Method for cold sizing a round workpiece having multiple diameters

Description

[0001] This invention relates to a method for cold sizing a workpiece having multiple diameters.

Background Art

[0002] Round metal parts are conventionally accurately sized after an initial turning operation by a subsequent grinding operation in order to provide the required tolerance for the application for which the workpiece is to be utilized. For example, universal joints for vehicle drives conventionally include a joint member having four round surfaces of cylindrical shapes that are coaxial about a central axis of the joint member and have different diameters. The largest round surface is utilized with a seal to provide sealing of the joint, while the next largest round surface supports a bearing that mounts the joint. Both of the two smaller round surfaces are subsequently formed with projections, the larger one with splines utilized to rotatively couple the joint and the smaller one with a thread used in securing the joint in position. Grinding of these round surfaces on such joint members is both time consuming and costly but has been necessary in the past to provide the required roundness for accommodating the seal and bearing utilized as well as for providing the required roundness prior to the spline and thread forming.

[0003] A cooperable pair of movable tools has also been utilized in the past to cold form noncylindri- cal workpieces. See, for example, US-A-419,292, US-A-446,934, US-A-1,446,447, US-A-1,469,174, US-A-3,044,332, US-A-3,466,918, US-A-3,498,095, and US-A-3,503,237 which disclose such forming.

[0004] Hot forming of an axle having round surfaces of cylindrical shapes with different diameters is disclosed by US-A-458,685 wherein a pair of straight tools are moved rectilinearly on opposite sides of the hot axle to provide the forming operation.

[0005] US-A-625,575 discloses a pair of straight tools that are moved rectilinearly to cold form a workpiece having a single cylindrical surface of a round shape.

[0006] Also, US-A-2,825,251 discloses a pair of tools used to perform forming by holding one of the tools stationary and moving the other one with the workpiece between the two tools.

Disclosure of the Invention

[0007] An object of the present invention is to provide a method for cold sizing a workpiece having a central axis and a plurality of round surfaces of cylindrical shapes that are coaxial about the central axis and have different diameters in a single operation. This object is met by a method as defined in claim 1 appended hereto.

[0008] In carrying out the above object, the method is performed by mounting the workpiece for rotation about its central axis between a pair of die assemblies. Each of the die assemblies utilized includes a plurality of dies having sizing surfaces that extend parallel to the central axis of the workpiece respectively in alignment with the round surfaces of the workpiece. Movement of the die assemblies in opposite directions as each other engages the sizing surfaces of the dies with the round surfaces of the workpiece as the workpiece rotates about its central axis such that the sizing surfaces pressure size the round surfaces of the workpiece.

[0009] Pressure sizing of the workpiece can be performed by two different preferred ways in which the method is practiced. In one preferred practice of the method, the die assemblies are moved rectilinearly in opposite directions as each other and the dies thereof are provided with flat sizing surfaces that engage the round surfaces of the workpiece at diametrically opposite locations. In another preferred practice of the method, the die assemblies are rotated and the dies thereof have round sizing surfaces that engage the round surfaces of the workpiece at diametrically opposite locations.

[0010] In performing the method, it is also possible to continue the movement of the die assemblies in order to engage forming projections on the trailing end of one die of each die assembly with the aligned round surface of the workpiece to thereby form projections on this aligned round surface of the workpiece. Such projection forming can be utilized to provide splines on one of the round surfaces and can also be utilized to subsequently provide a helical thread on another round surface of the workpiece.

[0011] In the preferred practice of the method disclosed, splines are formed on one of the round surfaces of the workpiece and a helical thread is formed on another round surface during successive operations after the initial sizing. It should be noted that only one round surface of the workpiece can be formed with projections at any given time due to the fact that the round surfaces have different speeds of circumferential movement for any given rate of workpiece rotation and the die assemblies can each only have a single speed at any given time due to their meshed relationship with the workpiece at the projections being formed. To perform sizing and subsequent projection forming of certain types of workpieces, a particular machine with which the apparatus is utilized may not have sufficient die length to permit the complete operation to be performed during a single movement of the die assemblies in opposite directions as each other. In such cases, the workpiece can be axially shifted to engage one of the round surfaces with forming projections on one die of each die assembly as the direction of movement is reversed.

