Method for machining a forged blank, use of such a forged blank as a gear blank, method for producing a gear blank and method for producing a gear

Abstract

The invention relates to a method for machining a nominally rotationally symmetrical forged blank (10) obtained by die forging, which, during the die forging process, has first outer contours defined by the shape of an engraving (211) of a fixed die (21), namely a bottom surface (11) and an outer circumferential surface (12), and second outer contours defined by the shape of an engraving (221) of an adjusting die (22) axially displaceable relative to the fixed die (21), namely a top surface (13), wherein the top surface (13) has axial recesses (131) with axially aligned recess walls (132, 133), comprising the steps: - Clamping the forged blank (10) onto a workpiece carrier using a chuck having clamping jaws, - Finishing the forged blank (10) using a machining tool movable relative to the chuck, The invention is characterized in that the post-processing is carried out by turning at least the first outer contours in a lathe, wherein the clamping jaws of the chuck engage exclusively on the recess walls (132, 133) when clamping the forged blank (10).

Description

[0001] The invention relates to a method for machining a nominally rotationally symmetrical forged blank obtained by die forging, which, during the die forging process, has first outer contours defined by the shape of an engraving of a fixed die, namely a bottom surface and an outer circumferential surface, and second outer contours defined by the shape of an engraving of an adjusting die axially displaceable relative to the fixed die, namely a top surface, wherein the top surface has axial recesses with axially aligned recess walls. comprehensively the steps: - Clamping the forged blank onto a workpiece carrier using a chuck with clamping jaws, - Finishing the forged blank using a machining tool that can be moved relative to the chuck.

[0002] The invention further relates to the use of such a post-processed forged blank as a gear blank, i.e. as a starting workpiece for the manufacture of a gear, as well as to methods for producing such a gear blank and for manufacturing a gear therefrom.

[0003] A generic method for machining forged blanks is known from DE 694 18 629 T2.

[0004] This publication discloses in general terms the provision of a forged blank by drop forging as a starting workpiece for the manufacture of a gear. As is generally known to those skilled in the art, in drop forging a workpiece, usually a so-called sheared blank, i.e., a section cut to length, in particular sheared, from a metallic bar stock, is pressed between two dies, each having a shaping engraving. As a rule, one of the dies, typically the lower die, is fixed at the base of the press, while the other die, typically the upper die, is moved axially relative to the lower die. In addition to this so-called vertical forging, horizontal forging is also known to those skilled in the art, in which the dies are moved in a horizontal direction relative to each other.Since, in the context of the present invention, the relative direction of movement of the dies plays no role, nor does the question of which of the two dies is fixed to the machine base and which is movable relative to it, a fixed die (fixed to the machine base) and an adjustable die (adjustable relative to the machine base) are generally referred to here.

[0005] The shear die is typically inserted into the engraving of the fixed die. This defines the majority of the outer contours of the forged blank to be produced, namely its fixed-die-side surface, which, without limitation of generality and solely for the sake of simplicity, is referred to here as the bottom surface, as well as its outer circumferential surface. These outer contours defined by the fixed die are collectively referred to here as the first outer contours. The engraving of the adjusting die, on the other hand, essentially defines the adjusting-joint-side outer contour of the resulting forged blank, which, without limitation of generality, is also referred to here as the top surface.

[0006] When the shear is inserted into the fixed die, it does not completely fill the fixed die engraving. Only when the upper die is pressed does the material of the shear flow into the outer areas of the engravings and finally fill the entire volume defined by the two engravings completely and exactly. At least, that's the theory. In practice, it often happens that the volume of the shear does not exactly match the volume defined by the two engravings. To avoid defects in the resulting forged blank, slightly oversized shears are often used. The corresponding excess material, which does not fit within the shape defined by the engravings, hinders the precise guidance of the adjusting die. In particular, this can lead to misalignment or tilting of the adjusting joint relative to the lower die. As a result, the precise alignment or...The relative alignment of the first outer contours created by the fixed die with the second outer contours created by the adjusting die is lost or impaired. This results in mass distributions that deviate from the plan. In the case of nominally rotationally symmetric forged blanks, such as those used as starting material for gear production, such a mass imbalance can lead to imbalances in the resulting gears. A "nominally rotationally symmetric" forged blank is understood here to be one that, under practically impossible ideal manufacturing conditions, would be exactly rotationally symmetric, i.e., designed to be exactly rotationally symmetric. In practice, however, deviations from ideal rotational symmetry will always occur, particularly due to the phenomenon described above, which arises when there is an excess of mass in the forging blank underlying the forging process.A similar phenomenon can also be observed with non-ideal press guidance on the machine side or with the excess use of release agents intended to facilitate the demolding of the shear from the die.

