WO1986003437A1

WO1986003437A1 - Press device for producing a steering rack

Info

Publication number: WO1986003437A1
Application number: PCT/EP1985/000662
Authority: WO
Inventors: Ansgar Betz
Original assignee: Zahnradfabrik Friedrichshafen Ag
Priority date: 1984-12-13
Filing date: 1985-12-03
Publication date: 1986-06-19
Also published as: DE3542672A1

Abstract

A press device for producing a steering rack (4), especially a rack with a variable ratio obtained by different tooth profiles, has an upper forging piece (1) and a lower forging piece (2). A forging piece (2) forms the negative die for the lower part of the steering rack which is to be made from a blank and the other forging piece (1) serves to shape the toothed profile of the rack to be produced in the negative die. The steering rack is produced by cold pressing whereby a forging piece (1) effects a tumbling motion over the forging blank during the pressing process. A gap (13) is formed between the two forging pieces (1, 2) for the lateral flow of the material during the pressing operation, the gap being at least partly filled by strips (8) which form on both longitudinal sides of the steering rack which is produced (4). The mutually facing surfaces (10, 11) of the two forging pieces (1, 2) are designed laterally next to the negative shapes of the steering rack (4) in the region of the gap (13) in such a way that the gap is at least partly widened towards the outside.

Description

Press device for producing a rack

The invention relates to a pressing device for producing a rack according to the kind described in the preamble of claim 1.

DE-AS 21 41 205 describes a steering gear for vehicles, in which a toothed rack is explained, the teeth of which have a different profile shape in the central region than in the outer parts. In this way, a variable translation is achieved. Steering gear with such racks can e.g. can be used advantageously for passenger cars. The reduction changes relatively quickly from the center of the rack to both sides until an approximately constant reduction ratio is reached. The rack works together with a pinion, which is provided with helical teeth and whose axis encloses an angle other than 90 ° with the rack axis. In the middle area of the rack, the flank lines of the teeth form an angle with the pinion axis, which angle is changed compared to the angle in the outer parts of the rack. With such a configuration, reduction ratios of 2: 1 can be achieved without difficulty.

However, the economical production for series production of such a rack is associated with difficulties. It is proposed in ^' DE-AS 21 41 205 to produce the rack by a straight-line broaching process for the majority of the teeth. However, a number of teeth in the central area of the rack must be manufactured in a special way. For this purpose, these profiles are to be modified accordingly in a special treatment using a special broaching method. A disadvantage of this Positioning method is. However, it is very complex and expensive, or is not economically feasible in this way at all.

DE-OS 32 02 254 already describes a method and a device for producing a toothed rack, which is produced by a pressing process. For this purpose, a blank is treated in a press with an upper die and a lower die by cold forming, a die part performing a wobble movement over the blank during the pressing process. With these manufacturing processes, the manufacturing time is shorter and the material requirement is lower. Furthermore, an increase in material strength and smooth surfaces are achieved.

Press devices for cold extrusion with a tumbling die are also described in VDI reports No. 266 (^ ö "), pp. 29-35.

In the manufacturing process described in DE-OS 32 02 254, there is a gap between the two die parts for the lateral outflow of material during the pressing process. The unnecessary material can flow into this gap during the pressing process and thus forms strips running on both longitudinal sides of the resulting rack. These strips can be removed after the manufacturing process.

However, this gap has the disadvantage that it is possible to drain excess material in a relatively simple manner. This means that the gap will fill with material very quickly during the wobble press. The resulting material bar thus offers a corresponding resistance to the further pressing process. A high degree of compression occurs in the two strips and there is a risk that a further collapse ken of the two die parts is no longer possible. This means that cavities can remain in the negative form, in particular in the area of the tooth tips, or that the tooth tips are not compressed sufficiently and are therefore not resistant enough and are not geometrically perfect.

The present invention is therefore based on the object of creating a pressing device of the type mentioned at the beginning, in which a material drain is possible to a sufficient extent, but which does not adversely affect the production of the toothed rack.

