VARIABLE-THICKNESS EXTRUSION METHOD AND EXTRUSION UNIT IN ACCORDANCE WITH SAID METHOD

Description

[0001] The present invention relates to an innovatory method of variable-thickness extrusion and to an extrusion unit applying said method.

[0002] Known in the prior art is an extrusion method identified as "impact extrusion", in which the slug or blank to be extruded is placed in a closed-bottom die and a punch is forced to penetrate into the blank so as to compress the material and cause it to flow into the annular space existing between the die and punch, thereby generating a piece having a cylindrical wall of constant thickness.

[0003] To make collapsible casings of very soft metal such as lead, for producing toothpaste tubes for example, in US 1,702,278 the die bottom has been proposed to be made movable. The relative movement of the punch and die bottom (the latter embodied as a counter-punch) enables very elongated products like toothpaste tubes to be extruded.

[0004] In this case too, the obtained article has a constant diameter and walls of constant thickness.

[0005] CH 633 980 discloses an extrusion device, wherein the counter-punch is supported by a spring in order to soften the raugh strain fluctuations connected with the metal flow in the extrusion chamber.

[0006] The general object of the present invention is to provide a method and an extrusion unit applying said method which enable articles having walls of variable thickness to be obtained.

[0007] This is particularly advantageous for making cartridge cases where the area which is the closest to the bottom undergoes the strongest stresses on bursting of the charge.

[0008] In the known art there was nothing suggesting the possibility of obtaining articles having walls of variable thickness, by extrusion. By the method in accordance with the invention thickness variations can be achieved both inwardly and outwardly of the extruded body.

[0009] In addition, it has been possible to ascertain that the invention enables extrusion of materials traditionally considered as unable to be extruded (non-extrusile materials), such as ferrous materials for example.

[0010] In view of the above objects, in accordance with the invention, a method of cold impact extrusion for hollow metal elements has been provided, according to claim 1.

[0011] In accordance with this method, a cold impact extrusion unit for hollow metal elements has been devised, according to claim 5.

[0012] For better explaining the innovatory principles of the present invention and the advantages it offers over the known art, possible embodiments of the invention applying said principles will be described hereinafter by way of example, with the aid of the accompanying drawings. In the drawings:

• Fig. 1 diagrammatically shows extrusion steps with a first extrusion unit in accordance with the invention;
• Fig. 2 diagrammatically shows extrusion steps with a second extrusion unit in accordance with the invention;
• Fig. 3 diagrammatically shows extrusion steps with a third extrusion unit in accordance with the invention;
• Fig. 4 is an enlarged view of a punch head.

[0013] With reference to the drawings, shown in Fig. 1a is a first embodiment of an impact extrusion unit, generally identified by 10 and made in accordance with the invention.

[0014] Unit 10 comprises a punch 11 and a counter-punch 12, facing each other and axially movable within a die 13, so as to identify an extrusion chamber 14 therebetween.

[0015] In an innovatory manner, the chamber within the die has a varying transverse size along the movement axis of the punch and counter-punch, unlike the known art in which the transverse size of the chamber is constant. For example, shown in Fig. 1 is a barrel-shaped chamber of a maximum transverse size intermediate the ends.

[0016] As shown in the drawings, the solution of making the punch with a head of greater diameter than the shank and a cone-shaped point has been found advantageous. This is clearly shown in Fig. 4, where a punch 11 is shown with a head 18 having a cone-shaped end 19 and a rear union length 20 for connection to a shank 21 of reduced section. For example, for a head of a 7.53 mm diameter the shank can have a 7.37 mm diameter, with a connecting conicity of 10° and a 0.50 mm thickness of the cylindrical portion of the head. The cone-shaped head enables accomplishment of a cone-shaped bottom which is advantageous in the case of cartridge cases.

