Cladding welding process and welding torch and welding apparatus for performing such cladding welding process

Abstract

The invention relates to a cladding welding process in which molten material of consumable welding wires (D) is deposited on a surface (O) of a workpiece (W) using a cold metal transfer (CMT) welding process with cyclically alternating arc phases (tLB) and short-circuit phases (tKS), and to a welding torch (SB) and a welding apparatus (SG) for performing such a cladding welding process. According to the invention, at least two consumable welding wires (D1, D2) are used, which are conveyed to the workpiece (W) by means of a common welding torch (SB) having at least two contact tubes (KR1, KR2), each having at least two contact shells (KRT11, KRT21, KRT12, KRT22) movably arranged in a sleeve (H1, H2), said at least two welding wires (D1, D2) being connected to at least one welding power source (SQi).

Description

Technical Field

[0001] The present invention relates to a cladding welding process, wherein molten material of a consumable welding wire is deposited on the surface of a workpiece using a cold metal transfer (CMT) welding process having a cyclic alternation of an arc phase and a short circuit phase, wherein during the arc phase, the welding wire is fed in the direction of the workpiece until it contacts the workpiece, and then, after a short circuit is formed in the short circuit phase, the wire feeding direction is reversed and the welding wire moves away from the workpiece until the short circuit is broken, wherein welding parameters (such as welding current, welding voltage and wire feed speed) are controlled by a welding power source, the welding voltage and the wire feed speed of the welding wire are correspondingly controlled and applied to the welding wire, and in the arc phase the welding wire melts and forms molten droplets, which are transferred to the surface of the workpiece in the short circuit phase.

[0002] Furthermore, the present invention relates to a welding torch for performing the above-mentioned cladding welding process.

[0003] Finally, the present invention also relates to a welding device for performing the above-mentioned cladding welding process, the welding device having the above-mentioned welding torch. Background Art

[0004] Cladding welding is the coating of metal workpieces by welding, whereby a filler material in the form of a consumable or molten welding wire is used to create a covering layer on the workpiece. The coating is applied to the metal workpiece in one or more layers as surface protection against wear or corrosion. Arc welding processes (mainly MIG / MAG (metal inert gas / metal active gas) welding processes) and laser deposition welding processes are often used. Repair of workpieces can also be carried out using this cladding welding process.

[0005] In the cladding welding process, consumable welding wires made of particularly soft materials are usually used, which are fed into the welding torch at the highest possible speed to achieve the highest possible deposition rate and the fastest possible cladding production. In order to obtain good adhesion of the protective coating to the workpiece substrate, the surface of the workpiece is usually pre-treated before cladding, such as degreasing or sandblasting.

[0006] For example, CN102248265A and CN11748265A describe such cladding welding processes.

[0007] Cladding is mainly carried out using very soft wire materials with low melting points, for example alloys with lead Pb and tin Sn, such as babbitt. Invented by the American inventor Isaac Babbitt, babbitt alloys vary in their material composition and mainly consist of tin Sn, antimony Sb, copper Cu as well as lead Pb and arsenic As (see examples in the table below). The relatively high coefficient of thermal expansion in the range of 23 to 27 ppm / °C can lead to clogging of the wire in the contact tube, especially during rapid feeding of the wire. Therefore, for safety reasons, the wire feed speed is reduced in order to be able to perform the welding process with the longest possible service life. Slow feeding of the wire naturally leads to lower cladding rates and longer production times.

[0008]

[0009] In order to achieve higher cladding rates and shorter production times, tandem torches are used in the cladding welding process, whereby two (or theoretically more) welding wires can be fed to the welding point simultaneously. However, using such a tandem torch with two contact tubes to feed two welding wires increases the possibility that the welding wire made of soft material will get stuck in the contact tube and the welding process will have to be stopped.

[0010] For example, US 2021 / 0339332 A1 describes a welding torch with two contact tubes for feeding two welding wires to the welding point.

[0011] US Pat. No. 9,539,663 B2 describes a device and a method for contacting a welding wire in a welding torch, wherein a contact tube consists of two housings which are arranged in a sleeve so as to be movable relative to one another. Summary of the invention

[0012] The object of the present invention is therefore to create a cladding welding method as mentioned above and a welding torch and a welding device for carrying out such a cladding welding method, by means of which even with particularly soft welding wire materials such as babbitt, the fastest possible cladding of workpieces can be achieved while at the same time achieving the longest possible service life. The cladding welding process should be as simple and cost-effective as possible, and the manufacture of the welding torch and the welding device should also be as simple and cost-effective as possible. The disadvantages of the known cladding welding processes and devices for carrying out the cladding welding processes should be avoided or at least reduced.

