Coil for deforming metal parts by magnetic pulse, methods for producing and reconditioning such a coil

Abstract

The invention relates to a coil (100) for deforming a metal part (200) by magnetic pulse comprising a body (120) having a first surface (122) intended to be positioned facing the part to be deformed (200). The coil (100) comprises at said first surface (122) a reinforcement (180), said reinforcement (180) consisting of a metal material deposited by cold thermal spraying.

Description

[0001] Coil for deformation of metal parts by magnetic pulse, methods of producing and reconditioning such a coil

[0002] Field of invention

[0003] The present invention relates to the field of forming, welding or crimping metal parts. More particularly, it relates to the field of forming, welding or crimping metal parts by magnetic pulse, commonly referred to as magneto-forming (MPF), magneto-welding (MPW) or magneto-crimping (MPC). The present invention relates to an improved coil for extending its service life. The present invention also relates to a method for producing said coil and a method for reconditioning said coil.

[0004] State of the art

[0005] The deformation of metal parts by magnetic impulse is carried out under the action of electromagnetic forces generated by a coil. This deformation makes it possible to carry out either forming operations to shape a metal part according to the shape of a die, or welding or crimping operations to permanently assemble two parts together.

[0006] Typically, a device for deforming metal parts by magnetic pulse comprises several capacitors, forming an electrical energy storage unit, and a switch, connected to a coil to create a brief and intense magnetic field. The electrical energy storage unit is used to store a large amount of electrical energy. When the switch closes, the electrical energy stored in the electrical storage unit is discharged very quickly into the coil, in the form of a very high intensity variable current, in a very short time, thus creating an intense magnetic field. For example, some devices can reach a current of a few hundred thousand amperes in a few microseconds.

[0007] The current generates a variable and intense magnetic field between the coil and the metal part to be deformed, previously placed nearby, and induces eddy currents in this part. These eddy currents, associated with the surrounding magnetic field, develop Laplace forces in the metal part to be deformed which generate a sharp acceleration of the part towards either a die or another part.

[0008] Depending on the intensity level of the generated current, the collision angle and the collision speed, a part is either formed, welded or crimped to another part.

[0009] However, magnetic pulse deformation processes have the disadvantage of requiring very high intensities to form a part or weld / crimp it to another part, which involves the use of a considerable amount of electrical energy. The use of such intensities also generates local temperatures and significant mechanical stresses in the coil that can weaken it, shorten its lifespan, and lead to irreparable damage to the coil, particularly in an area called the "active part". By active part, we mean an area of ​​the coil where the current, delivered by the electrical energy storage unit, is concentrated and circulates to create the magnetic field.

[0010] Damage to the coil, usually in the form of cracks and / or crazing, degrades the performance of magnetic pulse deformation processes.

[0011] For example, for a coil made conventionally from a copper alloy material, such as CuCr, the coil's lifetime is estimated at 25,000 discharges. After 25,000 discharges, crazing at the active part of the coil critically degrades the performance of the magnetic pulse deformation process, and has too strong an impact on the quality of forming, welding or crimping. For a coil made conventionally from a steel material such as 40CMD8, the coil's lifetime is estimated at 15,000 discharges.

[0012] However, these lifespans prove very limiting when the coils are used in industry, on production lines for example. The coils need to be changed regularly, which leads to a shutdown of the production line and generates significant costs.

[0013] There is therefore a real need to extend the service life of the coils used in processes for deforming metal parts by magnetic pulse. Description of the invention

[0014] The present invention, which results from work carried out in collaboration with the UTBM (University of Technology of Belfort Montbéliard), aims to overcome the aforementioned drawbacks.

[0015] The present invention aims in particular to provide an effective solution for extending the service life of a coil for deforming a metal part by magnetic pulse (for example, by magneto-forming and / or magneto-welding and / or magneto-crimping).

[0016] The invention thus relates to a coil for deforming a metal part by magnetic pulse, comprising a body which has a first surface intended to be positioned opposite the metal part to be deformed. At said first surface, the coil comprises a reinforcement, and said reinforcement is constituted by a metallic material deposited by cold thermal spraying.

[0017] The reinforcement thus forms a coating on the first surface of the coil body. However, adding a coating to the first surface of the coil body goes against a constant prejudice in the state of the art according to which adding a coating to this first surface is not viable. Indeed, on the one hand, it proves difficult to maintain electrical continuity at the interface between the coil body and the coating. An electrical discontinuity will influence the creation of the magnetic field and can degrade the quality of the final product by the process of magnetic pulse deformation. On the other hand, adding a coating to the first surface can create potential cavities at the interface between the coil body and the coating. There is a significant risk that an electric arc will form in these cavities and cause degradation of the coil.

