Patent Application
20210187578
The present invention pertains to the field of forming, more particularly stamping.
The present invention relates to a device and a method for stamping blanks by magnetic pulse for producing stamped parts, in particular parts called deep stamped parts.
In the field of forming, in particular metal forming, stamping is a very often selected method because it is robust and well mastered.
Stamping is commonly used in industry, in particular in the automotive industry, in particular to form trim panels, such as a motor vehicle bonnet or door, because of the high admissible production rates.
Stamping is a forming method consisting in obtaining by plastic deformation of a blank, under the action of pressure, a part of more or less complex shape.
The stamping device for implementing this method consists essentially of a die and a punch of almost complementary shape, between which the blank is positioned. The shape is obtained by driving the blank under the action of the punch in the die. The movement of the blank is generally controlled by a blank holder, imposing a retaining pressure thereon, in order to reduce the appearance of wrinkles or tears on the final stamped part.
However, in the presence of a part which is difficult to shape, in particular a deep stamped part, the choice of the clamping force to be applied on the blank holder proves to be difficult. If the force of the blank holder is too high, the wrinkles are removed but the risk of tearing is high. If the force of the blank holder is too low, the risk of wrinkles is high.
To produce deep stamped parts, alternatives to the stamping method are known.
Among them, the hydraulic forming method can be mentioned. In this method, the blanks are formed by the action of a pressurised fluid.
The associated hydraulic forming device consists of a hermetically closed enclosure formed in two portions including a hollow mould having a recess complementary to the shape of the part desired to be obtained. The blank is placed inside the enclosure. A hydraulic pressure is exerted thereon pressing it against the recess of the mould. This quasi-static shaping method has the major advantage of dispensing with punching and producing complex shapes, which are in particular undercut. However, high pressures are essential for forming, which tends to require large tonnage presses for large parts. Therefore, this method is mainly used for the forming of tubular parts. One of the disadvantages of the method is the cycle time, often several tens of seconds due to the filling and pressurisation times.
Among the existing hydraulic forming methods, mention may be made of the Electro Hydraulic Forming method, known as the EHF method, which is, in turn, a high speed deformation method. Such a method has many advantages, in particular a significant reduction in elastic return and increased formability of metals. However, the major disadvantages lie in the need to bring the part to be formed into contact with water (corrosion possible and drying necessary) and water management.
Mention may also be made of hot forming methods, such as the Superplastic Forming method, known as the SPF method. This method is based on the ability of some alloys, for example titanium, to withstand significant deformation. These alloys, hereinafter called superplastic alloys, can reach elongations sometimes going beyond 1000% under certain conditions of temperature, of pressure and deformation while the conventional alloys generally deform only within a typical range of a few % to 50%.
The associated SPF forming device consists of a hermetically closed enclosure formed in two portions including a hollow mould having a recess complementary to the final external geometry of the part desired to be obtained. The blank is placed inside the enclosure and fixedly maintained between the two portions. A pressurised gas is injected into the enclosure and presses the blank, while deforming it, against the recess. The pressure and temperature, of the order of 900° C. for titanium alloys, must be perfectly controlled.
The obvious disadvantages associated with this SPF forming device and the associated method lie in the cycle time, the cost and the fact that only some materials can be used.
The object of the present invention is in particular to overcome all or part of the limitations of the solutions of the prior art, in particular those set out above, by proposing a solution which allows obtaining stamped parts, and in particular deep stamped parts.
To this end, the invention aims firstly at a device for stamping a blank for producing a stamped part including:
The term blank means a thin plate, in particular made of metallic material. A plate is said to be thin when one of its dimensions is significantly smaller than the other two, typically at least an order of size.
In an initial position, that is to say before the stamping phase, the stamping device is configured such that:
The magnetic field generation means are facing the first face. The anvil is facing a second face of the blank, opposite the first face, at a distance from said second face. The die is intended to be disposed facing the second face, at another portion of the blank.
The magnetic field generation means are intended for and configured to apply on the blank a pressure in the direction of the anvil, in a direction Z′Z.
