Basicinformation
Exciteelectronsormoleculestogenerateconcentratedandphase-identicallightbeamsduringtheconversionintoenergy.LasercomesfromthefirstletterofLightAmplificationbyStimulatedEmissionRadiation.composition.
Itiscomposedofanopticaloscillatorandamediumplacedbetweenthemirrorsatbothendsofthecavityoftheoscillator.Whenthemediumisexcitedtoahigh-energystate,itstartstogeneratelightwavesofthesamephaseandreflectbackandforthbetweenthemirrorsatbothends,formingaphotoelectricstringjunctioneffect,amplifyingthelightwaves,andobtainingsufficientenergytostartemittinglaserlight.Lasercanalsobeinterpretedasadevicethatconvertsprimitiveenergysuchaselectricenergy,chemicalenergy,heat,lightornuclearenergyintocertainspecificlightfrequencies(electromagneticradiationbeamsofultravioletlight,visiblelightorinfraredlight.)TheconversionformisinsomeItiseasytocarryoutinsolid,liquidorgaseousmedia.Whenthesemediaareexcitedintheformofatomsormolecules,theyproducelightbeamswithalmostthesamephaseandnearlyasinglewavelength—laser.Becauseofthesamephaseandsinglewavelength,thedifferenceangleisverysmall,andthedistancethatcanbetransmittedisquitelongbeforebeinghighlyconcentratedtoprovidefunctionssuchaswelding,cutting,andheattreatment.
Thefirstlaserbeamintheworldwasproducedbyusingaflashbulbtoexciterubycrystalgrainsin1960.Duetothethermalcapacityofthecrystal,itcanonlyproduceaveryshortpulsebeamwithaverylowfrequency.Althoughtheinstantaneouspulsepeakenergycanbeashighas10^6watts,itisstillalowenergyoutput.Theuseofneodymium(ND)astheexcitationelementofyttriumaluminumgarnetcrystalrods(Nd:YAG)canproduceacontinuoussingle-wavelengthbeamof1-8KW.YAGlaser,withawavelengthof1.06uM,canbeconnectedtothelaserprocessingheadthroughaflexibleopticalfiber,theequipmentlayoutisflexible,andthesuitableweldingthicknessis0.5-6mm.UsingCO2laser(wavelength10.6uM)withCO2astheexciter,theoutputenergycanreach25KW,anditcanmake2mmplatethicknesssinglepassfullpenetrationwelding.Ithasbeenwidelyusedintheindustryformetalprocessing.
Mostoftheearlylaserweldingresearchexperimentsusedrubypulsedlasers.Althoughhigherpulseenergycouldbeobtainedatthattime,theaverageoutputpoweroftheselaserswasquitelow,whichwasmainlycausedbytheverylowworkofthelasers.Determinedbytheefficiencyandtheexcitabilityoftheluminescentmaterial.LaserweldingmainlyusesCO2lasersandYAGlasers.YAGlasershavebecomethepreferredequipmentforlaserspotweldingandlaserseamweldingbecauseoftheirhighaveragepower.Thesignificantdifferencebetweenlaserweldingandelectronbeamweldingisthatlaserradiationcannotproduceperforationwelding.Infact,whenthelaserpulseenergydensityreaches10tothe6thpowerW/CM2,aweldholewillbeformedontheweldinginterfaceoftheweldedmetalmaterial,andtheformationconditionsofthesmallholewillbemet,sothatthelaserbeamcanbeusedfordeepening.Fusionwelding.
Beforethe1970s,becausehigh-powercontinuouswaveformlasershadnotyetbeendeveloped,researchfocusedonpulsedlaserwelding.Mostearlylaserweldingresearchexperimentsusedrubypulsedlasers.TheweldingprocessofYAGlasersiscarriedoutbyweldingjoints.Afterthebirthofcontinuouspowerwaveformlasersabove1KW,thereallaserseamweldingcanberealized.
Withthesuccessofthekilowatt-levelcontinuousCO2laserweldingtest,laserweldingtechnologymadeabreakthroughintheearly1970s.CO2laserweldingwascarriedoutonalargethicknessstainlesssteelspecimen,andapenetrationweldwasformed,whichclearlymarkedtheformationofsmallholes,andthedeeppenetrationweldproducedbylaserweldingwassimilartoelectronbeamwelding.TheseearlyworkusingCO2lasersformetalweldingprovedthegreatpotentialofhigh-powercontinuouslaserwelding.Intheaerospaceindustryandmanyotherapplications,laserweldingcanrealizetheconnectionofmanytypesofmaterials,andlaserweldingusuallyhasmanyadvantagesthatotherfusionweldingprocessescannotmatch,especiallylaserweldingcanconnectthemoredifficulttoweldintheaviationandautomotiveindustriesThin-platealloymaterials,suchasaluminumalloy,etc.,andthedeformationofthecomponentsissmall,andthejointqualityishigh.Anotherattractiveapplicationoflaserprocessingistheuseoflaserstoachievelocalandsmall-scaleheatingcharacteristics.Thishotspotoflasersmakesthemverysuitableforweldingelectronicdevicessuchasprintedcircuitboards.Laserscanbeusedinelectronicdevices.Averysmallareaonthedeviceproducesahighaveragetemperature,whiletheareaoutsidethejointisbasicallyunaffected.
Itbelongstofusionwelding,whichuseslaserbeamasenergysourcetoimpactontheweldmentjoint.Thelaserbeamcanbeguidedbyaflatopticalelement(suchasamirror),andthenareflectivefocusingelementorlensisusedtoprojectthebeamontheweld.Laserweldingisnon-contactwelding.Nopressureisrequiredduringtheoperation,butinertgasisrequiredtopreventoxidationofthemoltenpool.Fillermetalisoccasionallyused.LaserweldingcanbecombinedwithMIGweldingtoformlaser-MIGhybridweldingtoachievelargepenetrationwelding,andatthesametime,theheatinputisgreatlyreducedcomparedwithMIGwelding.