[0018] The present invention overcomes the aforementioned drawbacks and overcomes the technical prejudice by depositing a metallic material by the cold thermal spraying process. The cold thermal spraying process is generally known by the English name of cold spray.

[0019] The cold thermal spraying process consists of projecting particles onto a surface. More precisely, the cold thermal spraying process consists of projecting particles of metallic material at very high speed, by a gas under high pressure, onto the first surface of the body. The impact force cold welds this metallic material onto said first surface of the body, and cohesion of the particles to form a dense reinforcement there. The particles of metallic material weld, first onto the first surface of the coil body, then onto themselves. The cold thermal spraying process advantageously allows good cohesion with the first surface of the body subjected to projection as well as low porosity of the deposited metallic material. Thus, electrical continuity is well maintained at the interface between the coil body and the reinforcement, and the formation of an electric arc at this interface is reduced.In addition, thanks to the low porosity of the deposited metallic material, the formation of an electric arc in the reinforcement is also reduced.

[0020] Thus, when using the coil according to the invention in a method for deforming the metal part by magnetic pulse, the current which flows in said coil is concentrated in an active part which is then located at the level of the reinforcement, whereas initially, without the reinforcement, the current is concentrated on the first surface of the body.

[0021] Such reinforcement thus makes it possible to significantly increase the lifespan of the coil.

[0022] Preferably, the material used to form the reinforcement has mechanical and thermal resistance characteristics superior to the body material, in order to further improve the life of the coil.

[0023] According to preferred embodiments, the invention further meets the following characteristics, implemented separately or in each of their technically effective combinations.

[0024] According to preferred embodiments, the coil comprises a magnetic field concentrator at the first surface of the body. The magnetic field concentrator comprises a first surface intended to be positioned opposite the metal part to be deformed. The coil comprises, at the first surface of the magnetic field concentrator, the reinforcement consisting of a metallic material deposited by cold thermal spraying. In the case of the use of the magnetic field concentrator, the reinforcement is now formed on the first surface of the magnetic field concentrator and no longer on the first surface of the body of the coil.When using the coil in a method for deforming the metal part by magnetic pulse, the current flowing in the coil is concentrated in an active part which is then located at the reinforcement, whereas initially, without the reinforcement, the current is concentrated on the first surface of the magnetic field concentrator. The invention also relates to a method for producing a coil in at least one of its embodiments. The production method comprises the successive steps of:

[0025] - depositing, on the first surface of the body of the coil, or of the field concentrator when present, a metallic material by cold thermal projection to form the reinforcement,

[0026] - heat treatment of the body, or the magnetic field concentrator, and the reinforcement,

[0027] - finishing machining of the reinforcement.

[0028] According to preferred embodiments, the invention further meets the following characteristics, implemented separately or in each of their technically effective combinations.

[0029] According to preferred embodiments, the production method comprises, prior to the deposition step, a step of removing, from an initial surface of the body of the coil, or of the magnetic field concentrator when it is present, a layer of material forming said body, or said field concentrator, to the first surface of the body of the coil, or of the magnetic field concentrator.

[0030] The invention also relates to a method for reconditioning a coil in at least one of its embodiments, when it is used. The reconditioning method comprises the successive steps of:

[0031] - removal of the reinforcement over its entire thickness,

[0032] - removing, from the first surface of the body, or of the magnetic field concentrator when present, a layer of material forming said body or said magnetic field concentrator, of a predefined thickness, to a second surface of the body, or of the magnetic field concentrator,

[0033] - deposition at the second surface of the body or field concentrator, of a metallic material by cold thermal spraying to form a new reinforcement, over a predefined thickness, corresponding at least to the sum of the thickness of the previous reinforcement removed and the thickness of the layer of material removed,

[0034] - heat treatment of the body, or the magnetic field concentrator, and the new reinforcement, - finishing machining of the new reinforcement.

[0035] The reinforcement removal step advantageously allows the removal of any traces of cracks and / or crazing which could impact the future performance of the reconditioned coil.

[0036] The step of removing a layer of material forming the body of the coil, or the magnetic field concentrator, advantageously makes it possible to remove all traces of the deformation of the first surface by the projection of particles of metallic material. This guarantees a new clean surface to receive a new deposit of metallic material by cold thermal projection.

[0037] At the end of the finishing machining, the new reinforcement thus has a thickness equal to the sum of the thickness of the previous reinforcement removed and the thickness of the layer of material removed.

[0038] According to preferred embodiments, the invention further meets the following characteristics, implemented separately or in each of their technically effective combinations.

