Coil for deforming metal parts by magnetic impulse, methods for manufacturing 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 opposite the part to be deformed (200). The coil (100) has, at said first surface (122), a reinforcement (180), said reinforcement (180) being made of a metallic material deposited by cold thermal spraying. Figure for the abstract: Fig. 6

Description

Title of the invention: Coil for deforming metal parts by magnetic impulse, methods for manufacturing and reconditioning such a coil Scope of the invention

[0001] 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 impulse, commonly referred to as magnetic pulse forming (MPF), magnetic pulse welding (MPW), or magnetic pulse crimping (MPC). The present invention relates to an improved coil that extends its service life. The present invention also relates to a method for manufacturing said coil and a method for reconditioning said coil. State of the art

[0002] 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 perform either forming operations to shape a metal part according to the shape of a die, or welding or crimping operations to permanently join two parts together.

[0003] Conventionally, 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 serves to store a large amount of electrical energy. When the switch closes, the electrical energy stored in the electrical energy storage unit is discharged very rapidly into the coil, in the form of a very high-intensity variable current, in a very short time, thus creating an intense magnetic field. By way of example, some devices can reach a current of several hundred thousand amperes in a few microseconds.

[0004] 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, combined with the surrounding magnetic field, develop Laplace forces in the metal part to be deformed, which generate a sharp acceleration of the part either towards a die or towards another part.

[0005] Depending in particular on the level of intensity of the current generated, the angle of collision and the speed of collision, a part is either formed, welded or crimped to another part.

[0006] However, magnetic pulse deformation processes have the drawback of requiring very high currents to form a part or to weld / crimp it to another part, which implies the use of a considerable amount of electrical energy. The use of such currents also generates significant local temperatures and mechanical stresses within the coil, which can weaken it, shorten its lifespan, and lead to irreparable damage to the coil, particularly in an area known as the "active part." The active part is defined as an area of ​​the coil where the current, delivered by the electrical energy storage unit, is concentrated and flows to create the magnetic field.

[0007] Damage to the coil, generally in the form of cracks and / or crazing, degrades the performance of magnetic pulse deformation processes.

[0008] By way of example, for a coil conventionally made of a copper alloy material, such as CuCr, the coil life is estimated at 25,000 discharges. After 25,000 discharges, crazing on the active part of the coil critically degrades the performance of the magnetic pulse deformation process and significantly impacts the quality of the forming, welding, or crimping. For a coil conventionally made of a steel material such as 40CMD8, the coil life is estimated at 15,000 discharges.

[0009] However, these lifespans prove very limiting when the reels are used in industry, for example on production lines. The reels need to be changed regularly, which leads to a stoppage of the production line and generates significant costs.

[0010] There is therefore a real need to extend the service life of the coils used in magnetic pulse deformation processes for metal parts. Description of the invention

[0011] The present invention, which results from work carried out in collaboration with UTBM (University of Technology of Belfort Montbéliard), aims to overcome the aforementioned drawbacks.

[0012] The present invention aims in particular to provide an effective solution for extending the life of a coil for deforming a metal part by magnetic impulse (for example, by magnetic forming and / or magnetic welding and / or magnetic crimping).

[0013] The invention thus relates to a coil for deforming a metal part by magnetic impulse, comprising a body which has a first surface intended to be positioned opposite the metal part to be deformed. At the level of said first surface, the coil has a reinforcement, and said reinforcement consists of a metallic material deposited by cold thermal spraying.

[0014] 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 contradicts a long-standing assumption in the prior art that adding a coating to this first surface is not feasible. Indeed, on the one hand, maintaining electrical continuity at the interface between the coil body and the coating proves difficult. An electrical discontinuity will influence the creation of the magnetic field and can degrade the quality of the final product through the magnetic pulse deformation process. 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 lead to coil degradation.

[0015] The present invention overcomes the aforementioned drawbacks and surmounts the technical prejudice by depositing a metallic material using the cold thermal spraying process. The cold thermal spraying process is generally known by its English name, cold spray.