Featuresoflaserwelding
Firstofall,laserweldingcanreducetheamountofheatinputtotheminimum,themetallographicchangerangeoftheheat-affectedzoneissmall,andthedeformationcausedbyheatconductionisalsolowest.Thereisnoneedtouseelectrodes,andthereisnoconcernaboutelectrodecontaminationordamage.Andbecauseitisnotacontactweldingprocess,thewearanddeformationoftheequipmentcanbeminimized.Thelaserbeamiseasytofocus,alignandbeguidedbyopticalinstruments.Itcanbeplacedatanappropriatedistancefromtheworkpiece,andcanbeguidedbetweentoolsorobstaclesaroundtheworkpiece.Otherweldingmethodscannotbeusedduetotheabove-mentionedspacelimitations..Secondly,theworkpiececanbeplacedinaclosedspace(vacuumedortheinternalgasenvironmentisundercontrol).Thelaserbeamcanbefocusedonasmallarea,canweldsmallandcloselyspacedparts,canweldawiderangeofmaterials,andcanalsojoinvariousheterogeneousmaterials.Inaddition,itiseasytoautomatehigh-speedwelding,anditcanalsobecontrolledbydigitalorcomputer.Whenweldingthinmaterialsorthin-diameterwires,itisnotaseasytobetroubledasarcwelding.
Advantagesoflaserwelding
(1)Theheatinputcanbereducedtotheminimumrequiredamount,themetallographicchangerangeoftheheat-affectedzoneissmall,andthedeformationcausedbyheatconductionisalsothelowest.
(2)Theweldingprocessparametersof32mmplatethicknesssinglepassweldinghavebeenverifiedandqualified,whichcanreducethetimerequiredforthickplateweldingandevensavetheuseoffillermetal.
(3)Thereisnoneedtouseelectrodes,andthereisnoconcernaboutelectrodecontaminationordamage.Andbecauseitisnotacontactweldingprocess,thewearanddeformationoftheequipmentcanbeminimized.
(4)Thelaserbeamiseasytofocus,alignandbeguidedbyopticalinstruments,canbeplacedatanappropriatedistancefromtheworkpiece,andcanbere-guidedbetweentoolsorobstaclesaroundtheworkpiece,otherweldingThelawcannotbeexertedduetotheabove-mentionedspaceconstraints.
(5)Theworkpiececanbeplacedinaclosedspace(undervacuumorinternalgasenvironmentundercontrol).
(6)Thelaserbeamcanbefocusedonasmallareaandcanweldsmallandcloselyspacedparts.
(7)Therangeofweldablematerialsiswide,andtheycanalsobejoinedtoeachother.Allkindsofheterogeneousmaterials.
(8)Itiseasytoautomatehigh-speedwelding,anditcanalsobecontrolledbydigitalorcomputer.
(9)Whenweldingthinmaterialsorthin-diameterwires,itwillnotbeaseasytobetroublesomeasarcwelding.
(10)Itisnotaffectedbythemagneticfield(arcweldingandelectronbeamweldingareeasy),andcanaccuratelyaligntheweldment.
(11)Twometalswithdifferentphysicalproperties(suchasdifferentresistances)canbewelded
(12)NovacuumorX-rayprotectionisrequired.
(13)Withperforationwelding,thedepth-to-widthratiooftheweldbeadcanreach10:1
(14)Thedevicecanbeswitchedtotransmitthelaserbeamtomultipleworkstations.
Processparameters
ProcessparametersofcontinuousCO2laserwelding
Thickness/mm | Weldingspeed/(cm/s) | Seamwidth/mm | Aspectratio | Power/kw | |
Buttweld | |||||
321stainlesssteel(1Cr18Ni9Ti) | 0.13 | 3.81 | 0.45 | Fullpenetration | 5 |
0.25 | 1.48 | 0.71 | Fullpenetration | 5 | |
0.42 | 0.47 | 0.76 | Partialpenetration | 55 | |
17-7stainlesssteel(0Cr7Ni7A1) | 0.13 | 4.65 | 0.45 | Fullpenetration | 5 |
302stainlesssteel(1Cr18Ni9) | 0.13 | 2.12 | 0.50 | Fullpenetration | 5 |
0.20 | 1.27 | 0.50 | Fullpenetration | 5 | |
0.25 | 0.42 | 1.00 | Fullpenetration | 5 | |
6.35 | 2.14 | 0.80 | 7 | 3.5 | |
8.9 | 1.27 | 1.00 | 3 | 8 | |
12.7 | 0.42 | 1.00 | 5 | 20 | |
20.3 | 21.1 | 1.00 | 5 | 20 | |
6.35 | 8.47 | —— | 3.5 | 16 | |
InconelAlloy600 | 0.10 | 6.35 | 0.25 | Fullpenetration | 5 |
0.25 | 1.69 | 0.45 | Fullpenetration | 5 | |
NickelAlloy200 | 0.13 | 1.48 | 0.45 | Fullpenetration | 5 td> |
Monel400 | 0.25 td> | 0.60 | 0.60 | Fullpenetration | p>5 |
Industrialpuretitanium | 0.13 | 5.92 | 0.38 | Fullpenetration | 5 td> |
0.25 | 2.12 | 0.55 | Fullpenetration | 5 | |
Mildsteel | 1.19 | 0.32 | —— | 0.63 | 0.65 |
Lapweld | |||||
Tin-platedsteel | 0.30 | 0.85 | 0.76 | Fullpenetration | 5 |
302stainlesssteel(1Cr18Ni9) | 0.40 | 7.45 | 0.76 | Partialpenetration | 5 |
0.76 | 1.27 | 0.60 | Partialpenetration | 5 | |
0.25 | 0.60 | 0.60 | Fullpenetration | 5 | |
FilletSeamWelding | |||||
321stainlesssteel(1Cr18Ni9Ti) | 0.25 | 0.85 | —— | —— | 5 |
Terminalweld | |||||
321stainlesssteel(1Cr18Ni9Ti) | 0.13 | 3.60 | —— | —— | 5 |
0.25 | 1.06 | —— | —— | 5 | |
0.42 | 1.90 | —— | —— | 5 | |
17-7stainlesssteel(0Cr17Ni7A1) | 0.13 | 3.60 | —— | —— | 5 |
Inconel600 | 0.10 | 1.06 | —— | p>—— | 5 |
