CN111097975B

CN111097975B - Method for producing a workpiece with spur gear teeth and workpiece with spur gear teeth

Info

Publication number: CN111097975B
Application number: CN201911023491.0A
Authority: CN
Inventors: N.约尔丹
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 2018-10-25
Filing date: 2019-10-25
Publication date: 2021-07-30
Anticipated expiration: 2039-10-25
Also published as: CN111097975A; DE102018126699B4; DE102018126699A1

Abstract

The invention relates to a method for producing a workpiece with spur gear teeth having a predetermined final tooth size on the side, comprising the following steps: a) providing a workpiece blank, b) machining the workpiece blank by means of a cutting tool for producing a coarse toothing on the periphery of the workpiece blank, c) press-deburring the end-side toothing edges of the coarse toothing by means of a pressing tool, and d) machining the press-deburred coarse toothing by means of the cutting tool of step b for removing secondary burrs (16) which occur in the region of the coarse toothing sides (12;121) in the case of press-deburring of step c for producing a toothing (12) of ultimately determined dimensions. The invention is characterized in that the flank dimensioning of the coarse toothing produced in step b corresponds to the final flank dimensioning and the cutting operation in step d is carried out with a cutting tool withdrawal of 5 to 20 micrometers. The invention further relates to a correspondingly produced workpiece with spur gear teeth.

Description

Method for producing a workpiece with spur gear teeth and workpiece with spur gear teeth

Technical Field

The invention relates to a method for producing a workpiece with spur gear teeth having a predetermined final tooth size on the side, comprising the following steps:

a) providing a preferably rotationally symmetrical, in particular turned, workpiece blank,

b) machining the workpiece blank by means of a cutting tool for producing a rough toothing (or so-called rough toothing, Rohverzahnung),

c) the end-side tooth edges of the coarse teeth are pressed together by means of a pressing tool to remove the burrs,

d) the press-deburred coarse toothing is machined by means of the cutting tool of step b for removing secondary burrs which occur in the region near the end edges of the coarse toothing side in the case of the press-deburring of step c for producing a toothing of ultimately determined dimensions.

The invention further relates to a correspondingly produced workpiece with spur gear teeth.

Background

Such a method for producing spur gears (or so-called spur gears, i.e. Sitrnräder) and correspondingly produced spur gears are known from DE 102015013497 and from EP 2066473B 1, which is incorporated herein by reference.

The concept of a workpiece with spur gear toothing is to be understood broadly in the context of the present description and includes all workpieces with at least one spur gear toothing, in particular in the form of a gear or a shaft with spur gear toothing, such as for example a pinion or spur gear shaft with a single or multiple (ein-odd) toothing.

For producing spur or helical gear teeth, usually disk-or shaft-shaped workpiece blanks, which are usually turned, are machined, in particular by means of so-called circular grinding hobs. In this case, it is usual to first produce a coarse toothing during a first cutting machining step (the first step of the so-called pre-milling or two-step method), the flank dimensioning of which, in particular, the flank convexity and the hardening deformation maintenance (or quenching deformation maintenance, Härteverzugsvorhaltung), differ from the predetermined final dimensioning of the flanks of the toothing to be produced. In particular, the flanks are usually made with a rolling or spherical excess of 200 to 400 μm (i.e. greater than the 200 to 400 μm specified for the final toothing). The background for this targeted, temporary misdimensioning is the necessity of a subsequent step of press deburring of the flanks and the positive edges of the teeth. At these edges, burrs arise in the case of a cutting operation, which in turn has a number of disadvantages. On the one hand, it disturbs the regularity of the end-side tooth edges, so that it cannot be used as a reliable orientation mark, for example for the orientation of the tool, in a subsequent machining step. The end faces are frequently functionally determined planar clamping, contact or fixing faces, for which in part a high planar parallelism requirement is required. Furthermore, the corresponding burrs can break off in the event of operation of the transmission constructed from such gears, wherein the broken pieces can lead to damage in the transmission. This risk is particularly great when the workpiece, as is normally provided for spur gear teeth, is hardened (otherwise known as quenched, gehärtet) after its shaping in order to achieve the desired root core and surface hardness. In such a hardening step (or quenching step, Härtungsschritt), the burr is prone to embrittlement, specifically a so-called glass hardening at the tooth edges (Glashärte), which can then be prone to micro-fracture under a compliant load. In addition, the burrs which remain present in the case of the cutting process form an injury risk in the case of subsequent handling of the finished spur gear. Furthermore, the burrs occurring at the edges also conceal an increased risk of damage on the machining and transport paths to the components to be assembled and during the assembly process.

