Note: Descriptions are shown in the official language in which they were submitted.
L-7608
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~
L-7608
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~
1313902 L-7608
~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
-- 7 --
~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
- 10 -
13 L3902
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
12 -
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
- 13
~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
- 14 -
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
- 15 -
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 ~.
- 16 -
~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
17 -
~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
18
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:
- 20 -
~ ~3~
L-7608
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~
- 22 -
~ 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
- 23 -
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
- 26 -
` ~ 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 -