[0012] It should be noted that during the initial sizing operation, sliding takes place between at least one of the round surfaces of the workpiece and the associated dies due to the difference in speeds thereof with the die assemblies moving only at a single speed. This is possible due to the fact that the sizing performed by the die assemblies initially only forms cylindrical shapes that do not present any interlocking relationship with the sizing surfaces of the dies of the die assembly. However, during subsequent forming of workpiece projections, the meshed relationship of the die projections and the workpiece projections being formed prevents forming of projections on more than one round surface of the workpiece at any given time as previously mentioned.

[0013] The method of the invention may be carried out by several apparatuses, which are to be described, that are utilized to cold size the workpiece. These apparatuses each include a support for rotatably mounting the workpiece about its central axis and also include a pair of die assemblies mounted for movement with the workpiece between the die assemblies. Each die assembly of the apparatuses includes a plurality of dies respectively aligned with the round workpiece surfaces of different diameters. Each die has a sizing surface that extends parallel to the workpiece axis and engages the aligned round surface of the workpiece upon movement of the die assemblies as the workpiece rotates about its central axis such that the sizing surfaces pressure size the round surfaces of the workpiece.

[0014] In one preferred apparatus disclosed, the pair of die assemblies have elongated shapes and have dies with flat sizing surfaces. These elongated die assemblies are mounted for rectilinear movement in a parallel relationship to each other to perform the pressure sizing of the round surfaces of the workpiece by engagement therewith at diametrically opposite locations. A machine including lower and upper bases that define a work space therebetween is preferably utilized to mount the elongated die assemblies for their rectilinear movement in a parallel relationship to each other. Suitable slideways provided on the upper and lower bases of the machine respectively mount the pair of elongated die assemblies for such rectilinear movement in the parallel relationship.

[0015] Another preferred apparatus includes a pair of rotary die assemblies having dies with round sizing surfaces. These rotary die assemblies are respectively mounted by a pair of spindles for rotary movement to perform the pressure sizing of the round surfaces of the workpiece at diametrically opposite locations. Each spindle is disclosed as including a clamp mechanism that clamps the rotary dies of the associated die assembly to perform the pressure sizing upon spindle rotation.

[0016] In both preferred types of apparatus, one of the dies of each die assembly includes a trailing end having projections for forming projections in the aligned round surface of the workpiece. Such projections can be provided on the trailing ends of different dies of each die assembly but at different locations along the length thereof in order to permit successive forming of the projections on different round surfaces of the workpiece such as the spline and thread forming discussed.

[0017] It should be mentioned that only a relatively small reduction takes place in the diameters of the round surfaces of the workpiece as the pressure sizing is performed. Such diameter reduction is always less than 0.5mm (twenty thousandths of an inch) and preferably less than 0.25mm (ten thousandths of an inch). In the most preferred practice of the invention, the diameter reduction during the pressure sizing is only on the order of about 0.1 to 0.15 millimeters (four to six thousandths of an inch). This latter range in diameter reduction has been found to give accurate sizing of the round surfaces even with the relative sliding that takes place between the dies and certain of the round workpiece surfaces due to the different rates of speed as previously mentioned.

[0018] Also, it should be noted that the dies of each die assembly are disclosed as being separable from each other since this is the easiest and hence most economical way to manufacture the die assembly. However, in certain applications, it may be possible to utilize a die assembly wherein the dies are all made unitary with each other. Such unitary die assemblies would be more difficult to manufacture and hence more costly but, nevertheless, could be used to practice the invention.

Brief Description of Drawings

[0019] 

Figure 1 is a schematic front view of a machine to perform the cold sizing method on a round workpiece.

