METHOD FOR JOINING VERY THICK TUBULAR PARTS BY MAGNETIC PULSES AND CORRESPONDING ARTICLE

Abstract

A method for joining two tubular parts, an internal part and an external part, by magnetic pulses. The external part includes an annular wall having an outer surface. Over a longitudinal portion of the external part, a thickness of the annular wall of the external part is reduced such that the annular wall has a decreasing thickness over the longitudinal portion. The tubular parts are positioned one inside the other to form an overlap region covering the longitudinal portion. The tubular parts are positioned next to a coil such that the longitudinal portion is disposed opposite an active part of the coil. The two tubular parts are connected by magnetic pulses.

Claims

1-9. (canceled)

10. A magnetic pulse method for joining two tubular parts, an internal part and an external part, the external part comprising an annular wall having an outer surface, the external part having an inner diameter greater than an outer diameter of the internal part, the method comprising steps of: on a longitudinal portion of the external part, reducing a thickness of the annular wall of the external part such that the annular wall has a decreasing thickness on the longitudinal portion, the thickness of the annular wall of the external part being reduced by removing a layer of material from the outer surface of the annular wall; positioning the two tubular parts one inside the other to form an overlap region that at least covers the longitudinal portion; positioning the two tubular parts opposite a coil such that the longitudinal portion is arranged opposite an active part of the coil; and connecting the two tubular parts by magnetic pulses.

11. The joining method according to claim 10, wherein the thickness of the annular wall of the external part is reduced such that the thickness is monotonically decreasing towards a first end of the external part.

12. The joining method according to claim 10, wherein the thickness of the annular wall of the external part is reduced such that the thickness is constant over a first portion of the longitudinal portion and is monotonically increasing on a second portion of the longitudinal portion.

13. The joining method according to claim 10, wherein the thickness of the annular wall of the external part is reduced by removing a layer of material from an inner surface of the external part.

14. The joining method according to claim 10, wherein the thickness of the annular wall of the external part is reduced by machining.

15. The joining method according to claim 10, further comprising a step of forming at least one pattern on an outer surface of an annular wall of the internal part, the forming step being carried out prior to the positioning steps.

16. The joining method according to claim 15, wherein said at least one pattern is produced by machining.

17. The joining method according to claim 15, wherein the step of forming said at least one pattern and the step of reducing the thickness of the annular wall of the external part are carried out simultaneously.

18. An article comprising two tubular parts, the external part comprising a decreasing thickness over the longitudinal portion; wherein the two tubular parts are joined together, at the longitudinal portion, by a combined welded part and crimped part obtained using the joining method according to claim 10.

Description

DESCRIPTION OF THE FIGURES

[0047] The invention will be better understood from reading the following description with reference to the accompanying drawings:

[0048] FIG. 1 shows a schematic of a perspective view of a joining device;

[0049] FIG. 2 illustrates a perspective view of a yoke and a tube prior to joining;

[0050] FIG. 3 shows a cross section of an annular coil of the joining device of FIG. 1, in which two tubular parts are positioned, the external part showing a first embodiment;

[0051] FIG. 4 shows a cross section of an annular coil of the joining device of FIG. 1, in which two tubular parts are positioned, the external part showing a second embodiment;

[0052] FIG. 5 shows a cross section of an annular coil of the joining device of FIG. 1, in which two tubular parts are positioned, the external part showing a third embodiment;

[0053] FIG. 6 shows a cross section of an annular coil of the joining device of FIG. 1, in which two tubular parts are positioned, the external part showing a fourth embodiment, and the tubular opening of the coil showing an alternative embodiment; and

[0054] FIG. 7 shows a cross section of an annular coil of the joining device of FIG. 1, in which two tubular parts are positioned, the tubular opening of the coil showing an alternative embodiment.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

[0055] The invention is now described in detail in the case of joining two tubular parts 2, 3, preferably very thick parts.

[0056] A particularly preferred field of application of the invention, although not being limitative in any way, is the automotive industry. In a preferred embodiment, the invention is particularly suitable for the joining of a tubular part 2 and a mechanical yoke 3, as illustrated in FIG. 2.