0.25 | 0.60 | —— | —— | 5 | |
0.42 | 0.76 | —— | —— | 5 | |
NickelAlloy200 | 0.18 | 1.06 | —— | —— | 5 |
Monel400 | 0.25 |
Themainprocessparametersoflaserdeeppenetrationwelding
Laserpower
Thereisalaserenergydensitythresholdinlaserwelding.Belowthisvalue,thepenetrationdepthisveryshallow.Oncethisvalueisreachedorexceeded,thepenetrationdepthwillbegreatlyincreased.Onlywhenthelaserpowerdensityontheworkpieceexceedsthethreshold(relatedtothematerial),plasmawillbegenerated,whichmarkstheprogressofstabledeeppenetrationwelding.Ifthelaserpowerislowerthanthisthreshold,onlysurfacemeltingoftheworkpieceoccurs,thatis,weldingisperformedinastablethermalconductivitytype.Whenthelaserpowerdensityisnearthecriticalconditionfortheformationofsmallholes,deeppenetrationweldingandconductionweldingalternatelybecomeanunstableweldingprocess,resultinginlargefluctuationsinpenetration.Duringlaserdeeppenetrationwelding,thelaserpowercontrolsthepenetrationdepthandweldingspeedatthesametime.Theweldingpenetrationisdirectlyrelatedtothebeampowerdensity,andisafunctionoftheincidentbeampowerandthebeamfocalspot.Generallyspeaking,foralaserbeamwithacertaindiameter,thepenetrationdepthincreasesasthebeampowerincreases.
Beamfocalspot
Beamspotsizeisoneofthemostimportantvariablesinlaserwelding,becauseitdeterminesthepowerdensity.Butforhigh-powerlasers,itsmeasurementisadifficultproblem,althoughtherearemanyindirectmeasurementtechniques.
Thediffraction-limitedspotsizeofthebeamfocuscanbecalculatedaccordingtothetheoryoflightdiffraction,butduetotheaberrationofthefocusinglens,theactualspotislargerthanthecalculatedvalue.Thesimplestactualmeasurementmethodistheisothermalprofilemethod,whichistomeasurethefocalspotandperforationdiameterafterscorchingthickpaperandpenetratingthepolypropyleneplate.Thismethodshouldbepracticedthroughmeasurementtomasterthesizeofthelaserpowerandthetimeofbeamaction.
Materialabsorptionvalue
Theabsorptionoflaserlightbyamaterialdependsonsomeimportantpropertiesofthematerial,suchasabsorptivity,reflectivity,thermalconductivity,meltingtemperature,evaporationtemperature,etc.,amongwhichthemostTheimportantthingistheabsorptionrate.
Thefactorsaffectingtheabsorptivityofthelaserbeamincludetwoaspects:thefirstistheresistivityofthematerial.Aftermeasuringtheabsorptivityofthepolishedsurfaceofthematerial,itisfoundthattheabsorptivityofthematerialisproportionaltothesquarerootoftheresistivity.,Andtheresistivitychangeswithtemperature;secondly,thesurfacestate(orsmoothness)ofthematerialhasamoreimportantinfluenceonthebeamabsorptionrate,whichhasasignificanteffectontheweldingeffect.
TheoutputwavelengthofCO2laserisusually10.6μm.Theabsorptionrateofceramics,glass,rubber,plasticsandothernon-metalsisveryhighatroomtemperature,whiletheabsorptionofmetalmaterialsisverypooratroomtemperature.,Untilthematerialmeltsandevenvaporizes,itsabsorptionincreasessharply.Themethodofusingsurfacecoatingorgeneratingoxidefilmonthesurfaceisveryeffectiveinimprovingtheabsorptionofthelightbeambythematerial.
Weldingspeed
Weldingspeedhasagreatinfluenceonpenetration.Increasingthespeedwillmakethepenetrationshallower,butifthespeedistoolow,itwillcauseexcessivemeltingofthematerialandweldpenetrationoftheworkpiece.Therefore,thereisasuitableweldingspeedrangeforacertainlaserpowerandacertainthicknessofacertainmaterial,andthemaximumpenetrationdepthcanbeobtainedatthecorrespondingspeedvalue.
Shieldinggas
Thelaserweldingprocessoftenusesinertgastoprotectthemoltenpool.Whensomematerialsarewelded,thesurfaceoxidationmaynotbeconsidered,buttheprotectionmaynotbeconsidered,butformostapplicationsGasessuchashelium,argon,andnitrogenareoftenusedforprotectiontopreventtheworkpiecefrombeingoxidizedduringtheweldingprocess.
Heliumisnoteasytoionize(highionizationenergy),whichallowsthelasertopasssmoothly,andthebeamenergyreachesthesurfaceoftheworkpiecewithouthindrance.Thisisthemosteffectiveshieldinggasusedinlaserwelding,butitismoreexpensive.
Argonischeaperanddenser,sotheprotectioneffectisbetter.However,itissusceptibletohigh-temperaturemetalplasmaionization,whichshieldspartofthebeamfromreachingtheworkpiece,reducestheeffectivelaserpowerforwelding,andalsodamagestheweldingspeedandpenetration.Thesurfaceoftheweldmentprotectedbyargonissmootherthanwhenprotectedbyhelium.
Nitrogenisthecheapestshieldinggas,butitisnotsuitableforweldingcertaintypesofstainlesssteel,mainlyduetometallurgicalproblems,suchasabsorption,whichsometimescreatesporesintheoverlaparea.
