Die for forging

A die for forging a toothed section of a gear rack of a steering device, including a first die part (9) having a first molding recess (11) for molding the toothing and a second die part (10) having a second molding recess (12), which has the shape of the back area of the gear rack opposite the toothing. The die parts (9, 10) can be moved toward each other in a closing direction (13) into an end position, in which the die parts have a distance (s) from each other, wherein a main cavity (14) is formed between the die parts (9, 10) in a region of the molding recesses (11, 12) of the die parts (9, 10), the main cavity being open on opposite sides to secondary cavities (16, 17), which lie in respective regions between the first and second die parts (9, 10). The die further includes at least two secondary molding parts (18, 19), which lie in respective regions between the first and second die parts (9, 10) and which at least partially form the walls that bound the secondary cavities and which can each be moved relative to the die parts (9, 10) in an adjusting direction (29, 30) oriented at an angle to the closing direction (13).

BACKGROUND

The invention relates to a die for forging a toothed portion of a toothed rack of a steering device, comprising first and second die parts, of which the first die part has a first molding recess for molding the toothing of the toothed rack, and the second die part has a second molding recess, which has the form of the back region of the toothed rack, lying opposite the toothing, and which can be moved together in a closing direction from an open position into an end position, in which they are at a distance from one another, while shaping a blank placed into the die, wherein, in the region of the molding recesses of the die parts, there is formed between the die parts a main cavity, which in the moved-together end position of the die parts is open on opposite sides toward secondary cavities, which respectively lie in a region lying between the first and second die parts. The invention also relates to a forging method for forging a toothed portion of a toothed rack for a steering device, wherein a blank is shaped between two die parts, of which the first die part has a first molding recess for molding the toothing of the toothed rack, and the second die part has a second molding recess, which has the form of the back region of the toothed rack, lying opposite the toothing, and which can be moved together in a closing direction from an open position into an end position, in which they are at a distance from one another, while shaping the blank placed into the die, wherein, in the region of the molding recesses of the die parts, there is formed between the die parts a main cavity, which in the moved-together end position of the die parts is open on opposite sides toward secondary cavities, which respectively lie in a region lying between the first and second die parts, and wherein, when the die parts move together, material of the blank is displaced into the secondary cavities.

Toothed racks for steering devices of motor vehicles that have constant toothings are often produced by machining, allowing a high degree of precision to be achieved. Such toothed racks may also be produced with sufficient accuracy by shaping. Shaping methods are often more cost-effective than machining methods. Toothed steering racks with variable toothing, in which the spacing of the teeth and/or the form of the teeth and/or the inclined position of the teeth changes over the extent of the toothing, are very difficult to produce. For cost-effective mass production, the methods of production become more complex.

Toothed steering racks which have a triangular cross section or a Y cross section in the region of their toothed ends are known. For example, such a toothed rack is disclosed by EP 0 738 191 B1 and the production of this toothed rack is performed by hot forging. Such toothed racks are well suited for variable toothings and are supported in their guidance against the influence of rolling moments that occur due to contact forces between the teeth of the pinion and the teeth of the toothed rack as a result of inclined positions by their longitudinal guidance. Toothed steering racks with a round back profile or D cross section also exist. Such toothed racks have some advantages over toothed racks with a Y cross section in production, including in their non-toothed regions, and in the fitting and sealing of the toothed rack. The required installation space is also significantly smaller and the geometry of the thrust piece mounting the toothed rack is simpler. However, these toothed racks are more susceptible to the influence of rolling moments, which can cause canting and associated noise (rack roll). For producing toothed racks, in particular round-back toothed racks, for steering devices by shaping techniques, forging methods with flash and forging methods without flash are known.

