Method for joining by welding two bars made of metal material

Abstract

The invention relates to a method for joining by welding two substantially longitudinal bars (12) made of metal material with determined first transverse thicknesses (e1), comprising the steps of: - (ET1) placing said bars (12) longitudinally side by side with free ends (14) of said bars (12) in the same transverse plane (P) so as to form a part blank (16) having a transverse thickness (E1) comprising the cumulative first transverse thicknesses (e1) of said bars (12), - (ET2) positioning a welding tool (18) at the free end (14) of said bars (12), and welding said free ends (14) of said bars (12) with a weld (20) of determined width (E2), characterized in that it comprises an additional step (ETS) during which the part blank (16) is widened transversely in end sections (24) of said bars (12) so that its transverse thickness (E3) is greater than the width (E2) of said weld (20).

Description

[0001] DESCRIPTION

[0002] TITLE: PROCESS FOR ASSEMBLING TWO METALLIC BARS BY WELDING

[0003] Technical field of the invention

[0004] The invention relates to a method of assembling two bars made of metallic material by welding.

[0005] Technical background

[0006] In an electrical organ or a power component, or more generally in an organ through which high electrical powers are transmitted, it is common to have to weld relatively large conductive metal bars, these bars being made of copper for certain applications.

[0007] For certain applications, such as the welding of an electric machine rotor with its excitation system, it may be necessary to butt weld two substantially longitudinal metal bars placed parallel to each other. Such bars are generally of a thickness of the order of a few millimeters, typically 2 to 4 mm, which allows butt welding to be carried out by numerous welding processes known in the state of the art.

[0008] In certain specific applications, however, it may be necessary to use bars of a reduced thickness, typically of the order of 1 mm, which limits the choice of available welding processes and complicates their execution.

[0009] In the context of large-scale production, it is generally preferred to use a laser welding process, which allows the end assembly of the bars to be carried out by a welding robot at high speeds and with high quality.

[0010] However, when assembling bars with a thickness reduced to the order of a millimeter, such as those used for the connection of an electrical machine rotor with its excitation system, it has been found that the melting of the metal at the end of the bars under the effect of the laser beam produces a drop of molten metal which is of a dimension much greater than the cumulative thickness of the bars, which has the consequence of causing a flow of metal along the bars and a weld which is on the one hand unsightly and which can on the other hand pose reliability problems in the long term.

[0011] However, it is not possible in this type of application to increase the thickness of the bars so that the drop of molten metal remains contained at the end of the bars, nor is it possible to use a welding process generating a drop of molten metal of smaller size.

[0012] There is therefore a real need for a welding assembly process for two bars of reduced thickness which prevents any flow of molten metal along the said bars.

[0013] Summary of the invention

[0014] The invention meets this need by proposing an assembly method making it possible to contain the drop of molten metal at the end of the two bars.

[0015] For this purpose, the invention proposes a method of assembling by welding two substantially longitudinal bars of metallic material of first determined transverse thicknesses, said method comprising the steps of:

[0016] - ET1 placing said bars longitudinally side by side with free ends of said bars in the same transverse plane to form a blank part having a transverse thickness comprising the first cumulative transverse thicknesses of said bars,

[0017] - ET2 positioning a welding tool capable of carrying out a weld of determined width at the free end of said bars, and welding said free ends of said bars, characterized in that it comprises an additional step ETS during which the blank part is transversely widened in end sections of said bars so that its transverse thickness is greater than the width of said weld.

[0018] The widening of the blank in end sections of said bars advantageously makes it possible to provide a surface at the end of the bars which is capable of containing the drop of molten metal generated by the welding tool at the end of these bars and of preventing it from flowing along these bars.