[0013] The object of the present invention is solved by a cladding welding process as described above, wherein at least two consumable welding wires are used, which are fed to the workpiece by a common welding torch having at least two contact tubes, each having at least two contact shells movably arranged in a sleeve, the at least two welding wires being connected to at least one welding power source. Thus, the cladding welding process using the CMT welding process according to the present invention uses a tandem welding torch known per se, having at least two contact tubes, each consisting of two parts or contact shells that can be moved relative to each other. These are, for example, the applicant's Brand contact tubes, which are also described in US 9,539,663 B2. By using at least two welding wires, the melting rate of the coating material can be increased, thereby accelerating the production of the coating. On the other hand, by using a movable contact tube, the welding wire can be fed to the welding point at particularly high wire feed speeds (even those made of relatively soft materials, such as welding wires made of babbitt alloy) and melted there in the arc. The moving parts of the contact tube prevent clogging in the welding torch even at high wire feed speeds and achieve a longer service life. The use of contact tubes with movable parts in tandem welding torches is relatively easy to implement, and it is only necessary to adjust the holder of the contact tube (the so-called nozzle holder) so that the sleeve of the contact tube (the part of the contact tube or the contact shell is movably mounted in the sleeve) can be held accordingly.

[0014] According to one feature of the present invention, at least two identical welding wires are used. In this variant, two or more welding wires of the same material are used, and the cladding rate is correspondingly increased by one or more times.

[0015] Alternatively, at least two different welding wires are used in the cladding welding process. If different welding wires made of correspondingly weldable and connectable materials are used, special coatings can be produced with special material compositions.

[0016] In the case of at least two different welding wires, welding wires with different materials and / or different diameters are preferably used. This enables the coating produced by the cladding welding process to have certain properties.

[0017] Good cladding results can be achieved if at least one welding wire is made of a lead and tin alloy, preferably a babbitt alloy, which is particularly suitable for certain applications, such as bearing bushings where wear is reduced.

[0018] The welding speed can be increased if, viewed in the welding direction, at least two welding wires are fed to the workpiece one behind the other. In particular, when using different welding wires, this arrangement helps to achieve a mixing of the weld pools of the at least two welding wires. When using at least two identical welding wires, it is also possible to arrange the two welding wires next to each other in the welding direction. In this case, the welding speed is slower, but the width of the weld bead is greater.

[0019] According to another feature of the invention, the at least two welding wires are connected to at least two welding power sources and use different CMT welding processes with different welding parameters. For example, the leading wire seen in the welding direction can be fed toward the welding point at a higher speed than the trailing wire seen in the welding direction. Other welding parameters (such as welding current) can also be different.

[0020] Alternatively, at least two welding wires can also be connected to one welding power source and use the same CMT welding process with predetermined welding parameters. In this case, at least two contact tubes (through which the at least two welding wires are conveyed to the welding point) are connected to the same welding power source and the same welding current is applied.

[0021] Preferably, the at least two welding wires are fed into the workpiece at a working angle between -1.5° and +1.5°. Such an angle has proven to be particularly suitable for cladding welding.

[0022] The at least two welding wires may be fed towards the workpiece at different average wire feed speeds.As mentioned above, by adjusting the respective wire feed speeds, an optimal placement and therefore an optimal deposition of the coating on the workpiece may be achieved, in particular when using different welding wires.

[0023] The molten material of the welding wire can be applied to the surface of the workpiece along a substantially serpentine path. This is a preferred variant of cladding welding, whereby the overlap of the welding paths is selected in a suitable manner in order to achieve a coating that is as uniform as possible on the workpiece.

[0024] Typically, the molten material of the welding wire is applied to the surface of the workpiece in the form of several layers, and the welding parameters (such as average welding current, average welding voltage or average wire feed speed in the direction of the workpiece) are varied between the layers. Depending on the purpose of the coating, it may be necessary to have a few to many layers of coating on the surface of the workpiece.