[0039] According to preferred embodiments, each time the reinforcement of the coil is worn, the steps of removing the reinforcement over its entire thickness and removing an additional layer of material from the body of the coil, or from the magnetic field concentrator, are successively repeated, then the step of depositing a metallic material by a cold thermal projection process until a new reinforcement is obtained, said new reinforcement having, after each reconditioning, a thickness corresponding to the thickness of the previous reinforcement, increased by the thickness of the layer of material from the body of the coil, or from the magnetic field concentrator removed.

[0040] Such a reconditioning process allows the coil to be renewed at a significantly reduced cost compared to a total replacement of the coil or the magnetic field concentrator.

[0041] According to preferred embodiments, the steps of the reconditioning process are repeated until a predefined maximum thickness of the reinforcement is reached. Indeed, the cold thermal spraying process generates high stresses in the particles of metallic material, if the reinforcement has too great a thickness, detachments of said reinforcement could appear.

[0042] This predetermined maximum thickness depends in particular on the material of the metal coating and the material of the body of the coil or the magnetic field concentrator.

[0043] Presentation of figures

[0044] The invention will be better understood by reading the following description, given as a non-limiting example, and made with reference to the figures which represent:

[0045] Figure 1 schematically represents a perspective view of an annular type coil according to the invention,

[0046] Figure 2 schematically represents a front view of the annular coil of Figure 1,

[0047] Figure 3 shows a cross-section of the annular coil of Figure 2 along line AA, in which two metal pieces to be welded are positioned,

[0048] Figure 4 schematically represents a perspective view of an annular coil comprising a magnetic field concentrator according to another embodiment of the invention,

[0049] Figure 5 schematically represents a front view of the annular coil of Figure 4,

[0050] Figure 6 shows a cross-section of the annular coil of Figure 5 along line AA, in which a metal part and a die are positioned,

[0051] Figure 7 represents the steps of a method for producing an annular coil according to Figure 4,

[0052] Figure 8 represents the steps of a process for reconditioning an annular coil according to Figure 4, used,

[0053] Figure 9 schematically represents a perspective view of a flat-type coil according to the invention.

[0054] Detailed description of the invention

[0055] Different figures and elements within a figure are not necessarily represented on the same scale. In all figures, identical elements bear the same numerical reference.

[0056] The terminology used in this description should not be interpreted in any way as limiting or restrictive, simply because it is used in conjunction with a detailed description of certain embodiments of the invention.

[0057] The present invention relates to a coil for deforming metal parts by magnetic pulse, such as by magneto-forming, by magneto-welding or by magneto-crimping.

[0058] The coil 100 is an integral part of a device further comprising a storage unit 500 and one or more switches 510, as illustrated in FIG. 1.

[0059] The storage unit 500 is conventionally connected to the coil 100 and to the switch(es) 510. The storage unit 500 is configured to store high energy, for example of the order of a few tens of kilojoules (kJ). The storage unit 500 is for example a capacitor bank.

[0060] A very rapid discharge of this electrical energy into the coil 100, in the form of a very high intensity variable current, makes it possible to create an intense magnetic field.

[0061] In the remainder of the text, as illustrated in Figures 1 to 8, the invention will be described, in a non-limiting manner, in a coil configuration where the coil is of the annular coil type. This coil configuration is particularly suitable for carrying out operations for deforming tubular parts.

[0062] The coil 100 comprises a body 120. A tubular opening 110 is made in said body. Said opening is sized and configured to receive:

[0063] - either two tubular parts, called first part 200 and second part 300, arranged one inside the other for the purpose of welding or crimping them, as illustrated in figure 3, the first part 200 being arranged around the second part 300,

[0064] - either a die 400 and a tubular part, called first part 200, arranged around the die, for the purpose of forming said first part, as illustrated in figure 6.

[0065] The body 120 of the coil 100 has a peripheral surface, called the first surface 122, delimiting the opening 110. Thus the first surface 122 of the body 120 is intended to be positioned opposite the part to be deformed, therefore the first part 200, received in the opening 110.

[0066] The body 120 of the coil 100 further comprises a narrow slot 130 extending from the opening 110. The body may comprise two symmetrically opposed contact plates 140a, 140b extending on either side of the slot 130. The contact plates 140a, 140b are connected to the energy storage unit 500 and to the switch(es) 510.

[0067] The body 120 of the coil is made of a material having specific properties in terms, on the one hand, of electrical conductivity to circulate a very high intensity current, of the order of several hundred thousand Amperes and, on the other hand, of mechanical resistance to avoid plastic deformation during the magneto-forming, magneto-welding or magneto-crimping process.

