Coil for deforming metal parts by magnetic pulses, method for producing and reconditioning such a coil

Abstract

The present invention relates to a coil (100) for deforming a metal part (200) by magnetic pulses, the coil (100) comprising a body (120) having a first surface (122) adapted to be positioned facing the part (200) to be deformed, the coil (100) including a stiffener (180) at the first surface (122), the stiffener (180) being made of a metallic material deposited by cold spraying.

Description

[Technical Field]

[0001] The present invention is in the field of forming, welding or crimping metal parts. More specifically, the invention is in the field of forming, welding or crimping metal parts by magnetic pulses, commonly referred to as Magnetic Pulse Forming (MPF), Magnetic Pulse Welding (MPW) or Magnetic Pulse Crimping (MPC). The present invention relates to a reinforced coil that allows its service life to be extended. The present invention also relates to a method for producing said coil and a method for reconditioning said coil. [Background technology]

[0002] The deformation of the metal part by the magnetic pulse is carried out under the action of the electromagnetic force generated by the coil, which makes it possible to carry out either a forming operation to shape the metal part according to the shape of the die, or a welding or crimping operation to permanently assemble two parts together.

[0003] Conventionally, devices for deforming metal parts by magnetic pulses include several capacitors forming an electrical energy storage unit and a switch connected to a coil to generate a short-term, powerful magnetic field. The electrical energy storage unit is used to store large amounts of electrical energy. When the switch is closed, the electrical energy stored in the electrical storage unit is very rapidly released into the coil in the form of a variable current of very high intensity for a very short time, thus generating a powerful magnetic field. For example, some devices are capable of reaching currents of hundreds of thousands of amperes in a few microseconds.

[0004] The current generates a variable, strong magnetic field between the coil and the metal part to be deformed (previously placed nearby), inducing eddy currents in the part. These eddy currents, coupled with the surrounding magnetic field, develop Laplace forces in the metal part to be deformed, which cause strong acceleration of the part towards either the die or another part.

[0005] Depending on the intensity of the generated current, the impact angle, and the impact speed, among other things, the part is either formed, welded, or crimped to another part.

[0006] However, the magnetic pulse deformation method has the drawback of requiring very high intensities to form the part or to weld / crimp it to another part, which involves the use of a significant amount of electrical energy. Furthermore, the use of such intensities generates localized temperatures and significant mechanical stresses in the coil, which can weaken the coil, shorten its lifespan, and potentially cause irreparable damage to the coil (especially in zones referred to as "active parts"). The active parts refer to the zones of the coil where the current delivered by the electrical energy storage unit is concentrated to generate the magnetic field.

[0007] Damage on the coil (typically in the form of cracks and / or crazing) degrades the performance of the magnetic pulse deformation method.

[0008] For example, for conventional coils made from copper alloy materials (e.g., CuCr, etc.), the coil lifespan is estimated to be 25,000 discharges. After 25,000 discharges, crazing in the active parts on the coil severely degrades the performance of the magnetic pulse deformation method, significantly affecting forming quality, welding quality, or crimping quality. For conventional coils made from steel materials (e.g., 40CMD8, etc.), the coil lifespan is estimated to be 15,000 discharges.

[0009] However, these life times prove to be very limiting when the coils are used in industry, for example in production lines: the coils need to be replaced periodically, which causes shutdowns of the production line and incurs non-negligible costs.

[0010] Therefore, there is a real need to extend the lifespan of coils used in methods for deforming metal parts with magnetic pulses. Summary of the Invention [Problem to be solved by the invention]

[0011] The aim of the present invention, which resulted from research carried out in collaboration with UTBM (Universite de Technologie de Belfort Montbeliard), is to overcome the above-mentioned drawbacks.

[0012] The object of the present invention is, inter alia, to provide an effective solution for increasing the life time of coils for deforming metal parts by magnetic pulses, for example by magnetic pulse forming and / or magnetic pulse welding and / or magnetic pulse crimping. [Means for solving the problem]

[0013] The present invention therefore relates to a coil for deforming metal parts by magnetic pulses, the coil comprising a body having a first surface adapted to be positioned facing the metal part to be deformed, at said first surface the coil comprises a stiffener, the stiffener being made of a metallic material deposited by cold thermal spraying.

[0014] Thus, the stiffener forms a coating on the first surface of the coil body. However, adding a coating on the first surface of the coil body contradicts the consistent preconception in the prior art that adding a coating on this first surface is not feasible. Indeed, on the one hand, it is difficult to maintain electrical continuity at the interface between the coil body and the coating. Electrical discontinuity can affect the generation of the magnetic field and degrade the quality of the final product produced by the magnetic pulse deformation method. On the other hand, adding a coating on the first surface can create potential cavities at the interface between the coil body and the coating. There is a significant risk of electrical arcing in these cavities, causing coil degradation.

