EP1107840B1 - Method for producing a gear rack, and a stamping device for carrying out the method - Google Patents

Description

The invention relates to an embossing device for producing a blank for a rack for rack and pinion steering of motor vehicles.

It is generally known that the blank for the manufacture of a toothed rack has a shape deviating from a circular cylinder, at least in the area of its toothing. Such a blank has hitherto been able to be produced, for example, by a machining process, by extrusion molding or by another shaping process. With such a metal-forming manufacturing process, greater strain hardening could occur in the blank in various areas. Such strain hardening, however, makes subsequent non-cutting forming processes considerably more difficult. A remedy was possible by switching additional annealing processes between the individual forming processes. However, such heat treatment processes mean an interruption in the cold forming from the starting material via the blank to the finished rack.

Further processing in a non-cutting process is known, for example, from DE-C2-32 02 254. In this process, a toothed rack is produced by tumbling from a cylindrical starting material between an upper and a lower tool. This process can also be used in the area of the toothing of the toothed rack Strain hardening occurs, which make the manufacture of the rack difficult.

From JP-A-57 206546 an embossing device is known which consists of a substance filled with an inherent substance during the deformation Hollow bar blank forms a rack that is at least partially toothed. For this purpose, the embossing device has a plurality of shaping tools which can be moved relative to one another and act on the hollow bar blank in a shaping manner due to the forces and reaction forces which occur.

Furthermore, US-A-4 715 210, which forms the basis for the preamble of claim 1, describes a die for forming a Y-shaped rack part by forging, in which the die has a group of four shaped elements which are symmetrical about the plane of symmetry of the longitudinal plane corresponding to the toothed rack part is arranged and at least three of these shaped elements are movable relative to one another.

In the case of embossing devices according to JP-A-57 206546 and US-A-4 715 210, the shaping tools required for the deformation act on the toothed rack blank from different directions, and therefore forces from different directions must also be compensated for by the device. Housing parts of the embossing device must be dimensioned higher due to these forces and the drive devices for the shaped elements are of complex construction and cost-intensive, which at the same time has negative effects on the dimensions of the embossing device.

The object of the invention is to produce a blank for a toothed rack in such a way that - especially in the area of the toothing of the toothed rack to be subsequently produced - only a slight strain hardening occurs. This area is of such great importance because large flow movements of the material occur here in the subsequent forming process, for example a tumbling process. Through the device Overall, the manufacturing costs are greatly reduced and the device itself should be simple and small.

This object is achieved by the embossing device disclosed in claim 1

The embossing device according to the invention for producing a blank for a toothed rack contains at least three shaping tools which are movable relative to one another, one of which is fixed, while the other two are moveable relative to one another and to the stationary shaping tool. Two of the shaping tools have effective surfaces which are inclined towards one another and which lie symmetrically to a plane of symmetry of the toothed rack. This plane of symmetry is perpendicular to the later toothing of the rack and contains the longitudinal axis of the rack. The third of the molding tools has an effective surface that is perpendicular to the plane of symmetry of the rack mentioned.

The advantages achieved by the invention are, in particular, that the starting material is formed into a blank for the toothed rack, which is given a shape deviating from a circular cylinder at least in the axial region of the toothed rack teeth the starting material can be molded into the areas of the blank that undergo major deformations in the course of the production of the toothed rack without major strain hardening. An additional advantage of a method that can be used by the device according to the invention is that a blank shape can be achieved in a simple manner, with which burr formation is avoided in a subsequent forming process, in particular in a wobble process. A blank for a toothed rack can also be produced with such an embossing device, without that being formed greater friction forces would have to be overcome in the starting material and without excessive strain hardening occurring in critical areas.

Appropriate and advantageous developments of the invention are contained in the subclaims. With the embossing device, it is advantageous if only one of the three shaping tools is stationary. The fixed mold is one of the two molds arranged symmetrically to the plane of symmetry. The mold, the effective surface of which is perpendicular to the plane of symmetry of the rack, is coupled to the other mold in such a way that it moves at half the speed of the other movable mold.

It is thereby achieved that the plane of symmetry of the toothed rack remains unchanged in its position in relation to the molding tool, the effective surface of which is perpendicular to the plane of symmetry. Since this mold advantageously contains the counterpart to the concave or convex longitudinal profile of the blank, this longitudinal profile always remains in the plane of symmetry of the rack.

