Domov Technika Artefakt

Artefakt



Definition

Workpiecereferstotheprocessingobjectinthemachiningprocess.Itcanbeasinglepartoracombinationofseveralpartsfixedtogether.Therearevarioustypesofworkpieceprocessingmethods,includingturning,milling,planing,grinding,casting,forgingandsoon.Theprocessingprocedureoftheworkpiecealsochangeswiththechangeoftheprocessingmethod.

Workpiecepositioning

Workpiecepositioningreferstotheprocessinwhichtheworkpieceoccupiesthecorrectpositioninthemachinetoolorfixture.Thepurposeistomakethesamebatchofworkpiecesoccupythesamecorrectprocessingpositionduringprocessing.Themaincontentincludes:

(1)Masterthepositioningprincipleoftheworkpiece,andensurethatthepositionoftheworkpieceisconsistentduringprocessing.

(2)Chooseordesignareasonablepositioningmethodandcorrespondingpositioningcomponents.

Principleofsix-pointpositioning

Anyworkpiecehasandonlysixdegreesoffreedominthespatialrectangularcoordinatesystem,namelyalongtheand

,Three-axismovement,,Thedegreeoffreedomandrotationaroundthethree-axisDegreesoffreedom,,.Ifsixcorrespondingfixedconstraintpointsareusedandthesesixdegreesoffreedomareeliminatedatthesametime,thepositionoftheworkpieceinthespaceisunique,whichisthesix-pointpositioningprincipleoftheworkpiece.

AsshowninFigure1,thepositioningofahexagonalworkpieceisshown.Themethodoflimitingthesixdegreesoffreedomoftheworkpieceisanalyzed:

(1)VTři podpěrné hřeby1,2,3jsounastavenynarovinuaobrobekjeumístěnnatřipodpěrnéhřebíky, aby se omezila třístupňová volnost obrobku,,.

(2)Setuptwosupportingnails4and5ontheplaneof,andplacetheworkpieceonthesetwosupportingnailstolimitthe,Twodegreesoffreedom.

(3)Thereisnosupportingnail6ontheplaneof.Leaningtheworkpieceonthissupportingnailcanlimitthefreedomof.

Throughtheabovemethod,maketheworkpiececontactwithsixsupportingpoints,limititssixdegreesoffreedom,andensurethattheworkpieceoccupiesthecorrectpositioninthemachinetoolorclamp

Proces určování polohy.

Inordertobetterapplythesix-pointpositioningprincipleinfixturedesign,thefollowingissuesneedtobediscussed:

1.Součásti podpory a umístění

Itismentionedinthesix-pointpositioningprinciple:thesixdegreesoffreedomoftheworkpieceneedtobeeliminatedbysixsupportingpointsorsupportsarrangedonthefixtureaccordingtocertainrequirements,exceptforthesupportingnails,whichcanbeintuitivelyunderstoodasoneInadditiontothesupportingpoints,otherpositioningelementsarejudgedbythenumberofdegreesoffreedomrestrictedbythenumberofsupportingpoints.

Forexample,Figure2showsthepositioningschemeforprocessingthelarge-endholeoftheconnectingrod.Theconnectingrod4isinstalledonthesupportplate2withitsbottomsurface.Thesupportplatelimitsthethreedegreesoffreedomoftheworkpiece(

,,),equivalenttothreesupportingpoints,thesmallheadholeissleevedontheshortcylindricalpin1,whichlimitsthetwodegreesoffreedomoftheworkpiece(
,),whichareequivalenttotwosupportingpoints;thecylindricalpin3isincontactwiththesideoftheworkpiece,whichlimitsthelastdegreeoffreedomoftheworkpiece(),whichisequivalenttoasupportpoint.Itshouldbenotedherethatthepositioningelements1and3arealsocylindricalpins,buttheequivalentnumberofsupportingpointsforthetwoaredifferent.Thisisbecausetheformerrestrictstwodegreesoffreedom,whilethelatterrestrictsonlyonedegreeoffreedom.

Arfact

Obrázek 3 (2 fotografie)

Figure3showsthenumberofdegreesoffreedomorequivalentsupportpointsrestrictedbythepositioningelementsinseveralcommonpositioningmethods.

2.Completepositioningandincompletepositioning

Thesixdegreesoffreedomoftheworkpieceareallrestrictedbythepositioningelementsofthefixture,sothattheworkpieceisinacompletelydeterminedpositioninthefixture,thatis,whenthefixedconstraintThepositioningwhenthenumberisexactlysixdegreesoffreedomoftheworkpieceiscalledcompletepositioning.

TheconnectingrodpositioningshowninFigure2isfullypositioned.