[0025] A better weld quality can be achieved if a shielding gas, in particular argon or helium, is used, which is preferably supplied via a carrier gas nozzle arranged downstream of the welding torch as seen in the welding direction. The use of a carrier gas nozzle is particularly useful for achieving an optimal weld quality when using materials that oxidize quickly in the presence of oxygen.

[0026] It may be advantageous if the workpiece is preheated before starting the cladding welding process. The workpiece may be preheated preferably to a temperature of 80°C to 200°C, most preferably to a temperature of 80°C to 130°C, for example, by means of an industrial furnace. In the case of larger workpieces, a flame gun may also be used to preheat at least a portion of the workpiece surface. Other heat sources may also be used, such as laser, plasma, electrical energy and high frequency.

[0027] Higher coverage rates can be achieved if at least one of the welding wires is preheated. Preheating of the welding wires can be done by resistance heating.

[0028] The objects of the invention are also solved by a welding torch as described above, wherein at least two contact tubes are provided for guiding at least two consumable welding wires, each contact tube having at least two contact shells arranged movably in a sleeve, each contact tube being arranged in a nozzle holder. By using a special two-section, movable contact tube, such a welding torch can be adapted for welding wires which are usually very soft in cladding welding processes. Reference is made to the above description of the cladding welding process for an understanding of the advantages which can be achieved thereby.

[0029] The at least two contact tubes are preferably arranged one after the other in the welding direction. As mentioned above, through this arrangement, a higher welding speed will be achieved.

[0030] The at least two contact tubes can be arranged parallel to each other, or arranged at an angle to each other. For example, as described in US Pat. No. 11,794,269 B2, different angles between the contact tubes can be used in different occasions.

[0031] If a gas nozzle is provided to supply shielding gas, a better welding quality can be obtained because oxidation of the molten metal during solidification can be prevented.

[0032] The nozzle holder of the contact tube can be cooled. In this way, the heat generated can be better dissipated and the service life of the welding torch can be increased. Cooling can be achieved using cooling air or cooling liquid.

[0033] From the welding direction, a carrier gas nozzle for applying a shielding gas, in particular argon or helium, can be arranged behind the at least two contact tubes. As mentioned above, an optimal welding quality can be obtained by using such a carrier gas nozzle.

[0034] Finally, the objects of the invention are also solved by a welding device for carrying out the above-mentioned cladding welding process with the above-mentioned welding torch, wherein the welding torch is connected to at least one welding power source for applying welding parameters to each welding wire and in each case a wire feeder is provided for feeding each welding wire to and away from the workpiece. Reference is made to the above description of the cladding welding method and the welding torch for the advantages that can be achieved thereby.

[0035] Using two identical wires doubles the amount of molten material if the torches are connected to one welding power source for applying the same welding parameters to all wires.

[0036] Special effects can be achieved, preferably when using two or more different welding wires, if the welding torch is connected to at least two welding power sources for applying different welding parameters to each welding wire.

[0037] Preferably, the welding torch is connected to a carrier gas nozzle. As mentioned above, the best welding quality can be obtained by using such a carrier gas nozzle.

[0038] If the welding torch is connected to a robot, the cladding welding process can be performed automatically.

[0039] For the advantages that can be obtained from this, please refer to the description of the cladding welding process above. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention is explained in more detail with reference to the accompanying drawings. The accompanying drawings show:

[0041] Figure 1 is a block diagram of a welding apparatus for performing a cladding welding process according to the prior art, and some examples of workpieces that have been coated using a cladding welding process with different torch motion paths;

[0042] Figure 2 A tandem welding torch of the present invention having two contact tubes, each of which is composed of two movable contact shells;

[0043] Figure 3 The exploded view shows Figure 2 welding torch;

[0044] Figure 4 is a perspective view of an example of a contact tube consisting of two contact shells arranged movably relative to each other;

[0045] Figure 5 is a cross-sectional view of the contact tube and the nozzle holder;

[0046] Figure 6 Schematically shows the arrangement of two contact tubes at different angles relative to each other in a tandem welding torch;

[0047] Figure 7 Schematically showing a carrier gas nozzle arranged thereon Figure 2 and Figure 3 Tandem welding torch;

[0048] Figure 8schematically showing a tandem welding torch viewed along the welding direction to illustrate different working angles relative to the workpiece surface; and

[0049] Figure 9-13 Various examples of workpieces that can be coated by the cladding welding process are shown. DETAILED DESCRIPTION