[0019] According to other characteristics of the invention:

[0020] - the additional step ETS is a step prior to step ET2 during which a pad of said metallic material is added transversely on each side of the blank on each of said end sections, each pad being flush in said transverse plane and a second determined thickness of each pad being chosen so that the sum of the first two thicknesses and the second two thicknesses has a transverse thickness at least equal to the width of the weld,

[0021] - during the additional ETS step, each pellet is welded onto one of the bars of the blank,

[0022] - during the additional ETS step, the pellets are welded onto the bars by resistance,

[0023] - the additional step ETS is a step prior to step ET 1, - during the additional step ETS, the end sections of said bars are milled so that the total thickness of each bar is at least equal to half the width of the weld,

[0024] - during step ET1, said bars are placed longitudinally side by side with their end sections transversely opposite each other, to form a bowl between the two bars, a bottom of said bowl determining the free ends of said bars,

[0025] - during step ET2, said free ends of said bars are welded into said bowl,

[0026] - during the additional step ETS, the end sections of said bars are folded back on themselves so that a total thickness of each bar at its folded end section is at least equal to half the width of the weld, each folded section determining a main branch and a folded branch joined by an elbow forming the free end of said bar,

[0027] - during step ET1, said bars are placed longitudinally side by side with the folded branches of their end sections facing each other,

[0028] - during step ET1, said bars are placed longitudinally side by side with the folded branches of their end sections transversely opposite each other,

[0029] - during step ET2, the said ends of the said bars are welded in the transverse plane which passes through the elbows,

[0030] - the welding tool is a laser welding tool.

[0031] The invention finally relates to a part produced by assembling two bars according to the assembly method previously described, comprising the blank part widened transversely in the end sections of the bars. Brief description of the figures

[0032] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which reference will be made to the appended drawings in which:

[0033] [Fig. 1] Figure 1 is an assembly of two bars according to a state-of-the-art method;

[0034] [Fig. 2] Figure 2 is an assembly of two bars according to a first embodiment of a method which is the subject of the invention;

[0035] [Fig. 3] Figure 3 is an assembly of two bars according to a second embodiment of a method which is the subject of the invention;

[0036] [Fig. 4] Figure 4 is an assembly of two bars according to a third embodiment of a method which is the subject of the invention;

[0037] [Fig. 5] Figure 5 is an assembly of two bars according to a fourth embodiment of a method which is the subject of the invention;

[0038] [Fig. 6] Figure 6 is a block diagram illustrating the steps of a state-of-the-art assembly process;

[0039] [Fig. 7] Figure 7 is a block diagram illustrating the steps of an assembly method according to the first embodiment of the invention;

[0040] [Fig. 8] Figure 8 is a block diagram illustrating the steps of an assembly method according to the first to fourth embodiments of the invention.

[0041] Detailed description of the invention Figure 1 shows schematically an assembly 10, this assembly being produced by a laser welding process.

[0042] The two bars 12 are substantially longitudinal and each have a first determined transverse thickness e1.

[0043] This is, for example, an assembly for the electrical connection of an electric machine rotor with its electrical excitation system. Thus, the first bar 12 belongs to the rotor, while the second bar 12 belongs to the electrical excitation system. For this purpose, the bars 12 must be able to conduct electricity. They are, for example, made of copper.

[0044] According to the state-of-the-art method, during a step ET1 which has been represented in the block diagram of figure 6, the bars 12 are placed longitudinally side by side with free ends 14 of said bars in the same transverse plane P. A blank part 16 is thus formed having a transverse thickness E1 accumulating the first transverse thicknesses e1 of the bars 12.

[0045] Then, during a step ET2, a welding tool 18 is positioned capable of performing a weld at the free end 14 of the bars 12, and the free ends 14 of the bars 12 of determined width e1 are welded. A drop of molten metal 19 forms at the free ends 14 of the bars 12.

[0046] The drop of molten metal 19, when solidifying, transforms into a weld 20, which will be represented in dotted lines in the remainder of this description.

[0047] In the context of large-scale production, and in order to obtain high-quality welds that can be performed at high speeds by a welding robot, a welding tool 18 is generally used, which is a laser welding tool. Currently, as illustrated in FIG. 1, such a laser welding tool causes the metal of the bars 12 to melt such that the drop 19 of molten metal that forms at the ends 14 of the bars 12 has a width E2 that is greater than the width of the blank 16. For example, each bar 12 has a thickness e1 of 1 mm, the blank 16 thus having a width E1 of 2 mm. This configuration is penalizing because it risks causing drips 21 of molten metal (shown in dotted lines in FIG. 1) along the bars 12, these drips 21 being on the one hand unsightly and on the other hand being able to prevent the bars 12 from being placed in a housing provided for this purpose.Furthermore, the deficit of molten metal at the ends of the bars 12 can lead to a weakness of the weld 20 after the solidification of the drop 19 of molten metal, which goes against the desired reliability.

[0048] To overcome this drawback, the invention proposes a method comprising, as illustrated in Figures 2 to 5, an additional step ETS during which the blank 16 of the part is transversely widened in end sections 24 of the bars 16 so that its transverse thickness E3 is greater than the width E2 of said weld 20.

[0049] According to a first embodiment of the method which is the subject of the invention, which has been represented in figures 2, 7 and 8, the additional step ETS is a step prior to step ET2, this step being able to occur between step ET1 and step ET2 as represented in figure 7, or prior to step ET1 as represented in figure 8.

[0050] During this ETS step, a pad 22 of the same metallic material as the bars 12 is added transversely on each side of the blank 16 to each of these end sections 24. As can be seen in FIG. 2, each pad 22 is flush in the transverse plane P and a second determined thickness e2 of each pad 22 is chosen so that the sum E3 of the first two thicknesses e1 and of the two second thicknesses e2 is at least equal to the width E2 of the weld 20.

[0051] Thus, the weld 20, of the same width as the drop of molten metal 19, does not overflow the bars 12.

[0052] Without this being limiting of the invention, during this additional step ETS, each pellet 22 is welded onto each of the end sections 24 of the bars 12 of the blank 16. This configuration is not limiting of the invention, and the pellets 22 could be held by clamping on the bars 12, the pellets 22 then being finally assembled during step ET2 during the laser welding operation.

[0053] Preferably, the pellets 22 are however previously welded onto the bars 12 by resistance, this in order to not cause deformation of the bars 12.

[0054] In second, third, and fourth embodiments of the method which is the subject of the invention, which have been represented in Figure 8, the additional step ETS is a step prior to step ET1.

[0055] According to the second embodiment of the method illustrated in Figure 3, during the additional step ETS, the end sections 24 of the bars 12 are milled.

[0056] As a reminder, we recall that jockeying is a double-folding operation of a flat sheet, at the end of which we obtain two parallel planes offset by a distance of the same order of magnitude as the thickness of the sheet.

[0057] Thus a total thickness e3 of each bar 12, with the end sections 24 included, is of thickness at least equal to half the width E2 of the weld 20 once the drop of molten metal 19 has solidified, so that the total thickness E3 of the two bars 12 with their end sections 24 grooved is greater than the width of the weld 20. Then, this done, during the following step ET1, the bars 12 are placed longitudinally side by side with their end sections 24 grooved transversely opposite each other, to form a bowl 26 between the two bars 12. A bottom of this bowl 26 thus determines the free ends 14 of the bars 12.

[0058] Finally, during the next step ET2, the free ends 14 of the bars 12 are welded in the bowl 26 so that the drop 19 of molten metal forms at the ends 14 of the bars 12. By solidifying, the drop 19 forms the weld 20 of width E2.

[0059] This configuration is particularly advantageous because the drop of molten metal 19 is contained by the end sections 24 of the bars 12, which guarantees that the drop 19 of molten metal is of a width less than the thickness E3 of the blank 16.

[0060] According to the third and fourth embodiments of the method, as shown in Figures 4 and 5, during the additional step ETS, the end sections 24 of said bars are folded back on themselves so that a total thickness e4 of each bar 12 at its folded end section 24 is at least equal to half the width E2 of the weld 20.

[0061] Each folded section 24 of the bar 12 determines a main branch 12a and a folded branch 12b joined by an elbow forming the free end 14 of the bar 12.

[0062] Then, in the third embodiment of the invention, as shown in Figure 4, during step ET1, the bars 12 are placed longitudinally side by side with the folded branches 12b of their end sections 24 transversely opposite each other. This produces a blank 16 with a thickness E4 greater than the width of the drop of molten metal 19, and therefore than the width E2 of the corresponding weld 20 once the drop of molten metal 19 has solidified. In the fourth embodiment of the invention, as shown in Figure 5, during step ET1, the bars 12 are placed longitudinally side by side with the folded branches 12b of their end sections 24b facing each other.

[0063] In either case, it is therefore the elbows forming the free end 14 of the bar 12 which determine the plane P in which the weld 20 will be made.

[0064] Then, whether in the third or the fourth embodiment of the invention, during step ET2 the ends 14 of the bars 12 are welded in the transverse plane P which passes through the elbows. The drop of molten metal 19 occupies a width E2 corresponding to the width E2 of the weld 20 once the drop of molten metal 19 has solidified.