Thesecondfunctionofusingshieldinggasistoprotectthefocusinglensfrommetalvaporcontaminationandliquiddropletssplashing.Especiallyinhigh-powerlaserwelding,becausetheejectionbecomesverypowerful,itismorenecessarytoprotectthelensatthistime.
Thethirdfunctionoftheshieldinggasistodissipatetheplasmashieldingproducedbyhigh-powerlaserwelding.Themetalvaporabsorbsthelaserbeamandionizesintoaplasmacloud,andtheshieldinggasaroundthemetalvaporisalsoionizedbyheating.Ifthereistoomuchplasma,thelaserbeamisconsumedbytheplasmatosomeextent.Plasmaexistsasthesecondkindofenergyontheworkingsurface,whichmakesthepenetrationdepthbecomeshallowerandtheweldpoolsurfacebecomeswider.Increasetheelectronrecombinationratebyincreasingthethree-bodycollisionofelectronswithionsandneutralatomstoreducetheelectrondensityintheplasma.Thelightertheneutralatom,thehigherthecollisionfrequency,andthehighertherecombinationrate.Ontheotherhand,onlytheshieldinggaswithhighionizationenergywillnotincreasetheelectrondensityduetotheionizationofthegasitself.
Atomic(molecular)weightandionizationenergyofcommonlyusedgasesandmetals
Materialhelium,argon,nitrogen,aluminum,magnesium,iron
Atomic(molecular)weight44028272456
Ionizationenergy(eV)24.4615.6814.55.967.617.83
Fromthetable,thesizeoftheplasmacloudvarieswiththeprotectivegasused.HeliumisthesmallestandnitrogenSecond,thelargestwhenusingargon.Thelargertheplasmasize,theshallowerthepenetrationdepth.Thereasonforthisdifferenceisfirstlyduetothedifferenceinthedegreeofionizationofgasmolecules,andalsoduetothedifferenceinmetalvapordiffusionduetothedifferentdensityoftheprotectivegas.
Heliumhasthesmallestionizationandthesmallestdensity.Itcanquicklydriveouttherisingmetalvaporgeneratedfromthemoltenmetalpool.Therefore,usingheliumasashieldinggascansuppresstheplasmatothegreatestextent,therebyincreasingthepenetrationdepthandincreasingtheweldingspeed;becauseofitslightweight,itcanescape,anditisnoteasytocausepores.Ofcourse,judgingfromouractualweldingeffect,theeffectofargonprotectionisnotbad.
Theinfluenceofplasmacloudonpenetrationismostobviousinthelowweldingspeedarea.Whentheweldingspeedincreases,itsinfluencewillbeweakened.
Theshieldinggasisejectedthroughthenozzleopeningatacertainpressuretoreachthesurfaceoftheworkpiece.Thehydrodynamicshapeofthenozzleandthediameteroftheoutletareveryimportant.Itmustbelargeenoughtodrivethesprayedshieldinggastocovertheweldingsurface,butinordertoeffectivelyprotectthelensandpreventmetalvaporcontaminationormetalsplashfromdamagingthelens,thesizeofthenozzlemustalsobelimited.Theflowrateshouldalsobecontrolled,otherwisethelaminarflowoftheshieldinggaswillbecometurbulent,andtheatmospherewillbedrawnintothemoltenpoolandeventuallyformpores.
Inordertoimprovetheprotectioneffect,anadditionalsideblowingmethodcanbeused,thatis,theshieldinggasisdirectlyinjectedintothedeeppenetrationweldingholeatacertainanglethroughasmallerdiameternozzle.Theshieldinggasnotonlysuppressestheplasmacloudonthesurfaceoftheworkpiece,butalsoexertsaninfluenceontheformationofplasmaandsmallholesinthehole,andthepenetrationdepthisfurtherincreased,andaweldwithanidealdepthandwidthisobtained.However,thismethodrequiresprecisecontrolofthesizeanddirectionoftheairflow,otherwiseitiseasytoproduceturbulentflowanddestroythemoltenpool,makingtheweldingprocessdifficulttostabilize.
Lensfocallength
Whenwelding,focusisusuallyusedtoconvergethelaser.Generally,alenswithafocallengthof63~254mm(2.5”~10”)isused.Thefocalspotsizeisproportionaltothefocallength,theshorterthefocallength,thesmallerthespot.However,thefocallengthalsoaffectsthefocaldepth,thatis,thefocaldepthincreasessynchronouslywiththefocallength,soashortfocallengthcanincreasethepowerdensity,butbecausethefocaldepthissmall,thedistancebetweenthelensandtheworkpiecemustbeaccuratelymaintained,andthepenetrationdepthisnotlarge.Duetotheinfluenceofspatterandlasermodeduringwelding,theshortestfocaldepthusedinactualweldingismostlyfocallength126mm(5").Whentheseamislargeorthespotsizeneedstobeincreasedtoincreasetheweldseam,Choosealenswithafocallengthof254mm(10").Inthiscase,inordertoachievethedeeppenetrationpinholeeffect,ahigherlaseroutputpower(powerdensity)isrequired.
Whenthelaserpowerexceeds2kW,especiallyforthe10.6μmCO2laserbeam,duetotheuseofspecialopticalmaterialstoformtheopticalsystem,inordertoavoidtheriskofopticaldamagetothefocusinglens,thereflectivefocusingmethodisoftenused.Apolishedcoppermirrorisusedasareflector.Becauseofitseffectivecooling,itisoftenrecommendedforhigh-powerlaserbeamfocusing.
Focusposition
Whenwelding,inordertomaintainsufficientpowerdensity,thefocuspositionisveryimportant.Thechangeoftherelativepositionofthefocusandthesurfaceoftheworkpiecedirectlyaffectsthewidthanddepthoftheweld.
Inmostlaserweldingapplications,thefocalpointisusuallysetatabout1/4oftherequiredpenetrationdepthbelowthesurfaceoftheworkpiece.