In the case of a forging method with flash, in which a die of the type mentioned at the beginning is used, when the two die parts are moved together, material of the blank is forced out of the main cavity into secondary cavities lying on both sides of the main cavity in the region of the parting plane between the die parts and this material forms flash, which is removed after the forging operation. This flash also makes up for volume tolerances of the blank. When the die parts are moved together, the opening of the main cavity toward the secondary cavities is continuously reduced (this is also referred to as the “die gap”), the internal die pressure increasing and parts of the material flowing from the main cavity into the secondary cavities. Particularly at the edges, there is a strong flow of the material of the blank under high pressure. This leads to great wear on the die parts, in particular at the edges of the die parts that bound the main cavity toward the secondary cavities. The die parts therefore have short service lives. Furthermore, the achievable toothing accuracies are limited. These also depend on the die gap geometry, which can be changed only by reworking the die parts themselves.

EP 1 007 243 B1 discloses a forging method with flash for producing round-back toothed racks with flash, the secondary cavities bounding the flow of the material of the blank from the main cavity. The total volume of the secondary cavities in the end position of the die parts corresponds in this case to the difference in volume between the toothed rack blank and the finished toothed rack in the toothed region. Consequently, in the end position of the die parts, the secondary cavities are closed and completely filled with material of the blank. As a result, an increased hydrostatic final pressure can be formed. One disadvantage of this method is that the volume of the blank has to be defined very accurately, and so it must be exactly pre-ground, or produced in some other way. This increases the complexity of the production considerably.

WO 2005/053875 A1 discloses a forging method without flash for producing round-back toothed racks. Two punches are provided between the two die parts. In the closed state of the two die parts, these parts abut against the two punches on both sides. At this point in time, the main cavity is not yet completely filled with the material of the blank. Thereafter, the two punches are forced into the main cavity, reducing the volume of the main cavity, whereby the material of the blank is pressed on all sides against the walls of the main cavity. The die that is used in this method, and is not of the generic type concerned here, consequently does not have any secondary cavities. Also in the case of this method, the volume of the blank must be accurately defined. Therefore, in the region of the toothed rack in which the toothing is formed there is formed a preform, which is reduced by the proportion of the volume that would occur in the case of production by machining. It has also been found that, in order to obtain a pleasing result, a geometrical shaping of the preform that approximates to the final form is generally required. The geometry of the preform must be empirically determined here, which is technologically complex. Moreover, the production of the preform causes significant additional costs, due to the machining itself and due to the requirements applying to the volume accuracy. Furthermore, the process control is complex and even minor deviations in the volume of the preform or in the volume of the main cavity may lead to the formation of flash, thereby generating further additional costs as a result of the reworking required.

SUMMARY

The object of the invention is to provide a die and a forging method of the type mentioned at the beginning by which improved production of a toothed rack for a steering device is made possible. This is achieved by a die with the features of the invention and by a forging method with the features of the invention. Advantageous developments are described below and in the claims.

The die according to the invention has an open main cavity, wherein, in the moved-together end position of the two die parts, the main cavity that is formed in the region of the molding recesses between the die parts is adjoined on both sides by secondary cavities. When the die parts move together, the secondary cavities are entered by material of the blank, whereby lateral bulges or flash are formed. According to the invention, the die has in addition to the two die parts at least two secondary molding parts. These are respectively located in the region that lies between the first and second die parts, and the walls that bound the secondary cavities are at least partly formed by the secondary molding parts. The secondary molding parts are respectively displaceable here with respect to the die parts in an adjusting direction that is oriented at an angle to the closing direction. The angle which the adjusting direction of the respective secondary molding part forms with the closing direction favorably lies in an interval from 45° to 135°, angles in the range from at least 70° to 110° being preferred and a right angle to the closing direction being particularly preferred.

The forging method according to the invention for forging a toothed portion of a toothed rack is characterized by the features of claim11. The material displaced into the secondary cavities abuts against secondary molding parts, which respectively partially bound the flow of the displaced material in the respective secondary cavity. The material displaced into the respective secondary cavity is displaced into an intermediate space, which is arranged within the respective secondary cavity (i.e. forms part of the respective secondary cavity) and is bounded by a face of the respective secondary molding part that is directed in the direction of one of the die parts and the end face of the die part or by a face of the respective secondary molding part that is directed in the direction of one of the die parts and a surface of a further secondary molding part, which is arranged in the same secondary cavity. The respective intermediate space therefore lies between the respective secondary molding part and one of the die parts or between two respective secondary molding parts that respectively partially bound the same secondary cavity.