Indraftingthepositioningplanoftheworkpiece,accordingtotheprocessingrequirementsoftheworkpiece,itisnotalwaysnecessarytocompletelypositionit.AsshowninFigure4,whereFigure4(a)showsthatthekeywayismilledontheworkpiece,itisrequiredtoensurethattheprocessdimensionsx,y,zareparalleltothebottomsurface,sosixdegreesoffreedommustberestrictedduringprocessing,thatis,Fullypositioned.Figure4(b)showsthemillingstepsurfaceoftheworkpiece.Itisrequiredtoensurethattheprocessdimensionsyandzareparalleltothebottomsurfaceandthesidesurface.Therefore,itissufficienttolimitfivedegreesoffreedom.Atthistime,itisnotnecessarytolimitthemovementalongtheXaxis.Degreeoffreedom(),becauseithasnoeffectonthemachiningaccuracyoftheworkpiece.Figure4(c)showsthatthetopsurfaceismilledontheworkpiece.Onlytheprocesssizezandparalleltothebottomsurfacearerequired.Therefore,onlythreedegreesoffreedom(,

,).Accordingtotheprocessingrequirements,thepositioningthatallowsoneorseveraldegreesoffreedomtobeunrestricted,butstillmeetstheprocessingrequirements,iscalledincompletepositioning.

Metoda polohování obrobku a součásti polohování

Umístění obrobku podle roviny

Accordingtowhethertheplaneisprocessedornot,itisdividedintoroughdatum(Commonlyknownas:roughsurface)andfinedatum(commonlyknownas:smoothsurface),thestructureofthepositioningcomponentsusedinthecorrespondingfixturesarealsodifferent.

1.Obrobekjeumístěnnapovrchu

Whentheworkpieceispositionedontheroughsurface,becausetheroughsurfaceisroughandtheerrorislarge,itcannotbesurfacecontactwiththepositioningelement,onlythethreehighpointsontheroughsurfacecancontactfirst,Thecorrespondingpositioningelementisusuallysupportnails,asshowninFigure5,thebottomsurfaceisgenerallyrigidB-typeroundheadsupportnailstomakestablecontactwiththeroughsurface,andthesidesurfacesgenerallyusenettedsupportnailstoincreasethefrictionbetweenthecontactsurfaces..

2.Obrobek je umístěn na hladkém povrchu

Whentheworkpieceispositionedonasmoothsurface,itcanbeviewedasaplane,butitwillnotbeabsolutelyflat.Thepositioningelementusedisstillasmallplane.Whenthecontactsurfaceissmall,theAtypeisgenerallyusedFlat-headsupportnails;whenthecontactsurfaceislarge,asupportplateisgenerallyused,asshowninFigure6.Amongthem,TypeAisflat,simpleinstructureandconvenienttomanufacture,butitiseasytoaccumulatechipsinthecountersunkscrewpit,anditisnoteasytoremove.Itismainlyusedforsideortoppositioning.TypeBisachutetype,whichisconvenientforremovingchipsandismainlyusedforbottompositioning.

Theabove-mentionedsupportingnailsandsupportingplatesareallfixedsupportsusedwhentheworkpieceispositionedonaplane.Thefixedsupportisatypeofsupportthatmakesthepositionoftheworkpiecefixedandnon-adjustablewhentheworkpieceispositioned.

3.Nastavitelná podpora

Adjustablesupportisakindofsupportthatallowsthepositionoftheworkpiecetobeadjustedwhenitispositioned.AsshowninFigure7,thereareseveralcommonlyusedadjustablesupportstructures.Thistypeofadjustablesupportstructureisbasicallyascrewandnuttype.Figure7(a)istodirectlyadjusttheheightbytwistingthecylinderheadbyhandoraplaterod,whichisgenerallysuitableforsmallworkpieces.Figure7(b),(c),youneedtouseawrenchtoadjust,soitissuitableforheavierworkpieces.Figure7(d)issetonthesideforadjustment.Oncethepositionoftheadjustablesupportisadjustedproperly,itmustbelockedwithalocknut.Therefore,alocknutforanti-looseningmustgenerallybeprovidedtopreventthelooseningofthethreadandthepositionoftheadjustablesupportfromchanging.

Steppingupoftheworkpiece

Thepositioningoftheworkpiecemainlysolvesthepositioningmethodoftheworkpiece,ensuringthenecessarypositioningaccuracy,sothattheworkpieceoccupiesthecorrectpositionbeforeprocessing.Aftertheworkpieceispositioned,onlythefirsthalfoftheworkpiececlampingtaskiscompleted.Iftheworkpieceisnotclamped,theworkpiecemaymoveordeflectundertheactionofexternalforce.Therefore,thecorrectpositionoftheworkpieceinthepositioningprocessmustbeachievedbyclamping.Maintenance,onlywhenthecorrespondingclampingdeviceissetinthefixturetoclamptheworkpiece,canitbeconsideredthatalltasksoftheworkpiececlampingarecompleted.

