EP2051831A1

EP2051831A1 - Tig braze-welding with metal transfer in drops at a controlled frequency

Info

Publication number: EP2051831A1
Application number: EP07823570A
Authority: EP
Inventors: Jean-Marie Fortain; Olivier Revel
Original assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude; Air Liquide Welding France
Current assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude; Lincoln Electric Co France SA
Priority date: 2006-08-03
Filing date: 2007-07-12
Publication date: 2009-04-29
Also published as: US20100012638A1; WO2008015353A1; CA2658969A1; AU2007280344A1; FR2904576B1; JP2009545449A; FR2904576A1

Abstract

The invention relates to a braze-welding or arc-welding method using a TIG torch equipped with a non-consumable electrode (1) and a consumable filler wire (2) of a given diameter, wherein the transfer of metal to the welded joint occurs in successive droplets of molten metal deposited at a frequency of between 20 Hz and 90 Hz, and the size of said drops is between 1, 2 and 4 times the diameter of the consumable wire.

Description

TIG weld-brazing with frequency controlled droplet metal transfer

The present invention relates to a method of welding or welding, preferably robotized, with TIG torch and filler metal in the form of one or more fusible wires, in particular one or more pieces of coated steel or aluminum or aluminum. aluminum alloy, in which the transfer of the metal from or to the solder bath is by successive drops at a controlled frequency.

It is known from US-A-5512726 and DE-A-3542984, a conventional configuration of fused-wire TIG torch, in which the supply of the fusible wire into the melt is operated horizontally or substantially. horizontal so as to obtain a molten transfer of molten metal from the molten end of the fuse wire to the melt, that is to say to the welding zone on the parts to be welded or solder-brazing.

However, with such a torch, the sixth axis of the robot carrying the TIG torch is blocked and its degrees of freedom are limited since a certain directivity is necessary to guide the supply of wire in the axis of the weld joint of the makes the horizontal arrival of the wire.

In addition, with this type of configuration, the productivity of the process is affected by a limited wire melting speed and therefore a limited welding speed.

EP-A-1459831 proposes an arc welding method not posing the aforementioned problems. In this case, the supply of fusible wire is operated at an angle less than 50 ° relative to the axis of the electrode, preferably an angle between 15 and 35 °, and the end of the fuse wire is guided and kept permanently at a distance of less than 2 mm from the end of the tungsten electrode.

Such a method makes it possible to obtain good results in the majority of applications. However, it has been observed that during the welding or brazing of certain particular materials, particularly coated steels, for example galvanized or electro-galvanized, and aluminum and its alloys, problems of quality of the weld , in particular problems of compactness of cords and / or large-grain microstructure of the molten metal.

Moreover, on aluminum, it was not possible to obtain an equivalent quality of cords, in particular of appearance and aesthetics, to that obtained by manual welding. An object of the present invention is therefore to improve the process described in document EP-A-1459831 so as to obtain an effective welding or brazing-welding especially of specific materials, in particular coated steels and aluminum, and its alloys, so as to mitigate, minimize or at least mitigate the aforementioned quality problems.

The solution of the invention is a brazing or arc welding process using a TIG torch provided with a non-fuse electrode and a fuse wire of given diameter, in which:

a) the TIG torch is fed with said fuse wire in such a way that the supply of fusible wire is operated at an angle less than 50 ° with respect to the axis of the electrode, that is to say that the axis of the end of the wire at the non-fusible electrode and the axis of said electrode form an angle less than 50 °,

b) the end of the fuse wire is permanently guided and maintained at a distance of less than 2 mm, preferably at least 1 mm (about 1.5 times the diameter of the wire), with respect to the end of the electrode tungsten torch TIG,

c) a progressive fusion of the end of the fuse wire by the electric arc generated between the non-fuse electrode and at least one part to be welded so as to carry out a transfer of molten metal from the end of the wire to said at least one part and thus obtain a weld or weld-solder joint,

characterized in that the transfer of metal to the weld joint is effected by successive molten metal droplets, said droplets being deposited at a frequency of between 20 Hz and 90 Hz, and the size of the drops being equal, for these frequencies respectively, 1.5 to 4 times the diameter of the fuse wire.

