机械毕业设计英文外文翻译80冲压变形.docx
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机械毕业设计英文外文翻译80冲压变形.docx
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机械毕业设计英文外文翻译80冲压变形
附录1
Categoriesofstampingforming
Manydeformationprocessescanbedonebystamping,thebasicprocessesofthestampingcanbedividedintotwokinds:
cuttingandforming.
Cuttingisashearingprocessthatonepartoftheblankiscutformtheother.Itmainlyincludesblanking,punching,trimming,partingandshaving,wherepunchingandblankingarethemostwidelyused.Formingisaprocessthatonepartoftheblankhassomedisplacementformtheother.Itmainlyincludesdeepdrawing,bending,localforming,bulging,flanging,necking,sizingandspinning.
Insubstance,stampingformingissuchthattheplasticdeformationoccursinthedeformationzoneofthestampingblankcausedbytheexternalforce.Thestressstateanddeformationcharacteristicofthedeformationzonearethebasicfactorstodecidethepropertiesofthestampingforming.Basedonthestressstateanddeformationcharacteristicsofthedeformationzone,theformingmethodscanbedividedintoseveralcategorieswiththesameformingpropertiesandtobestudiedsystematically.
Thedeformationzoneinalmostalltypesofstampingformingisintheplanestressstate.Usuallythereisnoforceoronlysmallforceappliedontheblanksurface.Whenitisassumedthatthestressperpendiculartotheblanksurfaceequaltozero,twoprincipalstressesperpendiculartoeachotherandactontheblanksurfaceproducetheplasticdeformationofthematerial.Duetothesmallthicknessoftheblank,itisassumedapproximatelythatthetwoprincipalstressesdistributeuniformlyalongthethicknessdirection.Basedonthisanalysis,thestressstateandthedeformationcharacteristicsofthedeformationzoneinallkindofstampingformingcanbedenotedbythepointinthecoordinatesoftheplaneprincipalstress(diagramofthestampingstress)andthecoordinatesofthecorrespondingplaneprincipalstains(diagramofthestampingstrain).Thedifferentpointsinthefiguresofthestampingstressandstrainpossessdifferentstressstateanddeformationcharacteristics.
Whenthedeformationzoneofthestampingblankissubjectedtoplanetensilestresses,itcanbedividedintotwocases,thatisσγ>σθ>0,σt=0andσθ>σγ>0,σt=0.Inbothcases,thestresswiththemaximumabsolutevalueisalwaysatensilestress.Thesetwocasesareanalyzedrespectivelyasfollows.
2)Inthecasethatσγ>σθ>0andσt=0,accordingtotheintegraltheory,therelationshipsbetweenstressesandstrainsare:
εγ/(σγ-σm)=εθ/(σθ-σm)=εt/(σt-σm)=k(1.1)
where,εγ,εθ,εtaretheprincipalstrainsoftheradial,tangentialandthicknessdirectionsoftheaxialsymmetricalstampingforming;σγ,σθandσtaretheprincipalstressesoftheradial,tangentialandthicknessdirectionsoftheaxialsymmetricalstampingforming;σmistheaveragestress,σm=(σγ+σθ+σt)/3;kisaconstant.
Inplanestressstate,Equation1.1
3εγ/(2σγ-σθ)=3εθ/(2σθ-σt)=3εt/[-(σt+σθ)]=k(1.2)
Sinceσγ>σθ>0,so2σγ-σθ>0andεθ>0.Itindicatesthatinplanestressstatewithtwoaxialtensilestresses,ifthetensilestresswiththemaximumabsolutevalueisσγ,theprincipalstraininthisdirectionmustbepositive,thatis,thedeformationbelongstotensileforming.
Inaddition,becauseσγ>σθ>0,therefore-(σt+σθ)<0andεt<0.Thestraininthethicknessdirectionoftheblankεtisnegative,thatis,thedeformationbelongstocompressiveforming,andthethicknessdecreases.
Thedeformationconditioninthetangentialdirectiondependsonthevaluesofσγandσθ.Whenσγ=2σθ,εθ=0;whenσγ>2σθ,εθ<0;andwhenσγ<2σθ,εθ>0.
Therangeofσθisσγ>=σθ>=0.Intheequibiaxialtensilestressstateσγ=σθ,accordingtoEquation1.2,εγ=εθ>0andεt <0.Intheuniaxialtensilestressstateσθ=0,accordingtoEquation1.2εθ=-εγ/2.
Accordingtoaboveanalysis,itisknownthatthiskindofdeformationconditionisintheregionAONofthediagramofthediagramofthestampingstrain(seeFig.1.1),andintheregionGOHofthediagramofthestampingstress(seeFig.1.2).
2)Whenσθ>σγ>0andσt=0,accordingtoEquation1.2,2σθ>σγ>0andεθ>0,Thisresultshowsthatfortheplanestressstatewithtwotensilestresses,whentheabsolustevalueofσθisthestraininthisdirectionmustbepositive,thatis,itmustbeinthestateoftensileforming.
Alsobecauseσγ>σθ>0,therefore-(σt+σθ)<0andεt<0.Thestraininthethicknessdirectionoftheblankεtisnegative,orinthestateofcompressiveforming,andthethicknessdecreases.
Thedeformationconditionintheradialdirectiondependsonthevaluesofσγandσθ.Whenσθ=2σγ,εγ0;whenσθ>σγ,εγ<0;andwhenσθ<2σγ,εγ>0.
Therangeofσγisσθ>=σγ>=0.Whenσγ=σθ,εγ=εθ>0,thatis,inequibiaxialtensilestressstate,thetensiledeformationwiththesamevaluesoccursinthetwotensilestressdirections;whenσγ=0,εγ=-εθ/2,thatis,inuniaxialtensilestressstate,thedeformationcharacteristicinthiscaseisthesame
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