[0017] According to the method of the invention, as shown in Fig. 1a, first the counter-punch is close to one entrance end of the punch into the die. A metal blank 15 to be extruded is introduced into the die and subsequently the punch is forced towards the counter-punch, while the latter is caused to move backward, as shown in Fig. 1b. The punch and couter-punch movements take place in the same direction but at different velocities (in particular the punch moves at a first velocity and the counter-punch at a second velocity smaller than the first one), so as to reduce the space between the respective faced heads and have an extrusion action between die and punch, whereas the relative flowing between the blank outside and the die is in favour of the extrusion operation. In particular, the relative velocity between the die side wall and the extruded material between die and punch must be substantially zero. This enables extrusion of metal materials that traditionally are unable to be extruded, such as iron for example. It is also possible to use lower extrusion pressures, thereby the unit being subjected to less wear. Obviously, the absolute movement velocities of the punch and counter-punch relative to the die will depend on the type of the extruded material and the mechanical features of the extrusion unit.

[0018] In accordance with the method, the extrusion annulus formed between the die and punch, has a varying thickness during the extrusion operation. In other words, the punch head is caused to pass through areas of the die having different radial widths.

[0019] As shown in Fig. 1c, once the extrusion stroke has been completed, punch and counter-punch are retracted and the die is opened in a transverse direction so as to free the extruded piece or extrusion.

[0020] Shown in Fig. 1c by way of example is an extrusion 16 the form of which is of variable diameter, which had been hitherto considered as unfeasible by extrusion.

[0021] A second embodiment 110 of an extrusion unit is shown in Fig. 2. The extrusion unit 110, in addition to the above mentioned steps of the claimed method also carries out a further step.

[0022] In the same manner as in the embodiment in Fig. 1, unit 110 is comprised of a punch 111 and a counter-punch 112, facing each other and axially movable within a die 113, so as to identify an extrusion chamber 114 therebetween. The chamber has varying transverse sizes along its axis. For instance, a chamber is shown which has a shape similar to the one already described above.

[0023] After introduction of a blank 115 into the die, the extrusion operation (Fig. 2b) takes place in the same manner as above disclosed.

[0024] Unlike the embodiment in Fig. 1, the die 113 has an end opening 117, from which the punch enters and which embodies the aperture for drawing the blank out. If opening 117 has a smaller width than the maximum width of the extrusion chamber, this opening constitutes the die for a second extrusion or forming operation, which is carried out on the blank when the punch is retracted and the counter-punch forces the blank out of the die (Fig. 2c). In other words, the method according to the invention may comprise the further step of drawing the punch out of the die and causing advance of the counter-punch so as to extrude the blank through a die end, which end therefore constitutes the forming end for a further extrusion operation of the forward type.

[0025] This further step makes it possible to reproduce within the blank the variation which was present in the outer transverse size of the blank itself, whereas the outer transverse size of the drawn blank will be constant and equal to the extrusion opening 117.

[0026] In conclusion, an extruded piece 116 is obtained which has an inward variation in the wall thickness. Such a shaping has been hitherto deemed still more unfeasible by extrusion than shaping shown in Fig. 1.

[0027] Obviously, the chamber shape and consequently the resulting extrusion shape is not limited to the one shown by way of example.

[0028] For instance, a further embodiment of an extrusion unit 210 in accordance with the invention is shown in Fig. 3. The extrusion unit 210 comprises a punch 211, a counter-punch 212 and a die 213 identifying an extrusion chamber 214. The chamber has a varying transverse size along its axis getting bigger in a direction opposite to that of the punch, so as to form a truncated cone, for example. After completion of the extrusion operation as above described, the punch is drawn out and the counter-punch moves forward to extrude the blank through a drawing opening 217. Thus an extruded piece of cylindrical outer form is obtained, the wall of which becomes thicker towards the bottom.

[0029] At this point it is apparent that the intended purposes have been achieved by providing an extrusion method and extrusion units enabling an easy manufacture of extruded pieces the shapes of which have been hitherto considered as unfeasible.

[0030] It is also to point out that surprisingly with the method of the invention extrusions can be obtained even with metal materials traditionally judged as unable to be extruded, ferrous alloys for example.

