METHOD AND DEVICE FOR WOLFRAM INERT GAS WELDING

Description

[0001] The invention relates to a method and a welding torch for tungsten inert gas welding, wherein an arc burns between a non-consumable electrode and a workpiece, wherein the electrode has a cavity inside and wherein an electrically conductive filler material is supplied through the cavity of the electrode in the direction of the workpiece. State of the art

[0002] Tungsten inert gas (TIG) welding is an arc welding process used, for example, for surfacing, welding, or brazing one, two, or more workpieces made of metallic materials. The workpiece and a tungsten electrode of a suitable TIG welding torch are electrically connected to a welding power source. An electric arc burns between the tungsten electrode and the workpiece. The workpiece is at least partially melted, forming the weld pool. The tungsten electrode is typically used as the cathode and the workpiece as the anode, with electrons transferring from the tungsten electrode into the workpiece.

[0003] Unlike metal inert gas (MIG) welding, the tungsten electrode does not melt in tungsten inert gas (TIG) welding. The melting of a wire electrode in a welding torch during MIG / MAG welding can lead to overheating and vaporization of this electrode, releasing large quantities of harmful emissions in the form of welding fumes. Welding fumes consist of particulate pollutants (mostly metal oxides) that are inhalable, respirable, toxic, and / or carcinogenic. Such emission particles are particularly harmful to the health of a welder.

[0004] In metal inert gas (MIG) welding, molten droplets from the wire electrode transfer into the weld pool. The consumable wire electrode acts simultaneously as the filler material and as the arc carrier. In tungsten inert gas (TIG) welding, however, a filler material must be added (see, e.g., US 5,994,659 A). This filler material (e.g., wire-shaped) is introduced laterally into the arc. This melts the filler material. Molten droplets of the filler material detach and transfer into the weld pool. This process of melting the filler material, droplet formation, droplet detachment, and droplet interaction with the workpiece is called material transfer.

[0005] In metal inert gas (MIG) welding, a large portion of the energy required to melt the wire electrode is supplied by electrons that transfer from the electrode into the workpiece. This energy supplied by the electrons is called condensation. This energy is transferred over a relatively small area (namely, the arc base) and contributes significantly to the superheating and vaporization of the wire electrode, and thus to the release of particulate emissions.

[0006] Since the filler material is introduced into the arc without current during tungsten inert gas (TIG) welding, it is heated only by conduction and convection. Condensation, i.e., energy introduced by electrons, does not occur in TIG welding. Therefore, overheating and vaporization of the filler material are either nonexistent or minimal in TIG welding.

[0007] Tungsten inert gas (TIG) welding thus has the advantage over metal inert gas (MIG) welding in that only a very small amount of emissions is released and, in particular, hardly any welding fumes are produced, even when filler material is added externally. On the other hand, TIG welding has the disadvantage compared to MIG / MAG welding that the melting of the filler material occurs with lower efficiency or a lower deposition rate than in MIG / MAG welding. Furthermore, due to the lack of current flow through the filler material, electromagnetic forces such as Lorentz forces cannot be generated. Such electromagnetic forces promote the detachment of molten droplets in current-carrying filler materials, a phenomenon known as "pinching." Since the filler material, which is usually wire-like, is typically fed laterally to the arc, the rotational symmetry of the welding torch is also lost.

[0008] The tungsten electrode used in tungsten inert gas welding can, for example, be designed as a hollow electrode or hollow cathode. Such a hollow electrode has a cavity inside. In particular, this cavity extends over the entire axial dimension of the hollow electrode.

[0009] Such a hollow electrode is known, for example, from EP 2 457 681 A1. This patent describes how a filler material can be fed through the hollow electrode cavity for tungsten inert gas welding. While this overcomes the disadvantage of the lack of rotational symmetry, the disadvantages of low filler material melting efficiency and / or lower melting rate remain.

[0010] Furthermore, the melting of the filler material is made more difficult, particularly with hollow electrodes, because the cavity in the hollow electrode also leads to a lower axial energy density in the arc. Moreover, no electromagnetic forces occur with such a filler material, and no energy is introduced from electrons.

[0011] The invention is therefore based on the objective of improving the supply of filler material in tungsten inert gas welding and carrying it out with higher efficiency. Disclosure of the invention

[0012] This problem is solved by a method for tungsten inert gas welding and a welding torch for tungsten inert gas welding with the features of the independent claims. Advantageous embodiments are the subject of the respective dependent claims and the following description.

