EP1206983B1 - Method and device for notching a tube of a frame for a vehicle seat, especially a tube of a headrest frame - Google Patents

Description

The present invention relates to a method and a device for locking a reinforcing tube for a motor vehicle seat, in particular a headrest reinforcement tube.

It is particularly but not limited to head restraints adjustable in height and having several notches distributed longitudinally on at least one reinforcing tube, each notch defining a setting position. A conventional type of head restraint comprises a frame formed for example of an inverted U-shaped curved tube, each leg of the U constituting a rod slidable in a guide integral with the seat back, for positioning the headrest according to the wishes of the user. To maintain the selected adjustment position, locking systems such as a spring latch engaging with notches of one or both of the head restraint rods are commonly used.

Moreover, to prevent the headrest from descending in the event of a major effort of the head of the user, during an accident for example, it is known to achieve the setting notches with a substantially orthogonal upper sidewall in the longitudinal direction of the headrest rod, to constitute a positive abutment opposing sliding down, unless the headrest is unlatched voluntarily. The lower side of the notch is preferably inclined to facilitate the movement of the headrest upwards, without being blocked by the locking latch.

Also, an extreme lower notch can be made with an abrupt lower flank, to form a positive stop opposing an involuntary extraction the head restraint out of its guides when it is pulled up, except after a voluntary unlocking.

As can be seen on the headrest reinforcement tube shown in FIG. 1, it is therefore possible to have a plurality of notches located towards the front or towards the rear of the headrest, and these notches may have, according to FIG. intended application, several configurations: an abrupt upper flank and an inclined lower flank or an abrupt lower flank and an inclined upper flank, or two steep sides.

The realization of these notches on solid metal rods can be done easily by punching or stamping. But, to reduce the weight of these headrest frames, we try to use reinforcements made from tube. The realization of notches on such a tube by a simple transverse stamping inevitably causes crushing deformation of the tube. This does not make it possible to obtain, for the flanks of the notches that one wishes to be as much as possible at a sharp angle, the desired sharp angles.

To try to solve this problem, it has already been proposed to perform a machining of a preform previously obtained by stamping. But this method, in addition to the additional cost of machining, leads to removing the material and thus to weaken the tube at the notches.

It has also already been proposed, for example by DE 29714315, to introduce into the tube, in the zone where the notches must be formed, a sleeve or a metal rod to locally fill the tube and thus allow the realization of notches by stamping, as would be done on a solid rod. But the use of this sleeve reported strike the weight, and further it is necessary to ensure the proper positioning of the sleeve in the front tube stamping, which creates additional problems.

It has also been proposed to perform notches by hydroforming, but this method requires specific and very expensive means to generate the very high pressures required.

Also known from EP 974409, a method for performing on tubes a notching at sharp angle without removal of material, and aimed at keeping substantially constant thickness of the tube at the notches and the arrangement of the metal fibers, and without deformation of the tube at a distance from the notches. This method consists in using a riveting machine on which a tool for forming notches is fitted as a tool. The notch is then achieved by the hammering exerted by the machine, which leads to a gradual shaping of the notches, allowing the realization of relatively sharp angles, because each tool stroke deforms the material only very locally and with a small amplitude. But this method has the disadvantage of requiring a relatively long operation time to achieve each notch.

The present invention aims to solve the problems mentioned above and aims to provide a method and a tube notching machine that is simple to implement and allows to ensure economically the realization of notches sharp angles on tubes. It is particularly intended to be able to achieve on tubes, generally of substantially circular section, a notch which at least one face of the notches has a sharp angle with the outer surface of the tube wall. It aims to be able to achieve these notches without removing material, and without deforming the outer section of the tube, in particular to not interfere with the sliding of the tube in a guide.

It also aims to obtain said notching without excessive reduction of the thickness of the wall at the level of the notch and its vicinity, seeking to satisfy the desire for a substantially constant thickness, or even greater than the bottom of the notch, to ensure the best mechanical strength of the armature in the event of heavy efforts on the notches.

