FR2889466A1 - MANUFACTURE OF A METALLIC PIECE BY HOT STAMPING AND PIECE OBTAINED - Google Patents

Abstract

The present invention relates to the manufacture, by stamping, of a metal part from a blank made at least partially of a quenching material. The blank is heated to a temperature suitable for its subsequent quenching and then stamped in a stamping tool. (27, 29) which gives the workpiece (1) the required shape, causing quenching, and cutting to the required inner and / or outer contour (22, 24, 26, 42). Localized heating means (32, 39, 40, 41) are used to temporarily heat a marginal zone (30, 33, 34, 35) along the contour (22, 24, 26, 42) to prevent the appearance of constraints to cut or relax the stresses appearing at the cut.Application to the prevention of cracks along the contour of the stamped part.

Description

The present invention relates to a method of manufacture, by

  stamping, of a metal part having a determined shape and a determined outline, inside and / or outside, from a blank made at

  less partially in a so-called soaking material, said method comprising a succession of steps of: a) heating the blank to a first temperature, suitable for a subsequent quenching of said material, b) placing the blank in a stamping tool suitable for set it to said determined shape and cut it according to said determined contour, the stamping tool having a second predetermined temperature lower than said first determined temperature and such that the contact of the blank with the stamping tool is likely to cause quenching said material, c) stamping the blank by means of the stamping tool, to bring the blank to said determined shape, by causing the quenching of said material, and cutting it to said determined contour, so as to separating said part, d) disengaging said part from the stamping tool.

  Such a process is known as the hot stamping process, and it is used for the manufacture of metal parts combining lightness, high yield strength and high mechanical strength, used for example in the automotive industry as structural parts and of chassis.

  To produce such a part, a blank made or at least partially made of a so-called quenching material, that is to say of steel capable of being tempered, such as a steel MnB5 marketed under the name BTR 165 or under the name USIBOR 1500, which is advantageously coated with an aluminum silicate alloy.

  Initially, the blank is heated in an oven to a temperature suitable for causing austenitization of the steel, and it is maintained at the required temperature for the time necessary for this austenitization, ie for example of the order from 5 to 10 minutes at a temperature of the order of 900 C. Worn at this temperature, the coating alloy is combined with steel.

  The blank is then conveyed to a stamping press, in which it is placed, while still hot, in contact with the stamping tool, which is placed at a comparatively low temperature in order to provoke, in the The stamping tool itself, sufficiently fast quenching, ie for example greater than 27 C / s, to communicate to the steel a final martensitic structure that will give the stamped part the desired mechanical properties.

  Simultaneously with the shaping of the part or, more generally, at the end of this shaping, the stamping tool proceeds to cut it according to the required determined contour, namely according to an outer contour, to separate the pressed piece and an outer fall of the blank, and, where appropriate, along at least one inner contour, to form at least one hole in the room by separating an inner fall of the blank.

  To these different effects, the stamping tool may comprise a single punch-die assembly, suitable for practicing in a single stamping operation the shaping of the piece from the blank, accompanied by the quenching, and cutting of the part according to the required determined contour, or of the workpiece, to separate it from at least one drop of the blank, or two distinct punch-die sets, on which the blank is successively placed and a first one proceeds to the shaping of the piece from it, accompanied by the quenching, and the second at the trimming of the piece.

  In either case, the suitably shaped, quenched and cut-out part is then released from the stamping tool to be routed to other treatments or assembly to other parts. .

  The hot stamping process, as it is currently practiced, has the disadvantage that the combination of quenching and cutting along the or each contour of the part being stamped causes, in a marginal zone thereof, along the or each contour, the development of constraints that may themselves lead to crack initiation, whose subsequent development is poorly controlled.

  The object of the present invention is to remedy this drawback and, for this purpose, the present invention proposes a manufacturing method, by hot stamping, comprising the steps a to d listed in the preamble and characterized in that, during the step c or subsequent to step d, a temporary heating of the blank or said part, respectively, closely localized in a zone along said determined contour and corresponding to a marginal zone of said piece, to maintain or carry , respectively, temporarily said zone at a temperature to reduce the constraints that may result from a combination of quenching and cutting.