By droplet transfer, it is meant that the transfer of metal from the end of the wire to the solder bath or brazing is by successive droplets, dissociated from each other and therefore without permanent contact between the filler wire and the molten metal.

The solution of the invention is therefore based on the fact of making a transfer of molten metal in the form of drops whose frequency and size depend on the wire speed, the wire electrode distance and the coin electrode distance. These trends and variations are presented in Tables 1 and 2 below. Table 1: Influence of the variation of the wire-electrode distance

As shown in Table 1, for constant wire speed (Vfil) and electrode-to-room distance: - as the wire-electrode distance increases, one deviates from the hottest area of the arc to lie within the zone between 2000 and 5000 ⁰ K, the size of the drops increases and the frequency decreases according to the laws set out below in the description.

- Conversely, when the wire electrode distance decreases, the wire transfers into the hot zone of the arc, namely between about 5000 and 10000 ⁰ K, the drop size decreases and the transfer frequency increases. We can then accelerate the welding speed. Table 2: Influence of the variation of the electrode-room distance

As shown in Table 2, for a wire speed (Vfil) and a constant coin wire electrode distance: when the coin electrode distance increases, the size of the drops increases and the frequency decreases according to the laws set out below, until large drops are obtained capable of damaging the active part of the electrode.

- Conversely, when the electrode-room distance decreases, the drops evolve to a transfer mode in which they are almost simultaneously in connection with the wire and the melt to pass the thresholds of the transfer by liquid bridge.

The data recorded in Tables 1 and 2 have been schematized in the attached FIG. 2 which represents a drop transfer according to the present invention obtained with a stainless steel grade wire ER308LSi and a diameter of 1.2 mm determined by: fairly open range of wire speed (diameter equal to 1.2 mm) ranging from

0.5 m / min at about 3.5 to 4.m / min for which a drop transfer regime is maintained characterized by a minimum wire speed (Vfil) for which an average drop size of 3.5 times the diameter of the wire is associated with a transfer frequency of 20 Hz and a maximum wire speed of 3 m / min for which a drop size of 1.2 wire diameter is associated with a transfer frequency of 90 Hz.

between these two terminals, the variation in drop size (TG) and transfer frequency (FT) is linear and can be associated with the laws of type:

FT (in Hz) = 28. Vfil (m / min) + 6 TG (in mm) = k. wire diameter = - 0.6. Vfil (m / min) + 3.3 For a given wire-gas pair, these transfer curves are to be associated with a distance wire electrode and a distance electrode part previously defined and fixed.

One can for example proceed as indicated in Table 3 below to choose the frequency and the size of the drops, when welding aluminum alloy test specimens of thickness equal to 2 mm, in 2 different shades of aluminum, namely 6061 and 5083, for clinch, angled and butt joint configurations.

Table 3: Transfer by drops on aluminum

Dce = distance; G = drop

The above Table 3 shows a way to adapt the drop transfer according to the invention for different configurations of joints and two types of aluminum alloys.

As can be seen, for the 6061 material, lower wire speeds in both clinching and angle welding with reduced associated wire electrode distances, i.e. order of 1 to 2 times the diameter of the wire, to have a size reduced drop and higher frequency, which allows to better control the directivity of the transfer in the blink.

For the material 5183, the gait remains the same between clm welding and butt welding with a greater adjustment latitude in butt welding with respect to the electrode / wire distance and the generally higher wire speed.

These settings for low wire speeds, that is to say less than or equal to about 1.5 m / min, especially for wires of large diameter, that is to say at least about 1.2 mm, require a appropriate unwinding, for example type of advance / recoil ("push pull" in English), in which the roller platen of the reel ensures the unwinding of the wire and the rollers of the torch regulating the unwinding.

The transfer by droplets at a particular frequency according to the invention allows the production of cords whose aesthetic quality is similar to those achieved by manual welding, in particular on aluminum, allowing with this process a reproduction of "solidification waves" surface.

Moreover, it also makes it possible to solve problems of compactness of cords and microstructure of the coarse-grained molten metal encountered with the known processes.

In the case of austenitic stainless steel, the conditions for obtaining drop transfer with a 308LSi grade yarn are given comparatively in Table 4.