[0068] In a preferred embodiment, the material of the body 120 of the coil is made of steel, of the 40CMD8 type, of copper, of the 1 / 2 hard or 3 / 4 hard Cu type, or of copper alloy, of the CuCr type.

[0069] The coil is therefore configured so that a high intensity current can flow through it and produce a magnetic field.

[0070] The coil 100 is also configured so that the current density in an area of ​​the coil is sufficient to satisfy the desired deformation conditions. This area is called the active portion.

[0071] In the case of a conventional annular coil of the prior art, the current is concentrated in the active part, on a layer delimited by the first surface 122 and of thickness corresponding to the skin thickness. The current generates a concentrated magnetic field between the active part of the coil and the first part 200.

[0072] In the non-limiting example of a coil 100 made of steel, the skin thickness is of the order of a few millimeters for a frequency of a few tens of kHz.

[0073] In an alternative embodiment of the coil, illustrated in Figures 4 to 6, the coil 100 may comprise, at the first surface 122 of the body, a magnetic field concentrator, called concentrator 160. Said concentrator is an annular part intended to be arranged in the opening 110 of the body 120 of the coil and which makes it possible to concentrate the magnetic field even more in the opening 110 of the body 120 of the coil. The concentrator 160 has an opening, also tubular, sized and intended to receive either the first and second parts 200, 300, or the first part 200 and the die 400. The concentrator 160 has a peripheral surface, called the first surface 162, delimiting the opening of the concentrator 160. The first surface 162 of the concentrator 160 is thus intended to be positioned opposite the part to be deformed, therefore the first part 200, received in the opening of the concentrator 160.

[0074] The hub 160 further comprises a narrow slot 150 extending from the opening of said hub. The slot 150 is aligned with the slot 130 of the body 120 of the coil 100.

[0075] In a preferred embodiment, the material of the concentrator 160 is steel, of the 40CMD8 type, or copper alloy, of the CuCr type. Preferably, the material of the concentrator 160 is identical to the material of the body 120 of the coil.

[0076] In the case of this variant embodiment of the coil 100, the current is concentrated in the active part which is then located at the level of the first surface 162 of the concentrator 160. The current is concentrated, in the active part, on a layer delimited by the first surface 162 of the concentrator 160 and of thickness corresponding to the skin thickness. The current generates, between the active part of the concentrator and the first part 200, a magnetic field even more concentrated than the magnetic field created between the active part of the coil and the first part 200, in the absence of a concentrator.

[0077] According to the invention, the coil 100 advantageously comprises, at the level of the first surface 122 of the body 120, or at the level of the first surface 162 of the concentrator 160 when the coil 100 comprises a concentrator 160, a reinforcement 180, as illustrated in figures 1 to 3 and 4 to 6 respectively.

[0078] The reinforcement 180 has a first surface 181 intended to be opposite the part to be deformed, therefore the first part 200.

[0079] This 180 reinforcement results from a deposit of metallic material carried out by a cold thermal projection process.

[0080] The cold thermal spraying process is a conventional metallization process. Particles of metallic material are projected at very high speed, by a high-pressure gas, onto the first surface 122 of the body 120 (or onto the first surface 162 of the concentrator 160 when the coil 100 comprises a concentrator 160). The pressure and the projection speed of the particles of metallic material cause plastic deformation of the projected metallic material when it comes into contact with the first surface 122 (or 162) to be coated, the impact force then cold-welding this metallic material onto said first surface 122 (or 162), and cohesion of the particles to form a dense reinforcement there.The cold thermal spraying process advantageously allows good cohesion with the first surface 122 (or 162) subjected to the spraying, low porosity of the deposited metallic material, and a reduced level of oxidation due to the moderate temperature to which the metallic material is brought.

[0081] The cold thermal spraying process also makes it possible to achieve thicknesses of several millimeters while retaining these qualities.

[0082] The cold thermal spraying method is advantageously implemented in the invention to obtain the desired mechanical and electrical performance of the reinforcement without damaging the body 120 of the coil or the concentrator 160.

[0083] The material used to form the reinforcement 180 advantageously has specific properties, in particular in terms of, on the one hand, electrical conductivity to circulate a very high intensity current, for example of the order of several hundred thousand Amperes, and on the other hand, mechanical resistance to plastic deformation and to high temperatures (i.e. a high melting temperature) so as not to melt during the magneto-forming, magneto-welding or magneto-crimping process.

