AU2015291457A1

AU2015291457A1 - Electrode for a welding torch for tungsten gas-shielded welding and welding torch having such an electrode

Info

Publication number: AU2015291457A1
Application number: AU2015291457A
Authority: AU
Inventors: Erwan Siewert
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2014-07-15
Filing date: 2015-07-07
Publication date: 2017-01-19
Anticipated expiration: 2035-07-07
Also published as: EP3169473A1; CN107000103B; CA2954309C; HUE045749T2; ES2750786T3; WO2016008572A1; AU2015291458B2; AU2015291458B9; BR112017000740A2; DE102015001456A1; CN107073632A; BR112017000740B1; ES2750351T3; WO2016008573A1; CA2954309A1; CA2953731A1; EP3169473B1; AU2015291458A1; AU2015291457B2; BR112017000692A2

Abstract

The present invention relates to an electrode (200) for a welding torch (100) for tungsten gas-shielded welding, in particular for tungsten inert gas welding or for plasma welding, wherein the electrode (200) comprises at least one insert (210) composed of a material (211) different from the electrode material (201), wherein the insert (210) at least partially forms an arc-side surface (202) of the electrode, the electrode (200) has, on the arc-side surface thereof, a plurality of focusing-gas bores (220) for supplying a focusing gas (222) for focusing an arc (120), and the electrode (200) has at least one axially extending gas removal bore (230) for removing a gas (132) from the arc-side surface (202) of the electrode (200) through the axially extending gas removal bore (230).

Description

PCT/EP2015/001382 WO 2016/008572

SPECIFICATION

ELECTRODE FOR A WELDING TORCH FOR TUNGSTEN GAS-SHIELDED

WELDING AND

WELDING TORCH WITH SUCH AN ELECTRODE

The invention relates to an electrode for a welding torch for tungsten gas-shielded welding, in particular for tungsten inert-gas welding or plasma welding, as well as to a corresponding welding torch.

Prior Art

Tungsten gas-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 gas-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 1 generates a plasma. In particular argon or a gas mixture of argon and shares of hydrogen or helium are used as the plasma 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 gas-shielded welding most often utilizes rodshaped 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. 2

The polarity of the tungsten electrode and the workpiece can be reversed. (The tungsten electrode is then the anode and the workpiece is the cathode). In this case, the electrons pass from the workpiece into the tungsten electrode (physical 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 3 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.

Electrodes are most often fixed as a rod in the torch by means of a collet chuck, which is in turn indirectly cooled via the torch wall. Correspondingly, the electrode is fixed in place by clamping. The collet chuck is most often introduced from the side of the welding torch facing away from the workpiece.

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 more complex 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 gas-shielded welding. However, these options are not suitable for improving the current carrying capacity of an electrode supplied as an anode during tungsten gas-shielded welding. 4

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 physical mechanisms are here at work than during use as the anode. Therefore, inserts like these are unsuitable for tungsten gas-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 (which runs much more slowly by 5 comparison) and effective cooling are unable to prevent a destruction of the anode.

For this reason, it is desirable to improve tungsten gas-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 by an electrode for a welding torch for tungsten gas-shielded welding, in particular for tungsten inert-gas welding or plasma welding, as well as a corresponding welding torch with the features in the independent claims. Advantageous embodiments are the subject of the respective subclaims and the following description. A welding torch according to the invention for tungsten gas-shielded welding, in particular for tungsten inert-gas welding or plasma welding, exhibits an electrode according to the invention. The electrode according to the invention is in particular set up to be supplied as the anode, and is in particular designed as a high current anode. In particular, the anode is supplied with currents of between 80 A and 500 A. In particular, the welding torch is used for high current welding.

The welding torch according to the invention can be used for build-up welding, welding or soldering one, two or more workpieces made out of metallic materials. If the electrode and a workpiece to be welded are connected with a welding current source, an electric arc is initiated between the electrode and workpiece. This electric arc is applied to an 6 electric arc-side surface on the electrode. The electrode is preferably supplied as the anode.

In particular, the welding torch encompasses a shielding gas nozzle for supplying a 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.

