Surface roughness.docx

Surface roughness.docx

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Surfaceroughness

MA14008XUEYIBO

Surfaceroughnessisexpressedby

wheretheCspeed,f,adepthandrdeptharethecuttingspeed,feedrate,axialdepthandradialdepthrespectively.Generally,Surfaceroughnessvaluereducesonincreasingcuttingspeedandfrequency,anddecreasingthelaserpowerandgaspressure.Alsonitrogengivesbettersurfacefinishthanoxygen[1].Thelaserpowerandcuttingspeedhasamajoreffectonsurfaceroughnessaswellasstriationfrequency[2].Theaimofthisworkistopresentanddiscussabouttheexperimentalinvestigationsusingresponsesurfacemethodandacrylicsheetsinordertopredictthesignificantfactorsandtheireffectsonqualitycharacteristicsforbettercuttingperformanceandshowingtheeffectrelationshipbetweenprocessvariablesandperformancecharacteristics.Surfaceroughnessisalsosignificantlyaffectedbythetipdistancefollowedbythepowerrequirement,cuttingspeedandmaterialthickness.Surfaceroughnessbecomeslargerwhenusinglowpower,tipdistanceandmaterialthickness.Combinationoflowcuttingspeed,highpower,tipdistanceandmaterialdistanceproducefinesurfaceroughness.TheoptimisedparametersbyPSOarecuttingspeed（2600pulse/s）,tipdistance（9.70mm）,power（95%）andmaterialthickness（9mm）whichproduceroughnessaround（0.0129µm）.Theerrorofroughnessobtainedbyoptimizedroughnessmodelis0.085%.Atmaterialsthickness（6mm）,tipdistance（9.5mm）,cuttingspeed（3000pulse/s）andpower（95%）,thereisameltingandburningarea.

Surfacetreatmentsincludingnitriding,coldrollingandshotpeeningthatproducedcompressiveresidualsurfacestressescanprolongthefatiguelife.Thesesurfacetreatmentscausethemaximumtensilestresstooccurbelowthesurfaceofthematerials.However,thetensileresidualsurfacestressesarefoundtobeespeciallydetrimentalandcanpromotecorrosionfatigue.Inaddition,Surfacetreatmentscanalsoincreasetheendurancelimitofthematerialused.AdiffusionprocesssuchasThenitridingprocesshasthecombinedeffectofproducingahighermaterialstrengthonthesurfaceandcausingthevolumetricchangeswhichproducetheresidualcompressivestresses.Thisprocessiscapableofincreasingthestrengthofthematerialonthesurfaceaswellascausingthevolumetricchanges,whichproducetheresidualcompressivesurfacestresses.Thusthenitridingcouldbeappliedtothefatiguecriticalareaofthesubjecttoimprovethefatiguelifeandalsoimprovethefrettingresistance,sincethecylinderblockisincontactwithothercomponents.Inordertoenhancethesurfacepropertiesoftoday’smaterials,producersofcomponentsareturningtodifferentsurfacetreatments[3].Thereareseveraltechniquesavailableformechanicallyimprovingthesurfacepropertiesofthecomponents,suchaspolished,ground,machined,hotrolled,forged,cast,etc.Someofthesetechniquesproduceanimprovesurfacebyplasticdeformationofsurfaceirregularities[4].Variousmethodshavesofarbeenemployedinordertoimprovefatiguestrength,includingoptimizationofgeometricdesign,stronger,materialsandsurfaceprocessingsuchasnitriding,coldrolled,shotpeeningetc.Amongthemshotpeeninghaslongbeenwidelyusedasalowcostandsimplemethodforincreasingthefatiguestrengthofthecomponent[5].

REFERENCES

[1].K.A.GhanyandM.Newishy,Cuttingof1.2mmthickausteniticstainlesssteelsheetusing

pulsedandCWNd:

YAGlaser,J.Mat.Proc.Tech.,Vol.168（2005）,438–447.

[2].N.Rajaram,J.S.Ahmad,S.H.Cheraghi,CO2lasercutqualityof4130steel,Int.J.Mach.ToolsManuf.,Vol.43（2003）351–358.

[3]M.M.Rahman,A.K.Ariffin,N.JamaludinandC.H.C.Haron,“Influenceofsurfacetreatmentsonfatiguelifeofafreepistonlineargeneratorenginecomponentusingrandomloading”,JournalofZhejiangUniversityofScience7（11）,1819-1830（2006）.

[4]M.M.RahmanandA.K.Ariffin,“Effectsofsurfacefinishandtreatmentonthefatiguebehaviourofvibratingcylinderblockusingfrequencyresponseapproach”,JournalofZhejiangUniversityofScience,7（3）,352-360（2006）.

[5]M.M.RahmanandA.K.Ariffin.“Improvementoffatiguelifeofaluminiumalloyscylinderheadofanewfreepistonengineusingshotpeeningprocess”,InternationalJournalofMechanicalandMaterialsEngineering,2

（1）,19-28（2007）.