EP1427564A1

EP1427564A1 - Hybrid laser-arc welding method with gas flow rate adjustment

Info

Publication number: EP1427564A1
Application number: EP02774857A
Authority: EP
Inventors: Karim Chouf; Philippe Lefebvre; Olivier Matile
Original assignee: Air Liquide SA; LAir Liquide SA a Directoire et Conseil de Surveillance pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2001-09-13
Filing date: 2002-07-29
Publication date: 2004-06-16
Also published as: US20050011868A1; WO2003022512A1; FR2829414B1; CA2460094A1; FR2829414A1; JP2005501737A

Abstract

The invention concerns a hybrid arc-laser method for welding metal parts, such as a tube or tailored blanks by producing at least a weld joint between edges to be welded and by using a laser beam and an electric arc combined with each other so as to melt and subsequently solidify the metal along said edges to be welded. Said method consists in: (a) striking at least a pilot arc between an electrode and a hybrid welding head nozzle, said electrode being powered with electric current and being contacted with a first gas input in said hybrid welding head, said first gas having a gas composition capable of promoting sparking of the pilot arc; (b) transferring the thus sparked pilot arc to the edges of the part(s) to be welded; and (c) feeding said hybrid welding head with a second gas so as to obtain a protective gaseous atmosphere consisting of a mixture of the first gas and the second gas, said protective gaseous atmosphere being evacuated towards the welding zone by said hybrid welding head and protecting at least part of the welding zone during welding of the weld joint by combining the laser beam and the electric arc, the volume flow rate of the first gas (Q1) and the volume flow rate of the second gas (Q2) being adjusted such that: 0 < Q1 < Q2, preferably, 2 < Q2/Q1 < 55.

Description

Laser-arc hybrid welding process with gas flow adjustment

The present invention relates to a hybrid welding method and installation combining a laser beam and an electric arc, in particular a plasma arc, using particular gases or gas mixtures as starting gas for the electric arc and assistance of the laser beam, and its application to the welding of tubes or flanks butted (tailored blan s), in particular usable in the automobile industry.

In plasma arc welding, performing a correct and efficient ignition of the arc, at the start of a welding operation, is essential and essential since, if ignition does not take place at all, welding cannot have fault due to an electric arc, whereas if it is done incorrectly, it may result in damage to certain elements of the welding head, for example the nozzle.

Currently, there are different ways of proceeding to strike an arc in an electric arc torch, namely:

- pilot spark ignition resulting from the use of either a high voltage, typically from 2000 to 5000 volts, or a high frequency, for example from 10 to 50 kHz. However, this way of doing things has the drawback of being the source of electromagnetic disturbances by radio or by conduction, which involves a risk of deterioration of electrical or electronic equipment.

- ignition by pilot arc with creation of a low power electric arc between the electrode and the nozzle of the torch. This technique has the advantage of not causing any radio interference.

In both cases, when the arc is struck, it is then transferred to the part or parts to be welded.

However, whatever the technology used, the arc is preferably struck in a gas with low ionization potential which must, moreover, be neutral so as not to cause contamination or deterioration of the electrode or react well negatively with the molten metal.

As shown in the following table, argon meets these conditions because it is neutral and has a relatively low ionization potential, unlike nitrogen or C0 ₂ which, although having ionization potentials even weaker, can react with the molten metal with, for example, the formation of nitrides for nitrogen and deterioration of the tungsten electrode for C0 ₂ .

In addition, in plasma arc welding, it is usual to use plasma gases mainly containing argon.

In other words, in plasma arc welding, no argon or an argon gas is used to strike the arc, and then thereafter to carry out the actual welding operation.

Furthermore, in laser beam welding, in particular with CO gas type laser sources, due to the high specific powers used, generally several kilowatts, the production of the weld is based on localized melting phenomena of the matter at the point of impact of the laser beam where a capillary is formed filled with metallic vapors ionized at high temperature, called keyhole (keyhole). The walls of this capillary are made of molten metal.

This capillary has an important role as it allows to transfer the ener ^gy directly to the heart of the material. The molten bath thus formed and maintained is gradually moved between the parts to be assembled, as a function of the relative displacement of the laser beam relative to the parts to be welded, and the metal of the weld joint solidifies, after the passage of the laser beam, in ensuring the joint assembly of the parts.

The appearance of the capillary is accompanied by the formation of a plasma of metallic vapors, that is to say of an ionized gaseous medium, electrically neutral and at a temperature of several thousand degrees.

