Note: Descriptions are shown in the official language in which they were submitted.
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Specification
A Method for Tungsten Shielded Welding
The invention relates to a method for tungsten shielded
welding, in particular tungsten inert-gas shielded welding,
or for plasma welding, wherein an electrode and a workpiece
are supplied with a welding current, wherein the electrode
is supplied as the anode and the workpiece as the cathode,
wherein an electric arc is initiated and burns between an
electric arc-side face of the electrode and the workpiece.
Prior Art
Tungsten shielded welding, in particular tungsten inert-gas
shielded welding (WIG welding), and plasma welding involve
a method for electric arc welding, for example which can be
used for build-up welding, welding or soldering one, two or
more workpieces made out of metallic materials. The workpiece
and a tungsten electrode of a corresponding torch for
tungsten shielded welding are here electrically connected
with a welding current source. An electric arc burns between
the tungsten electrode and the workpiece. The workpiece is
here at least partially melted, and there forms the weld
pool. In most materials, the tungsten electrode is used as
the cathode, and the workpiece as the anode, wherein
electrons pass from the tungsten electrode into the workpiece
based on the physical current direction.
Plasma welding is a special version of tungsten inert-gas
welding. In plasma welding, at least two independent gases
or gas mixtures are supplied. Firstly, a plasma gas (also
referred to as center gas) is used, which is (at least
partially) ionized by the high temperature and high energy
of the electric arc. As a consequence, the electric arc
generates a plasma. In particular argon or a gas mixture of
argon and shares of hydrogen or helium are used as the plasma
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gas. The outside gas here acts as a shielding gas. The use
of helium or a helium-containing gas mixture as the shielding
gas makes it possible to improve thermal conductivity and
increase the energy input into the workpiece. However, helium
is significantly more expensive by comparison to other
shielding gases, and not available everywhere. In comparison
to tungsten inert-gas welding, the disadvantage to plasma
welding is that a corresponding torch for plasma welding is
more complicated and expensive, and the larger torch detracts
from accessibility and handling. For this reason, plasma
welding can most often only be performed if automated.
Tungsten shielded welding most often utilizes rod-shaped
electrodes comprised of pure tungsten or tungsten with
additives of rare earth metals (e.g., lanthanum, cerium,
yttrium), zirconium and thorium. These additives are most
often present as oxides. The electrodes are sharply ground
on the tool side for cathodic polarization. The mentioned
additives in the tungsten reduce the work function of the
electrons, so that the electrodes supplied as cathodes can
be operated at very high currents.
Tungsten inert-gas welding or plasma welding with a
negatively polarized tungsten electrode can only be
conditionally used, if at all, for aluminum, aluminum alloys,
bronze, magnesium, magnesium alloys, titanium or other
materials that form high-melting oxides. The problem is that
these high melting oxides are not dissolved. For this reason,
the weld pool is hard to control, and it is difficult to
observe the weld pool formation under the oxide layer. There
is a danger of oxide inclusions. In addition, energy input
into the component is slight.
The polarity of the tungsten electrode and the workpiece can
be reversed by using the tungsten electrode as the anode and
the workpiece as the cathode. In this case, the electrons
pass from the workpiece into the tungsten electrode (physical
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current direction) These electrons exiting the workpiece or
a corresponding ion bombardment can dissolve an oxide layer
that forms or is present on the workpiece, thereby achieving
a cleaning effect. This cleaning effect makes it possible to
avoid oxide inclusions in the weld seam. In plasma welding
with tap hole, this effect is intensified by comparison to
tungsten inert-gas welding, for example, since the entire
flanks of the joining parts come into contact with the
plasma, and are effectively cleaned.
However, it is impossible or all but impossible to
effectively and economically polarize the tungsten electrode
as the anode in this way, since the capacity of the tungsten
electrode supplied as the anode, in particular the thermal
capacity and current carrying capacity, are highly limited.
For example, the current carrying capacity of a tungsten
electrode with a diameter of 3.2 mm typically measures
between 20 A and 35 A.
Despite these low amperages, there is still a danger that
the tungsten electrode will melt, and that melted material
will detach from the tungsten electrode. This can lead to a
destruction of the tungsten electrode and process
fluctuations on the one hand, and to contaminations of the
weld seam on the other, if melted material gets from the
tungsten electrode into the weld pool of the workpiece.