The invention is particularly but not exclusively intended to achieve notches commonly called anti-sag or anti-ejection notches in a headrest support frame, benefiting from the reduced weight possible through the use of a tube for to achieve the said armature, and without harming the strength and reliability of this frame.

With these objectives in view, the subject of the invention is a method of notching a reinforcing tube for a motor vehicle seat, in particular a headrest reinforcement tube, a method according to which the tube is produced on the tube at least one notch having at least one locking flank transverse to the longitudinal direction of the tube and forming a sharp angle with the outer surface of the tube.

• on maintient le tube, dans la zone environnant le cran à former, enserré entre des mors de serrage définissant une surface de serrage de forme cylindrique enveloppant la périphérie du tube,
• on utilise un poinçon guidé à travers les mors selon une direction de travail concourante avec l'axe de la surface de serrage et inclinée par rapport au dit axe d'un angle de travail prédéterminé compris entre environ 15° et environ 45°, l'extrémité du poinçon comportant une dent de formage du cran, qui présente une face d'attaque parallèle au dit flanc de verrouillage du cran à réaliser, une face arrière qui s'étend dans un plan incliné par rapport à l'axe du tube, et une face frontale reliant la face d'attaque à la face arrière, l'intersection de la face d'attaque et de la face frontale constituant une arête d'attaque,
• et on exerce sur le poinçon un effort de poinçonnage apte à faire pénétrer la dent dans la paroi du tube, selon la dite direction de travail, jusqu'à ce que l'arête d'attaque ait pénétré dans le tube d'une distance radiale égale à la profondeur du cran à réaliser.

According to the invention, this method is characterized in that:

• the tube is held in the area surrounding the notch to be formed, sandwiched between clamping jaws defining a cylindrical clamping surface surrounding the periphery of the tube,
• a guided punch is used through the jaws in a concurrent working direction with the axis of the clamping surface and inclined with respect to said axis by a predetermined working angle of between about 15 ° and about 45 °; end of the punch having a tooth forming the notch, which has a leading face parallel to said locking flank of the notch realize, a rear face which extends in a plane inclined relative to the axis of the tube, and a front face connecting the leading face to the rear face, the intersection of the leading face and the face frontal constituting a leading edge,
• and the punch is exerted on a punching force capable of causing the tooth to penetrate into the wall of the tube, in the said direction of work, until the leading edge has penetrated into the tube by a radial distance equal to the depth of the notch to be made.

Thus, thanks to the method according to the invention, and in particular thanks to the inclination of the direction of movement of the punch relative to the axis of the tube, it is possible to achieve a notch as desired in the tube, ie having a sufficiently sharp angle with the outer surface of the tube, and this simply and quickly, in a single drawing operation.

In general, when using the headrest, the steep side of the rod cooperates with the latch to ensure reliable locking of the headrest and, for this purpose, the inclination of this steep flank relative to the axis of the headrest rod is about 90 °, ie for example between 80 and 100 °. But, to make the locking even more reliable, this flank can even form with the generatrix of the rod on which the notch is made an acute angle, for example up to 70 ° or even less. Such an acute angle, which would be difficult to obtain by known methods, can be easily achieved by the method according to the invention.

The working angle between 15 and 45 °, and preferably between 30 ° and 40 °, makes the penetration of the tool in the metal of the tube is made in a direction sufficiently inclined so that there is no crushing effect of the tube, or at least almost negligible compared to the crushing that would occur if the punching was performed in a direction perpendicular to the axis of the tube. During the penetration of the leading edge into the metal of the tube, this metal is forced towards the inside of the tube, but because the pressure is exerted in a direction relatively close to the axial direction of the tube, the Inward discharge effect is relatively less than the axial spinning effect of the metal produced by the punch leading face.

Note in this regard the importance of clamping the tube, all around it, not only to avoid, obviously, an axial displacement under the effect of the stamping force, but also to prevent deformation of swelling of the tube around the stamped area.