  A person skilled in the art will readily understand that, as soon as the constraints which may result from a conjunction of quenching and cutting in the or each marginal zone of the part are reduced or even completely eliminated, pressed, it avoids the creation of crack initiation in this area and therefore eliminates any risk of subsequent propagation of such cracks.

  Naturally, the temporary heating must remain closely localized and, if it is practiced in step c, must be compatible with the cooling of the blank everywhere else, under conditions suitable for causing quenching and, although many modes of Temporary heating can be used, it is preferred to cause said temporary heating by induction.

  The moment when this temporary heating is practiced can be chosen freely, but it is preferred to provoke it either during step c, preferably during the forming of the piece and the quenching and immediately before cutting the blank. according to said determined contour, that these operations are performed in the same punch-matrix assembly or in two distinct, successive punch-matrix assemblies of the stamping tool, so that the quenching does not take place in the marginal zone thus heated temporarily and that it is thus along a non-hardened area that is practiced cutting, which reduces the stresses appearing during it, either during step c but after cutting the blank , or even after step d, temporarily placing the stamped part in a post-processing tool thereof, to detension the marginal area, that is to say to reduce the stresses that have appeared there during the D cutting, by closely localized annealing in this edge region; this tool for later processing of the workpiece may be a tool for conveying it to another workstation, or a tool provided for applying another treatment to the workpiece in a workstation following the stamping station.

  In relation to these two preferred embodiments of the method according to the invention, the latter furthermore proposes: a tool for manufacturing, by stamping, a metal part having a determined shape and a determined outline, interior and or outside, from a blank made at least partially of a said soaking material, said tool having a shape complementary to said determined shape, at least in a zone along said determined contour and corresponding to a marginal zone of said part, means for cutting the blank according to said determined contour and / or internal cooling means, characterized in that it comprises heating means closely located in said zone along said determined contour and corresponding to a marginal zone of said room, and a tool for treating a stamped metal part, having a determined shape and a determined contour, interior r and / or outside, and consisting at least partially of a hardened material, characterized in that it comprises at least one zone having a shape complementary to that of a marginal zone of said part, along said determined contour, and heating means closely located in said area.

  In either case, the heating means can be chosen freely, but it is preferably induction heating means.

  Insofar as a metal part stamped according to the process according to the invention has a particular structure, because of the absence or the disappearance of the quenching in its marginal zone, along the or each determined contour, inside or outside, of cutting, the present invention also extends to a stamped metal part, having a determined shape and a determined outline, inside and / or outside, and made at least partially from a so-called soaking material, characterized in that said material is quenched except in a marginal zone of said part, along said contour.

  Other features and advantages of these various aspects of the present invention will emerge from the description below, relating to a nonlimiting example of implementation, as well as the accompanying drawings.

which accompany this description.

  FIG. 1, unique, shows a perspective view of a hot-stamping punch, intended for the production of a motor-vehicle midfoot from an initially planar blank, and the arrangement of holes in this foot-medium, whose silhouette is also shown while it is still positioned on the punch after stamping, that is to say after forming and cutting according to an outer peripheral contour and in peripheral contours interiors defining holes.

  Naturally, it is understood that the present invention is not limited to the manufacture of a foot-medium for a motor vehicle and that, when applied to the manufacture of such a foot-medium, it can present a conformation different from that which has been illustrated and which will now be described briefly.

  In this embodiment, the central foot 1 has the general shape of an I, defined by a central portion 2, elongate in a longitudinal direction 3 intended to be oriented approximately vertically once the foot-medium 1 integrated into a body of automobile, and two longitudinally extreme parts 4, 5 elongate substantially in the same transverse direction 9, the first of which is intended to fit on a chassis frame of the vehicle and to be secured to the spar while the second is intended to fit on a roof frame of the vehicle and to be secured to this roof frame.

  The central portion 2 has the general shape of a longitudinal beam of cross section at S2, defined by a longitudinal core 6, bordered by two longitudinal wings 7, themselves bordered by a respective longitudinal rim, flat 8, the opposite 6. Only one wing 7 and one flange 8 are visible in FIG. 8, but, as is well known to a person skilled in the art, the flanges 8 extend mutually in the transverse direction 9 and protruding opposite each other, along this direction 9, with respect to an assembly consisting of the core 6 and the two wings 7.

