Patent Application
20190374992
This present disclosure relates to the field of forming, more particularly to stamping.
This present disclosure relates to a device and a method for stamping blanks by magnetic pulse for the production of stamped parts, in particular parts referred to as deep drawn.
In the field of forming, in particular metals, stamping is a method that is very often chosen, because it is robust and controlled well.
Stamping is commonly used in industry, in particular in the automobile industry for forming in particular lining panels, such as a bonnet or a door of a motor vehicle, due to the high production speeds that are possible.
Stamping is a process for forming consisting in obtaining via the plastic deformation of a blank, under the action of a pressure, a part with a more or less complex shape.
The device for stamping for implementing this method is comprised substantially of a die and of a punch of practically complementary shape, between which the blank is positioned. The obtained of the shape is done by the driving of the blank under the action of the punch in the die. The movement of the blank is generally controlled by a blank-holder, which imposes on it a retaining pressure, with the purpose of decreasing the appearance of folds or of tears on the final stamped part.
However, in the presence of a part that is difficult to form, in particular a deep-drawn part, the choice of the clamping force to be imprinted on the blank-holder is difficult. If the force of the blank-holder is too high, the folds are suppressed but the risk of a tear is high. If the force of the blank-holder is too weak, the risk of the formation of folds is high.
In order to produce deep-drawn parts, alternatives to the method for stamping are known.
Among them, mention can be made of the hydro forming method. In this method, the blanks are formed by the action of a pressurised fluid.
The associated device for hydro forming is comprised of hermetically-sealed chamber formed of two pieces of which one is a hollow mould that has an imprint complementary with the shape of the part that is sought to be obtained. The blank is placed inside the chamber. A hydraulic pressure is exerted on the latter that thrusts it against the imprint of the mould. The fluid can be pressurised in various ways. Among the existing methods of hydro forming, mention can be made of the electro hydraulic forming method (EHF).
Such a method has many advantages, in particular a substantial reduction in the elastic return, or lower manufacturing costs. However, the major disadvantages reside in the cycle time required for the stamping of the part (water management time) and in the need to place the part to be formed in contact with water (corrosion possible).
Mention can also be made of the hot methods of forming, such as the method for superplastic forming, referred to as SPF. This method is based on the capacity of certain alloys, for example titanium, to withstand substantial deformation. These alloys, called in what follows superplastic alloys, can reach elongations that sometimes range beyond 1000% under certain conditions of temperature, pressure and deformation while conventional alloys are deformed generally only by about 20%.
The associated device for SPF forming is comprised of a hermitically-sealed chamber formed of two pieces of which one is a hollow mould that has an imprint complementary to the final external geometry of the part that is sought to be obtained. The blank is placed inside the chamber and fixedly maintained between the two pieces. A pressurised gas is injected into the chamber and thrusts the blank, by deforming it, against the imprint. The pressure and the temperature, of about 900° C. for titanium alloys, must be perfectly controlled.
The obvious disadvantages linked to this device for forming SPF and to the associated method reside in the cycle time, the cost and the fact that only certain materials can be used.
This present disclosure has in particular for objective to overcome all or a portion of the limitations of the solutions of prior art, in particular those mentioned hereinabove, by proposing a solution that allows for the obtaining of stamped parts, and in particular of deep-drawn parts.
To this effect, the present disclosure aims firstly a device for stamping a blank in order to produce a stamped part comprising:
The term blank means a thin plate, in particular made of metal material. A plate is said to be thin when one of its dimensions is clearly less than the other two, typically at least one magnitude.
In an initial position, i.e. before the stamping phase, the device for stamping is configured in such a way that:
a. the bearing surface of the punch is intended for receiving a portion of a first surface of the blank,
b. the anvil and the means for generating a magnetic field are intended for being arranged on either side of another portion of the blank.
The anvil is facing the first surface, and the means for generating a magnetic field are facing a second surface, opposite the first surface. The means for generating a magnetic field are distant from said second surface.
The means for generating a magnetic field are intended and configured to imprint on the blank a pressure in the direction of the anvil, in a direction ZZ′. This pressure projects the blank, in particular the portion of the blank with respect to the anvil, against the anvil. Thus, the pressure exerted partially thrusts in part the blank against the anvil, causing a deformation of said blank.
The device for stamping further comprises movement means arranged to move the punch, relative to the means for generating a magnetic field, in a direction Z′Z, opposite the direction ZZ′. The punch is advantageously moved in translation.
The punch and the anvil are preferably made from a metallic material in order to contain the high pressures generated by the means for generating a magnetic field.