[0084] Preferably, the material used to form the reinforcement 180 is different from the material constituting the body 120 and / or the concentrator 160. Preferably, the material used to form the reinforcement 180 has mechanical and thermal resistance characteristics greater than the material of the body 120 or the concentrator 160, to reinforce the coil 100 and improve the service life of the coil 100.

[0085] In preferred embodiments, when the material of the coil body, or of the hub 160, is a copper alloy, such as CuCr, the material used to form the reinforcement 180 is a copper silver alloy CuAg.

[0086] Thus, in the coil 100 according to the invention, the current is concentrated in the active part which is then located at the level of the reinforcement 180.

[0087] The current is concentrated on a layer delimited by the first surface 181 of the reinforcement and of thickness corresponding to the skin thickness. In the non-limiting example of a reinforcement made of CuAg, the skin thickness is of the order of 1 mm for a frequency of a few tens of kHz.

[0088] Preferably, the reinforcement 180 has a minimum thickness hmin at least equal to this skin thickness. Thus, the current is then concentrated only in the reinforcement 180. When using the coil 100, the cracks and / or crazing are thus limited to the reinforcement 180 and do not propagate in the body 120 of the coil 100, or in the concentrator 160 when the coil comprises such a concentrator.

[0089] Preferably, the reinforcement 180 has a maximum thickness h ma x predefined. This maximum thickness is defined to avoid detachments of the reinforcement 180 from the first surface 122 of the body 120 of the coil 100, or from the first surface 162 of the concentrator 160. It is in fact known that the cold thermal spraying process generates strong stresses in the particles of metallic material, and with excessively large thicknesses, detachments of the reinforcement may appear.

[0090] According to preferred embodiments, the reinforcement thickness 180 is between 1 mm and 20 mm.

[0091] In an exemplary embodiment, when the material of the body 120 of the coil 100, or of the concentrator 160, is CuCr and the material of the reinforcement 180 is CuAg, the minimum thickness hmin of the reinforcement 180 is of the order of 5 mm and the maximum thickness hmax of the reinforcement 180 is of the order of 9 mm.

[0092] Uniaxial tensile tests were also carried out on samples with different substrates (steel, CuCr, etc.) and different particles of metallic material (CuAg, CuNiCoSi, etc.) to evaluate the adhesion strength. The tensile strength was evaluated at the particle / substrate interface. Indeed, in use, during a discharge, Laplace forces will deform the metal part to be deformed, as described in the prior art. By action / reaction, similar forces will be created in the body 120 of the coil 100 (or in the concentrator 160), which will generate tensions at the first surface 122 (or 162). The tests showed that the CuCr / CuAg couple has a tensile strength of around 190 MPa, a value sufficient to withstand repeated discharges during use of the coil 100.

[0093] Such a reinforcement 180 thus makes it possible to significantly increase the lifetime of the coil 100. For example, as mentioned in the prior art, the lifetime of a conventional coil 100 (i.e. without reinforcement) made of a CuCr material is estimated at 25,000 discharges. The lifetime of a coil 100 with a reinforcement 180 made of a CuAg material makes it possible to achieve at least 100,000 discharges. The lifetime of the coil is thus multiplied by four. A method for producing a coil 100 according to the invention is now described. The method will be described below, without limitation, for the production of a coil 100 with a concentrator 160. It will only concern the first surface 162 of the concentrator 160. It is clear, however, that, by analogy, when the coil 100 does not include a concentrator, the first surface stated will be that of the body 120 of the coil 100.

[0094] Figure 7 illustrates the steps of the method for producing an annular coil 100 with the concentrator 160. The annular coil 100 is shown partially in cross-section as in Figure 6.

[0095] To produce a coil 100 according to the invention, a first step consists of depositing, on a coil without reinforcement, a metallic material by a cold thermal spraying process, to form the reinforcement 180. The deposition of said metallic material is carried out on the first surface 162 of the concentrator 160.

[0096] Particles of metallic material are projected at very high speed, by a pressurized gas, onto the first surface 162 of the concentrator. The particles weld together, first onto the first surface 162 of the concentrator 160, then onto themselves until a desired thickness is obtained for the reinforcement 180.

[0097] The particles of metallic material are projected in particular with a predefined speed and at a predefined impact angle. The projection speed and the impact angle advantageously ensure good adhesion of the deposit of the particles of metallic material and limit the shear forces at the first surface 162.

[0098] In an exemplary implementation, the metallic material particles are projected with a nozzle. The nozzle can move to form the reinforcement over the entire first surface 162.

