CA1313902C - Apparatus and method of short circuiting arc welding - Google Patents

Abstract

APPARATUS AND METHOD FOR SHORT-ARC WELDING
Abstract In a short circuiting arc welding apparatus and method wherein a continuously fed welding wire alternates between an arcing condition during which the wire is spaced from the molten pool of the workpiece and a short circuit condition during which the melted metal on the end of the welding wire is in contact with the molten metal pool and thereafter transfer to the workpiece by a necking action breaking the melted metal from the wire, there is provided an improvement including providing a first high inductance current control circuit for continuously directing a low level, arc sustain-ing, backgroung current between the welding wire and She workpiece and providing, a second current control circuit for controlling current flow during the arcing condition of the process. This second current control circuit includes time delay means for causing the initiating, arc at the start of the arcing condition to have an area determined primarily by the background current for a preselected time during which the molten metal on the tip of the welding wire and in the molten metal pool are drawn, by surface tension, to the wire and pool respectively, is essentially quelled and means for then passing a high current pulse through the arc between she wire and pool with a preselected energy for melting a relatively constant volume of metal on the end of the wire and space from the pool. This high energy pulse is near the start of the arcing condition and terminates generally be-fore the mid-point of the arcing condition so that the wire is first melted and then driven into the molten metal pool after the pool has essentially quelled or become quiescent.

Description

APPARATUS ~ ETHOD OF SHORT CIRC~IITING ARC WELDING

This application is related to Unitsd States patent 4,717,807, which issued on January 5, 1988, and the reader is referred thereto for background.
As background information, reference should be made to prior United States patents to Sevenco 3,459,920, 8/1969; Needham 3,792,225, 2/1974; Pijls 4,020,320, 4/1977; and Ogasawara 4,546,234, 10/1985.
BACRGRO~ND OF I ~ NTION
The pre~ent inventlon relates to the ~rt o~ elecerlc arc weldlng and more particularly to ~n apparatus and ~ethod for ~hor~ circu~elng ~rc welding.
Shor~ circuiting src eype electrlc ~rc ~eldin~ has been ! e~ployed for ~any years; however, thls type of weldin8, with it6 ~any adv~neagesD h~ had ~ubstantial disadvan~age~, For in~ance, 1~ ha~ been lim~ted to ~ relstlvely lo~ rate of depositiDn. In addition, shor~ clrculeing arc welding hss been . ll capnble of employlng only a relati~el~ low energy level and has produced non-uniform ~ld beads requlring post we~ding operation~. In ~dd~tion3 the shieldln~ ga~ u~ed wi~h ~hort circuit1ng arc weldlng often required at least a portlon of an expen~ive inert gas, ~uch as Argon ~o eh~t sn electrio plnch , I ~ction can be e~ployed for ~ranaferring molten meeal fro~ the I l drlven welding wlre to the molten metal pool d~r~ng the fihort 1! 25 circu1t stage or condition of ~he short circuitlng arc ~elding¦1 process.
As the welding wire ls fed eo~ard the molten pool durlng the short clrcuiting arc ~elding proceas, the process alter-naees betweerl a condition with the wlre ~paced fro~ the weld pool ~lth a gap aep~rated by a plasma or arc, known a~ ~he arcing condl~lon, and a condition wlth the ~reldlng wire touehing the weld pool for the purpo~e of transferring ~k 313~

molten met~l from th~ electrode into ~he weld pool, known as the short circuit coDdition. In the P~ ;D these two eond~
tiolls were n~tural phenomena ~re~ed ~y u8~ g 3 con~tant voltsge power supply snd by driving or feeding the weld~og electrode tow~rd the weld pool ~ 8 pres~lected feed rete.
Durlrlg the ~rc~ng condi~ion, a ball of mel~ed metal would be formed on the end of the ~dv~ncln~ w~ldlng wire, When the ball grew to a ~ufficient size i~ would con~ct ~che weld pool causin~g ~ uhort circu~ t ~nd initiatin~ the shor~ clr-cu~t condition of the w~lding process. Output chsr~cteri~-~:iC8 of the power supply contrl)lled th~ curren~t flow dur~8 the ~rcing ~nd ~hort circult cond~tion~. Con~equen~ly, ~
~ize of the Dlel~ed me~l bsll on ~che eDd of ~he ~dvanciog electrode or wire W~l3 d~termined by mech~ni 91, electro~
netic and arc par~t~r~ whlch v~rled durln~ succe~ive ey-cl~ of the proce~. The alze of the ball on the end o~ eh~
wire wa~ lneonsi~ti3nt ~nd the re~ultant ~eld be~d on t~e workplec~ WIEI8 not uni~o~. For th~t rea~on, the ~nergy e~-ployed for ~hort circui~ing ~c welding wa~ rel~tiv~ly lo~
~0 that ~ low tot~l melting r~te W88 obs~ined ~roducing low depos~eion r~te during the total weldin~ proc~
Even with the Y~r~ous diæ~dvant~ge~ ~nd di~ficultie~
~xperlenced in ~hort circuitlng ;~rc w~ldlng,, the industry hs~ been anxious to develoE~ this ~y~e~ for the purpose e~
high productlon ~elding; however, the~e ef fort~ haYe bee~
prim~rily thwarted by an preeminent di~dv~rltage of 3hort circuiting src welding, f.e. high ~patter ~s~oci~ced with h ener~y ~rc ~lternAtfng between ~hort cireuit condl-tion~. Oper~ors were ~w~æe of the ~p~tter problem ~or~
~h~n oper~tional limi~tion~ on the proee~. Bead ~ppe~r~ncæ
wa~ un~at~6~acto~y ~nd the welding ~ube bec~me clo~ged b~
~pattered met~l. It iB not surprising th~t eh~se ~ppare~e limitation~ tool~ precedent whe~eby ~h~ ~f ort~ in receTIt ye~r~ to develop i~proved ehor circui~ing ~rc welding ~ppa-r8tu2 snd methods h~ve bee~ devoted p~lmarily to the coocept 1~3~

. ,- L-7608 of reduc~llg sp~tter. The reduction of sp~tter decrease~ the mo~t obvious dis~dv~nt~ge of short circ~iting ~rc electric welding I~IB experlenced by the oper~tor; however, it did no~
~llow higher deposition rste~ rge welding w1res to pro-duce ~ de~ired weld bead h2ving a unifc>rm sppe~ranCe st hi~,h ~peed or really ~ddres~ more baeic, yet le~s ~pp~rent liht~-t~tion~ ~n pr~or attempts to improve ~hort circulting ~rc weld lng .
THE I NVENTI ON
The pre~ent invention relate~ to ~n ~mprovement in an app~ratua and ~ethod or ~hort cireuitinp, src electric ~eld-ing which overcome~ dis~dvan~ge~ of prior st~empt~ ~o em-ploy ehors-~rc electr~c weldln~,. The~e improvements giYe high depbsition rate~, ~llow ~se of l~rge weldin~, wire~, sllow high ener~,y lnput to she proce~s ~nd prodtJce ~ wide weld b~d hsvin~, ~ uniform, ple~ing app~r~nce. Furtller~
~n accordsnce with the pre~ent invention, the mol~en met~l ball for~d on the end of ~che welding wire as it i~ b~lng driven tow~rd the molten ~et~l pool on the workpiece 1~ e~-~entlally the ~me ~ize during each ~ucces~ive cycle of the 0hor~ circuitlng ~c welding proce~. The~e adv~nt~ge~ and :~ fe~tur2~ ~re obt~ined in accord~nce with the presene ~nYen-tion whlle retaining ~p~tter c~n~rol ~n a ~nner de~cribed in the related United States patent 4,717,807, which issued on January 5, 1988.
In ~ecordance with the pre~ent inven~ion there i~ pro~
vided ~n improve~ent in 8 short circuiting ~rc welding appa-r~tu~ COmpriBin~ ~ ~in~,le const~nt volt~ge D.C. power ~upply me~n~ for causing welding curren~ to p~0 ehrough a weld~ng ~ire ~o 8 workpiece ~ ~ molten metal pool, w~re feeding mean~ for feedlng the welding wire ~ow~rd the workple e ~t controlled rAte whereby the welding ~Ire ~ltern~tes bet~een n ~rcing condition during which the wlre l~ spaced f~om the pool of ~he workpiece but drlven toward the pool and a ~hort circuit condition duri~ which ~elted met~l on the ead o 3~ 760~

the welding wire i~ in contact with the molt~n metal pool and then tr~n~fer~ to the workpiece by ~ necking ae~lon breaking the melted me~al from the w~r~ to initiat~ th~ arc in a ~ubsequen~ ~rclng condf tion . The i~provement in ~ccor-d~nce with ~he pre~ent lnvention ie the provision of ~ ffrst high inductance current con~rol circui t for continuously dire~ting ~ low level, ~rc su~tallling, background current between the welding wire and th~ worl~piece snt a ~econd cur-r~nt control circui~ for controlling curren~ flow during the ~rcing, condl~ion~ tbis second current control circui~ ln-cludes time delay means for c~using the in~ tiated ~rc to have ~ low ~re~ determ~ned by the background current for ~
preselected tlme T2. i)uring thts tim~ the ~olten metal r~-mainin~s, on ~he welding wire ~nd in Ithe pool l~ drawn by sur-face tension to the wire ~nd pool respectively ~t~cre~lng the conductive Crt)B8 eect~on E10 the pl~8DI~1 boo~t may be 8p-plied s~i~hs:~ut c~uslng, ~pAteer. The plaama boo~t pule~ iB
c~eated by the eecond current control cfrcuit meAn~ for then paRsing, a higtl curren~ pul8e ~:hrough the ~rc with ~ prese-ler~d I (t) ~r~a or energy for mel~ciLng a relatively c3n~ts~t volume of metal on the end of the wlre EIDd ~p~ced fro~ the pool. In accord~Tlce wi~h the ~nven~ion, the energy creaeed durln8, ~he pl~m~ boo~ auiEfilci¢nt to cre~te ~ ~pheric~l hlet~l ball h~ving 8 diameter no mors th~n ~wice the diame~er of the weldinR wire. The hlgh current pulse iB in ~he ~ir~t portion of ~he ~rclng corldition cycle BO that th~ ~econd portion of tl e arclng condition cycle i8 ~t the high induc-tance, low b~ckgroun~ current level whereby the advancin~
welding wire i8 f lrst melted by the high current or high energy pul~e or plssma boo~t ~nd the pool i8 then ~llowed to.
bec~me qUieBCent before the b~ 0 fed i~to the pool.
By providing ~ hlgh energy bur~t or boost sfter ~ pre selected time del~y ~nd during ~he ini~ial portion of tlhe ~rclng condition, melting occurs only by the high ener~y pu1~8 ~nd not by back8,round fur~en~. In ~hi~ m~nner, ~h~