According to the present disclosure, the blank is intended to conform to the shape of the punch in order to form the final stamped part.
The device for stamping according to the present disclosure is differentiated from the conventional devices for stamping in that the stamping is not carried out by the punch itself, but by the means for generating a magnetic field.
Likewise, the means for generating a magnetic field are used differently in the conventional framework of a magnetic forming method that forms the whole of the blank at a single time. The means for generating a magnetic field are arranged in such a way as to not generate magnetic pulses only on a portion of the blank. The relative displacement in translation of the punch in relation to the means for generating make it possible to move the zone of the blank that will be touched by the magnetic pulses.
Such a device advantageously makes it possible to work primarily in compression but also in expansion.
Such a device for stamping is thus particularly suitable for the production of stamped parts, in particular deep-drawn parts, without generating folds or tears in the part.
It is also suitable for the production of turned out edges, with the advantages that can be provided by magnetic forming, such as the obtaining of radii of curvature less than 2 mm, fine edging, or of close tolerances, as well as the avoiding of cracking of the material in the zones with high elongation, in particular for aluminium.
According to preferred aspects, the present disclosure further responds to the following characteristics, implemented individually or in each of their technically operative combinations.
According to preferred aspects of the present disclosure, the movement means comprise a linear actuator.
According to preferred aspects of the present disclosure, the means for generating a magnetic field comprises at least one coil.
According to preferred aspects of the present disclosure, the device for stamping comprises adjusting means configured to adjust the space between the anvil and the means for generating a magnetic field.
According to preferred aspects of the present disclosure, the device for stamping comprises a blank-holder configured to impose a retaining pressure on the movement of the blank, against the punch.
The present disclosure also relates to a method for stamping by magnetic pulse a blank in order to produce a stamped part, using a device for stamping in accordance with one of its embodiments. The method comprises the steps of:
a) positioning the blank in the device for stamping,
b) subjecting the blank to a magnetic field caused by the means for generating a magnetic field in such a way that a pressure is exerted on the second surface of the blank in a direction ZZ′ and thrusts said blank against the anvil,
c) moving the punch by the movement means in a direction Z′Z, opposite the direction ZZ′, with the steps b) and c) being repeated, preferably synchronised, until the desired shape is obtained for the finished stamped part.
The term synchronised means that the steps are carried out either successively, one after the other, or simultaneously.
The blank is positioned in the device for stamping in such a way that the blank rests solely on the bearing surface of the punch.
As the punch moves, a magnetic pulse is generated by the means for generating, exerting, on the one hand, an axial pressure on the blank in the direction of the anvil, thrusting said blank on said anvil, and on the other hand, a radial pressure on the blank in the direction of the punch, thrusting said blank on said punch.
The axial pressure projects a portion of the blank against the anvil. The radial pressure projects another portion of the blank against the punch.
This double pressure, axial and radial, advantageously allows for both the deformation of the blank and thrusting of it against the punch, making it match the shape of the latter.
The present disclosure shall be better understood when reading the description hereinafter, given as an example that is in no way limiting, and given in reference to the figures which show:
In these figures, identical references from one figure to another designate identical or similar elements. For reasons of clarity, the elements shown are not shown to scale, unless mentioned otherwise.
A device for stamping 10, such as shown in
In an aspects of the present disclosure, the blanks 50 are made of a metallic material, such as steel.
The blank 50 has a first surface 51 and a second surface 52, opposite the first.
In a preferred non-limiting aspect of the present disclosure, the device for stamping 10, such as shown as a cross-section in
Those skilled in the art will easily understand that the teaching of this present disclosure can be transposed to other aspects.
In this description, the terms such as upper, lower, top, bottom, left, right are used with a concern for simplicity, in reference to the orientation of the various elements shown in
The device for stamping 10 comprises a first frame 20 and a second frame 30. The first frame 20 can represent an upper portion of the device for stamping and the second frame 30, a lower portion, such as shown in figures. As an alternative, and without leaving the scope of the present disclosure, the first frame 20 can represent a lower portion, left or right, of the device for stamping and the second frame 30, respectively an upper portion, right or left.
The first frame 20 carries a punch 21, preferably central.
Said punch comprises a bearing surface 211 and lateral walls 212.
In the particular example wherein the final stamped part is a cup, the punch has the form of a cylindrical body, preferably full.
According to the present disclosure, the blank 50 is intended to conform to the shape of an outer surface of the punch 21.
Thus, the punch 21 has, on said outer surface, an imprint that corresponds to the shape of the final part, once stamped.
The punch 21 is mobile in translation, according to a vertical axis, thanks to movement means 23 that can move the punch between a retracted position and a deployed position.
