热敏感材料的低能量电弧连接工艺.docx

热敏感材料的低能量电弧连接工艺.docx

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热敏感材料的低能量电弧连接工艺

LowEnergyArcJoiningProcessforMaterialsSensitivetoHeat

热敏感材料的低能量电弧连接工艺

Modern,ultra-lightweightplacesdemandsonweldingtechnologythatsimplycannotbemetwithtraditionalshieldinggas

现代，超轻型不能使用传统的气体保护焊接工艺的地方需要采用的焊接技术。

weldingprocesses.Variantsoftherobustarcweldingprocessneedtobedevelopedwhichfeedverylittleheatintothematerial

需要开发对材料输入非常少的热量

butwhichstillguaranteestrongconnections.ThecoldArcisavariantoftheMIG/MAGprocessthatmeetsthesedemands.In

并仍能保证牢固的连接的新的电弧焊接工艺。

coldArc是满足这些需要的新的MIG/MAG工艺

thisprocess,allinterventionsintheprocessflowarecarriedoutdirectlyinthepowersourcewithoutmechanicalinterventionin

这种工艺，处理过程中的所有调整都在电源内部直接完成，不需要在送丝中进行机械调整

thewirefeed,whichmeansthatstandardweldingtorchescanbeusedandtheprocesscanalsobeusedtoproduceexcellent

这意味着，使用标准焊枪也能完成卓越的手工焊接效果。

manualweldingresults.

1Introduction

简介

Inadditiontotheconceptsof"higher,further,faster"whichhaverepresentedthechallengestothemodernworldoftechnology

除更高、更远、更快的概念，来描述当今技术面临的挑战

formanyyears,recentlyademandfor"easier"hasalsocometothefore.Thisappliesprimarilyinvehicleconstructionwhere

最近，更简单的要求也走到前面。

这些应用主要

fuelcanbesavedduringacceleration,drivingandwhenbrakingbyreducingweight,whichinturnpreservesresources,

在加速时减少油耗，驾驶和制动时减轻重量，回收利用，降低成本并环保

reducescostsandprotectstheenvironment.

的车体结构中

Thismorerecentdemandhasproducedincreasinglylightweightmodelswhichareonlymadepossiblebytheuseofthinner

最近

high-strengthsteelmetalsheets,normallyplated,andlightermaterialssuchasaluminiumandmagnesium.However,thistype

oflightweightdesignplacesdemandsonweldingtechnologywhichsimplycannotbemetusingstandardweldingmachines.

Thismeantitwasnecessarytodevelopnewprocessesthatexposethejointtoanextremelylowlevelofheatduringthe

weldingprocess.ThecoldArcisjustsuchaprocess.

2Theshortarc;theconventionalmethodforlow-energywelding

TheshortarcisusedinMIG/MAGweldinginthelowerpowerrange,i.e.atlowercurrentsandlowervoltages.Inthisprocessa

formofmaterialtransferisusedwhichfeaturescyclical,repeatingarcphasesandshortcircuitphases,Figure1.

Figure1Materialtransfer（schematic）,currentandvoltageoutlinesinshortarcwelding.

Afteraspecificarcburningduration,adropformsonthetipoftheelectrodewhich,asthearcisrelativelyshort,quicklycomes

intocontactwiththemoltenpool,andthearcgoesout.Thesurfacetensionofthepooldrawsthedropawayfromtheelectrode

tip–inthefinalphaseoftheseparationprocessifthebridgehasalreadybeenconstricted,thepincheffectalsocontributesto

thisviatheLorentzForceaswellastheJouleheatingeffectfromtherapidlyincreasingcurrentdensity–andaftertheliquid

bridgebetweentheelectrodeandtheworkpiecebreaks,thearcre-ignites.Whathappensintermsoftheelectricalforcesis

alsoshowninFigure1.Atthestartoftheshortcircuit,thevoltagefallsbecausetheelectricalresistanceoftheliquidbridgeis

nowlowerthanthepreviousresistancelevelinthearc.Atthesametime,thecurrentstartstoincreasetothevalueoftheshort

circuitcurrent.Assoonasthebridgebetweentheelectrodeandtheworkpiecebreaks,thevoltagethenincreasesveryquickly

asthereisanincreaseinvoltagerequiredtoignitethearc.Thevoltagefallstartingatthatpointisveryslow,however,dueto

theinductivitiesintheweldingcurrentcircuit,there-ignitionprocesstakesplaceunderarelativelyhighelectricaloutput.Inthis

process,partoftheliquidbridgecanevaporateinanexplosivewayifnotcounteractedbysufficientchokeeffectinthecurrent

circuitinadvanceoftheincreaseincurrent.Theconsequenceiseithersignificantspatterformationoraverylowprocess

dynamicthroughtoinstability.

Forweldingtasksrequiringlowheateffects,e.g.whenweldingverythinmetalsheetswithpoorfitup,itismuchmore

damagingbecausetheweldmetaldropsthroughatthere-ignitionpoint,creatingahole.Whenweldingmetalsheetswith

surfacefinishes,e.g.zincplatedsheets,thereisalsoariskofthesurfacecoatingevaporatingandburningawaynexttothejoint

andonthereverseside.Withhigherstrengthsteels,softeningcanoccuriftheheatfeedingistoogreat.Thenormalshortarc,

otherwiseanexcellenttoolforweldingthinsheets,isthereforenotsuitableforthesetypesofweldingtaskswhichare

extremelysensitivetoheat.