[0099] In one form of implementation, this first deposition step can be carried out according to one or more of the following operating parameters:

[0100] - particles preferably between 5 and 80 pm,

[0101] - gas temperature between 400°C and 1000°C, preferably around 500°C,

[0102] - gas pressure between 20 and 50 bars, preferably around 30 bars,

[0103] - particle projection speed between 0.5 and 1.5 km / s,

[0104] - choice of carrier gas: nitrogen or helium or a mixture of these two gases. The person skilled in the art has the skills to choose the operating parameters to be implemented in order to obtain a desired reinforcement thickness, preferably between the two values ​​hmin and hmax.

[0105] View (b) of Figure 7 illustrates the coil, after this first deposition step.

[0106] Preferably, to promote the conditions for the attachment of the particles of metallic material to the first surface 162 of the concentrator, the method may comprise a step, prior to the first deposition step, of removing a layer of material from the concentrator 160. The layer of material is removed from an initial surface 164 to the first surface 162. As previously specified, the angle of impact of the particles of metallic material on the first surface advantageously guarantees good adhesion of the deposition of said particles of metallic material and limits the shear forces at the first surface 162. Those skilled in the art have the skills to determine the necessary angle of impact.

[0107] The removal of the layer of material from the concentrator 160 is preferably carried out by machining.

[0108] View (a) of Figure 7 illustrates the coil, after this preliminary step. The removed layer of concentrator material 160 appears dotted. The first surface 162 is, in the non-limiting example of view (a), inclined relative to the initial surface 164.

[0109] The method for producing a coil 100 according to the invention comprises, after the first deposition step, a second step of heat treatment of tempering the body of the coil, the magnetic concentrator 160 and the reinforcement 180.

[0110] This second step is classic as such and aims to give the reinforcement 180 the desired elastic and electrical conductivity properties.

[0111] In an exemplary implementation, the coil is placed in a tempering furnace, at a predefined temperature, and for a predefined duration.

[0112] The tempering heat treatment is preferably carried out at a temperature between 200 and 400°C, for a period between 2 and 8 hours.

[0113] The method for producing a coil 100 according to the invention then comprises a third step of finishing machining of the reinforcement 180.

[0114] The finishing machining step is conventional as such and allows surface defects to be eliminated to achieve the desired final shape and dimensional dimensions of the reinforcement 180.

[0115] View (c) of Figure 7 illustrates the coil, after this third step.

[0116] At the end of this third step, the coil 100 is ready to be used for a forming, welding or crimping process.

[0117] In one embodiment, the manufacturing method may comprise, before or after the third step, a step of cutting the reinforcement 180, in its thickness, at the level of the slot 150 of the concentrator 160 so that the reinforcement 180 has a slot in alignment with the slot 150 of the concentrator 160 and the slot 130 of the body 120 of the coil 100. Indeed, during the first step of depositing the particles of metallic material by the cold thermal spraying process, the particles cover the slot 150. If the slot is obstructed, in use, the current will not be able to flow in the coil 100 and create the magnetic field necessary to carry out the forming, welding or crimping processes.

[0118] In one embodiment, the method may comprise, upstream of the first deposition step, a step of masking the concentrator 160 on the parts of the concentrator 160 other than the first surface 162. Such a step makes it possible to prevent other parts of the concentrator 160 from receiving the particles of metallic material during the first step. Consequently, after the first step, the method comprises a step of unmasking the concentrator 160.

[0119] The cutting of the reinforcement 180 is preferably carried out by electroerosion.

[0120] In addition to the fact that the coil 100 according to the invention is reinforced at the active part and thus has a service life much longer than the service life of a conventional coil, the coil 100 according to the invention can also be reconditioned several times in order to be reused and to extend its service life even further. After a first use of the coil 100 according to the invention to deform a part by magneto-forming, magneto-welding or magneto-crimping, and when the crazing at the active part on the reinforcement critically degrades the performance of the magnetic pulse deformation process and has too strong an impact on the quality of the forming, welding or crimping, the coil 100 can be reconditioned with a new reinforcement 180.

[0121] A method will be described below, without limitation, for the reconditioning of a coil 100 with a concentrator 160. This will only concern the first surface 162 of the concentrator 160. It is clear, however, that, by analogy, when the coil 100 does not include a concentrator, the first surface stated will be that of the body 120 of the coil 100.

[0122] Figure 8 illustrates the steps of the method of reconditioning an annular coil 100 with the concentrator 160. The annular coil 100 is shown partially, in cross-section, as in Figure 6. Figure 8 illustrates the first reconditioning of the coil 100.

[0123] View (a) of Figure 8 shows the coil 100 with the used reinforcement 180. The crazing in the reinforcement 180 is schematically represented by the lines 190.

[0124] The reconditioning method comprises a first step of removing the reinforcement 180. The reinforcement is removed, over its entire thickness, up to the first surface 162 of the concentrator 160.