The stamping device includes first displacement means arranged to displace the punch, relative to the die, in the direction Z′Z. The punch is advantageously displaced in translation.
The stamping device includes second displacement means arranged to displace the anvil, relative to the die, in the direction Z′Z.
The punch, the anvil and the die are preferably made of a metallic material to contain the high pressures generated by the magnetic field generation means.
The stamping device according to the invention differs from conventional stamping devices in that the stamping is not carried out by the punch itself, but by the magnetic field generation means.
Similarly, the magnetic field generation means are used differently from the conventional framework of a magnetic forming method which forms the entire blank at once. The magnetic field generation means are arranged so as to generate magnetic pulses only on a portion of the blank. The relative displacement of the punch relative to the generation means allows displacing the area of the blank which will be affected by the magnetic pulses.
Such a device thus advantageously allows to work at high speed of expanding deformation, with the advantages that the magnetic forming can bring, such as obtaining radii of curvature less than 2 mm, fine engravings, or tight tolerances, as well as the avoidance of cracking or tearing of the material in areas with high elongation, in particular for aluminium.
Such a stamping device is thus particularly adapted for producing stamped parts, in particular deep stamped parts, without generating tears in the part.
It is also adapted for making flanging edges, with the advantages of the magnetic forming mentioned above.
According to preferred embodiments, the invention also meets the following features, implemented separately or in each of their technically operative combinations.
According to preferred embodiments, the first displacement means include a linear actuator.
According to preferred embodiments, in order to obtain good efficiency of the method, the magnetic field generation means are in the form of a flat coil, for example in a spiral. The coil is disposed substantially in a plane parallel to the bearing surface of the punch.
According to preferred embodiments, the stamping device includes a blank holder configured to maintain the other portion of the blank against the die, to impose a retaining pressure on the movement of the blank, against the die in order to limit the formation of wrinkles.
The invention also relates to a method for stamping a blank by magnetic pulse for producing a stamped part, from a stamping device in accordance with at least one of its embodiments. The method includes the steps of:
a) positioning the blank in the stamping device,
b) subjecting the blank to a magnetic field caused by the magnetic field generation means so that a pressure is exerted on the first face of the blank in the direction Z′Z and presses said blank against the anvil,
c) displacing the punch by the first displacement means and the anvil by the second displacement means, relative to the die, in the direction Z′Z,
steps b) and c) being repeated, preferably in a synchronised manner, until the desired shape for the finished stamped part is obtained.
Synchronised means that the steps are carried out either successively, one after the other, or simultaneously.
As the punch displaces, a magnetic pulse is generated by the magnetic field generation means, exerting, on the one hand, an axial pressure on the blank in the direction of the anvil, pressing said blank on said anvil, and on the other hand, a radial pressure on the blank in the direction of the die, pressing said blank on said die.
This axial and radial double pressure advantageously allows deforming the blank, without the risk of generating tears in the part desired to be obtained and with excellent shaping precision.
The invention will be better understood upon reading the description below, given by way of non-limiting example, and made with reference to the figures which show:
In these figures, identical references from one figure to another designate identical or similar elements. For the sake of clarity, the elements shown are not to scale, unless stated otherwise.
A stamping device 10, as illustrated in
In an exemplary embodiment, the blanks 50 are made of a metallic material, such as steel.
The blank 50 has a first face 51 and a second face 52, opposite the first one.
In a preferred non-limiting exemplary embodiment of the invention, the stamping device 10, as shown in section in
The person will easily understand that the teaching of the present invention can be transposed to other embodiments.
In the present description, the terms such as upper, lower, high, low, left, right are used for the sake of simplicity, with reference to the orientation of the various elements presented in
The stamping device 10 includes a first frame 20 and a second frame 30. The first frame 20 may be a lower portion of the stamping device and the second frame 30, an upper portion, as illustrated in the figures. Alternatively, and without departing from the scope of the invention, the first frame 20 may be an upper, left or right portion, of the stamping device and the second frame 30, respectively a lower, right or left portion.
The first frame 20 is in the form of a first hollow body delimiting a first open cavity 23, which is preferably central.