[0015] The present invention alleviates the above-mentioned drawbacks and overcomes the technical prejudices by depositing metallic materials by a cold spraying process, commonly known as cold spray.

[0016] Cold spraying involves spraying particles onto a surface. More specifically, cold spraying consists in spraying metallic material particles onto the first surface of the body at a very high velocity using gas under high pressure. The impact force ensures cold welding of this metallic material onto the first surface of the body and cohesion of the particles to form a high-density stiffener thereon. The metallic material particles are first welded onto the first surface of the coil body and then welded onto themselves. The cold spraying method advantageously allows for good cohesion with the first surface of the body being sprayed and low porosity of the deposited metallic material. Therefore, electrical continuity is maintained at the interface between the coil body and the stiffener, reducing electrical arc formation at this interface. Furthermore, low porosity of the deposited metallic material also reduces electrical arc formation in the stiffener.

[0017] Thus, during the use of the coil according to the invention in a method for deforming a metal part by means of a magnetic pulse, the current flowing in said coil is then concentrated in the active part located on the stiffener, whereas initially, in the absence of a stiffener, the current is concentrated on the first surface of the body.

[0018] Such a stiffener therefore makes it possible to significantly increase the life time of the coil.

[0019] Preferably, the material used to form the stiffener has better mechanical and thermal resistance characteristics than the material of the body to further improve the life time of the coil.

[0020] According to preferred embodiments, the invention furthermore fulfils the following characteristics, implemented either separately or according to any of their technically feasible combinations:

[0021] According to a preferred embodiment, the coil includes a magnetic field concentrator on a first surface of the body. The magnetic field concentrator includes a first surface configured to be positioned facing the metal part to be deformed. The coil includes a stiffener on the first surface of the magnetic field concentrator, the stiffener being made of a metallic material deposited by cold spraying. When using the magnetic field concentrator, the stiffener is now formed on the first surface of the magnetic field concentrator and no longer on the first surface of the coil body. During use of the coil in a method for deforming a metal part by magnetic pulses, the current flowing in the coil is then concentrated on the active part located at the stiffener, whereas initially, when no stiffener is provided, the current is concentrated on the first surface of the magnetic field concentrator.

[0022] The invention also relates in at least one of its embodiments to a method for producing a coil, said method comprising the following successive steps: - depositing a metallic material by cold spraying onto the first surface of the coil body or, when present, of the magnetic field concentrator to form a stiffener; - tempering the body or the magnetic field concentrator and the stiffener; - machining and finishing the stiffener; Includes.

[0023] According to preferred embodiments, the invention furthermore fulfils the following characteristics, implemented either separately or according to any of their technically feasible combinations:

[0024] According to a preferred implementation, the production method includes a step of removing a layer of material forming the coil body or the magnetic field concentrator, if present, from the initial surface of the coil body or the initial surface of the magnetic field concentrator, prior to the deposition step, to the first surface of the coil body or the magnetic field concentrator.

[0025] The invention also relates, in at least one of its embodiments, to a method for reconditioning a coil when it has worn out, said method comprising the following steps: - removing the stiffener through its entire thickness; - removing a layer of material forming said body or said magnetic field concentrator of a predefined thickness from a first surface of said body or said magnetic field concentrator, if present, to a second surface of said body or said magnetic field concentrator; - depositing a metallic material by cold spraying on the second surface of the body or of the magnetic field concentrator to form a new stiffener over at least a predefined thickness corresponding to the sum of the thickness of the previous stiffener removed and the thickness of the layer of material removed; - tempering the body or magnetic field concentrator and the new stiffener; - Machining and finishing the new stiffener; Includes.

[0026] The step of removing the stiffeners advantageously makes it possible to remove any signs of cracking and / or crazing that may affect the future performance of the reconditioned coil.

[0027] The step of removing the layer of material forming the coil body or the magnetic field concentrator advantageously makes it possible to remove any traces of deformation of the first surface due to the spraying of metallic material particles, thus ensuring a new, clean surface to receive a new deposition of metallic material by cold spraying.

[0028] Following finishing machining, the new stiffener therefore has a thickness equal to the sum of the thickness of the previous stiffener that was removed and the thickness of the layer of material that was removed.