[0125] The removal of the reinforcement 180 is preferably carried out by machining.

[0126] View (b) of Figure 8 illustrates the coil at the end of this first step. The removed reinforcement 180 appears in dotted lines.

[0127] The reconditioning method then comprises a second step of removing, from the first surface 162 of the concentrator 160, a layer of material from said concentrator.

[0128] The layer of material of the concentrator 160 is reduced by a predefined, preferably constant, thickness to a second surface 162' of the concentrator 160.

[0129] Preferably, the predefined thickness of removed material layer is less than the removed thickness of the reinforcement.

[0130] The step of removing a layer of material forming the concentrator 160 advantageously makes it possible to remove any trace of the deformation of the first surface 162 by the projection of the particles of metallic material.

[0131] The removal of the material layer is preferably carried out by machining.

[0132] View (c) of Figure 8 illustrates the coil at the end of this second stage. The removed layer of concentrator material appears dotted.

[0133] The reconditioning process then comprises a third step of depositing a metallic material by the cold thermal spraying process to form a new reinforcement 180.

[0134] The deposition of the metallic material is carried out on the second surface 162' of the concentrator 160.

[0135] The deposition of the metallic material is carried out to a predefined thickness, slightly greater than the sum of the thicknesses of the previous reinforcement removed and the layer of concentrator material removed.

[0136] The implementation of this third step is identical to the first step of the coil production process.

[0137] View (d) of Figure 8 illustrates the coil at the end of this third step. The reconditioning process then comprises a fourth step of heat treatment of tempering the body 120, the concentrator 160, and the new reinforcement 180.

[0138] The implementation of this fourth step is identical to the second step of the method for producing the coil 100. This fourth step thus makes it possible to give the new reinforcement 180 the desired elastic and electrical conductivity properties. The reconditioning process then comprises a fifth step of finishing machining the reinforcement 180.

[0139] The implementation of this fifth step is identical to the third step of the method for producing the coil 100. This fifth step makes it possible to achieve the desired final shape and dimensional dimensions of the new reinforcement 180.

[0140] The thickness of the new reinforcement 180 thus preferably corresponds to the sum of the thickness of the previous reinforcement removed and the thickness of the layer of material removed.

[0141] View (e) of Figure 8 illustrates the reconditioned coil at the end of this fifth step.

[0142] At the end of this fifth step, the coil with its new reinforcement can be used.

[0143] The coil with its new 180 reinforcement can again be used for a forming, welding or crimping process.

[0144] In one embodiment of the reconditioning method, the reconditioning method may comprise, before or after the fifth step, a step of cutting the reinforcement, in its thickness, at the level of the slot 150 of the concentrator 160 so that the reinforcement 180 has a slot in alignment with the slot 150 of the concentrator 160 and the slot 130 of the body 120 of the coil 100.

[0145] In one embodiment of the reconditioning method, the method may comprise, upstream of the third step, a step of masking the concentrator 160 on the parts of the concentrator 160 other than the first surface 162.

[0146] The cutting of the reinforcement 180 is preferably carried out by electroerosion. Each time the reinforcement 180 of the coil 100 is worn and the crazing at the reinforcement has too strong an impact on the quality of the process of deformation of a metal part by magnetic pulse, it is possible to advantageously repeat the reconditioning process several times, to again extend the service life of the coil 100. Each time, the reinforcement is removed over its entire thickness and an additional layer of material from the concentrator 160 is removed. The new reinforcement thus each time has a thickness corresponding to the thickness of the previous reinforcement, increased by the thickness of the removed layer of material from the concentrator 160.

[0147] Preferably, the reconditioning process can be repeated until the thickness of the reinforcement 180 reaches the predefined maximum thickness h max .

[0148] In an exemplary implementation, the material of the concentrator 160 is CuCr and the material of the reinforcement 180 is CuAg. The minimum thickness of the reinforcement is 5 mm. The maximum thickness of the reinforcement is 9 mm. By removing only 0.2 mm of material layer thickness from the concentrator at each reconditioning, the coil 100 can thus be reconditioned 20 times and therefore be used 21 times.

[0149] Therefore, the total lifetime of said coil 100 can reach 2,100,000 discharges (21 x 100,000). Compared with the lifetime of the CuCr coil without reinforcement which is of the order of 25,000 discharges, the lifetime of the CuCr coil 100 with the CuAg reinforcement 180, by using the reconditioning process, is considerably increased.

[0150] The invention has been described in the preferred configuration of an annular coil. It is however possible, without departing from the scope of the invention, to adapt the invention to any other coil configuration, such as for example flat type coils.