Figure 2 is a sectional view taken along the direction of line 2-2 in Figure 1 to illustrate elongated die assemblies which are moved rectilinearily in opposite directions as each other to perform the cold sizing operation;

Figure 3 is a schematic view of another apparatus to perform the cold sizing method by rotary movement of a pair of rotary die assemblies;

Figure 4 is a sectional view taken along the direction of line 4-4 in Figure 3 to illustrate the construction of the rotary die assemblies;

Figure 5 is a view illustrating the workpiece after cold sizing thereof has been performed; and

Figure 6 is a view which illustrates the workpiece after projections in the form of splines and a thread have been formed on its two smallest round surfaces.

Best Mode for Carrying Out the Invention

[0020] With reference to Figure 1 of the drawings, a schematically illustrated machine is generally indicated by reference numeral 10 and includes apparatus 12 constructed to cold size a round workpiece 14 at room temperature as is hereinafter more fully described. Machine 10 includes a lower base 16, an upper base 18, and a rear connecting portion 20 that cooperatively define a work space 22 in which the sizing apparatus 12 is located. Elongated lower and upper die assemblies 24a and 24b are respectively mounted on the lower and upper bases 16 and 18 by suitable slides 26 (Figure 2) that are movable along slideways 28 of the bases. These slideways 28 extend in a parallel relationship to each other as shown in Figure 1 such that operation of a schematically indicated drive mechanism 30 moves the die assemblies 24a and 24b in a parallel relationship to each other as illustrated by arrows 32. Drive mechanism 30 may be of any suitable type such as, for example, the one disclosed by US-A-3,793,866.

[0021] As seen in Figure 2, a pair of tool boxes 34 are respectively mounted on the pair of slides 26 above and below the workpiece 14. Each tool box 34 includes horizontal and vertical legs 36 and 38 for providing vertical and lateral support to dies of the die assemblies 24a and 24b as is hereinafter more fully described.

[0022] As illustrated in Figure 2, the round workpiece 14 is shown as the female member of a universal joint of the type used in vehicle drives. This universal joint member 14 has a central axis A and includes a cup shaped end 40 whose interior has grooves 42 for receiving balls that provide a coupling thereof to a male joint member which is not shown. A shaft 44 of joint member 14 projects toward the left from its cup-shaped end 40 and includes round surfaces 46, 48, 50, and 52. These round surfaces have cylindrical shapes that are coaxial about the central axis A of the joint member 14 and have different diameters than each other. The largest diameter round surface 46 immediately adjacent the cup shaped end 40 of the joint member 14 is used to mount a seal that is used with the joint, while the next smaller round surface 48 receives a bearing that is utilized to mount the joint member during use. As is hereinafter more fully described, the round surface 50 which is just slightly smaller than the round surface 48 is ultimately provided with splines to couple the joint during use. The smallest round surface 52 is ultimately provided with a helical thread for receiving a suitable nut that secures the joint member in position during use.

[0023] As illustrated in Figure 2, apparatus 12 includes a workpiece support having a headstock center 54 and a tailstock center 55 that rotatably mount the workpiece 14 about its central axis A. Headstock center 54 is mounted in a suitable manner on the connecting portion 20 of the machine 10 illustrated in Figure 1, while the tailstock center 55 is mounted in a suitable manner on an unshown arm that projects forwardly from either the lower base 16 or the upper base 18 of the machine.

[0024] As illustrated in Figure 2, each of the pair of die assemblies 24a and 24b includes a plurality of dies 56, 58, 60, and 62 mounted on the associated tool box 34 for movement with the slide 26 on which the tool box is mounted. End clamps and/or bolts (not shown) secure the dies to the horizontal leg 36 of the tool box 34 and cooperate with bolts 64 that secure the dies to the vertical leg 38 of the associated tool box. Dies 56, 58, 60, and 62 have associated sizing surfaces 66, 68, 70, and 72 of a flat shape that extend parallel to each other and to the central axis A of the rotatably mounted workpiece 14 respectively in alignment with its round surfaces 46, 48, 50, and 42. Operation of the drive mechanism 30 moves the die assemblies 24a and 24b in opposite directions as each other as illustrated by arrows 32 to engage the sizing surfaces 66, 68, 70 and 72 at diametrically opposite locations with the round surfaces 46, 48, 50 and 52 of the workpiece 14 as the workpiece rotates about its central axis A. The spacing between the sizing surfaces on the lower and upper die assemblies 24a and 24b is such that the round workpiece surfaces 46, 48, 50, and 52 are pressure sized during the die assembly movement to provide accuracy in the roundness thereof as well as removal of surface defects.

