METHOD FOR MANUFACTURING OUTER PARTS OF CONSTANT VELOCITY JOINTS

Abstract: In a method for manufacturing outer parts of constant velocity joints by plastic deformation of a preform (3) having a cavity open on one side to produce axial non-undercut ball tracks (6) and cage guide surfaces (7), wherein the preform (3) is received in an outer tool (2) and the inner tool (1) plastically forms inner wall regions to ball tracks (6) and cage guide surfaces (7) with the application of pressure, the inner tool (1) comprises a one-piece wobble pressing die having segments of diffrent convex curvature which is first of all plunged centrally into the cavity in the preform (3), after which the desired final contours of the ball tracks (6) and cage guide surfaces (7) are produced using multiple wobbling movements with a corresponding orbital angle alpha .

Description: Method for manufacturing outer parts of constant velocity joints The invention relates to a method for manufacturing outer parts of constant velocity joints of the kind set forth in the preamble of claim 1. German Offenlegungsschrift 37 12 301 discloses a press tool for plastic deformation of a preform having a cavity open on one side to produce non-undercut axial ball tracks and cage guide surfaces. The preform is received in an outer tool and the shaping of the wall regions is then performed by an inner tool with the application of pressure. In this case the inner tool consists of an inner die having individual radial ribs which reach through segments of a sleeve die to provide a forming surface which is closed in the circumferential direction. The joint between the two parts of the inner tool is always in the transition between the ball track forming region and the cage guide surface forming region. The part of the inner tool for making the ball tracks is formed by a one-piece solid tool part which can accept large forces without distortion or change in shape. This makes it possible to shape the ball track portions so precisely that no finishing operation is needed in these regions. The intervening undercut cage guide surface regions are formed by the outwardly crowned segments of the sleeve die of the inner tool, the segments of which, after removal of the inner die, can be removed from the finished workpiece by springing them radially inwards. The known press tool has the disadvantage that the two- piece inner tool is extremely complex and costly to manufacture and, owing to the parting surfaces formed between the two parts of the tool, namely the inner die and the sleeve die, has increased susceptibility to wear. A further disadvantage is that the tolerances required for making the forming tool in two parts necessarily lead to an increase in the workpiece tolerances, that is to say, the current tool tolerances must be added to the specified workpiece tolerances. German Offenlegungsschrift 42 14 444 discloses a method for the manufacture of ball sockets for constant velocity joints wherein a cup-shaped blank is progressively locally plastically deformed radially as a function of time, with plastic reduction in section, to shape its inner form against a profiled mandrel which in the circumferential direction is corrugated and which in the axial direction has different convex curvatures which vary, preferably segmentally, around the circumference. The profiled mandrel used here is multipart and consists of radially separable profiled mandrel segments . This known method, too, has the disadvantage that the profiled mandrel used, because of its multipart design, is complex and expensive to manufacture and is susceptible to wear. A further disadvantage is that the tolerances required for the division of the forming tool in two necessarily lead to increase in the workpiece tolerances, i.e. the current tool tolerances must be added to the specified workpiece tolerances. The object of the invention is to provide a method for the manufacture of outer parts of constant velocity joints of the kind referred to in which the disadvantages of the known manufacturing process which have been pointed out are avoided and in which ball tracks can be made either without or with undercuts . To this end, in accordance with the invention in a method of the kind referred to in the preamble of the claim for manufacturing outer parts of constant velocity joints the tool and process steps indicated in the characterising part of claim 1 are employed. As a result of using as the inner tool a one-piece pressing die having segments with different convex curvatures and having a particular external contour, which is introduced into the cavity and which, by wobble pressing, produces the desired final form of the inner wall regions for the ball track and the cage guide surfaces in a plurality of locally progressive revolutions, a very robust forming tool is provided which leads to improved workpiece tolerances . The invention will be described in more detail with reference to the accompanying drawings, in which: Fig. 1 shows a vertical section through the tool-preform arrangement at the start of the forming; Fig. 2 shows a vertical section through the tool-workpiece arrangement after the wobble forming; and Fig. 3 is a bottom view of the one-piece inner tool. The inner tool 1 is in the form of a one-piece wobble pressing die the outer contour of which has, by segments, different convex curvatures and includes rib-shaped contours 4 for the ball tracks and adjacent contours 5 for the cage guide surfaces. The corresponding outer contours 4 and 5 are designed on the basis of a particular orbital angle in order to produce the desired final guide surfaces. The preform 3 is received and fixed in an outer tool 2. At the start of the working the outer tool 2 is moved upwards to the shaping die 1, which is still disposed centrally with respect to the machine axis, and then fixed. The shaping die 1- is now set in wobbling movement. An intermittent shaping force moves corresponding to the course of the movement - depending on the wobble frequency and the orbital angle α - circularly over the surfaces of the preform 3 which are being shaped. Thus only a fairly small region of the ball tracks 6 and cage guide surfaces 7 is being worked in any unit of time. The shaping die is rolled on the preform 3, i.e. between material and shaping tool 1 there is rolling sliding friction: this is considerably smaller than the frictional parameter in the conventional shaping process. The yield stress of the material is only slightly exceeded by the maximum stress occurring, thereby ensuring a better flow of material. As soon as the desired final contours of the ball tracks 6 and the cage guides 7 have been reached, the inner tool 1 is again disengaged centrally of the axis of the machine and the workpiece 3' can be ejected from the outer tool 2 by an ejector. As a result of the stepwise displacement of material produced by the wobble pressing very precise shaping and very high surface quality can be relied on, so that subsequent machining of the ball tracks and the cage guide surfaces is no longer necessary. Simultaneously with the production of the inner contour of the outer joint part, external splines 8 can be formed on the outer contour of the preform 3. The outer splines 8 hold the preform 3 precisely in position and prevent it from twisting in the outer tool 2 under the influence of the wandering torque of the wobbling movement. With suitable design the external splines can be used as speed sensor for an ABS system.

Claims: CLAIMS 1. A method for manufacturing outer parts of constant velocity joints by plastic deformation of a preform having a cavity open on one side to produce axial ball tracks and cage guide surfaces, wherein the preform (3) is received in an outer tool (2) and the inner wall regions are formed to ball tracks (6) and cage guide surfaces (7) by means of an inner tool (1) with the application of pressure, characterised in that the inner tool (1) comprises a one-piece wobble pressing die having segments of different convex curvature which is first of all introduced centrally into the cavity in the preform (3), after which the desired final form of the ball tracks (6) and cage guide surfaces (7) is produced using multiple wobbling movements with a corresponding orbital angle (α) . 2. A method as claimed in claim 1, characterised in that an axial plunging movement is superimposed on the wobble pressing movement. 3. A method as claimed in claim 1 or claim 2, characterised in that both non-undercut and undercut ball tracks (6) can be produced.

Inventors: NOLDEN REINER, NOLDEN, REINER
Applicants: FORD GLOBAL TECH INC, NOLDEN REINER, FORD GLOBAL TECHNOLOGIES, INC., NOLDEN, REINER
Application year: 1997
Main classification: B21K1
IPC codes: B21J9, B21K1