[0029] According to preferred embodiments, the invention furthermore fulfils the following characteristics, implemented either separately or according to any of their technically feasible combinations:

[0030] According to a preferred implementation, each time a stiffener of the coil wears, the steps of removing the stiffener over its entire thickness and removing an additional layer of material from the coil body or from the magnetic field concentrator are successively repeated, followed by a step of depositing metallic material by a cold spraying method until a new stiffener is obtained, said new stiffener having, after each readjustment, a thickness corresponding to the thickness of the previous stiffener, increased by the thickness of the layer of material of the coil body or of the magnetic field concentrator that has been removed.

[0031] Such a reconditioning method allows for the coil to be refurbished at a significantly reduced cost compared to completely replacing the coil or field concentrator.

[0032] According to a preferred implementation, the steps of the readjustment method are repeated up to a predefined maximum thickness of the stiffener. Indeed, since the cold spraying method generates high stresses in the metallic material particles, detachment of said stiffener may occur if it has an excessive thickness.

[0033] This predetermined maximum thickness depends, among other things, on the material of the metal coating and the material of the coil body or magnetic field concentrator.

[0034] The invention will be better understood on reading the following description, given by way of non-limiting example and made with reference to the drawings, in which: [Brief explanation of the drawings]

[0035] [Figure 1] 1 is a diagram schematically illustrating a perspective view of an annular type coil according to the present invention; [Figure 2] FIG. 2 is a diagram schematically illustrating a front view of the toroidal coil of FIG. [Figure 3] 3 is a cross-section of the toroidal coil of FIG. 2 along line AA, in which two metal parts to be welded are positioned; FIG. [Figure 4] FIG. 10 schematically depicts a perspective view of a toroidal coil including a magnetic field concentrator according to another embodiment of the present invention. [Figure 5] FIG. 5 is a diagram schematically illustrating a front view of the toroidal coil of FIG. 4. [Figure 6] 6 is a cross-section of the toroidal coil of FIG. 5 along line AA, with the metal part and die positioned thereon; FIG. [Figure 7] 5A-5C are diagrams illustrating steps of a method for producing a toroidal coil according to FIG. [Figure 8] 5A-5C are diagrams illustrating steps of a method for reconditioning a toroidal coil according to FIG. 4 in a worn state. [Figure 9] 1 is a diagrammatic representation of a perspective view of a flat type coil according to the invention; DETAILED DESCRIPTION OF THE INVENTION

[0036] Different figures, and elements in the same figure, are not necessarily drawn to scale. Identical elements are given the same reference numerals in all figures.

[0037] The terminology used herein should not be construed as limiting or restrictive in any way, merely because it is used in connection with detailed descriptions of particular embodiments of the invention.

[0038] The present invention relates to a coil for deforming metal parts by magnetic pulses (eg, by magnetic pulse forming, magnetic pulse welding, or magnetic pulse crimping, etc.).

[0039] The coil 100 is an integral part of a device that further includes a storage unit 500 and one or more switches 510, as shown in FIG.

[0040] A storage unit 500 is conventionally connected to the coil 100 and a switch 510. The storage unit 500 is configured to store high energy (e.g., on the order of tens of kilojoules (kJ)). The storage unit 500 is, for example, a capacitor bank.

[0041] The very rapid discharge of this electrical energy in the coil 100 (in the form of a very high intensity variable current) makes it possible to generate a strong magnetic field.

[0042] In the remainder of the text, the invention will be described in a non-limiting manner in a coil configuration in which the coil is of the toroidal coil type, as illustrated in Figures 1 to 8. This coil configuration is particularly adapted to perform deformation operations on tubular parts.

[0043] Coil 100 includes a body portion 120. A tubular opening 110 is created in the body portion, the opening being sized and configured to receive 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 together, as shown in FIG. 3, with the first part 200 arranged around the second part 300, or a die 400 and a tubular part (called first part 200), the tubular part being arranged around the die in order to form said first part, as shown in Figure 6.

[0044] The body 120 of the coil 100 has a peripheral surface (referred to as first surface 122) that bounds the opening 110. The first surface 122 of the body 120 is therefore adapted to be positioned facing the part to be deformed (and thus the first part 200) that is received in the opening 110.

[0045] The body 120 of the coil 100 further includes a narrow slot 130 extending from the opening 110. The body may include two symmetrically opposed contact plates 140a, 140b, which extend on either side of the slot 130. The contact plates 140a, 140b are connected to an energy storage unit 500 and a switch 510.

[0046] The coil body 120 is made from a material that has particular properties, on the one hand, in terms of electrical conductivity to allow very high intensity currents (of the order of hundreds of thousands of amperes) to circulate therein, and on the other hand, in terms of mechanical resistance so as not to undergo plastic deformation during the magnetic pulse forming, welding or crimping methods.