The forging method according to the invention makes it possible to combine a free shaping (that is a shaping that is only partially restricted to walls of the die or in other words is partially unrestricted) and a mold-bound shaping of the material of the blank into the secondary cavities. The flow of material into the secondary cavities is necessary to achieve the shaping of the desired form of the toothed rack, and thereby reduce the preliminary work for preforming blanks.

Being formed in this way makes it possible for the secondary molding parts to be positioned in a defined manner, adjusted with increasing wear or exchanged. As a result, an exchange or reworking of a die part can be avoided, or at least delayed.

Furthermore, the geometry of the secondary cavities is at least co-determined by the secondary molding parts. The geometry and/or setting of the secondary molding parts consequently allows the geometry of the secondary cavities to be changed or adapted, whereby the flow of material of the blank during the forging can be optimized. Improvements in the quality of the completed toothed rack can be achieved as a result. In particular, the flow resistance for the displaced material of the blank can be set, allowing tooth shaping at lower pressures to be achieved, at least over part of the feed path of the die parts, which in turn has a favorable effect on the service life. Moreover, the risk of cracks forming in the toothed rack can be reduced.

In the moved-together end position of the die parts, the secondary cavities are advantageously not filled completely with the material of the blank, i.e. there are in any event regions that have not been reached by the material of the blank. The secondary cavities are preferably open toward the outside here. That is to say that the secondary cavities are not only open toward the main cavities, but are also not bounded by a wall at at least one further location. However, a forming of the secondary cavities that is “open” in the sense mentioned would also be obtained if the secondary cavities were not closed toward the outside in the end position of the die parts but their volume was so great as to not be filled completely by the displaced material of the blank. In the case of a cylindrical blank that is preferably used, the volume of the secondary cavities together is consequently greater than the proportion of the volume of the blank that would have to be removed in the case of production of the toothed rack by machining.

Between a respective secondary molding part and an end face of one of the die parts that is facing the other of the die parts, or between two secondary molding parts that respectively bound portions of the same secondary cavity, there is favorably an intermediate space. Its width is reduced when the die parts are moved together. In the moved-together end position, however, this intermediate space still exists, i.e. it is not completely closed, its width in the moved-together end position (measured in the closing direction) preferably being at least 2 mm.

The flow of material can be controlled by the secondary molding parts in such a way that, although the secondary cavities are not completely filled with material, the flow stresses that are required for the shaping of the toothing are achieved. Nevertheless, the workpiece blank has to be formed less precisely than in the case of the prior art, since fluctuations in the amount of material can be compensated to the greatest extent by the free space in the secondary cavity.

An advantageous embodiment of the invention provides that a respective secondary molding part has first and second side faces, of which the first side face abuts against an end face of one of the two die parts, which is facing the other die part, and at least a portion of the second side face forms a wall bounding the respective secondary cavity. The first and second side faces of the secondary molding part are connected to one another by way of an end face. This end face favorably forms an angle of less than 45°, preferably less than 20°, with the closing direction, a parallel alignment with the closing direction being particularly preferred. The end face of a respective secondary molding part is preferably drawn back from the main cavity, that is to say does not protrude into the main cavity or does not finish flush with it, but rather forms a wall bounding the secondary cavity against which material of the blank coming out from the main cavity abuts when the die parts are moved together.

The end face is advantageously set back from the main cavity by at least a tenth, preferably at least a fifth, of the distance between the die parts in their end position. Here there extends between the end face and the main cavity a portion of the end face (lying next to the molding recess) of the die part against which the secondary molding part abuts, the extent of this portion of the end face of the die part, seen in cross section through the die (which is aligned at right angles to the longitudinal extent of the toothed rack or of the main cavity), being at least a tenth, preferably at least a fifth, of the distance between the end faces of the die parts (measured in regions next to the molding recesses) in their moved-together end position.