Laserbeamposition
Whenlaserweldingdifferentmaterials,thelaserbeampositioncontrolsthefinalqualityoftheweld,especiallyinthecaseofbuttjointsthanlapjointsMoresensitivetothis.Forexample,whenahardenedsteelgearisweldedtoalow-carbonsteeldrum,thecorrectcontrolofthelaserbeampositionwillhelptoproduceaweldmainlycomposedoflow-carboncomponents,whichhasbettercrackresistance.Insomeapplications,thegeometryoftheweldedworkpiecerequiresthelaserbeamtobedeflectedbyanangle.Whenthedeflectionanglebetweenthebeamaxisandthejointplaneiswithin100degrees,theworkpiece'sabsorptionoflaserenergywillnotbeaffected.
Powercontrol
Thelaserpoweratthestartandendpointsoftheweldingisgraduallyincreasedanddecreased.
Duringlaserdeeppenetrationwelding,nomatterthedepthoftheweld,smallTheholephenomenonalwaysexists.Whentheweldingprocessisterminatedandthepowerswitchisturnedoff,pitswillappearattheendoftheweld.Inaddition,whenthelaserweldinglayercoverstheoriginalweld,excessiveabsorptionofthelaserbeamwilloccur,causingtheweldmenttooverheatorproducepores.
Inordertopreventtheoccurrenceoftheabovephenomenon,thepowerstartandendpointscanbeprogrammedtomakethepowerstartandendtimeadjustable,thatis,thestartpowerrisesfromzerotozeroinashortperiodoftimeusingelectronicmethods.Setthepowervalueandadjusttheweldingtime.Finally,whentheweldingisterminated,thepowerisgraduallyreducedfromthesetpowertozero.
AdvantagesandDisadvantages
(1)Thepositionoftheweldmentmustbeverypreciseandmustbewithinthefocusrangeofthelaserbeam.
(2)Whentheweldmentneedstouseajig,itmustbeensuredthatthefinalpositionoftheweldmentisalignedwiththeweldingpointthatthelaserbeamwillimpact.
(3)Themaximumweldablethicknessisrestrictedtopenetratetheworkpiecewithathicknessfarexceeding19mm,andlaserweldingisnotsuitablefortheproductionline.
(4)Formaterialswithhighreflectivityandhighthermalconductivity,suchasaluminum,copperandtheiralloys,theweldabilitywillbechangedbylaser.
(5)Whenperformingmediumtohighenergylaserbeamwelding,aplasmacontrollermustbeusedtodriveouttheionizedgasaroundthemoltenpooltoensurethereappearanceoftheweldbead.
(6)Theenergyconversionefficiencyistoolow,usuallylessthan10%.
(7)Theweldbeadsolidifiesrapidly,andtheremaybeconcernsaboutporosityandembrittlement.
(8)Theequipmentisexpensive.
Inordertoeliminateorreducethedefectsoflaserweldingandmakebetteruseofthisexcellentweldingmethod,someotherheatsourceandlaserhybridweldingprocesseshavebeenproposed,mainlylaserandarc,laserandplasmaArc,laserandinductionheatsourcehybridwelding,duallaserbeamweldingandmulti-beamlaserwelding,etc.Inaddition,variousauxiliaryprocessmeasureshavebeenproposed,suchaslaserfillerwirewelding(whichcanbesubdividedintocoldwireweldingandhotwirewelding),externalmagneticfieldassistedenhancedlaserwelding,shieldinggascontrolledmoltenpooldepthlaserwelding,andlaserassistedfrictionstirweldingWait.
(1)Powerdensity.Powerdensityisoneofthemostcriticalparametersinlaserprocessing.Withahigherpowerdensity,thesurfacelayercanbeheatedtotheboilingpointwithinamicrosecondtimerange,resultinginalargeamountofvaporization.Therefore,highpowerdensityisbeneficialformaterialremovalprocessing,suchaspunching,cutting,andengraving.Forlowerpowerdensities,ittakesseveralmillisecondsforthesurfacetemperaturetoreachtheboilingpoint.Beforethesurfacelayervaporizes,thebottomlayerreachesthemeltingpoint,whichmakesiteasytoformagoodfusionweld.Therefore,inconductivelaserwelding,thepowerdensityisintherangeof10^4~10^6W/CM^2.
(2)Laserpulsewaveform.Thelaserpulsewaveformisanimportantissueinlaserwelding,especiallyforsheetwelding.Whenahigh-intensitylaserbeamhitsthesurfaceofthematerial,60~98%ofthelaserenergywillbereflectedandlostonthemetalsurface,andthereflectivitychangeswiththesurfacetemperature.Duringalaserpulse,thereflectivityofthemetalchangesgreatly.
(3)Laserpulsewidth.Pulsewidthisoneoftheimportantparametersofpulselaserwelding.Itisnotonlyanimportantparameterdifferentfrommaterialremovalandmaterialmelting,butalsoakeyparameterthatdeterminesthecostandvolumeofprocessingequipment.
(4)Theeffectofdefocusingamountonweldingquality.Laserweldingusuallyrequiresacertaindegreeofseparation,becausethepowerdensityinthecenterofthespotatthelaserfocalpointistoohighanditiseasytoevaporateintoahole.Oneachplaneawayfromthelaserfocus,thepowerdensitydistributionisrelativelyuniform.Therearetwodefocusingmethods:positivedefocusandnegativedefocus.Ifthefocalplaneisabovetheworkpiece,itisapositivedefocus,otherwiseitisanegativedefocus.Accordingtothegeometricopticstheory,whenthedistancebetweenthepositiveandnegativedefocusplanesandtheweldingplaneisequal,thepowerdensityonthecorrespondingplanesisapproximatelythesame,buttheshapeofthemoltenpoolobtainedisactuallydifferent.Whenthedefocusisnegative,agreaterpenetrationdepthcanbeobtained,whichisrelatedtotheformationprocessofthemoltenpool.Experimentsshowthatthematerialstartstomeltwhenthelaserisheatedfor50~200us,formingliquidmetalandvaporizing,formingcitypressuresteam,whichissprayedataveryhighspeedandemitsdazzlingwhitelight.Atthesametime,thehighconcentrationofvaporcausestheliquidmetaltomovetotheedgeofthemoltenpool,formingadepressioninthecenterofthemoltenpool.Whenthedefocusisnegative,theinternalpowerdensityofthematerialishigherthanthatofthesurface,anditiseasytoformstrongermeltingandvaporization,sothatthelightenergycanbetransmittedtothedeeperpartofthematerial.Therefore,inpracticalapplications,whenthepenetrationdepthisrequiredtobelarge,thenegativedefocusisused;whenthethinmaterialiswelded,thepositivedefocusshouldbeused.