[0047] In a preferred embodiment, the material of the coil body 120 is made from steel (40CMD8 type), copper (Cu 1 / 2 hard type or 3 / 4 hard type), or copper alloy (CuCr type).

[0048] The coil is therefore constructed to allow a high intensity electrical current to pass through it to create a magnetic field.

[0049] Additionally, the coil 100 is configured so that the current density in a zone of the coil is sufficient to meet the desired deformation conditions. This zone is referred to as the active part.

[0050] In the case of conventional toroidal coils of the prior art, the current is concentrated in the active part in a layer of thickness corresponding to the skin thickness, bounded by the first surface 122. The current generates a concentrated magnetic field between the active part and the first part 200 of the coil.

[0051] In the non-limiting example of a coil 100 made from steel, the skin thickness is on the order of a few millimeters for frequencies of tens of kHz.

[0052] In an alternative embodiment of the coil illustrated in FIGS. 4 to 6 , the coil 100 can include a magnetic field concentrator (referred to as concentrator 160) at the first surface 122 of the body. The concentrator is an annular part configured to be disposed in the opening 110 of the coil body 120, which allows for further concentration of the magnetic field within the opening 110 of the coil body 120. The concentrator 160 has a (also tubular) opening sized and configured to receive either the first and second parts 200, 300, or the first part 200 and die 400. The concentrator 160 has a peripheral surface (referred to as first surface 162) that bounds the opening of the concentrator 160. The first surface 162 of the concentrator 160 is therefore adapted to be positioned facing the part to be deformed (hence, the first part 200) received in the opening of the concentrator 160.

[0053] Concentrator 160 further includes narrow slot 150 extending from the opening of the concentrator. Slot 150 is aligned with slot 130 in body 120 of coil 100.

[0054] In a preferred embodiment, the material of the concentrator 160 is made of steel (40CMD8 type) or copper alloy (CuCr type). Preferably, the material of the concentrator 160 is the same as the material of the coil body 120.

[0055] In this alternative embodiment of the coil 100, the current is concentrated in the active part, which in turn is located on the first surface 162 of the concentrator 160. The current is concentrated in the active part in a layer of a thickness corresponding to the skin thickness, bounded by the first surface 162 of the concentrator 160. The current generates a magnetic field between the active part and the first part 200 of the concentrator that is more concentrated than the magnetic field that would be generated between the active part and the first part 200 of the coil in the absence of the concentrator.

[0056] According to the present invention, the coil 100 advantageously includes a stiffener 180 at the first surface 122 of the body 120, or, when the coil 100 includes a concentrator 160, at the first surface 162 of the concentrator 160, as shown in Figures 1 to 3 and 4 to 6, respectively.

[0057] The stiffener 180 has a first surface 181 configured to face the part to be deformed (and thus the first part 200).

[0058] This stiffener 180 results from a deposition of metallic material carried out by a cold spraying process.

[0059] Cold spraying is a conventional metallization method. Metallic material particles are sprayed at a very high velocity onto the first surface 122 of the body 120 (or onto the first surface 162 of the concentrator 160 when the coil 100 includes the concentrator 160) by gas under high pressure. The spraying pressure and velocity of the metallic material particles cause plastic deformation of the sprayed metallic material upon contact with the first surface 122 (or 162) to be coated, and the impact force then cold welds this metallic material onto the first surface 122 (or 162) and coheses the particles, forming a dense stiffener thereon. The cold spraying method advantageously allows for good cohesion with the sprayed first surface 122 (or 162), low porosity of the deposited metallic material, and a reduced oxidation level due to the moderate temperatures to which the metallic material is subjected.

[0060] Moreover, the cold spraying method makes it possible to achieve thicknesses of several millimeters while maintaining these qualities.

[0061] A cold spray process is advantageously implemented in the present invention to obtain the desired mechanical and electrical performance of the stiffener without degrading the coil body 120 or the concentrator 160.

[0062] The material used to form the stiffener 180 advantageously has particular properties, notably in terms of electrical conductivity to allow very high intensity currents (for example of the order of hundreds of thousands of amperes) to circulate therein, and on the other hand, mechanical resistance to plastic deformation and high temperatures (i.e. a high melting point) so as not to melt during the magnetic pulse forming, welding or crimping method.

[0063] Preferably, the material used to form stiffener 180 is different from the material forming body 120 and / or concentrator 160. Preferably, the material used to form stiffener 180 has better mechanical and thermal strength characteristics than the material of body 120 or concentrator 160 to reinforce coil 100 and improve the lifespan of coil 100.

