METHOD OF WELDING A NICKEL STRENGTH LUG WITH A BRONZE CONNECTING PIN AND A BRASS CONTACT RING IN AN ACCELEROMETER SENSOR

Abstract

The present invention consists in a method of welding a nickel strength lug with a bronze connecting pin and a brass contact ring in an accelerometer sensor, the strength lug being interleaved between the connecting pin and the contact ring, the welding being effected electrically with the strength lug pressed simultaneously against the connecting pin and the contact ring. Before welding, the strength lug undergoes deformation of its external surface at least on each of two portions of the surface respectively facing the connecting pin and the contact ring, the surface deformation creating on each of the portions asperities intended to come into local contact with the connecting pin and the contact ring, respectively.

Claims

1. Method of welding a nickel strength lug (1) with a bronze connecting pin (2) and a brass contact ring (3) in an accelerometer sensor (8), the strength lug (1) being interleaved between the connecting pin (2) and the contact ring (3), the welding being effected electrically with the strength lug (1) pressed simultaneously against the connecting pin (2) and the contact ring (3), wherein, before welding, the strength lug (1) undergoes deformation of its external surface at least on each of two portions (7) of the surface respectively facing the connecting pin (2) and the contact ring (3), the surface deformation creating on each of said portions asperities (4) intended to come into local contact with the connecting pin (2) and the contact ring (3), respectively.

2. Method according to claim 1, wherein, before welding, the strength lug (1) is pressed simultaneously against the connecting pin (2) and the contact ring (3), the pressure causing the asperities (4) of the portions (7) of the surface of the strength lug (1) to dig into the connecting pin (2) and the contact ring (3), respectively.

3. Welding method according to claim 1, wherein the surface deformation is obtained by knurling (B, B′) or striation.

4. Welding method according to claim 3, wherein the asperities (4) are in the form of spikes carried by the respective portions (7) of the surface of the strength lug (1) locally contacting the connecting pin (2) and the contact ring (3).

5. Welding method according to claim 3, wherein the asperities (4) are in the form of series of separate and parallel striations carried by the portions (7) of the surface of the strength lug (1), the striations having peaks locally contacting the connecting pin (2) and the contact ring (3), respectively.

6. Welding method according to claim 5, wherein the series of striations extend transversely on the strength lug (1).

7. Method according to claim 3, wherein a die stamping step (A) to flatten the strength lug (1) is carried out before the knurling step (B, B′) or the striation step.

8. Method according to claim 1, wherein the surface deformation is effected by grinding increasing the roughness of the respective surface portions (7) facing the connecting pin (2) and the contact ring (3).

9. Method according to claim 1, wherein the strength lug (1) is tinned before welding.

10. Accelerometer sensor (8) including at least two electrical connection pins (2) connected by a respective strength lug (1) to a respective contact ring (3), wherein each strength lug (1) is welded to the respective connecting pin (2) and contact ring (3) by the method according to claim 1.

11. Welding method according to claim 2, wherein the surface deformation is obtained by knurling (B, B′) or striation.

12. Method according to claim 4, wherein a die stamping step (A) to flatten the strength lug (1) is carried out before the knurling step (B, B′) or the striation step.

13. Method according to claim 5, wherein a die stamping step (A) to flatten the strength lug (1) is carried out before the knurling step (B, B′) or the striation step.

14. Method according to claim 6, wherein a die stamping step (A) to flatten the strength lug (1) is carried out before the knurling step (B, B′) or the striation step.

15. Method according to claim 2, wherein the surface deformation is effected by grinding increasing the roughness of the respective surface portions (7) facing the connecting pin (2) and the contact ring (3).

