支撐掩護(hù)式液壓支架總體及立柱設(shè)計(jì)

摘要礦井液壓支架的應(yīng)用對(duì)增加采煤工作面產(chǎn)量、提高勞動(dòng)生產(chǎn)率、降低陳本、減輕工人的體力勞動(dòng)和保證生產(chǎn)是不可缺少的有效措施，因此液壓支架的設(shè)計(jì)師技術(shù)上先進(jìn)、經(jīng)濟(jì)上合理、安全上可靠、是實(shí)現(xiàn)采煤綜合機(jī)械化和自動(dòng)化的主要體現(xiàn)。采煤綜合機(jī)械化，是加速我國煤炭工業(yè)發(fā)展，大幅度提高勞動(dòng)生產(chǎn)率，實(shí)現(xiàn)煤炭工業(yè)現(xiàn)代化的一項(xiàng)戰(zhàn)略措施。綜合機(jī)械化不僅產(chǎn)量大，效率高，成本低，而且能減輕笨重的體力勞動(dòng)，改善作業(yè)環(huán)境，是煤炭工業(yè)技術(shù)的發(fā)展方向。液壓支架是綜合機(jī)械化采煤方法中最重要的設(shè)備之一。液壓支架主要由以下幾個(gè)基本部分組成：頂梁，掩護(hù)梁和四連桿機(jī)構(gòu)，側(cè)護(hù)板，底座，立柱，千斤頂。設(shè)計(jì)要遵從從支柱性能好、強(qiáng)度高、移架速度快安全可靠等原則。支架采用四連桿機(jī)構(gòu)，改善支架的受力狀況，縮小支架升降過程中的頂梁前段前后移動(dòng)的距離。立柱采用雙伸縮液壓缸，以滿足支架最低及最高位置時(shí)的高度要求關(guān)鍵字：液壓支架;立柱;掩護(hù);支撐。AbstractTheapplicationofhydraulicsupportincoalminingfaceofincreasingproductionandraiselaborproductivityreducecosts,reduceworkersandtoensuresafetyinproductionisindispensableforeffectivemeasuresto,Thereforethedesignofhydraulicsupportistechnicallyadvancedandeconomicallyrational,safeandreliableisthemainmanifestationofthecomprehensiveofthecomprehensivemechanizationandautomationofmining.Thecomprehensivemechanizationofcoalminingisaccelerationcoalindustry.Synthesizemechanizationnotonlyoutputbig,efficiencyhaslowcosthighandcanalleviateheavyphysicallaborandimprovementschoolworkenvironment,isthetechnologyofcoalindustrydevelopdirection.Hydraulicsupportistheoneofcomprehensivemostimportantequipmentinthemechanizationmethodofcoalmining.Hydraulicsupportmajorformsomefollowingbasicallypartialcompositions:Topbeam,screensbeamand4linkagemechanisms,sidefender,base,prop.Designtofollowprotectperformancegood,strengthisspeedhigh,moverapidreliableetc.principle.Thesupportusesfourlinkmotiongears,improvethesupportthestresscondition,reducesthesupporttoriseandfullthedistancewhichintheprocessfortendthetop-beamaroundmoves.Thecolumnusesthelistexpansionandcontractionhydrauliccylinder,frontendhaslegthensthepole,satisfiesthesupporttobelowestandtimethehighestpositionshighrequest.KeyWords:coal;mechanization;bracket;column目錄TOC\o"1-3"\h\u8790前言 ④建立軟件來檢查零件，程序和機(jī)器的可得性，并且考察三者是否能相容。大體上，計(jì)劃使用生產(chǎn)力政策需要詳細(xì)的描述，對(duì)制造業(yè)程序詳細(xì)的理解和他們的準(zhǔn)確性。以不同政策為基礎(chǔ)的制造業(yè)決定采取幾個(gè)標(biāo)準(zhǔn)來解決個(gè)人的操作問題，并且適應(yīng)或調(diào)整他們所需要的地方附錄BAutomaticAssemblyThemodernassemblylinetechniquewasfirstemployedintheassemblyofaflywheelmangneto.Intheoriginalmethod,oneoperatorassembledamagnetoin20min.Itwasfoundthatwhentheprocesswasdividedinto29indibidualoperations,carriedoutbyseparateoperatorsworkingatassemblystationsspacedalonganassemblyline,thetotalassemblytimewasreducedto13min10s.Whentheheightoftheassemblylinewasraisedby8in,thetimewasreducedto7min.Afterfurtherexperimentswerecarriedouttofindtheoptimumspeedoftheassemblylineconveyor,thetimewasreducedto5min,whichwasonlyone-fourthofthetimetakenbytheoriginalprocessofassembly.ThisresultencouragedHenryFordtoutilizehissystemofassemblyinotherdepartmentofthefactory,whichwereproducingsubassembliesforthecar.Subsequently,thisbroughtacontinousandrapidlyincreasingflowofsubassembliestotheoperatorsworkingonthemaincarassembly.Itwasfoundthattheoperatorscouldnotcopewithincreasedflow,anditsoonbecameclearthatthemainassemblywouldalsohavetobecarriedoutonanassemblyline.Atfirst,themovementofthemainassemblieswasachievedsimplybypullingthembyaropefromstationtostation.Howere,eventhisdevelopmentproducedtheamazingresultofareductioninthetotaltimeofassemblefrom12h28minto5h50min.Eventuallyapower-drivenendlessconveyerwasinstalled.Itwasfulshwiththefloorandwideenoughtoaccommodateachassis.Spacewasprovidedforworkerstoeithersitorstandwhiletheycarriedouttheiroperationsandtheconveyrsmovedataspeedof6ft/minpast45separateworkstations.Withtheintroductionofthisconveyor,thetotalassembletimewasreducedto93min.Furtherimprovementsledtoanevenshorteroverallassemblytimeandeventually,aproductionrateofonecarevery10softheworkingdaywasachieved.Thetypeofassemblyoperationdealtwithaboveisusuallyreferredtoasoperatorassembly,anditisstillthemostwidespreadmethodofassemblingmass-orlarge-batch-producedproducts.However,incertaincases,morerefinedmethodsofassemblyhavenowemerged.Asalogicalextensionofthebasicassemblylineprinciple,methodsofreplacingoperatorsbymechanicalmeansofassemblyhavebeendebised.Here,itisusualtoattempttoreplaceoperatorswithautomaticworkheadswherethetasksbeingperformedwereverysimpleandtoretaintheoperatorsfortasksthatwouldbeuneconomicaltomechanize.Thismethodofassemblyhasrapidgainedpopularityformassproductionandisusuallyreferredtoasautomaticassembly.However,completeautomationwheretheproductisassembledcompletelybymachineisessentialynonexistent.ChoiceofAssemblymethodWhenconsideringtheassemblyofaproduct,amanufacturerhastotakeintoaccountthemanyfactorsthataffectthechoiceofassemblysystem.Foranewproduct,thefollowingconsiderationsaregenerallyimportant:① Costofassembly;② Productionratrequired;③ Availabilityoflabor;④ Marketlifeoftheproduct.Ifanattemptistobemade3tojustifytheautomationofanexistingoperatorassemblyline,considerationhastobegiventotheredeploymentofthoseoperatorswhowouldbecomeredundant.Iflaborisplentiful,thedegreeofautomationdependsonthereductionincostofassemblyandtheincreaseinproductionratebroughtaboutbytheautomationoftheassemblyline.However,itmustberememberedthat,ingeneral,thecapitalinvestmentinautomaticmachineryhastobeamortizedoverthemarketlifeoftheproductunlessthemachinerymaybeadaptedtoassembleanewproduct.Itisclearthatifthisisnotthecaseandthemarketlifeoftheproductisshort,automationisgeneralllynotjustifiable.AdvantagesofAutomaticAssemblyFollowingaresomeoftheadvantagesofautomation:① Reductioninthecostofassembly;② Increasedproductivity;③ Amoreconsistentprodect;④ Removalofoperatorsfromhazardousoperations.Areductionincostsisoftenthemainconsiderationand,exceptforthespecialcircumstanceslistedabove,itcouldbeexpectedthatautomationwouldnotbecarriedoutifitwasnotexpectedtoproduceareductionincost.Productivityinanadvancedindustrialsocietyisanimportantmeasureofoperatingefficiency.Increasedproductivity,althoughnotdirectlybeneficialtomanufacturerunlesslaborisscarce,isnecessarytoanexpandingeconomybecauseitreleasespersonnelforothertasks.Itisclearthatwhenputintoeffect,automationofassemblylinesgenerallyreducesthenumberofoperatorsrequiredandhenceincreasesproductivity.Someoftheassemblytasksthatanoperatorcanperformeasilyareextremelydifficulttoduplicateoneventhemostsophisticatedautomaticworkhead.Anoperatorcanoftencarryoutavisualinspectionoftheparttobeassembled,andpartsthatareobviouslydefectivecanbediscarded.Sometimesaberyelaborateinspectionsystemisrequiredtodetecteventhemostobviouslydefectivepart.Ifanattemptismadetoassembleapartthatappearstobeacceptablebutisinfactdefective,anoperator,afterunsuccessfullytryingtocompletetheassembly,canrejectthepartveryquicklywithoutasignificantlossinproduction.Inautomaticassembly,however,unlesstheparthasbeenrejectedbythefeedingdevice,anautomaticworkheadwillprobablystopantimewillthenbewastedlocatingandeliminatingthefault.Ifaparthasonlyaminordefect,anoperatormaybeabletocompletetheassembly,buttheresultingprodectmaynotbecompletelysatisfactory.Itisoftensuggestedthatoneoftheadvantagesofautomaticassemblyisthatitensuresaproductofconsistentlyhighqualitybecausethemachinefaultsifthepartsdonotconformtotherequiredspecifications.Insomesituations,assemblybyoperatorswouldbehazardousduetohightemperaturesandthepresenceoftoxicsubstancesandothermaterials.Underthesecircumstances,assemblybymechanicalmeansisobviouslyadvantageous.Theincreasingneedforfinishedgoodsinlargequantitieshas,inthepast,ledengineerstosearchforandtodevelopnewmethodsofproduction.Manyindibidualdevelopmentsinthevariousbranchesofmanufacturingtechnologyhavebeenmadeandhaveallowedtheincreasedproductionofimprovedfinishedgoodsatlowercost.Oneofthemostimportantmanufacturingprocessesistheassemblyprocess.Thisprocessisrequiredwhentwoormorecomponentpartsaretobebroughttogethertoproducethefinishedproduct.Theearlyhistoryofassemblyprocessdevelopmentiscloselyrelatedtothehistoryofthedevelopmentofmass-productionmethods.Thus,thepioneersofmassproductionarealsothepioneersofthemoderassemblyprocess.Theirnewideasandconceptshavebroughtsignificantimprovementsintheassemblymethodsemployedinlarge-volumeproduction.However,althoughsombranchesofmanufacturingengineering,suchasmetalcuttingandmetalformingprocesses,haverecentlybeendevelopingveryrapidly,thetechnologyofthebasicassemblyprocesshasfailedtokeeppace.Table28.1showsthatintheUnitedStatesthepercentageofthetotallaborforceinbolvedintheassemblyprocessbariesfromabout20%forthemanufactureoffarmmachinerytoalmost60%forthemanufactureoftelephoneandtelegraphequipment.Becauseofthis,assemblycostsoftenaccountformorethan50%ofthetotalmanufacturingcosts.Statisticalsurveysshowthatthesefiguresareincreasingeveryyear.Inthepastfewyears,certaineffortshavebeenmadetoreduceassemblycostsbytheapplicationofautomationandmoderntechniques,suchasultrasonicweldinganddie-casting.Howerer,successhasbeenverylimitedandmanyassemblyoperatorsarestillusingthesamebasictoolsasthoseemployedatthetimeoftheIndustrialRevolution.Intheearlydaysofmanufacturingtechnology,thecompleteassemblyofaproductwascarriedoutbyasingleoperatorandusually,thisoperatoralsomanufacutredtheindividualcomponentpartoftheassembly.Consequently,itwasnecessaryfortheoperatortobeanexperinallthebariousaspectsofthework,andtraininganewoperatorwasalongandexpensivetask.Thescaleofproductionwasoftenlimitedbytheavailabilityoftrainedoperatorsratherthanbythedemandfortheproduct.In1798,theUnitedStatesneededalargesupplyofmusketsandfederalarsenalscouldnotmeetthedemand.BecausewarwiththeFrenchwasimminent,itwasalsonotpossibletoobtainadditionalsuppliesfromEurope.However,Eliwhitney,nowrecognizedasoneofthepioneersofmassproduction,offeredtocontracttomake10000musketsin28menths.Althoughittook10.5yuarstocompletethecontract,Whitney’snovelideasonmassproductionhadbeensuccessfullyproved.ThefactoryatNewHaven,Connecticut,builtspeciallyforthemanufactureofthemuskets,containedmachinesforproducinginterchangeableparts.Thesemachinesreducedtheskillsrequiredbythebariouoperatorsandallowedsignificantincreasesintherateofproduction.Inanhistoricdemonstrationin1801,Whitneysurprisedhisdistinguishedvisitorswhenheassembledmusketlocksafterrandomlyselectedpartsfromaheap.TheresultsofEliWhitney’sworkbroughtaboutthreeeprimarydevelopmentsinmanufacturingmethods.First,partsweremanufacturedonmachines,resultinginaconsistentlyhigherqualitythanthatofhand-madeparts.Thesepartswerenowinterchangeableandasaconsequenceassemblyworkwassimplified.Second,theaccuracyofthefinalproductcouldbemaintainedatahigherstandard,andthird,productionratescouldbesignificantlyincreased.OliverEbans’sconceptionofconveyingmaterialsfromoneplacetoanotherwithoutmanualeffortledeventuallytofurtherdevelopmentsinautomationforassembly.In1793,heusedthreetypesofconveyorsinanautomaticflourmill,whichrequiredonlytwooperators.Thefirstoperatorpouredrainintoahopperandthesecondfilledsackswithflourprocducedbythemill.Alltheintermediatoperationswerecarriedoutautomaticallywithconveyorscarryingthematerialfromoperationtooperation.ThenextsignificantcontributiontothedevelopmentofassemblymethodswasmadebyElihuRoot.In1849,ElihuRootjoinedthecompanythatwasproducingColt“six–shooters”.Eventhoughatthattimethevariousoperationofassemblingthecomponentpartswerequitesimple,hedividedtheseoperationsintobasicunitsthatcouldbecompletedmorequicklyandwithlesschanceoferror.Toot’sdivisionofoperationsgaverisetotheconcept“dividetheworkandmultiplytheoutput”.Usingthisprinciple,assemblyworkwasreducedtoverybasicoperationsandwithonlyshortperiodsofoperatortraining,highefficienciescouldbeobtained.FrederickWinslowTaylorwasprobablythefirstpersontointroducethemethodsoftimeandmotionstudytomanufacturingtechnology.Theobjectivewastosavetheoperator’stimeandenergybymakingsurethattheworkandallthingsassociatedtotheworkwereplacedinhebestpositionsforcarryingouttherequiredtasks.Tayloralsodiscoveredthatanyworkerhasanoptimumspeedofworkingwhich,ifexceeded,resultsinareductioninoverallperformance.Undoubtedly,theprincipalcontributortothedevelopmentofproductionandassemblymethodswasHenryFord.Hedescribedhisprinciplesofassemblyinthefollowingwords:“First,placethetoolsandthenmeninthesequenceoftheoperationssothateachpartshalltraveltheleastdistancewhilstintheprocessoffinishing”.“Second,useworkslidesorsomeotherformofcarriersothatwhenaworkmancompletehisoperationhedropsthepartalwaysinthesameplacewhichmustalwaysbethemostconvenientplacetohishandandifpossiblehavegravitycarrytheparttothenextwokman.