[0007] It is therefore common practice to machine the resulting forged blank. For this purpose, it is typically clamped in a chuck with jaws and fed to a machining tool that moves relative to the chuck. The typical approach is to first clamp the forged blank at an "exact" outer contour, namely the one formed by the die, i.e., to engage the jaws of the chuck at this point. In the corresponding machining step, the "deviant" outer contour, formed by the offset or angled die, can be machined, with the clamping at the "exact" outer contours serving as a reference point. In a subsequent step, the partially machined forged blank is then re-clamped to allow machining of the outer contours that were previously clamped.The clamping is carried out on contours that were machined in the first post-processing step.

[0008] This approach is effective if, in the first post-processing step, all "defective" outer contours are reworked and referenced to the "exact" contours. However, this approach fails for complexly shaped components, such as gears, as disclosed in DE 10 2019 130 185 A1. Such gears, particularly on their top surface, have recesses located between spoke-like webs that extend to create a weight- and material-saving connection between a radially inner hub area and a radially outer gear ring area. Simple post-processing operations, such as surface turning using a lathe, are not possible within these recesses. Material misalignments that have formed in these areas cannot be corrected by machining.

[0009] The aforementioned DE 694 18 629 T2 solves this problem through highly complex post-processing using a spark erosion electrode, which, however, appears to be not very economical in mass production.

[0010] The object of the present invention is to further develop a generic method for machining a forged blank in such a way that, when said forged blanks are used as gear blanks, gears with a more uniform mass distribution, i.e. with lower imbalances, can be manufactured.

[0011] This problem is solved in conjunction with the features of the preamble of claim 1 by carrying out the post-processing by turning at least the first outer contours in a lathe, wherein the clamping jaws of the chuck engage exclusively on the recess walls when clamping the forged blank.

[0012] The use of a forged blank according to the invention is the subject of claim 4. Methods for producing a corresponding gear blank or a gear are the subject of claims 5 and 6.

[0013] Preferred embodiments of the invention are the subject of the dependent patent claims.

[0014] The core idea of ​​the present invention lies in the following: when machining a forged blank, particularly during simple surface turning on a lathe, the forged blank is clamped at its "defective" outer contours (i.e., those formed by the adjusting die) and the "exact" outer contours (formed by the fixed die) are machined, referencing the "defective" outer contours. This may result in slightly more chip waste. However, overall, all proportions are precisely aligned because, according to the invention, reference is made to structures that, while initially defective, cannot be corrected during a turning process. The originally defective contours are thus subsequently elevated to the correct standard, and the originally exact contours are adapted to this new standard.The result is a forged blank with significantly reduced mass misdistribution, which allows the production of gears with lower imbalance.

[0015] An additional advantage of the inventive approach is that the entire machining process can be performed in a single setup. Re-clamping, which is time-consuming and prone to errors, is eliminated. Clamping at positions that are inaccessible for machining anyway does not impede simultaneous access to all surfaces requiring machining.

[0016] As explained, the clamping according to the invention takes place on axially aligned walls of the recesses in the top surface produced by the die, i.e., in the preferred embodiment of the invention, on the inner walls of the areas between the spoke-like webs that connect the hub area of ​​a gear blank to its gear rim area. These recesses have, on the one hand, axially aligned and additionally azimuthally (i.e., circumferentially extending) first recess walls, and on the other hand, also axially aligned but additionally radially extending second recess walls. Preferably, the clamping jaws of the chuck engage exclusively on said first recess walls when clamping the forged blank. In other words, the clamping according to the invention of the forged blank or gear blank preferably takes place on the outside of its hub area and / or on the inside of its gear rim area.

[0017] Preferably, the clamping is carried out exclusively on the outer circumference of the wheel hub area. This design is particularly preferred because the chuck can be reduced to the radial central area of ​​the forged blank, so that both axial sides of the gear ring area are accessible for machining.

