FR3039442A1 - METHOD FOR WELDING A STEEL WORKPIECE ON AN ALUMINUM PART BY PARTIALLY COVERING AN INTERNAL SIDE OF A PERIPHERAL EDGE WITH A WELDING WELD - Google Patents

Abstract

A method for welding a first piece (P1) made of steel and comprising a peripheral edge (BP) delimited by end faces (FE1), internal (FI) and external (FE2), on a part (PS) a second piece (P2) of aluminum. This method comprises a first step where the part (PS) is inclined with respect to a horizontal direction and the external (FE2) non-oxidized face is pressed against the part (PS), and a second stage where generates on the part (PS), at a selected distance above the end face (FE1), an aluminum-based solder bath (BS) with a cold metal transfer torch, and is then lowered by gravity the solder bath (BS) until it completely covers the end face (FE1) and a selected part (PC) of the inner face (FI), then the solder bath is left (BS) ) to solidify.

Description

METHOD FOR WELDING A STEEL PART ON AN ALUMINUM PART BY PARTIALLY COVERING AN INTERNAL SIDE OF A PERIPHERAL EDGE WITH A SOLDER BATH The invention relates to methods for welding steel parts onto aluminum parts .

As known to those skilled in the art, in certain fields, such as that of vehicles, possibly automobiles, the realization of certain objects (or devices) comprises a step of welding a steel part on an aluminum part . This is for example the case of so-called hybrid wheels in which one of the parts is a steel web intended to be secured to a hub of one axle of the vehicle, and the other part is an aluminum rim.

Among the welding processes used, there may be mentioned that which consists in pressing the outer face of the peripheral edge of the steel piece against a portion of the aluminum piece, then generating on the latter, against the end face of this peripheral edge, an aluminum-based solder bath with a cold metal transfer torch (or CMT ("Cold Metal Transfer")) and then let this solder bath solidify. Such a welding method is described in particular in patent document FR 2994668.

With this type of process, the arc at the end of the torch induces a great heat which simultaneously generates a local melting of the aluminum part and a local melting of the peripheral edge of steel. Alas, this last local merger prevents the realization of a good brazing with the solder bath, and thus impairs the quality of the steel / aluminum connection, which can lead to a scrapping of the two parts because of a disability to support certain planned efforts.

In order to try to improve the situation, it has been proposed to use a peripheral edge of the steel part whose end face makes an obtuse angle (strictly greater than the usual 90 °) with its external face which is pressed against the aluminum part. The solder bath is thus deposited in a concave zone delimited by the inclined end face and the aluminum part. Such an embodiment variant is described in particular in patent document EP 0944483. Since the volume of the concave zone for receiving the solder bath is rather small, this variant embodiment does not bring complete satisfaction, and in particular still does not allow support certain planned efforts. The invention is therefore particularly intended to improve the situation.

It proposes in particular for this purpose a method for welding a first piece made of steel and comprising a peripheral edge delimited by an end face, an inner face and an outer face, on a part of a second piece of aluminum, and comprising: - a first step in which the part of the second part is positioned in an inclined manner with respect to a horizontal direction and the outer face of the non-oxidized peripheral edge is pressed against this part of the second part, and - a a second step in which an aluminum-based solder bath with a cold metal transfer torch is generated on the part of the second part, in an area at a selected distance above the end face, then the gravity bath is lowered by gravity until it completely covers, under this zone, the end face and a chosen part of the inner face which extends the face of the weld. end, then let the solder bath solidify.

Thanks to the covering of the selected portion of the inner face by the brazing resulting from the solidification of the solder bath, the brazing has a very good adhesion in the horizontal direction and therefore can now ensure good mechanical strength of the connection.