16. Method according to claim 2, wherein the strength lug (1) is tinned before welding.

17. Method according to claim 3, wherein the strength lug (1) is tinned before welding.

18. Method according to claim 4, wherein the strength lug (1) is tinned before welding.

19. Method according to claim 5, wherein the strength lug (1) is tinned before welding.

20. Method according to claim 6, wherein the strength lug (1) is tinned before welding.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Other features, objects and advantages of the present invention will become apparent on reading the following detailed description with reference to the appended drawings provided by way of nonlimiting example and in which:

[0035] FIG. 1 is a diagrammatic perspective view in half-section of an accelerometer sensor comprising connecting pins welded to respective contact rings by a strength lug, the welding being possible according to a method according to the present invention,

[0036] FIGS. 2 and 3 are diagrammatic representations of a section of an assembly comprising a connecting pin, strength lug and contact ring respectively before and after welding by a prior art method,

[0037] FIG. 4 shows the succession of steps according to a first embodiment of the welding method according to the present invention, the strength lug undergoing a surface treatment by die stamping followed by knurling before welding,

[0038] FIG. 5 shows the succession of steps according to a second embodiment of the welding method according to the present invention, the strength lug undergoing a surface treatment by knurling over its entire surface before welding.

DETAILED DESCRIPTION OF THE INVENTION

[0039] It should be borne in mind that the figures are provided by way of example and are not limiting on the invention. They constitute diagrammatic and theoretical representations intended to facilitate the understanding of the invention and are not necessarily at the scale of practical applications. In particular, the dimensions of the various elements shown are not representative of reality.

[0040] For example, in the figures the strength lug shown is of cylindrical shape, which is not limiting on the invention. In FIG. 3, the fused zones can have a shape other than oval. In FIG. 4, in step B, the deformed shape of the strength lug has been shown enlarged relative to its non-deformed shape to show the asperities better. Those asperities can also take shapes other than those shown. The final shape of the strength lug is shown very diagrammatically and may also differ significantly from that shown in step E. The same applies to FIG. 5 where the star-shaped cross section of the strength lug shown is also not limiting on the invention.

[0041] FIGS. 1 to 3 have already been described in the introductory part of the description of the present patent application.

[0042] Referring to FIGS. 4 and 5, which show two nonlimiting embodiments of the welding method according to the present invention, as well as referring to FIG. 1 for reference numbers not included in FIGS. 4 and 5, for these two embodiments the welding method is applied to a nickel strength lug 1 with a bronze connecting pin 2 and a brass contact ring 3 in an accelerometer 8. The strength lug 1 is interleaved between the connecting pin 2 and the contact ring 3. The welding is effected electrically with the strength lug 1 pressed simultaneously against the connecting pin 2 and the contact ring 3.

[0043] In the context of the present invention, what is meant by the welding method does not comprise only the welding step itself but also the steps from preparation of the welding lug 1 to a welding step as such, the welding method according to the invention being broader and comprising more steps than the welding operation itself.

[0044] Nickel as the base material of the strength lug 1 has welding parameters, such as its melting point, for example, very different from the parameters of brass or bronze. Too high a welding temperature will create too much melting of the nickel into the bronze and therefore excessive penetration of a part of the strength lug 1 into the connecting pin 2, which is to be avoided.

[0045] According to the present invention, before welding, the strength lug 1 undergoes a deformation of its external surface at least on each of the two portions 7 of the surface facing the connecting pin 2 and the contact ring 3, respectively. The surface deformation creates asperities 4 on each of said portions intended to come locally into contact with the connecting pin 2 and the contact ring 3, respectively.

[0046] Only one asperity is referenced in FIGS. 4 and 5 for each step of the method, but what is indicated for the reference 4 applies to all the asperities.

[0047] By asperities 4 is meant all uneven projections from the deformed surface portion. They can be symmetrical or not, advantageously projecting to the same height from the defined surface portion, although series of different heights can also be used.

[0048] It is advantageous to restrict the surface deformation to the respective portions 7 of the external surface directly facing the connecting pin 2 or the contact ring 3. This is shown in FIG. 4.

[0049] It is also possible to provide the entire external surface of the strength lug 1 with asperities, the surface deformation then applying to the whole of the external surface, as shown in FIG. 5. For example, this may be required on an external surface of a cylindrical strength lug 1 when the surface deformation is done during rotation of the strength lug 1, for example when the knurling B, B′ is effected on a lathe, complete deformation of the external surface being easier to obtain during manufacture than deformation of portions 7 of the external surface of the strength lug 1.