[0025] It should be noted that during the sizing operation described above, only one of the workpiece surfaces and the aligned die engage each other in a rolling manner, while the other workpiece surfaces are engaged by their aligned dies in a combined rolling and sliding manner. Such sliding along with the rolling accommodates for the difference in speed of the different surfaces and the fact that the die assemblies can only move at a single speed. The particular workpiece surface at which just rolling takes place depends upon the extent of friction generated at surfaces and the balancing of the resultant torques applied to workpiece 14.

[0026] After the initial sizing, the universal joint member 14 has the construction illustrated in figure 5 where its round surfaces 46, 48, 50 and 52 are slightly smaller than the initial size. The reduction in size of the diameters of the round surfaces is very small as it is always less than 0.5 millimeters (twenty thousandths of an inch). Preferably, the reduction in the diameters of the round surfaces is less than 0.25 millimeters (ten thousandths of an inch) and, most preferably, in the range of about 0.1 to 0.15 millimeters (four to six thousandths of an inch).

[0027] As illustrated in figure 1, one of the dies 60 of each die assembly includes a trailing end 74 having projections 76 for forming projections in the aligned round surface 50 of the workpiece 14.

[0028] Similarly, one of the dies 62 of each die assembly includes a trailing end 78 having projections 80 for forming projections in the aligned round surface 52 of the workpiece. As illustrated in Figure 6, the universal joint member 14 has its round surface 50 provided with projections in the form of splines 82 while the round surface 52 has its projections provided in the form of a helical thread 84. It should be noted that the projections can only be formed on a single round surface of the workpiece at any given time due to the difference in speeds of the different surfaces as previously discussed. Also, with certain machines, there may not be a sufficient stroke length of the die assemblies to provide the sizing and subsequent splining and threading operations. In such case, one or both of the projection forming operations can be performed during a reverse stroking of the die assemblies after first axially shifting the workpiece into alignment with dies having suitable projections for providing the required forming operations after the initial sizing.

[0029] After the complete operation, the drive mechanism 30 drives the die assemblies 24a and 24b out of engagement with the completed workpiece 14. This can be done by continuing the movement in the direction of arrows 32 in Figure 1 or, if no projections are formed, by reversing the direction for return stroking movement back to an end to end relationship of the die assemblies. Upon disengagement of the dies from the workpiece surfaces, the workpiece is removed from between the die assemblies for use or any further processing that may be necessary. If the workpiece removal is performed without any reversal, a return stroking movement must be performed prior to the next cycle.

[0030] With reference to Figures 3 and 4, another apparatus to provide cold sizing of a round workpiece at room temperature is indicated generally by reference numeral 12' and includes a pair of rotary die assemblies 24a' and 24b' spaced on opposite sides of the workpiece 14. A pair of spindles 85 respectively support the pair of die assemblies 24a' and 24b' for rotation about associated axes B spaced on opposite sides of the workpiece axis A along which the workpiece 14 is rotatably mounted by the support provided by a headstock center 54 and tailstock center 55.

[0031] Each of the rotary die assemblies 24a' and 24b' includes a plurality of rotary dies 86, 88, 90, and 92 respectively aligned with the round surfaces 46, 48, 50, and 52 of the workpiece 14. These rotary dies each have an annular shape through whose center a shaft 94 of the associated spindle 85 extends along the axes B about which the rotary die assemblies are rotatively driven in any suitable manner. Rotary dies 86, 88, 90, and 92 have round sizing surfaces 96, 98, 100, and 102 that extend parallel to the central axis A of the workpiece 14 and engage the aligned round surfaces 46, 48, 50, and 52 of the workpiece upon rotary movement of the die assemblies 24a' and 24b' in the clockwise direction as illustrated by arrows 104 in Figure 3. Suitable notches 106 are provided in the dies to permit the axial positioning of the workpiece 14 therebetween in preparation for the sizing operation performed by the apparatus 12'.