The leading edge is rectilinear, insofar as the leading face and the front face are themselves flat, to form a locking flank and a notch bottom themselves planar. However, it could be expected to similarly realize flanks and non-planar notches funds, adapting the shape of the leading and front faces of the punch forms desired for the flanks of the notch.

It will also be noted that, preferably, the leading edge is formed of a radius radius of less than 0.8 mm, more preferably of the order of 0.2 mm. This rounding makes that the leading edge does not shear the stamped metal, but instead tends to push it back under the front face, the rounded sliding somehow on the deformed area as the progress of the tool.

The inclination of the rear face relative to the direction of work is preferably between 0 ° and said working angle and still preferably of the order of 20 °. The value of this angle has two effects. Firstly, it determines the inclination of the side of the notch opposite the steep side, and must therefore respect the constraints resulting from the locking system, so as not to hinder the movement of the head restraint in the authorized direction, as it has previously indicated. Secondly, the inclination of the rear face influences the stamping operation itself. Indeed, depending on this inclination relative to the direction of movement of the punch, the rear face of the punch tooth has a direct effect of drawing more or less accentuated. For example, if the angle of inclination is 0 °, the rear face of the tooth will simply be guided by sliding against the inclined flank portion formed, without causing specific deformation. If, on the contrary, the angle of inclination is relatively large, and particularly if it is close to the working angle, the rear face will participate directly in the deformation of the metal by pushing back the portion of wall of the tube which will form the said inclined side of the notch, and goes by the other by the reactive force resulting, tend to push the punch forward, ie in the direction of advance of the punch .

It is the combination of the effects of these different angles that finally leads to the notch being formed without crushing the tube around the said notch, and thus forming an angle as close as possible between the locking flank and the cylindrical wall of the tube.

The front face of the tool is preferably flat and substantially parallel to the axis of the clamping surface, to form a notch bottom substantially parallel to the axis of the tube. However, we can also, if need, realize this face with a predetermined shape and in particular with a certain inclination with respect to the axis of the tube. At the limit, the front face could be almost removed, or somehow confused with the back side, to form then a notch of triangular profile.

According to a particular embodiment of the invention, to produce a notch comprising two sharp-edged flanks, the forming operations of the notch are renewed by inverting the working angle, symmetrically with respect to a plane orthogonal to the axis of the tube, and so that the front face of the tooth arrives during the second operation at the bottom of the notch formed by the end face during the first forming operation.

If the front face of the tooth is small relative to the length of the notch, it may remain after the two previous operations, in an intermediate zone between the two formed notches, a medially insufficiently stamped area. We can then finish the shaping of the bottom of the notch by a punch moved perpendicular to the axis of the tube and whose end face is shaped according to the desired shape of the bottom of the notch.

To make several notches on the tube, we can use a single set of clamping jaws and punch, and perform the notches one after the other, moving the tube from one position to another relative to the jaws of clamping, for example by means of an automated positioner. It is also possible to perform on the tube simultaneously several notches, using a machine equipped with several punches.

The invention also relates to a reinforcing tube for a motor vehicle seat, in particular a headrest reinforcement tube, characterized in that it is provided with a sharp angle notch obtained by the method mentioned above, without removal of material, and without deformation of the outer section of the tube

• des mors de serrage définissant une surface de serrage de forme cylindrique enveloppant la périphérie du tube, pour enserrer le tube dans la zone environnant le cran à former,
• un poinçon guidé à travers les mors selon une direction de travail concourante avec l'axe de la surface de serrage et inclinée par rapport au dit axe d'un angle de travail prédéterminé compris entre 15° et 45°, l'extrémité du poinçon comportant une dent de formage du cran, qui présente une face d'attaque parallèle au dit flanc de verrouillage du cran à réaliser, une face arrière qui s'étend dans un plan incliné par rapport à l'axe de la surface de serrage, et une face frontale reliant la face d'attaque à la face arrière, l'intersection de la face d'attaque et de la face frontale constituant une arête d'attaque,
• des moyens de commande pour exercer sur le poinçon un effort de poinçonnage apte à faire pénétrer la dent dans la paroi du tube, selon la dite direction de travail.