[0050] Before welding, the strength lug 1 may be pressed simultaneously against the connecting pin 2 and the contact ring 3, the pressure causing the asperities 4 on the portions 7 of the surface of the strength lug 1 to dig into the connecting pin 2 and the contact ring 3. Nickel is in fact a harder material than bronze or brass and the free ends of the asperities 4 of the portions 7 of the external surface of the strength lug 1 can therefore be pressed against the facing surfaces of the connecting pin 2 and the contact ring 3 and penetrate at least slightly into those two parts. This step is shown under reference C in FIGS. 4 and 5.

[0051] As shown in FIGS. 4 and 5, the surface deformation can be effected by knurling B, B′ or striation. The knurling B, B′ is an operation that consists in producing striations on a surface, said striations possibly crossing, for example at least two series of striations parallel to one another in the same series, the striations of one series being at an angle to the striations of the other series. By striation is meant the creation of series of striations parallel to one another. The knurling B, B′ is very suitable for a cylindrical part, this being a shape that a strength lug 1 may have. The knurling B, B′ may be done on the strength lug 1 by machining it on a lathe.

[0052] As previously mentioned, a plurality of shapes of asperities 4 are possible. For example, the asperities 4 can take the form of spikes carried by the respective portions 7 of the surface of the strength lug 1 locally contacting the connecting pin 2 and the contact ring 3. In another example, the asperities 4 may take the form of series of separate and parallel striations carried by the portions 7 of the surface of the strength lug 1, the striations having peaks locally contacting the connecting pin 2 and the contact ring 3. This is the case when the portions 7 of the external surface of the strength lug 1 have undergone striation.

[0053] In this case, it is preferred that the series of striations extend transversely on the strength lug 1.

[0054] In FIG. 4, in the first embodiment of the welding method according to the present invention, in the step A, a die stamping step A may be carried out before the knurling step B, B′ or the striation step, the die stamping step A starting from a strength lug 1 in step 0 flattening the strength lug 1.

[0055] Then, after this die stamping step A, the knurling step B can follow, and then the step C of pressing the strength lug 1 simultaneously against the connecting pin 2 and the contact ring 3. In this step C, the contact ring 3 can be under the strength lug 1, itself under the connecting pin 2, as also shown in FIGS. 1 to 3, but this arrangement can also be reversed.

[0056] At the end of this method according to the first embodiment of the present invention, there follows the welding step D and the production of the final welded assembly E consisting of the connecting pin 2, the strength lug 1 and the contact ring 3.

[0057] According to the second embodiment of the invention, starting from the starting strength lug 1 referenced in the step 0, there may follow a striation step B′ without the strength lug 1 being deformed beforehand.

[0058] The striation step B′ can be done over the whole of the strength lug 1 but in this second embodiment this is not obligatory. This knurling striation step B′ is then followed by the welding step D and the production of the final welded assembly E, the latter two steps D and E being common to both embodiments of the welding method according to the present invention.

[0059] The strength lug 1 in its final state in the step E can have been deformed as a result of digging in or being flattened in the two embodiments of the invention. To give an idea of this and without limiting the invention, in the step 0 the strength lug 1, which is advantageously cylindrical, could have a diameter or a thickness between pin 2 and contact ring 3 of 0.5 mm while the strength lug 1 in the final welded assembly E has a diameter or a thickness of only 0.25 mm, i.e. digging in by 0.25 mm. This is not limiting on the invention.

[0060] Another possible surface deformation that can be employed in the welding method according to the present invention may be a surface deformation by grinding that increases the roughness of the respective portions 7 of the surface facing the connecting pin 2 and the contact ring 3.

[0061] The strength lug 1 can be tinned before welding. Tinning is a surface treatment operation that consists in applying a layer of tin to the strength lug 1, which protects it against corrosion and improves its weldability.

[0062] The invention also concerns an accelerometer sensor 8 having at least two electrical connection pins 2 connected by a strength lug 1 to a respective contact ring 3. Each strength lug 1 is welded to the respective connecting pin 2 and to the respective contact ring 3 by a method of this kind.

[0063] The present invention makes it possible to reduce the flattening of the strength lug 1 caused by excessive penetration of a part of the strength lug 1 into the connecting pin 2. In fact, with a method according to the present invention the penetration of the strength lug 1 into the connecting pin 2 is reduced at the same time as increasing the welding area through a greater area of bonding of the strength lug 1 with on the one hand the connecting pin 2 and on the other hand the contact ring 3.