~me amount of energy i8 introduGed intc3 th~ wIre for th0 purpo~e of melting a pre~elected smourl~ o~ w~e durln~ e~ch ~rcing condition. The m~ltislg of the end of the wire ~
accompli~he~ durillg the pl~ma boo~ condi~ion. The melted wire ~ 8 BUpported by 'che hi~h ~et orce~ of the ~rc during ~she pla~ma boo0t until tsrminatlon of th~ pl~sm~ boo~ wh~n, st the low background curren~:, lt i~ 3110wed to fs)tm into sphere that provides the most ef f iei ent ~hape ~t ~he ~ime o~
contsct between the pool ~nd wlre. In ~he p~, curren~ im-mediaeely increa~ed ~nd was m~int~lned rel~ively high dur-ing the total ~rcing condition ~o th~ meltinB oecur~ con-tinuou~ly. Melt~ng i~ "ot done r~p~dly and allowed ~o set-tle before the short cIrcul~. Indeed, melting ~n sane of the prior ~y~tem~ conl:lnue~ even during th~ short circuit coadi-tion. By employfng th2 pre~ent inven~ion~ ~he meltirlg iB
sccDmp1ished and the ball i~ formed prit)r to being 10wered into the mo1 ten m~t~1 pool ~t ~ low b~ckground current iev-el. The back~round cl3rrent c~n be ~ 10w B8 ~bout 20 am~
pere~. Preferably, it i~2 in the r~nge oP ~bou~ 2û-8û abl-pere~ ~nd i~ pr1m~ri1y ~e1ec~ed ~UBt above the le~el nec~s-s~ry for main~ainin~, th~ ~rc. By employln~ high induct~nce in the buckground current circuit, the currerlt le~rel can be further reduced ~nd st111 a~ure mainten~nce o~ the fl~c d~r-ing the 1~st portion of the ~rcing conditiorl ~nd st the bre~k caused by the necking ~ction which te~ain~e~ tbe short circui~ condition. By employing ~:hiQ new concept, the dyn~mics oP the molten weld pool ~re cor trolled where~ pri-or ~Iy8teDI~ were primari1y d~rec~ed tow~rd the concept o ~pstte~ controlO Controll~ng the dyna~ic6 of the molten weld pool overco~e~ the di~adv~ntfiges melltiolled above, ~IB
well aB control1ing spatter in ~ccordance w1th the concept~
~et for~h in the prior cop~nding appl lc~ion incorpor~ted by refet ence herein .
In accordance w$th another a~pec~ of the present inven~
tion there i8 provided a met~1 ~cr~nsfer currene control ~3139 ~2 L-7608 circuit ~or controlling current flow ~ur~ng the short cir-c~it condition of the ~hor~ circultlng src welding prQce~s wherein the met~l sran~fer current contr~l circuit lncludes ~ timing me~n~ for mainta~ning the low level b~ckground cur-rent untll the molten metnl of the welding wire i~ prim~rily transferred into the molten mee~l pool of th~ wor~piec~ by ~urf~ce tension action snd mean~ for thereaf~er applyin~ a high current pinch pul~e acro~s the short~d mel~ed met~l~ A
detector mean~ dlsconnect~ the pinch pul~e in re~ponse to an anticipation of the impending bre~ing of the melted metal from the wirs to st~rt the arclng condi~lon of ~he proce~s.
By provldlng both a~pects o~ the presen~ invention ln n ~hort circuitiRg arc welding proceee, Bpgt~er i8 con~tolled wh~le the melted ball has a pre~elected and consistent vol-ume before bein~ driven into the molten metal pool. The dy-namic~ of t~e molten metal pool ~re ~uch th~t A uniform, wide weld bead i~ obtainable.
In ~ccordance with another aspect of the invention, ~
meshod o~ ~hort circuiting ~rc welding 1B provided by ~in8 the apparatu~ di~cu~ed above~
The ~bo~e-identified inv¢ntion l~ not taught by Sevenco 3,4S~,920 which rel~tes eo in~ection o~ ~ pul~e dur~ng the arcin8 conditlon for the ~lleged purpo~ of preh~ting and melting the work ln prep~r~tion Por ~ æubsequent perlod of ~5 welding ~n ~ manner which does not ~f~ect the formul~tion of ~he droplet in any way. The pre~ent lnvention ~ rel~ted speciically to the concept of employing a pla~ma boo~t or pul~e o ~ known energy for the purpose of completlng the ~eltlng prep~ratory to feeding the molten ~et~l ball to th~
mol~en pool 60 ~t sn in~ertion and tr~nsfer of molten Det al between the welding w~re ~nd molten metal pool 1~ dur~n~
a qUieBCent period ~or the molte~ ~et~l pool. In Sevenco the wire i8 melted durin~ the ~horting cond~isn. In the ps~e, ~B set forth in thl~ particul~r prior ~rt ps~ent, tbe u~e of high induction as snticlp~ted by the present invention for 131390~ L-7~08 the ba~kground current cau~ed creat~on of an ~rc which pre-heated and melted the tip of the wire befor~ ~h2 ~hort cir~
cuit. Th~ wa~ avoided by the ~lleged concepe set forth in Sev~nco which h~ no ~ppl~catlon to th~ molten metsl pool dynamlc control of th~ present ~nvention.
One attemp~ to control th~ dynamica o the pool i~
found ln Pi~ls 4,020,320 which employ~ both a current ~ource and voltage ~ource pow~r ~upply ~nd involves th~ concept of extingui3hlng the src during the ~rcing condition to dsst~-b~lize the dhort circuit~ng arc weldlng procee~.
I~ O~a~w~r~ 4,546,234, ~ ~hort circuiting ~rc control ~ 1UBtr~ted wherein ~ high energy pul~e occur~ i~m~dist~
ly upon fr~cture of the neck to start the srcing condltion of the proce~s. By employing thls prior con epe~ hlgh cur~
r~n~ i8 applied to the proce~s during the mo~t un~t~ble por-tion of ~he proces~, i.e. ~t the rup~ure of ~he ~hort and immedi~te reioni~tlon of the BrC or plas~. In ~ddltloo~
this proce~e employæ ~ high level current or the purpos~ of tran~ferrln~ metRl by th~ ~lec~ric pinch ac~ion 8~ oppo~d ~0 to su~f~ce tension ~ ~nticip~ed by ebe pre~ent inv~ntion.
The p~e3ent lnven~ion, ~9 de~cribed ~bo~e, ~nvolve~
~ub~t~ntial improvements oYer one or mor~ o~ th~ prior art p~tent~ ~et for~h abov~ by appro~ching control o~ th~ BhO
circuiting ~rc welding proce~ ~r ~ the mol~en metal pool dyn~ic~ ~ns~e~d of direc~ing the proce~ control to sp~tter control conrept~. The invention UBe~ ~ bsckground current provided by high impedance current control elrcuit ~t the ~utput of the const~nt vol~ge power ~upply. In this m~-ner, the con8t8nt eurrent control e~ture~ wbich mu~t be tuned pr~cisely in Ogs~w~r~ 4,546,234 ~re not need~d. In ~ccordsnce wieh tbe pres~nt invention th~ de~ired pool dy-namic~ ~nd sp~tter control 8re ob~ined withoue 3uch precise optimization of conflicting par~meters. The feed r~t~ ~ay be nd~u~ted to prevent ~ticking or the high energy ~elting pul~e m~y be Dd~u~ed from the ener~y ~tandpoint ~313~2 L-7608 accommod~te a de~ired depo~ition r~te with ~ known feed r~t~
without the complexities created by ~ttempting to contrDl the system in accordance with theore~ic~l concepts ~e~ forth in the prior ~r~.
In accordance w~ ~h ~nother ~pect of the in~ention, there i8 provided a ~hor~ circuit welding ~pp~r~tus compri~-in~ a ~ingle con~nt volt~ge d . ~ . power ~upply for c~u~ing weldin~, current to pass through ~h~ weldin~ Wit~! to thc workpiec¢ ~t a molten me~al pool wher~in there i8 included firnt high induls:t~nce current con~rol circuit for continu-ou~ly direct~n8, a low level, ~rc su~t~ining, b~ekground ~ur-rent in the range of ~bout 20-80 amperes between the welding wfre and workpiece during bo~h ~che short circuit ~nd arc conditions. A second, low induc~nce control c~rcuit for controllin~ currene flow above s~id b~ck~,round currcnt le~el during the ~rcing condf tion ~nd ~ th~rd low f nductsnce cur-rent oontrol circuit for controlling current above the b~ck-ground current level durlng the ~hort eircu~t conditlon.
Thee~ ~epar~te control circuit~ for ~ ~ingle power ~upply provide flexibili~y to contrt)l botlh up~tt~r ~nd the weld pool dynaRIic~ w~thout ~d~pting the ~ep~ratc power ~upply concept of Needh~m 3, 792, 225 ~
The p~imary ob~i;ee~ o~ the presen~ lnv~ntio~ he pro-vision of 8 method ~nd spp~r~tu~ ~o~ al~ort circui~lng ~
welding which method And App~rstus reduce~ ~he turbulenc~ of the molten met~l pool or puddle, trnn~ers fro~ eh~ ~rc or pl~m~ conditlon to ~he sh~rt circui~ condi~ion Dt low ener-gy snd provide~ uniormlty of operatlon.
Yet ~nother ob,~ect of ~he pre~en'c invention is ~h~ pro-vision of a method and ~3pp8ratu9, a~ defined above, whlch method ~nd ~ppar~tus provide~ ~dequste control to ~s~ure thet the bsll on the end of th~ ~dvancing wire dur~ng ~he ~rcin~, condition 1B subal:~ntially the ~a~ne ~nd cre~t~d by a pre~elec~ed energy inpue to 888ure ~ mall uniform ball ond a uniform, ple~sing weld be~d ~ppe~r~nce.