[0151] Figure 9 illustrates an example of a flat coil. This coil is particularly suitable for carrying out deformation operations on flat parts.

[0152] The coil 100 comprises a body 120. The body 120 is in the form of a plate. A through opening 110 is made in the body. The opening 110 is sized and configured to come opposite the first part 200 to be deformed (not shown).

[0153] In a non-limiting embodiment, as illustrated in FIG. 9, the opening 110 has a cross section of substantially oblong shape. The body 120 of the coil 100 further comprises a narrow slot 130 extending from the opening 110. The body may comprise two symmetrically opposed contact plates 140a, 140b extending on either side of the slot 130. The contact plates 140a, 140b are connected to the energy storage unit 500 and to the switch(es) 510.

[0154] Said body has, on one face of the plate, a boss 126 arranged around the periphery of the opening 110.

[0155] The body 120 of the coil 100 comprises, at the top of the boss 126, a first surface 122, intended to be positioned opposite the first part 200 to be deformed (not shown).

[0156] According to the invention, the coil 100 comprises, at the level of the first surface 122 of the body 120, a reinforcement 180 formed by a metallic material deposited by cold thermal spraying.

[0157] In this flat coil configuration, the current is also concentrated in the active part which is located in the reinforcement 180.

[0158] The manufacturing process of the flat coil and the process of reconditioning this flat coil are identical to the processes described for the annular coil.

Claims

CLAIMS Claim 1. Coil (100) for deforming a metal part (200) by magnetic pulse comprising a body (120) having a first surface (122) intended to be positioned opposite the metal part (200) to be deformed, characterized in that the coil (100) comprises, at the level of said first surface (122), a reinforcement (180), said reinforcement (180) being constituted by a metallic material deposited by cold thermal projection. Claim 2. Coil (100) for deforming a metal part (200) by magnetic pulse comprising a body (120), having a first surface (122), and a magnetic field concentrator (160), at the first surface (122) of the body (120), said magnetic field concentrator (160) comprising a first surface (162) intended to be positioned opposite the metal part (200) to be deformed, characterized in that the coil (100) comprises, at the level of said first surface (162) of the magnetic field concentrator (160), a reinforcement (180), said reinforcement (180) being constituted by a metallic material deposited by cold thermal spraying. Claim 3. Method of producing a coil (100) according to claim 1 or claim 2, comprising the successive steps of: - depositing, on the first surface (122, 162) of the body (120) or of the magnetic field concentrator (160), a metallic material by cold thermal spraying to form the reinforcement (180), - heat treatment of the body (120) or the magnetic field concentrator (160) and the reinforcement (180), - finishing machining of the reinforcement (180). Claim 4. Method for producing a coil according to claim 3, comprising, prior to the deposition step, a step of removing, from an initial surface of the body (120), or of the magnetic field concentrator (160), a layer of material forming said body (120), or said magnetic field concentrator (160) to the first surface (122, 162) of the body, (120) or of the magnetic field concentrator (160). Claim s. Method for reconditioning a coil (100) according to claim 1 or claim 2, comprising the successive steps of: a) removing the reinforcement (180) over its entire thickness, b) removing, from the first surface (122, 162) of the body (120) or the magnetic field concentrator (160), a layer of material forming said body (120) or said magnetic field concentrator (160), of a predefined thickness, to a second surface of the body (120) or the magnetic field concentrator (160), c) depositing at the second surface of the body (120) or the magnetic field concentrator (160), a metallic material by a cold thermal spraying process to form a new reinforcement (180), over a predefined thickness corresponding at least to the sum of the thickness of the previous reinforcement removed and the thickness of the removed layer of material,d) tempering heat treatment of the body (120) or magnetic field concentrator (160) and the new reinforcement (180), e) finish machining of the new reinforcement (180), the new reinforcement (180) having a thickness equal to the sum of the thickness of the previous reinforcement removed and the thickness of the removed layer of material., Claim 6. Reconditioning method according to claim 5 wherein, each time the reinforcement of the coil is worn, the steps of removing the reinforcement over its entire thickness and removing an additional layer of material from the body (120) of the coil (100) or the magnetic field concentrator (160) are repeated, then the step of depositing a metallic material by a cold thermal spraying process until a new reinforcement (180) is obtained, said new reinforcement having, after each reconditioning, a thickness corresponding to the thickness of the previous reinforcement, increased by the thickness of the layer of material of the magnetic field concentrator removed. Claim 7. A reconditioning method according to claim 6 wherein the steps are repeated until a predefined maximum thickness of the reinforcement (180) is reached.

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