[0016] The cold thermal spraying process consists of projecting particles of metallic material at very high speed, using a high-pressure gas, onto the first surface of the coil body. The impact force cold-welds this metallic material to said first surface of the body, and the particles cohesion to form a dense reinforcement. The particles of metallic material weld first to the first surface of the coil body, and then to themselves. The cold thermal spraying process advantageously provides good cohesion with the first surface of the body subjected to the spray, 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.Furthermore, thanks to the low porosity of the deposited metallic material, the formation of an electric arc in the reinforcement is also reduced.

[0017] Thus, when using the coil according to the invention in a method for deforming the metal part by magnetic impulse, the current flowing 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.

[0018] Such reinforcement thus makes it possible to significantly increase the lifespan of the coil.

[0019] Preferably, the material used to form the reinforcement has characteristics of superior mechanical and thermal resistance to the body material, in order to further improve the lifespan of the coil.

[0020] According to preferred embodiments, the invention also meets the following characteristics, implemented separately or in each of their technically operative combinations.

[0021] According to preferred embodiments, the coil includes a magnetic field concentrator at the first surface of its body. The magnetic field concentrator has a first surface intended to be positioned opposite the metal part to be deformed. When using the magnetic field concentrator, the reinforcement is formed on the first surface of the magnetic field concentrator and no longer on the first surface of the coil body. 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 portion located at the reinforcement, whereas initially, without the reinforcement, the current is concentrated on the first surface of the magnetic field concentrator.

[0022] The invention also relates to a method for manufacturing a coil in at least one of its embodiments. The manufacturing method comprises the successive steps of: - deposition, on the first surface of the coil body, or of the field concentrator when present, of a metallic material by cold thermal spraying to form the reinforcement, - heat treatment of the body's tempering, or of the magnetic field concentrator, and of the reinforcement, - final machining of the reinforcement.

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

[0024] According to preferred embodiments, the embodiment process includes, prior to the deposition step, a removal step, from an initial surface of the coil body, or of the magnetic field concentrator when present, of a layer of material forming said body, or said field concentrator, to the first surface of the coil body, or of the magnetic field concentrator.

[0025] 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: - removing the reinforcement over its entire thickness, - removing, from the first surface of the body, or the field concentrator genetic, when present, of a layer of material forming said body or magnetic field concentrator, of a predefined thickness, up to a second surface of the body, or of the magnetic field concentrator, - deposition, at the level of the second surface of the body or field concentrator, of a metallic material by cold thermal spraying to form a new reinforcement, to 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, - heat treatment of the body's temper, or of the magnetic field concentrator, and of the new reinforcement, - final machining of the new reinforcement.

[0026] The step of removing the reinforcement advantageously eliminates any trace of cracks and / or crazing which could impact the future performance of the reconditioned coil.

[0027] The step of removing a layer of material forming the body of the coil, or the magnetic field concentrator, advantageously eliminates any trace of deformation of the first surface caused by the projection of metallic material particles. This ensures a new, clean surface ready to receive a new deposit of metallic material by cold thermal spraying.

[0028] After 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.

[0029] According to preferred embodiments, the invention also meets the following characteristics, implemented separately or in each of their technically operative combinations.

[0030] According to preferred embodiments, each time the coil reinforcement is worn out, the steps of removing the reinforcement over its entire thickness and removing an additional layer of material from the coil body, or magnetic field concentrator, are repeated successively, followed by the step of depositing a metallic material by a cold thermal spraying 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 coil body, or magnetic field concentrator removed.

[0031] Such a reconditioning process makes it possible to renew the coil at a significantly reduced cost compared to a total replacement of the coil or the magnetic field concentrator.

[0032] According to preferred embodiments, the steps of the reconditioning process are repeated until a predefined maximum thickness of the reinforcement is reached. Indeed, since the cold thermal spraying process generates high stresses in the metallic material particles, if the reinforcement is too thick, delamination of said reinforcement could occur.