~L 313 9 ~ L-7608 Still ~ further ob~ect of the pre~nt inYention i~ the provi~lon of ~ method ~nd ~ppar~tuep ~ deirled ~boYe, which method nnd ~ppar~tu~ allow~ ~ high depo~ition r~ by ~llow~
~n~, larE~er welding wire and eon~rolled inereased energ~ t~
provide ~ weld bead ~ub~t~n~islly gre~er ehan the dl~s~e~er s)f the weldlng wire ~i~chou~ ereat~ng lh~,h ~rbul~nce 1~ the molteD metsl pool into which ~he weld laetal i8 tr~nBfer~ed.
Yet ~ furthe~ ob~ect of the pre~en'C inYent~On i8 the provision of ~ method snd apparatuB 88 defined ~bove, which metho~ ~nd ~pp~rstu~ transfers th~ met~l rom the el~c~r~de or welding wire into the molten met~l pool prf~n~rily by sur-fsee tension action.
Another ob~ect of the pr~ent i1lvent~0n 1~ the provi~
~ion of ~ ~ethod snd ~pp~r~tu~ ~8 defined ~bove, which meth-od snd app~r~tu~ c~n be us~d wi~h ~ ~rle~y o shi~ldin~
gs~e~, lncludlng csr~on dioxide, Another ob ~ect of the pre~ent inver~tion 1~ the provi ~
sion of ~ meshod and ~pparatu~ ~ defined ~bove, wlhich ~eth-od ~nd apparatu~ ~orce~ the melt~d b~ll to ~EIE18Ul~le ~tl~ natu-~0 r~l ~pher~c~l 0h~pe ~nd then move~ thi~ ball irlto the`w~ld be~d whlle only ~ 11 src~ng cuE~rent ~ flow~n~"
Another ob~ct of the pre~ent inv~nt~on i~ i~he pro~-~ion oP ~ n~ethod ~nd spp~r~tus, ~ de~ined ~^bove, which me~hod and app~ratu~ nc~t onl~ controls turbulence of th~
molten ~etal pool lr~to which the ~et~ trsnsfelered but 81EIO re~ult~ in reduced sp~tt~r .
These ~nd other ob~ect~ and ~dv~ntagea will beco~ p p~rent from ~che followlng de~etiptilon lt~kell tog~th~r wieh the drawlngs a~ de~cribed below.
BRIEF DESCRIPTION OF DE~AWINGS
~IGURE 1 1~ ~ ~ch~D~a~lc di~gr~ tra~clDg t~ c~-rent control circuit employed for ~ single power ~upply in ~ccord~nce lw~th ~he preferred e~bodiD~ent of ~he pre~ent ln-ventlon;

g _ 11 3:13~ L-7608 FIGURE 2 are upper ~nd lower gr~ph~ illu~tr~ti~g sche-maeicAlly the agc or pl~sm~ volt~8~e fr~m ~ const~nt pot~n-ti~l po~er supply ~nd the welding curr~nt contrc~lled in ~c-cordance wi th the preferred ~mbodiment of th~ p~e~nt in-vent i on;
FIGURE 3 iB a combined arc vcle~g~ and weld~n~; cu~rent gr~ph simll~r to ~he graphs shown in FIGURE 2 but ~ken from specific ex~mple of the present invention a3 see fnrth in th~ p~r~meters at th~ lower por~ion of FIGURE 3;
FIGURES 4A and 4B ~re par~ l drawing~ of th~ end of a welding wire which i8 melted in ~ccord~nce with th~ present invention prep~r~tory to beirt~, ~dv~nc~d into ~ molten met~l pool ~nd con~sfn~ng dimensions t~ expl~in a cer~c~in ElBp~Ct of energy spplled by the presen~ invention;
FIGURE 4C ~ ~ dlstr~bu~ion curve aho~in~ the d~tribu-tion of ~cceptability for b~ll s~ze~ in accordarlce wlth the diDlenslon~l aspec~:~ illu~tr~d ln FIGURES 4A, 4B.
FIGURES 5A-5F are ~chem~tic illustrstion~ of th~ sd~
vancing wl~lding s~ire a~ i~ progresse~ throu~,h v~riou~ condi-tions when employing the preferred embodiment of the pre~ellt inventl on;
FIGURE 6 ie ~ wclding current g~ph ~howing a high en-er~,y curren~ pulse employed during ehe ~hort circuit condi-t~on of the present ~nvention and havin~ odified puJl~s eonf igur~tion;
FIGURE 7 iB 8 modif ic~tion of one uepect of the pre-ferred e~bodiment of tl-e pre~ent invention ~hown ln FIGURE 1 ts~ produce an h:lg,h energy pulse ~IB shown in FIGURE 8; ~nd, 3~ FIGURE 8 is 8 welding current grAph ~howlng th~ rel~- :
~iYe rel~tionship of the current pul~ee crested during the short eircuit condition ~nd sub~equent Arcing conditlon io ~ccord~nce with the present invention tQgether with two mod-if icatione of the src~ng conditlon control sircuit one of which employs the modification illu~trated in FIGURE 71 L~7608 PREFERR~D EMBOD IMENT
Referr~ng now to the dr{lwing,s wherein the showing0 ~re for the purpo~e of 111UBtr~t~ d preferr~d embodi~ent o the invcntion only ~nd not ft~r the purpo~e ~f limitlng ~a~, FIGURE 1 lllt~8tr8te8 thre~ l}eparste curs~e~t control clrcu~t~
employed in a short circuiting a~c weldin~ ~yste~ of the general type disclosed in the related United States patent 4,717,807, which issued on January 5, 1988. The short circuiting arc welding apparatus A includes a constant potential power supply 10 feeding transformer 12 that directs currents through a plurality of current control network 20 in a curren~ control network to output tenNnals 30, 32. In accordance with the present invention, current control network 20 ~cludes a f~rst high ir~duct~nce ba~kground current ~lrcuit 22 for con-~nuously dir~ctin~ ~ ~el~tively low b~c~ground current with b~gh inductive react~nce acro~ termin~l~ 30, 32. A eecond current co~trol circuit 24 d1rects &dditlon~1 current 8cro~
termlnBlB 30, 32 during the 8rcing cond1tion of ehe ahor~-~rc weldin~ proce~ per~ormed by ~pp~r~tu~ A. Thie eecond c~rrent control clrcui t produce~3 ~ pla~md boo~t or current puls2 h~vlng ~ pre~elec~ed energy level ~nd pDsielc3ned ~e~r the ront of the arclng condition. A thlrd current con~rol clrcuit 26 control~ ~ddition~l current ~cro~0 ter~in~l3 30, 32 du~ing ~he ~hort clrcui~ condieion c~P ~h$ ah~r~ ~ir~uit-in8, arc prooes~ performed by ~ppsr~tu~ A ln ~ccord~nce with ~he present inven~ion. In ~ccortsnce wiPh ~t~ndsrd prD~-tice, a welding wire feeder 40 ~ove~ weldlng wlre 50 through contsct tube 42 from 8 0pool or other wire supply 52 llt a ~onstsnt controlled rate through ~n exten~io~3 54 toward workpiece 60 snto which mol~cen metal le ~o be depo~ited. ~n ~ppropriste ahleldin~, g8~1 56, wh~ch in th~ pr~f~tr~d embod~-ment ~8 c~rbon dioxlde, flow~ fr~m ~ube 42 srouod wire e~-tenslon 54 for the purpo~e o ~hieldlng the ~hort ~irc~ g ~rc welding proces~ in sccordance with ~t~nd~rd prsctlc~.
Worl~piec~ 60 is ~teel, li~e wire 50, snd il~ grounded by L-760~
13~3~2 being connected to output termln~l 32 of current control network 20. Of course, wire feeder 40 includes an arrsnge-ment for controlling the eed r~tc of wire 50 through eube 42 a~ well ~B ~ppropri~ce circu~try which la well known ~n the ~rt ~nd form~ no p~rt o the pre~en~ invent~on.
Referring now to FI~V~E 2, rircuit~ 22, 24 snd 26 of network 20 ~re oper~ted to control the weldlng curren~ ~B
~et forth in the lower gr~ph. The ~pper ~rsph illustrate~
the theoretical volt~ge ~cro~ ~ermin~ls 30, 32 ~ the cir-cuit~ of ne~worl~ 20 control the ~hort circui~in~, arc weld~ng, process to obtain the theoretical curren~ ch2r~cteri~tic~
schematic~lly lllustr~ted in ~he lower gr~ph. Short cir-cuiting ~rc weldlng involve~ contin~ou01y feeding weldin~
wire 50 ~hrough ex~en~ion 54 while ehielded by ga~ 5S ~neo molten met~l pool on workpiece 60 ln ~ proces~ ~ltern~ting between a ~hort circuit condition with the wire iD electrlW
c~l cont~c~ with the molten ~etal pool ~nd ~n ~rcing cond~-tion with the welding wire ~p~ced from the ~olten met~l pool and beinB bridged by 8 pla~ma or ~rc. The sr~ condltion PC