Application
Laserweldingmachinetechnologyiswidelyusedinhigh-precisionmanufacturingfieldssuchasautomobiles,ships,airplanes,high-speedrailways,etc.,whichhasbroughtsignificantimprovementstopeople’squalityoflife,andhasledThehomeapplianceindustryhasenteredtheeraofSeiko.
Especiallyafterthe42-meterseamlessweldingtechnologycreatedbyVolkswagen,whichgreatlyimprovedtheintegrityandstabilityofthebody,HaierGroup,aleadinghomeappliancecompany,grandlylaunchedthefirstwashingmachineproducedbylaserseamlessweldingtechnology.,Thehomeappliancecherishestheadvancementofscienceandtechnologyforthepeople,andadvancedlasertechnologycanbringhugechangestopeople'slives.Withthecontinuousconsolidationoftheglobalbrandstatusofwashingmachines,itsleadershipintheindustryhasbeguntobefullydemonstrated.However,withthesupportoflaserweldingmachinetechnology,itwillalsohaveadeeperreformofthehomeapplianceindustry.AccordingtoHaier'sR&Dpersonnel,mostofthemanufacturingtechnologyoftheinnertuboffullyautomaticwashingmachinesonthemarketadopts"snap-and-loop"technology.Therewillbegapsorunevennessinthejointsoftheinnertub,resultinginlowstrengthofthetubandunnecessarywearandtearontheclothes.Inordertofurtherimprovethereliabilityandrefinementoftheinnertub,Haierwashingmachinetakestheautomobileandshipbuildingindustriesasthereferencebase,andappliesthelaserseamlessweldingtechnologytothenewuniformpowerwashingmachine,avoidingthegapandunevennessoftheinnertub,andimprovingtheoverallperformance.Improvethereliabilityoftheproductwhiletakingcareoftheclothes.Duetotheincreaseinthestrengthoftheinnertub,themaximumspeedoftheuniformpowerwashingmachineduringthedehydrationprocessisalsoincreasedby25%comparedwiththeordinaryfullyautomaticwashingmachine,thedehydrationefficiencyisgreatlyimproved,andthepowerconsumptionislessandthetimeissaved.
Inaddition,Ialsolearnedthatthe"high-powerlaserweldingmachinetechnology"jointlydevelopedbytheSino-Germanshipbuildingindustryensuresthesafetyofshipsandfurtherstrengthensthehullstructure;intheaviationfield,laserseamlessWeldingtechnologyhasalsobeenwidelyusedinthemanufactureofaircraftengines.Atthesametime,thelaserseamlessweldingtechnologyofaluminumalloyfuselagecanreplacerivets,therebyreducingtheweightofthefuselageby20%;China'shigh-speedrailtrackhasalsointroducedlaserseamlesswelding.Technology,whileimprovingsafetyperformance,alsogreatlyreducesnoise,bringingpassengersaquietandcomfortableridingenvironment.
Withtheall-rounddevelopmentofscienceandtechnology,thecontinuousconsolidationandapplicationoflaserweldingmachinetechnologyhasalsoledtheglobalhomeapplianceindustryintoanewera.Thenewprocessisnotonlyanupgradeofproducts,butalsomoretechnologyDisplayandapplication.
1.ManufacturingindustryapplicationTailoredBlandLaserWeldingtechnologyhasbeenwidelyusedinforeigncarmanufacturing.Accordingtostatistics,in2000,thereweremorethan100lasertailoredweldingproductionlinesforcuttingblanksworldwide,withanannualoutputThereare70milliontailor-weldedblanksforcarcomponents,anditcontinuestogrowatarelativelyhighrate.ThedomesticallyproducedimportedmodelsPassat,Buick,Audi,etc.alsousesomecutblankstructures.JapanusesCO2laserweldinginsteadofflashbuttweldingfortheconnectionofrolledsteelcoilsinthesteelindustry.Intheresearchofultra-thinplatewelding,suchasfoilswithathicknessoflessthan100microns,theycannotbewelded,buttheyhavespecialoutputpowerwaveforms.ThesuccessofYAGlaserweldingshowsthebrightfutureoflaserwelding.JapanhasalsosuccessfullydevelopedtheuseofYAGlaserweldingforthemaintenanceofsteamgeneratorthintubesinnuclearreactorsforthefirsttimeintheworld.InChina,SuBaorongandothershavealsocarriedoutlaserweldingtechnologyforgears.
2.ThefieldofpowdermetallurgyWiththecontinuousdevelopmentofscienceandtechnology,manyindustrialtechnologieshavespecialrequirementsformaterials,andmaterialsmadebysmeltingandcastingmethodscannolongermeettheneeds.Becausepowdermetallurgymaterialshavespecialpropertiesandmanufacturingadvantages,theyarereplacingtraditionalsmeltingmaterialsincertainfieldssuchasautomobiles,airplanes,andtoolandcuttingtoolmanufacturing.Withtheincreasingdevelopmentofpowdermetallurgymaterials,thereareproblemswiththeconnectionbetweenthemandotherparts.Appearsincreasinglyprominent,sothattheapplicationofpowdermetallurgymaterialsisrestricted.Intheearly1980s,laserweldingenteredthefieldofpowdermetallurgymaterialprocessingwithitsuniqueadvantages,openingupnewprospectsfortheapplicationofpowdermetallurgymaterials,suchastheuseofbrazingmethodscommonlyusedinpowdermetallurgyLowstrength,wideheat-affectedzone,especiallyincapableofadaptingtohightemperatureandhighstrengthrequirements,causingthesoldertomeltandfalloff.Theuseoflaserweldingcanimprovetheweldingstrengthandhightemperatureresistance.
