模具专业英语 教学课件 作者 王浩钢 14456第17章.ppt

《模具专业英语 教学课件 作者 王浩钢 14456第17章.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、Lesson17CastingsShawinvestmentcastingThemanufactureofcavitiesandcoresinsteelbytheconventionalcastingmethodusingsandmouldsisnotsatisfactoryowingtothepoorfinishobtainedandtotheporositywhichoccurson,orjustbelow,thesurfaceofthecasting.①Theexpenditureinvolvedinplu

2、gging,machiningandfinishinguneconomic.TheShawinvestmentcastingprocessdoesnot,however,sharethedisadvantagesassociatedwithsandcastingandisthereforeapplicabletospecialistsandthemouldmakersuppliesthecompanywithapatternoftherequiredmouldpart.②Asthefinalcastingwill

3、beanaccuratereproductionofthepatternsupplied,thismustbemanufacturedtoclosetolerancesandhaveagoodsurfacefinish.Toallowforthecontractionofthesteeloncoolingthepatternismadeapproximately0.020mm/mm(in/in)oversize.Theprocedureadoptedinthemanufactureofamouldpartbyth

4、isprocessisillustrateddiagrammaticallyinFigure17-1.Figure17-1stagesofmanufactureofcorebyShawinvestmentcastingprocessThemajorlimitationassociatedwiththeprocessisthatitisnotpossibletoguaranteeanoveralltolerancebetterthan0.005mm/mm(in/in)whichmeansthatforlargemo

5、uldcastingsthereisthepossibilityofconsiderableerror③.Forexample,thediscrepancyonacomponent500mm(20in)longmaybeasmuchas2.5mm(0.1in)whichwouldcertainlynecessitatesubsequentmachiningoperation.④However,inmanycases,asforexampleinthetoyindustry,extremeaccuracyinthe

6、dimensionofthefinalproductisnotasimportantastheform,inwhichcasetheprocessoftenshowsconsiderablesavingoverconventionalmachiningmethods.PRESSURECASTINGBeryllium-copperisamaterialwhichisincreasinglybeingusedinmouldconstructionbecauseitpossessesseveraldesirablech

7、aracteristics.Inparticularithasahighthermalconductivitycombinedwithareasonablehardness(BrinellHardnessNumberofabout250)whichmakesitsuitableforcertaintypesofcavityandcore,andforothermouldparts,suchashot-runnerlessonsecondarynozzles.Itshighthermalconductivityme

8、ansthatwhenberyllium-copperisusedforacavityoracoretheheatfromthemeltwillbetransferredawayfromtheimpressionfasterthanifacorrespondingsteelcavityandcoreareused,andthisoftenresultsinashorter