Such contamination produces defects in the weld seam that
can only be eliminated in a complex reworking process. The
low current carrying capacity, and hence the low welding
currents with which the tungsten electrode can be supplied,
most often make it possible to achieve only a slight energy
input into the workpiece. Therefore, the tungsten electrode
can most often only be polarized as the anode in this way
for very thin workpieces, or cannot be polarized at all due
to the potential danger of tungsten inclusions. In addition,
the welding speed is low.
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In order to increase the capacity of the electrode and
simultaneously achieve a good cleaning effect, tungsten
electrodes can be supplied with alternating current. For
example, the current carrying capacity of a tungsten
electrode with a diameter of 3.2 mm can be increased to
approx. 200 A. However, power sources that provide this type
of alternating current are very complicated and
significantly more expensive than corresponding direct
current sources. In addition, a strong acoustic burden is
placed on the operator when operating the tungsten electrode
with alternating current. Furthermore, more of a strain is
put on the eyes of the welder, since the intensity of
electric arc radiation continually varies due to the changing
welding current. Beyond that, alternating current operation
is also associated with the danger of the weld seam becoming
contaminated. In addition, the energy introduced into the
workpiece is reduced by comparison to a positively polarized
tungsten electrode.
Prior art does offer ways for improving the thermal capacity
of electrodes during tungsten shielded welding. However,
these options are not suitable for improving the current
carrying capacity of an electrode supplied as an anode during
tungsten shielded welding. The basic idea underlying these
concepts here most often has to do with efficiently
dissipating the large amount of heat that hits the electrode.
On the one hand, an attempt was made to improve cooling of
the electrode, as described in DE 42 34 267 Al, DE 42 05 420
Al, DE 29 27 996A1 or US 3 569 661 A, for example.
On the other hand, a high melting insert can be introduced
into a body made out of copper, and this insert can be cooled
with water, as described in US 4 590 354 or DE 10 2009 059
108 Al or DE 29 19 084 C2, for example. However, a
corresponding insert is here used as the cathode. Completely
different mechanisms are here at work than during use as the
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tungsten shielded welding, in which the tungsten electrode
is supplied as the anode.
A corresponding construction that is used as the anode is
described in EP 0 794 696 B1 or US 3 242 305, for example.
However, even these types of electrodes only exhibit a slight
current carrying capacity, and using these types of
electrodes at welding currents beyond the range of 20 A to
35 A ("high-current welding") is hardly possible, if not
impossible.
The reason why is that a good cooling of the electrode
supplied as the anode can lead to a point application of the
electric arc on the anode, which can result in very high
current densities, and thus to a destruction of the anode.
Once this type of point electric arc application has been
reached, anode material is evaporated, causing a self-
amplifying effect to arise. The electric arc encounters
especially favorable application conditions at the
evaporation site, and focuses energy input on this location.
Since the processes in the plasma take place faster than in
a solid by orders of magnitude, even good thermal conduction
and effective cooling are unable to prevent a destruction of
the anode.
For this reason, it is desirable to improve tungsten shielded
welding, in particular tungsten inert-gas welding or plasma
welding, with an electrode supplied as an anode, in
particular with an eye toward achieving an increased current
carrying capacity for the electrode, especially for high
current welding.
Disclosure of the Invention
This object is achieved with a method for tungsten shielded
welding, in particular for tungsten inert-gas welding or
plasma welding, having the features described herein.
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Advantageous embodiments are the subject of the following
description.
An electrode and a workpiece are supplied with a welding
current, where= the electrode is supplied as the anode, and
the workpiece as the cathode. An electric arc is initiated
between an electric arc-side face of the electrode and the
workpiece and burns there. According to the invention, an
energy density of the electric arc-side surface of the
electrode and/or an electric arc application of the electric
arc on the electric arc-side surface of the electrode are
influenced in a targeted manner. As explained further below
in detail, this makes it possible to significantly increase
the current carrying capacity of the electrode.
During tungsten shielded welding, one, two or more workpieces
made of metallic materials can be build-up welded, welded or
soldered, or subjected to surface treatment, for example.