Thepurposeofclampingtheworkpieceistoensurethattheworkpiecealwaysmaintainstheestablishedpositionduringthemachiningprocess.Itisrequiredthattheclampingmustbereliable,andatthesametime,thepositioningoftheworkpiecemustnotbedamagedduringtheclampingprocess,andtheworkpiecemustnotbegeneratedDeformationisnotallowed.Tosolvetheclampingoftheworkpiece,themostbasicproblemindesigningtheclampingdeviceistousetheclampingforcecorrectlyandreasonably.

Typický utahovací mechanismus

Theclampingmechanismisanimportantpartoftheclampingdevice.MostoftheclampingmechanismsusedinmachinetoolfixturesareUsetheprincipleofinclinedwedgetoclamptheworkpiece,themostbasicformistodirectlyusetheinclinedwedge,thatis,theinclinedwedgeclampingmechanism.Screwclampingmechanism,eccentricclampingmechanism,etc.arejustvariantsofwedges.

Wedgeclampingmechanism

Thewedgeclampingmechanismisamechanismthatusesthepressuregeneratedwhentheinclinedsurfaceofthewedgemovestoclamptheworkpiece.AsshowninFigure8,thewedgeblockswedgesbetweentheworkpieceandtheclampingbodyundertheactionofforce,andhasawedgingeffect.Theoriginalforcecanbedrivenbymanual,pneumaticorhydraulictransmission.

Screwclampingmechanism

Thescrewclampingmechanismisamechanismthatusesthepressuregeneratedbytherotationofascrewornuttoclampaworkpiece.Itisthemostwidelyusedinmachinetoolfixtures.Amongthem,therearemainlysinglescrewclampingandscrewplatecombinedclamping.

1.SinglescrewclampingFigure9showsthesinglescrewclampingmechanism.Figure7(a)isthesimplestscrewclamping.Whentightening,awrenchisrequired.Whenthescrewrotates,itmaydrivetheworkpiecetodamagethepositioning,andthecontactareabetweentheendandtheworkpieceissmall,whichiseasytocrushthesurfaceoftheworkpiece.InthestructureshowninFigure9(b),thelowerendofthescrew1isequippedwithafloatingpressureblock3,andthereisagapbetweenthepressureblockandthescrew,whichcanswingtoensuregoodcontactwiththesurfaceoftheworkpiece.Figure9(c)showsamechanismforclampingwithanut.Theadditionofasphericalwasherbetweenthenutandthesurfaceoftheworkpiececanevenlydistributetheclampingforceontheworkpiecewhileavoidingbendinganddeformationofthescrew.Thespiralcanberegardedasawedgearoundthecylinder,sotheclampingforcecalculationofthespiralclampingmechanismissimilartothatofthewedge.Figure10showsaschematicdiagramoftheforceofthescrewintheclampedstate.

2.Upínací mechanismus šroubové desky

Thescrewplateclampingmechanismisaclampingdevicecomposedofascrewandalever(ieapressureplate),whichisenoughtoscrewasacomponenttogeneratetheoriginalforce,andthenusethepressureplatetochangetheclampingforceThesize,directionandclampingstrokeareusedtoclamptheworkpiece.

AsshowninFigure11,thestructureinFigure11(a)isamovablescrewplatenclampingmechanism,andtheplaten4isprovidedwithakgrooveunderneath,sothattheplatencanmovealongthedirectionofthegroove,whichisconvenientfortheworkpieceLoadingandunloading.Thespring2playstheroleofsupportingthepressureplatesothatitwillnotfallaftertheworkpieceisremoved.Asphericalwasher5isinstalledunderthenut,sothatwhentheheightoftheworkpiecechangestomakethepressureplatetilt,thescrewwillnotbebentwhentheworkpieceisclamped.ThestructureinFigure11(b)isaclampingmechanismwithahingedpressureplate,whichcangenerateclampingforcesintwodirectionsandrespectivelypointtothesupportingsurfacesofthetwopositioningelements.ThestructureshowninFigure12isahook-shapedguanidineplateclampingmechanism.Itsoutstandingfeatureisthatthestructureiscompact,thescrewisnotsubjecttobendingmoment,anditiswidelyusedinclamps.Inordertofacilitatetheloadingandunloadingoftheworkpiece,thehook-shapedpressingplatecanberotatedarounditsaxis.

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