[0031] It is obvious that the method of the invention is very advantageous for making cartridge cases. Actually, by a single working, cartridge cases with walls of varying thicknesses along the case axis are produced. Thus, as shown in Fig. 3, manufacture of cartridge cases in which a stronger wall is provided close to the area near their bottom, i.e. the blast-initiating area, is made possible. Similarly, particular conformations of the detonation chamber can be obtained, as shown in Fig. 2.

[0032] Since the method is carried into effect by a mere backward and forward movement of the punch and counter-punch, accomplishment of simple machinery having high production rates can be envisaged, so as to obtain a perfectly formed cartridge case during each machine cycle.

[0033] Obviously, the above description of embodiments applying the innovatory principles of the present invention is given by way of example only and therefore must not be considered as a limitation of the scope of the invention as herein claimed.

[0034] For example, movements between die, punch and counter-punch are obviously to be intended as relative movements, no matter which element is actually moved and which is maintained really stationary. In addition, the die may have a shape different from that shown and movements producing articles having an outwardly thickened portion and an inwardly thickened portion can be easily conceived.

Claims

1. A cold impact extrusion method for hollow metal elements, in particular cartridge cases, comprising the steps of placing a slug or blank in a die, pressing the blank within the die between a punch and a counter-punch facing each other, during compression the punch being caused to move forward in the die at a first velocity and the counter-punch being caused to move backward at a second velocity slower than the first one, so as to reduce the distance between the punch and counter-punch, during said movement causing the punch head to pass through die areas having different distances from the punch sides so as to identify an extrusion annulus of variable width between the die and punch.

2. A method as claimed in claim 1, comprising the further step of reversing the punch and counter-punch movement relative to the die, to draw the punch out of the die and force the blank, by means of the counter-punch, through the thus obtained opening, so as to extrude it from the die.

3. A method as claimed in claim 1, comprising the further step of transversely opening the die to draw the therein-extruded blank out of it.

4. A method as claimed in claim 1, in which there is such a ratio between the first and second velocities that the relative velocity between the die side wall and the extruded material between die and punch is maintained to a substantially zero value.

5. A cold impact extrusion unit intended to carry out the method according to claim 1, comprising a punch (11, 111, 211) and a counter-punch (12, 112, 212) facing each other and coaxially movable within a die (13, 113, 213) to identify an extrusion chamber (14, 114, 214) therebetween, the extrusion chamber (14, 114, 214) having a varying transverse size along the movement axis of the punch and counter-punch characterized by means for moving the punch forward in the die at a first velocity and moving the dounter-punch backward at a second velocity slower than the first one, so as to reduce the distance between the punch and counter-punch, during said movement causing the punch head to pass through die areas having different distances from the punch sides so as to identify an extrusion annulus of variable width between the die and punch.

6. A unit according to claim 5, characterized in that the die can be transversely opened for drawing the therein-extruded piece out of it.

7. A unit according to claim 5, characterized in that the die (114, 214) has an end opening (117, 217) for introduction of the punch thereinto, said opening also embodying the aperture for drawing the extruded piece out, upon a thrust action by the counter-punch.

8. A unit according to claim 7, characterized in that the drawing opening (117, 217) has a smaller width than the maximum transverse size of the extrusion chamber.

9. A unit according to claim 5, characterized in that the' extrusion chamber has its maximum transverse width at a position intermediate its ends.

10. A unit according to claim 8, characterized in that the extrusion chamber has its maximum transverse width close to an end opposite to the drawing aperture.

11. A unit according to claim 1, characterized in that the punch (11, 111, 211) has a cone-shaped end (18, 118, 218) and a rear union length for connection to a shank (21, 121, 221) of reduced section relative to the head.