[0033] This predetermined maximum thickness depends in particular on the material of the metallic coating and the material of the coil body or magnetic field concentrator. Presentation of the figures

[0034] The invention will be better understood upon reading the following description, given by way of non-limiting example, and made with reference to the figures which represent:

[0035] Figure 1 schematically represents a perspective view of an annular-type coil according to the invention,

[0036] Figure 2 schematically represents a front view of the annular coil of the [Fig.l],

[0037] Figure 3 shows a cross-section of the annular coil of Figure 2 along line AA, in which two metal parts to be welded are positioned,

[0038] Figure 4 schematically represents a perspective view of a coil annular structure comprising a magnetic field concentrator according to another embodiment of the invention,

[0039] Figure [Fig. 5] schematically represents a front view of the annular coil of Figure [Fig. 4],

[0040] 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.

[0041] Figure 7 shows the steps of a process for making an annular coil. according to [Fig.4],

[0042] Figure 8 shows the steps of a process for reconditioning a used annular coil according to Figure 4.

[0043] Figure 9 schematically represents a perspective view of a coil of type plate according to the invention. Detailed description of the invention

[0044] The different figures, as well as the elements of the same figure, are not necessarily represented at the same scale. Across all the figures, identical elements bear the same numerical reference.

[0045] The terminology used in this description should in no way be interpreted in a limiting or restrictive manner, simply because it is used in conjunction with a detailed description of certain embodiments of the invention.

[0046] The present invention relates to a coil for deforming metal parts by magnetic impulse, such as by magneto-forming, by magneto-welding or by magneto-crimping.

[0047] 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].

[0048] The storage unit 500 is conventionally connected to the coil 100 and to the switch(s) 510. The storage unit 500 is configured to store a high amount of energy, for example on the order of a few tens of kilojoules (kJ). The storage unit 500 is, for example, a capacitor bank.

[0049] A 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 create an intense magnetic field.

[0050] In the following text, as illustrated in Figures 1 to 8, the invention will be described, without limitation, in a coil configuration where the coil is of the annular type. This coil configuration is particularly suitable for performing deformation operations on tubular parts.

[0051] The coil 100 comprises a body 120. A tubular opening 110 is made in said body. Said opening is dimensioned and configured to receive: - either two tubular pieces, called first piece 200 and second piece 300, arranged one inside the other for welding or crimping, as illustrated in [Fig.3], the first piece 200 being arranged around the second piece 300, - or a die 400 and a tubular piece, called first piece 200, arranged around the die, for forming said first piece, as illustrated in [Fig.6].

[0052] 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.

[0053] 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 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(s) 510.

[0054] The coil body 120 is made of a material having specific properties in terms of, on the one hand, electrical conductivity to allow a very high intensity current to flow through it, on the order of a few hundred thousand Amperes and, on the other hand, mechanical resistance so as not to deform plastically during the magnetic forming, magnetic welding or magnetic crimping process.

[0055] In a preferred embodiment, the material of the coil body 120 is steel, type 40CMD8, copper, type Cu 1 / 2 hard or 3 / 4 hard, or copper alloy, type CuCr.

[0056] The coil is therefore configured so that a high intensity current can flow through it and produce a magnetic field.

[0057] The coil 100 is also configured so that the current density in a zone of the coil is sufficient to satisfy the desired deformation conditions. This zone is called the active part.

[0058] 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 a thickness corresponding to the skin thickness. The current generates a concentrated magnetic field between the active part of the coil and the first piece 200.

[0059] In the non-limiting example of a coil 100 made of steel, the skin thickness is on the order of a few millimeters for a frequency of a few tens of kHz.

[0060] In an alternative embodiment of the coil, illustrated in figures 4 to 6, the coil 100 may include, at the level of the first surface 122 of the body, a magnetic field concentrator, called concentrator 160. Said concentrator is an annular piece intended to be disposed in the opening 110 of the body 120 of the coil and which allows to concentrate even more the magnetic field in the opening 110 of the body 120 of the coil. The concentrator 160 has a tubular opening, dimensioned 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, i.e. the first part 200, received in the opening of the concentrator 160.