The process according to the invention may comprise other characteristics which may be taken separately or in combination, and in particular: in the first step, the peripheral edge provided with a zinc coating may be plated or after having pickled with a deoxidizer; in the first step, it is possible to use a peripheral edge having an end face substantially perpendicular to the inner and outer faces. In this case, the selected portion of the inner face extends over a distance of between about 0.5 mm and about 4 mm; alternatively, in the first step, it is possible to use a peripheral edge having an end face substantially perpendicular to the external face and an internal face whose chosen portion makes an acute angle, strictly less than 90 °, with the face of end, then is extended by a complementary portion substantially parallel to the outer face; the acute angle may be between about 30 ° and about 60 °; in the first step, the part of the second piece can be tilted with respect to the horizontal direction by an angle which is between about 70 ° and about 90 °; in the second step, the weld pool can be lowered by gravity by separating and then bringing the end of the torch at least once closer to the solder bath; this spacing may be between about 1 mm and about 3 mm; in the second step, the zone may be located at a distance above the end face which is between about 1 mm and about 3 mm; in the second step, a solder bath based on aluminum, silicon and manganese can be generated. The invention also proposes a hybrid wheel intended to equip a vehicle and comprising a first piece of steel secured to a second aluminum part by the implementation of a welding method of the type presented above.

For example, the first part may be a web intended to be secured to a hub of an axle of the vehicle, and the second part may be a rim. Other features and advantages of the invention will emerge on examining the following detailed description, and the accompanying drawings, in which: FIGS. 1A to 1C schematically and respectively show, in perspective views, an example Hybrid wheel veil before welding, an example of hybrid wheel rim before welding, and a hybrid wheel consisting of the sail and rim of FIGS. 1A and 1B just prior to welding; FIG. 2 is a diagrammatic illustration in a sectional view in FIG. a plane ZY, the hybrid wheel of FIG. 1C; FIGS. 3A to 3C show schematically and respectively, in sectional views in the plane ZY, the hybrid wheel of FIGS. 1C and 2 at the beginning, at an intermediate stage and at the end of the implementation of the welding method according to the invention, and - Figure 4 schematically illustrates, in a sectional view in the ZY plane, a hybrid wheel consisting of the rim of Figure 1B and a variant e of the web of Figure 1A at the end of the implementation of the welding process according to the invention. The object of the invention is in particular to propose a method for allowing the welding of a first piece P1 of steel on a part PS of a second part P2 of aluminum.

In the following, by way of nonlimiting example, the first P1 and second P2 parts are respectively considered to be a steel sail and an aluminum rim intended to form a hybrid wheel RH of a vehicle, possibly of the automotive type. . But the invention is not limited to this type of application. It concerns indeed any type of device or system or installation comprising a first piece of steel welded to a second aluminum part.

In the figures, the direction X is a first horizontal direction, the direction Y is a second horizontal direction, perpendicular to the first horizontal direction X, and the direction Z is a so-called vertical direction, perpendicular to the first X and second Y horizontal directions.

FIGS. 1A and 1B respectively show schematically an example of a first piece P1 of steel (here constituting a Hybrid RH web) before welding, and a first example of a second piece P2 made of aluminum (here constituting a hybrid wheel rim). RH) before welding. Moreover, FIGS. 1C and 2 are schematically represented by an example of a hybrid wheel RH consisting of the webs P1 and the rim P2 of FIGS. 1A and 1B, just before the implementation of a welding method according to the invention.

As illustrated, the first piece P1 steel comprises a peripheral edge BP (here annular) provided with an end face FE1, an internal face Fl and an outer face FE2 (opposite its inner face Fl), and intended to be secured to a selected part PS of the second piece P2 aluminum having its outer face FE2 oriented towards the latter (P2). This securing can be done on the entire peripheral edge BP of the web P1 or in selected areas (for example four).

The welding method according to the invention comprises first and second steps.

As illustrated in FIG. 3A, in the first step the portion PS of the second piece P2 is positioned in an inclined manner with respect to a horizontal direction (for example the second Y), then the external face FE2 of the peripheral edge BP is plastered, unoxidized, of the first piece P1 against this part PS of the second piece P2, by orienting the end face FE1 upwards.