In a first aspect according to the invention, the electrode exhibits at least one insert made out of a material differing from the electrode material. This insert at least partially forms the electric arc-side surface of the electrode. The 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.

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 7 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 electric arc-side surface of the electrode exhibits several focusing gas boreholes for supplying a focusing gas to focus an electric arc. The focusing gas is supplied in addition to the shielding gas and/or plasma gas. In particular, the focusing gas is supplied in the form of a focusing gas flow. Focusing the electric arc is here to be 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., constricted on a specific region of the electrode or moved over a specific 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 welding 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 particular, the focusing gas is supplied to a specific region before the electric arc-side surface of the electrode. In particular, the focusing gas is further supplied to the electric arc. 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.

In a third aspect according to the invention, the electrode exhibits at least one axially running gas discharge borehole for discharging a gas from the electric arc-side 8 surface of the electrode through the axially running gas discharge borehole of the electrode. The electrode is here designed in particular as a hollow electrode. In particular, a corresponding welding 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. 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 gas. As a consequence, shielding gas that is heated by the electric arc can be discharged via the gas discharge borehole. In particular, gas can also be centrally supplied to generate a flow to the workpiece.

Advantages of the Invention

The mentioned three aspects of the invention influences the respective application of the electric arc on the electric arc-side surface of the electrode in a controlled manner.

In particular a point application on the electrode is avoided. In addition, the energy density on the electrode is reduced by the three aspects. This reduces the loads acting on the electrode, in particular a thermal load. As a consequence, the invention increases a capacity of the electrode, in particular a thermal capacity and current carrying capacity.

The insert makes it possible to influence the application of the electric arc in a targeted manner. In particular, the electric arc is here applied directly to the insert. In comparison to the electrode material, the material of the insert or physical properties of this material (in 9 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 these physical properties of the insert are adjusted to the amperage. In particular, the physical properties are selected in such a way that the insert is melted to a marginal extent over the entire surface. 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 insert, the electrode is not heated as intensively as an electrode without an insert according to the invention.

This makes it possible to prevent the destruction of the electrode along with contaminants or defects in the weld seam caused by an otherwise intensively melted electrode.

In particular, the diameter of the insert is adjusted to the amperage of the welding current to be achieved. In particular, a larger diameter is used for higher amperages. In particular, comparatively smaller diameters are used for materials of the insert 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.

In addition, the application of the electric arc on the electric arc-side surface of the electrode is influenced in a targeted manner by supplying 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. As a consequence, the electric arc can be cooled in the edge regions. This cooling effect, the 10 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. A Lorentz force acting on the electric arc depends especially on the diameter of the electric arc 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. Since the invention prevents a pointwise application of the electric arc, the electric arc flow is also stabilized and in particular increased, thereby increasing the energy input into the workpiece to be welded and improving process stability.

Gas that is heated by the electric arc and other thermal effects and accumulates before the electrode is discharged through the gas discharge borehole. This makes it possible to indirectly 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. The gas discharge borehole 11 and discharging of 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, the electrode 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 via the gas discharge borehole also prevents a point application of the electric arc.

In particular, the invention is suitable for using the electrode as an anode in a welding torch. As mentioned at the outset, the capacity, in particular the thermal capacity and current carrying capacity, are traditionally limited when using the electrode as an anode in this way. Since the electrode is cooled by the invention, and a point application of the electric arc is prevented, the capacity of an electrode used as an anode can be increased. The electrode according to the invention can thereby be supplied with higher currents than conventional electrodes. 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 gas-shielded welding. The electrode according to the invention can be operated with welding amperages of up to 500 A. The electrode in the welding torch according to the invention is preferably supplied with a welding current having an amperage of between 80 A and 500 A. Therefore, the welding torch can be used in 12 particular for high current, positively polarized tungsten gas-shielded welding, during which the anode can also be operated at high welding amperages.

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.

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.

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 13 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.

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 surface covered by the electric arc depends on the amperage, and becomes larger as amperage increases, i.e., the electric arc application increases, so that the current density, and hence the energy density, remains nearly constant.

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 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 14 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 consists of an overlap of a first direction tangential to this axis and a second, axial direction parallel to this axis.

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.