[0050] Figure 1 A block diagram of a welding device SG for performing a cladding welding process according to the prior art is shown. The welding device SG comprises a welding torch SB which is designed to feed two welding wires D1, D2 to a workpiece W. This allows more material to be applied to the surface O of the workpiece W and allows the cladding process to be performed more quickly. The two welding wires D1, D2 are connected in series via two contact tubes KR1, KR2 (see Figure 2 and Figure 3 ) is delivered to the welding point. The welding torch SB can be moved by a robot R. The welding wires D1, D2 are located on wire reels M1, M2 and are delivered to the welding torch SB via wire feeders DV1, DV2 and hose package HO. The necessary welding current I and welding voltage U are supplied to the contact tubes KR1, KR2 of the welding torch SB via one or two welding power sources SQ1, SQ2, so that an arc (not shown) can be ignited between the ends of the welding wires D1, D2 and the workpiece W, which is also connected to the welding power sources SQ1, SQ2. If only one welding power source SQ is used, the two contact tubes KR1, KR2 will be subjected to the same welding current I and the same welding voltage U. The arc melts the material of the welding wires D1, D2, and the molten material forms the desired coating on the workpiece W during the cladding process. In Figure 1 In the top example, the welding path X1 meanders along the direction indicated by the arrow, and the transition from one direction to the opposite direction is circular.

[0051] The workpiece W arranged below shows various examples of the workpiece W having different welding paths X2-X5. Figure 1 In the example on the left side of the center, the surface O of the workpiece W is coated with a serpentine welding path X2, in which the transition from one direction to the opposite direction is at right angles. The distance between the parallel segments of the welding path X2 is usually constant, but can also be variable (as shown in the figure).

[0052] exist Figure 1 In the example of the workpiece W on the right in the middle, the welding torch SB always approaches the surface O of the workpiece W in the same direction. This forms parallel welding paths X3. The welding process is paused while the welding torch SB moves from the end of one welding path X3 to the start of the next welding path X3. During the meandering movement of the welding torch, the cladding welding process can always remain active.

[0053] Figure 1The example on the left in the last row shows the coating of the surface O of the front side of a cylindrical workpiece W. In this case, the welding torch SB is moved along a spiral welding path X4 extending across the front side of the workpiece W from the outside to the inside.

[0054] Figure 1 The example at the bottom right shows the coating of a surface O of the inside of a tubular workpiece W. In this case, the welding torch SB is moved along a spiral welding path X5.

[0055] Of course, the cladding welding process can be performed in several layers, whereby the movement of the welding torch SB over the surface O of the workpiece W can also vary from layer to layer, ie with respective welding paths X.

[0056] Figure 2 An embodiment of a tandem welding torch SB according to the invention is shown, which has two contact tubes KR1, KR2, each consisting of two movable contact shells KRT11, KRT12, KRT21, KRT22. The tandem welding torch SB comprises a torch body TB with a connection for a hose package HO (not shown), which contains the corresponding electrical components for the welding wires D1, D2 and the shielding gas G as well as any control lines (not shown). The connection to the hose package HO is usually achieved by means of corresponding plug-in connections, which are particularly quick and convenient to connect and disconnect. The tandem welding torch SB has a gas nozzle GD, the free end of which is a conical mouth. The tandem welding torch SB comprises two contact tubes KR1, KR2 for guiding the two welding wires D1, D2. With the help of such a tandem welding torch SB, cladding welding processes with a higher cladding rate can be carried out. In this exemplary embodiment, the two contact tubes KR1 , KR2 and therefore the two welding wires D1 , D2 extend parallel to one another; the angle β between the two contact tubes KR1 , KR2 and the two welding wires D1 , D2 is zero.

[0057] exist Figure 3In the exploded view of the tandem welding torch SB in FIG. , the various parts of the tandem welding torch SB can be seen more clearly. In this figure, the basic components of the tandem welding torch SB can be seen. Therefore, the torch body TB has two interfaces at the end facing the gas nozzle GD, which preferably have a rectangular cross-section for receiving two nozzle assembly receptacles NAR1, NAR2, which are designed as replaceable inserts. The nozzle assembly receptacles NAR1, NAR2 can be connected to the interfaces in the torch body TB, for example by screws. Each of the nozzle assembly receptacles NAR1, NAR2 has an opening for receiving the nozzle assemblies NA1, NA2, which are preferably arranged at an angle of 0° to 20° to each other. When the nozzle assemblies NA1, NA2 and the contact tubes KR1, KR2 that can be connected thereto are placed in the corresponding openings of the nozzle assembly receptacles NAR1, NAR2, the central axes of the contact tubes KR1, KR2 and the welding wires D1, D2 extending in the contact tubes KR1, KR2 form this angle β relative to each other (see Figure 6 ). Therefore, by simply replacing a pair of nozzle assembly receiving parts NAR1, NAR2, a new tandem welding torch SB can be created so that the central axes of the contact tubes KR1, KR2 and the welding wires D1, D2 extending therein have different angles β. Common angles β are, for example, 0°, 4°, 8° and 11.5°.