Table 4: Austenitic Stainless Steel Welding

Vf: speed wire - Vs: welding speed

ARCAL ™ 15 is a commercial gas mixture of L'Air Liquide formed from argon and 5% by volume of hydrogen.

This table 4 demonstrates the advantage of the drop transfer of the invention compared to conventional TIG welding of the prior art, wherein the fusion of the wire is only by conduction in contact with the melt.

Indeed, a transfer according to the invention makes it possible to significantly increase the speed of welding (Vs) since, with a transfer by drops according to the invention, the fusion of the wire is accelerated by its passage in the temperature zone of between about 5000 and 10000 ⁰ K which imposes a 40% increase in the wire speed and therefore, a 66% increase in welding speed.

In the case of the brazing of galvanized carbon steels as can be seen in the following Table 5, the operating range for obtaining the drop transfer remains closely related to the nature of the wire used Cu Al or Cu Si.

In this type of transfer, for a material thickness of 1 mm, the maximum wire feed speeds allow welding speeds of the order of 1 to 1.2 m / min.

Table 5: Braze-welding of galvanized carbon steels

ARCAL ™ 1 is gaseous argon marketed by L'Air Liquide and ARCAL ™ 10 is a commercial gas mixture of L'Air Liquide formed by 2.5% by volume of hydrogen and argon for the remainder.

In both cases of applications, that is to say at clin and melting lines, the yarn speed operating ranges remain sufficient, with respectively 2 to 5.5m / min and 1 to 3.2 m / min, to be industrially exploitable.

These differences are due to the different nature of the alloys of the filler metals with different liquidus solidus temperatures, as well as the 10 μm coating for spot welding which imposes different zinc degassing conditions from the interface requiring operate at the highest possible welding speed. In the case of CuSi wire, Arcal ™ 10 gas has been used to slow the formation of silicates on the surface of cords.

Furthermore, as the case may be, the method of the invention may comprise one or more of the following characteristics:

the droplet transfer frequency is preferably between 30 Hz and 80 Hz.

- The size of the drops is equal to 1.5 to 3 times the diameter of the fuse wire.

the droplet transfer frequency is between 20 Hz and 40 Hz and the size of the drops is between 3 and 4 times the diameter of the fusible wire, preferably the frequency is of the order of 30 Hz.

the droplet transfer frequency is the result of a pulse frequency of the wire combined with a pulsating frequency of the direct or alternating current in the case of aluminum and its alloys (or of variable polarity type) which allows more precise control of the welding and stripping phases. the droplet transfer frequency is between 70 Hz and 90 Hz and the size of the drops is between 1, 2 and 1.5 times the diameter of the fusible wire, preferably of the order of 80 Hz.

it is welded with a wire speed of up to 20 m / min, in particular between 1 and 10 m / min. The wire speed is chosen according to the diameter of said wire. the supply of fusible wire is operated at an angle between 10 and 30 ° relative to the axis of the electrode, preferably between 10 and 20 °.

the end of the fuse wire is permanently guided and maintained at a distance of less than 1.5 mm from the end of the tungsten electrode of the TIG torch, preferably at a minimum distance of 1 mm. However, in all cases, the surface of the end of the wire should not come into contact with the tungsten electrode.

during welding, a gaseous protection is applied to the electrode, the wire and the molten metal.

a gaseous protection is carried out with a gas chosen from argon, helium and argon / helium mixtures with or without micro-additions of nitrogen, and mixtures of argon and hydrogen. the method is implemented on a robotic welding arm carrying a TIG torch with a non-fuse electrode and fuse welding wire feeding means or in manual or automatic welding.

- the process is used to weld or braze one or more parts - the parts are in coated steel, in particular in galvanized or electro-galvanized steel, in austenitic or ferritic stainless steel, in nickel and nickel alloys, titanium and alloys titanium, as well as aluminum or aluminum alloys.

the intensity of the direct current supplying the TIG torch is between 10 A and 400 A Max, and the voltage is between 10 V and 20 V. The wire has a diameter between 0 6 mm and 1.6 mm, preferably between 1 mm and 1.2 mm.