In particular, a shielding gas is supplied while welding. A
corresponding welding torch in particular encompasses a
shielding gas nozzle for supplying the shielding gas. The
shielding gas directly influences the electric arc. A
composition of the shielding gas can directly influence the
efficiency of welding. In the case of a welding torch for
plasma welding, this plasma torch alternatively or
additionally encompasses a plasma gas nozzle for supplying
a plasma gas, which is at least partially ionized.
Advantages of the Invention
In particular, influencing the energy density and/or
electric arc application in a targeted manner avoids a point
application of the electric arc on the electrode. This
prevents high energy densities, in particular high current
densities, which can destroy the electrode. In addition, the
electrode is effectively cooled. As a consequence, a
destruction of the electrode can be prevented. In addition,
Date Recue/Date Received 2022-01-24
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electrode is effectively cooled. As a consequence, a
destruction of the electrode can be prevented. In addition,
contamination or defects in the weld seam can be prevented,
which can arise as the result of an extensively melted
electrode.
Since the invention makes it possible to prevent high energy
densities on the electrode and cools the electrode, the
capacity of the electrode used as the anode can be increased.
During tungsten shielded welding according to the invention,
the electrode can be supplied with a lot higher amperages
than is the case for conventional tungsten shielded welding.
As a consequence, a cleaning effect of the workpiece can
further be increased when using the electrode as the anode
and the workpiece to be welded as the cathode. This causes
an oxide layer that might have formed on the workpiece to
dissolve with a high efficiency.
Therefore, the invention makes it possible to increase a
current carrying capacity of the electrode supplied as the
anode during tungsten shielded welding. The invention allows
the electrode to be operated with welding amperages of up to
500 A. As a consequence, in particular a high current welding
is carried out, and the electrode is used in particular as
a high current anode. The electrode is preferably supplied
with a welding current having an amperage of between 80 A
and 500 A. Therefore, the invention enables a high current,
positively polarized tungsten shielded welding, during which
the anode can also be operated at high welding amperages.
The invention makes it possible to achieve a high energy
input into the workpiece wired as the cathode. This high
energy input is caused in particular by high drop voltages
in the cathode drop area, as well as by the energy input by
way of ions. In addition, a high welding speed and deep weld
penetration can be achieved. Even comparatively thick
workpieces or components can be economically welded using
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the invention. Inclusions of oxides or electrode material in
the workpiece can be avoided, since the surface of the
workpiece wired as the cathode is effectively cleaned, and
the electrode wired as the anode is not melted by the high
thermal capacity.
A Lorentz force acting on the electric arc depends especially
on the diameter of the electric light application on the
anode and cathode (i.e., on the electrode and workpiece).
The Lorentz force brings about a stability of an electric
arc flow. In particular, this electric arc flow denotes a
flow of energy between the electrode and workpiece, and is
crucial for the stability of the process. The more stable
and stronger this electric arc flow to the workpiece, the
higher the energy input into the workpiece, and the more
uniform the formation of the weld seam. In particular,
influencing the energy density and/or electric arc
application in a targeted manner can amplify this flow,
thereby increasing the energy input into the workpiece to be
welded and improving process stability.
In particular, the invention makes it possible to reliably
and efficiently weld light metals like aluminum, aluminum
alloys, magnesium, magnesium alloys, titanium or other
materials, for example bronze. This is enabled in particular
by the high energy input of a high current electric arc into
the workpiece wired as the cathode.
In a first advantageous embodiment of the invention, the
energy density and/or electric arc application are
influenced in a targeted manner by choosing or using a
material for a selected region of the electric arc-side
surface of the electrode that differs from an electrode
material of the remaining electrode. In particular, the
electric arc-side surface of the electrode consists
partially of the electrode material and partially of this
material differing from the electrode material.
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This selected region can be used to influence the application
of the electric arc in a targeted manner. In particular, the
electric arc is applied directly to this region. In
comparison to the electrode material, the material of the
selected region or physical properties of this material (in
particular the melting point, boiling point, electrical and
thermal conductivity as well as work function) are selected
in such a way that electric arc application favors this
selected region. This is achieved in particular by virtue of
the fact that the physical and geometric properties of this
material are adjusted to the amperage. In particular, the
physical and geometric properties are selected in such a way
that the material is melted to a maximally marginal extent,
but uniformly. This avoids the danger of a point application
of the electric arc on the electrode itself, and the
resultant melting of the electrode. Since electric arc
application favors the selected region, the electrode is not
heated as intensively as an electrode during conventional
tungsten shielded welding. This makes it possible to prevent
the destruction of the electrode along with contaminants or
defects in the weld seam caused by an intensively melted
electrode.
The material of the selected region that differs from the
electrode material is preferably chosen as a function of an
amperage of the welding current. A diameter of the selected
region is preferably chosen as a function of an amperage of
the welding current. In particular, a larger diameter is
used for higher amperages. In particular, smaller diameters
are used for materials with a lower work function. In
particular, the electric arc is not applied pointwise, but
rather uniformly as a result, and the electrode is not
destroyed by excessively high energy densities.
A high melting material is preferably used as the material
for the selected region. In particular, a higher melting
material than the electrode material, further in particular
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a higher melting refractory metal is chosen as the electrode
material for the selected region. Since the electric arc is
applied in particular to the selected region, using a high
melting material can prevent the material of the selected
region from melting. As a consequence, the remaining
electrode made out of comparatively low melting material is
further prevented from melting.
Zirconium, carbon, rhenium, tantalum, yttrium, niobium,
hafnium, pure tungsten or tungsten with additives consisting
of rare earth metals (such as lanthanum, cerium, and
yttrium), zirconium and/or thorium are preferably used as
the material for the selected region. These additives in
tungsten are present in particular as oxides.
When using hafnium, active gases like carbon dioxide or
oxygen can especially advantageously also be used as the
shielding gas, without the electrode being destroyed. During
conventional tungsten shielded welding, the electrode would
be destroyed due to the high oxygen affinity of active gases.
In an advantageous embodiment of the invention, the material
for the selected region is used in the form of an insert in
the electric arc-side surface of the electrode. Accordingly,
use is made in particular of an electrode that exhibits at
least one insert made out of the material differing from the
electrode material. In particular, this insert is introduced
into the electrode in such a way that the insert is situated
at least partially on the electric arc-side surface of the
electrode. The electric arc-side surface of the electrode is
thus comprised partially of the electrode material and
partially of the material of the insert, but can also consist
entirely of a high melting material. The insert can here
protrude out of the electrode, or form a closed surface with
the remaining electrode.
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The insert can here be designed with a suitable geometric
shape, for example cubical, square or cylindrical. In
particular, this insert can extend over the complete axial
extension of the electrode. In particular, the insert can
further have only a limited extension in the axial direction
of the electrode, and thus be situated only indirectly on
the electric arc-side surface of the electrode, for example.
In particular, the diameter, work function and melting point
of the insert are adjusted to the amperages of the welding
current to be achieved. In particular, these parameters are
adjusted in such a way as to uniformly heat the insert during
operation over the entire corresponding part of the electric
arc-side surface of the electrode.
In a second advantageous embodiment of the invention, the
energy density and/or electric arc application are
influenced in a targeted manner by supplying a focusing gas
to the electric arc-side surface of the electrode in the
form of at least one focusing gas flow. In particular, the
focusing gas is supplied in addition to a shielding gas
and/or a plasma gas. In particular, the focusing gas is
supplied in the form of a focusing gas flow. Focusing the
electric arc is here understood to mean that the application
of the electric arc is focused or moved on the electric arc-
side surface of the electrode, i.e., constructed on a
specific region of the electrode or moved over a specific
surface. In particular, the quantity and composition of the
focusing gas can be varied. Argon, helium or a mixture of
argon and helium are preferably supplied as the focusing
gas.
The supplied focusing gas or focusing gas flow here exerts
a cooling effect on the electrode, in particular on the
electric arc-side surface of the electrode. The focusing gas
cools the electrode directly. In addition, the focusing gas
or the pulsed focusing gas flow exerts a pressure on the
electric arc, in particular on the electric arc application.
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As a consequence, the electric arc can be cooled in the edge
regions. This cooling effect, the exerted pressure along
with the physical and chemical properties of the focusing
gas influence the application of the electric arc.
Depending on how the focusing gas flow is directed relative
to the electrode or relative to the electric arc, the
application of the electric arc can be focused on the
electric arc-side surface of the electrode, and constricted
on a specific region. As a consequence, the focusing gas
also prevents the point application of the electric light on
the electrode, or on the region of the electrode with a low
melting point.