[0061] The concentrator 160 further includes a narrow slot 150 extending from the opening of said concentrator. The slot 150 is aligned with the slot 130 of the body 120 of the coil 100.

[0062] In a preferred embodiment, the material of the concentrator 160 is steel, type 40CMD8, or copper alloy, type CuCr. Preferably, the material of the concentrator 160 is identical to the material of the coil body 120.

[0063] In this 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 cor responding to skin thickness. The current generates, between the active part of the concentrator and the first piece 200, a magnetic field even more concentrated than the magnetic field created between the active part of the coil and the first piece 200, in the absence of a concentrator.

[0064] 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.

[0065] The reinforcement 180 has a first surface 181 intended to be opposite the part to be deformed, therefore the first part 200.

[0066] This reinforcement 180 results from a deposit of metallic material produced by a cold thermal spraying process.

[0067] The cold thermal spraying process is a conventional metallization process. Particles of metallic material are projected at very high speed, by a gas under high pressure, onto the first surface 122 of the body 120 (or onto the first surface 162 of the concentrator 160 when the coil 100 includes a concentrator 160). The pressure and the speed at which the metallic material is projected cause plastic deformation of the projected metallic material upon contact with the first surface 122 (or 162) to be coated. The impact force then cold-welds this metallic material to said first surface 122 (or 162), and the cohesion of the particles forms a dense reinforcement.The cold thermal spraying process advantageously allows good cohesion with the first surface 122 (or 162) subjected to 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.

[0068] The cold thermal spraying process also makes it possible to achieve thicknesses of several millimeters while retaining these qualities.

[0069] The cold thermal spraying process 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.

[0070] The material used to form the reinforcement 180 advantageously has specific properties, in particular in terms of electrical conductivity to allow a very high intensity current to flow through it, for example on the order of a few hundred thousand Amperes, and in terms of mechanical resistance to plastic deformation and to high temperatures (i.e. a high melting temperature) so as not to melt during the magnetic forming, magnetic welding or magnetic crimping process.

[0071] 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 superior mechanical and thermal resistance characteristics to the material of the body 120 or the concentrator 160, to strengthen the coil 100 and improve the service life of the coil 100.

[0072] In preferred embodiments, when the material of the coil body, or of the concentrator 160, is copper alloy, such as CuCr, the material used to form the reinforcement 180 is silver copper alloy CuAg.

[0073] 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.

[0074] The current is concentrated on a layer delimited by the first surface 181 of the reinforcement and of a thickness corresponding to the skin thickness. In the non-limiting example of a reinforcement made of CuAg, the skin thickness is on the order of 1 mm for a frequency of a few tens of kHz.

[0075] Preferably, the reinforcement 180 has a minimum thickness hmin at least equal to this skin thickness. Thus, the current is then concentrated solely in the reinforcement 180. When using the coil 100, cracks and / or crazing are therefore limited to the reinforcement 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.

[0076] Preferably, the reinforcement 180 has a predefined maximum thickness hmax. This maximum thickness is defined to prevent detachment 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 known that the cold thermal spraying process generates high stresses in the particles of metallic material, and with excessive thicknesses, detachment of the reinforcement may occur.

[0077] According to preferred embodiments, the reinforcement thickness 180 is between 1 mm and 20 mm.

[0078] In one 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 on the order of 5 mm and the maximum thickness hmax of the reinforcement 180 is on the order of 9 mm.

[0079] Uniaxial tensile tests were also carried out on samples with different substrates (steel, CuCr, etc.) and different metallic material particles (CuAg, CuNiCoSi, etc.) to evaluate adhesion strength. The tensile strength was evaluated at the particle / substrate interface. Indeed, during operation, during 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 stresses at the first surface 122 (or 162). The tests have showed that the CuCr / CuAg couple exhibits a tensile strength of around 190MPa, a value sufficient to withstand repeated discharges when using coil 100.

[0080] Such a reinforcement 180 thus makes it possible to significantly increase the lifespan of the coil 100. For example, as mentioned in the prior art, the lifespan of a conventional coil 100 (i.e., without reinforcement) made of CuCr material is estimated at 25,000 discharges. The lifespan of a coil 100 with a reinforcement 180 made of CuAg material reaches at least 100,000 discharges. The lifespan of the coil is thus multiplied by four.