3.AutomobileindustryInthelate1980s,kilowatt-levellasersweresuccessfullyappliedtoindustrialproduction.Nowadays,laserweldingproductionlineshaveemergedfrommodernautomobilemanufacturingonalargescaleandbecomeoneoftheoutstandingachievementsofautomobilemanufacturing.EuropeanautomobilemanufacturerssuchasAudi,Mercedes-Benz,Volkswagen,andVolvoofSwedentooktheleadinadoptinglaserweldingforroof,body,sideframesandothersheetmetalweldingasearlyasthe1980s.Inthe1990s,GM,FordandChryslercompetedintheUnitedStates.Theintroductionoflaserweldingintoautomobilemanufacturing,despiteitslatestart,hasdevelopedrapidly.ItalianFiatuseslaserweldingintheweldingandassemblyofmoststeelplatecomponents.Japan'sNissan,Honda,andToyotaMotorCorporationuselaserweldingandcuttingprocessesinthemanufactureofbodypanels.High-strengthsteellaserweldingassemblypartsareduetotheirexcellentperformance.Itisusedmoreandmoreinautomobilebodymanufacturing.AccordingtothestatisticsoftheUSmetalmarket,bytheendof2002,theconsumptionoflaserweldedsteelstructureswillreach70,000tons,whichisthreetimesmorethanin1998.Accordingtothecharacteristicsoflargebatchesandhighdegreeofautomationintheautomotiveindustry,laserweldingequipmentisdevelopinginthedirectionofhigh-powerandmulti-channel.Intermsoftechnology,SandiaNationalLaboratoryoftheUnitedStatesandPrattWitneyhavejointlyconductedresearchonaddingpowdermetalandmetalwireinthelaserweldingprocess.TheInstituteofAppliedBeamTechnologyinBremen,Germanyhasconductedalotofresearchontheuseoflaserweldingofaluminumalloybodyframes.Itisbelievedthataddingfillerresiduesintheweldwillhelpeliminatehotcracks,increaseweldingspeed,andsolvetoleranceproblems.ThedevelopedproductionlinehasbeenputintoproductionattheMercedes-Benzfactory.
4.ElectronicsindustryLaserweldinghasbeenwidelyusedintheelectronicsindustry,especiallyinthemicroelectronicsindustry.Duetothesmallheat-affectedzoneoflaserwelding,theheatingconcentrationisrapidandthethermalstressislow.Therefore,itisshowinguniqueadvantagesinthepackagingofintegratedcircuitsandsemiconductordeviceshells.Inthedevelopmentofvacuumdevices,laserweldinghasalsobeenapplied,suchasmolybdenumFocusingelectrodeandstainlesssteelsupportring,fasthotcathodefilamentassembly,etc.Thethicknessoftheelasticthin-walledcorrugatedsheetinthesensororthermostatis0.05-0.1mm,whichisdifficulttosolvebytraditionalweldingmethods.TIGweldingiseasytoweldthrough,theplasmastabilityispoor,andtherearemanyinfluencingfactors.Thelaserweldingeffectisverygood,anditiswidelyused.Applications.
5.Laserweldingofbiomedicalbiologicaltissuesbeganinthe1970s.Klinketal.andJain[13]usedlaserweldingtoweldfallopiantubesandbloodvesselssuccessfullyanddemonstratedsuperiority,whichledtomoreresearchTheauthorstrytoweldvariousbiologicaltissuesandpromotetheweldingofothertissues.Theresearchonlaserweldingnerveathomeandabroadmainlyfocusesonthelaserwavelength,doseanditsfunctionrecoveryandtheselectionoflasersolder.OnthebasisofbasicresearchonlaserweldingofsmallbloodvesselsandskinThecommonbileductoftheratwaswelded.Comparedwiththetraditionalsuturemethod,laserweldinghastheadvantagesoffastanastomosis,noforeignbodyreactionduringthehealingprocess,maintainingthemechanicalpropertiesoftheweldedpart,andthegrowthoftherepairedtissueaccordingtoitsoriginalbiomechanicalproperties.Itwillbeusedinfuturebiomedicine.Getawiderrangeofapplications.
6.Otherfields.Inotherindustries,laserweldingisalsograduallyincreasing,especiallyinspecialmaterialswelding.Manydomesticresearcheshavebeencarriedout,suchaslaserweldingofBT20titaniumalloy,Hel30alloy,Li-ionbattery,etc.,GermanglassmachinerymanufacturerGlamacoCoswigandIFWJointTechnologyandMaterialsExperimentalResearchInstitutehavedevelopedanewlaserweldingtechnologyforflatglass.
Advantagesofhybridwelding
Laserhybridweldingtechnologyhassignificantadvantages.Forlasermixing,theadvantagesaremainlyreflectedintoday's:largerpenetration/largergapweldingability;bettertoughnessoftheweld,theadditionofauxiliarymaterialscanaffecttheweldlatticestructure;thebackoftheweldwithoutburn-throughThephenomenonofsagging;thescopeofapplicationiswider;withthehelpoflaserreplacementtechnology,theinvestmentisless.ForthehybridlaserMIGinertgasshieldedwelding,theadvantagesaremainlyreflectedintoday's:higherweldingspeed;largefusionweldingdepth;lessweldingheatgenerated;highweldstrength;smallweldwidth;smallweldprotrusion.Thereby,theproductionprocessofthewholesystemisstableandtheequipmentavailabilityisgood;theworkloadofweldingseampreparationandweldingseamprocessingafterweldingissmall;theweldingproductiontimeisshort,thecostislow,andtheproductionefficiencyishigh;ithasgoodopticalequipmentconfigurationperformance.