[0013] In a tungsten inert gas welding process according to the invention, an electric arc burns between a non-consumable electrode and a workpiece. The electrode has a cavity inside, and an electrically conductive filler material is fed through this cavity towards the workpiece. This filler material is then energized.

[0014] The electrode with the cavity inside is referred to as a hollow electrode in the following description. The filler material is, in particular, wire-shaped. Specifically, the filler material is electrically insulated from the hollow electrode.

[0015] The electrode can be used as the cathode, and the workpiece as the anode. It is also possible to use the electrode as the anode and the workpiece as the cathode. The electrode is used as the cathode particularly when it is made of tungsten, hafnium, or tungsten with dopants (such as cerium, thorium, lanthanum, and / or other rare earth elements). The electrode is used as the anode particularly when it is made of copper or copper with such dopants or inserts. Advantages of the invention

[0016] By applying an electric current to the filler material, it is heated or preheated, particularly to a temperature of approximately 600°C or more (up to about 1000°C). With a conventional hollow electrode, the filler material is supplied to the welding process essentially at room or ambient temperature. The filler material must first be heated by the arc or by the arc's thermal effects (conduction and convection) until it melts. In contrast, according to the invention, the filler material is preheated before being supplied to the welding process. The current flow, or rather the electrons, already supply a large portion of the energy to the filler material (condensation). Only a small amount of energy needs to be supplied to the filler material by the arc to enable its melting.

[0017] The flow of current through the additive material, combined with its electrical resistance, causes the additive material to heat up. This heating is known as Joule heating. Joule heating significantly influences the formation of droplets of the additive material and the temperature of these droplets. The invention allows the Joule heating of the additive material to be deliberately utilized.

[0018] The invention improves the feeding of the filler material through the cavity of a hollow electrode in such a way that the melting of the filler material occurs with high efficiency. Molten droplets of the filler material can thus be easily formed and detach at a high frequency, transferring into the melt pool. This allows the entire material transfer to be carried out with high efficiency. The melting rate is increased. Furthermore, the penetration, i.e., the amount of energy transferred into the workpiece, can be increased.

[0019] The invention combines the advantages of metal inert gas (MIG) welding and tungsten inert gas (TIG) welding. The advantages of MIG welding—namely, highly efficient material transfer, high deposition rate, and deep penetration—can also be utilized for TIG welding. However, in TIG welding according to the invention, the filler material does not vaporize. Therefore, no or virtually no harmful emissions in the form of welding fumes are released. Furthermore, the supply of the filler material within the hollow electrode enables rotational symmetry in TIG welding according to the invention and in the welding torch according to the invention.

[0020] Furthermore, the advantage of tungsten inert gas welding is retained, namely that the deposition rate is decoupled from the energy input into the workpiece and can be variably adjusted. This is made possible in particular by a variable feed rate or wire feed rate and an adjustable current supply to the filler material.

[0021] Advantageously, the electrode is energized with a welding current. The filler material is heated with a separate heating current, independent of or in addition to the welding current. The current intensities of the heating current and the welding current are set independently of each other. The filler material is electrically insulated from the hollow electrode. The welding current controls the arc, while the heating current controls the preheating of the filler material. Therefore, the preheating of the filler material can be set and carried out independently of the arc. The preheating of the filler material can thus be flexibly adjusted. In particular, the heating current is adapted to the wire feed rate, the diameter, and / or the material of the filler material.

[0022] Preferably, the heating current or its intensity is regulated or controlled as a function of the temperature of the filler material. The temperature of the filler material is measured, for example, using a sensor such as a thermocouple or a pyrometer. Alternatively or additionally, the temperature of the filler material can also be determined by the heating voltage of the heating current source applied to the filler material. The current applied to the filler material is thus regulated or controlled in such a way that a desired temperature of the filler material is reached and the filler material is therefore preheated at a constant temperature.

[0023] According to a preferred embodiment of the invention, the filler material is electrically connected to current contact points of a heating current source and then inserted into the hollow electrode. The heating current is applied to the wire electrode at these current contact points. In particular, the filler material is first energized by the heating current until it reaches the desired temperature. Only when the filler material has reached this desired temperature and is thus sufficiently preheated is it inserted into the hollow electrode.

[0024] Preferably, the distance between the electrical contact points is varied. In particular, the electrical contact points are designed such that their positions on the filler material relative to each other can be changed. For example, such electrical contact points are designed as roller or sliding contacts. Alternatively or additionally, the current supplied to the filler material, in particular the heating current, is preferably varied. By means of this distance between the electrical contact points or this current, the preheating or temperature of the filler material can be flexibly adjusted. In particular, the distance and / or the current are adjusted such that the filler material does not overheat and does not evaporate.