[0081] A method for producing a coil 100 according to the invention is now described. The method will be described below, by way of non-limiting example, for producing a coil 100 with a concentrator 160. Only the first surface 162 of the concentrator 160 will be discussed. It is clear, however, that by analogy, when the coil 100 does not have a concentrator, the first surface referred to will be that of the body 120 of the coil 100.

[0082] Fig. 7 illustrates the steps of the process of making an annular coil 100 with the concentrator 160. The annular coil 100 is shown partially in cross-section as in Fig. 6.

[0083] 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.

[0084] Particles of metallic material are projected at very high speed, by a pressurized gas, onto the first surface 162 of the concentrator. The particles bond, first to the first surface 162 of the concentrator 160, then to themselves until a desired thickness for the reinforcement 180 is obtained.

[0085] The metallic material particles are projected, in particular, with a predefined speed and impact angle. The projection speed and impact angle advantageously ensure good adhesion of the metallic material particle deposit and limit shear stresses at the first surface 162.

[0086] In one embodiment, the metallic material particles are projected with a nozzle. The nozzle can move to form the reinforcement over the entire first surface 162.

[0087] 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 and 80 pm, - gas temperature between 400°C and 1000°C, preferably in the order of 500°C, - gas pressure between 20 and 50 bar, preferably around 30 bar, - particle projection speed between 0.5 and 1.5 km / s, - choice of carrier gas: nitrogen or helium or a mixture of these two gases.

[0088] A 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.

[0089] View (b) of [Fig.7] illustrates the coil, after this first deposition step.

[0090] Preferably, to promote the adhesion of the metallic material particles to the first surface 162 of the concentrator, the process may include 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 stated, the angle of impact of the metallic material particles on the first surface advantageously ensures good adhesion of the deposit of said metallic material particles and limits the shear forces at the level of the first surface 162. A person skilled in the art has the expertise to determine the necessary angle of impact.

[0091] The removal of the material layer from the concentrator 160 is preferably carried out by machining.

[0092] View (a) of [Fig. 7] illustrates the coil after this preliminary step. The removed layer of material from the concentrator 160 is shown as a dashed line. The first surface 162 is, in the non-limiting example of view (a), inclined relative to the initial surface 164.

[0093] The method for producing a coil 100 according to the invention comprises, after the first deposition step, a second heat treatment step for tempering the coil body, the magnetic concentrator 160 and the reinforcement 180.

[0094] This second step is conventional as such and aims to give the reinforcement 180 the desired elastic and electrical conductivity properties.

[0095] In one example of implementation, the coil is placed in a tempering oven, at a predefined temperature, and for a predefined duration.

[0096] The heat tempering treatment is preferably carried out at a temperature between 200 and 400 °C, for a period of between 2 and 8 hours.

[0097] The method for producing a coil 100 according to the invention then comprises a third finishing machining step of the reinforcement 180.

[0098] The finishing machining step is conventional as such and allows the elimination of surface defects to achieve the desired final shape and dimensional dimensions of the reinforcement 180.

[0099] View (c) of [Fig.7] illustrates the coil, after this third step.

[0100] At the end of this third step, the coil 100 is ready to be used for a forming, welding or crimping process.

[0101] In one embodiment, the manufacturing process may include, before or after the third step, a step of cutting the reinforcement 180, in its thickness, at the slot 150 of the concentrator 160 so that the reinforcement 180 has a slot aligned 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, during 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.

[0102] In one embodiment, the process may include, upstream of the first deposition step, a masking step of the concentrator 160 on parts of the concentrator 160 other than the first surface 162. Such a step prevents other parts of the concentrator 160 from receiving the metallic material particles during the first step. Consequently, after the first step, the process includes a step of unmasking the concentrator 160.

[0103] The cutting of the reinforcement 180 is preferably carried out by electro-erosion.