After the first cutting profile, the end-side tooth edges are therefore usually deburred by means of press deburring. In the case of press deburring, a tooth-making tool, which is designed specifically for the application and depends on the geometry, is driven under pressure into the coarse tooth portions of the workpiece to be deburred. In the hobbing movement that follows at this time, the desired chamfer (or chamfer, Fase) occurs at the tooth edge during the deformation that occurs. In this case, the workpiece material is plastically compressed by pressure in the region of the tooth flanks in the case of a hobbing movement. However, secondary burrs, i.e. bulges of plastically displaced material in the case of press deburring, are also obtained here in the region of the tooth flanks in the vicinity of the end edges and in the region of the protective chamfers.

The coarse teeth thus press deburred are then subjected to a further cutting process (so-called finish milling (or called fettigfräsen) or a second step of the two-step process), in particular with the same cutting tool as in the case of the first cutting process. Likewise, the workpiece clamping (or called tooling, i.e. werksttuckfannung) is the same as in the case of the first cutting machining step. Here, however, the commonly used circular grinding hobs are fed in excess (typically 200 to 400 μm) as already mentioned above. In other words, the tooth is cut "to final size" in this second cutting step, that is to say in particular the final flank-side dimensioning is set, together with the required convexity and the required hardening deformation maintenance, wherein the secondary burrs are removed simultaneously.

The results of this method in view of the material representatives show that: this produces spur gear teeth with accurately dimensioned teeth and burr-free chamfered tooth edges and end faces. However, the circular grinding hobs used are subject to significant wear. Furthermore, a shorter cycle time of the milling operation is desirable from an economic point of view.

Disclosure of Invention

The object of the present invention is to improve a method of this type in such a way that the service life of the cutting tool, in particular a circular grinding hob, is increased and the method sequence is accelerated.

This object is achieved in that the flank dimensioning of the coarse toothing produced in step b corresponds to the final flank dimensioning and the cutting operation in step d is carried out with a cutting tool retraction of 5 to 20 μm.

The invention is based on the recognition that cutting tools, in particular round milling hobs, are designed for dry hobbing on solid materials and exhibit a fully acceptable service life in the case of machining solid materials, in particular in the optimum chip thickness range (kopfsplandicken-Bereich) of 200 to 240 micrometers. The scraping use of such cutting tools, in particular of round grinding hobs, is known to the inventors in the context of the present invention to be very wear-prone and therefore service-life-demanding. Within the scope of the invention, it is also known to the inventors that, during the second machining step of a method of this type, very small chips of a defined size occur, as a result of the smaller cutting depth. The method typically conducts away a large part of the heat generated in the cutting process via the chips, so that the chips can melt or burn in on the tooth flank in unfavorable cases. In the case of cutting speeds typically applied in industry, about 80% of the heat is transferred into the chip, which ultimately results in temperatures of about 1000 ℃ or more being able to occur. In order to avoid such disadvantageous scraping applications (as they are usually used in the second cutting step in the prior art), the invention proposes that the coarse toothing be already produced "to the final dimension" in the first cutting step (pre-milling), that is to say with a lateral dimensioning corresponding to the final lateral dimensioning, in particular with a lateral convexity and hardening deformation maintenance corresponding to the final specification.