[0025] Preferably, the Joule heating of the additive material is influenced or adjusted. According to Joule's law, the heat generated at an electrical resistor is proportional to the electrical power dissipated at the resistor and a corresponding time period. Joule heating is defined as heat energy per unit time, which arises from continuous losses of electrical energy in a conductor due to the current and the resistance per unit length (electrical resistance of the conductor relative to its length).

[0026] A free wire length can be determined using the electrical contact points. l This free wire length can be adjusted. l The distance between the electrical contact points is particularly important. This free wire length is used to determine this distance. l can be caused by the heating current (with the current intensity) I ) converted electrical power Pthe additive material is adjusted according to the following formula: P = I 2 R = I 2 ρ l A

[0027] This is A the cross-sectional area of ​​the filler material. It is particularly suitable to use a wire-shaped filler material. ρ is the specific electrical resistance of the additive material.

[0028] The Joule heating Δ W over a period of time Δ t This electrical power results in: Δ W = P Δ t = I 2 ρ l A Δ t

[0029] Preferably, the filler material is energized in relation to the wire feed rate. As the filler material melts, it must be fed forward. A wire-like filler material, fed at a (preferably variable) feed rate, is particularly suitable. The preheating of the filler material is thus coupled with the wire feed rate. Especially for manual welding, the heating current is automatically adjusted to the wire feed rate. The welder only needs to set the wire feed rate; the current is adjusted automatically.

[0030] The wire feed can be further adjusted, particularly depending on the welding speed and / or the gap size or width of the workpiece. The gap size or width of the workpiece describes the volume to be filled with the melted filler material. The volume of filler material to be melted is thus adjusted to the volume to be filled.

[0031] In particular, the current applied to the filler material can be increased by increasing the feed rate. The heating of the filler material is kept constant, and the droplets detach from the filler material at a higher frequency. Thus, the filler material can be advanced at a higher feed rate. Conversely, if the feed rate is reduced, the current can be decreased.

[0032] According to a preferred embodiment of the invention, the feed rate of the filler material is varied such that an oscillating motion in the feed direction is superimposed on the feed rate. This variation of the feed rate induces an oscillation of the filler material. The feed rate of the filler material is therefore not continuous, but oscillating. This superimposed oscillating motion moves the filler material at a specific frequency both towards the workpiece and away from the workpiece in the opposite direction. In particular, the movement of the filler material away from the workpiece narrows the area between the droplet and the remaining, unmelted filler material. This facilitates the detachment of the droplet. The superimposed oscillating motion stimulates or actively supports the detachment of the droplets.To put it simply, the drops are "shaken off" by the superimposed oscillating movement of the additive material.

[0033] Preferably, the oscillation frequency of this (superimposed) oscillating motion of the additive material corresponds essentially to a natural frequency or resonance frequency of a droplet melting from the additive material. The superimposed oscillating motion of the additive material particularly excites the droplet to vibrate in the region of its natural frequency. This further supports or excites the detachment of the droplet. Preferably, the oscillation frequency of the (superimposed) oscillating motion of the additive material is between 350 Hz and 450 Hz, particularly 400 Hz.

[0034] It is advantageous to supply an additional gas to the filler material. In particular, the additional gas can be supplied through the cavity. The additional gas flows through the cavity towards the workpiece, specifically around or along the filler material. The additional gas exerts pressure on the filler material droplet and, moreover, reduces the surface tension of the droplet. This can stimulate or actively support the detachment of the droplets. Furthermore, the additional gas, especially an inert or reducing gas, can prevent oxidation of the heated filler material.

[0035] The filler gas can also be an active gas. Its composition and quantity can be varied, especially during the welding process. Oxygen, or a gas mixture containing oxygen, is particularly common as a filler gas. The oxygen primarily reduces the surface tension.

[0036] Oxidizing gases or oxidizing gas mixtures are supplied as additive gases, particularly via the heated additive material. Specifically, an oxidizing gas or gas mixture is separated from the electrode to prevent (immediate) electrode degradation. Preferably, a gas mixture of argon and oxygen (particularly with a maximum oxygen content of 10%) or a gas mixture of argon and carbon dioxide (particularly with a maximum carbon dioxide content of 20%) is supplied as the additive gas.