[0104] In addition to the fact that the coil 100 according to the invention is reinforced at the active part and thus has a lifespan much longer than that of a conventional coil, the coil 100 according to the invention can also be reconditioned several times for reuse and to further extend its lifespan. After initial use of the coil 100 according to the invention to form a part by magnetic forming, magnetic welding, or magnetic crimping, and when crazing at the active part on the reinforcement critically degrades the performance of the magnetic pulse forming process and significantly impacts the quality of the forming, welding, or crimping, the coil 100 can be reconditioned with a new reinforcement 180.

[0105] A method will be described below, by way of non-limiting example, for the reconditioning of a coil 100 with a concentrator 160. It will only refer to the first surface 162 of the concentrator 160. It is clear, however, that by analogy, when the coil 100 does not have a concentrator, the first surface referred to will be that of the body 120 of the coil 100.

[0106] Figure 8 illustrates the steps in the process 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.

[0107] View (a) of [Fig. 8] shows the coil 100 with the used reinforcement 180. The crazing in the reinforcement 180 is schematically represented by lines 190.

[0108] The reconditioning process includes 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.

[0109] The removal of the reinforcement 180 is preferably carried out by machining.

[0110] View (b) of [Fig.8] illustrates the coil at the end of this first step. The removed reinforcement 180 appears in dotted line.

[0111] The reconditioning process then includes a second step of removing, from the first surface 162 of the concentrator 160, a layer of material from said concentrator.

[0112] The material layer of the concentrator 160 is reduced by a predefined thickness, preferably constant, to a second surface 162' of the concentrator 160.

[0113] Preferably, the predefined thickness of the removed material layer is less than the removed thickness of the reinforcement.

[0114] 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.

[0115] The removal of the material layer is preferably carried out by machining.

[0116] View (c) of [Fig.8] illustrates the coil after this second step. The removed layer of concentrator material appears as a dashed line.

[0117] The reconditioning process then includes a third step of depositing a metallic material by the cold thermal spraying process to form a new reinforcement 180.

[0118] The deposition of the metallic material is carried out on the second surface 162' of the concentrator 160.

[0119] The metallic material is deposited to a predefined thickness, slightly greater than the sum of the thicknesses of the previous reinforcement removed and the layer of material from the concentrator removed.

[0120] The implementation of this third step is identical to the first step of the coil manufacturing process.

[0121] View (d) of [Fig.8] illustrates the coil at the end of this third step.

[0122] The reconditioning process then includes a fourth heat treatment step for tempering the body 120, the concentrator 160, and the new reinforcement 180.

[0123] The implementation of this fourth step is identical to the second step of the process for manufacturing the coil 100. This fourth step thus makes it possible to give the new reinforcement 180 the elastic and electrical conductivity properties desired. The reconditioning process then includes a fifth finishing machining step for reinforcement 180.

[0124] The implementation of this fifth step is identical to the third step of the process for making the coil 100. This fifth step makes it possible to achieve the desired final shape and dimensional dimensions of the new reinforcement 180.

[0125] The thickness of the new reinforcement 180 thus corresponds preferentially to the sum of the thickness of the previous reinforcement removed and the thickness of the layer of material removed.

[0126] View (e) of [Fig.8] illustrates the reconditioned coil at the end of this fifth step.

[0127] At the end of this fifth step, the reel with its new reinforcement can be used.

[0128] The coil with its new 180 reinforcement can again be used for a forming, welding or crimping process.

[0129] In one embodiment of the reconditioning process, the reconditioning process may include, 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.

[0130] In one implementation of the reconditioning process, the process may include, upstream of the third step, a masking step of the concentrator 160 on the parts of the concentrator 160 other than the first surface 162.

[0131] The cutting of the reinforcement 180 is preferably carried out by electro-erosion.

[0132] Whenever the reinforcement 180 of the coil 100 is worn and the crazing at the reinforcement excessively impacts the quality of the magnetic pulse deformation process of a metal part, it is advantageous to repeat the reconditioning process several times to further extend the service life of the coil 100. Each time, the reinforcement is removed to its full thickness, and an additional layer of material from the concentrator 160 is removed. The new reinforcement thus has a thickness corresponding to the thickness of the previous reinforcement, plus the thickness of the removed layer of material from the concentrator 160.