The focusing gas is preferably supplied in a targeted manner
around the or around the selected region of the electric
arc-side surface of the electrode in the form of the at least
one focusing gas flow. By combining the suitable choice of
the material differing from the electrode material for the
selected region and the supply of suitable focusing gas, the
electric arc is applied in particular distributed over the
entire selected region, and the material of the selected
region does not melt. In particular, the focusing gas is
supplied to the electric arc. The focusing gas is preferably
supplied on the electric arc application.
The focusing gas is preferably supplied in the form of the
at least one focusing gas flow as a turbulent flow. A
turbulent flow (also referred to as "swirl") is understood
to mean that the focusing gas flow expands spirally or
helically around an axis. This axis runs in particular in
the direction of the axial extension of the electrode,
further in particular in the direction of the expansion of
the electric arc. In particular, this axis corresponds to an
electric arc axis of the electric arc. In particular, the
turbulent flow is thus helically directed around the electric
arc. As a consequence, the direction of the turbulent flow
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consists of an overlap of a first direction tangential to
this axis and a second, axial direction parallel to this
axis.
In an advantageous embodiment, the focusing gas is supplied
through several focusing gas boreholes, wherein the
electrode exhibits these focusing gas boreholes for
supplying the focusing gas on its electric arc-side surface.
The focusing gas boreholes can here each exhibit varying
diameters, geometries and distances relative to each other.
Alternatively, the focusing gas boreholes can also be
identically designed and/or arranged equidistantly from each
other. In particular, the electrode exhibits at least four
focusing gas boreholes. In particular, the torch encompasses
a suitable focusing gas supply. In particular, the electrode
can be connected with this focusing gas supply. The focusing
gas supply is set up to supply the focusing gas through the
focusing gas boreholes.
In a third advantageous embodiment of the invention, the
energy density and/or electric arc application are
influenced in a targeted manner by discharging a gas from
the electric arc-side surface of the electrode. The gas is
here discharged from a specific region before the electric
arc-side surface of the electrode.
The electric arc heats the gas before the electric arc-side
surface of the electrode. This heated gas is discharged via
the gas discharge. In particular, the discharged gas is a
shielding, plasma or focusing gas. As a consequence,
shielding gas, which is also heated by the electric arc, can
be discharged. In particular, gas can also be centrally
supplied to generate a flow to the workpiece.
As a consequence, the gas that is heated by the electric arc
and other thermal effects and accumulates before the
electrode is discharged. This makes it possible to indirectly
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reduce the temperature of the gas before the electrode. Due
to such a diminished gas temperature before the electrode,
the electrode is not heated as intensively or can cool off
more easily. Discharging the gas indirectly cools the
electrode, and increases its thermal capacity.
In addition, local thermal fluctuations can thereby be
prevented from arising in the gas before the electrode. As
a consequence, electrodes can further be prevented from being
locally heated more intensively in some regions than in other
regions. The point application of the electric arc favors
these types of locally overheated regions on the electrode.
Therefore, discharging the gas also prevents a point
application of the electric arc.
The discharged gas is preferably supplied as a shielding
gas. As mentioned further above, in particular shielding gas
is discharged. In the process of being returned, this gas
can again be supplied as the shielding gas. This makes it
possible to increase the average temperature of the shielding
gas and energy input into the workpiece.
In an advantageous embodiment of the invention, the gas is
discharged from the electric arc-side surface of the
electrode through an axially running gas discharge borehole
in the electrode. The electrode is here designed in
particular as a hollow electrode. In particular, a
corresponding torch encompasses a gas discharge. This gas
discharge is set up in particular to discharge the gas from
the electric arc-side surface of the electrode through the
axially running gas discharge borehole of the electrode.
It is preferable to use an electrode made out of an electrode
material with a high thermal conductivity, preferably copper
and/or brass. It is especially preferable to use a mixed
alloy of copper and tungsten. As a consequence, the electrode
can be cooled very effectively, and additionally has a high
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melting point. Since the electric arc is applied in
particular to the selected region discussed above, the
electrode does not necessarily have to consist of a high-
melting material, and the electrode can still be prevented
from melting.
