jì)算機(jī)輔助加工(CAM)在很多年前就成為了生產(chǎn)工序的重要部分。CAD/CAM系統(tǒng)的成本也降到幾年前的一小部分。即便是小車間也發(fā)現(xiàn)現(xiàn)代技術(shù)帶來的巨大優(yōu)勢不容忽視.有幾種編程系統(tǒng)在不同計(jì)算機(jī)上都可以使用,可以處理任何作業(yè).對于常見的加工車間,一個基于Windows的編程系統(tǒng)非常有益。典型的應(yīng)用軟件諸如使用廣泛功能強(qiáng)大的MasterCAM,還有很多其它軟件。手工編程很多年前零件加工程序最常用的編程方法就是手工編程。新型的CNC控制器可以提供固定循環(huán)、多種類型的編程、刀具運(yùn)動的圖型模擬、標(biāo)準(zhǔn)的數(shù)學(xué)輸入以及其它節(jié)省時間的特性,這使得手工編程比以前簡單了許多。手工編程時所有的計(jì)算都是通過便攜式計(jì)算器不用計(jì)算機(jī)而手工完成的。通過電纜,程序數(shù)據(jù)可以從便宜的臺式機(jī)或筆記本電腦傳送到CNC機(jī)床上.比較而言這種方法速度快而且可靠。更簡短的程序可以通過機(jī)床的鍵盤直接輸入。穿孔紙帶是過去常用介質(zhì),目前基本上從機(jī)加工車間消失了.缺點(diǎn)手工編程有一些缺點(diǎn).或許最突出的就是編制一個完整功能CNC程序消耗的時間量過于龐大。手工計(jì)算、核對等等工作都很費(fèi)時間。其它的缺點(diǎn)也是很明顯,諸如錯誤率高、不能進(jìn)行刀路檢查、程序的修改也是相當(dāng)不便。優(yōu)點(diǎn)從有利的一面看,手工編程也有

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