In the example of
The movement means 23 are actuated manually or automatically.
In an aspect of the present disclosure, the movement means 23 comprise at least one linear, hydraulic or pneumatic, actuator, such as a cylinder operating between the first frame 20 and the punch 21. In this embodiment, preferably, the fixed portion of the linear actuator—for example the body of the cylinder—is housed in a recess (not shown) made in the first frame 20. The mobile portion of the linear actuator, for example the piston of the cylinder, is able to be moved out of the recess in order to deploy the punch 21 and able to be moved to the recess in order to return the punch 21 to its initial position. Particularly advantageously, the movement of the punch 21 is controlled by control means.
In an alternative aspect of the present disclosure, the movement means 23 have the form of a support carrying a pressure screw able to cooperate with the punch 21 in order to move it in translation.
The first frame 20 further comprises an anvil 22.
Said anvil is arranged around lateral walls 212 of the punch 21, when said punch is in its retracted position.
The anvil and the punch are spaced apart from one another by a predetermined distance.
In an aspect of the present disclosure, when the punch 21 has the form of a cylindrical body, the anvil 22 has the form of an annular body surrounding the punch.
In an aspect of the present disclosure, the anvil 22 can form the first frame 20.
The punch, on its bearing surface, and the anvil, on a free end 221, are at separate heights.
The second frame 30 comprises a hollow body that delimits an open cavity 33.
As shown in
The second frame 30 is arranged with respect to the first frame 20 in such a way that:
The free ends 321 of the lateral sides 32 of the hollow body of the second frame are substantially facing the free end of the anvil 22.
The hollow body and the punch 21 have dimensions such that the punch 21 can be moved freely in the open cavity 33 with, between their respective surfaces, a non-negligible space for the passing of the blank 50, in its thickness.
In a non-limited aspect of the present disclosure, when the punch 21 has the form of a cylindrical body, the open cavity 33 has the form of an annular body surrounding the punch.
In an aspect of the present disclosure, the outer surface of the punch 21 and the inner wall of the hollow cavity 33 are of practically the same shape, to the nearest thickness of the final stamped part and an operating clearance.
The second frame 30 further comprises means for generating a magnetic field 34.
The means for generating a magnetic field 34 are arranged, on free ends 321 of the lateral sides 32 of the hollow body, facing the anvil 22.
As shown in
More precisely, regarding the initial position of the device for stamping shown in
The means for generating a magnetic field 34 are configured for and intended to create a magnetic field concentrated in a delimited space and over a very short period.
Preferably, such as shown in
In an aspect of the present disclosure, the means for generating a magnetic field 34 are a coil.
The means for generating a magnetic field are more preferably an integral part of a set that further comprises an electrical energy storage unit and one or several switches (not shown).
The electrical energy storage unit is configured for and intended to store a moderate energy, for example of about a few kilojoules to a few tens of kilojoules (kJ).
In a preferred aspect of the present disclosure, the storage unit is a discharge capacitor battery.
The first frame 20, the second frame 30, the anvil 22 and the punch 21 are preferably made from a metallic metal, for example steel, so as to have a structural resistance that makes it possible to contain the high pressures generated by the impact of the blank 50 on the anvil 22, during the method for stamping which shall be described hereinafter.
In an aspect of the present disclosure, the device for stamping 10 comprises adjusting means (not shown) arranged to move the anvil 22 vertically, in translation. Such means make it possible to reduce or to increase the space e that separates the anvil from the means for generating a magnetic field 34. The sizing of the space e is according in particular to the material and the geometric shape of the punch, as well as the pulse of the current. The sizing of the space e is maximised in order to reduce the number of discharges and consequently the forming time.
In aspects of the present disclosure, the adjusting means are a linear, hydraulic or pneumatic actuator.
In an aspect of the present disclosure, shown in
In an aspect of the present disclosure, the blank-holder is maintained thrust against the second surface 52 of the blank 50 by means of compression 61.
In aspects of the present disclosure, the means of compression are a spring or a linear, hydraulic or pneumatic actuator, such as a cylinder, operating between the blank-holder and an inner surface 311 of the second frame 30.
An example of the method for stamping from such a device for stamping is now described.
In a prior step, the blank 50 is cut, to the desired dimensions (length and width, or diameter, and thickness), in a sheet metal.
In a first step, referred to as step a), the blank 50 is positioned in the device for stamping 10.
The blank 50, of substantially flat shape, is positioned between the first frame 20 and the second frame 30, as shown in
In an aspect of the present disclosure, the blank 50 is arranged on the one hand on its central portion on the punch 21. The blank 50 is arranged in such a way that its first surface 51 bears against the bearing surface 211 of the punch.
