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《机电专业英语 教学课件 作者 杨寿智 刘水平 机电专业英语.Lesson 2.ppt》由会员上传分享，免费在线阅读，更多相关内容在应用文档-天天文库。
1、Lesson2TOOLBITMATERIALSTextThematerialsusedfortoolbitsmustpossesscertainqualitiestobeeffective.Theymustpossesshardness,strength,andtoughness,andtheymustbeheatresistant.Thereareconditionsassociatedwiththematerialbeingcutthataffecttheselectionofthetoolmaterials:th
2、echaracteristicsandconditionoftheworkpiecematerial,theamountofstocktoberemoved,therequiredprovisionofthefinishedworkpiece,thesurfacefinish,therigidityoftheworkpieceandtoolholder,theconditionofthemachinetool,theheatgeneratedbyaparticularoperation,andsoon.Allofthe
3、seitemsmustbeconsideredwhenselectingatoolmaterial.Cuttingtools,tooperateefficiently,musthavepropertiessuchashothardness,toughness,resistancetocratering,wearresistance,andresistancetoshock.Itshouldbenotedthatsomehardenedmaterialswillretaintheirhardnessafterbeings
4、ubjectedtohightemperaturesduringthecuttingoperationandcooledtoroomtemperature.Suchtoolmaterialsareceramics,carbides,castmaterials,andhigh-speedsteel(HSS)upto1000℉.Carbonsteellosesitshardnessalmostimmediatelyuponbeingcooledfromelevatedtoroomtemperature.High-carbo
5、nsteel:Toolsmadefromhigh-carbonsteels,0.80to1.3%,areusedforsmall-quantityproductionofwoodpartsormachiningsoftmaterialssuchasfree-cuttingsteelsandbrass.Itisimportantthattheoperationaltemperaturesbekeptbelow400℉becausethemateriallosesitshardnessabovethistemperatur
6、e.Forthisreasoncoolantsshouldbeusedfreely.Sometimesvanadiumandchromiumareaddedtogivebetterhardeningability.However,anytemperatureincreasewillaffectthehardnessandeffectivenessofthetool.High-speedsteel:Thesetoolmaterialsareofseveralvarieties.Themostcommontypeisthe
7、18-4-1high-speedsteel.Thistoolmaterialhasapproximately18%tungsten,4%chromium,and1%vanadiumasitsalloyingelements.Anothertypehasaboutthesamepercentageoftungstenbutfrom5to12%cobaltaddedasoneoftheprincipalalloyingelements.Thisimprovetheredhardnessofthematerial.Thist
8、ypeoftoolmaterial,althoughabletooperateathighertemperaturesthan18-4-1steel,ismoreexpensive.Toreducetheamountoftungstenrequired,anotherhigh-speedsteelhasbeendeveloped,