The thickness of the secondary molding parts (measured in the closing direction) is favorably at least a quarter, preferably at most three quarters, of the distance between the mutually facing end faces of the die parts (in their portions lying next to the molding recesses) when the die parts assume their moved-together end position.

An advantageous variant of an embodiment of the method according to the invention provides that, during the forging of the toothed portion of the toothed rack, the secondary molding parts are kept stationary with respect to their adjusting directions, that is to say there is no movement in the adjusting direction, at least from the point in time from which material of the blank abuts against the secondary molding parts. The secondary molding parts are kept stationary here with respect to one of the two die parts; preferably it is only on the fixed die part that secondary molding parts are held, and are consequently stationary with respect to said fixed part during the forging.

In another possible embodiment of the method according to the invention, however, at least one of the secondary molding parts could be adjusted in its adjusting direction during the forging of the toothed portion of the toothed rack. This allows the flow of material to be influenced further. Such an adjustment of at least one of the secondary molding parts, favorably all of the secondary molding parts, may be performed here at the same time as the moving together of the die parts and/or thereafter. A path-controlled traversing of the movement of the secondary molding parts, in which the movement is coupled to the closing movement of the die parts by corresponding wedge and/or slotted-link guides, is in this case conceivable and possible. Alternatively, one or both of the secondary molding parts may be specifically moved by additional hydraulic rams during the shaping process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Elements that are the same or act in the same way are designated by the same reference numerals in the figures.

FIG. 1schematically shows a possible way of forming a steering device for a motor vehicle. The steering device comprises a steering wheel1and a steering shaft2, which comprises two or more portions connected to one another in an articulated manner. Attached or coupled to the steering shaft2for rotation therewith is a steering pinion3, which meshes with a toothed portion5of a toothed rack4. The toothed rack4is mounted displaceably in the direction of its longitudinal axis, for example in a steering housing6. Tie rods are directly or indirectly in connection with the two ends of the toothed rack4by way of ball joints that are not represented. The tie rods7are each connected to a steered wheel of the motor vehicle in a known manner by way of steering knuckles.

There may be various devices to assist the driver in the steering movement, for example auxiliary drives acting on the toothed rack4or auxiliary drives acting on the steering shaft2.

An enlarged portion of the toothed rack4is represented in a perspective view inFIG. 2. The toothed rack4has a toothed portion5, which for the sake of simplicity is represented in a shortened form inFIG. 2. The toothed portion extends over part of the longitudinal extent of the toothed rack4lying parallel to the longitudinal axis39of the toothed rack4. In the installed state, the toothed rack4is mounted displaceably in a displacing direction40lying parallel to its longitudinal axis39, which is indicated inFIG. 2by a double-headed arrow.

The teeth8of the toothed portion are represented inFIG. 2as straight toothing5with the same spacings and the same tooth forms. It is often intended to use tooth geometries deviating from this, it being possible for helical toothings to be provided. The spacings of the teeth and/or their inclined positions and/or their forms can be varied here by way of the extent of the toothed portion, reference then being made to toothed racks that are variably toothed.

In the exemplary embodiment shown, the region of the toothed rack4lying diametrically opposite the toothing5is cylindrically formed. A toothed rack for a steering device that has such a form is also referred to as a round-back toothed rack. In the region lying diametrically opposite the toothing5(that is the back region), the contour of the toothed rack4is consequently arcuate when seen in cross section. In the region of the toothing5, the toothed rack is of a flattened form when seen in cross section. With regard to this forming, such a toothed rack is also referred to as a toothed rack with a D profile.

A die (that is a mold) for forging the toothed portion of the toothed rack is schematically represented in cross section inFIG. 3, in its open position. The die comprises first and second die parts9,10. The first die part9has a first molding recess11, which serves for molding the portion having the toothing5. The second die part10has a second molding recess12. This has the form of the back region of the toothed rack in the toothed portion, lying diametrically opposite the toothing5, that is to say in the exemplary embodiment is of an arcuate form when seen in cross section at right angles to the longitudinal axis39.