The invention also relates to a device for locking a reinforcing tube for a motor vehicle seat, in particular a headrest reinforcement tube, characterized in that it comprises:

• clamping jaws defining a cylindrical clamping surface surrounding the periphery of the tube, for gripping the tube in the area surrounding the notch to be formed,
• a punch guided through the jaws in a direction of work concurrent with the axis of the clamping surface and inclined relative to said axis of a predetermined working angle of between 15 ° and 45 °, the end of the punch comprising a tooth forming the notch, which has a leading face parallel to said notch locking flank to be formed, a rear face which extends in a plane inclined relative to the axis of the clamping surface, and a front face connecting the leading face to the rear face, the intersection of the leading face and the front face constituting a leading edge,
• control means for exerting on the punch a punching force capable of penetrating the tooth into the wall of the tube, according to said working direction.

• la face d'attaque de la dent du poinçon forme avec l'axe de la surface de serrage un angle compris entre 70 et 100°.
• la face arrière de la dent du poinçon forme avec l'axe de la surface de serrage un angle compris entre 10° et la valeur de l'angle de travail.
• les mors de serrage comprennent un mors d'appui fixe et un mors de serrage mobile perpendiculairement à l'axe du tube et commandé par un vérin de serrage.
• un des mors est réalisé en deux parties jointives et comporte un trou de guidage du poinçon, formé par la combinaison de deux rainures réalisées respectivement dans les deux parties du mors au niveau du plan de joint entre les deux dites parties. Ce mode de réalisation permet de créer un trou de guidage de section par exemple rectangulaire, pour recevoir en coulissement une partie d'extrémité du poinçon, de section rectangulaire similaire, ce qui permet de réaliser simplement outil et mors de serrage en empêchant tout pivotement du poinçon autour de son axe.
• la dent de formage est réalisée proéminente par rapport à une face de bout du poinçon, la dite face de bout venant tangenter le tube en fin de course d'emboutissage du poinçon. La face de bout peut aussi présenter une concavité correspondant à la surface extérieure du tube, de manière à envelopper le tube autour du cran en fin de formage du dit cran, de manière à repousser les éventuels gonflements localisés qui auraient pu apparaître suite à l'emboutissage, pour s'assurer qu'au bout du compte il n'y ait aucune augmentation de la section du tube, en quelque zone que ce soit.

According to other special provisions:

• the leading face of the punch tooth forms with the axis of the clamping surface an angle of between 70 and 100 °.
• the rear face of the punch tooth forms with the axis of the clamping surface an angle of between 10 ° and the value of the working angle.
• the clamping jaws comprise a fixed support jaw and a movable jaw perpendicular to the axis of the tube and controlled by a clamping jack.
• one of the jaws is made in two contiguous parts and comprises a punch guide hole, formed by the combination of two grooves respectively formed in the two parts of the jaw at the joint plane between the two said parts. This embodiment makes it possible to create a guide hole of rectangular cross-section, for example, to slidably receive an end portion of the punch, of similar rectangular section, which makes it possible to simply produce a tool and a jaw by preventing any pivoting of the punch around its axis.
• the forming tooth is made protruding with respect to an end face of the punch, said end face coming tangentially to the tube at the end of the drawing stroke of the punch. The end face may also have a concavity corresponding to the outer surface of the tube, so as to wrap the tube around the notch at the end of forming the said notch, so as to repel any localized swelling that may have occurred following the stamping, to ensure that at the end there is no increase in the section of the tube, in any area whatsoever.

Other features and advantages will become apparent in the description which will be made of a device and a method of notching a headrest reinforcement tube, according to the invention.