2~ ~nd ~hort circuit cond~cion SC in ~hi~ proce~s ~re illu~-trated in FIGURE 2. AB 000n ~ge the weldlng wire tou~hes t~e molten met~l pool of workpiece 60, the ~rc voltage drop0 r~pldly 810ng vertic~l line 90 Bt po8ition (a~ to initi~te the ~hort circu~t condit~on SC controlled by circuit 26 of network 20 showo ln FIGURE 1. For ~ ~ime period Tl between po~ition (8) snd po~tion (b) molten met~ trsnsferre~
f~om the end of wire 50 to the molten metsl pool on ~orlt-piece 60 by ~urf~ee tension actiorl ~nd- the act~on of gr~Yity in ~ do~n-hand oper~ting mode. At po~ition (b) the me~c21 h~ been 0ub~t~ntially transferred to the molten met~l pool and a necking ~ction h~ stsrted. A~ ~chat time, 8 piTIch pul~e PP i8 created b~ cir~uit 26 snd spplied acro3~ te~i-nale 30, 32 In ~ddition to the constantly ~pplied b~ckground current provided by circuit 22. Thi~ pinch pul~e i~ free to as~ume the ~hor~ circuit current level which progre~ea 13139~, L-7608 along vertlc~ lne lO0, over line 102 ~ffected by ~ chsn~,e in re8i~t8nCe of the n~ck tD ~ po~itlon 104 wherein the vol~age level 105 indic~tes an impending fuae of ehe neck.
Th~ change ~n vol~age may be detected by a ch~nge in the ~gn of dv/dt to iod~cate the impending, fUBe c~u~ed by the ~brupt p~ nching actioo of pulse PP . The voltsg~ to level 105 ~rogresse~ untll ~ ch~nge ln Bign i8 produced by ~ dv~dt detector indlcatinR the impendin~, fuee which immediately removes current f~om circuit 26 from ~ermlnsls 30, 32, Con-~equently, the pinch pul~e PP iB ~bruptly termin~ted ~long line 106 before ~ep~r~tion of l:he fu~ c~used by the elec~
tric pineh ~ctlon on khe molten me~al formlng ~ ~hort c~-cuit bridg~ between welding wlre 50 ~nd wo~kpiece 60 ~t the end of short condition SC. The ~brupt drop in currf~nt ~long line 106 immediately bef~re the p~nching ~ctIon bre~ the ~hor~ eircuit prevent~ ~patter c~ueed by ~he pre~ence of higll energy at the time of the fll~e explo~ion. This current reduct~on At po~iLtion ~c) lniti~te~ the ~rcin~, conditlon or pl~s oondition PC lmmediately following ~he Hhort circult oondition SC, a~ ~hown in FIGURE 2.
The ~rcirlg condition ~ in~ti~ted with only the lh~
induct~nce b~ckg~ound current IB f lowiLn~, be~weerl ~he weldln~, wir~ snd the workpiece. Con~equerltly, th~ arc :tn~tially formed h~ ~ very low curren~ flow ~nd eub~tantially only sm~ rc ~re~ ~o th~t the puddling effect ~t the ~solten met~t pool i8 m~nor. Con~equently, the molten metal i~ e~
senti~lly quelledl w~th the ourrent ~t a low level ~t tlhe ~tsrt of th~ a~cinæ condition. The high induct~nce s~f clr-GUit 22 ~ures ~rc continuity ~nd ioniz~ion of the g~p be~cwe~n the moving welding wire and the f lxed wo~kpiece ~ ~
soon tlB a fuse explode~. A~ the two seo~ions of D~ol~en met-81 are dr~wn by surf~ce tension toward the tip of th~ ~ire ~nd the molten posl during ~he ~ime del~y T2 between po~i-tlon~ ~c), (d), the volt~ge ~cro~s termin~l~ 30, 32 iB pro~
gre~sing along line 110 to ~n upper level 112 which i~ the ~3 l3~ 7608 ~te~dy state, equllibrium condition created by ~he continu-ou~ly opernted baekground curren~ clrcuit 22 ~nd the power supply 10. Between position~ (c)~td) the ~olten ~et~l of the w~ld pool become~ quie~cent. Ti~e~T2, i~ at le~t ~ou~
5% o the total proc~sa cycle including the ~rcing condieion and shorting condition. In practic~, ehis time is ~pproxl-mately 0.20 ms ~hich i~ ~ufficient for stabiliz~tion of both the met~l on the wire ~nd the pool. Upon the exp~r~tion of the stabilizing tlme T29 pl~am~ boo~t circuit 24 dire~ts high current boost pul~e BP into ~he weld operstion ~eross terminnls 30, 32. Sinee th~ circui~ h~ ~ low ~nduct~nce, the pul~e hs~ ~n sbrupt le~d~ng ed8e 120 and ~n abrupt tr~iling edge 122 with ~n upper level 124 to produce ~ metal Melting energy in the welding pro~e~s, whlch energy 1~ con-~rolled by the ~re~ Itt) of the bigh energy boo~t puls~ BP, This energy l~ ~pplied r~pidly ~nd h~ ~ v~lue to ~re~t~ D
pre~elect~d b~ll size no gre~ter in diameter th~n about twlce the di~eeer of the weld~n~ wlre. The volt~e 8CrO~B
terminal~ 30, 32 incresse~ naturally to a level 130 during pl~ema booat pulse BP ln acoord~nee with st~nd~rd ch~rActer BtieB 0~ A con~tsnt potenti~l t~rpe power ~upply. I~medi-~tely following, ~he boo~e p~llse spplied acro6~ te~min~ 30, 32, the welding current iB ~hifted back to the b~ckgrou~d eurrerlt level IB. Con~equ~ntly, further ~ellting, of wi~e 50 doe~ not t~ke pl~ce ~ince the I2R nece~ry fvr meltin~, the met~l of the wire i~ no~ obt~inabl~ throug,h ~n ar~ c~rry~n~
only the b~ckground current wh~eh only 3erve~ to ~ai~ n the ~rc flnd the 'b~l l of metsl ir~ ~he molten Bt~
In sccordance with the invention9 pul~e BP cre~tes the ~elting ef ect ~fter the tlme T2 . Thu~, the melting at th~
end of the welding ~ire by pul~e BP produee~ a prese~ ected volume of molten metal on the end of the wire and then ter-minste~ melting fo~ the reet of the ~rcing condition. ~ter pul~e BP ~ ~ termin~ted only the b~ckground current iElow~ to ~ssure that ~urf~ce ten~ion i~ allowed to form khe molten 13~ 3902 L-7608 wire into a ~phere and the weld pool 1~ quelled. Th~ molt2n metal b~ B lowered ~nto the weld pool by w~re feeder 4û.
A~ the end of wlre 50 i8 melted, ~et f~rce~ of boo~t pul~e BP repel the melted met~l from the pool until the pre~el~ct-S ed ~DOUnt of metsl hs~ been mel~ed. Then ~he current 1~
reduc~d allowlng the mol~n met~l to form into ~ b~ll and the pool in s~bil~zed prep~ring for ~ ~mooth cont~ct be-tween the ~pherlc~l ball ~nd ~he quelled pool. Between posi-tion (e) and the ~ubsequent ~hs~rc position (a~ ~ low current lû flows BO th~t there i~ not mech~t)îc~l snd electro-m~gnetlc actlon between the pool ~nd b~ll a~ it i~ beiog progressed tow~rd the molten met~l pool ~t the l~tter p~rt of ~rcing condition PS.
Referring now to FIGURES 4A, 4B, h~gh energy mel~ing pul~e BP hns n con~rolled enesgy ~el~c~ed ~o ~elrc ~ ~iven portion 200 on rod 50 ~B shown in FIGU~E 4A. I2R he~t~nB
during the pl~ boost portlon of the sr~lng ~ond~tion melt~ ~ selected portlon a from the end of wir~ 50 ~ th~
wire i~ mov~ng, ~o~ard ~he molten metal pool dur~ng, ~h~ ~rc-2~ ing condition. Th~ hlgh current iB ~el~cted ~o th~t the I2R
he~ting ~t the ~nd of wire 50 combined with th~ hlgh redl~-tion he~t c8u8ed by the drastic increa~e in the ~re~ o~ the ~rc i~ ~ufficient to D~elt only ~ sm~ll portlon 20û ~roDI th~
end of wire 50. In pr~ctice, the melted end or portion 200 hn~ ~ len~,th which ~8 about .6 .9 x di~met~r d of the wlre.
Thi8 produce~ ~ molten met~l ball 202 bein~, gener~lly spher-ical !in ehape after it hsa stabllized unde~ the lnflueDce of ~urface ten~ion after psul~e BP. The b~ll h~a a din~eter generslly in the neig~borhood o~ 1. 5 t:lmea the diameter s~f wire 50. Since the s~me energy i8 ~pplied to the end of the wire each tlme, melted end port~on 200 iB obt~ned by the s~me current flow ~nd the ~ame r~di~nt ~rc he~t which co~n-bine to melt a ~elected volume to ultim~tel~ form the same ~ize ball 202 durlng e~ch pl~ma boost of the ~rc~n~, cond:l-tion. FIGURE 4C indfcate~ that the di~me~er x of b~ll 202 13:13902 L-7608 iB between a lower limit equal to the dls~eter d ~nd an ~p-per limit cqual generslly to twic~ the diam~ter d For ~ach particular Betting, the b~ll ha~ the ~me BiZ~ from ~ycl~ to cycle with the di~tribution curve of FI~URE 4C illustrating generally the distribution of sccept~bility of th~ di~meter x in a ~hort circuit~ng arc proce~. AB ~oon 8~ the bo~t pulse BP is removed, only the background current p~Bse~
~hrough wire 50 ~nd the are~ of the ~rc is dra~t~cally re-duced ~ince 8rc Brea i ~ dep2ndent upon ~rc cu~rent. Con8e-quently, the combinet I2R hes~i~g together with the ~rc heating i~ not ~ufficient to ~elt mor~ met~l fro~ the end of wire 50.
B~ll 202 iD formed during the booet pul~e only and it i~ then forced into the met~l pool by feeding welding wire 50 into the pool. This melting action take~ pl~ce at the boo~t portion of th~ arcing condition or p1asma condition PC
~o that th~ tim~ b~e (t) o~ ~he puls~ BP i~ ~ff~ciently ~hort to a7low for the melted metal on the end o~ the wire to have t~lme, after pu1se BP, to or~ lnSo a ~phe~e ~t ~
dlstance spsced from thg ~ol~en pool 3110w~ng ~he ~phere to fo~ without contact with t~e pool. Then the for~ed b~11 can be lowered into the pool to tenmin~te the pl~ma condi-tion PC. This tim~ i~ les~ th~n 50% o~ ~h~ arcin~ condition time ~nd iB termin~ted befor~ 60%0f the src~ng condition h~
expired B0 th~t the wire i~ melted by the high current pul~e and the pool can be quelled or become quieecent beore ~elt-~d ball 202 i~ moved into the pool while under the inf1uence of a rel~tively amall ~rc are~ sust~lned by background c~r-rent IB. Indeed~ the time base length of the boost pul8e iB
~ener~lly les~ ~hsn 50% ~nd preferably les~ th~n about 30 of the ~rcing condition which will be more ~pp~rent froM ~
review of ~ pr~ctic~l ~pplic~tion or example of the inven-tion ~hown in FIGURE 3. The timc T2 iB ~t least 570 of th~
time nece~ary for ~hc sot~l short condi~on snd ~rcing con-dition. In pr~etice, ehl~ tlm~ $s approxl~at~ly 0.20 ~.

