A welding torch for plasma arc welding apparatus has an inert gas applied circumferentially about the arc column externally of the constricting nozzle so as to apply a constricting force on the arc after it has exited the nozzle orifice and downstream of the auxiliary shielding gas. The constricting inert gas is supplied to a plenum chamber about the body of the torch and exits through a series of circumferentially disposed orifices in an annular wall forming a closure at the forward end of the constricting gas plenum chamber. The constricting force of the circumferential gas flow about the arc concentrates and focuses the arc column into a more narrow and dense column of energy after exiting the nozzle orifice so that the arc better retains its energy density prior to contacting the workpiece

McGee, William F.

Rybicki, Daniel J.

NASA Technical Reports Server

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United States Patent [19] 
USOO5302804A 
[ii] Patent Number: 5,302,804 
McGee et ai. [45] Date of Patent: Apr. 12, 1994 
[54] GAS ARC CONSTRICTION FOR PLASMA 5,233,154 8/1993 Horai et al. .......... 219A21.48 
Primaru Examiner-Mark H. Paschal1 ARC WELDING 
[75] Inventors: 
[73] Assignee: 
[21] Appl. No.: 
[22] Filed: 
William F. McCee, Decatur; Daniel 
J. Rybicki, Huntsville, both of Ala. 
represented by the Administrator of 
he N~~~~~ Aeronnutics Space 
81,890 
Jun. 25,1993 
Arrorniy, Agent, or Firm-Robert L. Broad, Jr.; Guy M. 
Miller; John R. Manning 
The United States of America as [571 ABSTRACT 
A welding torch for plasma arc welding apparatus has 
an inert gas applied circumferentially about the arc 
column externally of the constricting nozzle so as to 
apply a constricting force on the arc after it has exited 
the nozzle orifice and downstream of the auxiliary 
washington, D.C. 
[51] Int. (3.5 ....................... B23K 1O/W, B23K 9/167 
[52] U.S. CI. ................................. 219/121.51; 219/75; 
2 19/12 1.5; 2 19/12 1.48 
[58] Field of Search ...................... 219A21.480, 121.5, 
219A21.51, 121.49, 121.59, 74, 75 
t561 References Cited 
U.S. PATENT DOCUMENTS 
4,125,754 11/1978 Wasserman et al. ............. 219A21.5 
4,389,559 6/1983 Rotolico et al. ................. 219A21.5 
4,162,977 8/1988 Browning ....................... 219A21.47 
5,194,715 3/1993 Severance, Jr. et al. ...... 219/121.48 
shielding gas. The constricting inert gas is supplied to a 
plenum chamber about the body of the torch and exits 
through a series of circumferentially disposed orifices in 
an annular wall forming a closure at the forward end of 
the constricting gas plenum chamber. The constricting 
force of the circumferential gas flow about the arc con- 
centrates and focuses the arc column into a more nar- 
row and dense column of energy after exiting the nozzle 
orifice so that the arc better retains its energy density 
prior to contacting the workpiece. 
2 Claims, 1 Drawing Sheet 
https://ntrs.nasa.gov/search.jsp?R=20080003995 2019-08-30T02:05:54+00:00Z
U.S. Patent Apr. 12, 1994 5,302,804 
FIG. 2 
5,302,804 
1 2 
apparatus so as to maintain the energy density of the arc 
column after the arc exits the orifice. 
It is a further object of the present invention to pro- 
vide plasma arc welding apparatus wherein an inert gas 
5 is applied circumferentially to externally constrict the 
arc after it has exited the orifice of the constricting 
nozzle so as to concentrate and focus the arc column as 
it exits the orifice. 