In the exemplary embodiment shown, the first die part9, which has the first molding recess11, forming the toothing, is movable and the second die part10is fixed. The first die part9is moved here in the closing direction13, in the direction of the second die part10, from the open position until a completely moved-together end position is reached. The moved-together end position is represented inFIG. 5(with the blank15formed into the toothed rack4) and for further illustration inFIG. 9(without a blank15formed into the toothed rack). A converse way of forming, in which the first die part9is fixed and the second die part10is adjustable in a closing direction (which is opposed to the closing direction13), in the direction of the first die part9, for the molding of the toothed portion of the toothed rack is conceivable and possible.

Between the die parts9,10, to be precise in the region in which the molding recesses11,12lie, there is formed a main cavity14, cf.FIG. 9. The main cavity14consequently comprises the regions of the molding recesses11,12and also the region between the two die parts9,10that lies between the molding recesses11,12. InFIG. 9, this region lying between the molding recesses11,12is delimited schematically by dashed lines from regions lying between the die parts9,10that lie laterally in relation to the molding recesses11,12. The delimitations are depicted here inFIG. 9as running in a straight line between edges at the borders of the molding recesses11,12. Instead, the delimitations could also continue the profile—arcuate here—of the second molding recess12, that is to say be formed in a way corresponding to the cross-sectional contour of the cylindrical blank15placed into the second molding recess12before its shaping. As seen in cross section (corresponding toFIG. 9), the mold cavity that is bounded by the molding recesses11,12of the two die parts9,10in the position in which the two die parts9,10are moved closest together during the shaping process and also by the lines that are formed by the tangential extensions of the inner contours of the molding recesses11,12of the respective die part11,12beyond the associated edge27,28or24,25up to the point of intersection of these tangential extensions, taken from the two die parts9,10, may also be regarded as the main cavity14. The exact profile of the delimitation, that is to say whether for example the possibility represented inFIG. 9or the other possibility described is chosen, is unimportant.

The main cavity14is consequently open on opposite sides—with respect to a mid-plane lying parallel to the closing direction13and passing through the die parts9,10or through the (shaped) blank15. The main cavity14is adjoined here on both sides by secondary cavities16,17. The openings between the main cavities14and the secondary cavities16,17may also be referred to as “die gaps”. The secondary cavities16,17respectively lie within a region that lies between the two die parts9,10; to be precise, these regions lie on both sides (with respect to the previously mentioned mid-plane) next to the molding recesses11,12.

A separate secondary molding part18,19is also respectively arranged in the regions lying between the die parts9,10and on both sides of the molding recesses11,12. A respective secondary molding part18,19has first and second side faces20,21and an end face22, which is directed toward the main cavity14and connects the first and second end faces20,21. The first side face20of the respective secondary molding part18,19abuts against the end face23of the second die part10that is directed toward the first die part9. The opposite, second side face21of the respective secondary molding part18,19forms a wall bounding the respective secondary cavity16,17. The end face22of the respective secondary molding part18,19is drawn back from the respective edge24,25, which lies between the end face23of the second die part10that is directed toward the first die part9and the second molding recess12of the second die part10. Here, the distance a of the respective secondary molding part18,19from the respective edge24,25is favorably at least a tenth, preferably at least a fifth, of the distance s that the two die parts9,10or their end faces26,23are from one another. The portion of the end face23of the second die part that lies between the respective secondary molding part18,19and the respective edge24,25of the second die part10forms a further portion of the walls bounding the respective secondary cavity16,17.

A further portion of the walls bounding the respective secondary cavity16,17is also formed by the end face26of the first die part9that is facing the second die part, these portions of the walls respectively adjoining the edges27,28, which lie between the end face26of the first die part9and the first molding recess11of the first die part9.

A respective secondary molding part18,19is mounted displaceably in the respective adjusting direction29,30with respect to the fixed, second die part10. In the exemplary embodiment shown, the adjusting directions29,30lie parallel to one another and at right angles to the closing direction13and to the longitudinal axis39. Angular alignments of the adjusting directions29,30with respect to the closing direction13and/or with respect to the longitudinal axis39are also conceivable and possible, the adjusting directions29,30not having to lie parallel to one another. Deviations from the right-angled alignment to the closing direction13and/or to the longitudinal axis39of less than 20° are preferred.