[0064] In a preferred exemplary embodiment, when the material of the coil body (or concentrator 160) is made from a copper alloy (e.g., CuCr), the material used to form the stiffener 180 is made from a silver-copper alloy, CuAg.

[0065] Thus, in the coil 100 according to the invention, the current is concentrated in the active part, which in turn is located on the stiffener 180 .

[0066] The current is concentrated in a layer of thickness corresponding to the skin thickness, bounded by the stiffener's first surface 181. In the non-limiting example of a stiffener made from CuAg, the skin thickness is of the order of 1 mm for frequencies of tens of kHz.

[0067] Preferably, the stiffener 180 has a minimum thickness h at least equal to this skin thickness. min Thus, the current is then concentrated only in the stiffener 180. During use of the coil 100, cracks and / or crazing are therefore limited to the stiffener 180 and do not propagate into the body 120 of the coil 100, or into the concentrator 160 when the coil includes such a concentrator.

[0068] Preferably, the stiffener 180 has a predefined maximum thickness h maxThis maximum thickness is defined so as to prevent detachment of the stiffener 180 from the first surface 122 of the body 120 of the coil 100 or from the first surface 162 of the concentrator 160. In fact, it is known that the cold spraying process generates high stresses in the metallic material particles, and that excessive thicknesses can lead to detachment of the stiffener.

[0069] According to a preferred embodiment, the thickness of the stiffener 180 is between 1 mm and 20 mm.

[0070] In one exemplary embodiment, when the material of the main body 120 of the coil 100 (or the concentrator 160) is made of CuCr and the material of the stiffener 180 is made of CuAg, the minimum thickness h of the stiffener 180 is min is on the order of 5 mm, and the maximum thickness h of the stiffener 180 max is of the order of 9 mm.

[0071] Uniaxial tensile tests were also performed on samples with different substrates (steel, CuCr, etc.) and different particles of metal materials (CuAg, CuNiCoSi, etc.) to evaluate adhesion strength. Traction was evaluated at the particle / substrate interface. Indeed, during discharge in use, Laplace forces will deform the metal part to be deformed, as described in the prior art. Due to action / reaction, a similar force will be generated in the main body 120 of the coil 100 (or in the concentrator 160), which will generate stress at the first surface 122 (or 162). Tests showed that the CuCr / CuAg couple has a tensile strength on the order of 190 MPa, which is sufficient to withstand repeated discharges during use of the coil 100.

[0072] Such a stiffener 180 therefore makes it possible to significantly increase the lifespan of the coil 100. For example, as described in the prior art, the lifespan of a conventional coil 100 made of CuCr material (i.e., without a stiffener) is estimated at 25,000 discharges. The lifespan of a coil 100 with a stiffener 180 made of CuAg material makes it possible to reach at least 100,000 discharges. Thus, the lifespan of the coil is increased by a factor of four.

[0073] A method for producing a coil 100 according to the invention will now be described. The method will be described hereinafter with reference to producing a coil 100 with a concentrator 160, without limitation. Only the first surface 162 of the concentrator 160 will be discussed therein. However, it is clear by analogy that when the coil 100 does not include a concentrator, the first surface being mentioned will be the first surface of the body 120 of the coil 100.

[0074] 7 illustrates the steps of a method for producing a toroidal coil 100 with a concentrator 160. The toroidal coil 100 is shown partially in cross section, similar to FIG.

[0075] To produce the coil 100 according to the invention, the first step consists in depositing a metallic material by cold spraying onto the coil without stiffeners, in order to form the stiffeners 180. The deposition of said metallic material is carried out on the first surface 162 of the concentrator 160.

[0076] Metallic material particles are sprayed at a very high velocity by gas under pressure onto the first surface 162 of the concentrator. The particles are first welded onto the first surface 162 of the concentrator 160 and then welded onto themselves until the desired thickness for the stiffener 180 is obtained.

[0077] The metal material particles are sprayed, inter alia, at a predefined speed and angle of impact, which advantageously ensures good adhesion of the deposit of metal material particles and makes it possible to limit shear forces on the first surface 162.

[0078] In one exemplary implementation, the metal material particles are sprayed by a nozzle that can be moved to form the stiffener across the first surface 162.

[0079] In one embodiment, this first deposition step can be carried out according to one or more of the following operating parameters: - particles preferably between 5 μm and 80 μm, a gas temperature between 400°C and 1000°C, preferably of the order of 500°C; a gas pressure between 20 and 50 bar, preferably of the order of 30 bar; - particle spraying speed between 0.5km / s and 1.5km / s, - Choice of carrier gas: nitrogen or helium, or a mixture of these two gases.

