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)V
(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.
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.