[0037] Argon, a gas mixture of argon and hydrogen (in particular with a maximum hydrogen content of 10%), a gas mixture of argon and nitrogen (in particular with a maximum nitrogen content of 10%) or a gas mixture of argon and helium (in particular with a maximum helium content of 90%) is preferably used as an additional gas.

[0038] In particular, a shielding gas is supplied to the welding process. The welding torch includes a suitable shielding gas nozzle for this purpose. The additional gas is supplied to the filler material in addition to and independently of the shielding gas.

[0039] The invention further relates to a welding torch for tungsten inert gas welding. Embodiments of this welding torch according to the invention are described analogously in the above description of the inventive method.

[0040] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.

[0041] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0042] The invention is schematically illustrated in the drawing using an exemplary embodiment and is described in detail below with reference to the drawing.

[0043] Brief description of the drawing Figure 1 shows a preferred embodiment of a welding torch according to the invention for tungsten inert gas welding. embodiment(s) of the invention

[0044] In Figure 1Figure 100 schematically shows a preferred embodiment of a welding torch according to the invention for tungsten inert gas welding. The welding torch 100 is configured to carry out a preferred embodiment of a method according to the invention. By means of the welding torch 100, a first workpiece 151 is welded to a second workpiece 152 by means of a joining process.

[0045] The welding torch 100 has an electrode 110 that tapers towards the side facing the workpiece. The electrode 110 is designed as a hollow electrode and has a cylindrical cavity 200 inside, which extends over the entire axial dimension of the electrode 110.

[0046] The first workpiece 151 and the hollow electrode 110 are electrically connected to a welding power source 140. The hollow electrode 110 is thus supplied with a welding current.

[0047] In this specific example, the hollow electrode 110 is made of tungsten and is used as the cathode. The first workpiece 151 is used as the anode in this specific example. It should be noted that the hollow electrode 110 can also be used as the cathode and the first workpiece 151 as the anode, for example, if the hollow electrode 110 is made of copper.

[0048] An electric arc 120 burns between the hollow electrode 110 and the first workpiece 151. The electric arc 120 melts the first and the second workpieces 151 and 152 at least partially, creating a melt pool 160.

[0049] The welding torch 100 also has a shielding gas nozzle 130 to supply a shielding gas in the form of a shielding gas flow to the welding process or in the direction of the arc 120 or in the direction of the weld pool 160, indicated by reference numeral 131.

[0050] An electrically conductive filler material 210 is fed into the welding process, in particular by a feed device 230. The filler material 210 is wire-shaped and is fed through the cavity 200 in the direction 230a of the first and second workpieces 151 and 152. The cavity 200 has electrical insulation 201 to electrically insulate the filler material 210 from the hollow electrode 110.

[0051] Before the filler material 210 is inserted into the hollow electrode 110, it is electrically connected to two electrical contact points 221 of a heating current source 220. The electrical contact points 221 are specifically designed as sliding contacts. The filler material 210 is supplied with a heating current via the electrical contact points 221 and the heating current source 220.

[0052] By applying a heating current to the filler material 210, the filler material 210 heats up. When the filler material 210, here wire, has reached a predetermined temperature of, for example, 600°C, the feed begins. The filler material 210 is inserted into the cavity 200 to such an extent that a tip 212 of the filler material 210 protrudes from the cavity 200 in the direction of the workpiece 151.

[0053] The electric arc 120 further heats the tip 212 of the filler material 210. This heating melts the filler material 210 at the tip 212. Thus, a molten droplet 211 of the filler material 210 is formed.

[0054] The droplet 211 ultimately detaches from the filler material 210, enters the molten pool 160, and forms a weld seam (joint between the workpieces 151 and 152). The formation of the droplet 211, its detachment from the filler material 210, and its transition into the molten pool 160 are referred to as material transfer.

[0055] The distance between the electrical contact points 221 is variable during the welding process. The electrical contact points can also be positioned in front of the cavity to improve accessibility. Both electrical contact points 221 can be moved independently of each other along the filler material 210, as indicated by the double arrow 221a. By adjusting the distance between the electrical contact points 221 and by adjusting the current of the heating current, the Joule heating of the filler material 210 is specifically controlled.

[0056] Joule heating is the heat energy per unit of time by which the additive material 210 is heated due to its electrical resistance and the heating current.

[0057] The feed device 230 allows the filler material 210 to be advanced or fed further into the cavity 200. One feed direction, in which a corresponding feed occurs, corresponds to direction 230a, which is directed towards the workpieces 151 and 152. The filler material 210 can, for example, be wound on a roll and unwound by the feed device 230.