[0080] Those skilled in the art will appreciate that (preferably, two values ​​h min and h max The person skilled in the art has the expertise to select the operating parameters to be implemented in order to obtain the desired stiffener thickness (between ).

[0081] View (b) of Figure 7 illustrates the coil after this first deposition step.

[0082] Preferably, in order to promote conditions for the deposition of the metallic material particles on the first surface 162 of the concentrator, the method can include a step of removing a material layer from the concentrator 160 before the first deposition step. The material layer is removed from the initial surface 164 down to the first surface 162. As previously specified, the angle of impact of the metallic material particles with the first surface advantageously ensures good adhesion of the deposition of said metallic material particles and makes it possible to limit shear forces at the first surface 162. A person skilled in the art has the expertise to determine the required angle of impact.

[0083] Removal of the layer of material from the concentrator 160 is preferably performed by machining.

[0084] 7(a) illustrates the coil after this previous step. The layer of material removed from the concentrator 160 is indicated by the dotted line. The first surface 162 is inclined relative to the initial surface 164 in the non-limiting example of FIG. 7(a).

[0085] The method for producing the coil 100 according to the present invention includes, after the first deposition step, a second step of tempering the coil body, magnetic concentrator 160 and stiffener 180.

[0086] This second step, conventional in itself, has the purpose of imparting the desired elastic and electrical conductivity properties to the stiffener 180 .

[0087] In one exemplary implementation, the coil is placed in a tempering furnace at a predefined temperature for a predefined duration.

[0088] The tempering heat treatment is preferably carried out at a temperature between 200°C and 400°C for a period of between 2 and 8 hours.

[0089] The method for producing the coil 100 according to the invention then includes a third step of machining and finishing the stiffener 180 .

[0090] The finishing machining step is conventional per se and makes it possible to remove surface imperfections in order to achieve the desired final shape and dimensions of the stiffener 180 .

[0091] View (c) of Figure 7 illustrates the coil after this third step.

[0092] Following this third step, the coil 100 is ready to be used for forming, welding, or crimping methods.

[0093] In one implementation, the manufacturing method can include, before or after the third step, a step of cutting the stiffener 180 through its thickness at the slots 150 of the concentrator 160, so that the stiffener 180 has slots aligned with the slots 150 of the concentrator 160 and the slots 130 of the body 120 of the coil 100. Indeed, during the first step of depositing metallic material particles by cold spraying, the particles cover the slots 150. If the slots are blocked, in use, electrical current will not be able to flow through the coil 100, and the magnetic fields required to perform the forming, welding, or crimping methods will not be able to be generated.

[0094] In one implementation, the method can include a step of masking the concentrator 160 on parts of the concentrator 160 other than the first surface 162, upstream of the first deposition step. Such a step makes it possible to prevent other parts of the concentrator 160 from receiving metal material particles during the first step. Therefore, after the first step, the method includes a step of unmasking the concentrator 160.

[0095] The cutting of the stiffener 180 is preferably performed by electroerosion.

[0096] Besides the fact that the coil 100 according to the invention is reinforced in the active parts and therefore has a lifespan substantially greater than that of conventional coils, the coil 100 according to the invention can also be reused and reconditioned several times in order to further extend its lifespan. After the first use of the coil 100 according to the invention to deform parts by magnetic pulse forming, magnetic pulse welding or magnetic pulse crimping, and when crazing in the active parts above the stiffeners significantly degrades the performance of the magnetic pulse deformation method and too significantly affects the forming, welding or crimping quality, the coil 100 can be reconditioned with new stiffeners 180.

[0097] A method for reconditioning a coil 100 with a concentrator 160 will be described hereinafter without limitation. Only the first surface 162 of the concentrator 160 will be discussed therein. However, it is clear by analogy that when the coil 100 does not include a concentrator, the first surface being mentioned will be the first surface of the body 120 of the coil 100.

[0098] Figure 8 illustrates method steps for reconditioning the toroidal coil 100 with the concentrator 160. The toroidal coil 100 is shown partially in cross section, similar to Figure 6. Figure 8 illustrates the initial reconditioning of the coil 100.

[0099] 8(a) shows a coil 100 with a worn stiffener 180. Crazing in the stiffener 180 is represented diagrammatically by lines 190.

[0100] The reconditioning method includes a first step of removing the stiffener 180. The stiffener is removed throughout its thickness down to the first surface 162 of the concentrator 160.

[0101] Removal of the stiffener 180 is preferably performed by machining.