The metal vapor plasma results from a good coupling between the laser beam and the part, and it is therefore inevitable. This type of plasma absorbs a small amount of incident energy and does not cause a significant change in the width and depth of the weld bead.

Under certain conditions of power, speed, thickness, nature and composition of the gas, configuration, etc., the metal vapor plasma transfers part of its energy to the shielding gas used to protect the welding area from contamination of it. ci by atmospheric impurities, and there is then a risk of the formation of another plasma from the shielding gas.

However, the creation of such a plasma of the shielding gas can absorb the energy of the incident Jaser beam and, in this case, the weld bead becomes wider on the surface and penetrates much less in the thickness of the parts to be welded. To remedy the formation of the plasma of the shielding gas, it is necessary to use a gas with high ionization potential and it turns out that helium is the most suitable gas to limit the appearance of this type of plasma.

In recent years, in parallel with the above-mentioned welding processes, a welding process called hybrid arc-laser welding has been developed based on a combination of a laser beam and an electric arc.

Hybrid arc and laser welding methods have been described in particular in documents EP-A-793558 EP-A-782489; EP-A-800434; US-A-5,006,688; US-A-5,700,989; EP-A-844042; Laser GTA'Weiding of aluminum alloy 5052, TP Diebold and CE Albright, 1984, p. 18-24; SU-A-1815085, US-A-4,689,466; Plasma arc augmented laser welding, RP Walduck and J. Biffin, p.172-176, 1994; or ΗG or MIG arc augmented laser welding of thick mild steel plate, Joining and Materials, by J Matsuda et al., p. 31-34, 1988.

In general, a hybrid plasma-laser welding process, or more generally laser-arc welding, is a combined or mixed welding process which associates electric arc welding with a laser beam. The arc-laser method consists in generating an electric arc between an electrode, fuse or non-fuse, and the part to be welded, and in focusing a power laser beam, in particular a laser of type YAG or of type C0 ₂ , in the area arc, that is to say at the level or in the joint plane obtained by joining edge-to-edge of the parts to be welded together.

Such a hybrid process makes it possible to considerably improve the welding speeds compared to laser welding alone or to arc or plasma welding alone, and also makes it possible to significantly increase the tolerances for positioning the edges before welding as well. that the play tolerated between the edges to be welded, in particular with respect to welding by laser beam alone which requires a high precision of positioning of the parts to be welded because of the small size of the focal point of the laser beam.

The implementation of a hybrid arc-laser welding process requires the use of a welding head which makes it possible to combine the laser beam and its focusing device, as well as a suitable welding electrode. Several head configurations are described in the documents mentioned above and it can be said, in summary, that the laser beam and the electric arc or the plasma jet can be delivered by a single welding head, c that is to say, they exit through the same orifice, or else through two separate welding heads, one delivering the laser beam and the other the electric arc or the plasma jet, these meeting in the welding zone, as for example taught by documents WO-A-01/05550 or EP-A-1084789.

Hybrid arc-laser processes are known to be perfectly suited for welding tailored blanks for the automotive industry, as they allow a well-welded bead free from gutters, as mentioned EP-A-782489 or Laser plus arc equals power, Industrial Laser Solutions, February 1999, p.28-30.

When making the weld joint, it is essential to use an assist gas to assist the laser beam and protect the welding area from external aggressions and a gas for the electric arc, in particular a plasma gas used to create the arc plasma jet in the case of an arc-plasma process.

From this, it is easily understood that, when a laser source is coupled with a plasma arc welding device to implement a hybrid plasma-laser arc welding process, the above problem then becomes very complex because it is therefore necessary not only to avoid the formation of the plasma of the shielding gas at the level of the molten bath but also to be able to obtain correct ignition of the arc generated by the electrode.

As explained above, the plasma gas must contain essentially argon to allow effective arc striking. However, in contact with the metallic vapor plasma generated by the impact of the laser beam on the material to be welded, a plasma gas rich in argon can be easily ionized and lead to the formation of an absorbent plasma for the laser beam and therefore harmful for the quality of the weld because it reduces the depth of penetration of the beam, conversely, the shielding gas of the weld pool must mainly contain helium to avoid the formation of an absorbent plasma.

However, if the end of the electrode is surrounded and in contact with helium in high proportion, the plasma arc cannot strike properly.

The object of the present invention is therefore to propose a hybrid arc-laser welding process which does not pose these problems, that is to say a hybrid arc-laser welding process, in particular plasma-laser arc, with effective ignition. and absence or near absence of formation of absorbent plasma.