However,theinvestmentcostoflaserhybridweldinginpowerequipmentisrelativelyhigh.Withthefurtherexpansionofthemarket,thepriceofpowerequipmentwillalsodrop,andlaserhybridweldingtechnologywillbeappliedinmorefields.Atleastthelaserhybridweldingtechnologyisaverysuitableweldingprocessintheweldingofaluminumalloymaterials,andwillbecomethemainweldingproductiontoolinalongperiodoftime.
Developmentstatus
Foreignlasertechnologyandmanufacturingarerelativelydeveloped.Theyhavealreadybeguntostudyhowtoapplymodernlasertechnologytotraditionalmanufacturingasearlyasthe1980s.WesterncountriessuchastheEuropeanUnion,theUnitedStates,andJapaninAsiarelyontheirowndevelopedscientificandtechnologicalstrengthandagoodmanufacturingfoundation,underthereasonableguidanceandfinancialsupportofthegovernment,thedevelopmentoflaserweldingtechnologyisveryrapid,especiallyafterenteringthenewcentury.Theapplicationoflaserweldingtechnologycanbeseeninmanymanufacturingandotherindustries,includingtheelectronicsindustry,shipbuildingindustry,automobileindustry,etc.,andtheapplicationofmodernlaserweldingtechnologycanbeseen.Andtheindustrystandardofweldingtechnologyhasbeenpreliminarilyformed,sothatitcanbeappliedinareasonableandcontrollablerange.Atthesametime,inordertofurtherimproveweldingefficiencyandenablelaserweldingtechnologytobebetterappliedtomodernlarge-scaleproduction,especiallylarge-scalemanufacturingandconstructionindustries,Westerndevelopedcountrieshavebeenactivelystudyinghowtoimprovetheefficiencyoflaserweldinginrecentyears.Theresearchofpowerlasersfurtherpromotesandrealizestherealizationofhigh-powerlaserweldingtechnology,thustrulyapplyingittolarge-scalemanufacturing,construction,andevenmilitaryfieldsforthemanufacturingofsubmarinesandwarships.
In2016,theHarbinWeldingResearchInstitutewastheleaderinlaserweldingtechnologyresearchinChina.Inrecentyears,inadditiontofurtherbroadeninganddevelopingnewtypesoflaserweldingandequipment,itisalsoactivelyimitatingandreferringtothelatesttrendsinforeignresearch,andconstantlyseekingbreakthroughsanddevelopmentsinhigh-powerlaserweldingtechnology.Thelatestresearchresultsshowthattheysuccessfullyovercometheweldingproblemsofdomesticlarge-scalecomponents,whichundoubtedlymarksamajorbreakthroughinthefieldoflaserweldingtechnologyinmycountry,andalsolaysthefoundationformajorapplicationsinlarge-scaleprojectsinthefuture.Inaddition,thedomesticlaserweldingtechnologyresearchin2016wasalsoconcentratedinthefieldsoflaserhotwirewelding,dissimilarmetalwelding,etc.,whicharethelatesttopicsofmodernlaserweldingtechnologyresearch.Andforeigncountrieshavemadebreakthroughsinrelatedresearchfields,especiallyGermanyhasinitiallymasteredthetechniquesandmethodsofdissimilarmetalwelding.Inthefuture,ourcountrymustbetrulyproficientintheapplicationandmasteryoflaserweldingtechnology,andapplyittomorefieldsandIntheindustry,itisundoubtedlynecessarytoovercometheabove-mentionedissuesandtofurtherimproveandoptimizethelaserweldingtechnology.
Prospects
Laserweldingisacombinationofmoderntechnologyandtraditionaltechnology.Comparedwithtraditionalweldingtechnology,laserweldingisespeciallyuniqueanditsapplicationfieldsandapplicationlevelsaremoreextensive.,Cangreatlyimprovetheefficiencyandaccuracyofwelding.Itshighpowerdensityandfastenergyreleasecanbetterimproveworkefficiency.Atthesametime,itsownfocuspointissmaller,whichundoubtedlymakestheadhesionbetweenstitchedmaterialsbetter,andwillnotcausematerialdamageanddeformation.Theemergenceoflaserweldingtechnologyhasrealizedthefieldsthattraditionalweldingtechnologycannotapply.Itcansimplyachievevariousweldingrequirementsofdifferentmaterials,metalsandnon-metals,andbecauseofthepenetrationandrefractionofthelaseritself,itcanbebasedonThetrajectoryofthespeedoflightitselfcanachieverandomfocuswithin360degrees,whichisundoubtedlyunimaginableunderthedevelopmentoftraditionalweldingtechnology.Inaddition,becauselaserweldingcanreleasealargeamountofheatinashortperiodoftimetoachieverapidwelding,ithaslowerenvironmentalrequirementsandcanbeperformedundergeneralroomtemperatureconditions,withouttheneedforvacuumorgasprotection.Afterdecadesofdevelopment,peoplehavethehighestlevelofunderstandingandrecognitionoflasertechnology,andithasgraduallyexpandedfromtheinitialmilitaryfieldtothemoderncivilianfield,andtheemergenceoflaserweldingtechnologyhasfurtherexpandedtheapplicationrangeoflasertechnology.Inthefuture,laserweldingtechnologycannotonlybeusedinfieldssuchasautomobiles,steel,andinstrumentmanufacturing,butalsoinmilitary,medical,andotherfields,especiallyinthemedicalfield,withthehelpofitsownhighheatandhightemperature.Thecharacteristicsofintegrationandhygienecanbebetterappliedinclinicaldiagnosisandtreatmentsuchasneuromedicineandreproductivemedicine.Anditsownprecisionadvantageswillalsobeappliedinmoreprecisioninstrumentmanufacturingindustries,whichwillcontinuetobenefitthedevelopmentofmankindandsociety.