In the exemplary embodiment shown, the end faces22of the secondary molding parts18,19are planar and lie parallel to the closing direction13and parallel to the longitudinal axis39. The end faces22of the opposing secondary molding parts18,19face in the direction of the main cavity14and here preferably in the direction of a central region of the toothed rack4to be formed.

The end faces22could also form an angle that is favorably less than 45°, preferably less than 20°, with the closing direction13and/or with the longitudinal axis39.

The forging of the toothed rack is explained below on the basis ofFIGS. 3 to 6.

In the open position of the two die parts9,10, the blank15is placed into the second molding recess12of the fixed, second die part10, cf.FIG. 3. The blank15has here a temperature that is suitable for hot forging. For a blank made of steel, this lies above the recrystallization temperature of steel, preferably between 600° and 1250° Celsius.

In principle, the mold and the method can, however, also be used for cold forging. On account of the high shaping forces and the resultant loads on the mold, however, hot shaping is preferred in the case of shaping steel.

As a consequence, the movable, first die part9is moved in the closing direction13, the blank15being shaped, and beginning to flow in the plastified state under the hydrostatic pressure forming, after impingement of the first die part9. An intermediate position during the moving together of the two die parts9,10is represented inFIG. 4. The shaping of the blank15has already commenced and material of the blank has come out into the region of the secondary cavities16,17, material of the blank already having run up against the end faces22of the secondary molding parts18,19.

As the first die part9moves further in the closing direction13, the blank15is deformed further and further material of the blank15passes into the secondary cavities16,17. As the moving together of the die parts9,10continues, material of the blank passes into the respective intermediate space42,43between the second side faces21of the secondary molding parts18,19(these second side faces21lie opposite the first side faces20, which abut against one of the die parts9,10, here against the second die part10) and the end face26of the first die part9(if the secondary molding parts18,19were to abut with their one side face against the first die part9, the respective intermediate space would lie between the other side face of the respective secondary molding part18,19and the end face23of the second die part10). These intermediate spaces42,43become smaller as the first die part9increasingly approaches the moved-together end position of the die parts9,10, which is represented inFIG. 5. This results in an increased hydrostatic pressure in the material of the blank15in the final phase of the moving together. Under this high pressure, there is furthermore an increased flow of the material of the blank15around the edge31of the respective secondary molding part18,19that lies between the second side face21, bounding the gap mentioned, and the end face22of the respective secondary molding part18,19. These edges31are consequently exposed to a relatively increased amount of wear.

Once the die parts9,10have reached the moved-together end position, cf.FIG. 5, and the method of forging the blank15has been completed, the first die part9is opened, counter to the closing direction13, and the toothed rack4that has been formed by shaping of the blank15is removed from the die, cf.FIG. 6.

InFIG. 6, the arcuate profile41in the non-toothed portion of the toothed rack4can be seen. The molding recesses11,12of the die parts9,10extend into the non-toothed portion of the toothed rack4, which is indicated for the die part9by a dashed line.

After the forging, the toothed rack4still has flash32,33on both sides, which can be subsequently detached.

The secondary molding parts18,19consequently represent at least parts of the geometry of the flash32,33. Consequently, they also influence the flow of the material of the blank15during the forging operation.

During the method of forging the exemplary embodiment described above, the secondary molding parts18,19remain stationary with respect to the second die part10. With increasing wear, the secondary molding part18,19can be adjusted by a displacement in the respective adjusting direction29,30. When doing so, a stop plate34,35, which lies between the end of a respective secondary molding part18,19that is directed away from the main cavity14and a respective stop36,37, can be exchanged. The stops36,37are stationary with respect to the die part on which the respective secondary molding part18,19is displaceably guided, here that is with respect to the second die part10.