[0018] Based on the described invention, a method for manufacturing a gear blank can be defined, comprising - Die forging for forming a shear into a nominally rotationally symmetric forged blank by pressing the shear between a fixed die and an adjusting die axially displaceable relative to the fixed die, whereby the forged blank receives first outer contours defined by the shape of an engraving of the fixed die, comprising a bottom surface and an outer circumferential surface, and second outer contours defined by the shape of an engraving of the adjusting die, comprising a top surface having axial recesses with axially aligned recess walls, - Clamping the forged blank using a chuck of a lathe with clamping jaws, wherein the clamping jaws of the chuck engage exclusively on the recess walls, - machining of the forged blank by turning down at least its first outer contours.

[0019] Such a gear blank can be used as a basis for manufacturing a gear. For this purpose, it must be provided with face teeth on its outer circumference in an additional post-processing step by machining.

[0020] Further features and advantages of the invention will become apparent from the following detailed description and the drawings.

[0021] They show: Fig. 1 a forged blank suitable for application of the reworking process according to the invention in a first perspective view, Fig. 2 a cross-sectional view through the forged blank of Fig. 1 with suggested forging dies, Fig. 3 the forged blank of Fig. 1 in a second perspective view, Fig. 4 a schematic cross-sectional view through the forged blank of Fig. 1 to illustrate the problem underlying the present invention, Fig. 5 an illustration of the method according to the invention, Fig. 6 a schematic sectional view of a forged blank machined according to the invention, Fig. 7 a gear produced according to the invention in a first perspective view as well as Fig. 8 the gear of Fig. 7 in a second perspective view.

[0022] Identical reference symbols in the figures indicate identical or analogous elements.

[0023] The Fig. Figures 1 to 3 show in different representations a forged blank 10 as it is suitable for further processing using the method according to the invention.

[0024] Fig. Figure 2 shows a sectional view of the forging blank 10 together with schematically indicated dies of a forging press, namely a fixed die 21, shown here as the lower die, and an adjusting die 22, shown here as the upper die, which is adjustable axially on the fixed die 21, which is fixed with respect to a machine base. During the forging process, a shear (not shown in detail) is inserted into the engraving 211 of the fixed die 21. The engraving 211 of the fixed die 21 defines the shape of the bottom surface 11 and the shape of the outer circumferential surface 12 of the forging blank 10 to be produced. The engraving 221 of the adjusting die 22, on the other hand, defines the shape of the top surface 13 of the forging blank 10 to be produced.In the illustrated embodiment, where the forged blank is suitable as a gear blank, its radial center is formed as a hub region 14, its radial periphery as a gear ring region 15, and the radially intervening region in the form of bottle-shaped webs 16, between which recesses 131 are arranged in the top surface 13. The recesses 131 are bounded by axially oriented recess walls 132, 133. The substantially axially / azimuthally oriented recess walls 132, 133 form the radial outer surfaces of the hub region 14 and the radial inner surfaces of the gear ring region 15. The substantially axially / radially oriented recess walls 133 form the side surfaces of the webs 16.

[0025] Even those in Fig. The particularly clearly visible bottom side 11 of the forged blank 10 reveals the central hub area 14 and the peripheral gear ring area 15. However, on this side, there are no webs between them, but rather a disc-like connecting body with a star-shaped reinforcement 17.

[0026] Particularly due to manufacturing tolerances in the preparation of the die, but also due to tolerances in the dosage of the release agent, which is added to the engraving 211 along with the die, the volume defined by the engravings 211 and 221 can become overfilled. This can lead to an inclination or misalignment of the adjusting die 22 relative to the fixed die 21. The same error can occur due to imperfect press guidance.

[0027] The result of such a misalignment is greatly exaggerated in Fig. 4 is shown. The outer contours shown here are those that are shown according to Fig. 2 are formed by the engraving 211 of the die 21. This refers in particular to the base surface 11 and the outer circumferential surface 12. These outer contours are also referred to here as the first outer contours. In Fig. The outer contours shown in 6 are those that are according to Fig. 2 are formed by the engraving 221 of the setting die 22. This is in particular the upper surface 13 with the recesses 131 and their recess walls 132, 133. The dashed representation in Fig. Figure 4 shows the actual, defective shape of the top surface 13. For comparison, the ideal shape of the top surface 13 is shown in Fig. 4 shown as dotted lines.