Accordingly, the present invention provides a 
stricting force on the arc exiting the orifice of the nozzle 
of plasma arc welding torch to retain the energy density 
of the arc column after the arc exits the nozzle to maxi- 
mize the energy available for contacting a workpiece. 
gas circumferentially about the arc to concentrate and 
prevents the diameter of the arc column from expand- 
ing or flaring after leaving the nozzle, and maintains or 
(2) Description of Related Art 20 even narrows the diameter to that a more narrow weld 
Plasma arc welding is a process wherein coalescence bead and heat zone is created. Additionally, a symmetn- 
of metals is produced by heating them with a con- cal dimensional shape of the arc is maintained which 
stricted arc between a nonconsumable refractory elec- alleviates asymmetrical weld bead shapes and related 
trode and the work or between the electrode and a defects which now occur with conventional plasma arc 
constricting nozzle having an orifice. A filler metal may 25 welding apparatus. 
or may not be added during the process. Thus, plasma To provide a circumferential'flow of inert gas about 
arc welding is a method of electrical arc welding in a the arc, the invention provides an arc constricting gas 
protective gas atmosphere wherein the arc is main- flow circumferentially about the shielding gas and the 
tained between the workpiece and a nonconsumable arc, i.e., circumferentially about the shielding gas nozzle 
electrode of a high melting point metal such as tungsten, 30 and the constricting nozzle. The constricting gas is 
the plasma of the arc being passed through a nozzle. directed upon the arc externally of the constricting 
The electrode is disposed within and insulated from a nozzle orifice through a plurality of circumferentially 
welding torch body and a front end having the con- disposed spaced apart orifices. Preferably the constrict- 
body and is channeled about the electrode exiting 35 tially disposed plenum about the shielding gas nozzle 
to constrict its shape to that of a narrow column and 
becomes ionized in the arc to form the plasma. In addi- 
tion the orifice gas provides some shielding effect to the 4o 
molten weld zone and the electrode and acts on the arc 
to constrict its shape and shield the weld. In most, if not 
substantially all cases, an auxiliary shielding gas is pro- 
vided by channeling a second inert gas stream to blan- 
GAS ARC CONSTRICTION FOR PLASMA ARC 
WELDING 
ORIGIN OF THE INVENTION 
mance of work under a NASA contract and is subject to 
the provisions of Section 305 of the National Aeronau- 
435; 42 U.S.C. 2457). 
The invention described herein was made in 
tics and Space Act Of 1958, Public h W  85-568 (72 stat. lo method and apparatus for providing an external con- 
BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
This invention relates to Plasma arc welding (PAW), 15 The constricting force is provided by applying an inert 
focus the arc column after it leaves the nozzle. This 
and m ~ r e  Particularly to Plasma arc welding apparatus 
arc column to concentrate and focus it to maintain a 
dense column of energy. 
wherein an external constricting force is applied to the 
stricting nozzle. An inert gas is supplied to the torch 
through the orifice. This gas acts upon the electric arc 
ing gas flows from a supply conduit into a circumferen- 
and, the Outer wall ofthe latter may form the inner wall 
Of the constricting gas plenum. 
BRIEF DESCRIPTION OF THE DRAWINGS 
The particular features and advantages of the inven- 
tion as well as other objects will apparent from 
the following description taken in connection with the 
accompanying drawings in which: 
is a cross sectional view of a manual plasma FIG, 
ket the area Of arc plasma On the work- 45 arc welding torch head incorporating constricting gas 
piece to avoid Of the Po'. An ex- supp1y apparatus constructed in accordance with the 
ample of plasma arc welding apparatus is illustrated in 
U.S. Pat. No. 3,612,807. 