This adjustment of the secondary molding parts18,19allows the changes in the material flow that are caused by the wear to be at least partially compensated. The service life of the die can be increased as a result.

If the wear on the secondary molding parts18,19has become too great, they can be exchanged in a simple way, without reworking of the die parts9,10themselves being required. The wear occurring on the die parts9,10is much less than the wear occurring on the secondary molding parts18,19. In the final phase of the moving together of the die parts9,10, in which the hydrostatic pressure is particularly high, a much smaller flow occurs around the edges24,25,27,28of the die parts9,10.1

It would also be conceivable and possible to form the secondary molding parts18,19such that they are adjustable during the process (between individual forging operations). Corresponding actuators, by which the secondary molding parts18,19can be adjusted in the adjusting directions29,30, could be provided for this purpose.

Optimizations of the flow can be performed in a simple way on the device for the forging method. For this purpose, the positions of the secondary molding parts18,19may be changed and/or secondary molding parts with different geometries, for example with respect to their thickness (that is the distance between their side faces20,21), may be used. In this way, optimizations of the flow can be carried out without the die parts9,10themselves being worked.

A second exemplary embodiment of the invention is represented inFIGS. 10 to 13. This exemplary embodiment corresponds to the exemplary embodiment described above, apart from the differences described hereafter.

The secondary molding parts18,19are here likewise mounted displaceably in the adjusting directions29,30on the fixed, second die part10. However, in the moved-together end position of the die parts9,10, the one end faces20of the secondary molding parts18,19are not abutting against the second die part10but against the end face26of the first die part9, cf.FIG. 12. The side faces abutting against the die parts9,10are in turn referred to as first side faces20. The opposite, second side faces21are directed toward the end face23of the second die part10and are at a distance from it. Between these second side faces21and the end face23there consequently lies an intermediate space42,42, which represents part of the secondary cavities16,17and into which material of the blank15flows in the final phase of the moving together of the die parts9,10, as can be seen from the comparison ofFIGS. 11 and 12.

In this exemplary embodiment, the secondary cavities16,17are not open toward the outside in the moved-together end position of the die parts9,10. However, these secondary cavities16,17are only partially filled with the displaced material of the blank15in the end position of the die parts9,10. In this sense it is likewise possible to speak of “open” secondary cavities or to speak of an “open overall cavity”, which comprises the main cavity14and secondary cavities16,17.

The flash geometries32,33differ from the geometry of the flash32,33of the first exemplary embodiment.

The secondary molding parts18,19in turn remain stationary during the moving together of the die parts9,10.

FIG. 14shows a third exemplary embodiment, which corresponds to the first exemplary embodiment apart from a modification in the region of the secondary molding parts18,19. Here, the secondary molding parts18,19have in the region of their ends directed toward the main cavity14projections38, by which the intermediate space42,43between the secondary molding parts18,19and the end face26of the first die part9is reduced in the region of the projections38. As a result, incisions are formed in the flash32,33, whereby detachment of the flash32,33is made easier. In order to place the incisions at the starting point of the flash32,33from the main body to be formed of the toothed rack4, the secondary molding parts18,19here reach further up to the main cavity14, i.e. the end faces22of the secondary molding parts18,19bound the main cavity. The material coming out into the second cavities passes here directly into the intermediate spaces42,43lying between the secondary molding parts18,19and the end face26(lying next to the molding recess11) of the second die part9. The secondary molding parts18,19in turn remain stationary during the moving together of the die parts9,10.

A mounting of the secondary molding parts18,19analogous to the second exemplary embodiment would also be possible to form such incisions. The projections38would then be aligned with the end face23of the second die part10.