[0102] View (b) of Figure 8 illustrates the coil following this first step, with the removed stiffener 180 shown as a dotted line.

[0103] The reconditioning method then includes a second step of removing a layer of material from the first surface 162 of the concentrator 160 .

[0104] 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.

[0105] Preferably, the predefined thickness of the layer of material removed is less than the thickness removed from the stiffener.

[0106] The step of removing the layer of material forming the concentrator 160 advantageously makes it possible to remove any traces of deformation of the first surface 162 due to the spraying of the metal material particles.

[0107] The removal of the material layer is preferably performed by machining.

[0108] View (c) of Figure 8 illustrates the coil following this second step, with the layer of material being removed from the concentrator shown as a dotted line.

[0109] The reconditioning method then includes a third step of depositing a metallic material by cold spraying to form the new stiffener 180 .

[0110] The metallic material is deposited on the second surface 162 ′ of the concentrator 160 .

[0111] The metal material is deposited over a predefined thickness that is slightly greater than the sum of the thicknesses of the previous stiffeners that were removed and the layer of material removed from the concentrator.

[0112] The implementation of this third step is identical to the first step of the method for producing a coil.

[0113] View (d) of Figure 8 illustrates the coil following this third step.

[0114] The reconditioning method then includes a fourth step of tempering the body 120 , the concentrator 160 and the new stiffener 180 .

[0115] The implementation of this fourth step is identical to the second step of the method for producing the coil 100. This fourth step therefore makes it possible to impart the desired elastic and electrical conductivity properties to the new stiffener 180. The reconditioning method then includes a fifth step of machining and finishing the stiffener 180.

[0116] 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 dimensions of the new stiffener 180.

[0117] Thus, the thickness of the new stiffener 180 preferably corresponds to the sum of the thickness of the previous stiffener that was removed and the thickness of the layer of material that was removed.

[0118] View (e) of Figure 8 illustrates the retuned coil following this fifth step.

[0119] Following this fifth step, the coil with its new stiffener can be used.

[0120] The coil with its new stiffener 180 can be reused for forming, welding or crimping processes.

[0121] In one implementation of the retuning method, the retuning method may include, before or after the fifth step, a step of cutting the stiffener 180 through its thickness at the slot 150 of the concentrator 160 so that the stiffener 180 has slots aligned with the slots 150 of the concentrator 160 and the slots 130 of the main body 120 of the coil 100.

[0122] In one implementation of the reconditioning method, the method may include, upstream of the third step, a step of masking the concentrator 160 over parts of the concentrator 160 other than the first surface 162 .

[0123] The cutting of the stiffener 180 is preferably performed by electroerosion.

[0124] Whenever the stiffener 180 of the coil 100 wears and crazing in the stiffener too greatly affects the quality of the method for deforming metal parts by magnetic pulses, it is possible to advantageously repeat the readjustment method several times in order to further extend the service life of the coil 100. Each time, the stiffener is removed over its entire thickness and an additional layer of material is removed from the concentrator 160. Thus, the new stiffener has a thickness corresponding to the thickness of the previous stiffener, increased each time by the thickness of the layer of material removed from the concentrator 160.

[0125] Preferably, the realignment method involves adjusting the thickness of the stiffener 180 to a predefined maximum thickness h max This can be repeated until

[0126] In one exemplary implementation, the material of the concentrator 160 is made of CuCr and the material of the stiffener 180 is made of CuAg. The minimum thickness of the stiffener is 5 mm. The maximum thickness of the stiffener is 9 mm. By removing only 0.2 mm of the thickness of the material layer from the concentrator at each reconditioning, the coil 100 can therefore be reconditioned 20 times and therefore used 21 times.

[0127] Therefore, the total lifespan of the coil 100 can be up to 2,100,000 (21 x 100,000) discharges. Compared to the lifespan of a CuCr coil without a stiffener, which is on the order of 25,000 discharges, the lifespan of a CuCr coil 100 with a CuAg stiffener 180 using the reconditioning method is significantly increased.

[0128] The present invention has been described in the preferred configuration of a toroidal coil, but it is possible to adapt the invention to any other coil configuration (e.g., a flat type coil, etc.) without departing from the scope of the invention.

[0129] Figure 9 illustrates an example of a flat coil, which is adapted, among other things, to perform an action for deforming a flat part.

[0130] The coil 100 includes a body 120. The body 120 is in the form of a plate. A through opening 110 is created in the body. The opening 110 is sized and configured to face a first part 200 (not shown) to be deformed.

[0131] In one non-limiting embodiment, as illustrated in FIG. 9, the opening 110 has a substantially oval cross-section.