[0057] FIG. 1 describes a joining device by magnetic pulses. In the following description, such a device shall be referred to as a joining device.

[0058] The joining device is known to comprise a coil 10, a storage unit 50 and one or more switches 51.

[0059] The storage unit 50 is configured and designed for storing significant amounts of energy, for example up to several tens of kilojoules (kJ).

[0060] In a preferred embodiment, the storage unit is a battery of discharge capacitors.

[0061] The coil 10 is in turn configured and designed for creating a concentrated magnetic field in a limited space, described later.

[0062] The joining device is designed to hold the two tubular parts 2, 3 for joining.

[0063] The two tubular parts 2, 3 are, in the following description, of circular cross-section. Although the tubular parts 2, 3 are described and illustrated in detail in the case of a circular cross section, other cross-sectional shapes, such as square, rectangular, triangular or oval, may also apply.

[0064] A first tubular part, referred to as the external part 2, comprises an annular wall 20 having an inner surface 21 and an outer surface 22, as illustrated in FIGS. 3 and 4.

[0065] A second tubular part, referred to as the internal part 3, comprises an annular wall 30 having an inner surface 31 and an outer surface 32, as also illustrated in FIGS. 3 to 7.

[0066] The external part 2 has an inner diameter d.sub.21 that is greater than an outer diameter d.sub.32 of the internal part 3, such that the internal part 3 can penetrate into the external part 2, with clearance.

[0067] The two tubular parts 2, 3 are designed to be arranged one inside the other coaxially, forming, where they overlap, an overlap region 25, and then to be joined irreversibly by magnetic pulses, across all or a part of said overlap region 25 by the coil 10, as will be described later.

[0068] The coil 10 and the two tubular parts 2, 3 form a welding joining when said two tubular parts are in position with said coil.

[0069] Preferably, the overlap region 25 is located at one end of at least one part, for example an end of the external part 2.

[0070] The two tubular parts are preferably made of a metallic material.

[0071] In an example of an embodiment, the two tubular parts are made of the same material.

[0072] In another example of an embodiment, the two tubular parts are made of different materials.

[0073] As a non-limiting example of the invention, the internal part and the external outer part may be made of steel or aluminium respectively.

[0074] In the non-limiting example where the internal part 3 and external part 2 are made of steel or aluminium, the annular walls of the external part and the internal part are more than 3 mm thick.

[0075] In an embodiment that is not shown here, when the external part 2 is made of a material having a very low electrical conductivity, such as a part made of steel for instance, an intermediate part, called a pusher, which is preferably tubular with a circular section, is positioned against the outer surface 22 of the annular wall 20 of the external part 2. This intermediate part has a good electrical conductivity.

[0076] A material with a very low electrical conductivity refers to a material whose electrical conductivity is less than 10 MS/m.

[0077] The coil 10, preferably an annular coil, comprises, as illustrated in FIG. 1, a body 11 that has tubular opening 12 delimited by a peripheral surface 121. Said tubular opening is configured to hold the two tubular parts 2, 3 arranged one inside the other for their joining. In other words, the tubular opening 12 has a circular cross section whose diameter d is larger than an outer diameter d.sub.22 of the external part 2.

[0078] The body 11 is made of a material with specific characteristics in terms of, on the one hand, mechanical resistance to plastic deformation in order to withstand the circulation of a very high intensity current of approximately several hundreds of thousands of amperes and, on the other hand, resistance to elevated temperatures (i.e. a high melting point) to ensure that it does not melt during welding.

[0079] In an example of an embodiment, the body is made of steel.

[0080] The coil 10 is connected to the energy storage unit 50 and to the switch/switches 51.

[0081] In operation, when the switch/switches 51 close(s), the body of the coil 10 is connected to the storage unit 50, and a very high intensity current flows in the coil 10 producing a magnetic field.

[0082] The coil 10 is designed such that the current density in an area of the coil is sufficient to meet the welding conditions. This area is referred to as the active part 125. It is described in document WO 2012/103873, for instance.