3Approachestoimprovingtheshortarcprocess

Therehavebeennoshortageofattemptstoimprovethebehaviouroftheshortarc,especiallyonre-ignitionaftertheshort

circuit,andtouseashortarcwithreducedheatfeeding.Asearlyasthe1980s,attemptsweremadetoreducethecurrent

immediatelybeforetheshortcircuitbridgebreaksandthentoprovideahighvoltagepulsetoeasethere-ignitionprocess.This

didreducethespatterformation,buttheheatfeedingwasonlyslightlyreduced,[1]and[2].Furtherstepsdownthispathwere

themodifiedshortarcChopArc,[3]and[4],whichasaprocess-safeMAGweldingprocessachievedconsiderableprogress,

especiallyintheminimumthicknesssheetrange0.8-0.2mm.Inaddition,anadaptivecontrolsystemwasdevelopedhere

whichoptimisedtheprocessqualityinreal-time,[5].Morerecentdevelopmentshaveworkedwithadiscontinuouswirefeed,

i.e.thedurationoftheshortcircuitisreducedsothatthewireelectrodeisretractedslightlyduringtheshortcircuitsothatthe

shortcircuitbridgebreaksmoreeasily.Thismeansthatalowerenergyweldingprocesswithlowspatterformationcanbe

achieved,[6].Becauseapush-pulldrivewithtwowirefeedmotorswithhighdynamicsisrequired,thisprocessismoresuitable

forautomatedweldingandisonlyusedincombinationwithweldingrobots.

4coldArc–successfuljoiningintasksdemandinglowheat

Developmentworkwiththeaimofachievingalowenergyprocesswithoutmechanicalinterventioninthewirefeedprocess,

resultedinaprocessvariantinwhichallnecessaryinterventionsintheprocesstakeplaceinthepowersourcealone.This

variantoftheMIG/MAGprocess,knownascoldArc,isalsoashortarcprocess,andiscalledsuchduetothecyclicalchange

betweenthearcandshortcircuitphases.Astheelectricaloutputduringthere-ignitionprocessisacriticalcriterionfor

successfullyweldingthinsheets,activeinterventioniscarriedoutintheoutlineofthepowerintakefortheoverallprocess,

however,inotherwordsduringthearcphase,intheshortcircuitphaseandespeciallywhenre-ignitingthearc,Figure2,the

voltageoutlineremainsthesameasinthenormalshortarcprocess.

Figure2Materialtransfer（schematic）,currentandvoltageoutlineinthecoldArcprocess.

Itisusedasaguidelinevaluewhencontrollingthecurrent.However,thecontinuousmeasurementofthevoltagewiththe

correspondingreactiontoallchangesinvoltageisrequiredtoachievethis（highlydynamicinstantaneousvalueregulation）.A

digitalsignalprocessor（DSP）canthenbeusedtoextractthepowerfromthearcimmediatelybeforere-ignitioninaperiodof

lessthan1μs,Figure2,sothatthereignitiontakesplaceverygently.

Sothatasufficientquantityofmoltenmaterialcanbeformedimmediatelyontheelectrodetiphowever,thereisanincreasein

theamountofenergyrequired.Immediatelyafterthearcre-ignites,thecurrentisthereforeraisedbackupagainforadefined

shortperiodtowhatisknownasthemeltpulse.Onlythenisthecurrentloweredtoanextremelylowbasicleveltominimise

furthermelting,andthenextcyclebegins.Thismeltpulseaftereachshortcircuitgeneratesameltingconeofaconstantsize

ontheelectrodewhichmeansthatprocesscontinuesverysmoothlyandevenly.Thisistheonlywayithasbeenpossibleto

workatextremelylowcurrentsinthephasesbetweentheshortcircuits,withoutthewiremeltingfurtherorthearcgoingout.All

thisgoestomakeuptheverylow-energycoldArcprocess.Figure3showsasequenceofimagesfromahighspeedfilm,which

highlighttheveryevenmaterialtransferandthegentleignitionofthearc.

Figure3SequenceofthematerialtransferinthecoldArcprocesstakenfromhigh-speedpictures,8,000B/s.

5.WhatthecoldArcprocesscando

Theoutlineofthearcoutputonarcre-ignitionisshowninFigure4.TheadvantagesofthecoldArcprocessincomparisonto

thestandardshortarcatthemomentofre-ignitionandimmediatelyafterwardsbecomeveryclear.Heretheoutputatthe

momentofarcre-ignitionisconsiderablylowernotjustasanabsolutevalue.

Infact,immediatelyafterthearcignites,theoutputisreducedinanexceptionallydynamicandcontrolledway,andthen,afterthearchasbeenstabilised,increasedtothedefinedmeltingoftheelectrodetipinapulsedway.

Aprocessofthistypecanbeusedformanyweldingtasks,especiallyinvehicleconstructionwherethenormalshortarcisnolongersuitable.

Evenjustafewyearsago,itwasassumedthattheMIG/MAGprocessshouldbeusedforsteeloverapanelthicknessof0.7mmandforaluminiumover3mm[7].Thepanelthicknessesinvehicleconstructiontodayarebecomingincreasinglythin,

however.Theyalreadygodowntoaslowas0.3mm,and0.2mmisalreadybeingtestedforcompositeconstructionwork.Thedifficultiesinachievinganevengrooveareevengreateriftherearelargerairgapstobebridged.ThisisatypicaltaskforthecoldArcprocess.

Figure4MinimisedarcoutputofthecoldArcprocessonr