One of the main advantages of the plasma arc is the 
directional stability and focusing effect brought about 50 
by arc constriction. This constriction narrows the arc DESCRIPTION OF THE PREFERRED 
column into an extremely dense energy source. How- EMBODIMENT 
ever, upon exiting the orifice, the arc column begins to plasma 
flare and become larger in diameter due to the absence arc welding torch 10 incorporating the principle of the 
Of a Constricting mechanism. Thi: effects a decTease in 55 present invention is illustrated in FIG. 1, the torch hav- 
the energy density of the arc Pnor to contacting the ing a handle 12 for holding by an operator. Torches for 
workpiece and thus reduces the effectiveness and e a -  mechanized and automated plasma arc welding appara- 
ciency of the process. tus are similar to manual torches except for the handle 
portion and are intended to be included within the SUMMARY OF THE INVENTION 
It is a primary object of the present invention to pro- The torch 10 includes a high temperature melting 
vide apparatus for constricting the arc column exiting p i n t  electrode 14, such as tungsten, secured within the 
the nozzle of plasma arc welding apparatus to harness body or head 16 of the torch by means of an insulated 
the energy from the electric arc more effectively than in collet 18 so that the electrode is insulated from the 
the prior art. 65 body. Electrical power, either alternating current or 
It is another object of the present invention to pro- direct current, may be supplied from a source 20 
vide a constricting force upon the arc exiting from the through electrical leads 19, 21 between the workpiece 
orifice of the constricting nozzle of plasma arc welding W and the electrode as is conventional. A plenum 
principles of the present invention; and 
outlet end of the torch illustrated in FIG. 1. 
FIG. 2 is an enlarged cross sectional view of the 
Referring to the drawings, a typical 
60 scope of the present invention. 
3 
5,302,804 
chamber 22, as best illustrated in FIG. 2 is formed 
within the torch head spaced between the electrode 14 
and the inside wall 24 of a constricting nozzle body 26, 
generally formed from copper alloy. The plenum cham- 
ber communicates with a passageway 28 extending 5 
through the body of the torch and the handle 12. An 
inert gas such as argon is supplied to the passageway 28 
and flows into the plenum chamber 22 about the elec- 
trode to provide a protecting atmosphere and exits the 
nozzle body 26 through a small orifice 30 in the front of 10 
the electrode. As the orifice gas passes through the 
plenum chamber, 22 it is heated by the arc, expands and 
exits through the nozzle orifice 30 at an accelerated 
rate. The arc is columnated into an extremely dense 
energy source and focused by the constricting nozzle on 
a relatively small area of the workpiece W. This gas, 
known as the orifice gas, supplies the necessary atmo- 
sphere for allowing electrical transfer of the arc across 
the gap between the electrode and the workpiece, and 
becomes ionized in the arc to form the Dlasma which 2o 
issues from the orifice as the plasma jet. 
Another passageway 32 is formed within the torch 
body 16 and the handle 12 and communicates with a 
chamber 34 formed between the nozzle body 26 and an 
outer wall or cup 36. The passageway 32 is supplied 
with a shielding gas, which may be an inert gas, such as 
argon, to blanket the area of arc plasma impingement 
upon the workpiece to provide a total inert atmosphere 
at the weld zone to prevent contamination. However, 
the shielding gas does not constrict the arc column so 
that after the arc column issues from the orifice 30 it 
becomes larger in diameter and, as it does, the energy 
density is reduced prior to contact with the workpiece. 
Although not illustrated, a coolant such as water may 
be circulated through the torch to cool and dissipate the 
heat generated in the constricting nozzle. 
In order to prevent or reduce the tendency of the arc 
from enlarging in diameter after it has exited the nozzle 
orifice 30 which, as aforesaid, decreases the energy 
density of the arc, the present invention provides an 
external constricting force on the arc downstream of 
the orifice. To this end an arc constricting inert gas such 
as argon, is directed circumferentially about the arc 
externally of the nozzle orifice. Thus, an additional 
plenum chamber 38 is formed about the torch body 
externally of the shielding gas chamber 34 and commu- 
nicates with a passageway 40 formed within the torch 
body 16 and the handle 12, the passageway 40 receiving 
the inert gas. 