The solution of the invention is then a hybrid arc-laser welding process of one or more metal parts to be welded by making at least one weld joint between edges to be welded carried by the said metal part or parts, said joint of welding being obtained by implementing at least one laser beam and at least one electric arc combining with one another so as to obtain a fusion then a subsequent solidification of the metal along said edges to be welded , in which the procedure is as follows: (a) ignition of at least one pilot arc between an electrode and a nozzle of a hybrid welding head, said electrode supplied with electric current and being brought into contact with a first gas introduced in said hybrid welding head, said first gas having a gaseous composition capable of promoting the ignition of the pilot arc, (b) subsequent transfer in step (a) of the pilot arc thus initiated towards the edges of the said piece or pieces to be welded,

(c) supplying said hybrid welding head with a second gas so as to obtain a protective gas atmosphere formed from a mixture of the first gas and the second gas, said protective gas atmosphere being expelled towards the welding zone by said hybrid welding head and making it possible to protect at least part of the welding zone during the welding of the weld joint by combination of the laser beam and the electric arc, the volume flow rate of the first gas (Ql) and the volume flow rate of the second gas (Q2) being adjusted such that: 0 <Ql <Q2.

Depending on the case, the method of the invention may include one or more of the following technical characteristics:

in step (a), the first gas forming the priming gas composition contains more than 50% by volume of argon, preferably from 70 to 100% by volume of argon.

- in step (a), the first gas forming the gaseous initiation composition contains, moreover, at least one additional non-oxidizing compound chosen from helium, H ₂ , and N ₂ in a content of 0.05 to 30 % in volume.

- In step (c), the second gas contains at least 40% by volume of helium, preferably from 50 to 100% by volume of helium.

- In step (c), the second gas also contains at least one additive compound chosen from argon, H ₂ , 0 ₂ , C0 ₂ and N ₂ in a content of 0.05 to 30% by volume.

- the volume flow of the first gas (Ql) and the volume flow of the second gas (Q2) are adjusted such that: 2 <Q2 / Ql <55. - the volume flow of the first gas (Ql) and the volume flow of the second gas

(Q2) are adjusted such that: 3 <Q2 / Ql <50, preferably 10 <Q2 / Ql <40.

- In step (c), the laser beam and the plasma arc are delivered, by being combined together, through the same orifice of a welding nozzle.

the gaseous protective atmosphere formed by a mixture of the first gas and the second gas obtained in step (c) contains helium and argon, the proportion by volume of helium being greater than the proportion by volume argon.

- Or the parts to be welded have a thickness between 0.1 and 70 mm, preferably between 0.3 and 50 mm.

- where the parts to be welded are tailored blanks forming elements of an automobile body.

the part or parts to be welded are made of a metal or a metal alloy chosen from coated or uncoated steels, in particular joining steels, steels with high yield strength, carbon steels, steels with a zinc alloy layer on the surface, stainless steels, aluminum or aluminum alloys.

in step (c), the protective gaseous atmosphere contains argon and more than 60% of helium and optionally one or more compounds chosen from Hz, 0 ₂ , C0 ₂ and N ₂ .

- the adjustment of the respective volume flow rates of said first and second gases is carried out during the transfer of step (b) or immediately after transfer of the pilot arc, preferably after the transfer of the pilot arc

- the part to be welded is welded so as to obtain a tube. the approximation of the welding head of the piece or pieces to be welded so as to create a plasma arc is effected after detection of a pilot arc, preferably said approximation is effected almost simultaneously with the sending of the atmosphere protective gas containing at least 50% by volume of helium in step (c).

- The laser beam is emitted simultaneously or subsequently to the formation of the plasma arc so that said beam combines with the arc plasma.

The invention also relates to a method for manufacturing automobile body elements, in which parts forming elements of an automobile body are welded together by implementing a hybrid welding method according to the invention, as well as a method of manufacturing a welded tube, longitudinally or in a spiral, in which the edges of the tube are welded together by implementing a hybrid welding method according to the invention.

- The gas mixture containing said first and second gas contains a proportion of the first gas such that a gaseous plasma from this gas is not formed in contact with the plasma of metallic vapors. The invention is illustrated in the appended figure in which a part of a hybrid welding installation according to the invention is seen, usually comprising a gas laser oscillator (type C0 ₂ laser) producing a coherent high energy monochromatic beam 3. , an optical path equipped with reflecting mirrors making it possible to bring the laser beam 3 to a welding head situated opposite the tube to be welded.