Ansprüche

1. Kalt-Schlagfließpressverfahren für hohle Metallelemente, insbesondere Patronenhülsen, umfassend die Schritte des Plazierens eines Kerns oder Rohlings in einer Form, des Pressens des Rohlings in der Form zwischen einem Stempel und einem Gegenstempel, die sich gegenüberliegen, wobei während des Pressens der Stempel in der Form mit einer ersten Geschwindigkeit vorwärts bewegt wird und der Gegenstempel mit einer zweiten Geschwindigkeit rückwärts bewegt wird, die langsamer als die erste ist, um den Abstand zwischen dem Stempel und dem Gegenstempel zu reduzieren und während der genannten Bewegung den Stempelkopf durch Formbereiche mit unterschiedlichen Abständen von den Stempelseiten hindurch zu bewegen, um ein extrudiertes Werkstück variabler Weite zwischen der Form und dem Stempel zu erzeugen.

2. Verfahren nach Anspruch 1, umfassend den weiteren Schritt der Umkehr der Stempel- und Gegenstempelbewegung relativ zur Form, des Herausziehens des Stempels aus der Form und des Hindurchdrückens des Rohlings durch die so erhaltene Öffnung, um ihn aus der Form zu extrudieren.

3. Verfahren nach Anspruch 1, umfassend den weiteren Schritt des seitlichen Öffnens der Form, um den darin extrudierten Rohling aus ihr herauszuziehen.

4. Verfahren nach Anspruch 1, bei dem ein solches Verhältnis zwischen der ersten und zweiten Geschwindigkeit vorhanden ist, daß die relative Geschwindigkeit zwischen der Seitenwand der Form und dem extrudierten Material zwischen der Form und dem Stempel auf einem Wert von im wesentlichen Null gehalten wird.

5. Kalt-Schlagfließpresseinheit zur Ausführung des Verfahrens nach Anspruch 1, umfassend einen Stempel (11, 111, 211) und einen Gegenstempel (12, 112, 212), die sich gegenüberliegen und innerhalb einer Form (13, 113, 213) koaxial bewegbar sind, um dazwischen eine Extrusionskammer (14, 114, 214) zu bilden, wobei die Extrusionskammer (14, 114, 214) unterschiedliche Querabmessungen längs der Bewegungsachse des Stempels und Gegenstempels aufweist, gekennzeichnet durch Mittel zum Vorwärtsbewegen des Stempels in der Form bei einer ersten Geschwindigkeit und zum Zurückbewegen des Gegenstempels bei einer zweiten Geschwindigkeit, die langsamer als die erste ist, um den Abstand zwischen dem Stempel und dem Gegenstempel zu reduzieren, wobei während dieser Bewegung der Stempelkopf durch die Formbereiche mit unterschiedlichen Abständen von den Stempelseiten hindurch bewegbar ist, um ein extrudiertes Werkstück veränderlicher Weite zwischen der Form und dem Stempel zu bilden.

6. Einheit nach Anspruch 5, dadurch gekennzeichnet, daß die Form zum Herausziehen des darin extrudierten Werkstücks in Querrichtung geöffnet werden kann.

7. Einheit nach Anspruch 5, dadurch gekennzeichnet, daß die Form (114, 214) eine Endöffnung (117, 217) zum Einführen des Stempels hat, wobei die Öffnung auch die Öffnung zum Herausziehen des extrudierten Werkstücks nach einer Druckausübung durch den Gegenstempel verkörpert.

8. Einheit nach Anspruch 7, dadurch gekennzeichnet, daß die Ausziehhöffnung (117, 217) eine kleinere Weite als die maximale Querabmessung der Extrusionskammer hat.

9. Einheit nach Anspruch 5, dadurch gekennzeichnet, daß die Extrusionskammer ihre maximale Querabmessung in einer Position zwischen ihren Enden hat.

10. Einheit nach Anspruch 8, dadurch gekennzeichnet, daß die Extrusionskammer ihre maximale Querabmessung in der Nähe eines Endes hat, das der Ausziehöffnung gegenüberliegt.

11. Einheit nach Anspruch 1, dadurch gekennzeichnet, daß der Stempel (11, 111, 211) ein konisch geformtes Ende (18, 118, 218) und einen hinteren Verbindungsabschnitt zu einem Schaft (21, 121, 221) mit einem geringeren Querschnitt als der Kopf hat.