[0028] According to the in Fig. In the inventive method shown in Figure 5, during machining of the forged blank 10, clamping takes place in the chuck (not shown) of a lathe against the recess walls 132 of the recesses 131 in the top surface 13. As indicated by the empty arrows in Fig. As shown in Figure 5, this clamping preferably takes place on the axially / azimuthally aligned recess walls 132, in particular on the walls forming the outer surfaces of the hub area 14. The post-processing is thus expressly directed to the “defective” outer contours created by the adjusting die 22. As indicated by the filled arrows in Fig. As shown in Figure 5, with this clamping setup almost all external contours created by the die 21 are accessible for post-processing by turning. Additionally, the radial outer edge region of the top surface 13, i.e., the top surface of the gear ring area 14, can also be turned in the same operation. Thus, in a single turning step without intermediate reclamping of the forged blank 10, post-processing is carried out that references originally defective external contours.

[0029] The result is a Fig. 6 shown, reworked forged blank 10, which has significantly lower material misdistributions and thus a significantly lower imbalance potential for gears to be produced from it than would be possible with clamping on originally exact outer contours created by the die 21 and subsequent reclamping and reworking.

[0030] The Fig. 7 and Fig. Figure 8 shows a gear 100 in different perspective views, as it can be produced from the forged blank 10 processed according to the invention by a further post-processing step, in which in particular a toothing 151 is engraved into the gear ring area 15.

[0031] Naturally, the embodiments discussed in the detailed description and shown in the figures represent only illustrative examples of the present invention. A wide range of variations is available to those skilled in the art in light of the disclosure herein. In particular, the specific detailed shaping of the forged blank is not essential to the basic idea of ​​the present invention. Steel is currently the preferred material for applying the process according to the invention. However, other forgeable metals can also be used. Reference symbol list 10 forged blanks 11 Floor area 12 External perimeter area 13 Top surface 131 Exclusion 132 Recess wall 133 Recess wall 14 Hub area 15 Gear ring area 151 Gearing 16 Bridge 17 reinforcements 21 Fixed die 211 Engraving of 21 22 Settlement 221 Engraving 22 QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 694 18 629 T2 [0003, 0009] DE 10 2019 130 185 A1

[0008]

Claims

[1] Method for machining a nominally rotationally symmetric forged blank (10) obtained by die forging, which, during the die forging process, has its first outer contours, namely a bottom surface (11) and an outer circumferential surface (12), defined by the shape of an engraving (211) of a fixed die (21), and its second outer contours, namely a top surface (13), defined by the shape of an engraving (221) of an adjusting die (22) axially displaceable relative to the fixed die (21), wherein the top surface (13) has axial recesses (131) with axially aligned recess walls (132, 133), comprehensively the steps: - Clamping the forged blank (10) onto a workpiece carrier using a chuck having clamping jaws, - Finishing the forged blank (10) using a machining tool movable relative to the chuck, characterized by , that the post-processing is carried out by turning at least the first outer contours in a lathe, wherein the clamping jaws of the chuck engage exclusively on the recess walls (132, 133) when clamping the forged blank (10). [2] Method according to claim 1, characterized by , that the recesses (13) have axially aligned and additionally azimuthally extended, first recess walls (132) as well as axially aligned and additionally radially extended, second recess walls (133), wherein the clamping jaws of the chuck engage exclusively on the first recess walls (132) when clamping the forged blank (10). [3] Method according to claim 2, characterized by , that the first recess walls (132) encompass an outer circumference of a hub area (14) and that the clamping jaws of the chuck engage exclusively on said outer circumference of the hub area (14) when clamping the forged blank (10). [4] Use of a forged blank (10) obtained by the method according to claim 1 as a gear blank, wherein the outer circumference of the gear blank is provided with a toothing (151) by machining. [5] Method for producing a gear blank, comprising - Die forging for forming a shear blank into a nominally rotationally symmetric forged blank (10) by pressing the shear blank between a fixed die (21) and an adjusting die (22) axially displaceable relative to the fixed die (21), whereby the forged blank (10) receives first outer contours, namely a bottom surface (11) and an outer circumferential surface (12), defined by the shape of an engraving (211) of the fixed die (21), and second outer contours, namely a top surface (13) having axial recesses (131) with axially aligned recess walls (132, 133), defined by the shape of an engraving (221) of the adjusting die (22), - Clamping the forged blank (10) by means of a chuck having jaws of a lathe, wherein the jaws of the chuck engage exclusively on the recess walls (132, 133), - machining of the forged blank (10) by turning at least its first outer contours. [6] Method for manufacturing a gear (100) comprising the steps: - Manufacturing a gear blank using the method according to claim 5, - Providing the outer circumference of the gear blank with teeth by machining (151).

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