The welding head conventionally comprises a lens or one or more focusing mirrors so as to focus the laser beam 3 at one or more focusing points in the thickness of the parts 10, 11 to be welded and at the joint plane 9 obtained by joining, edge-to-edge, lap or in another configuration, the edges of the parts to be assembled.

In addition, an arc plasma jet is obtained by means of an electrode 1 and a plasma gas 4.

The laser beam 3 and the plasma jet combine in the welding head so as to be expelled together through the single orifice of the nozzle 2 so as to locally concentrate enough power density to melt the edges of the parts to be welded.

It has been demonstrated by the inventors of the present invention that, in order to obtain an effective ignition and then ensure quality welding, it is necessary:

- during the priming phase, to use as the first gas pure argon or a gaseous mixture containing essentially argon, typically from 70 to 100% by volume of argon and the rest possibly being of l helium, hydrogen or any other suitable gas or non-oxidizing gas mixture. This gaseous ignition composition, originating from the source 4, is introduced into the welding head in the immediate vicinity and / or around the electrode 1 so as to effectively strike the pilot arc between said non-fusible electrode 1 and the nozzle 2. Then, when this pilot arc is struck, it is transferred to the parts to be welded together by being expelled through the single nozzle orifice 2 of the welding head. - At the time of welding, to carry out an additional supply of the hybrid head with a second gas, coming from a gas source 5, so as to obtain a mixture of the first and second gases into a protective gas used for. protect the bath of molten metal resulting from the combination of the plasma arc and the laser beam, that is to say the solder joint. The second gas is formed from pure helium or a gaseous mixture based on helium, which preferably contains from 50 to 100% by volume of helium, the remainder being argon, hydrogen, nitrogen, carbon dioxide, oxygen or any other suitable gas or gas mixture.

However, according to the invention, in order to obtain efficient welding, that is to say that no harmful plasma is formed from the shielding gas in contact with the metal vapor plasma and therefore that no no adsorption of a large part of the laser beam 3, it is essential to control, adjust, regulate or choose the volume flow rate of the first gas (Ql with Ql not zero) and the volume flow rate of the second gas (Q2) so that we obtain a flow rate of the second gas significantly higher than that of the first gas (Q2> Q1). The gas flow is managed by means of a conventional control box 6 so that, until a correct ignition is obtained, there is a supply of the welding head with plasma gas (4 ), while once the pilot electric arc has been detected by the control box 6, the latter controls a solenoid valve (not shown) which opens so as to deliver the shielding gas (5) to increase, for example , the helium content in the head so as to pass from a gaseous atmosphere containing mainly argon used to strike the pilot arc to a gaseous atmosphere containing mainly helium usable for welding. The priming cycle is for example the following: - Opening of the valve (not shown) controlling the arrival of the plasma gas 4 around the electrode, for example a flow rate of approximately 5 l / min of argon.

- a low amperage current is delivered between the electrode and the nozzle so as to generate a pilot arc and, when the pilot arc is detected, the welding head is brought closer to the parts to be welded so as to create the plasma of arc which is sent to the edges to be welded

- supplying the welding head with a protective gas, for example helium, at a flow rate of 20 l / min so as to protect the molten bath formed,

- emission of the laser beam 3 and fixing of the intensity of the plasma arc at its welding set point value.

The invention is applicable in particular to the welding of tubes, in axial or helical welding, or in butted flanks intended to constitute at least part of a vehicle body element.

The invention can be used to assemble by hybrid welding metal parts having equal or different thicknesses, and / or metallurgical compositions or identical or different metallurgical grades, and / or equal or different thicknesses.

In addition, depending on the welding methods and preparations used, the weld joint is often characterized by a difference in level between the upper planes of each of the parts to be welded, thus leading to the generation of a "step", but it is possible to also experience the opposite, namely the flanks type seals the tailored whose upper planes are aligned but the lower planes are not of the same level and where ^v market is located at the back of the weld joint.

This type of weld is frequently found in the automobile industry where the parts, once welded, are stamped to give them their final shapes, for example the various parts which are used in the manufacture of a car bodywork and in particular the doors, the roof, hood, trunk or structural elements of the passenger compartment.

Of course, in all cases, the part or parts to be welded and the welding head are driven in a movement of movement relative to one another, that is to say either the part or parts are fixed and the welding head moves, the reverse.

Furthermore, it goes without saying that the welding phase can be done in one or more passes, in particular according to the diameter and the thickness to be welded.