[0032] A suitable drive mechanism, such as of the general type disclosed by US-A-4,045,988, drives the rotary spindles 24a' and 24b' of apparatus 12' to engage the round sizing surfaces 96, 98, 100, and 102 of the rotary dies with the aligned round surfaces 46, 48, 50 and 52 of the workpiece 14 as the workpiece rotates about its central axis A. Such engagement of the dies with the workpiece pressure sizes the round surfaces of the workpiece to provide accuracy in the roundness thereof as well as removing surface defects.

[0033] Sizing performed by the rotary sizing apparatus 12' of figures 3 and 4 like the linear type previously described only reduces the diameter of the round workpiece surfaces a very small extent which is always less than 0.5 millimeters (twenty thousandths of an inch). This diameter reduction with the rotary embodiment like the linear embodiment is preferably less than 0.25 millimeters (ten thousandths of an inch) and, most preferably, in the range of 0.1 to 0.15 millimeters (four to six thousandths of an inch).

[0034] With reference to figure 4, each of the die spindles 85 includes a flange 106 that engages the adjacent rotary die 92. A threaded portion 108 of each spindle 85 receives a nut 110 that engages the adjacent rotary die 86 to cooperate with the flange 106 in providing a clamp mechanism for clamping the rotary dies in a stacked relationship.

[0035] One of the rotary dies 90 of each rotary die assembly 24a' and 24b' includes a trailing end 112 provided with projections 114 for forming projections on the aligned round surface 50 of the workpiece 14. Like the embodiment of figures 1 and 2, the projections formed on the round surface 50 are splines 82 as illustrated in figure 6 when the workpiece is a universal joint member 14 of the type previously described. Likewise, one die 92 of each rotary die assembly has a trailing end 116 including projections 118 for forming projections on the round surface 52 of the workpiece 14. These projections 118 are in the form of the helical thread 84 illustrated in Figure 6 when the workpiece is a universal joint member 14 as previously discussed.

[0036] With the rotary sizing apparatus 12', no return stroke in a reverse direction is necessary as with the linear embodiment of Figures 1 and 2. A reduced cycle time can thereby be achieved with the rotary sizing apparatus. Also, the rotary apparatus 12' like the linear apparatus only reduces the diameters of the workpiece surfaces a very small extend as previously described.

[0037] It should be appreciated that the invention can be carried out in its broadest practice by sizing of a workpiece having a plurality of round surfaces of different diameters without any subsequent projection forming. However, the apparatus and method disclosed have particular utility when constructed and utilized to perform subsequent projection forming such as the splines and/or thread previously discussed. Separate operations previously required can be eliminated by this single processing of the workpiece to thereby reduce its cost.

[0038] It should be appreciated that both types 12 and 12' of die assemblies can also be constructed with the dies thereof unitary with each other ratherthan separable as shown. However, it is much easier and hence economical to manufacture the dies separate from each other which is the reason that such a construction is illustrated.

[0039] While the best modes for practicing the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative ways of practicing the invention as defined by the following claims.

Claims

1. A method for cold sizing a preformed workpiece shaft (14) having a plurality of cylindrical coaxial portions with round surfaces of different diameters each having a uniform cross-section throughout its length, which comprises mounting the workpiece (14) for rotation about the shaft axis between a pair of die assemblies (24a, 24b) and moving the die assemblies (24a, 24b) in opposite directions to engage sizing surfaces of the dies (24a, 24b) with the workpiece (14) as the latter rotates about the shaft axis characterised in that the die assemblies (24a, 24b) have a plurality of opposed pairs of sizing surfaces (66, 68, 70, 72) corresponding to the number of cylindrical shaft portions (46, 48, 50, 52) so that each portion is disposed between a respective one of the pairs of sizing surfaces (66, 68, 70, 72), each sizing surface extends parallel to the shaft axis for a distance corresponding to the axial length of the respective shaft portion, pressure is applied simultaneously with the sizing surfaces (66, 68, 70, 72) to the respective shaft portions (46, 48, 50, 52) throughout their length to reduce the diameter thereof by an amount less than 0.5 millimeters (20 thousandths of an inch), and in that no more than one of said pairs of sizing surfaces (66, 68, 70, 72) is in only rolling contact with the round surface of its respective shaft portion, and any other of said plurality of opposed pairs of sizing surfaces (66, 68, 70, 72) is in sliding and rolling contact with the respective shaft portion (48, 50, 52 54),.