~3~39~2 L-7608 A0 can be ~een, the mol ten metal ~n the wlre ~nd in the E?ool, ln aecordance ~lth th~ invention, re~ches equilibrium ~nd i~ qule~cent between pO~tiOIl tc~ ~nd po~ition (d) ~hlch ~re ~et forth d8 time T2. Thereafter, u high energy pulse causing B l~rge Ire~ plaam~ arc and hlgh curreat flow through wire 50 mel~ elected po~tion at the end o~ the wire by the combined heatin~, ~ction of the current flow ~nd the heae of ~he pl~sms or ~rc. AP~er thi0 meltin~,, n ~ub-st~ntial time betw~en po~it~on (e) ~nd po~i~lon (a) ~llow~
~he melted wire ~o form b~il 202 and be moved into ~he mol-ten metal pool wh~le ~che pool is ~ub~ected to relatl~rely lsw arc force~. In thi~ marmer, ~he b~ll i8 ~he ~ole 812e dur-ing esch cycle ~nd ~hort~ng :IB ~s~ured ~inee ~chere ~ no turbulence cau~ed by large arc current to bcunce the ball flw~y from the mol~n met~l pool ~5 I t~ eng8ge8 the pc~ol .
There i no eub~equent energy ~v~ ble for melting, wire 5û;
therefore ~ the w~re ultiol~t~ly drlve~ mel~ed, formed ~met~l b~ll 202 into the pool ~o crente ~ ehor~ circ~ eondit~oo ~t po~i~ion (~), During, ~hortln8, condi~ion S(:, the melted ~oetal b~ 02 eng~g,e~ the molten met~l pool nrld i~ tr~naferred ~nto ~he pool by surface ten~ion. Thi~ ~ctlon causes ~n ultim~te neckilag down of the molten met~l ~xtending betw~en the pool ~nd ~te 50 ~nd then 8 rupture ~nd sep~rae~on of b~ll 202 from wir~ 50 ~ shown ln FIGURE 5E. Since ~here i~ ~ low bsckground current, ~hi~ Bepar~tion or fuse will h~ve low energy ~nd cflu~e little lf ~ny ~patter. Sirlce ~urf~c~ t~n-sion msy require difPerent time~ to neck and break b~ll 202 from s~lre 50, in ~ccord~nce with one ~pect of the inven-tion, piLnch pulP~e P~P between po~it~ons (b~, (c) i~ applied by c~rcui~ 26 st th~ end of ~che short circuit condieion.
Thle pinching ~ction i~ ~llowed to p~ogre~s n8tur811y by ~he par~meter~ of the power sllpply ~nd Ci1rCUit 26; thesefore, 8~
eoon ~IB the conerol circu~t i~ ~ctiv~eed, ehe current ehifts upw~rdly ~lon~ line 100. There~fter, ~ the neck r~pid ~3~3~2 I,-7608 reduces in diamet~r by electrlc pinch, the currQnt flow in-cres~es more ~r~du~lly untll 8 detection of ~n lmper3ding fu~e is obt~ined by the dv/dt at volta~e level 105. A8 t:sn be seen, the energy introdueed into the prOeeBB i~ rel~tive-ly low since the voltsge rises only ~lightly ~nd pulee PP i~
relatlvely short in time. Th~s pul~e i8 for electric pinch-ing action to terminate 8t A preselected ~ime the eho1rt cir-cuit eondition by pinching of f s:he oaet~l of bsll 202 ~fter surfsce ten6ion tr~nsfer iB e~eDti~lly comple~ed during the t~me Tl. Tl is at le~t sbou~ 10% o the to~l combi~ed cycle for shorting ~nd arc~ng ~nd IB gener~lly in exce~8 of 1.5 me. This 1~ co~op~ret to a T2 time of spproxiDI~tely 0.2 ms. The difference in the rel~tive timing i~ th~t time Tl 1B rel~tlvely long to allow for prim~ry ~cr~nsfer oiE the mol-ten metal by the elower surf~ce tenelon sct~on and/or by gravity if spplic~ble. The time T2 ~ïlows for ~he molten met~l on the w~re ~nd the moltea~ met~l of the pool to ~et-tl`e immed~ately ~fter ~ fuse break, ~ ~ho~dn gener~lly ln F~GURE 5F, eo th~t boo~t pul~e BP 1~ not Applied witn ~ree ~olten m~tal in ~ ~t~lac~ita/st~l~glDite form~t~on at the ~n~tant of ~ fu~e explo~ion, ae shown ~n FIGURE 5E. T~i~
~llow~ ehe molten metal to ach:leve ~ cros~ ~ect~on c~pable of carrying ~he boost current. The ~nd of wire 50 and th~
pool into which the Illet8l iD tr~nsf~rred dr~w ~ow~rd eRch other in ~ very shvr~ period o ~ime following the fuse, which eurf~ce tension ~ctis~n i~ ~llowed by ~he delay T2. A
high current pulae while me~ 8 extending in t~ g~p i~
~ource of ep~te~ gener~lly ignored in sho~t eireuit~ng arc welding .
CURRENT CIRCUIT NETWOR~
Referring ~g~ln to FIGURE 1 ~ varl~ty OIC curren~ cir-cuit~ could be provided ~or ~he purpo~e of uccompll~h~ng ~he pre~ent inveneion 88 de~ forth above; howev~r, ln ~ccord~nc~
with the illu~trated pref0rred embodisnent of ~h~ ~nvention current circui~ network 20 in~lud~ three aepar~te ~nd 13139~ L-7608 di~inct current control c~rcuit~ e~ch of which perf~ s ~
current control function directing curretlt from the output of the con~tant potential power ~upply'lO to th~ welding operation acros~ output termin~ls 30, 32. These circult~
~re current additive in nature and includ~ ~ constantly op-erated high induct~nce b~skground currerlt control circu~t 22 h~ving a tremendou6ly l~rge Inductor 210 to m~intain ~ cur-rent with high inductive re~ct~nce but at ~ low level ~uch ~18 20 ~mpe~es or slightly le~. In ~he illu~tr~t~d embodi-ment, lnduc1:0r 210 ha~ ~n induct~nc~ of 2.0 mh. The b~ck-ground current control circui~ i~ ope~stlve by ~ctu~tin~
power tr~nsi6tor 212 in re~ponse ~o et~rting circui~y of any type ~nd i~ controlled by clrcuit 22~ ~o ths~ the m~gniE-tude of the current iB controlled by lnductor 210 ~nd i~
sd~usted by potentlomet~r 214. Clrcuit 22 directs current continuou~ly through blocking diode 216 to the wire ~nd workp~ece. In thi~ manner, b~ck~,ro~n~ current IB flo~s c~n-tinuously ~nd ~u6t~in~ the ~rc during ~ rc 6itlJatio;l~.
Pinch control clrcuit 26l of ~he pinch circuit 26 ~
oper~tive durin~ thQ short circuit condition ~nd ~nclude~ a resistor 220 which i~ ~n ad~ustable pot which csn be ad~lulet-ed ~o ch~nge the current level of current ~ppl ied through tr~nsi~tor 226. T~m~ TL le cosstrolled by circult 26'. C~-pscitor 222 bal~nce~ the inductive re~ct~nce of tran~to~
12 for thi~ particu7~r circui~. Re~ or 224 ~cts ~e ~ fil-ter ~or current from power tr~n~l~tor 2Z6 wh~ch cause~ cllr-rent ~low through re~i~tor 22B. In ~hi~ manne~, trans~tor 226 i~ sctu~ted after ~che ti~e Tt to turn on the pinch cur-ren~ ~t ~he end of short condition SC. l'he pinch contr~l circuit i~ ~ctunted by ~n ~ppropriste voltage ~en~ing or detecting arrsng,emerlt ind~csting ~he in~t~nt when the weld--ing vole~ge plungee from the pl~eula l~vel to ~he ~h~rt c~r~
cuit level. Thi~ c~n be ~ccompll~h~d by a detector 240 DB
indicated by line 26~ or by other appropriate volt~ge Bens-in8 circul~s. After time 'rl~ power æwltcl or tr~n~tor 226 19 - .