Claims

claims

1. Hybrid arc-laser welding method for one or more metal parts to be welded by producing at least one weld joint between edges to be welded carried by said metal part or parts, said weld joint being obtained by placing work of at least one laser beam and at least one electric arc combining with each other so as to obtain a fusion then a subsequent solidification of the metal along said edges to be welded, in which one operates:

(a) striking at least one pilot arc between an electrode and a nozzle of a hybrid welding head, said electrode supplied with electric current and being brought into contact with a first gas introduced into said hybrid welding head, said first gas having a gaseous composition capable of promoting the ignition of the pilot arc,

(b) a subsequent transfer in step (a) from the pilot arc thus initiated towards the edges of the said piece or pieces to be welded,

(c) supplying said hybrid welding head with a second gas so as to obtain a protective gas atmosphere formed from a mixture of the first gas and the second gas, said protective gas atmosphere being expelled to the welding zone by said hybrid welding head and making it possible to protect at least part of the welding zone during welding of the weld joint by combination of the laser beam and the electric arc, the volume flow rate of the first gas (Ql) and the volume flow rate of the second gas (Q2) being adjusted such that: 0 <Ql <Q2.

2. Method according to claim 1, characterized in that in step (a), the first gas forming the priming gas composition contains more than 50% by volume of argon, preferably from 70 to 100% by volume of argon.

3. Method according to one of claims 1 or 2, characterized in that in step (a), the first gas forming the gaseous initiation composition contains, moreover, at least one additional non-oxidizing compound chosen from helium, H2, and l \ l ₂ in a content of 0.05 to 30% by volume.

4. Method according to one of claims 1 to 3, characterized in that in step (c), the second gas contains at least 40% by volume of helium, preferably from 50 to 100% by volume d 'helium.

5. Method according to one of claims 1 to 4, characterized in that in step (c), the second gas also contains at least one additive compound chosen from argon, H ₂ , 0 ₂ , C0 ₂ and N ₂ in a content of 0.05 to 30% by volume.

6. Method according to claim 1, characterized in that the volume flow rate of the first gas (Ql) and the volume flow rate of the second gas (Q2) are adjusted such that: 2 <Q2 / Ql <55.

7. Method according to one of claims 1 or 6, characterized in that the volume flow rate of the first gas (Ql) and the volume flow rate of the second gas (Q2) are adjusted such that: 3 <Q2 / Ql <50, of preferably 10 <Q2 / Ql <40.

8. Method according to one of claims 1 to 7, characterized in that in step (c), the laser beam and the plasma arc are delivered, by being combined together, through the same orifice of a nozzle welding.

9. Method according to one of claims 1 to 8, characterized in that the protective gaseous atmosphere formed of a mixture of the first gas and the second gas obtained in step (c) contains helium and argon, the volume proportion of helium being greater than the volume proportion of argon.

10. Method according to one of claims 1 to 9, characterized in that the part or parts to be welded have a thickness of between 0.1 and 70 mm, preferably between

0.3 and 50 mm.

11. Method according to one of claims 1 to 10, characterized in that the part or parts to be welded are butted flanks forming elements of an automobile body.

12. Method according to one of claims 1 to 11, characterized in that the part or parts to be welded are made of a metal or a metal alloy chosen from coated or uncoated steels, in particular joining steels, steels with high elastic limit, carbon steels, steels comprising on the surface a layer of zinc alloy, stainless steels, aluminum or aluminum alloys.

13. Method according to one of claims 1 to 12, characterized in that in step (c), the protective gaseous atmosphere contains argon and more than 60% of helium and optionally one or more compounds chosen from H2, O2, CO2 and N2.

14. Method according to one of claims 1 to 13, characterized in that the adjustment of the respective volume flow rates of said first and second gas is carried out during the transfer of step (b) or immediately after transfer of the pilot arc , de, preferably after the transfer of the pilot arc.

15. Method according to one of claims 1 to 14, characterized in that the part to be welded is welded so as to obtain a tube.

16. Method according to one of claims 1 to 15, characterized in that the approximation of the welding head of the part or parts to be welded so as to create a plasma arc is operated after detection of a pilot arc, preferably, said approximation is effected almost simultaneously with the sending of the protective gaseous atmosphere containing at least 50% by volume of helium in step (c).

17. Method according to one of claims 1 to 16, characterized in that the laser beam is emitted simultaneously or subsequently to the formation of the plasma arc so that said beam combines with the arc plasma.

18. A method of manufacturing automobile body elements, in which parts forming elements of an automobile body are welded together by implementing a hybrid welding method according to one of claims 1 to 17.

19. A method of manufacturing a welded tube, longitudinally or in a spiral, in which the edges of the tube are welded together by implementing a hybrid welding method according to one of claims 1 to 17.