In an especially preferred embodiment of the invention, use
is made of an electrode that exhibits at least one insert
made out of the material differing from the electrode
material and/or that exhibits the focusing gas boreholes on
its electric arc-side surface for supplying the focusing gas
and/or that exhibits the at least one axially running gas
discharge borehole for discharging the gas from the electric
arc-side surface of the electrode.
The insert is advantageously located essentially in the
center of the electric arc-side surface of the electrode. In
particular, the insert here comprises the center or a tip of
the electrode.
The focusing gas boreholes are preferably arranged around
the center of the electric arc-side surface of the electrode.
In particular, the boreholes are arranged concentrically
around the center. As a consequence, the supplied focusing
gas focuses the application of the electric arc in particular
on the center of the electric arc-side surface of the
electrode.
The insert is preferably located essentially in the center
of the electric arc-side surface of the electrode, and the
focusing gas boreholes are preferably arranged around the
insert. On the one hand, the insert causes the electric arc
to be applied in the center of the electric arc-side surface
of the electrode. On the other hand, the electric arc
application is additionally focused on the center by the
focusing gas.
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The electrode preferably tapers toward its electric arc-side
surface. As a consequence, the electrode in particular
exhibits a "tip". The electrode thus exhibits no rectangular
or nearly rectangular edges between its electric arc-side
surface and a side or shell surface. Therefore, the electric
arc-side surface is slanted in relation to the shell surface,
i.e., inclined by a specific angle to the shell surface. As
a result, the electric arc application cannot rapidly skip
from the electric arc-side surface onto the shell surface of
the electrode.
Instead, the electric arc application can be shifted along
the (slanted) electric arc-side surface. It is especially
preferred that the insert here be located in the center of
the electric arc-side surface of the electrode, and at least
partially form the tip or tapered portion of the electrode.
In particular, the electric arc application is focused onto
this tip or onto the tapered portion by the insert and
focusing gas. The application surface can become larger as
amperage increases, so that the current density remains
nearly identical.
In an advantageous embodiment of the invention, the focusing
gas boreholes are designed in such a way that the supplied
focusing gas or focusing gas flow expands in the form of the
turbulent flow discussed above. Properties of the turbulent
flow, for example a radius of curvature, a pitch and/or a
gradient, can be set by configuring the focusing gas
boreholes and focusing gas supply. For example, the turbulent
flow properties are set by the number of focusing gas
boreholes, by a geometry of the individual focusing gas
boreholes, by an arrangement of the focusing gas boreholes
in relation to the axis, in particular by an eccentricity of
the focusing gas boreholes in relation to the axis, and/or
by an arrangement of the focusing gas boreholes in relation
to the workpiece.
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It is advantageous to arrange the insert in a hollow space
inside of the electrode, in particular in a cylindrical
hollow space. The largest possible shell surface is selected
between the insert and remaining electrode, so as to ensure
a good heat dissipation. In particular, the insert is
overmolded or sintered with the base body of the remaining
electrode, or pressed into the latter, in particular in a
manufacturing process.
The electrode preferably encompasses several inserts. A
first insert is here preferably located essentially in the
center of the electric arc-side surface of the electrode. At
least one additional insert is preferably arranged around
this first insert. In particular, the electric arc is here
applied to all inserts. This makes it possible to reduce the
load placed on the individual inserts.
A shielding gas is preferably suppled while welding. Argon,
helium or a mixture of argon, helium and/or oxygen and/or
carbon dioxide are preferably supplied as the shielding gas.
Accordingly, in particular pure argon, pure helium or a
mixture of argon and oxygen, of argon and helium or of argon,
helium and oxygen are supplied as the shielding gas.
In these mixtures, use is made in particular of oxygen shares
of between 150 ppm and 1%, as well as helium shares of
between 2% and 50%. Given a workpiece made out of high
alloyed steel, in particular a shielding gas comprised of
argon or helium and a respective share of up to 10% hydrogen
are supplied. During plasma welding, analogous mixtures are
used as the shielding gas. In addition, use is made in
particular of the plasma gas and focusing gas comprised of
the mentioned gas mixtures.