[0058] Preferably, connections for the inflow of cooling fluid and connections for the outflow of cooling fluid are arranged at the ends of the torch body TB (not shown) in order to be able to optimally cool the components of the welding torch SB.

[0059] The sleeves H1 and H2 are fastened around the contact tubes KR1 and KR2. Each contact tube consists of two contact shells KRT11, KRT21, KRT12, and KRT22. The contact shells are arranged to be movable relative to each other. It is best to have a gas distributor GDP inside the gas nozzle GD, which regularly distributes the protective gas G through correspondingly arranged holes.

[0060] Figure 4 A perspective view of an example of a contact tube KR is shown, which consists of two contact shells KRT1, KRT2 arranged movably relative to each other. The contact shells KRT1 and KRT2 are asymmetrical and movable relative to each other, so that a welding wire D (not shown) made of soft material can be conveyed and contacted in an optimal manner and with reduced clogging. Even after the contact tube KR has worn out due to parts of the contact shells KRT1, KRT2 being worn away, the mobility of the contact shells KRT1, KRT2 relative to each other ensures an optimal electrical contact with the welding wire D and thus an optimal current transmission.

[0061] Figure 5The installation of the contact tube KR is shown in a sectional view. Two movable contact shells KRT1, KRT2 are arranged in a sleeve H. At the end of the contact tube KR opposite the opening for the welding wire D (not shown) at the contact tube KR, a pressure bolt PB with a pressure spring SP presses against the two contact shells KRT1, KRT2. The contact tube KR is fastened in the nozzle assembly receptacle NAR via the nozzle assembly NA (see FIG. Figure 3 ). A seal relative to the nozzle assembly receptacle NAR can be achieved by at least one O-ring RI. A contact tube KR designed in this way, whose contact shells KRT1, KRT2 are arranged movably relative to each other, is particularly suitable for feeding welding wires D made of soft material (e.g. babbitt metal) and having different diameters.

[0062] Figure 6 The arrangement of the two contact tubes KR1, KR2 of a tandem welding torch SB at different angles β relative to each other is schematically shown. In the above example, the contact tubes KR1, KR2 and the welding wires D1, D2 are arranged parallel to each other, so that the angle β between the two contact tubes KR1, KR2 and the welding wires D1, D2 is zero. In the following variant, the contact tubes KR1, KR2 or the welding wires D1, D2 enclose an angle β of 11.5° between the two contact tubes KR1, KR2 or the welding wires D1, D2.

[0063] Figure 7 The schematic diagram of the partly cut-away view shows a carrier gas nozzle SDG arranged thereon. Figure 2 and Figure 3 A tandem welding torch SB is provided. The carrier gas nozzle SDG is connected to the welding torch SB in a suitable manner and is arranged in such a way that the carrier gas nozzle sweeps over the newly welded area after the cladding welding process has been completed. During the cladding welding process, the carrier gas nozzle SDG covers the tail welding area, thereby preventing air from entering the welding area to achieve the best quality of the cladding on the workpiece surface O. The length of the carrier gas nozzle SDG is selected so that, at the required welding speed, the welding area is surrounded by the shielding gas G until the temperature of the welding area drops below the critical temperature at which a reaction with oxygen in the atmosphere occurs. The carrier gas nozzle SDG has an inlet GI and an outlet GO for the shielding gas G and a series of openings in the direction of the surface O of the workpiece W, through which the shielding gas G flows onto the welding area and the cladding C.

[0064] Figure 8 A tandem welding torch SB is schematically shown viewed along the welding direction X to illustrate different working angles α relative to the surface of the workpiece W. Α For example, the working angle α Α A range between -1.5° and +1.5° is suitable.