When the device for stamping comprises a blank-holder 60, the blank 50 is maintained bearing against the bearing surface 211 of the punch 21 by said blank-holder.
The blank 50 is arranged on the other hand, on its peripheral portion, between the means for generating a magnetic field 34 and the anvil 22. The first surface 51 of the blank is arranged facing the anvil 22, at a distance from the latter. The second face 52 of the blank is arranged facing the means for generating a magnetic field 34.
The blank bears against the bearing surface 211 of the punch 21. The blank does not bear against the anvil 22.
In an aspect of the present disclosure, when the blank 50 has been placed on the punch, the punch 21 is moved, from its retracted position, in translation along the direction Z′Z, in order to offset the blank 50 in such a way that the second surface 52 of said blank, on the peripheral portion of the blank, is placed in immediate proximity, for example of about a millimetre, from the means for generating a magnetic field 34.
The method then comprises a second step, referred to as step b), of deforming the blank 50 via magnetic forming.
The ends of the blank 50, located in the vicinity of the means for generating a magnetic field 34, are subjected to a magnetic field coming from the means for generating a magnetic field 34 in such a way that a pressure, axial, is exerted against the second surface 52 of the blank 50, and tightly thrusts said blank against the anvil 22. The arrow shown in
The blank 50 is consequently deformed to bear against the anvil 22.
During this step b) shown in
At the end of this step b), the blank 50 is deformed and has a first stamp.
In a third step, referred to as step c), the punch 21 is moved.
The punch 21 is translated by the movement means 23, in the direction Z′Z, in such a way as to drive in its movement the blank 50, by moving away the peripheral portion of the blank 50 from the anvil 22, as shown in
The movement of the punch 21, and consequently that of the blank 50, is carried out in the direction opposite the direction of the movement of the blank 50 during the step b).
In an aspect of this third step, the punch 21 is moved in the direction Z′Z by a height that is sufficient for the second surface 52 of the blank 50 to return to the immediate vicinity of the means for generating a magnetic field 34.
In an aspect of the present disclosure, the relative movement of the punch 21 with respect to the means for generating a magnetic field 34 and to the anvil 22 is carried out incrementally.
In an aspect of the present disclosure, the relative movement of the punch with respect to the means for generating a magnetic field and to the anvil is carried out continuously. The forming of the blank 50 by the means for generating a magnetic field 34 can be considered as instantaneous with respect to the movement of the punch. Indeed, the duration of the movement of the punch is generally very slow (of about one second) with respect to the duration of the magnetic pulse generated by the means for generating a magnetic field 34 (of about one microsecond). 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, the steps b) and c) are reproduced sequentially.
The steps b) and c) are reproduced until the obtaining of the depth P of the final stamped part that is sought to be obtained.
As the relative movement of the punch 21 takes place with respect to the means for generating a magnetic field 34, said means for generating a magnetic field 34 advantageously exert an axial pressure on the blank 50 in the direction of the anvil 22, thrusting said blank on said anvil. Said means for generating a magnetic field 34 also exert a radial pressure on the blank 50 in the direction of the punch 21, thrusting said blank on said punch. This radial pressure of the blank 50 against the punch 21 advantageously allows said blank to perfectly match the shape of the outer surface of the punch 21.
The number of iterations of the steps b) and c) depends in particular on the material comprising the blank, on the desired depth of the stamped part.
This present disclosure is not limited to the preferred embodiments described hereinabove as non-limiting examples and to the alternatives mentioned. It also relates to the alternative embodiments within the scope of those skilled in the art.
The description hereinabove clearly shows that through its various characteristics and their advantages, this present disclosure achieves the objectives that were set for it. In particular, it proposes a device for stamping suitable for the production of stamped parts, in particular of deep-drawn parts, without generating folds or tears on the part. Such a device for stamping and of the associated method for stamping can make it possible to work on the part mainly in compression but also in expansion. In addition, as the high speeds tends to minimise the appearance of folds, the present disclosure advantageously makes it possible to produce turned out edges.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1750370 | Jan 2017 | FR | national |
This application is a National Stage of International Application No. PCT/EP2018/051134, having an International Filing Date of 17 Jan. 2018, which designated the United States of America, and which International Application was published under PCT Article 21(2) as WO Publication No. 2018/134271 A1, which claims priority from and the benefit of French Patent Application No. 1750370, filed on 18 Jan. 2017, the disclosures of which are incorporated herein by reference in their entireties.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/051134 | 1/17/2018 | WO | 00 |