In particular, a corresponding torch encompasses a shielding
gas nozzle for supplying the shielding gas. The shielding
gas directly influences the electric arc. A composition of
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the shielding gas directly influences welding efficiency. In
the case of a welding torch for plasma welding, a
corresponding plasma welding torch alternatively or
additionally encompasses in particular a plasma gas nozzle
for supplying a plasma gas, which is at least partially
ionized.
In particular, influencing the energy density and/or
electric arc application in a targeted manner makes it
possible to reduce the share of helium in the shielding gas
or use an argon-oxygen mixture as the shielding gas. As a
consequence, tungsten shielded welding can also be
effectively used in locations with low helium resources. In
addition, the production outlay and costs to the user can be
reduced.
The electrode is advantageously cooled, in particular by
means of a water cooling device. As a result, the electrode
can be directly and/or indirectly cooled. This type of
indirect cooling is realized in particular over large contact
surfaces between the electrode and remaining welding torch.
Direct cooling is realized in particular by allowing cooling
water to flow against a wall or shell surface of the
electrode.
Additional advantages and embodiments of the invention may
be gleaned from the specification and attached drawing.
It goes without saying that the features mentioned above and
yet to be described can be used not just in the respectively
indicated combination, but also in other combinations or
alone, without departing from the framework of the present
invention.
The invention is schematically depicted in the drawing based
on an exemplary embodiment, and will be described in detail
below with reference to the drawing.
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Brief Description of the Drawings
Fig. 1 presents a schematic, side view of a welding torch
for tungsten shielded welding, which is set up to
implement a preferred embodiment of a method
according to the invention.
Fig. 2 presents a schematic, perspective view of an
electrode for a welding torch for tungsten
shielded welding, which is set up to implement a
preferred embodiment of a method according to the
invention.
Embodiment(s) of the Invention
Fig. 1 schematically depicts a welding torch marked 100 for
tungsten shielded welding, which is set up to implement a
preferred embodiment of a method according to the invention.
In this example, the welding torch 100 is designed as a
welding torch for tungsten inert-gas welding. The welding
torch 100 is used to weld a first workpiece 151 with a second
workpiece 152 in a joining process.
The welding torch 100 exhibits an electrode 200. The
workpieces 151 and 152 and the electrode 200 are electrically
connected with a welding current source 140. As a
consequence, the electrode 200 is supplied with a welding
current. The electrode 200 is here used as the anode, the
workpieces 151 and 152 as the cathode. An electric arc 120
is initiated between the electrode 200 and workpieces 151
and 152, and burns between the electrode 200 and workpieces
151 and 152. The electric arc 120 at least partially melts
the first and second workpieces 151 and 152, thereby
resulting in a weld pool 160.
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The welding torch 100 carries out high current welding, and
the electrode 200 is used as the high current anode. The
electrode 200 is here supplied with a welding current of
between 80 A and 500 A.
The welding burner 100 further exhibits a shielding gas
nozzle 130, so as to supply a shielding gas in the form of
a shielding gas flow to the welding process in the direction
of the electric arc 120 or in the direction of the weld pool
160, as denoted by reference number 131.
The electric arc 120 is applied to an electric arc-side
surface 202 of the electrode 200. A material that differs
from the electrode material of the remaining electrode is
used for a selected region of this electric arc-side surface
202.
To this end, the interior of the electrode 200 exhibits an
insert 210. The electrode is here made out of an electrode
material 201, and the insert 210 consists of a material 211
different than the electrode material 201. The insert
material 211 here has a higher melting point than the
electrode material 201. In this example, the electrode 200
is made out of copper 201, and the insert 210 out of tungsten
211.
In this example, the insert 210 extends over the complete
axial expansion of the electrode 200. The insert forms a
portion of the electric arc-side surface 202 of the electrode
200 in the selected region. The insert is here located in
the center of the electric arc-side surface 202. In addition,
the electrode 200 tapers toward its electric arc-side surface
202.
If the electrode 200 and workpieces 151 and 152 are
electrically connected with the welding current source 140,
the electric arc application favors the insert 210 consisting
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of tungsten 211, and less so the remaining electrode 200
made out of copper. As a consequence, an application 125 of
the electric arc 120 on the electrode 200 is influenced in
a targeted manner. In addition, the energy density of the
electric arc-side surface 202 of the electrode 200 is thereby
influenced in a targeted manner. In particular, the electric
arc 120 is applied directly to the insert 210, and hence in
the center of the electric arc-side surface 202.