In a particular embodiment, the first open cavity 23 has a cylindrical shape, preferably of circular cross section.
As illustrated in
A punch 40 is disposed in the first open cavity 23.
In the particular example where the desired final stamped part is a bucket, the punch 40 is in the shape of a cylindrical body, preferably of circular cross section, and of longitudinal axis Z′Z.
In the example of
The punch 40 is preferably full and made of a material capable of containing the high pressures generated by the magnetic field generation means, for example a metallic material.
Said punch includes a bearing surface 41 and a side surface 42. The bearing surface 41 is intended to receive a portion of the blank to be stamped. The side surface 42 is intended to be facing the inner wall 221 of the side portion 22 of the first hollow body, when said punch is positioned in the first open cavity 23.
The punch 40 is movable in the first open cavity 23. The punch 40 is movable in translation along its longitudinal axis Z′Z between:
The punch 40 displaces in a direction Z′Z, to its deployed position. The punch 40 displaces in a direction ZZ′, towards its retracted position.
In the example of
First displacement means 43 are configured to displace the punch 40 between the retracted position and the deployed position. The first displacement means 43 are actuated manually or automatically.
In an exemplary embodiment, the first displacement means 43 include at least one linear, hydraulic or pneumatic actuator, such as a cylinder operating between the first frame 20 and the punch 40. In this exemplary embodiment, preferably, the fixed portion of the linear actuator—for example the cylinder body—is housed in the first open cavity 23 formed in the first frame 20. The movable portion of the linear actuator, for example the cylinder piston, is capable of displacing out of the first open cavity 23 for deploying the punch 40 in the direction Z′Z and capable of displacing to the first open cavity 23 in the direction ZZ′ to return the punch 40 to its retracted position. In a particularly advantageous manner, control means control the first means 43 for displacing the punch.
In a variant embodiment, the first displacement means 43 are in the form of a support carrying a thrust screw capable of cooperating with the punch 40 to displace it in translation along the longitudinal axis Z′Z.
The stamping device 10 also includes magnetic field generation means 60.
The magnetic field generation means 60 are disposed, at the bearing surface 41 of the punch 40, inside said punch.
The magnetic field generation means 60 are configured to create a magnetic field concentrated in a delimited space and over a very short period, as will be described later.
In a preferred exemplary embodiment, the magnetic field generation means 60 are in the form of a flat coil, for example in a spiral. The flat coil is preferably disposed in a plane substantially parallel to the bearing surface 41 of the punch 40.
The magnetic field generation means 60 preferably form an integral portion of an assembly which further includes an electrical energy storage unit and one or more switches (not shown).
The electrical energy storage unit is configured for and intended to store moderate energy, for example of the order of a few kilojoules to a few tens of kilojoules (kJ).
In a preferred exemplary embodiment, the storage unit is a battery of discharge capacitors.
The second frame 30 is in the form of a second hollow body delimiting a second open cavity 33.
In a particular embodiment, the second open cavity 33 has a cylindrical shape, preferably of circular cross section.
As illustrated in
The second frame 30 is arranged relative to the first frame 20 so that the second open cavity 33 is intended to receive the punch 40, when the latter displaces along its longitudinal axis Z′Z, in the direction Z′Z, to its deployed position. A free end 322 of the side portion 32 of the hollow body of the second frame 30 is substantially facing a free end 222 of the side portion 22 of the first hollow body of the first frame 20.
The second hollow body and the punch 40 have dimensions such that the punch 40 can displace, in translation, freely in the second open cavity 33 and allow the passage of the blank 50, in its thickness, between the inner wall 321 of the second open cavity 33 and the side surface 42 of the punch 40.
In a preferred embodiment, the side surface 42 of the punch 40 and the side wall 32 of the second hollow cavity 33 are of almost complementary shape, except for the thickness of the final stamped part and an operating clearance.
In a non-limiting exemplary embodiment, when the punch 40 is in the shape of a cylindrical body, of circular cross section, the second open cavity 33 is cylindrical, of circular cross section, with a diameter greater than the external diameter of the punch.
In the example of
The stamping device further includes an anvil 70.