Fig. 1

die erfindungsgemäße Prägevorrichtung in schematischer Darstellung in ihrer Ausgangsstellung;

Fig. 2

die Prägevorrichtung nach Fig. 4 in einer Stellung, die dem Ende des Herstellungsverfahrens entspricht;

Fig. 3 bis 5

drei Ausführungsbeispiele einer mit der erfindungsgemäßen Vorrichtung hergestellten Rohlings für eine Zahnstange im Querschnitt und

Fig. 6

eine perspektivische Ansicht des Rohlings.

The invention is explained in more detail below with reference to several exemplary embodiments shown in the drawing.
Show it:

Fig. 1

the embossing device according to the invention in a schematic representation in its initial position;

Fig. 2

the embossing device of Figure 4 in a position corresponding to the end of the manufacturing process.

3 to 5

three embodiments of a blank produced with the device according to the invention for a rack in cross section and

Fig. 6

a perspective view of the blank.

The embossing device according to the invention contains three molds 1, 2 and 3 which can be moved relative to one another. One of the molds, in this case the mold 1, is fixed. The two other molds 2 and 3 are movable relative to one another and to the mold 1. The molds 1 and 2 have effective surfaces 4 and 5 which are inclined relative to one another and which are symmetrical to one another with respect to a plane of symmetry 6. The plane of symmetry 6 belongs to a starting material 7, which has an essentially circular cross section. The plane of symmetry 6 is defined in such a way that it lies perpendicular to the toothing of the later toothed rack formed from the starting material 7. In addition, the plane of symmetry 6 contains the longitudinal axis of the starting material 7 and thus the later rack. The molding tool 3 has an effective surface 8 which is perpendicular to the plane of symmetry 6.

The direction of movement of the mold 3 whose effective surface 8 is perpendicular to the said plane of symmetry 6 of the rack is also the direction of movement of the movable mold 2, which is one of the two molds 1 or 2, the effective surfaces 4, 5 of which are symmetrical to the plane of symmetry 6 of the rack lie at an angle of 90 degrees to the plane of symmetry 6 and the movement of the two movable molds 3 and 2 takes place at a distance from one another and parallel to one another.

A convex longitudinal profile 9 is formed on the effective surface 8 of the molding tool 3. The longitudinal profile 9 has an approximately semicircular cross section in the exemplary embodiment. However, the cross section can be formed with the same effect by a triangle, a rectangle or a combination of all of these shapes.

In the exemplary embodiment according to FIGS. 1 and 2, the two molding tools 2 and 3 which are movable relative to one another are coupled to one another in such a way that the molding tool 3 can be moved at half the speed of the molding tool 2 during the actual shaping process. The actual forming process begins as soon as the effective surface 4 comes into contact with the outer contour of the starting material 7.

2 shows the end of the forming process. Both the molding tool 2 and the molding tool 3 are in their respective end positions, in which a blank 10 is formed from the starting material 7.

The embossing device according to the invention for producing a blank for a toothed rack for a rack and pinion steering for motor vehicles is described functionally below.

In a first step, the starting material 7 with an essentially circular cross section is inserted into the embossing device between the molds 1, 2 and 3. In a second step, a force is exerted on the molding tool 2 in the direction of the arrow 11. The molding tool 3, which is coupled to the molding tool 2 in the manner described above, is moved such that the starting material 7 is at least in an axial region 12 receives a shape deviating from a circular cylinder. The axial region 12 is located in FIG. 6 where the toothing of a toothed rack made from the blank 10 lies.

During the second step, a concave longitudinal profile 13 is expediently incorporated into the starting material 7 by the convex longitudinal profile 9. The longitudinal profile 13 is expediently located in the blank 10 in the plane of symmetry 6, on the side opposite the later toothing of the rack second method step, the plane of symmetry 6 is shifted half the way of the molding tool 2 in the direction of the molding tool 1.

In a further process step, which is not the subject of this application, the toothed rack is formed from the blank 10 by wobble forging. The longitudinal profile 13 is incorporated into the blank 10 in order to be able to support the blank 10 against the wobble moments during the wobble forging.

Instead of the one longitudinal profile 13, the blank can also have two or more correspondingly smaller longitudinal profiles.

In the second process step, the blank 10 receives at least in the toothing region of the toothed rack two substantially symmetrically arranged, mutually inclined flats 14 and 15, which originate from the mutually inclined effective surfaces 4 and 5 of the molding tools 2 and 1. If the effective surfaces 4 and 5 are not formed flat, but with different partial surfaces that are at an angle to one another, the flattened areas 14 and 15 are given polygon-like surfaces. Likewise, the flats 14 and 15 can be made slightly spherical.