- The wire is cupro-sihcium alloy (Q1S1 ₃ ) or cupro-alummium (CuA18).

the wire is also made of pure aluminum or aluminum alloy, for example 2000, 4000 or 5000 series. According to the present invention, part of the energy of the arc is used for the melting of the end of the wire at fairly low wire speeds, typically of the order of 1 to 10 m / min, which explains that per unit of time, this energy will interest a longer wire length and thus give rise to the formation of drops which will be larger when the wire speed is low and the transfer frequency is also low; and vice versa, for a wire speed higher but lower than that of the appearance of a liquid bridge, the size of the drops will decrease and the transfer frequency will increase. The parameters, for a given wire diameter, are linked by the relation:

Vfil. section of the wire = frequency of drops. volume of drops with: (mm / s). (mm ² ) = (number of drops / s). (mm ³ ) So we can easily, via a wire speed setting and for a given arc speed

(electrical parameters and associated gas), control / adjust the diameter and frequency of the drops. These different parameters can be evaluated and controlled in a very precise manner using a high-speed video camera, e.e. for example 10000 frames per second. Visually, the effect is directly perceptible on the surface of the bead, by the presence of regular waves, called striations of solidification.

This drop transfer is different from those known in the state of the art of the conventional automatic TIG process, in which the wire is melted by direct thermal conduction melting bath and not, as in the present case, by a portion of the energy of the welding arc which increases the melting speed of said wire and the productivity of the process.

Indeed, comparative results show that for the same configuration of clin assembly or angle and same electrical parameters the increase in the deposition rate is of the order of 40%.

The method of the invention with droplet transfer can be applied to the welding or brazing of any assembly of coated steel, austenitic or ferritic stainless steel parts, nickel and nickel alloys, titanium and titanium alloys, aluminum or its alloys, for which aesthetic conditions are sought or favored, in particular regular striations on the surface of cords or for which important preparation tolerances must be compensated

This drop transfer gives rise to a cyclic thermal cycle of the melting bam, which may have effects on the microstructure of the melt but also on the compactness of the molten metal by the mechanical effect of the drop on the melt causing stirring. bam and thus promoting its degassing. This phenomenon is also visible and quantifiable as previously by high speed video camera.

The method of the invention is particularly advantageous for welding very thin galvanized sheets, for example less than 1 mm, to promote degassing of ZnO vapors, or welding aluminum or its alloys to promote degassing of H ₂ . The method of the invention is preferably implemented with a torch with fusible wire passing through the wall of the nozzle at an angle of less than 50 °, in particular the torch described in EP-A-1459831. Indeed, in such a torch, the wire feed, which is integrated in the torch, is at an angle of the order of generally 10 ° to 20 °, for example of the order of 15 °, compared to the axis of the non-fusible electrode and this, by maintaining a small distance between the end of the wire and the cone end of the tungsten electrode, for example 1 mm minimum or the diameter of the filler wire

In all cases, to obtain a dropwise metal transfer as mentioned above, the end of the fuse wire is guided and also maintained permanently at a distance of less than about 2 mm from the end of the electrode. tungsten, that is to say that the distance between the outer surface of the fuse wire and the electrode should not exceed 2 mm, preferably greater than 1 mm.

The drop transfer according to the invention has the following advantages:

- a point of impact below the arc, which facilitates the positioning of the torch - Transfer controlled by successive drops of metal well directed in the bath.

- An aesthetic appearance of the welding bead corresponding to particular recommendations sought.

- Gravity transfer and surface tension facilitates working in position. - Adjustment and control of the frequency and size of the drops by linked by the previous relationship to the wire speed for a given wire diameter.

- A realization of multi-directional welding cords without changing the orientation of the wire at the TIG torch.

- a possibility to achieve welding synergies, as for the MIG / MAG welding process. The preferred wire speed is given according to the various parameters chosen by the operator: material to assemble, nature and diameter of the filler wire, intensity, shielding gas, welding speed ....

The invention is illustrated in the attached figure which schematizes a transfer by drops according to the invention.

More specifically, there is shown a TIG welding torch with non-fusible electrode 1 fed with a fuse wire 2. As can be seen, the hottest part of the electric arc 6 which forms at the tip 7 of the electrode 1 makes it possible to obtain a progressive melting of the end 3 of the wire 2 in the arc zone 5 The transfer of the molten metal from the end 3 of the wire 2 to the solder bath 8 forming the welded bead on the part 10 is done by successive drops 4 whose drop diameter is between 1.2 and 4 times the diameter. The yarn typically has a diameter of between 0.6 and 1.6 mm. The frequency of the drops is between 20 and 90 Hz. The frequency of the droplets is generated by a pulsation of the wire combined with a pulsation of current.