Revendications

1. Procédé d'extrusion à froid par choc pour des éléments métalliques creux, en particulier des boîtiers de cartouches, comprenant l'étape consistant à placer un manchon ou un flan dans une matrice, à presser le flan à l'intérieur de la matrice entre un poinçon et un contre-poinçon dirigés vers l'autre, pendant la compression à commander le déplacement en avant du poinçon dans la matrice à une première vitesse et le déplacement en arrière du contre-poinçon à une seconde vitesse inférieure à la première vitesse de manière à réduire la distance entre le poinçon et le contre-poinçon, pendant ledit mouvement à faire passer la tête de poinçon à travers des zones de la matrice se trouvant à différentes distances par rapport aux côtés du poinçon de manière à définir un anneau d'extrusion de largeur variable entre la matrice et le poinçon.

2. Procédé selon la revendication 1, comprenant l'étape supplémentaire consistant à inverser le mouvement du poinçon et le mouvement du contre-poinçon par rapport à la matrice, pour retirer le poinçon de la matrice et forcer le flan, au moyen du contre-poinçon, à passer par l'ouverture ainsi obtenue, de manière à l'extruder de la matrice.

3. Procédé selon la revendication 1, comprenant l'étape consistant à ouvrir transversalement la matrice pour retirer le flan extrudé à l'intérieur.

4. Procédé selon la revendication 1, dans lequel le rapport entre la première vitesse et la seconde vitesse est tel que la vitesse relative entre la paroi latérale de la matrice et la matière extrudée entre la matrice et le poinçon est maintenue à une valeur sensiblement nulle.

5. Unité d'extrusion à froid par choc destinée à mettre en oeuvre le procédé selon la revendication 1, comprenant un poinçon (11, 111, 211) et un contre-poinçon (12, 112, 212) dirigés l'un vers l'autre et mobiles coaxialement à l'intérieur d'une matrice (13, 113, 213) pour délimiter une chambre d'extrusion (14, 114, 214) ayant une taille transversale variable le long de l'axe de mouvement du poinçon et du contre-poinçon, caractérisée par des moyens pour déplacer en avant le poinçon dans la matrice à une première vitesse et déplacer en arrière le contre-poinçon à une seconde vitesse inférieure à la première vitesse, de manière à réduire la distance entre le poinçon et le contre-poinçon pendant ledit mouvement pour commander la tête de poinçon de passer à travers des zones de la matrice se trouvant à distances différentes par rapport aux côtés du poinçon de manière à définir un anneau d'extrusion de largeur variable entre la matrice et le poinçon.

6. Unité selon la revendication 5, caractérisée en ce que la matrice peut être ouverte transversalement pour retirer la pièce extrudée à l'intérieur.

7. Unité selon la revendication 5, caractérisée en ce que la matrice (114, 214) présente une ouverture d'extrémité (117, 217) destinée à introduire le poinçon à l'intérieur, ladite ouverture incorporant également l'ouverture pour retirer la pièce extrudée, lors d'une action de poussée par le contre-poinçon.

8. Unité selon la revendication 7, caractérisée en ce que l'ouverture de retrait (117, 217) a une largeur inférieure à la taille transversale maximale de la chambre d'extrusion.

9. Unité selon la revendication 5, caractérisée en ce que la chambre d'extrusion a une largeur transversale maximale à une position intermédiaire entre ses extrémités.

10. Unité selon la revendication 8, caractérisée en ce que la chambre d'extrusion a sa largeur transversale maximale proche d'une extrémité opposée à l'ouverture de retrait.

11. Unité selon la revendication 1, caractérisée en ce que le poinçon (11, 111, 211) a une extrémité en forme de cône (18, 118, 218) et un tronçon de raccordement arrière destiné à se raccorder à une tige (21, 121, 221) de section réduite par rapport à la tête.

Drawing