~ 3 ~ 3 ~ ~ ~ L-7608 i8 clo~ed by control 26' to ~ctuate c~rcuit 26 ~o direc~
current flow through current limitin~ r~ietor 228. A
Darlington connected tr8n8i8tor swi~ch'230 i~ closed by con-trol 26l by logic in line 242 in re0ponse to a sign~l ~n line 267 and pa~s~s re~ or 232 snd p~rsllel cap~cl~or 234 for the purpose of ~llowing the pinch pul~e PP to p~
throu~h blocking diode 236. De~ector 240 ha~ ~ d~/dt ~en~or to open switch 230 sfter the switch h~ b~en closed by ths pinch control circuit 26 followlng ~ime Tl. In this manner, the pinch control circuit 26' lnitia~ee ~witch ~26 after time Tl ~nd ~witch 230 places re~istor 232 in ~erie~ w~tb re~i~tor 228 to termin~te the pinch pul~e. There~fter, thi~
c~rcuit becomes in~ctive unt~l ~he next eh~r~ de~ected by a ~udden drop in pl~m~ volt~e.
The pl~sma boost curren~ control circuit 24 i~ r to pinch control circult 26 and includee ~n ~dJ~stsbl~
potentiometor 250 for controlling current level. Time T~ i~
~e~ in con~rol 24'. Capac~or 252 bal~nce~ ~he ~nduc~nce of the power ~upply ~nd iB eo~bined with ilter re~istor ~54 2Q for th~ purpo~e of pr~duc~ng an ener~ pul~e BP indlc~t~d 3~0ve ~he clrcult. When power switch or tr80~i~tor ~56 i~
clo~cd by the pl~ boo~t control clr~uit th0 le~din~ edg~
of the pul0e 1B ~or~ed~ This high en~gy boo~ pul~e BP
p~es through re~l~tor 258. A D~rlin~ton c~nnected po~r ~witch 260 i~ conduc~ive to p~ pul~e BP. Swi~ch 260 ~ in par~llel w~th re~istDr 262 ~nd c~pscitor 264 t o ~top the high energy boo~ pulse upon receipt of ~ ~ign~l ~hrou~h line 265 to form ehe t~ailing ed~e o the pul~e. Bloeking diode 266 direc~s the current from circuit 24 ~cro~ t~sml-nal~ 30, 32. Io ~ummary, after ~ime T2 tr~nsi~tor ~wltch 256 i~ turned on. Thi3 creste~ the le~ding edge of the boost pul~e BP. A~ the ~nme time, ~w~ tcll 260 is on to pas~
the boost pul~e through diode 260. To termin~te the boo0t pulse, ~ ~lgn~l in line 265 de~ctiv~te~ ~witch 260 lnsertir~g reDietor 262 hav~n~, a resi~tsnce of 50 ohm~ ineo the QUltptll:

~ ~3~

circuit. This immedistely termin~te9 the pul~e ~nd cre~e~
the trailing edge ole the pl~8ma boo8t or bo~t pul~e BP. In thi~ manner, the pul~e hs6 a rel~tively, rect~n~ul~r sh~pe ~A
~hown 1n the lower portion of FIGURE 2 snd ~chem~tically ln da~hed 1 ine~ in FIGURE 8 .
A~ b~ckground for the $ntroduction of three aepsrate current~ ~cross the welding circui~ for shor~ circuiting nrc welding, reference should be made to Needham United States patent 3,792,225, 2/1974. This patent employs separate power supplies and does not have the pinch pulse and boost pulse forming the essence o~ the present invention.
EXAMPLF.
Referring now to FIGURE 3, ~ ~peci f ic ex~mple of a short circuiting ~rc proce~s employln?, the present inventlon is illu~trated ~howing the welding curselit ~t the v~r~ous 81ta~e~ ~nd the resulting voltage level~. After t~me T~ dur-ing which the volt~ge i~ ~t the norm~l ~t~bllized pl~ma level 112, pulse BP iB crested. This incre~ses the cur~ent ~long line 300 to ~pproxim~tely 400 smperes ~t which time the end of wire 50 st~r~ melting causing the current to droop ~long line 302 until ~wi~ch 260 of FIGURE 2 l~ opened.
1~oo8ter energy pulee BP i~ then ~bruptly te~inated / ~
indic~ted by tr~ilin~, ~dge 306 of the boo~t pul~e. This re-duce~ the current down to th~ b~ck~round level of I~B. A~
thDt tlme, the volt~ge i8 controlled by the bsckground cur-rent which hs~ ~ubse~n~ial induct~nce; therefore, pl~sma level 112 droops ~long the line indicsted by time T3. Thi~
time i8 the rem~inder of the ~rcin~, condition af~er ~he end of the ~elting pul~e. During thi~ time, the back~,round cur-rent from circui~ 22 i~ con~rolled by the po~der ~upply ~o thst there ~s very little arc sres and thls ~re~ i~3 only ~ufficient to ~u6t~in the ~rc B0 th~t l:he pool c~n phy~-c811y stnbilize during the l~ter p~rt ~f the arcing condi-tion. As 800n AB the melted metal b~ll formed orl the end of ~he wire engsge~ the mol~n pool, ~he ~oltage imD~edi~ely qæ3~
~ 3 1 3 9 ~ ~ L- 7 608 plunges ~qlong llne 306 cau~ed by the ~hort circuit. The current rem~in~ a~ the b~ckg,round level ~n~ ~0 held ~ ~hl~
level for ~ s~lbst~ntial period of time ~uch ~IB Approa~im8tely 1.5-2.0 ma. Thereafter, tr8n~1i8tOr 226 of circult 26 i8 closed while swi~ch 230 i~ al00 elosed. Thi~ introduces pinch pul~e PP by increasing the ~elding current slong l~n~
310 . A~ the c~rrent resches th~3 upper end of 1 ine 31û, the vol~age commence~ to ch~nge more grAdu~lly sinca ~h~ resis-tance of the decre~sing nesk i~ inCre~Bin~, during p~nc~.
ThiB C~lUBelEI the current ~o shil~t ~ore ~r~dually ~ow~rd ~he position 104 ,~UB~: before the ~lectr~c pirlch CIIIUB}~ the fu~e to explode. Before the fu~e, cur~ent 314 i~ plun~ed back to b~ckground curren~ level ~co reduce Sh~ ener~,y of the fu~
exploaion . Thls i~ accompl ished by opening, ~wi tch 230 by detector 240 ~hown in FIGURl~ 1. When that happens, the volt~ge i~ ~s~bilized ~long line 110 to the level 112 whicl ~B held during the arcing cond$tion fo~ time T2 . l`hereaf-ter~ the current boo~t pul~e ~ rep~s~ed. The p~r~meters of thie particulDr ex~mple Ire 8et forth in the lower portion of FIGURE 3.
PLASMA BOOST AND POOL DYNAMICS
Referr~FIg now ~o FlGURES 5A-5F, oper~in~, ch~r~cteri~-tic~ of the present In~rentiorl ~rs ~chem~tic~lly lll~l~trated to ahow lhow the u~e of the present ~nvent~on controls ~p~t-ter and produces a wide weld be~d ~t ~n incre~sed depo~iti~
r~te . ~hen the ~rc~ng condi tion i~ crested by ~ep~atiorl of ~ ~UBe c~u~ed by the electric plnch pulse, only the b~ck-g,round current flow~ for ~ short tlme 1'2. Then th~ boo~
pulse i8 ~ppl~ed and wire 50 i~ melted and repelled from pool P ~B illu~tr~ted in- FIGURE 5A. Thi~ pulse e~lly ~eltu the end of adv~ncing weldin~ wire 50 to p~od~lce a gener~l toroid~ elted metfll mas~ 202~ which iB repelled frosl pool P ~ distsnce r by the use s)f ~et fo~cee set forth ~ eever-al srrows in FIl;URE 5A. These force~ pueh mas~ 202 away from pool P 80 th~ the melted ~a~ of met~l 202a gsther~