[0132] The body 120 of the coil 100 further includes a narrow slot 130 extending from the opening 110. The body may include two symmetrically opposed contact plates 140a, 140b, which extend on either side of the slot 130. The contact plates 140a, 140b are connected to an energy storage unit 500 and a switch 510.

[0133] The body portion has bosses 126 located around the outer edge of the opening 110 on one side of the plate.

[0134] The body 120 of the coil 100 includes a first surface 122 at the top of the boss 126, which is adapted to be positioned facing a first part 200 (not shown) to be deformed.

[0135] According to the present invention, the coil 100 includes a stiffener 180 at the first surface 122 of the body 120, the stiffener 180 being made of a metallic material deposited by cold spraying.

[0136] Also, in this flat coil configuration, the current is concentrated in the active parts located within the stiffener 180 .

[0137] The methods for manufacturing the flat coil and for reconditioning the flat coil are identical to those described for the toroidal coil. [Explanation of symbols]

[0138] 100 coils 110 Opening 120 Main body 122 First Surface 126 Boss 130 slots 140a, 140b contact plates 150 slots 160 Concentrator 162 First Surface 162' Second Surface 164 Initial surface 180 stiffener 181 First Surface 190 Crazing 200 First Part 300 Second Part 400 Dies 500 storage units 510 Switch

Claims

1. A coil (100) for deforming a metal part (200) by a magnetic pulse, the coil (100) comprising a body (120) having a first surface (122) adapted to be positioned facing the metal part (200) to be deformed, The coil (100) is provided with a stiffener (180) on the first surface (122), the stiffener (180) being made of a metallic material deposited by cold spraying.

2. 1. A coil (100) for deforming a metal part (200) by a magnetic pulse, the coil (100) comprising: a body (120) having a first surface (122); and a magnetic field concentrator (160) disposed on the first surface (122) of the body (120), the magnetic field concentrator (160) having a first surface (162) adapted to be positioned facing the metal part (200) to be deformed, The coil (100) comprises a stiffener (180) on the first surface (162) of the magnetic field concentrator (160), the stiffener (180) being made of a metallic material deposited by cold spraying.

3. 3. A method for producing a coil (100) according to claim 1 or 2, said method comprising the successive steps: - depositing a metallic material by cold spraying onto the first surface (122) of the body (120) or the first surface (162) of the magnetic field concentrator (160) to form the stiffener (180); - tempering said body (120) or said magnetic field concentrator (160) and said stiffener (180); - machining and finishing said stiffener (180); A method comprising:

4. 4. The method of claim 3, wherein the method includes, prior to the step of depositing a metallic material, removing a layer of material forming the body portion (120) or the magnetic field concentrator (160) from an initial surface of the body portion (120) or an initial surface of the magnetic field concentrator (160) to form the first surface (122) of the body portion (120) or the first surface (162) of the magnetic field concentrator (160).

5. 3. A reconditioning method for reconditioning a coil (100) according to claim 1 or 2, said reconditioning method comprising the successive steps: a) removing said stiffener (180) through the entire thickness of said stiffener (180); b) removing a predetermined thickness of a layer of material forming the body portion (120) or the magnetic field concentrator (160) from the first surface (122) of the body portion (120) or the first surface (162) of the magnetic field concentrator (160) to form a second surface of the body portion (120) or a second surface of the magnetic field concentrator (160); c) depositing, by cold thermal spraying, a metallic material on the second surface of the body portion (120) or the second surface of the magnetic field concentrator (160) to form a new stiffener (180) over a thickness at least corresponding to the sum of the thickness of the previous stiffener removed and the thickness of the layer of material removed; d) tempering the body (120) or the magnetic field concentrator (160) and the new stiffener (180); e) machining and finishing the new stiffener (180), the thickness of the new stiffener (180) being equal to the sum of the thickness of the previous stiffener removed and the thickness of the layer of material removed; A reconditioning method, including:

6. 6. The reconditioning method of claim 5, wherein whenever the stiffener of the coil is worn, the steps of removing the stiffener over its entire thickness and removing an additional layer of material of the body portion (120) of the coil (100) or the magnetic field concentrator (160) are repeated, followed by a step of depositing metallic material by a cold spraying method until a new stiffener (180) is formed, the thickness of the new stiffener after reconditioning corresponding to the thickness of the previous stiffener increased by the thickness of the layer of material of the magnetic field concentrator that was removed.

7. 7. The method of claim 6, wherein each of said steps is repeated until the thickness of said stiffener (180) reaches a predetermined maximum thickness.

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