模具专业英语Bending-Dies7

Lesson10BendingDiesBendingistheuniformstrainingofmaterial,usuallyflatsheetorstripmetal,aroundastraightaxiswhichliesintheneutralplaneandnormaltothelengthwisedirectionofthesheetorstrip.Metalflowtakesplacewithintheplasticrangeofthemetal,sothatthebendretainsapermanentsetafterremovaloftheappliedstress.Theinnersurfaceofabendisincompression;theoutersurfaceisintensionApurebendingactiondoesnotreproducetheexactshapeofthepunchanddieinthemetal;suchareproductionisoneofforming.Theneutralaxisistheplaneareainbentmetalwhereallstrainsarezero.BendRadii.Minimumbendradiivaryfordifferentmetals;generally,differentannealedmetalscanbebenttoaradiusequaltothethicknessofthemetalwithoutcrackingorweakeningBendAllowances.Sincebentmetalislongerafterbending,itsincreasedlength.generallyofconcerntotheproductdesigner,mayalsohavetobeconsideredbythediedesignerifthelengthtoleranceofthebentpartiscriticalBendingMethods.Twobendingmethodsarecommonlymadeuseofinpresstools.Metalsheetorstrip,supportedbyaVblock(Figure10-la),isforcedbyawedge-shapedpunchintotheblock.Thismethod,termedVbending,producesabendhavinganincludedanglewhichmaybeacute,obtuse,orof90°Frictionbetweenaspring-loadedknurledpinintheveeofadieandthepartwillpreventorreducesidecreepofthepartduringitsbending.Edgebending(Figure10-1b)iscantileverloadingofabeam.Thebendingpunch1forcesthemetalagainstthesupportingdie2.Thebendaxisisparalleltotheedgeofthedie.Theworkpieceispreventitsmovementduringdownwardtravelofthepunch.ForUbending(channelbending)pressureswillbeapproximatelytwicethoserequiredforVbending;edgebendingrequiresaboutone-halfthoseneededforVbending.Springback.Afterbendingpressureonmetalisrelease,theelasticstressesalsoarereleased,whichcausesmetalmovementresultinginadecreaseinthebendangle(aswellasanincreaseintheincludedanglebetweenthebentportions).Suchametalmovement,termedspringbackform10°to15°.v-bendingdiescustomarilycompensateforspringbackwithVblocksandwedge-shapedpuncheshavingincludedanglesSomewhatlessthanthatrequiredinthepartThepartisbentthoughtagreateranglethanthatrequiredbutitspringsbacktothedesiredangle.Partsproducedinothertypesofbendingdiesarealsooverbentthroughanangleequaltothespring-backanglewithanundercutorrelievedpunch