The insert preferably consists of a high melting material, in particular a higher melting material than the electrode material, further in particular a higher melting refractory metal than the electrode material. Since the electric arc is applied in particular to the insert, using a high melting material can prevent the insert from melting. As a consequence, the remaining electrode made out of comparatively low melting material is further prevented from melting.

The insert preferably consists of 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. These additives in tungsten are present in particular as oxides. The insert can be fixed in place via pressing, sintering or overmolding. 15

When using hafnium as the material for the insert, active gases like carbon dioxide or oxygen can especially advantageously also be used as the shielding gas, without the electrode being destroyed. Electrodes consisting of tungsten in conventional welding torches would be destroyed due to the high oxygen affinity of active gases.

The electrode is preferably 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 melting point. Since the electric arc is applied in particular to the insert, the electrode does not necessarily have to consist of a high-melting material, and the electrode can still be prevented from melting. The mixed alloy can exhibit a graded progression from the electric arc-side surface to the welding torch side.

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. 16

The invention further relates to a welding torch for tungsten gas-shielded welding, in particular for tungsten inert-gas welding or plasma welding. Embodiments of this welding torch according to the invention may be analogously derived from the above description of the electrode according to the invention.

The welding torch preferably encompasses a shielding gas supply, which is set up to supply the gas discharged through the gas discharge borehole as a shielding gas or focusing gas. In particular, the shielding gas is supplied by means of a suitable shielding gas nozzle. As mentioned further above, in particular shielding gas is discharged through the gas discharge borehole. 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 .

The shielding gas supply can also supply a shielding gas or focusing gas independently of the discharged gas. Argon, helium or a mixture of argon, helium and/or oxygen are preferably supplied as the shielding gas or focusing 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 or focusing gas.

In these mixtures, use is made in particular of oxygen shares of between 50 ppm and 1%, as well as of 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 17 comprised of the mentioned gas mixtures. For example, a focusing gas can exhibit an oxygen content of 50 ppm to 3%.

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 welding torch advantageously encompasses a water cooling device, which is set up to directly and/or indirectly cool the electrode as a whole or the insert.

This type of indirect cooling is realized in particular over large contact surfaces between the electrode and remaining welding torch or the electrode holder. Direct cooling is realized in particular by allowing cooling water to flow against a wall or shell surface of the electrode.

In another preferred embodiment of the invention, the electrode is located in a holder, which accommodates the power cable and heat exchanger. The latter can especially advantageously be used in place of the conventional collet chuck.

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. 18

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.

Brief Description of the Drawings

Fig. 1 presents a schematic sectional view of a preferred embodiment of a welding torch according to the invention for tungsten gas-shielded welding.

Fig. 2 presents a schematic perspective view of a preferred embodiment of an electrode according to the invention for a welding torch for tungsten gas-shielded welding.

Fig. 3 presents both a schematic perspective (Fig. 3A) and sectional (Fig. 3B) view of another preferred embodiment of an electrode according to the invention for a welding torch for tungsten gas-shielded welding.

Embodiment (s) of the Invention

Fig. 1 schematically depicts a preferred embodiment of a welding torch according to the invention marked 100 for tungsten gas-shielded welding. 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 a preferred embodiment of an electrode 200 according to the invention. 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 19 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.

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 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 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 an electric arc-side surface 202 of the electrode 200. The electric arc 120 is applied to the electrode 200 on this electric arc-side surface 202. The insert is 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 of tungsten 211, and less so the remaining 20 electrode 200 made out of copper 201. As a consequence, an application 125 of the electric arc 120 on the electrode 200 can be influenced. 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.l, 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 arc 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.

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 21 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 222 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.

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. 22

Fig. 2 presents a schematic, perspective view of another preferred embodiment of the electrode 200 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 circularly arranged around the insert 210.

Fig. 3 presents a schematic, perspective view (Fig. 3A) along with a schematic, sectional view (Fig. 3B) of another preferred embodiment of the electrode 300 according to the invention.