According to the invention, this object is achieved by the feature mentioned in the characterizing part of claim 1.

The two surfaces of the die parts facing each other are no longer flat or even, but at least partially widen outwards. In this way, the tumbling die part, generally the upper die, can be kneaded into the material that has flowed out at the beginning of the pressing process. During the further pressing process, however, the gap can become ever narrower and less permeable, so that the pressing process can be carried out without interference from the emerging material.

Because the superfluous material can now flow outwards without any particular difficulties due to the formation of the gap according to the invention, the toothed rack can be produced from a blank, if necessary without pre-pressing, in one operation.

Various configurations are possible with regard to the widening of the gap. For example, the gap can widen outwards from the edges of the negative mold, ie the surfaces of the two die parts facing each other run directly at the edges of the negative molds without a transition 8 5 /

apart.

The gap can widen continuously or in steps. Due to the wobbling movement, small steps can occur in the gap.

The gap can be widened, i.e. the edge along the die shape is formed like a hammer fin.

It is advantageous if the half wedge angle is greater than the wobble angle of the swivel part that performs a wobble movement. In general, the wedge angle will be significantly larger than the wobble angle. A sufficiently large wedge opening then arises in which the material which has flowed out through the constriction at the edge of the die no longer has any contact with the upper or lower part of the die. The pressing process can no longer be significantly hindered by the material that has flowed out.

The gap width at the narrowest point at the end of the pressing process can be between 0.2 to 5 mm, preferably 0.4 to 1 mm. Of course, other values are also possible within the scope of the invention. This depends on the individual circumstances, e.g. Size and material of the rack.

An exemplary embodiment of the invention is described in principle below.

Show it:

Fig. 1: the two die parts of a pressing device with the 'rack in cross section according to the prior art. Fig. 2: the two die parts according to the invention with a rack in cross section.

3: Enlarged section of the circle A from FIG. 2 in a different embodiment.

Of the press device, only the two die parts, namely an upper die part 1 and a lower die part 2, are shown, since the press device itself is of a conventional design and thus its structure and mode of operation are generally known.

The upper part of the die is provided with a negative shape for the tooth profile and the lower part 2 is provided with a negative shape for the lower part of the toothed rack 3 to be produced from a blank. The blank can be a round rod, for example. The finished toothed rack 3 has - seen in cross section - essentially a Y-profile. On the Unter¬ side, the rack 3 is provided with a flat in the of symmetry extending approximately over the extending to interlocking portion in the longitudinal direction of the web ^"4. From the web 4 from run two Schrägfl surfaces 5 and 6, rod side to the toothed. The two inclined surfaces 5 and 6 represent the contact surfaces for a pressure piece after installation in a steering gear. The upper die part 1 is generally fastened in a bell, not shown, which is pivotably mounted in a bearing the bell and thus also the upper part of the die are made to tumble in relation to the stationary lower part 2. The forming force is thus concentrated only on a partial surface of the workpiece, the pressure zone being displaced over the entire surface of the workpiece and thus causing the forming. 1 shows an upper die part 1 and a lower die part 2 according to the prior art. As can be seen, there is a gap 7 between the two die parts, into which superfluous material in the form of side strips 8 can flow during the pressing process. The two mutually facing surfaces 10 and 11 of the upper die part 1 and the lower die part 2 are flat or lie parallel to one another. The strips 8 thus represent considerable resistance to deformation and the two die parts may not come close enough under certain circumstances. This means that 4 cavities 12 can remain in the area of the tooth heads of the toothed rack.

The pressing device according to the invention can be seen from FIG. As indicated, the mutually facing surfaces 10 and 11 of the upper die part 1 and of the lower die part Z are not parallel to one another, but rather strive apart. This results in a wedge-shaped gap 13. The gap width at the narrowest point can be between 0.2 and 5 mm, preferably between 0.4 and 1 mm.

The gap 13 widens continuously towards the outside.