“Third,useslidingassemblylinesbywhichpartstobeassembledaredeliveredatconvenientintervals,spacedtomakeiteasiertoworkonthem”.TheseprinciplesweregraduallyappliedintheproductionoftheModelTFordautomobile.Theincreasingneedforfinishedgoodsinlargequantitieshas,inthepast,ledengineerstosearchforandtodevelopnewmethodsofproduction.Manyindibidualdevelopmentsinthevariousbranchesofmanufacturingtechnologyhavebeenmadeandhaveallowedtheincreasedproductionofimprovedfinishedgoodsatlowercost.Oneofthemostimportantmanufacturingprocessesistheassemblyprocess.Thisprocessisrequiredwhentwoormorecomponentpartsaretobebroughttogethertoproducethefinishedproduct.Theearlyhistoryofassemblyprocessdevelopmentiscloselyrelatedtothehistoryofthedevelopmentofmass-productionmethods.Thus,thepioneersofmassproductionarealsothepioneersofthemoderassemblyprocess.Theirnewideasandconceptshavebroughtsignificantimprovementsintheassemblymethodsemployedinlarge-volumeproduction.However,althoughsombranchesofmanufacturingengineering,suchasmetalcuttingandmetalformingprocesses,haverecentlybeendevelopingveryrapidly,thetechnologyofthebasicassemblyprocesshasfailedtokeeppace.Table28.1showsthatintheUnitedStatesthepercentageofthetotallaborforceinbolvedintheassemblyprocessbariesfromabout20%forthemanufactureoffarmmachinerytoalmost60%forthemanufactureoftelephoneandtelegraphequipment.Becauseofthis,assemblycostsoftenaccountformorethan50%ofthetotalmanufacturingcosts.Statisticalsurveysshowthatthesefiguresareincreasingeveryyear.Inthepastfewyears,certaineffortshavebeenmadetoreduceassemblycostsbytheapplicationofautomationandmoderntechniques,suchasultrasonicweldinganddie-casting.Howerer,successhasbeenverylimitedandmanyassemblyoperatorsarestillusingthesamebasictoolsasthoseemployedatthetimeoftheIndustrialRevolution.HistoricalDevelopmentoftheAssemblyprocessIntheearlydaysofmanufacturingtechnology,thecompleteassemblyofaproductwascarriedoutbyasingleoperatorandusually,thisoperatoralsomanufacutredtheindividualcomponentpartoftheassembly.Consequently,itwasnecessaryfortheoperatortobeanexperinallthebariousaspectsofthework,andtraininganewoperatorwasalongandexpensivetask.Thescaleofproductionwasoftenlimitedbytheavailabilityoftrainedoperatorsratherthanbythedemandfortheproduct.In1798,theUnitedStatesneededalargesupplyofmusketsandfederalarsenalscouldnotmeetthedemand.BecausewarwiththeFrenchwasimminent,itwasalsonotpossibletoobtainadditionalsuppliesfromEurope.However,Eliwhitney,nowrecognizedasoneofthepioneersofmassproduction,offeredtocontracttomake10000musketsin28menths.Althoughittook10.5yuarstocompletethecontract,Whitney’snovelideasonmassproductionhadbeensuccessfullyproved.ThefactoryatNewHaven,Connecticut,builtspeciallyforthemanufactureofthemuskets,containedmachinesforproducinginterchangeableparts.Thesemachinesreducedtheskillsrequiredbythebariouoperatorsandallowedsignificantincreasesintherateofproduction.Inanhistoricdemonstrationin1801,Whitneysurprisedhisdistinguishedvisitorswhenheassembledmusketlocksafterrandomlyselectedpartsfromaheap.TheresultsofEliWhitney’sworkbroughtaboutthreeeprimarydevelopmentsinmanufacturingmethods.First,partsweremanufacturedonmachines,resultinginaconsistentlyhigherqualitythanthatofhand-madeparts.Thesepartswerenowinterchangeableandasaconsequenceassemblyworkwassimplified.Second,theaccuracyofthefinalproductcouldbemaintainedatahigherstandard,andthird,productionratescouldbesignificantlyincreased.OliverEbans’sconceptionofconveyingmaterialsfromoneplacetoanotherwithoutmanualeffortledeventuallytofurtherdevelopmentsinautomationforassembly.In1793,heusedthreetypesofconveyorsinanautomaticflourmill,whichrequiredonlytwooperators.Thefirstoperatorpouredrainintoahopperandthesecondfilledsackswithflourprocducedbythemill.Alltheintermediatoperationswerecarriedoutautomaticallywithconveyorscarryingthematerialfromoperationtooperation.ThenextsignificantcontributiontothedevelopmentofassemblymethodswasmadebyElihuRoot.In1849,ElihuRootjoinedthecompanythatwasproducingColt“six–shooters”.Eventhoughatthattimethevariousoperationofassemblingthecomponentpartswerequitesimple,hedividedtheseoperationsintobasicunitsthatcouldbecompletedmorequicklyandwithlesschanceoferror.Toot’sdivisionofoperationsgaverisetotheconcept“dividetheworkandmultiplytheoutput”.Usingthisprinciple,assemblyworkwasreducedtoverybasicoperationsandwithonlyshortperiodsofoperatortraining,highefficienciescouldbeobtained.FrederickWinslowTaylorwasprobablythefirstpersontointroducethemethodsoftimeandmotionstudytomanufacturingtechnology.Theobjectivewastosavetheoperator’stimeandenergybymakingsurethattheworkandallthingsassociatedtotheworkwereplacedinhebestpositionsforcarryingouttherequiredtasks.Tayloralsodiscoveredthatanyworkerhasanoptimumspeedofworkingwhich,ifexceeded,resultsinareductioninoverallperformance.Undoubtedly,theprincipalcontributortothedevelopmentofproductionandassemblymethodswasHenryFord.Hedescribedhisprinciplesofassemblyinthefollowingwords:“First,placethetoolsandthenmeninthesequenceoftheoperationssothateachpartshalltraveltheleastdistancewhilstintheprocessoffinishing”.“Second,useworkslidesorsomeotherformofcarriersothatwhenaworkmancompletehisoperationhedropsthepartalwaysinthesameplacewhichmustalwaysbethemostconvenientplacetohishandandifpossiblehavegravitycarrytheparttothenextwokman.“Third,useslidingassemblylinesbywhichpartstobeassembledaredeliveredatconvenientintervals,spacedtomakeiteasiertoworkonthem”.TheseprinciplesweregraduallyappliedintheproductionoftheModelTFordautomobile.Processplanninghasbeendefinedas“subsystemresponsiblefortheconversionofdesigndatatoworkinstruction”.Amorespecificdefinitionfoprocessplanningis“thatfunctionwithinamanufacturingfacilitythatestablishestheprocessesandprocessparameterstobeused(aswellasthosemachinescapableofperformingtheseprocesses)inordertoconvertapiece-partfromitsinitialformtoafinalformthatispredetermined(usuallybyadesignengineer)onadetailedengineeringdrawing.”Theinput(raw)materialtoaprocessmaytakeanumberofforms(inmachinning,thesematerialsnormallyresultfromametal-formingprocess;themostcommonofwhicharebarstock,castings,forgings,orperhapsjustaslabofmetal,otherprocesseshaveotherinputmaterials).Anothermachinningmaterialmightbeaburn-out(apartproducedbyaflame-cuttingoperation)cuttosomeroughdimension,orjustarectangularblockofmaterial.Thisinputmaterialmighthavealmostanyshapeandphysicalproperty.Someprocessesmayalterthesizeorsurfacetextureofapart.Otherprocess,likeheat-treating,changethephysicalpropertiesofmaterials.Morespecifically,annealingwouldtendtolessenthematerialhardnesssanddecreasetheworkpiecetensilestrength.Withthesetypesofrawmaterialsasabase,theprocessplannermustpreparealistofthose(machingning)processesneededtoconvertthisnormallypredeterminedmaterialintoitsspecifiedfinalgeometry.Thecommonestmetal-removalprocessthataprocessplannerhasathisdisposalareturning,facing,milling,drilling,boring,broaching,shaping,gundrilling,reaming,planing,sawing,trepanning,burnishaing,punching,andreinding.Somemanufacturingpeoplemayconsidersomeoftheoperationsassubsetsofamajorcategory.Reamingisoftenconsideredasubsetofdrilling.Othersmaydefinefurthermajorcategories.Someless-familiarprocesssuchaselectricdischargemachining(EDM),electrochemicalmachining(ECM),andlasermachiningzrealsousedformaterialremoval.Allapplicableprocessesthatareavailavleforproductionshouldbeconsideredbytheprocessplanner.ElementsofProcessPlanningDoyleseparatestheactivitiesperformedinprocessplanningintsveengeneralcategories.① Interpretthespecificationrequirements.② Positionthepartonthemachine.③ Determinetheintermediateproductrequirementsateachstageofprocessing.④ Selectthemajorpiecesofequipmenttohandletheprocessing.⑤ Selectthetoolingandsequenceofprocessingstepswithineachoperation.⑥ Computetheprocesstimerequirements.⑦ Documenttheprocessplan.Someoftheseactivitiescanbedividedintsmallerunits;however,theactivitiesdscribedprovidedaconbenientcategorizationforanalysis.Aprocessplannernormallyoperatesunderthefollowingconstraints.① Heplansforagivensetofmachines.② Themachinesarecapableofalimitednumberofmanufacturingoperations.③ Themachineshaveaspecificburden/workload.Giventhesemachineconstraints,andasetofengineeringdrawingscontainingspecificpatrtgeometryrequirements,theprocessplannerreliesonhisexperiencetodevelopasetofprocesscapableofproducingapart.Theselectionoftheprocessisneitherentirelyrandomnortotallypredictable.Thereisusuallymorethanoneprocesscapableofproducingaspecificsurface:theprocessplannermustchoosewhathebelievesisthebestprocess.Thisisnormallydonebyrecallingaimilarparts,oratleastsimilarsurfaces,andthemeansutilizedinmanufacturingthatpart.Inthismanner,theplannercomparesspecificprocessusedtoobtainsomesetoffinalspecificationsandchooseswhathebelievestobethebestalternative.Thistypeofplanningisknowasmanvariantprocessplanningandisthecommonesttypeofplanningusedforproductiontoday.Planningtheoperationtobeusedtoproduceapartrequiresknowledgeoftwogroupsofvariables:thepartrequirements(asindicatedbyanengineeringdrawing);andtheavailablemachinesandprocess,andthecapabilitiesofeachprocess.Giventhesevariables,theplannerselectsthecombinationofprocessesrequiredtoproduceafinishedpart.Inselectingthiscombinationofprocessesanumberofcriteriaareemployed.Productioncostortimeareusuallythedominatcriteriainprocessselection;however,machineutilizationandroutingoftenaffecttheplanschosen.Ingeneral,theprocessplannertriestoselectthebestsetofprocessesandmachinestoproduceawholefamilyofpartsratherthanjustasinglepart.Asonemightimagine,alargepartofprocessplanning,asitcurentlyexists,isanartratherthanascience.P