  The longitudinally extreme portion 4 has an inverted U-section, perpendicular to the transverse direction 9, and this section is defined by a web 10 extending the web 6, a transverse wing 11 bordering the web 10 opposite the connection of the web. it with the core 6 and having opposite the connection with the core 10 a free edge 12, oriented in the transverse direction 9, and two wing portions 13 which are respectively located on the side and other of the central portion 2 in the transverse direction 9 and each of which is connected to one, respectively, of the flanges 7 and has a flange 14 itself extending a flange 8 respectively corresponding, opposite the connection of the part 13 considered at the core 10 of part 4.

  The longitudinally extreme portion 5 has perpendicularly to the transverse direction 9 an S shape, defined by a core 15 to which the core 6 is connected longitudinally opposite its connection with the core 10, and which is oriented in the transverse direction 9 and obliquely to the longitudinal direction 3, by a flange 16 oriented in the direction 9 and offset with respect to the core 6 in a transverse direction 17 perpendicular to the directions 3 and 9 and from the flanges 8 and 14 to the webs 6 and 10, and by two flange portions 18 each of which extends the respective one of the flanges 8. The inclination of the web 15 is such that it moves away longitudinally from the portion longitudinally extreme 4, flange portions 18 to the flange 16, in the direction 17. Longitudinally opposite its connection to the core 15, the flange 16 has a free edge 19 oriented in the direction 9.

  The free edges 12 and 19 of the wings 11 and 16 are connected together, respectively on either side of the central foot 1 with reference to the transverse direction 9, by two other free edges 20 each of which is partially constituted by an edge free unreferenced that the respective one of the flanges 8 has the opposite to its connection to the corresponding flange 7, by a free edge that each of the flanges 14 and 18 has the opposite of its connection respectively to the wing portion 13 and to the core 15 and to which the free edge of the aforementioned flange 8 is connected by a free edge that each wing portion 13 and the core 15 have the opposite of their respective connection to a wing 7 of the central portion 2, and by free edges that the core 10 and the flange 11 of the longitudinally extreme portion 4 have the opposite of each other in the transverse direction 9.

  The free edges 12, 19 and 20 complement each other to form the outer peripheral contour 42 of the central foot 1.

  As will be readily understood by a person skilled in the art, the presence of an outer peripherally continuous edge, here constituted by the two free edges 20 and the two free edges 12 and 19, constituting an outer peripheral contour is common to all the parts made by stamping, namely by forming and cutting a blank, and the present invention can find its application along any free edge thus defining an outer contour of a stamped part.

  Optionally, it may also have at least one inner contour, defined by perforations or holes made during stamping, and the present invention may also find its application throughout the internal contours thus defined.

  In the example of the central foot 1 which has been illustrated in FIG. 1, the shaping thereof by stamping and the cutting, during the drawing, of its outer contour 42 defined by the free edges 20, 12 and 19 are accompanied by the arrangement, by cutting, three holes 21, each circular contour 22, in the core 10 of the longitudinally end portion 4, six holes 23 of each contour 24 circular or oval in the 6, and two holes 25 of respective rectangular contour 26 in one of the wings 7. It is understood that these numbers, shapes and locations of the holes 21, 23, 25 are only non-limiting examples, and different choices could be made, just as none of these holes could be expected.

  Respective faces of the webs 6, 10, 15, wings or wing portions 7, 11, 13, 16 and flanges 8, 14, 18 together define a particular shape, recessed, not visible in the figure 1, while their respectively opposite faces together define a specific shape, in relief, visible in Figure 1.

  In a manner known per se, these respectively recessed and raised shapes are obtained by stamping an initially planar or preformed blank, not illustrated, in a stamping tool comprising a punch 27, illustrated in FIG. having a forming face 28 of substantially complementary shape to said recessed shape except that it extends from all parts beyond the outer peripheral contour 42 to be imparted to the workpiece as defined the free edges 12, 19 and 20. If we consider the state of the punch 27 and the foot-medium 1 after the drawing thereof, as shown in Figure 1, the forming face 1 28 is turned in the direction 17.

  The drawing tool also comprises a matrix which is simply shown schematically in FIG. 1 by an arrow 29 in the direction opposite to the direction 17, which matrix has in the direction 29 a forming face, not shown, complementary to the raised form of the foot-medium 1 to achieve but having, as the forming face 8, larger dimensions than those of the contour 42 defined by the free edges 12, 19, 20.

  In a preferred manner in connection with the implementation of the method according to the invention, the matrix 29 has, along this contour 42, blank cutting means, also not shown, to disengage the footmilieu 1 at the end. stamping; in addition, the matrix 29 comprises perforation means for arranging the holes 21, 23, 25 by cutting a blank drop according to each of the contours 22, 24, 26 at the end of stamping.

  However, it would not be departing from the scope of the present invention to successively perform shaping, accompanied by quenching, and cutting into separate respective punch-die assemblies, adapting in a manner to be indicated thereafter. which will be described in connection with a unique punch-matrix assembly suitable for practicing this formatting and cutting.

  Such provisions are well known in themselves to a person skilled in the art and will not be detailed further.

  It only matters, in view of the present invention, that the stamping tool, here constituted by the punch 27 and the die 29, is capable of producing from the blank the hollow shapes and the reliefs required. by the coin to be stamped, whatever it is, here constituted by the central foot 1, as well as the cutting of the blank along the outer contour of this piece, as defined in the example illustrated by the free edges 12, 19 and 20, and optionally in at least one inner contour, such as the contours 22, 24, 26 in the illustrated example, causing, by appropriate cooling of the punch 27 and the matrix 29, suitably provided with this effect of a respective circulation circuit of a cooling fluid, not illustrated but well known in itself to a skilled person, a quenching of a quenching material constituting at least partially the blank.

  It is meant here, by mentioning that the quenching material constitutes at least partially the blank, that it can be made integrally of such a quenching material, for example of hardening steel marketed under the name USIBOR 1500, or be constituted exclusively such a quenching material and a coating thereof, such as an aluminum silicate alloy coating, or a plurality of layers, some of which may be localized only and at least one of which one consists of a quenching material, these different layers being stamped simultaneously to impart to the part the required shape and the required internal and / or external contour under conditions suitable for causing quenching of the quenching material.

  Since it is concerned with the cutting accompanying the stamping, that is to say reaches either the outer contour 42 defined by the free edges 12, 19, 20 or all or part of the inner contours 22, 24 , 26, the conjunction of quenching and cutting along these contours develops within this material constraints that the present invention aims to either avoid or to release if they appeared.

  For this purpose, the punch 27 illustrated in FIG. 1 has, in its forming face 28, heating means, advantageously by induction, closely located in a manner which will now be described, it being understood that at each The zones or parts of the coin 1 to be stamped correspond to a respective part of the forming face 28.

  In particular, if we consider the outer peripheral contour 42 of the central foot 1, as defined by the free edges 12, 19 and 20, and a marginal zone 30 of the central foot 1 along this outer peripheral contour 42 on the all of it, continuously, over a width of up to a few millimeters, from this outer peripheral contour 42, the forming face 28 has a zone 31 which corresponds to this zone 30 and on which this zone 30 applies during stamping.

  In this zone 31, the punch 27 is provided, in its forming face 28, with an induction heating circuit 32, which thus extends in the form of a substantially closed loop all along the outer peripheral contour 42 of the foot-medium 1 to be manufactured so as to be capable of heating the marginal zone 30 thereof over the whole of this outer peripheral contour 42.

  In its illustrated embodiment, in which it comprises the holes 21, 23, 25 defined by a respective inner peripheral contour 22, 24, 26, the central foot 1 furthermore has other marginal zones 33, 34, 35. each of which extends around a respective one of these inner contours 22, 24, 26, over a width of up to a few millimeters, and each of which corresponds to a respective annular zone 36, 37, 38 of the forming face 28.

  In each of these annular zones 36, 37, 38, respectively, the punch 27 is provided with a respective induction heating circuit 39, 40, 41 which forms a substantially closed loop opposite the respectively corresponding marginal zone 33, 34, 35, and can therefore cause the heating of this marginal zone.

  In each case, the heating thus obtained in a marginal zone of the central foot 1 remains sufficiently localized so as not to interfere with the quenching effect resulting, in the rest of the central foot 1, from the contact of the constituent blank thereof. with the forming face 28 of the punch 27 suitably cooled for this purpose.

