Welding torch

Abstract

The invention relates to a welding torch (10) comprising: - an electrode (11) which extends along a longitudinal axis (X) and is intended to form an electric arc with a part to be welded, the electrode comprising an internal duct (16) which opens at a free end, the internal duct being configured to circulate and then eject a protective gas, referred to as internal gas, via the free end; - a nozzle (12) which is arranged, preferably coaxially, around the electrode, the nozzle being configured to eject a protective gas, referred to as external gas, from the nozzle to the free end of the internal duct of the electrode; - flow adjustment means for ejecting an internal gas flow (Fint) having a composition and / or flow rate and / or pressure independent of that / those of the external gas ejection flow (Fext).

Description

[0001] WELDING TORCH

[0002] Technical field

[0003] The present invention relates to the field of gas-shielded arc welding torches, in particular TIG welding (the English acronym for “Tungsten Inert Gas”).

[0004] Gas shielded arc welding torches cover in particular the processes of families 13 (MIG / MAG), 14 (TIG / TAG) and 15 (Plasma) of the NF EN ISO 4063 standard.

[0005] Although the invention is described with reference to a TIG welding application, it can be considered for any other gas-shielded arc welding process.

[0006] Prior art

[0007] TIG welding processes, also called family 14 processes according to standard NF EN ISO 4063, use an electric arc between a non-fusible tungsten or tungsten alloy electrode and the workpiece to produce a weld.

[0008] Figure 1 illustrates a TIG welding method according to the prior art implemented by a TIG welding torch 1. Such a torch 1 comprises an electrode 2 made of tungsten or tungsten alloy and a nozzle 3 arranged around the electrode 2, coaxially therewith. The electrode 2 produces an electric arc E between the electrode 2 and the parts 4 a and 4b to be welded together. The electric arc E heats the parts 4 a and 4b to be welded, in order to create a molten pool 5 which, after the passage of the TIG welding torch 1, and its cooling, forms the weld 6, for example a weld bead. A flow of shielding gas F is ejected by the nozzle 3 towards the electric arc E. The flow of shielding gas F protects against oxidation of the electrode 2 and the parts 4 a and 4b, it also has a plasma function and cools the non-fusible elements of torch 1.

[0009] Generally, in a TIG process, material is supplied via a welding wire 7. In conventional TIG welding processes, the welding wire 7 is offset from the TIG welding torch 1, which complicates the handling of the torch 1 during welding. For example, during a manual TIG welding process, the welder must hold the TIG welding torch 1 in one hand and the welding wire 7 in the other hand. According to another example, during a robotic TIG welding process, at least one robot must perform large movements requiring high accelerations, particularly during curved trajectories, causing wear on said robot and reducing welding precision.

[0010] Patent applications WO2018 / 036122 A1, CN106312270 A, CN111266702 A and CN107186322 A each describe a TIG welding torch with a welding wire arranged and fed coaxially with the electrode. However, these TIG welding torches are particularly bulky, which complicates their use. In particular, their diameter is large near the electric arc generation zone. In addition, some of the TIG welding torches described by the aforementioned patent applications require an independent cooling system, which further increases the size and makes handling of said torches difficult.

[0011] There is therefore a need for a welding torch, particularly a TIG welding torch, which overcomes the above-mentioned drawbacks.

[0012] The aim of the invention is to respond, at least in part, to this(these) need(s).

[0013] Statement of the invention

[0014] To do this, the invention relates to a welding torch, comprising:

[0015] - an electrode extending along a longitudinal axis X and being intended to form an electric arc with a part to be welded, the electrode comprising an internal conduit opening out through a free end, the internal conduit being configured to circulate then eject a protective gas, called internal gas, through the free end;

[0016] - a nozzle arranged around the electrode, preferably coaxially, the nozzle being configured to eject a protective gas, called external gas, out of the nozzle towards the free end of the internal conduit of the electrode;

[0017] - means for ejecting an internal gas flow of composition and / or flow rate and / or pressure independent of that(those) of the external gas ejection flow.