As can be seen, this results in a wedge-shaped shape of the strips 8 seen in cross section. Due to the shapes of the gaps 13, the superfluous material can easily escape during the approach and during the tumbling process of the upper part 1 of the die. Since the cross section of the two strips 3 on the long sides of the rack is very small, the two strips 8 can be easily punched out subsequently.

Half the wedge angle A is significantly larger than the wobble angle of the upper die part 1. The toothed rack 4 is formed in the upper region, in particular in the region of the teeth 3, on both sides upwards to be slightly inclined, which is shown in FIG. 2 _. is represented by the angle B. In this way, compression also takes place from the side during the tumbling process.

It is also advantageous if the negative shape of the toothed rack in the upper part 1 of the die not only serves essentially as before to form the tooth profile shapes, but also absorbs more of the toothed rack. This is indicated in FIG. 2 by the dashed line 9. This measure makes production from a round rod easier, since it is better encompassed by the upper die part 1. The additional molding depth can be a few millimeters.

3 shows an embodiment of the die parts 1 and 2 in the area next to the toothed rack to be formed. As can be seen, the two die parts 1 and 2 have sharp edges there, the edge of the upper die part 1 even being able to overlap the edge of the lower die part somewhat. In this way, the bar 8 can be secured immediately at the end of the pressing process.

Another possibility or in addition to this is that the upper die part 1 has a leading edge 14 (shown in dashed lines) against which the emerging material runs and is bent downwards there during the further pressing process, as a result of which the strip 8 also breaks off . Of course, however, the leading edge can also be arranged on the lower part of the die for breaking off the strip 8. In this case it is bent upwards.

Claims

Patent claims

1. Press device for producing a toothed rack, in particular a toothed rack with variable translation through different tooth profiles, with a die upper part and a lower die part, a die part forming the negative form for the lower part of the toothed rack to be produced from a blank, and in the other die part 'the toothing profile of the toothed rack to be produced is molded in negative form, the toothed rack being produced by cold forming, for which purpose a die part performs a wobble movement over the blank during the pressing process and between the two die parts to the side ¬ Liche flow of material during the pressing process, a gap is formed, which is at least partially filled by bars forming on both long sides of the resulting rack, characterized in that the mutually facing surfaces (10, 11) of the two die parts (1 , 2) are formed laterally next to the negative forms of the toothed rack (4) in the area of the gap (13) in such a way that the gap (13) at least partially widens outwards.

2. Press device according to claim 1, d a d u r c h g e k e n n z e i c h n e t that the gap (13) widens outwards from the edges of the negative molds.

3. Press device according to claim 1 or 2, characterized in that the gap (13) widens at least approximately continuously er¬.

4. Press device according to claim 1 or 2, d a d u r c h g e k e n n z e i c h n e t that the gap (13) widens stepwise.

5. Press device according to one of claims 1 to 4, d a d u r c h g e k e n n z e i c h n e t that the gap (13) widens wedge-shaped.

6. Press device according to claim 6, so that the half wedge angle (A) is greater than the wobble angle of the swage part (1) that performs a wobble movement.

7. Press device according to one of claims 1 to 6, that the gap width at the narrowest point at the end of the pressing process is between 0.2 to 5 mm.

8. Press device according to claim 7, so that the gap width at the narrowest point at the end of the pressing process is between 0.4 and 1 mm.

9. Press device according to one of claims 1 to 8, d a d u r c h g e k e n n z e i c h n e t that in addition to the tooth profile shapes, the upper part of the rack lower part is also molded into the negative shape of the upper die part (1).

10. Press device according to one of claims 1-9, characterized in that the upper die part (1) and the lower die part (2) ^' laterally each have sharp edges next to the negative forms of the rack.

11. Press device according to one of claims 1-11, characterized in that a leading edge (14) for the bar (8) is arranged on the upper die part (1) or the lower die part (2) laterally next to the negative forms of the rack at a distance therefrom .