[0133] Preferably, the reconditioning process can be repeated until the thickness of the reinforcement 180 reaches the predefined maximum thickness hmax.

[0134] In one embodiment, the concentrator material 160 is CuCr and the reinforcement material 180 is CuAg. The minimum reinforcement thickness is 5 mm. The maximum reinforcement thickness is 9 mm. By removing only 0.2 mm of the concentrator material layer thickness at each reconditioning, the coil 100 can thus it can be refurbished 20 times and therefore used 21 times.

[0135] Consequently, the total lifespan of said coil 100 can reach 2,100,000 discharges (21 x 100,000). Compared with the lifespan of the CuCr coil without reinforcement, which is around 25,000 discharges, the lifespan of the CuCr coil 100 with CuAg reinforcement 180, using the reconditioning process, is considerably increased.

[0136] The invention has been described in the preferred configuration of an annular coil. However, it is 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.

[0137] Figure 9 illustrates an example of a flat coil. This coil is particularly suitable for carrying out deformation operations on flat parts.

[0138] 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 be opposite the first part 200 to be deformed (not shown).

[0139] In a non-limiting embodiment, as illustrated in [Fig.9], the opening 110 has a straight section of substantially oblong shape.

[0140] 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 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(s) 510.

[0141] Said body has, on one face of the plate, a boss 126 arranged around the periphery of the opening 110.

[0142] The body 120 of the coil 100 has, 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).

[0143] 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 projection.

[0144] In this flat coil configuration, the current is also concentrated in the active part which is located in the reinforcement 180.

[0145] The manufacturing process for the flat coil and the reconditioning process for this flat coil are identical to the processes described for the annular coil.

Claims

Demands

1. Coil (100) for deforming a metal part (200) by magnetic impulse 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 made of a metallic material deposited by cold thermal spraying.

2. Coil (100) according to claim 1 comprising a magnetic field concentrator (160) between the first surface (122) of the body (120) and the reinforcement (180), the magnetic field concentrator (160) comprising a first surface (162) at which the reinforcement (180) is formed.

3. Method of making a coil (100) according to claim 1 or, where the coil (100) includes a magnetic field concentrator (160), according to claim 2, comprising the successive steps of: - deposition, on the first surface (122, 162) of the body (120) or of the magnetic field concentrator (160), of a metallic material by cold thermal spraying to form the reinforcement (180), - tempering heat treatment of the body (120) or of the magnetic field concentrator (160) and of the reinforcement (180), - finishing machining of the reinforcement (180).

4. Method of making a coil according to claim 3, comprising, prior to the deposition step, a removal step, from an initial surface of the body (120), or of the magnetic field concentrator (160), of 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).

5. A method for reconditioning a coil (100) according to claim 1 or, where the coil (100) includes a magnetic field concentrator (160), according to claim 2, comprising the following steps: transfers of: a. removal of the reinforcement (180) over its entire thickness, b. removal, from the first surface (122, 162) of the body (120) or of the magnetic field concentrator (160), of a layer of material forming said body (120) or said magnetic field concentrator (160), of a predefined thickness, up to a second surface of the body (120) or of the magnetic field concentrator (160), c. deposition at the level of the second surface of the body (120) or of the magnetic field concentrator (160), of 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 layer of material removed, d. heat treatment of the tempering of the body (120) or of the magnetic field concentrator (160) and of the new reinforcement (180), e. finishing 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 layer of material removed.

6. A reconditioning method according to claim 5 wherein, each time the coil reinforcement is worn, the steps of removing the reinforcement to its full thickness and removing an additional layer of material from the coil body (120) (100) or the magnetic field concentrator (160) are repeated, followed by 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 from the magnetic field concentrator removed.

7. Reconditioning method according to claim 6 wherein the steps are repeated until a predefined maximum thickness of the reinforcement (180).