  Naturally, each of the induction heating circuits 32, 39, 40, 41 is connected to an electricity-controlled supply source, not shown, by non-referenced conductors whose sections closest to the corresponding circuit respectively are housed at the same time. interior of unrepresented passages of the punch 27.

  A person skilled in the art will easily understand how, under these conditions, the manufacture of a metal part such as the foot-medium 1 by stamping, in accordance with the present invention.

  In a first step, a non-represented flat or preformed blank made at least partially of a hardening material, namely for example a hardening steel of the type sold under the name BTR 165 or under the name USIBOR 1500, is conventionally heated. at a temperature, for example of the order of 900 C, suitable for the subsequent quenching of the quenching material, then it is placed in the stamping tool, that is to say between the punch 27 and the die 29 , initially mutually dissociated and having in turn a sufficiently low temperature so that the subsequent contact of the blank with them causes quenching of the quenching material.

  The stamping is then carried out by mutually bringing the punch 27 and the die 29, suitably carried by unrepresented plates of a press, which conforms the blank to the required shape of the central foot 1 and cuts the latter along. its outer peripheral contour 42 and each of its inner peripheral contours 22, 24, 25, with reference to the illustrated example.

  The quenching material then undergoes the required quenching by cooling itself abruptly in contact with the forming face 28, except that a temporary heating of each of the marginal zones 30, 33, 34, 35 by the induction heating circuit respectively corresponding 32, 39, 40, 41, preferably made before the actual cut but after forming the blank, during the drawing thereof, avoids the quenching of these marginal areas and thus prevents the cutting is translates into the appearance, in these marginal zones, of stresses likely to generate breakout primers.

  The punch 27 and the matrix 29 are then separated from each other to release the finished foot-medium 1, which is released to route it to other manufacturing steps.

  When the stamping tool has two distinct punch-matrix assemblies, one of which performs the shaping and the quenching and the second the cutting, it is the punch of the first set which is then equipped, as it was described with reference to the punch 27 to which it is substantially identical, temporary heating means, by induction in the illustrated example, suitable to prevent quenching localized in each marginal zone 30, 33, 34, 35.

  It is also possible to temporarily heat, by induction in the example illustrated, the marginal zones of the central foot 1 after the cutting and while the quenching material has been quenched there as elsewhere, in which case the heating of the marginal zones has for the purpose of relaxing by localized annealing the stresses which could then appear at cutting because it was carried out at least partially on a quenched material.

  This temporary heating can be carried out still inside the stamping tool, before the middle foot 1 is extracted, in which case it advantageously uses a punch 27 equipped for this purpose in the manner described in FIG. which has just been described if a unique punch-matrix set performs shaping, accompanied by quenching, and cutting; if the stamping tool comprises two separate punch-matrix assemblies, it is the punch of the assembly performing the cutting which is equipped for this purpose with localized temporary heating means, for example by induction, as described in relation to with the punch 27 which it advantageously takes up the design and conformation, at least in the zones 31, 36, 37, 38 of its face 28 corresponding to the marginal zones 30, 33, 34, 35.

  However, if one opts for such a temporary heating of the marginal zones of the central foot 1 after cutting it along its outer contour 42 and each of its inner contours 22, 24, 26, it is preferred to practice this temporary heating outside the stamping tool, to release it for a new stamping.

  Then, the punch 27 and the matrix 29 constituting the stamping tool in the illustrated example, as well as the punch and the die of each of the two punch-die assemblies constituting this tool in a manner not illustrated, are deprived of the means used. for this heating, namely in the example illustrated the induction heating circuits 32, 39, 40, 41, and, after mutually separating the die 29 and the punch 27 and cleared the foot-medium 1 embossed, transferring the one on another treatment tool, which can be a simple transport vehicle to another workstation or a tool for performing another operation on the foot-medium 1, and this tool has for this purpose a face reproducing the geometry of the forming face 28 at least in the areas 31, 36, 37, 38 thereof.

  In each of these zones corresponding to zones 31, 36, 37, 38, the tool has localized heating means, which may be induction circuits identical to circuits 32, 39, 40, 41, respectively, to cause heating. desired localization of the marginal zones 30, 33, 34, 35 of the central foot 1, the quenching material of which is then completely soaked, in order to remove the quench exclusively in these marginal zones 30, 33, 34, 35.