[0083] In the case of an annular coil as described in this embodiment, the current is concentrated in the active part 125, on a layer delimited by the peripheral surface 121 opposite the outer surface 22 of the external part 2 and on a thickness corresponding to the skin thickness. The current thus generates a concentrated magnetic field in the tubular opening 12.

[0084] In the non-limiting example of a coil 10 made of steel, the skin thickness is approximately a few millimetres at a frequency of a few tens of kHz.

[0085] A method for joining two tubular parts 2, 3 according to the invention is now described. The joining method is preferably carried out by the previously described joining device.

[0086] The method comprises a first step of reducing the thickness of the annular wall 20 of the external part 2, over a longitudinal portion 23 of length L.sub.23.

[0087] The thickness of the annular wall 20 of the external part 2 is reduced such that the external part 2 has, on the longitudinal portion 23, an annular wall 20 of decreasing thickness towards a first end 24.

[0088] Preferably, but not limiting in any way, the longitudinal portion 23 extends from the first end 24 of the external part 2.

[0089] The longitudinal portion 23 is located on the external part 2, such that it is in the overlap region 25 of the two tubular parts 2, 3, when said two tubular parts are positioned one inside the other, for subsequent bonding.

[0090] The length L.sub.23 of the longitudinal portion 23 is defined such that at the most, it is equal to an axial length L.sub.121 of the peripheral surface 121 of the coil 10.

[0091] According to one preferred embodiment, as illustrated in FIGS. 3 to 7, the thickness of the annular wall 20 is reduced by removing a layer of material from the outer surface 22.

[0092] According to an alternative embodiment, the thickness of the annular wall 20 is reduced by removing a layer of material from the inner surface 21.

[0093] According to another alternative embodiment, the thickness of the annular wall 20 is reduced by removing a layer of material from the outer surface 22 and the inner surface 21.

[0094] Whatever the embodiment or alternative embodiment, a layer of material is removed until the annular wall 20 has, over the length of the longitudinal portion 23, a decreasing thickness towards the first end 24.

[0095] In other words, when the longitudinal portion starts from the first end 24 of the external part 2, the thickness of the removed layer decreases from the first end 24, over the longitudinal portion. The thickness of the annular wall 20 of the external part 2, in turn, increases over the longitudinal portion 23, from the first end 24.

[0096] Preferably, the thickness of the annular wall 20 of the external part 2 at the first end 24 is reduced to 1 mm.

[0097] One way to implement this first step is, for example, to reduce the thickness of the annular wall of the external part by machining.

[0098] In an example of an embodiment, the thickness of the annular wall 20 of the external part 2 is reduced such that the thickness of said annular wall 20 monotonically decreases over the length L.sub.23 of the longitudinal portion 23 towards the first end 24. In the illustration given in FIG. 3, without this being limiting in any way, the thickness of the annular wall 20 of the external part 2 is only reduced from the outer surface 22. No changes are made to the outer surface 32 of the annular wall 30 of the internal part 3. The inner diameter d.sub.21 of the external part 2 remains constant over said longitudinal portion 23.

[0099] In an alternative embodiment, the thickness of the annular wall 20 of the external part 2, over the length of the longitudinal portion, is reduced such that: [0100] over a first portion 231 of the longitudinal portion 23, the thickness of said annular wall 20 is constant, [0101] over a second portion 232 of the longitudinal portion, the thickness of said annular wall 20 of the external part is monotonically increasing.

[0102] In the illustration given in FIG. 4, without this being limiting in any way, the thickness of the annular wall 20 of the external part 2 is only reduced from the outer surface 22. No changes are made to the outer surface 32 of the annular wall 30 of the internal part 3. The inner diameter d.sub.21 of the external part 2 remains approximately constant in the overlap region, especially over said longitudinal portion 23.

[0103] The first portion 231 is located on the side of the first end 24 of the external part 2.

[0104] The first portion 231 and the second portion 232 are preferably successive. The first portion extends over a length L.sub.231. The second portion extends over a length L.sub.232.