In the embodiment of the blank 10A according to FIG. 4, the effective surfaces 4 and 5 likewise do not have any flat surfaces, but are curved. This gives the blank 10A two substantially symmetrical Constrictions 16 and 17 arranged relative to one another, which are expediently limited to the toothing region of the future toothed rack.

The angle between the flats 14 and 15 and the plane of symmetry 6 is expediently in a range between 12 degrees and 30 degrees, in particular in the range of 20 plus / minus 5 degrees. These values also apply if the flats 14 and 15 are not designed as flat surfaces but as polygon-like surfaces or as constrictions 16 and 17. In these cases, the ranges apply to the averaged angles.

In the embodiments of the blank according to FIGS. 3 and 4, the longitudinal profile 13 is concave in each case. In FIG. 3, the longitudinal profile 13 is designed as a circular segment, in FIG. 4 as a triangular cross section.

Fig. 5 shows a rack blank 10B, the longitudinal profile of which is convex, so that the blank is given a so-called Y cross-section.

It is essential for all blank shapes that there is sufficient material in the toothing area of the future toothed rack to facilitate the reshaping of the toothing. The starting material 7 is therefore formed almost without strain hardening in such a way that material is primarily displaced from the center into the toothing area. This results in the cross-section of the blanks 10, 10A, 10B shown in FIGS. 3 to 5, deviating from the circular shape.

Other variations and combinations of different longitudinal profiles 13, flats 14, 15 and constrictions 16, 17 are within the scope of the invention.

Instead of coupling the two molding tools 2 and 3, two forces acting independently of one another can be applied to the two molding tools.

reference numeral

1

mold

2

mold

3

mold

4

effective area

5

effective area

6

plane of symmetry

7

starting material

8th

effective area

9

longitudinal profile

10

blank

11

arrow

12

axial area

13

longitudinal profile

14

flattening

15

flattening

16

constriction

17

constriction

Claims (5)

1. Stamping device for producing a blank for a rack for rack-and-pinion steering systems of motor vehicles, having the following features:

   - the stamping device contains at least three forming dies (1, 2, 3) moveable relative to one another,

   - one of the forming dies (1, 2, 3) is stationary and the other two are moveable relative to one another and to the one forming die,

   - two of the forming dies (1, 2, 3) have active surfaces (4, 5) which are inclined relative to one another and lie symmetrically to a plane of symmetry (6) of the subsequent rack, the plane of symmetry (6) being perpendicular to the toothing of the subsequent rack and containing the longitudinal axis of the rack,

   - the third of the forming dies (1, 2, 3) has an active surface (8) which is perpendicular to said plane of symmetry (6) of the rack,

   characterized in that

   - one of the two forming dies (1, 2, 3) moveable relative to one another and to the one forming die is one of the two forming dies (1, 2), the active surfaces (4, 5) of which lie symmetrically to the plane of symmetry (6) of the rack, and

   - the other of the two forming dies (1, 2, 3) moveable relative to one another and to the one forming die is that forming die (3), the active surface (8) of which is perpendicular to said plane of symmetry (6) of the rack,

   and in that

   - the direction of movement of that forming die (3), the active surface (8) of which is perpendicular to said plane of symmetry (6) of the rack, and the direction of movement of the one moveable forming die (1 or 2) which is one of the two forming dies (1 or 2), the active surfaces (4, 5) of which lie symmetrically to the plane of symmetry (6) of the rack, run at an angle of 90 degrees to the plane of symmetry (6), and in that

   - the cycle of movement of the two moveable forming dies (3 and 1 or 2) takes place at a distance from one another and parallel to one another.
2. Stamping device according to Claim 1, characterized in that the two forming dies (2, 3) moveable relative to one another and to the one forming die (1) are coupled to one another in such a way that that forming die (3), the active surface (8) of which is perpendicular to said plane of symmetry (6) of the rack, is moveable at half the speed of the other moveable forming die (2).
3. Stamping device according to one of Claims 1 and 2, characterized in that the angle between the active surfaces (4, 5), inclined relative to one another, of the two forming dies (1, 2) and the plane of symmetry (6) is in a range of between 12 degrees and 30 degrees.
4. Stamping device according to Claim 3, characterized in that the angle between the active surfaces (4, 5), inclined relative to one another, of the two forming dies (1, 2) and the plane of symmetry (6) is in the range of 20 plus/minus 5 degrees.
5. Stamping device according to one of Claims 1 to 4, characterized in that the active surface (8) of the forming die (3) is designed as a convex or concave longitudinal profile (9) which possesses a circular-segmental, triangular or rectangular cross section or a cross section which is composed of a combination of a circular segment, rectangle and triangle as elements.