The electrode on Fig. 3 exhibits an insert 310. In this case, the insert 310 represents the electric arc-side surface of the electrode itself. Focusing gas boreholes are not shown here. This conical configuration of the electrode 300 exhibits a "tip" 303. In particular, this configuration prevents the electric arc application from rapidly skipping onto the shell surface of the electrode 300. The insert 310 is here designed as an electric arc-side surface of the electrode, and forms aforesaid tip 303. The electric arc application is thereby focused onto this tip 303 of the electrode 300. The electric arc application onto the tip 303 of the electrode 300 becomes larger as amperage increases . 23

REFERENCE LIST 100 Welding torch 120 Electric arc 125 Application of electric arc 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 shielding gas 233 Returned shielding gas 300 Electrode 303 Tip 310 Insert 24

Claims

1. An electrode (200) for a welding torch (100) for tungsten gas-shielded welding, in particular for tungsten inert-gas welding or plasma welding, characterized in that - the electrode (200) exhibits at least one insert (210) made out of a material (211) differing from the electrode material (201), wherein the insert (210) at least partially forms an electric arc-side surface (202) of the electrode, - and/or the electric arc-side surface of the electrode (200) exhibits several focusing gas boreholes (220) for supplying a focusing gas (222) to focus an electric arc (120), - and/or the electrode (200) exhibits at least one axially running gas discharge borehole (230) for discharging a gas (132) from the electric arc-side surface (202) of the electrode (200) through the axially running gas discharge borehole (230) .

2. An electrode (200) for a welding torch (100) for tungsten gas-shielded welding, in particular for tungsten inert-gas welding or plasma welding, characterized in that - the electrode (200) exhibits at least one insert (210) made out of a material (211) differing from the electrode material (201), wherein the insert (210) at least partially forms an electric arc-side surface (202) of the electrode, - the electric arc-side surface of the electrode (200) exhibits several focusing gas boreholes (220) for supplying a focusing gas (222) to focus an electric arc (120), and that - the electrode (200) exhibits at least one axially running gas discharge borehole (230) for discharging a gas (132) from the electric arc-side surface (202) of the electrode (200) through the axially running gas discharge borehole (230) .

3. The electrode (200) according to claim 1 or 2, wherein the insert (210) is located essentially in the center of the electric arc-side surface (202) of the electrode (200).

4. The electrode (200) according to one of claims 1 to 3, wherein the focusing gas boreholes (220) are arranged around the center of the electric arc-side surface (202) of the electrode (200) .

5. The electrode (200) according to one of claims 1 to 4, wherein the focusing gas boreholes (220) are arranged around the insert (210) .

6. The electrode (200) according to one of the preceding claims, wherein the electrode (200) preferably tapers toward its electric arc-side surface (202) .

7. The electrode (200) according to one of the preceding claims, wherein the focusing gas boreholes (220) are designed in such a way that the supplied focusing gas (222) forms as a turbulent flow (223).

8. The electrode (200) according to one of the preceding claims, wherein the insert (210) consists of a high melting material (211) .

9. The electrode (200) according to one of the preceding claims, wherein the insert (210) consists of zirconium, carbon, rhenium, tantalum, yttrium, niobium, hafnium, tungsten or tungsten with an additive consisting of lanthanum, cerium, yttrium, zirconium and/or thorium or oxides thereof.

10. The electrode (200) according to one of the preceding claims, wherein the electrode (200) is made out of an electrode material (201) with a high thermal conductivity, in particular copper and/or brass, or out of a mixed alloy of copper and tungsten.

11. The electrode (200) according to one of the preceding claims, wherein the insert (210) is arranged in a hollow space inside of the electrode (200), in particular in a cylindrical hollow space.

12. The electrode (200) according to one of the preceding claims, wherein a first insert (200) is located essentially in the center of the electric arc-side surface (202) of the electrode, and wherein at least one additional insert is arranged around this first insert.

13. A welding torch (100) for tungsten gas-shielded welding, in particular for tungsten inert-gas welding or plasma welding, with an electrode (200) supplied as an anode according to one of the preceding claims.

14. The welding torch (100) according to claim 13, with a shielding gas supply set up to supply the gas (232) discharged through the gas discharge borehole (23) as a shielding gas (233) or focusing gas (220) .

15. The welding torch (100) according to claim 13 or 14, with a water cooling device set up to directly and/or indirectly cool the electrode (200) .