A fourth exemplary embodiment is explained on the basis ofFIGS. 15 to 17. The mounting of the secondary molding parts18,19corresponds to the first exemplary embodiment, represented inFIGS. 3 to 9, but could for example also correspond to the exemplary embodiment that is represented inFIGS. 10 to 13. As a difference from the exemplary embodiments described above, in this exemplary embodiment the secondary molding parts18,19are moved in the respective adjusting direction29,30during the moving together of the die parts9,10, to be precise at least also from the point in time from which displaced material of the blank15abuts against them (before that they may be stationary or likewise already be moved). This is also clear from the comparison ofFIGS. 16 and 17. This allows the flowing of the material of the blank15to be influenced further. Such influencing of the material of the blank allows an optimization of the flowing processes, and consequently of the overall forging method, to be achieved, for example in order to increase once again the hydrostatic pressure in a final phase of the moving together of the die parts9,10. When doing so, however, material can continue to flow into the secondary cavities16,17, since they are at least not completely filled. At least in the final phase of the moving together of the die parts9,10before reaching the moved-together end position, material of the blank15passes into the intermediate spaces42,43, which lie between the secondary molding parts18,19and the end face26of the die part9.

In addition to the possibilities of optimizing the flow on the device for the forging method by different geometries of the secondary molding parts18,19, optimizations can be carried out here by the positions and movements of the secondary molding parts18,19(which at least in this exemplary embodiment may also be referred to as punches) during the forging.

The adjustment of the secondary molding parts18,19may be performed by actuators that are not represented in the figures. Furthermore, a coupling with the movement of the adjustable die part9may take place, for example in that the movement of the die part9may be accompanied at the same time by adjustment of sloping faces, against which the ends of the secondary molding parts18,19that are remote from the main cavity abut.

FIG. 18shows a fifth exemplary embodiment, which corresponds to the first exemplary embodiment apart from the form of the molding recess12of the second die part10. Here, the molding recess12has side faces converging in a wedge-shaped manner, whereby the back region of the toothed rack4, lying opposite the toothing5, is formed over the toothed portion with a corresponding form. The form of the toothed rack that is formed could also be referred to as a toothed rack with a triangular cross section.

FIG. 19shows a sixth exemplary embodiment, which corresponds to the first exemplary embodiment apart from the differences mentioned hereafter. Here, secondary molding parts18,18′,19,19′ are mounted displaceably in the adjusting directions29,30both on the first die part9and on the second die part10. In each case, one of the side faces20,20′ of the secondary molding parts18,18′,19,19′ abuts against the respective die part9,10. The side faces21,21′, respectively directed toward one another, of the secondary molding parts18,18′ and19,19′ that are lying on the same side of the main cavity have between them a gap, the thickness of which is reduced when the die parts9,10are moved together but is not completely closed in the moved-together end position of the die parts9,10. At least in the final phase of the moving together of the die parts9,10, material of the blank4flows into these intermediate spaces42,43.

The secondary molding parts18,19are drawn back from the main cavity, while the secondary molding parts18′,19′ adjoin the main cavity flush, and their end faces, inclined here, represent portions of the walls bounding the main cavities. Various modifications of this are possible; for example, all of the secondary molding parts could be drawn back from the main cavity14. In the case of preferred embodiments, at least two of the secondary molding parts18,18′;19,19′ are drawn back from the main cavity.

The displaceable mountings of the secondary molding parts18,18′,19,19′ on the die parts9,10are not represented inFIG. 19for the sake of simplicity. For adjustment when wear commences, stop plates34,34′,35,35′ could in turn be provided for example.

In further exemplary embodiments, displaceably mounted secondary molding parts could be provided only on the movable die part9.

If secondary molding parts that are separate from the die parts9,10are provided both on the fixed die part10and on the movable die part9, at least the secondary molding parts that are arranged on one of the die parts9,10are mounted displaceably in adjusting directions29,30with respect to the die part9,10in the way described; preferably, such a displaceable mounting is then provided for all of the secondary molding parts18,19.

In the figures, the fixed die part10is represented at the bottom and the blank15is placed into this fixed die part. An inverted arrangement, with the blank15being placed into the movable die part9, is likewise possible.

In the exemplary embodiments shown, the molding recess forming the toothings is arranged in the movable die part9. An arrangement in the fixed die part10is also possible.

To the extent to which they can be applied or executed, all of the different individual features of the various examples can be exchanged and/or combined with one another without departing from the scope of the invention.