[0065] at last, Figure 9-13Various examples of workpieces W provided with a cladding or coating C by a cladding welding process are shown. Fig. 9 An engine is shown, in which a shaft-shaped workpiece W2 rotates inside a sleeve-shaped workpiece W1. By applying the cladding welding process, a cladding layer C1 can be produced on the inside of the sleeve-shaped workpiece W1 and a cladding layer C2 can be produced on the outside of the shaft-shaped workpiece W2 from a suitable material, thus reducing the wear of the workpieces W1, W2 and thus extending their service life.

[0066] Fig.10 A wind turbine is shown, wherein the wind turbine is arranged on a shaft-shaped workpiece W2 which is mounted in a sleeve-shaped workpiece W1. Here too, a cladding process can be used to produce a coating C1 on the inside of the sleeve-shaped workpiece W1 and a coating C2 on the outside of the shaft-shaped workpiece W2.

[0067] Fig.11 The example in shows an engine on which a crankshaft (workpiece W1) and a piston rod (workpiece W2) are arranged. A coating C1 can be produced on the crankshaft (workpiece W1) and a coating C2 can be produced on the inner side of the opening of the piston rod (workpiece W2).

[0068] Fig.12 The example in shows a pump, in which a coating C1 , C2 can also be produced on the workpieces W1 , W2 .

[0069] Fig.13 The last example in Figure 1 shows a ventilator, in which a cladding welding process is applied to the outer side of a shaft (workpiece W2) connected to the ventilator in a rotationally fixed manner, and a cladding C1 is applied to the inner side of a bearing (workpiece W1), in which the shaft (workpiece W2) is rotatably mounted.

[0070] Reference numerals :

[0071] C1,C2 coating

[0072] CMT Cold Metal Transfer

[0073] D Consumable welding wire

[0074] D1 First (consumable) welding wire

[0075] D2 Second (consumable) welding wire

[0076] DS1 Nozzle Holder Nozzle Holder

[0077] DS2 Second Nozzle Holder

[0078] DV1,DV2 wire feeding device

[0079] G Shielding gas

[0080] GD Gas Nozzle

[0081] GDP Gas Distributor

[0082] GO gas outlet

[0083] GP Guide Tube

[0084] H1 Sleeve of the first contact tube KR1

[0085] H2 Sleeve of the second contact tube KR2

[0086] HO Hose Package

[0087] I Welding current

[0088] I mean Average welding current

[0089] KR1 first contact tube

[0090] KR2 Second contact tube

[0091] KRT11 The first contact shell of the first contact tube KR1

[0092] KRT21 Second contact shell of the first contact tube KR1

[0093] KRT12 The first contact shell of the second contact tube KR2

[0094] KRT22 The second contact shell of the second contact tube KR2

[0095] KS Short Circuit

[0096] M1,M2 welding wire drum

[0097] NA1,NA2 Nozzle Assemblies

[0098] NAR1, NAR2 nozzle assembly housing

[0099] O Surface of workpiece W

[0100] P i ,P j Welding parameters

[0101] PB Pressure Bolts

[0102] R Robot

[0103] RI1,RI2 O-ring

[0104] S j Layers of coating formed by cladding welding process

[0105] SB welding torch

[0106] SDG Carrier Gas Nozzle

[0107] SG welding equipment

[0108] SP Compression spring

[0109] SQ welding power source

[0110] SQ1 First welding power supply

[0111] SQ2 Second welding power source

[0112] t KS Short circuit stage

[0113] t LB Arc stage

[0114] TB torch body

[0115] U Welding voltage

[0116] U mean Average welding voltage

[0117] v D Wire feeding speed

[0118] v D,mean Average wire feeding speed

[0119] W1,W2 Workpiece

[0120] X welding path

[0121] α A The working angle of the welding torch SB relative to the surface O of the workpiece W