Moreover, the distance D between the tip of the electrode 1 and the surface of the parts to be welded is between 2 mm and 3 mm approximately. Moreover, the minimum distance d between the wire 2 and the surface of the electrode 1, including at its point 7, is kept less than 2 mm but preferably greater than 1 mm.

Whatever the type of welded material, it is found that the wire speed range for obtaining drop transfer is wide and flexible with respect to the frequency and the size of the corresponding drops. The minimum wire speed (min Vf) and maximum wire speed (max Vf) are those to be applied to remain in a drop transfer. Above the maximum value, a liquid bridge transfer is achieved.

The drop transfer method of the invention can be applied to a variety of joint configurations: butt, lap, angle, and flanged welding, for degraded preparation conditions, such as games or misalignments, as this type of transfer. can absorb more specifically, and finally for reloading operations since it controls the energy provided respectively to the filler wire and the support material.

Claims

claims

1. A method of brazing or arc welding using a TIG torch provided with a non-fuse electrode and a fuse wire of given diameter, wherein:

a) the TIG torch is fed with said fuse wire in such a way that the fuse wire feed is operated at an angle less than 50 ° with respect to the axis of the electrode,

b) the end of the fuse wire is permanently guided and maintained at a distance less than 2 mm from the end of the tungsten electrode of the TIG torch,

c) a progressive melting of the end of the fuse wire by the electric arc generated between the non-fuse electrode and at least one part to be welded so as to achieve a transfer of molten metal by drops from the end of the wire to said at least one part and thus obtain a weld or weld-solder joint,

characterized in that the transfer of metal to the weld joint is operated by successive molten metal droplets, deposited at a frequency between 20 Hz and 90 Hz, and the size of said drops is between 1.2 and 4 times the diameter fusible wire.

2. Method according to claim 1, characterized in that the transfer frequency of the droplets is preferably between 30 Hz and 80 Hz.

3. Method according to one of claims 1 or 2, characterized in that the transfer frequency of the droplets is between 20 Hz and 40 Hz, and the size of the drops is between 3 and 4 times the diameter of the fusible wire, preferably of the order of 30 Hz.

4. Method according to one of claims 1 or 2, characterized in that the transfer frequency of the droplets is between 70 Hz and 90 Hz, and the size of the drops is between 1.2 and 1.5 times the diameter fusible wire, preferably of the order of 80 Hz.

5. Method according to one of claims 1 to 4, characterized in that the frequency of the droplets is generated by a pulsation of the wire synchronized with a current pulsation.

6. Method according to one of claims 1 to 5, characterized in that the supply of fusible wire is operated at an angle between 10 and 30 ° relative to the axis of the electrode, preferably between 10 and 20 °.

7. Method according to one of claims 1 to 6, characterized in that guides and permanently maintains the end of the fuse wire at a distance of less than 1.5 mm from the end of the electrode. tungsten torch TIG, preferably greater than 1 mm.

8. Method according to one of claims 1 to 7, characterized in that, during welding, a gaseous protection of the weld joint being formed and / or the tungsten electrode with a gas chosen from argon, helium and mixtures thereof, with or without the addition of nitrogen, and mixtures of argon and hydrogen.

9. Method according to one of claims 1 to 8, characterized in that it is used for welding or brazing one or more coated steel parts, in particular galvanized steel or electro-galvanized, or one or more parts made of austenitic or ferritic stainless steel, nickel or a nickel alloy, titanium or a titanium alloy, aluminum or an aluminum alloy.

10. Method according to one of claims 1 to 9, characterized in that the intensity of the direct current supplying the TIG torch is between 10 A and 400 A and / or the voltage is between 10 V and 20 V.

11. Method according to one of claims 1 to 10, characterized in that the wire has a diameter of between 0.6 mm and 1.6 mm.

12. Method according to one of claims 1 to 11, characterized in that welded together several metal parts

13. Method according to one of claims 1 to 12, characterized in that carries out reloading operations by welding with dilution and controlled deposition rates.