~ L-7608 ~3~31~
~round the unmelted encl o wire 50 which i~8 ~p~ced $rom pool P in the di~tance Sl. The high energy electric pl~m~ be-tween the wlre ~nd pool causes the jet forces ~ to ~ct on the pool a~ wel 1 ~8 on ma8a 202~ ~o hold the ma~ ~w~y from ~he pool as long aB the pla~ma boost i~ applied. When Argon i8 u~ed the m~s~ o~n ~hif t into ~ gener~lly conic~l ma~
202b having an end 350 which may exteod tow~rd pool P to g level below the n8~tlr~I level 360 of the pool a~ ~hown in FIGURE .5B. Thi~ shape i~ ~aused by ~lectrlc pinch ~nd form6 during the l~ter por~ion of the pl~m~ boo~ n ehi~ a~ ~-u~tion, pool P iB forced outw~rdly by ~he arcing forcea ~8 schematicslly illu~tr~ted in FIGURE 5B. The unmelted end of wire 50 i~ progre~lng tow~rd pool P 2nd i~ now ~t ~ lesner diet~nce S2. ~hen the boost pul~e iB di~eontinued, ~urf~ce ten~on form~ m~ss 202b into ~ ~pheric~l b~ 8 ~hc~wn in FI&URE 5C . When C02 iB used ~here ~ 5 no sub~t~n~ lec-tric pinch ~hu~ ~ when the hi8,h pl~m~ boo~t currcn~ stopa, the melted mas~ progre~ses ~rom mass 202~ ~hown ln FIGVRE 5A
to ball 202. Diat~nce S3 i~ ~uch eh~t wh~n the pool 'beco~ee quie~cent or generally fl~t, it doe~ not con~c~ Dlelt~d met~
al b~ll 202 aB the met~l of the pool returns lnto the con-cave cavi ty cau~ed by the high ~et force~ during the high energy pul 8e. These low arc~ng force~ cau~ed by only the b~ck~,round current no longer maintain the melted met~l aw~y from the pool ~nd a grEldu~l, positive shorting ~ction occurs when wire 50 i~ lowered downward 80 that ball 202 cootact3 pool P. ThiB i8 done while low ~et force~ ~re presen~ eo that there iB no tendency to bounce and the energy in the plB8mA gap iB ~n0ufflcient to cau~e pool agitation durin~, the shorting ~ICLion. The time Tl between the plasma boo~t or pul~e BP and the short clrcu~ t i~ d~ring ~he arclng con-dl~ion and iB ~Uf ficien~ly long to allow ~he b~ll to form and the pool to be quelled from the agi t~tion of the high current flow. When the ~hort occurs, the met~l of ball 202 iB tr~nsferred lnto the pool by ~urf~ee tension ~ ~ndic~ted 13~3~
by the conf iguration of the melt~d m~8 202c in FIGURE 5D.
Thi~ i~ at po3ition (b) wher~ th~ electrIc pi~ch puî~e PP
st~rt~. M~a 202c iB forming ~ ~mall- dismeter neck 400 I~B
surf~ce ten~ion pu118 the molten met~l from the end of wire SO. AB can be seen, with fl quiescent pool P, the metal can move outwDrdly to produce ~ bead greElter than three ~imes the di~meter of the wire 50. Con~equen~ly, ~ lsrge weld bead can be cre~ted which will f~cilitste incressed wire ~ize snd ener~,y with~u~ c~u~ing ~p~tter or weld be~d irregt~larities.
Melted metal 20~c i6 trsnsferred to the pool by ~ur~ace ten-Bion ~nd then ~n elec~ric pinching ~ction occurs. Before the pinching action rup~ure~ neck 400, the weld~ng current i 8 reduced ~o the background level . Tb~ B low curren~ prs:~duc-e~ an src h~ving ~ ~m~ll diameter Al wheo the neck iB rup~
tured ~ shown in FIGURE 5~O Th~ necklng ~ction 1t n~ck 4ûD
h~ U81t rllp~ur~d; therefore, there i8 met~l 402 extending from the end of wire 50 towsrd pool P . In ~ 1 ike manner, tbe pool portion of th~ neck cre~tee moltess met~l 404. By emp~oying ~ low bsckground current h~ving high induct~nce ~t ~0 the time of the fu~e explosion, the energy u~d to reignite the BrC i~l low to prevent ep~tter. In sddition, the boost curren~ not applied B0 th~t the metal portion 402, 404 can, 'by ~urf~ce ten3ion, progreeæ into their respective bas-es as shown in progress ~n FIGU~E 5F. Durlng ti~ T ~
~hown in FIGUR}; 5F, the molten ~net~l 402 on the ~p of wire 50 ~nd met~l 404 of pool P are dr~wn by ~urf~ ~ ten~ion ~o the wire ~nd pool, r~spectively. When this 1B E~C~OmP1iBhed~
the high energy pla~ma boo~t iB applied which will incre~se the ~res of the pla~ma or ~rc as ~ndic~ted by incseased di-~meter A~ in FIGURE 5F. A~ 80011 BB the boo0t 1B ~pplie~d, the etep~ set for~h in FIGURES 5A-5F ~re repe~ted. A~ c~n be ~een, t~e æize of ~he b~ll is determined by the enerxy during the eurrent booet ~t the ~t~rt of the nrcing condi-tion. ~hereafter, no more melting occur~ ~nd the weld pool iB quelled. Tranefer of metal i~ by the grsdu~l eurf~ce ~4 -~ 313~C~ L-7608 tenBiOn nction with only a minor a~ tance B~ the end of the 8horting condition for nn abrupt ele~ricnl pinch to break the neek positiYely ~nd in ~ ahor~ time.
MO~IFICATIONS
The preferred embodimen~ of ~he pre~en~ invention i8 described in connection with FIGURES l-S; however, certain modific~tion~ can be mad~ w~thou~ dep~rtlng from the intend-ed spirit and ~cope of the p~e8ent ~nvention. For in~nnce, referrin~ to FIGURE 6, pinch p~lse PP can be formed with ~
generslly flat upper maximum level 500 by ~ppropria~e ~elec-tion of p~rameters, i.e. resi~t~nce, in ~le plnch control circuit 26. In this ~anner, ~ const~nt current i8 ~pplied at the end of ~he ~hort circui~ condit~on ~o effec~ the fi-n~l electric pinch. This current ~8 abruptly dropped to the background curren~ level by 8 premonition circuit, euch ~8 a dv/dt detcctor 240.
Referring now ~o FIGURE 7, pla~ma boost control clrc~l~
24 can be modified by incorpornting ~n OUtptl~ inducts)r ~10 nnd a freewheel~n~ diode 512 ~o th~ the bos)et ps~lse i~ con-ver~ed from the dashed line profile ~ho~m ~n FIGURE 8 ~o the ~olid line profile. A high time constant leading edge 520 ~nd ~ ~lowing dec~ying tr~iling edge 522 controll~d by the Preewheelin~ diode form3 the pulse BP' with ehe energy o pul~e BP. Inductor S10 eould be sd~u~t~ble by employing ~
eecond~ry with an ~d~at~ble pot to control the prof~le o le~ding edge 520. In either of the boost pul~e~, the tot~l energy ~B determined by the integr~tion oP the proflle iB
~uch to melt a ~electet portion of wlre 50 during the pu~e.
Such melting9 ~a mentioned before ~nd a~ æet forth in FIGU~E
5 , re~ult~ from two heat~ng ~ource~ the energy cauaed by I R heating ~nd the energy C~UBed by ~he r~di~t ~rc heat-ing. The current level iB ~elected to that the ~2R he~ting will not melt ehe end of the wire wlthout the h~gh energy sccompanying the electric boo~ pulBe 80 th~t melting occur~
o~ly on the end of wire 50 expo~ed to the ~rc. The~e heat _ 25 -~z ` ~ 3 ~ 3 ~3 ~ 2 L-7608 ~ource~ combine to cau~e melting of ~ ~elected ~mount. As soon ~A the pul8e l~ ~erm~n~ted~ melting essenti~lly ~top~.
To select the energy, the ~rea in the c~rrent boo~t p~lse curvefi iB ~uch that ~pproxim~tely 18,000 calorie~ per ~ole S time~ the volume of ball 202 provides ~he ~ot~l energy de-veloped for the melting sction. This energy v~lue deter-mines essent~ally the amount of ~et~l in melted met~l b811 202 ~fter the high energy melting pul6e h~s been termin~ted.
This energy i~ the ~me in the boo6t pul6e BP in the pre-1~ ferred embodiment of ~he invention a~ well ~ the boo~t pul~e BP' obt~ined through use of ~he modific~tion Bet forth in FIGURE 7.
In sccordance with still ~ fur~her modlfic~tion of the present lnvention, the boost pulse csn t~ke the profile ~hown ~B pulse BP" as ~ dotted llne in FIGURE 8. Thie p~lse i~ cr~ated by a ~enerally 1~t profile pulse h~ving e levsl 530 combined with ~ second pulse having ~n upper current level 532 ~nd ~ ~ubet~nti~lly reduced t~me ba~e len~th. ~y combining the~e two ~ubpulse~ into ~ boo~t pul~e BP", melt-ing ~8 initiat~d by the heatin~ efect of the current 530.
The hesting i~ then ~ccelerated by the high level current 532. Some ~elting may occur wh~n the current i~ ~h~fted back to the elev~ted level 530. Thereafter, the ~elting i~
complete ~nd the welding eurren~ drop~ to the b~ckground ~5 level for the rema~nder of the arclng condition to carry b~ll 202 into the mo~ten metal pool P ~ ~et fo~th in FIGURE
5D.
GENERAL DISCUSSION
By employing the pre~ent invention, tr~nsfer of molten ~etal iB not dependent upon electric pinch; ~herefore, 10070 cArbon dioxide may be used n~ 8 Bhielding ga~. By using the delsy Tl, which iB sub~t~nti~lly greater than the del~y of the copending applicstion, there iB no tendency to initiste the hlgh current untll there iB ~ ~ub~tantiRl con~c~ be-.
tween ball 202 ~nd pool P. Indeed, this oont~ct has ` ~ 313~ L-7608 progre~ed by ~urf~ce tension to the pl~e where ths neck 400 has started.
A bead three times the ~lze of th~ wire 50 c~n be ~c-compl~hed by using the present inven~ion. W*en the boo~
current or pul~e ~ cre~ted, the 3e~ forces f tend to repel met~l 202~ from pool P which h~ endency eo keep the melted met~l mas~ ~w~y from the pool during the mel~ing ~c-tion 80 that it i~ ~s~ured that the metsl oont~ct c~u~lng ~hort will not occur until ~ubst~nti~lly after the boo~t current h~ been removed and b~ll 202 h~s formed. ~he ~rc length mu~t be more th~n half the d~ameter of ~he electrode when the boo~t iB ~pplied to melt ~he met~l b~ck ~way fr~
~he pool ~t the ~ame eime the pool i~ driven ~way from the ~re~ ~u~t below welding wire 50. Otherwise, electrical ~tubbin~ c~n oc ur. The boo~ pulee remain~ on a prese-lected time which causes a predeterm~ned ~mount of met~l to melt. In thi~ manner when the boo0t ~ removed and the mol-ten metal forms a ~phere 202 due to nurf~ce tension, b~ll 202 remaine above the pool un~il it iB lowered into ~he poo~
~ the wlre eed r~te eontrolled by wire feeder 40.
The pl~sms boo~t energy 1B only ~uffic~ent ~o m~lt ~
volume of wire e~uiv~lent to that indic~ted in FIGURE 4B. If an exce~ive amount of wire iB melted by the ener~y of the boo~ pul~e, ~r~n~fer of the ball ie mor~ difficult w~thout ~patter. For ~hst resson, the energy of the boo~t pul~e 1 controlled to obtain the p~r~eters set forth in FIGURE 4~.