[0065] Other embodiments of the method which have not been described more explicitly in the present description may be envisaged for the proper implementation of the method which is the subject of the invention, as long as it comprises an ETS step consisting of widening the blank 16. For example, instead of the pellets 22 described with reference to the first embodiment of the method, it could be envisaged to cover the ends 14 of the bars 12 with a cap of the same material, of adequate width, which would make it possible to widen the blank 16.

[0066] The invention makes it possible to considerably improve the laser welding operation of two bars made of metallic materials of reduced thickness, and to make the weld 20 thus obtained more reliable during the solidification of the drop of molten metal 19. It makes it possible to obtain a part of great solidity from a blank part 16 previously widened transversely in the end sections 24 of the bars 12.

Claims

CLAIMS 1. Method of assembling by welding two substantially longitudinal bars (12) made of metallic material of first determined transverse thicknesses (e1), said method comprising the steps of: - (ET1) placing said bars (12) longitudinally side by side with free ends (14) of said bars (12) in the same transverse plane (P) to form a blank part (16) having a transverse thickness (E1) comprising the first cumulative transverse thicknesses (e1) of said bars (12), - (ET2) positioning a welding tool (18) capable of carrying out a weld (20) of width (E2) determined at the free end (14) of said bars (12), and welding said free ends (14) of said bars (12), characterized in that it comprises an additional step (ETS) during which the blank part (16) is transversely widened in end sections (24) of said bars (12) so that its transverse thickness (E3) is greater than the width (E2) of said weld (20).

2. Assembly method according to the preceding claim, characterized in that the additional step (ETS) is a step prior to step (ET2) during which a pad (22) of said metallic material is added transversely on each side of the blank (16) on each of said end sections (24), each pad (22) being flush in said transverse plane (P) and a second determined thickness (e2) of each pad being chosen so that the sum (E3) of the two first thicknesses (e1) and of the two second thicknesses (e2) is at least equal to the width (E2) of the weld (20).

3. Assembly method according to the preceding claim, characterized in that, during the step additional (ETS), each pellet (22) is welded onto one of the bars (16) of the blank (12).

4. Assembly method according to the preceding claim, characterized in that, during the additional step (ETS), the pellets (22) are welded onto the bars (12) by resistance.

5. Assembly method according to claim 1, characterized in that the additional step (ETS) is a step prior to step (ET1).

6. Assembly method according to the preceding claim, characterized in that during the additional step (ETS), the end sections (24) of said bars (12) are milled, so that a total thickness (e3) of each bar (12) is at least equal to half the width (E2) of the weld (20).

7. Assembly method according to the preceding claim, characterized in that, during step (ET1), said bars (12) are placed longitudinally side by side with their end sections (24) transversely opposite each other, to form a bowl (26) between the two bars (12), a bottom of said bowl (26) determining the free ends (14) of said bars (12).

8. Assembly method according to the preceding claim, characterized in that, during step (ET2), said free ends (14) of said bars (12) are welded into said bowl (26).

9. Assembly method according to the preceding claim, characterized in that during the additional step (ETS), the end sections (24) of said bars are folded back on themselves so that a total thickness (e4) of each bar (12) at its folded end section (24) is at least equal to half the width (E2) of the weld (20), each folded section (24) determining a main branch (12a) and a folded branch (12b) joined by an elbow forming the free end (14) of said bar (12).

10. Assembly method according to the preceding claim, characterized in that, during step (ET1), said bars (12) are placed longitudinally side by side with the folded branches (12b) of their end sections (24) facing each other. 1 1. Assembly method according to the preceding claim, characterized in that, during step (ET1), said bars (12) are placed longitudinally side by side with the folded branches (12b) of their end sections transversely opposite each other.

12. Assembly method according to one of claims 10 or 11, characterized in that, during step (ET2), said ends (14) of said bars are welded in the transverse plane (P) which passes through the elbows.

13. Assembly method according to one of the preceding claims, characterized in that the welding tool is a laser welding tool.

14. Part produced by assembling two bars according to the assembly method of any one of the preceding claims, characterized in that it comprises the blank part (16) widened transversely in the end sections (24) of the bars (12).

Images