• la figure 1 est une vue en perspective d'une armature tubulaire d'appuie-tête réalisée par le procédé de l'invention,
• la figure 2 est un schéma de principe du procédé de l'invention pour réaliser un cran d'une telle armature,
• la figure 3 est un autre schéma illustrant la réalisation d'un cran comportant deux flancs opposés orthogonaux à l'axe du tube,
• la figure 4 est une vue simplifiée d'une machine conforme à l'invention pour la réalisation de crans sur une armature tubulaire,
• la figure 5 est une vue en coupe longitudinale du poinçon d'emboutissage,
• la figure 6 est une vue frontale du poinçon, selon la flèche F1 de la figure 5,
• la figure 7 est une vue de l'extrémité du poinçon, selon la flèche F2 de la figure 5,
• la figure 8 est une vue en perspective partielle de l'extrémité du poinçon,
• la figure 9 est une vue en perspective des mors de serrage du tube,
• la figure 10 est une vue frontale des mors enserrant le tube, au cours de l'emboutissage.

Reference is made to the accompanying drawings in which:

• FIG. 1 is a perspective view of a tubular head restraint made by the method of the invention,
• FIG. 2 is a schematic diagram of the method of the invention for producing a notch of such an armature,
• FIG. 3 is another diagram illustrating the production of a notch comprising two opposite flanks orthogonal to the axis of the tube,
• FIG. 4 is a simplified view of a machine according to the invention for producing notches on a tubular reinforcement,
• FIG. 5 is a longitudinal sectional view of the stamping punch,
• FIG. 6 is a front view of the punch, along arrow F1 of FIG. 5,
• FIG. 7 is a view of the end of the punch, along the arrow F2 of FIG. 5,
• FIG. 8 is a partial perspective view of the end of the punch,
• FIG. 9 is a perspective view of the clamping jaws of the tube,
• Figure 10 is a front view of the jaws enclosing the tube, during the stamping.

The armature 1 of the head restraint shown in FIG. 1 is formed of a steel tube, for example of the E36 type, having a breaking strength of 400 MPa and an elongation of 22%, and a diameter of 14 mm and greater. 2 mm thick. The tube is bent U-shaped having two branches 11 which constitute the holding rods and guide the headrest, sliding and lockable in a manner known per se in guides integral with the back of a motor vehicle seat. Each rod comprises notches 12, which have an abrupt upper flank 13, located substantially in a plane perpendicular to the axis of the rod, a bottom 14, substantially plane and parallel to the axis, and a lower flank 15 slightly inclined by relation to the said axis. On one of the branches, there is also a notch 16 of the same direction but located on the diametrically opposite side of the tube, and a lower notch 17, inverted with respect to other notches. The arrangement of the notches in FIG. 1 is given for illustrative purposes only and in no way limiting.

• une face d'attaque 22, située dans un plan faisant un angle α2 compris entre 70° et 100°, par exemple 90° dans l'exemple représenté, par rapport à l'axe A du tube 1.
• une face frontale 23, sensiblement parallèle à l'axe A,
• une face arrière 24, inclinée par rapport à l'axe B d'un angle α3 compris entre 0° et la valeur de l'angle α1.

2 schematically illustrates the production of a notch such as the notch 12, by a punch 2, movable in the direction of its axis B inclined relative to the axis of the tube of a working angle α1, by example of 35 °, and whose end forms a tooth 21 which has:

• a leading face 22, situated in a plane making an angle α2 between 70 ° and 100 °, for example 90 ° in the example shown, with respect to the axis A of the tube 1.
• a front face 23, substantially parallel to the axis A,
• a rear face 24, inclined relative to the axis B by an angle α3 between 0 ° and the value of the angle α1.

The notch 12 is made by pushing the punch 2, for example by means of a hydraulic jack, in the direction of the arrow F, until the edge 25 formed by the intersection of the leading face 22 and the front face 23 has penetrated into the tube a radial distance equal to the desired depth of the notch. This edge is shaped rounded radius less than 0.8 mm, preferably equal to 0.2 mm.