_ ~7 -

Claims (27)

1. In a short circuiting arc welding apparatus compris-ing a single constant voltage D.C. power supply means for causing, a welding current to pass through a welding wire to a workpiece at a molten metal pool, wire feeding means for feeding said welding wire toward said workpiece at a con-trolled rate whereby said welding wire alternates between an arcing condition during which said wire is spaced from said pool of said workpiece but driven toward said pool and a short circuit condition during which melted metal on the end of said welding wire is in contact with said molten metal pool and then transfers to said workpiece by a necking ac-tion breaking said melted metal from said wire to initiate the arc in a subsequent arcing, condition, the improvement comprising: a first high inductance current control circuit for continuously directing a low level, arc sustaining, background current between said welding wire and second work-piece and a second current control circuit for controlling current flow during said arcing condition, said second con-trol circuit including time delay means for causing said initiated arc to have an area determined primarily by said background current for a preselected time T2 during which melted metal on the welding wire and the molten metal pool are essentially quelled and means for then passing a high current pulse through said arc between said wire and pool with a preselected I(t) area or energy for melting a rela-tively constant volume of metal on the end of end wire and spaced from said pool, said high current pulse being termi-nated before about 60% of said arcing condition has tran-spired whereby said wire is melted by said high current pulse and said pool is again essentially quelled before said wire is fed into said pool whereby only said background cur-rent is flowing, through the arc when said short circuit condition is initiated by driving said electrode into said pool.

2. The improvement as defined in Claim 1 wherein time base length of said current pulse is less than 30% of said arcing condition.

3. The improvement as defined in Claim 1 wherein time T2 is at least 5% of the time required for both said short condition and said arcing, condition.

4. The improvement as defined in Claim 1 wherein said second current control circuit includes means for adding current to said background current during said arcing condi-tion and means for reducing said preselected area of said high current pulse in inverse proportion to the amplitude of said added current.

5. The improvement as defined in Claim 1 wherein said second current control circuit includes means for shaping said high current pulse into a pulse having a high time con-stant leading edge and a gradually decaying trailing edge.

6. The improvement a defined in Claim 1 including third current control circuit for controlling current flow during id short circuit condition, said third current con-trol circuit including timing means for allowing flow of only said background current until said melted metal of said welding wire is primarily transferred into said molten pool by surface tension and means for thereafter applying a high current pinch pulse across said shorted melted metal and detector means for discontinuing said pinch pulse in re-sponse to an anticipation of impending breaking of said melted metal from said wire to start said arcing condition.

7. The improvement as defined in Claim 1 wherein said detector means includes means for detecting the dv/dt across said shorted melted metal and means for discontinuing said pinch pulse when the dv/dt changes sign at the end of short circuit condition only.

8. The improvement as defined in Claim 7 wherein said third current control circuit includes a low inductance cur-rent output.

9. The improvement as defined in Claim 6 wherein said third current control circuit includes a low inductance cur-rent output.

10. The improvement as defined in Claim 6 wherein time base length of said current pulse is less than 30% of said arcing condition.

11. The improvement as defined in Claim 6 wherein time T2 is at least 5% of the time required for both said short condition and said arcing condition.

12. The improvement as defined in Claim 9 wherein said second circuit control circuit includes a low inductance current output.

13. The improvement as defined in Claim 1 wherein said second circuit control circuit includes a low incuctance current output.

14. The improvement as defined in Claim 1 wherein said wire has a given diameter and said volume is sufficient to form a sphere having a diameter no more than twice the diam-eter of said wire.

15. A method of short circuiting arc welding by a D.C.
power supply for supplying welding current between a welding wire being fed at a controlled constant rate and the molten metal pool of workpiece toward which said wire a being fed, said method including a succession of short circuit condi-tions separated by arcing conditions, said method comprising the steps of:
(a) providing a background current through said wire and pool during both of said short circuit conditions and said arcing conditions, said background current having a high inductance components and a low level just above the level necessary for sustaining an arc when said wire and pool are separated;
(b) at the start of said arcing condition, allowing said low background current to flow for a preselected time T2 sufficient to allow said molten pool to be quelled;
(c) after said pool is quelled, passing a high current pulse through said arc between said wire and said pool with a preselected I(t) area for melting a relatively constant volume of metal on the end of said wire and spaced from said pool;
(d) allowing said low background current to flow after said high current pulse for the remainder of said arcing condition; and, (e) then feeding said wire with said volume of melted metal on its end into said molten metal pool to start the short circuit condition with an arc sustained by only said low background current.

16. The method as defined in Claim 15 including the steps of detecting the end of a short circuit condition and starting said time T2 in response to said detecting step.

17. The method as defined in Claim 15 including the step of maintaining said background current at all times.

18. The method as defined in Claim 17 including the step of applying a high current pinch pulse at only the end of said short circuit condition until the melted metal is electrically pinched from said welding wire to terminate said short circuit condition and initiate said arcing condi-tion.

19. The method as defined in Claim 15 including the step of applying a high current pinch pulse at only the end of said short circuit condition until the melted metal is electrically pinched from said welding wire to terminate said short circuit condition and initiate said arcing condi-tion.

20. The method as defined in Claim 16 including the step of applying a high current pinch pulse at only the end of said short circuit condition until the melted metal is electrically pinched from said welding wire to terminate said short circuit condition and initiate said arcing condi-tion.

21. The method as defined in Claim 16 including the step of maintaining said background current at all times.

22. The method as defined in Claim 15 including the step of predicting the separation of said melted metal from said welding wire at the end of said short circuit condition and terminating said high current pinch pulse just before said predicting step.

23. In a short circuiting arc welding apparatus com-prising a single constant voltage D.C. power supply means for causing a welding current to pass through a welding wire to a workpiece at a molten metal pool, wire feeding means for feeding said welding wire toward said workpiece controlled rate whereby said welding wire alternates between an arcing condition during which said wire is spaced from said pool of said workpiece but driven toward said pool and short circuit condition during which melted metal on the end of said welding wire is in contact with said molten met-al pool and then transfers to said workpiece by a necking action breaking said melted metal from said wire to initiate the arc in a subsequent arcing condition, the improvement comprising: a first high inductance current control circuit for continuously directing a low level, arc sustaining background current between said welding wire and said work-piece and a metal transfer current control circuit for con-trolling current flow during said short circuit condition, said metal transfer current control circuit including timing means for allowing only said background current to flow un-til said melted metal of said welding wire is primarily transferred into said molten pool by surface tension and means for thereafter applying a high current pinch pulse across said shorted melted metal and detector means for dis-continuing said pinch pulse in response to an anticipaiton of impending breaking of said melted metal from said wire to start said arcing condition.

24. The improvement as defined in Claim 3 wherein said detector means includes means for detecting the dv/dt across said shorted melted metal and means for discontinuing said pinch pulse when the dv/dt increases at a selected rate at the end of a short circuit condition only.

25. The improvement as defined in Claim 23 wherein said metal transfer current control includes a low induc-tance current output.

26. In a short circuiting arc welding apparatus com-prising a single constant voltage D.C. power supply means for causing a welding current to pass through a welding wire to a workpiece at a molten metal pool, wire feeding means for feeding said welding wire toward said workpiece at a controlled rate whereby said welding wire alternates between an arcing condition during which said wire is spaced from said pool of said workpiece but driven toward said pool and a short circuit condition during which melted metal on the end of said welding wire is in contact with said molten met-al pool and then transfers to said workpiece by a necking action breaking said melted metal from said wire to initiate the arc in a subsequent arcing condition, the improvement comprising: a first high inductance current control circuit for continuously directing a low level, arc sustaining, background current in the range of about 20-80 amperes be-tween said welding wire and said workpiece during both of said short circuit and arcing conditions, a second low in-ductance current control circuit for controlling current flow above said background current level during said arcing condition, and a third low inductance current control cir-cuit for controlling current above said background current level during said short circuit condition.

27. In a short circuiting arc welding apparatus com-prising a single constant voltage D.C. power supply means for causing a welding current to pass through a welding wire of a given diameter to a workpiece at a molten metal pool, wire feeding means for feeding said welding wire toward said workpiece at a controlled rate whereby said welding wire alternate between an arcing condition during which said wire is spaced from said pool of said workpiece but driven toward said pool and a short circuit condition during which melted metal on the end of said welding wire is in contact with said molten metal pool and then transfers to said work-piece by a necking action breaking said melted metal from said wire to initiate the arc in a subsequent arcing condition, the improvement comprising: a first high induc-tance current control circuit for continuously directing a low level, arc sustaining, background current between said welding wire and said workpiece and a second current control circuit for controlling current flow during said arcing con-dition, said second control circuit including time delay means for causing said initiated arc to have an cross-section determined primarily by said background current for preselected time T2 during which melted metal on the weld-ing wire and the molten metal pool are essentially quelled and means for then passing a high current pulse through said arc between said wire and pool with a preselected I(t) area or energy for melting a relatively constant volume of metal on the end of said wire and spaced from said pool, said vol-ume being sufficient to form a sphere having a diameter no more than twice the diameter of said wire.