[0122] β Angle between the two contact tubes KR1 and KR2

Claims

1. A cladding welding process in which an arc having cyclically alternating phases (t LB ) and short-circuit phase (t KS ) cold metal transfer (CMT) welding process deposits molten material of a consumable welding wire (D) on a surface (O) of a workpiece (W), wherein In the arc stage (t LB ), the welding wire (D) is fed in the direction of the workpiece (W) until it contacts the workpiece (W) and then, during the short-circuit phase (t KS ) After the short circuit (KS) is formed, the wire feeding direction is reversed, and the welding wire (D) moves away from the workpiece (W) until the short circuit (KS) is disconnected, wherein the welding current (I), welding voltage (U) and wire feeding speed (v D ) and other welding parameters (P i ), such as welding current (I), welding voltage (U) and wire feed speed (v) of welding wire (D). D ) and other welding parameters (P i ) is controlled accordingly and applied to the wire (D), and, during the arc phase (t LB ), the welding wire (D) melts and forms a molten droplet, which is in the short circuit stage (t KS ) to a surface (O) of a workpiece (W), characterized in that at least two consumable welding wires (D1, D2) are used, the welding wires (D1, D2) are fed to the workpiece (W) by a common welding torch (SB) having at least two contact tubes (KR1, KR2), each of which has at least two contact shells (KRT11, KRT21, KRT12, KRT22) movably arranged in a sleeve (H1, H2), and the at least two welding wires (D1, D2) are connected to at least one welding power source (SQ i )superior.

2. The cladding welding process according to claim 1, characterized in that: Use at least two identical welding wires (D1, D2).

3. The cladding welding process according to claim 1, characterized in that: Use at least two different welding wires (D1, D2).

4. The cladding welding process according to claim 3, characterized in that: Use welding wires of different materials and / or different diameters (D1, D2).

5. The cladding welding process according to claim 1, characterized in that: At least one solder wire (D1, D2) made of a lead-tin alloy, preferably a solder wire (D1, D2) made of a babbitt alloy, is used.

6. The cladding welding process according to claim 1, characterized in that: At least one welding wire (D1, D2) is used which is made of a material having a thermal expansion coefficient between 23 ppm / °C and 27 ppm / °C.

7. The cladding welding process according to claim 1, characterized in that: Viewed along the welding direction (X), the at least two welding wires (D1, D2) are fed to the workpiece (W) one after the other.

8. The cladding welding process according to claim 1, characterized in that: The at least two welding wires (D1, D2) are fed at different average wire speeds (v D,mean ) is transported toward the workpiece (W).

9. The cladding welding process according to claim 1, characterized in that: The molten material of the welding wire (D1, D2) is formed in several layers (S j ) is applied to the surface (O) of the workpiece (W), such as the average welding current (I mean,j ), average welding voltage (U mean,j ) or the average wire feed speed (v) along the workpiece (W) direction D,mean,j ) and other welding parameters (P i )From one layer (S j ) to another layer (S j+1 ) varies between.

10. The cladding welding process according to claim 1, characterized in that: A shielding gas (G), in particular argon or helium, is used, which is preferably supplied via a carrier gas nozzle (SDG) arranged downstream of the welding torch (SB), as viewed in the welding direction (X).

11. A welding torch (SB) for carrying out a cladding welding process according to any one of claims 1 to 10, characterized in that At least two contact tubes (KR1, KR2) are provided to guide at least two consumable welding wires (D1, D2), each of the contact tubes (KR1, KR2) having at least two contact shells (KRT11, KRT21, KRT12, KRT22) movably arranged in a sleeve (H1, H2), and each contact tube (KR1, KR2) is arranged in a nozzle holder (DS1, DS2).

12. The welding torch (SB) according to claim 11, characterized in that The at least two contact tubes (KR1, KR2) are arranged one behind the other, viewed in the welding direction (X).

13. The welding torch (SB) according to claim 11 or 12, characterized in that A gas nozzle (GD) is provided to supply shielding gas (G).

14. The welding torch (SB) according to claim 11, characterized in that A carrier gas nozzle (SDG) for applying a protective gas (G), in particular argon or helium, is arranged downstream of the at least two contact tubes (KR1, KR2) as viewed in the welding direction (X).

15. A welding device (SG) for carrying out a cladding welding process according to one of claims 1 to 10, comprising a welding torch (SB) according to one of claims 11 to 14, characterized in that: The welding torch (SB) is connected to at least one welding power source (SQ i ) for applying welding parameters (P i ), and in each case a wire feeder (DV l ) for feeding each welding wire (D1, D2) toward and away from the workpiece (W).

16. Welding device (SG) according to claim 15, characterized in that The welding torch (SB) is connected to a welding power source (SQ) for applying the same welding parameters (P i ).

17. Welding device (SG) according to claim 15, characterized in that The welding torch (SB) is connected to at least two welding power sources (SQ1, SQ2) for applying different welding parameters (P i ,P j ).

Images