During the advance of the punch, the edge 25 penetrates into the metal of the wall of the tube, in the direction of the arrow F, the leading face 22 gradually pushing the metal in front of it to form the end of the race. steep side 13, while allowing the flow of said metal to the front face 23, which forms at the end of the race the bottom 14 of the notch. Simultaneously, the inclined flank 15 is shaped by the rear face 24 of the tooth.

In the case illustrated in FIG. 3, the notch 18 with two steep sides is formed in two successive operations, the first being illustrated by the dotted line 31 of the tool, inclined with respect to the axis of the tube of the angle α1, to form the first flank 18 'and the second, illustrated by the solid pattern 32, inclined with respect to a plane orthogonal to the tube symmetrically, to form the second flank 18' '. To finish the bottom of the notch, a third stamping operation can be performed by a tool 33 moved perpendicularly to the tube.

The machine shown in FIG. 4 comprises a frame 40 which comprises a punching head 41 and a clamping assembly vertically movable relative to the frame 40 and controlled by a clamping jack 43. The frame 40 carries fixed clamping jaws 52, such as the jaws shown in Figures 9 and 10 which will be described later. The movable clamping assembly carries movable clamping jaws 51. The punching head comprises an axially guided punch 6 controlled by a hydraulic jack 42. One end of the punch passes through the clamping jaw 52, in which it is guided. sliding in the direction of work F and immobilized in rotation.

The punch 6 used in the machine of Figure 4 is shown in Figures 5 to 8. It comprises a body 61, one end 62 is arranged in known manner to be connected to the control cylinder 42. To the other end, the body comprises a guide portion 63 of rectangular section which ends with an end face 64, inclined at a working angle α1 = 35 ° relative to the axis B of the punch. The forming tooth 21 of the notch is prominent with respect to the face 64 and extends over the entire width of this face, for example 11 mm, this width being furthermore determined so as to correspond to the width that the finished notch will have.

The clamping jaws, shown in Figure 9 in the inverted position relative to the representation of Figure 4, comprise a movable jaw 51 and a fixed jaw 52 made in two parts 52a and 52b separated by a joint plane 55. The movable jaw 51 is fixed on the movable clamping assembly, and the fixed jaw 52 is fixed on the frame 40 of the machine.

The jaw 51 has a recessed half-cylindrical shape 53, and each part of the fixed jaw 52 has a hollow shape 54 in a quarter-cylinder, so that when the two parts of the jaw 52 are joined together at the joint plane 55 and that the movable jaw is brought in front of all of the two fixed jaw parts, the surfaces of the hollow forms 53 and 54 constitute a cylindrical surface of the same section as the tube 1, and able to energetically grip said tube under the action of the clamping cylinder 43, to immobilize it completely during the formation of the notches.

The rectangular section of the punch is guided in a hole of corresponding section, consisting of the combination of two grooves 56 formed respectively in each part of the fixed jaw 52, the rectangular section avoiding any risk of pivoting of the punch about its axis.

The implementation of the machine for the realization of a notch will be readily deduced from the foregoing. The movable jaw 51 being lifted by the jack 43, it is sufficient to position the tube 1 in the hollow form of the lower jaw. The tube is then tightened by actuating the clamping cylinder 43. Then the actuator 42 acting on the punch is controlled so as to make the tooth of the punch penetrate into the wall of the tube until the desired depth, generally defined by the height of the tooth, which therefore corresponds to bringing the end face 64 of the punch tangent with the tube. It then controls the withdrawal of the punch, and then the spacing of the jaws, and we can then move the tube to achieve another notch or set up another tube.

The invention is not limited to the embodiment described above solely by way of example

In the example shown, the end face 64 is flat, which facilitates the realization of the active end of the punch. It is also possible to make this concave face to better fit the outer surface of the tube, as has already been explained.

Also, the shapes and dimensions of the guided end of the punch and the tooth can be modified, to adapt to the dimensions and materials of the tube, without departing from the scope of the invention as defined in the claims.