The anvil 70 is housed in the second open cavity 33. Said anvil is movable in the second open cavity 33. The anvil is movable in translation along the longitudinal axis Z′Z, Second displacement means 72 are configured to displace the anvil 70 in translation in the second open cavity 33.
The second displacement means 72 are actuated manually or automatically.
In an exemplary embodiment, the second displacement means 72 include at least one linear, hydraulic or pneumatic actuator, such as a cylinder operating between the second frame 20 and the anvil 70. In this exemplary embodiment, preferably, the fixed portion of the linear actuator—for example the cylinder body—is housed in the second open cavity 33. The movable portion of the linear actuator, for example the cylinder piston, is capable of displacing in the second open cavity 33 to displace the anvil 70 in said second cavity. In a particularly advantageous manner, control means control the second displacement means 72 of the anvil 70.
In a variant embodiment, the second displacement means 72 are in the form of a support carrying a thrust screw capable of cooperating with the anvil 70 to displace it in translation, along the axis ZZ′.
In a preferred embodiment, the first 43 and second 72 displacement means are similar.
The stamping device further includes a die 80.
The die 80 is disposed at the free end 322 of the side portion 32 of the second frame 30. The free end 322 of the side portion 32 of the second frame 30 forms a lower surface 81 of the die 80.
In a preferred embodiment, the side portion 32 of the second hollow body of the second frame 30 forms the die 80.
The anvil 70 and the die 80 are preferably made of a metallic material, for example steel, having sufficient structural strength allowing to contain the high pressures generated by the impact of the blank 50 on said anvil and said die, during the stamping method which will be described later.
The punch 40, the anvil 70, the die 80 and the magnetic field generation means 60 are disposed relative to each other so that, in an initial position of the stamping device 10 (
More specifically, the punch 40 is positioned so that its bearing surface 41, in a retracted or intermediate position of said punch, is intended to receive a portion of the first face 51 of the blank 50. In the example illustrated in
The lower surface 71 of the anvil 70 is disposed opposite the second face 52 of the blank 50, at another portion of the blank. In the example illustrated in
The lower surface 71 of the anvil 70 is disposed at a distance from the second face 52 of the blank 50.
Preferably, as illustrated in
In one embodiment, illustrated in
In an exemplary embodiment, the blank holder 90 is maintained pressed against the free end 322 of the side portion 32 of the second frame 30 by compression means such as for example gas springs.
An example of a stamping method is now described.
The blank 50 is intended to conform to the shape of the lower surface 71 of the anvil 70 and to the inner wall 321 of the side portion 32 of the second frame 30 to form a deep stamping, of the bucket type. The bucket obtained may or may not include a flanged rim.
In a prior step, the blank 50 is cut, to the desired dimensions (length and width, or diameter, and thickness), from a sheet.
In a first step, called step a), the blank 50 is positioned in the stamping device 10.
The blank 50, of substantially flat shape, is positioned between the first frame 20 and the second frame 30, as illustrated in
In one embodiment, the blank 50 is disposed on the one hand, at its central portion, on the punch 40. The blank 50 is disposed so that its first face 51 bears against the bearing surface 41 of the punch.
The blank 50 is disposed so that its second face 52 faces the lower surface 71 of the anvil 70. The lower surface 71 of the anvil 70 is positioned at a distance e from the second face 52 of the blank 50.
The distance e defines the desired depth for the deformation of the blank at each discharge (described below). The distance e is maximised so as to reduce the number of discharges and consequently the forming time.
The blank 50 is disposed on the other hand, at its peripheral portion, between the lower surface 81 of the die 80, therefore the free end 322 of the side portion 32 of the second frame 30i, and the free end 222 of the side portion 22 of the first frame 20. The second face 52 of the blank 50 is disposed facing the die 80, at a distance therefrom. The first face 51 of the blank 50 is disposed facing the free end 222 of the side portion 22 of the first frame 20.
In an exemplary implementation, when the blank 50 was deposited on the punch 40, said punch is displaced, from its retracted position, in translation along the direction Z′Z, to offset the blank 50 so that the second face 52 of said blank, at the peripheral portion of the blank, is placed in the immediate vicinity, for example of the order of a millimetre, of the free end 322 of the side portion 32 of the second frame 30, therefore of the lower surface 81 of the die 80.