[0105] In another alternative embodiment, the thickness of the annular wall 20 of the external part 2, over the length of the longitudinal portion 23 is reduced such that: [0106] over a first portion 233 of the longitudinal portion 23, the thickness of said annular wall 20 is monotonically decreasing, [0107] over a second portion 234 of the longitudinal portion 23, the thickness of said annular wall 20 of the external part is monotonically increasing.

[0108] The first portion 233 and second portion 234 are preferably successive.

[0109] In the illustration given in FIG. 5, without this being limiting in any way, the longitudinal portion 23 does not start at the first end 24 of the external part 2.

[0110] In the illustration given in FIG. 5, without this being limiting in any way, the thickness of the annular wall 20 of the external part 2 is only reduced from the outer surface 22. No changes are made to the outer surface 32 of the annular wall 30 of the internal part 3. The inner diameter d.sub.21 of the external part 2 remains approximately constant in the overlap region, especially over said longitudinal portion 23.

[0111] In another alternative embodiment, the thickness of the annular wall 20 of the external part 2, over the length of the longitudinal portion 23 is reduced such that: [0112] over a first portion 233 of the longitudinal portion 23, the thickness of said annular wall 20 is monotonically decreasing, [0113] over a second portion 234 of the longitudinal portion 23, the thickness of said annular wall 20 of the external part is monotonically increasing, [0114] in a third portion 235 of the longitudinal portion 23, located between the first portion and the second portion, the thickness of said annular wall 20 of the external part is constant.

[0115] In the illustration given in FIG. 6, without this being limiting in any way, the longitudinal portion 23 does not start at the first end (24) of the external part 2.

[0116] In the illustration given in FIG. 6, without this being limiting in any way, the thickness of the annular wall 20 of the external part 2 is only reduced from the outer surface 22. No changes are made to the outer surface 32 of the annular wall 30 of the internal part 3. The inner diameter d.sub.21 of the external part 2 remains approximately constant in the overlap region, especially over said longitudinal portion 23.

[0117] In a specific embodiment of the method, the method may comprise an additional step of forming of at least one pattern 37, on the outer surface 32 of the annular wall 30 of the internal part 3.

[0118] The at least one pattern 37 is designed to strengthen the connection of the two tubular parts 2, 3, once they are joined.

[0119] The at least one pattern 37 is located on the internal part 3, such that it is in the overlap region 25 of the two tubular parts 2, 3, when said two tubular parts are positioned one inside the other, for subsequent bonding. Preferably, said at least one pattern 37 is located in the longitudinal portion, when said two tubular pieces are positioned one inside the other, for their subsequent binding.

[0120] The at least one pattern 37 may be in the form of a protruding pattern or a sunken pattern.

[0121] A protruding pattern can be in the form of a radial projection with a peripheral or longitudinal bulge, for example, extending from the outer surface 32 of the annular wall 30 of the internal part 3 and projecting towards the outside the annular wall 30.

[0122] A sunken pattern may be in the form of a radial blind recess, a peripheral groove (as shown in FIG. 3) or longitudinal groove, extending in the thickness of the annular wall 30.

[0123] One method for designing the sunken pattern is, for example, to create the recess or groove by machining the outer surface 32 of the annular wall (30) of the inner part 3.

[0124] The internal part 3 can also comprise multiple patterns, either identical or different in shape.

[0125] The order in which the first step and the additional step are implemented is not mandatory and, depending on the method, may be performed in reverse of the described order or may be performed simultaneously without changing the result of said steps.

[0126] The method then comprises a step of positioning the tubular parts 2, 3 in the coil 10.

[0127] In a first phase, the two cylindrical tubular parts are positioned one inside the other, forming the overlap region 25.

[0128] The internal part 3 is engaged in the external part 2 such that the overlap region at least covers the longitudinal portion (23) of the external part 2 and the at least one pattern 37 of the internal part 3.

[0129] In a second phase, the two tubular parts 2, 3 are positioned in the tubular opening 12 of the coil 10.

[0130] The internal part 3 and external part 2 are preferably arranged in said coil such that all or a part of the overlap region 25 is opposite the peripheral surface 121 of the coil.