The plenum chamber 38 may be formed between the 
wall or cup 36 about the shielding gas plenum 34 and an 
additional external wall or cup 42. The forward ends of 
the cups 36 and 42 are disposed forwardly of the nozzle 
26 and are directed radially inwardly relative to the 
center of the torch, Le., toward the axis of the orifice 30 
and terminate in a circumferentially extending joining 
wall 44 spaced radially from the axis of the orifice 30, 
the wall 44 providing a closure for the plenum chamber 
38. Formed within the circumferential wall 44 and com- 
municating with the plenum chamber 38 are a plurality 
of spaced apart apertures or orifices 46 which direct the 
gas within the chamber 38 to impinge upon the arc 48. 
By controlling the pressure and flow of gas through the 
constricting gas plenum chamber 38, and by proper 
sizing of the orifices 46, the velocity of the gas and thus 
the force applied on the arc may be controlled to forci- 
bly constrict the arc into a narrow dense column and 
25 
30 
35 
40 
45 
50 
55 
60 
65 
4 
retain the density of the arc column after exiting the 
nozzle orifice 30. 
Consequently, the invention more efficiently har- 
nesses the energy of the arc than conventional plasma 
arc welding apparatus and permits a narrower weld 
bead and heat effected zone. Additionally, the narrower 
denser arc column aids in maintaining symmetry to the 
dimensional shape of the arc alleviating asymmetrical 
weld bead shapes and related defects. This latter advan- 
tage may result in a reduction or elimination of the need 
for torch rotation during the welding process and result 
in the process being less operator dependent. 
Numerous alterations of the structure herein dis- 
closed will suggest themselves to those skilled in the art. 
For example, the invention may be applied to gas tung- 
sten arc welding apparatus which conventionally has no 
arc constructing mechanism. However, it is to be under- 
stood that the present disclosure relates to the preferred 
embodiment of the invention which is for purposes of 
illustration only and not to be construed as a limitation 
of the invention. All such modifications which do not 
depart from the spirit of the invention are intended to be 
included within the scope of the appended claims. 
Having thus set forth the nature of the invention, 
what is claimed herein is: 
1. A plasma gas arc welding torch, comprising 
a. an annular nozzle body having a first orifice in a 
front end of the body and an axially extending first 
plenum chamber formed within said nozzle body in 
communication with said orifice, said first orifice 
having an axis, 
b. an axially extending electrode disposed within said 
chamber in alignment with said first orifice, 
c. means connected to the electrode for supplying 
electricity to the.electrode to form an arc extend- 
ing from the electrode through the first orifice to a 
workpiece positioned in front of the torch, 
d. a second plenum chamber formed by and between 
a pair of spaced inner and outer cups surrounding 
the forward end of the nozzle body, said cups hav- 
ing forward ends extending beyond the forward 
end of the nozzle body, the forward ends of the 
cups being directed radially inward toward the axis 
of the orifice and terminating in a circumferentially 
extending joining wall, said wall facing and being 
spaced from the axis of the orifice, said wall being 
provided with a plurality of spaced second orifices, 
said cups being spaced from the nozzle body to 
form a third plenum chamber between the nozzle 
body and the inner cup, said third plenum chamber 
having an annular third orifice surrounding the 
first orifice, said torch having therein a first pas- 
sageway for feeding an inert gas to the first plenum 
chamber to form a plasma exiting from said nozzle 
through said first orifice, said torch having a third 
passageway for feeding an inert gas through the 
third plenum chamber to exit from the third orifice 
and form a column of blanketing gas surrounding 
said plasma, said torch having a second passage- 
way for feeding an inert gas through the second 
plenum chamber to exit through said second ori- 
fices in the joining wall and impinge on the column 
of gas to constrict said column of gas. 
2. In a welding torch as recited in claim 1, wherein 
said first orifice has a smaller cross sectional area than 
said first plenum chamber, whereby inert gas exiting 
from said first orifice increases in velocity. * * * * *  


Gas arc constriction for plasma arc welding

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