[0018] The present invention therefore essentially consists of a welding torch adapted to eject an internal gas flow and an external gas flow, the flows being independent of each other. Advantageously, this improves the control of the supply of shielding gas at the emission zone of the electric arc. It is thus possible to precisely adjust the shape of the plasma generated by the electric arc and therefore the heat flows implemented during a welding process. Advantageously, the flow rates of the internal gas and the external gas can also be adjusted in order to avoid degradation of the welding torch, in particular of the electrode.

[0019] It is also possible to supply the electric arc emission zone with an internal gas having a composition different from the composition of the external gas, each of the gas compositions having a different preferred function.

[0020] For example, one of the compositions being particularly plasmagenic and the other composition being more protective against oxidation and / or thermally insulating. In particular, the external gas can be chosen for a plasmagenic function and the internal gas can provide chemical and thermal protection for the constituent elements of the welding torch.

[0021] Preferably, the internal gas and / or the external gas is argon. Other gases can of course be considered.

[0022] The internal and external gas ejection flow rates are advantageously of the order of Nl / min.

[0023] Preferably, the nozzle is convergent and longitudinally recessed relative to the electrode, the welding torch being configured so that the external gas flows while being attached along the external surface of the electrode to its free end projecting from the nozzle.

[0024] For the purposes of the present invention, a gas flow is attached along a surface when its streamlines are parallel to said surface and the gas flow remains concentrated in the immediate vicinity of said surface. This attachment is achieved by the convergent shape of the nozzle which makes it possible to accelerate the external gas flow in the direction tangential to said surface.

[0025] Preferably, the welding torch comprises a welding wire, preferably made of metal, housed in the internal conduit, preferably coaxially, projecting beyond the free end of the electrode.

[0026] Inserting the welding wire through the inner conduit of the electrode facilitates handling of the welding torch and simplifies the movements to be performed during a welding process using the welding torch. This makes it possible, for example, to reduce the number of movements required when using the welding torch according to the present invention by a robot. This also makes it possible to free a welder's hand during a manual welding process using the welding torch. Preferably, the welding torch comprises an electrically and thermally insulating guide tube, arranged, preferably coaxially, in the inner conduit of the electrode and into which the welding wire is threaded.

[0027] Preferably, the electrode is made of tungsten or tungsten alloy.

[0028] Preferably, the free end of the electrode has a surface of generally frustoconical external shape.

[0029] Preferably, the welding torch comprises an insulating structure arranged between the nozzle and the electrode so as to insulate them electrically and thermally.

[0030] The present invention also relates to a use of a welding torch according to the present invention for carrying out a welding process, preferably a TIG welding process.

[0031] Preferably, the external gas and / or internal gas ejected by the welding torch during the welding process is argon.

[0032] Other gases can of course be considered.

[0033] Brief description of the drawings

[0034] Other advantages and characteristics will become more apparent upon reading the detailed description, given for illustrative and non-limiting purposes, with reference to the following figures:

[0035] [Fig 1] Figure 1 is a schematic perspective view of a TIG welding torch according to the prior art during a TIG welding process.

[0036] [Fig 2] Figure 2 is a perspective view of a welding torch according to the present invention, the various elements of the welding torch being shown in transparency.

[0037] [Fig 3] Figure 3 is a bottom view of a welding torch according to the present invention.

[0038] [Fig 4] Figure 4 is a front view of a welding torch according to the present invention.

[0039] [Fig 5] Figure 5 is a longitudinal sectional view (A- A) of a welding torch according to the present invention.

[0040] [Fig 6] Figure 6 is a numerical simulation of the temperature field during a TIG welding process using a welding torch according to Figure 1. [Fig 7] Figure 7 is a numerical simulation of the temperature field during a TIG welding process using a welding torch according to the present invention.