[0131] More particularly, the internal part 3 and external part 2 are arranged in the tubular opening 12 of the coil 10 such that the longitudinal portion 23 of the external part 2 is placed opposite to the active part 125 of the coil.

[0132] The overlap area 25 opposite to the active portion 125 is referred to as the working area. Said working area has a predetermined length, referred to as the working length. This working length corresponds to a maximum welding length between the internal part and the external part. In practice, the welding length is slightly less than this working length.

[0133] The internal part 3 and external part 2 are held in the tubular opening 12, coaxially with respect to each other, in an axial direction XX and with the tubular opening 12 of the coil 10, laid out in said axial direction XX, by fastening means (not shown in the figures).

[0134] In a preferred example of an embodiment, when the longitudinal portion 23 starts from the first end 24, the external part 2 is positioned such that its first end 24 is positioned opposite to the peripheral surface 121.

[0135] The order in which the two phases are implemented is not mandatory and, depending on the method, may be performed in reverse of the described order, or performed simultaneously without changing the result of said steps.

[0136] At the end of this second step, the two tubular parts 2, 3 are positioned with each other and in the coil 10.

[0137] When the thickness of the annular wall 20 of the external part 2 is reduced by removing a layer of material from the outer surface 22, the outer surface 32 of the internal part 3 is approximately parallel to the inner surface 21 of the external part 2, as illustrated in FIGS. 3 and 4. The outer surface 22 of the external part 2 forms, in part, an angle with the peripheral surface 121 of the coil 10.

[0138] The method then comprises a step of bonding the two parts by magnetic pulses.

[0139] The working area is subjected to a magnetic field originating from the active part 125 of the coil 10 such that a pressure is exerted on the outer surface 22 of the annular wall 20 of the external part 2, or on an outer surface of the pusher when said pusher is required, and pushes it tightly against the outer surface 32 of the annular wall 30 of the internal part 3, causing them to bond permanently.

[0140] When the annular wall 20 of the external part 2 has a monotonically increasing thickness along the length L.sub.23 of the longitudinal portion 23, as shown in FIG. 3, the internal part 3 and external part 2 are welded over a first length, referred to as the welding length, where the annular wall of the external part is thin, and are then crimped on a second length, referred to as the crimping length.

[0141] When the annular wall 20 of the external part 2 has a constant thickness followed by an increasing thickness along the length L.sub.23 of the longitudinal portion 23, as shown in FIG. 4, the internal part 3 and external part 2 are welded over a greater length, because the annular wall of the external part is thinner over a greater length, and are then crimped.

[0142] The welding and crimping length is dependent upon the axial length of the coil 10 and energy used.

[0143] When the internal part 3, irrespective of the shape of the external part 2 at the longitudinal portion 23, comprises at least one pattern 37 on its outer surface 32, preferably located at the crimping length, said at least one pattern preferably allows locally enhancing the bonding between the tubular parts, increasing the contact area between the two tubular parts 2, 3 and improving the tensile strength of the bonding between said two tubular parts.

[0144] In an alternative embodiment of the coil as shown in FIGS. 6 and 7, the tubular opening 12 of the coil 10 may have a shape complementary to the outer surface 22 of the annular wall 20 of the external part 2, after the reduction in thickness of said external part over the longitudinal portion 23.

[0145] Such a shape of the tubular opening allows the coil to have a circular cross section whose diameter is tapered. Thus, at the longitudinal portion where the external part is thinner, the tubular opening of the coil has the smallest diameter. In such a configuration, the current is concentrated in this area of reduced diameter, which improves the performance of the magnetic pulse and thus facilitates the welding in said area.

[0146] The article obtained at the end of the joining method, such as a steering wheel of a motor vehicle for instance, comprises the two tubular parts 2, 3 connected together by a welded portion and then an attached crimped portion.

[0147] The above description clearly illustrates that through its various features and benefits, this invention achieves the goals it had set. In particular, it provides a magnetic pulse joining method suitable for joining very thick parts.

[0148] The method provides a stronger connection than what can be obtained with simple crimping, without compromising the structural strength of the outer part.