  Such a tool has not been illustrated in FIG. 1, but a person skilled in the art will readily deduce the design from the design described with regard to punch 27.

  It is understood that the choice of the manufacture of a foot-medium 1 as a part that can be manufactured by the embossing method according to the invention, by means of the stamping tool or the tool separate treatment that has just been described, is only a non-limiting example, and a skilled person will adapt without difficulty, to the manufacture of other metal parts, from a blank made at least partially in a quenching material, the arrangements that have just been described without departing from the scope of the present invention. Such a person skilled in the art will also easily understand that, while the equipment of a stamping punch, furthermore provided with cooling means, has been described exclusively in localized temporary heating means, it would also be possible to equip a stamping die and any other tool used either to proceed, during stamping, the shaping and / or cutting of the manufactured part, or to treat in any way the piece after it has been cleared from the stamping tool.

Claims (9)

  1. Method of manufacturing, by stamping, a metal part (1) having a determined shape and a determined outline, inside (22, 24, 26) and / or outside (42), from a blank made at less partially in so-called soaking material, said method comprising a succession of steps of: a) heating the blank to a first temperature, suitable for subsequent quenching said material, b) placing the blank in a stamping tool (28 29) adapted to set it to said determined shape and to cut it according to said determined contour (22, 24, 26, 42), the stamping tool (28, 29) having a second determined temperature lower than said first temperature determined and such that the contact of the blank with the stamping tool is likely to cause the quenching of said material, c) proceed to the stamping of the blank by means of the stamping tool (28, 29), to put the blank to said form of complete, by causing the quenching of said material, and cutting it according to said determined contour (22, 24, 26, 42), to separate said workpiece (1), d) to release said workpiece (1) from the embossing tool (28, 29), characterized in that, during step c or after step d, a temporary heating of the blank or said workpiece (1) is carried out, respectively, in a closely localized manner in a zone bordering on said determined contour (22, 24, 26, 42) and corresponding to a marginal zone (30, 33, 34, 35) of said workpiece (1), for maintaining or temporarily bringing said zone to a temperature of its own to reduce the stresses that may result from a combination of quenching and cutting.   2. The manufacturing method according to claim 1, characterized in that said induction heating is induced.   3. Manufacturing method according to any one of claims 1 and 2, characterized in that said temporary heating is caused during step c, preferably immediately before cutting the blank according to said determined contour (22, 24). , 26, 42).   4. The manufacturing method according to any one of claims 1 and 2, characterized in that said temporary heating is caused after step d, temporarily placing said piece in a subsequent processing tool thereof.   5. Drawing tool, by stamping, of a metal part having a determined shape and a determined contour (22, 24, 26, 42), inside (22, 24, 26) and / or outside (42), from a blank made at least partially of a said soaking material, said tool (28, 29) having a shape complementary to said determined shape, at least in a zone (31, 36, 37, 38) along said determined contour (22); , 24, 26, 42) and corresponding to a marginal zone (30, 33, 34, 35) of said part (1), means for cutting the blank according to said determined contour (22, 24, 26, 42) and / or internal cooling means, characterized in that it comprises heating means (32, 39, 40, 41) closely located in said zone (31, 36, 37, 38) along said determined contour (22, 24, 26, 42) and corresponding to a marginal zone (30, 33, 34, 35) of said part (1).   6. Manufacturing tool according to claim 5, characterized in that the heating means (32, 39, 40, 41) are induction heating means.   7. Tool for treating a stamped metal part, having a given shape and a defined contour (22, 24, 26, 42), interior (22, 24, 26) and / or outside (42), and constituted at least partially of a hardened material, characterized in that it comprises at least one zone (31, 36, 37, 38) having a shape complementary to that of a marginal zone (30, 33, 34, 35) of said part (1), following said determined contour (22, 24, 26, 42), and heating means (32, 39, 40, 41) closely located in said zone (31, 36, 37, 38).   8. Treatment tool according to claim 7, characterized in that the heating means (32, 39, 40, 41) are induction heating means.   A stamped metal part having a given shape and a defined contour (22, 24, 26, 42), interior (22, 24, 26) and / or external (42), and at least partially made from a said soaking material, characterized in that said material is quenched except in a marginal zone (30, 33, 34, 35) of said piece (1), along said contour (22,24,26,42).