It is important to note that the term "non-oxidized" here means being able to braze. This ability may result from the fact that the peripheral edge BP of the first piece P1 has previously been provided with a zinc coating, electrolytic or galvanized (before plating), or stripped with a deoxidizer. It is recalled that the very high temperature which is induced by a torch arc during a welding causes a spraying of the protective zinc layer which ensures that the peripheral edge BP is not oxidized at the moment when it will be effectively welded (or brazed) to the PS portion of the second piece P2.

Preferably, in the first step the portion PS of the second piece P2 is inclined with respect to the second horizontal direction Y by an angle which is between about 70 ° and about 90 °. It will be noted that in the nonlimiting exemplary embodiment illustrated in FIGS. 3A to 3C, this angle of inclination is substantially equal to 90 °. Therefore, the PS portion of the second piece P2 is substantially parallel to the vertical direction Z and substantially perpendicular to the second horizontal direction Y, and thus the end face FE1 of the peripheral edge BP is substantially parallel to this second horizontal direction Y (position called "cornice"). But other values of inclination angle can be used as long as they allow the realization of the second step.

In the second step, of the method according to the invention, one begins, as illustrated in FIG. 3A, to generate on the part PS of the second piece P2, in a zone Z which is located at a selected distance above the FE1 end face of the BP peripheral edge, an aluminum-based BS solder bath with a cold metal transfer TS (or CMT) torch.

It should be noted that here the term "solder bath" refers to a small amount of melted, molten solder metal that has been generated by the end (or wire) AND of a CMT TS torch. It is recalled that the CMT technique is an electric arc welding technique in which the AND wire undergoes back-and-forth movements which allow a transfer of material with a reduced current (almost zero), and therefore a deposit of material more "cold" than with a conventional welding technique. By way of non-limiting example, the solder bath BS may be based on aluminum, silicon and manganese. For example, it may comprise 3% silicon and 1% manganese.

As illustrated in FIGS. 3B and 3C, the rest of the second step consists in lowering by gravity the solder bath BS (arrow F1) until it completely covers, under the zone Z, the end face FE1 and a selected portion PC of the inner face Fl which extends the end face FE1, then let the solder bath BS solidify to define a weld or a final soldering SF (see Figures 3C and 4).

The initial deposit of molten metal (or solder bath BS) in a zone Z which is distant from the end face FE1 is intended to prevent the melting of the peripheral edge BP steel by the arc of the end ET of the CMT TS torch. This allows a final connection by brazing, quality.

It should be noted that the zone Z may, for example, be generated at a distance above the end face FE1 which is between about 1 mm and about 3 mm. For example, this distance may be chosen substantially equal to 2 mm. The inclination of the portion PS of the second piece P2 is intended to allow the descent by gravity of the solder bath BS (materialized by the arrow F1 of Figure 3B).

Furthermore, for the solder bath BS does not solidify before reaching the end face FE1, it is particularly advantageous to maintain it at an elevated temperature. For this purpose, it is possible, for example, to separate and then close at least once the welding bath BS (during descent by gravity) the ET end of the CMT torch TS. As illustrated by the arrow F2 of FIG. 3B, this variation in distance between the solder bath BS and the end ET (by going back and forth) can be substantially along the second horizontal direction Y. for example, the spacing (or variation in distance) may be between about 1 mm and about 3 mm. Thus, it can be chosen substantially equal to 2 mm.

The number of spacings and reconciliations (or back-and-forth) varies in particular as a function of the distance separating the zone Z from the end face FE1, the angle of inclination of the part PS of the second part P2, and the temperature of the solder bath BS.

As illustrated in Figures 3 and 4, the implementation of the invention can be done using a first piece P1 whose peripheral edge BP may have at least two different shapes.

In the first example shown nonlimitingly in FIGS. 3A to 3C, a peripheral edge BP having an end face FE1 substantially perpendicular to the internal faces F1 and external FE2 is used. In this case, the selected portion PC of the inner face F1 extends over a distance of between about 0.5 mm and about 4 mm. Thus, it (PC) can extend over a distance substantially equal to 2 mm.