The electrode 200 also exhibits focusing gas boreholes 220.
In the example on Fig.1, only two focusing gas boreholes 220
are shown for the sake of clarity. However, the electrode
200 preferably exhibits at least four, preferably six, eight,
ten, twelve or fourteen, focusing gas boreholes 220. The
focusing boreholes 220 are here arranged around the insert
210. The focusing gas boreholes 220 are connected with a
focusing gas supply 221. The focusing gas supply 220 is used
to supply a focusing gas in the form of a focusing gas flow
222 through the focusing gas boreholes 220 in the direction
of the electric arc 120. For example, focusing gas boreholes
220 can also be accommodated in other components of the
torch, e.g., the shielding gas nozzle. However, the effect
takes place at the anodic electric arc application.
In particular argon is here supplied as the focusing gas.
The focusing gas or focusing gas flow 222 focuses the
electric arc 120, in particular the electric arc application
125. The focusing gas or focusing gas flow 222 focuses the
electric light application 125 on the center of the electric
arc-side surface 202 of the electrode 200 (in addition to
the insert 210). In addition, the electrode 200, in
particular the electric arc-side surface 202 of the electrode
200, is cooled by supplying the focusing gas or focusing gas
flow 222. Furthermore, the energy density of the electric
arc-side surface 202 of the electrode is influenced in a
targeted manner as a result.
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The shielding gas can also be used for focusing by at least
partially directing it toward the electrode 220, for example
via screens. For this purpose, it is especially advantageous
for the welding torch 100 to be designed in such a way that
the electrode 200 protrudes out of the shielding gas nozzle
130. As a consequence, the electric arc 120 can be ignited
more easily, and accessibility and observability of the
process can be improved.
The focusing boreholes 220 are arranged in the electrode 200
in such a way that the focusing gas flow 22 forms as a
turbulent flow (also referred to as "swirl"). As a
consequence, the focusing gas flow 222 is directed around
the electric arc 120 as a spiral or helical shape 223.
In addition, the electrode 210 exhibits two axially running
gas discharge boreholes 230. The electrode 210 is hence
designed as a hollow electrode. In this example, the gas
discharge boreholes 230 run parallel to the insert 210. A
gas discharge borehole can also be formed in the insert 210.
The electric arc 120 or thermal effect of the electric arc
120 heats the supplied shielding gas. As a consequence,
heated shielding gas 132 accumulates before the electric
arc-side surface 202 (denoted by points). The gas discharge
boreholes 230 are connected with a gas discharge 231. The
gas discharge 231 discharges the heated shielding gas 132
from the electric arc-side surface 202, as denoted by
reference number 232.
Discharging the heated shielding gas 132 cools the electrode
200, in particular the electric arc-side surface 202 of the
electrode 200. As a consequence, the application 125 of the
electric arc 120 on the electrode 200 and energy density of
the electric arc-side surface 202 of the electrode 200 can
be influenced in a targeted manner.
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In addition, the discharged shielding gas 232 can be supplied
to the welding process anew through the gas discharge 231 as
a shielding gas or focusing gas 222. The returned shielding
gas is shown on Fig. 1 and denoted with reference number
233.
Fig. 2 presents a schematic, perspective view of another
electrode 200, which can be used to implement a preferred
embodiment of a method according to the invention. Identical
reference numbers on Fig. 1 and 2 denote structurally
identical elements.
The electrode on Fig. 2 exhibits an insert 210 and a
plurality of focusing gas boreholes 220. The insert is
located in the center of the electric arc-side surface 202
of the electrode 200. The focusing gas boreholes 220 are
here circularly arranged around the insert 210.
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Reference List
100 Welding torch
120 Electric arc
125 Electric arc application
130 Shielding gas nozzle
131 Shielding gas flow
132 Heated shielding gas
140 Welding current source
151 First workpiece
152 Second workpiece
160 Weld pool
200 Electrode
201 Electrode material, copper
202 Electric arc-side surface
210 Insert
211 Insert material, tungsten
220 Focusing gas borehole
221 Focusing gas supply
222 Focusing gas flow
223 Spiral shape, helical shape
230 Gas discharge boreholes
231 Gas discharge
232 Discharged shielded gas
233 Returned shielded gas