2. A method as claimed in claim 1 wherein the die assemblies (24a, 24b) are moved rectilinearly in opposite directions and have flat sizing surfaces (66, 68, 70, 72).

3. A method as claimed in claim 1 wherein the die assemblies (24a, 24b) are rotated and the sizing surfaces (66, 68, 70, 72) thereof are round.

4. A method as claimed in claims 1, 2, or 3, further including the step of sequentially forming projections on one of the shaft portions (50) by continuing to move the die assemblies (24a, 24b) following the cold sizing operation to cause said one shaft portion (50) to be engaged between an opposed pair of projection forming die surfaces (76) extending from the trailing end (24) of one of said pair of opposed sizing surfaces.

5. A method as claimed in claims 1, 2, or 3, wherein the diameters of the shaft portions (46, 48, 50, 52) are reduced from the preformed diameter by said sizing surfaces (66, 68, 70, 72) by an amount in the range 0.1 to 0.15 millimeters (4 to 6 thousandths of an inch).

Ansprüche

1. Verfahren zum Kaltwalzen einer vorgeformten Werkstückwelle (14), die mehrere koaxiale zylindrische Teile mit gekrümmten Oberflächen und verschiedenen Durchmessern aufweist, von denen jedes über seine gesamte Länge einen gleichbleibenden Querschnitt aufweist, wobei in dem Verfahren das Werkstück (14) zur Drehung um die Achse der Welle zwischen einem Walzwerkzeugpaar (24a, 24b) befestigt wird und die Walzwerkzeuge (24a, 24b) in entgegengesetzte Richtungen bewegt werden, so daß die Walzflächen der Werkzeuge (24a, 24b) mit dem Werkstück in Eingriff kommen, wenn dieses sich um die Achse der Welle dreht, dadurch gekennzeichnet, daß die Werkzeuge (24a, 24b) mehrere gegenüberliegende, einander paarweise zugeordnete Walzflächen (66, 68, 70, 72) entsprechend der Anzahl der zylindrischen Wellenteile (46, 48, 50, 52) aufweisen, so daß jedes Teil der Welle zwischen jeweils zwei Flächen eines Walzflächenpaares (66, 68, 70, 72) angeordnet ist, daß jede Walzfläche parallel zur Achse der Welle über eine Strecke verläuft, die der axialen Länge des jeweiligen Wellenteiles entspricht, daß mit den Walzflächen (66, 68, 70, 72) auf die jeweiligen Wellenteile (46, 48, 50, 52) über deren gesamte Länge gleichzeitig Druck ausgeübt wird, um ihren Durchmesser um weniger als 0,5 mm (20 Tausendstel eines Inch) zu vermindern, und daß nicht mehr als ein Walzflächenpaar (66, 68, 70, 72) ausschließlich in Walzkontakt mit der gekrümmten Oberfläche des jeweiligen Wellenteiles steht und alle anderen jeweils gegenüberliegenden Walzflächen der Walzflächenpaare (66, 68, 70, 72) in Gleit und Rollkontakt mit dem jeweiligen Wellenteil (48, 50, 52, 54) stehen.

2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Werkzeuge (24a, 24b) geradlining in entgegengesetzte Richtungen bewegt werden und flache Walzflächen (66, 68, 70, 72) aufweisen.

3. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Werkzeuge (24a, 24b) gedreht werden und ihre Walzflächen (66, 68, 70, 72) gekrümmt sind.