[0041] Detailed description

[0042] Figure 1 has already been described previously and will not be described further below.

[0043] Figures 2 to 5 illustrate a welding torch 10 according to the present invention. The welding torch 10 extends along a longitudinal axis X and comprises an electrode 11 made of tungsten or tungsten alloy and a nozzle 12 arranged coaxially with the electrode.

[0044] The nozzle 12 surrounds a portion of the electrode 11, the other portion of the electrode 11 projecting beyond the nozzle 12. In other words, the nozzle is set back longitudinally relative to the free end 14 of the electrode 11.

[0045] Preferably, the free end 14 projects relative to the nozzle 12 over a length L, measured along the longitudinal axis X, greater than or equal to 0.1 cm, preferably between 0.1 and 50 times the diameter d of the electrode 11.

[0046] The electrode 11 has the shape of a circular cylinder on its portion projecting outside the nozzle 12. The external diameter d of the electrode 11 can be of the order of 1 mm.

[0047] The external conduit 13 delimited between the nozzle 12 and the part of the electrode 11 is configured to eject a protective gas, called external gas.

[0048] The nozzle 12 is configured so that the external gas leaving the external conduit 13 flows along the longitudinal axis X while being attached to the external surface of the electrode 11 up to its free projecting end 14.

[0049] Figure 5 illustrates the flow F ex t of the external gas flowing into the external conduit 13 then along the electrode 11.

[0050] The external conduit 13 has an opening diameter at the outlet of the nozzle 12 through which the electrode 11 projects. This opening diameter is constant over an outlet portion 13a of the external conduit 13. Upstream of the outlet portion 13a, in the direction of the flow F ext of the external gas, the opening diameter of the external conduit 13 widens to an inlet portion 13b. The outer diameter of the nozzle 12 gradually widens away from said outlet along the longitudinal axis X until it reaches an outer diameter. The portion of the nozzle 12 along which its outer diameter widens.

[0051] The welding torch 10 comprises an insulating structure 15 arranged between the nozzle 12 and the electrode 11, in particular in the inlet portion 13b of the external conduit 13. The insulating structure 15 is made of an electrically and thermally insulating material, for example ceramic. In addition to electrically and thermally insulating the electrode 11 from the nozzle 12, the insulating structure 15 can mechanically maintain the coaxiality of the electrode 11 relative to the nozzle 12.

[0052] The electrode 11 is hollow with its free end 14 open, thus forming an internal conduit 16 through which a protective gas, called internal gas, is intended to be ejected. The opening diameter of the internal conduit 16 is between the diameter of the wire and the internal diameter of the electrode.

[0053] Figure 5 illustrates the flow Fint of the internal gas flowing inside and then out of the internal conduit 16.

[0054] The external gas supply in the external conduit 13 is independent of the internal gas supply in the internal conduit 16. Thus, the flow rates of the external gas and the internal gas can be adjusted differently from each other, in particular to adjust the shape of the plasma generated by the electric arc during a welding process. The composition of the external gas may be different from the composition of the internal gas. For example, the external gas may be argon and the internal gas may be helium or vice versa.

[0055] The internal conduit 16 also forms a passage for a welding wire 17. The welding wire 17 can be inserted along the longitudinal axis X, in particular coaxially with the electrode 11, from the portion of the electrode 11 housed in the nozzle 12 until it projects beyond the free end 14 of the electrode 11. The welding wire 17 brings material into the emission zone of the electric arc 18. Since the welding wire 17 is housed in the electrode 11, the movement of the welding wire 17 is intrinsically integral with that of the torch 10 in the directions orthogonal to the longitudinal axis X. This greatly simplifies the handling of the welding torch 10 during welding requiring the supply of material. This supply of material is carried out by sliding the welding wire 17 along the longitudinal axis X. The welding torch 10 comprises a guide tube 19 arranged in the internal conduit 16 extending to the free end 14 of the electrode 11.The guide tube 19 is coaxial with the electrode 11 along the longitudinal axis X. The welding wire 17 is threaded into the guide tube 19, which ensures the mechanical retention and centering of the welding wire 17 in the internal conduit 16 and guides the welding wire 17 during its insertion into the electrode I L.