[0058] The feed rate, i.e., the feed speed of the wire, can be advantageously varied by the feed device 230. In particular, the feed rate is varied such that an oscillating movement of the filler material 210 in the feed direction is superimposed on the feed. The filler material 210 oscillates both in and against the feed direction 230a. One frequency of this oscillation corresponds to a natural frequency of the droplet 211 and is, in particular, 400 Hz. The detachment of the droplet 211 is thus stimulated more strongly.

[0059] The welding torch 100 also has an additional gas supply 240 (only schematically indicated). An additional gas is supplied to the filler material 210 by means of the additional gas supply 240 in the form of an additional gas flow, indicated by the reference numeral 241. The additional gas flow 241 flows axially around the filler material 210 in the feed direction 230a. Gas flows onto the droplet 211 through the additional gas flow 241, thereby reducing the surface tension of the droplet 211 and further stimulating its detachment.

[0060] For example, a gas mixture of argon and oxygen with an oxygen content of 10% is supplied as an additional gas in the form of the additional gas flow 241. The additional gas flow is also separated from the hollow electrode 110 by the electrical insulation 201 between the filler material 210 and the hollow electrode 110, thus preventing damage to the hollow electrode 110 by the additional gas. Reference symbol list

[0061] 100 Welding torch 110 Electrode, hollow electrode 120 Arc 130 Shielding gas nozzle 131 Shielding gas flow 140 Welding power source 151 First workpiece 152 Second workpiece 160 Weld pool 200 Cavity 201 Electrical insulation 210 Wire-shaped filler material 211 Molten droplet 212 Tip 220 Heating power source 221 Current contact point, sliding contact 221a Double arrow 230 Feed device 230a Direction, feed direction 240 Supplementary gas supply 241 Supplementary gas flow

Claims

1. Method for tungsten inert gas welding, - an electric arc (120) arcing between a non-consumable electrode (110) and a workpiece (151), - the electrode (110) having an internal cavity (200), - an electrically conductive welding filler material (210) being fed through the cavity (200) of the electrode (110) in the direction (230a) of the workpiece (151), - the welding filler material (210) being energized, characterized in that - this cavity extends over the entire axial extent of the electrode (110).

2. Method according to claim 1, wherein the welding filler material (210) is energized on the basis of the feed rate, temperature and / or material of the welding filler material (210).

3. Method according to claim 1 or 2, wherein the electrode (110) is energized with a welding current and the welding filler material (210) is energized with a heating current independently of the welding current.

4. Method according to claim 3, wherein the heating current is controlled in a closed-loop or open-loop manner, on the basis of a temperature of the welding filler material (210).

5. Method according to any of the preceding claims, wherein the welding filler material (210) is electrically connected to current contact points (221) of a heating current source (220) and is then inserted into the cavity (200) of the electrode (110).

6. Method according to claim 5, wherein a distance between the current contact points (221) is changed.

7. Method according to any of the preceding claims, wherein a Joule heat of the welding filler material (210) is adjusted.

8. Method according to any of the preceding claims, wherein the feed rate of the welding filler material (210) is adjusted on the basis of a welding speed and / or a gap dimension of the workpiece(151).

9. Method according to any of the preceding claims, wherein a feed rate of the welding filler material (210) is varied such that an oscillating motion of the welding filler material (210) in the feed direction (230a) is superimposed on the feed rate.

10. Method according to claim 9, wherein an oscillation frequency of this oscillating motion of the welding filler material (210) corresponds substantially to a natural frequency of a droplet (211) melting off the welding filler material (210).

11. Method according to claim 9 or 10, wherein the oscillation frequency of this oscillating motion of the welding filler material (210) is between 350 Hz and 450 Hz, in particular 400 Hz.

12. Method according to any of the preceding claims, wherein an additional gas (240) is added to the welding filler material (210).

13. Welding torch (100) for tungsten inert gas welding, - comprising a non-consumable electrode (110), the electrode (110) having an internal cavity (200), - the welding torch (100) being designed to supply an electrically conductive welding filler material (210) through the cavity (200) of the electrode (110) in the direction (230a) of the workpiece (151), - the welding torch (100) being designed to energize the welding filler material (210). - characterized in that this cavity extends over the entire axial extent of the electrode (110).

14. Welding torch (100) according to claim 13, wherein the welding filler material (210) is electrically insulated from the electrode (110).

15. Welding torch (100) according to any of claims 13 to 14, having an additional gas supply (240), which is designed to supply an additional gas (241) to the welding filler material (210).