The final soldering SF, which here covers the selected part PC of the inner face Fl (in the ZX plane), has a very good adhesion in the vertical direction Z, and hence can now ensure a good mechanical strength of the SF / P1 bond .

In the second example shown non-limitatively in FIG. 4, a peripheral edge BP having an end face FE1 substantially perpendicular to the external face FE2 and an internal face F1 whose chosen part PC is made at an acute angle, strictly less than 90 °, with the end face FE1, then is extended (the side opposite the end face FE1) by a complementary portion PC 'which is substantially parallel to the outer face FE2.

For example, this acute angle can be between about 30 ° and about 60 °. Thus, it can be chosen sensiblemert equal to 45 °.

The internal face F1 is thus chamfered at its chosen part PC, which advantageously makes it possible to increase the area of the peripheral edge BP of the first piece P1 which is in contact with the final soldering SF, and therefore the mechanical strength of the SF / P1 link. This also makes it possible to reduce the normal stress on the brazing plane ZX because of the inclination of the connection SF / P1 with respect to the principal stress in the vertical direction Z. Moreover, this also makes it possible to optimize the plating of the first piece P1 on the second piece P2 during the heat shrinkage of the SF solder.

Claims (10)

A method of welding a first piece (P1) made of steel and comprising a peripheral edge (BP) delimited by end faces (FE1), internal (F1) and external (FE2), on a part (PS). ) of a second piece (P2) made of aluminum, characterized in that it comprises a first step in which said portion (PS) of the second piece (P2) is positioned in an inclined manner with respect to a horizontal direction and in a plate said outer face (FE2) of said peripheral edge (BP), unoxidized, against said portion (PS) of the second piece (P2), and a second step in which is generated on said portion (PS) of the second piece (P2 ) in an area (Z) at a selected distance above said end face (FE1), an aluminum-based solder bath (BS) with a cold metal transfer torch (TS), then, by gravity, said solder bath (BS) is lowered until it completely covers, under said zone (Z), said end face (FE1) and a selected portion (PC) of said inner face (F1) extending said end face (FE1), and then allowing said solder bath (BS) to solidify. 2. Method according to claim 1, characterized in that in said first step plate said peripheral edge (BP) provided with a zinc coating. 3. Method according to claim 1, characterized in that in said first step is said plate said peripheral edge (BP) after pickling with a deoxidizer. 4. Method according to one of claims 1 to 3, characterized in that in said first step is used a peripheral edge (BP) having an end face (FE1) substantially perpendicular to said inner faces (Fl) and external (FE2 ), and in that said selected portion (PC) of the inner face (F1) extends over a distance of between about 0.5 mm and about 4 mm. 5. Method according to one of claims 1 to 3, characterized in that in said first step is used a peripheral edge (BP) having an end face (FE1) substantially perpendicular to said outer face (FE2) and a face internal portion (F1) of which said selected portion (PC) makes an acute angle, strictly less than 90 °, with said end face (FE1), then is extended by a complementary portion (PC ') substantially parallel to said outer face ( FE2). 6. The method of claim 5, characterized in that said acute angle is between about 30 ° and about 60 °. 7. Method according to one of claims 1 to 6, characterized in that in said first step is inclined said portion (PS) of the second piece (P2) relative to said horizontal direction by an angle of between about 70 ° and about 90 °. 8. Method according to one of claims 1 to 7, characterized in that in said second step is lowered by gravity said weld pool (BS) by removing and then bringing closer to said weld pool (BS) at least once. end (ET) of said torch (TS). 9. hybrid wheel (RH) for a vehicle, characterized in that it comprises a first piece (P1) of steel secured to a second piece (P2) of aluminum by the implementation of a welding process according to the one of the preceding claims. 10. Hybrid wheel according to claim 9, characterized in that said first piece (P1) is a web intended to be secured to a hub of an axle of said vehicle, and said second piece (P2) is a rim.