When the stamping device 10 includes a blank holder 90, the blank 50 is maintained bearing against the free end 322 of the side portion 32 of the second frame 30 by said blank holder.
The method then includes a second step, called step b), of deforming the blank 50 by magnetic forming.
The central portion of the blank 50, located in the vicinity of the magnetic field generation means 60, is subjected to a magnetic field originating from said magnetic field generation means 60 so that an axial pressure is exerted against the first face 51 of the blank 50, and tightly presses said blank against the lower surface 71 of the anvil 70. The arrow illustrated in
Consequently, the blank 50 deforms to bear against the lower surface 71 of the anvil 70.
During this step b) shown in
The anvil 70 advantageously allows limiting the impact of the discharge on the blank and avoiding a tearing thereof.
At the end of this step b), the blank 50 is deformed and has a first stamp.
In a third step, called step c), the punch 40 and the anvil 70 are displaced.
The punch 40 is displaced by the first displacement means 43, in the direction Z′Z, until the bearing surface 41 of the punch is pressed again against the first face 51 of the blank 50, so that the central portion of the blank 50 returns in the immediate vicinity of the magnetic field generation means 60. The peripheral portion of the blank 50 is maintained at a distance from the die 80, as illustrated in
The displacement of the punch 40 is carried out in the same direction as the direction of displacement of the central portion of the blank 50 during step b).
The anvil 70 is displaced by the second displacement means 72, in the direction Z′Z.
In an exemplary implementation, the relative displacement of the punch 40 and the anvil 70 relative to the die 80 is carried out incrementally, preferably simultaneously.
The displacement of the punch 40 and that of the anvil 70 is not necessarily of the same amount.
The anvil 70 is displaced in the direction Z′Z by a sufficient distance so as to define the desired depth for the incremental deformation of the blank.
In an exemplary implementation, the relative displacement of the punch 40 and the anvil 70 is carried out continuously. The shaping of the blank 50 by the magnetic field generation means 60 can be considered instantaneous relative to the displacement of the punch 40 and to that of the anvil 70. Indeed, the duration of the displacement of the punch 40, and that of the displacement of the anvil 70, is generally very slow (of the order of a second) compared to the duration of the magnetic pulse generated by the magnetic field generation means 60 (of the order a few micro seconds). In the particular case of this embodiment, the second and third steps are carried out simultaneously without modifying the result of said steps.
In a fourth step, steps b) and c) are reproduced sequentially.
Steps b) and c) are repeated until obtaining the depth P of the final stamped part desired to be obtained.
As the punch 40 and the anvil 70 relatively displace relative to the die 80, said magnetic field generation means 60 advantageously exert an axial pressure on the central portion of the blank 50 in the direction of the anvil 70, pressing the central portion of said blank on said anvil. Said magnetic field generation means 60 also exert radial pressure on the blank 50 in the direction of the die 80, against the inner wall 321 of the side portion 32 of the second frame 30, pressing said blank against said inner wall. The horizontal arrows illustrated in
The number of iterations of steps b) and c) depends in particular on the material constituting the blank, on the desired depth of the stamped part.
At the end of the stamping method, the blank became a deep stamped part, of the bucket type, with or without a flanged rim.
In the example of
The present invention is not limited to the preferred embodiments described above by way of non-limiting examples and to the mentioned variants. It also relates to the variant embodiments within the reach of the person skilled in the art.
The above description clearly illustrates that by its various features and their advantages, the present invention achieves the objectives which it had set itself. Particularly, it provides a stamping device adapted for producing stamped parts, in particular deep stamped parts, without generating wrinkles or tears in the part. Such a stamping device and the associated stamping method allows working the part at high speeds, and advantageously deforming the blank without the risk of generating tears in the part desired to be obtained and with excellent shaping precision.
The invention also advantageously allows producing flanging edges.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1761765 | Dec 2017 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/083871 | 12/6/2018 | WO | 00 |