Claims (12)

1. Process for notching a support tube (1) for an automobile vehicle seat, and more particularly a headrest support tube, by which at least one notch (12) is made in the tube, this notch featuring at least one locking edge (13) perpendicular to the longitudinal direction (A) of the tube and forming a sharp edge with the external surface of the tube,
      characterized in that:

   - the tube (1) is gripped in the area surrounding the notch to be formed between clamping jaws (51, 52) defining a cylindrical clamping surface (53, 54) enclosing the periphery of the tube,

   - a punch (6) is guided across the jaws in a working direction (B) that converges with the axis (A) of the clamping surface and is angled with respect to the said axis at a predetermined working angle (α1) of between approximately 15° and 45°, with the tip (63) of the punch featuring a notch forming tooth (21) with a working face (22) parallel to the locking edge of the notch to be made, a rear face (24) that extends along a plane inclined with respect to the tube axis, and a front face (23) joining the working face and the rear face, with the intersection between the working face and the front face forming a working edge (25),

   - and a punching force is applied to the punch such that the tooth (21) penetrates the tube wall in the said working direction until the working edge has penetrated the tube by a radial distance equal to the depth of the notch to be produced.
2. Process in accordance with claim 1, characterized in that the working angle (α1) is between 30° and 40°.
3. Process in accordance with claim 1, characterized in that the angle (α3) of the rear face (24) with respect to the said working direction (B) is between 0° and the said working angle (α1).
4. Process in accordance with claim 1, characterized in that to make a notch (18) featuring two square edges, the notch forming operations are repeated by reversing the working angle symmetrically with respect to a plane orthogonal to the tube axis, and such that in the second operation the front face (23) of the tooth reaches the bottom of the notch (18) formed by the front face during the first forming operation.
5. Process in accordance with claim 4, characterized in that the forming of the notch bottom is finished using a punch (33) that moves perpendicularly to the tube axis and whose end face profile corresponds to the desired form of the bottom of the notch (18).
6. Device for notching a support tube for an automobile vehicle seat, and more particularly a headrest support tube, characterized in that it comprises:

   - clamping jaws (51, 52) defining a cylindrical clamping surface (53, 54) enclosing the periphery of the tube (1), to grip the tube in the area surrounding the notch (12) to be made,

   - a punch (6) guided across the jaws in a working direction (B) that converges with the axis (A) of the clamping surface and is angled with respect to the said axis at a predetermined working angle (α1) of between 15° and 45°, with the tip of the punch featuring a notch forming tooth (21) with a working face (22) parallel to the locking edge of the notch to be made, a rear face (24) that extends along a plane inclined with respect to the tube axis, and a front face (23) joining the working face and the rear face, with the intersection between the working face and the front face forming a working edge (25),

   - control means (42) to apply a suitable punching force to punch (6) to make tooth (21) penetrate the tube wall in the said working direction.
7. Device in accordance with claim 6, characterized in that the working face (22) of the tooth (21) of the punch (6) forms an angle (α2) of between 70 and 100° with the axis (A) of the clamping surface (53, 54).
8. Device in accordance with claim 6, characterized in that the rear face (24) of the tooth (21) of the punch (6) forms an angle of between 0° and the value of the working angle (α1) with the axis (A) of the clamping surface.
9. Device in accordance with claim 6, characterized in that the clamping jaws comprise a fixed jaw (52) and a moving jaw (51) perpendicular to the axis (A) of the tube and controlled by a clamping actuator (43).
10. Device in accordance with claim 9, characterized in that one of the jaws is made in contiguous two sections (52a, 52b) and features a hole to guide the punch (6), formed by the combination of two grooves (56) made in the two sections of the jaw, in the joining plane (55) between the said two parts.
11. Device in accordance with claim 10, characterized in that the tooth (21) protrudes with respect to an end face (64) of the punch, the said end face meeting the clamping surface at a tangent when the punch reaches end of travel after the drawing operation.
12. Device in accordance with claim 11, characterized in that the end face (64) has a concave profile corresponding to the clamping surface.