[0056] The guide tube 19 is made of an electrically and thermally insulating material, for example ceramic, which makes it possible to electrically and thermally insulate the welding wire 17 from the electrode 11 during the welding process.

[0057] Furthermore, the free end 14 projecting from the electrode 11 is a surface of generally external truncated cone shape, the apex of which forms the tip of the electrode IL.

[0058] The inventors carried out multiphysical numerical simulations, using the software marketed under the name “Cast3M”, in order to compare a welding torch 1 according to the state of the art, as illustrated in Figure 1, with a welding torch 10 according to the present invention.

[0059] The external gas flow is imposed on the gas inlet surface with the same opening diameter.

[0060] Figure 6, respectively 7, illustrates the thermal field 20, respectively 21, obtained by a simulation of the use of the welding torch 1 according to the prior art, respectively of the welding torch 10 according to the present invention.

[0061] For these simulations, the arc height, i.e. the distance between the free end 24 or 14 of the electrode 2 or 11 and the workpiece 4, was 10 mm. The simulation for the welding torch 1 according to the prior art was carried out with a shielding gas flow F ejected with a flow rate of 22.5 Nl / min, the shielding gas being argon. The simulation for the welding torch 10 according to the present invention was carried out with an external gas flow Fext ejected with a flow rate of 22.5 Nl / min and an internal gas flow Fint ejected with a flow rate of 1.5 Nl / min, the external gas being argon, the internal gas being argon.

[0062] These simulations show that the temperature at the free end 24 of the electrode 2 of the welding torch 1 according to the state of the art is 18000 K whereas it is only 10900 K for at the free end 14 of the electrode 11 of the welding torch 10 according to the present invention. In addition, these simulations show better control of the heat flows when using the welding torch 10 according to the present invention, the temperature being more homogeneous between the part to be welded 4 and the electrode 11.

[0063] Other variations and improvements may be envisaged without departing from the scope of the invention.

Claims

Claims 1. Welding torch (10), comprising: - an electrode (11) extending along a longitudinal axis (X) and being intended to form an electric arc with a part to be welded, the electrode comprising an internal conduit (16) opening out through a free end, the internal conduit being configured to circulate then eject a protective gas, called internal gas, through the free end, - a nozzle (12) arranged around the electrode, preferably coaxially, the nozzle being configured to eject a protective gas, called external gas, out of the nozzle to the free end of the internal conduit of the electrode, - flow adjustment means for ejecting an internal gas flow (Fint) of composition and / or flow rate and / or pressure independent of that(those) of the external gas ejection flow (F ex t), - an insulating structure (15) arranged between the nozzle and the electrode so as to insulate them electrically and thermally.

2. Welding torch according to claim 1, the nozzle being longitudinally recessed relative to the electrode, the welding torch being configured so that the external gas flows while being attached along the external surface of the electrode to its free end projecting out of the nozzle.

3. Welding torch according to one of the preceding claims, comprising a welding wire (17), preferably made of metal, housed in the internal conduit (16), preferably coaxially, projecting beyond the free end of the electrode.

4. Welding torch according to claim 5, comprising an electrically and thermally insulating guide tube (19), arranged, preferably coaxially, in the internal conduit of the electrode and into which the welding wire is threaded.

5. Welding torch according to one of the preceding claims, the electrode being made of tungsten or tungsten alloy.

6. Welding torch according to one of the preceding claims, the free end of the electrode having a surface of generally frustoconical external shape.

7. Use of a welding torch (10) according to one of the preceding claims for carrying out a welding process, preferably a TIG welding process.

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