4. Verfahren nach Anspruch 1, 2 oder 3, ferner dadurch gekennzeichnet, daß an einem der Wellenteile (50) nacheinander Vorsprünge gebildet werden, indem die Werkzeuge (24a, 24b) anschließend an den Kaltwalzvorgang weiterbewegt werden, so daß dieses eine Wellenteil (50) zwischen zwei paarweise gegenüberliegende, Vorsprung-bildende Werkzeugflächen (76) zu liegen kommt, die sich an dem hinteren Ende (24) des einen Paares der gegenüberliegenden Walzflächen erstrecken.

5. Verfahren nach Anspruch 1, 2 oder 3, dadurch gekennzeichnet, daß die Durchmesser der Wellenteile (46, 48, 50, 52) gegenüber dem vorgeformten Durchmesser durch die Walzflächen (66, 68, 70, 72) um 0,1 bis 0,15 mm (4 bis 6 Tausendstel eines Inch) verringert werden.

Revendications

1. Procédé pour le formage à froid d'un arbre (14) de pièce à usiner préformée présentant une pluralité de parties coaxiales cylindriques à surfaces circulaires de différents diamètres ayant chacune une section transversale constante sur toute sa longueur, qui consiste à monter la pièce (14) de façon tournante autour de l'axe de l'arbre entre deux dispositifs de matriçage (24a, 24b) et à déplacer les dispositifs de matriçage (24a, 24b) dans des directions opposées de manière à amener des surfaces de calibrage des matrices (24a, 24b) en contact avec la pièce (14) tandis que celle-ci tourne autour de l'axe de l'arbre, caractérisé en ce que les dispositifs de matriçage (24a, 24b) comprennent une pluralité de paires opposées de surfaces de calibrage (66, 68, 70, 72) correspondant au nombre de parties cylindriques (46, 48, 50, 52) de l'arbre de sorte que chaque partie est située entre une paire respective des surfaces de calibrage (66, 68, 70, 72), chaque surface de calibrage s'étend parallèlement à l'axe de l'arbre sur une distance correspondant à la longueur axiale de la partie d'arbre respective, une pression est appliquée simultanément par les surfaces de calibrage (66, 68, 70, 72) aux parties d'arbre respectives (46, 48, 50, 52) surtoute leur longueur de manière à réduire leur diamètre d'une quantité inférieure à 0,5 mm (20 millièmes de pouce), et en ce que pas plus d'une desdites paires de surfaces de calibrage (66, 68, 70, 72) est en contact seulement de roulement avec la surface circulaire de sa partie d'arbre respective, et toute autre paire de ladite pluralité de paires opposées de surface de calibrage (66, 68, 70, 72) est en contact de glissement et de roulement avec la partie d'arbre respective (48, 50, 52, 54).

2. Procédé suivant la revendication 1, dans lequel les dispositifs de matriçage (24a, 24b) sont dé placés de façon rectiligne dans des directions opposées et présentent des surfaces de calibrage planes (66, 68, 70, 72).

3. Procédé suivant la revendication 1, dans lequel les dispositifs de matriçage (24a, 24b) sont rotatifs et leurs surfaces de calibrage (66, 68, 70, 72) sont circulaires.

4. Procédé suivant les revendications 1, 2 ou 3, comprenant en outre l'opération de formage séquentiel de saillies sur l'une des parties d'arbre (50), par poursuite du déplacement des dispositifs de matriçage (24a, 24b) à la suite de l'opération de calibrage à froid, de manière à amener ladite partie d'arbre (50) en prise entre deux surfaces opposées de matrice (76) de formage de saillies s'étendant à partir de l'extrémité arrière (24) d'une dite paire de surfaces de calibrage opposées.

5. Procédé suivant les revendications 1, 2 ou 3, dans lequel les diamètres des parties d'arbre (46, 48, 50, 52) sont réduits à partir du diamètre préformé, par lesdites surfaces de calibrage (66, 68, 70, 72), d'une valeur comprise entre 0,1 et 0,15 mm (4 à 6 millièmes de pouce).

Drawing