Of course, the occurrence of secondary burrs in the context of press deburring is not avoided thereby. Also, the invention preserves the concept of cut removal of this secondary burr. However, the invention is directed to the second machining step not providing a feed of the tool by a few 100 micrometers, but rather a relief of several micrometers thereof, in relation to the prior art. The setback is dimensioned extremely small and is only 5 to 20 μm, preferably approximately 8 to 12 μm, in particular 10 μm. Such a tool withdrawal is sufficient to avoid contact between the cutting tool, in particular the circular grinding hob, and in most cases the tooth flank during the second cutting machining step. The scraping process, which, as explained above, would negatively affect the service life of the circular grinding hob, is eliminated as much as possible. Only in the lateral regions in the vicinity of the end edges, i.e. where secondary burrs are present, a mechanical, mainly scraping interaction is achieved, in which the secondary burrs are removed in a cutting manner. It is understood by those skilled in the art that the secondary burrs are not removed at the level of the remaining flanks precisely here. Instead, a seat (socket) corresponding to the tool withdrawal according to the invention remains present. Such a small sized seat of several microns high may prove unimportant even for precision spur gears. In particular, they are in the size range of the cutting marks typical of the method in the case of milling, which can even be used advantageously for hardening and fine-machining processes which are possible subsequently, such as, for example, honing (or so-called honing) of the teeth, i.e. Verzahnungshonen. The quality of the honing process is furthermore strongly influenced by the initial quality of the tooth flanks, which occurs in the case of milling. Chips of a smaller size (as they occur in the second step in the case of the conventional two-step method and adhere to the tooth flanks, but do not occur in the context of the method according to the invention) can act here with a strong process disturbance.

Due to the avoidance as far as possible of the scraping interaction between the cutting tool, in particular the circular grinding hob, and the tooth flank, the wear of the cutting tool is significantly reduced, i.e. its service life is significantly extended. Furthermore, for the reasons described above, by the method according to the invention, small-sized milling chips which are burnt onto the tooth flanks do not occur.

A further advantage of the invention is that the cutting tool, in particular a circular grinding hob, can be moved very quickly in the axial direction from end edge to end edge in the second cutting process step, since no mechanical interaction is indeed carried out between these end edges. Accordingly, a movement with a maximum feed speed can be achieved, which in particular significantly accelerates the second machining step and thus reduces the method duration overall.

Furthermore, it is a further advantage that spur gear teeth which, as a matter of design, have only one-sided tooth outlets (or tooth gaps, namely Verzahnungsauslauf) also have to be deburred only on one side in the context of the method according to the invention. Accordingly, the machining time for the second machining step can be significantly reduced, since the secondary burr removal has to be carried out only on one side and only in the region of the secondary burr width.

And finally, the invention shows the advantage that in the case of press deburring it is not necessary to "over-press" the previously occurring side excesses, but only the final side excesses that have been obtained in the first cutting machining step. This results in a reduction of secondary burrs in the guard chamfers.

Additional features and advantages of the invention will be apparent from the detailed description and drawings that follow.

Drawings

Wherein:

FIG. 1: there is shown a schematic representation of a workpiece of spur gear teeth according to the present invention at three intermediate stages during its manufacture,

FIG. 2: there is shown a schematic representation of a workpiece having spur gear teeth according to the prior art at three intermediate stages during its manufacture.

The same reference numbers in the drawings identify the same or similar elements.

REFERENCE SIGNS LIST

10 teeth

12 flanks (final sized)

121 flank (excess)

14 end edge

141 chamfered end edge

15 end face

16 secondary burrs

161 secondary burr base

And 17, chamfering is protected.

Detailed Description

Fig. 1 shows a strongly schematic view of a tooth 10 of a spur gear toothing according to the invention in three different stages during its production. Fig. 1a shows a tooth 10 directly after the end of a first cutting machining step, in which a coarse toothing is formed by means of a cutting tool, in particular by means of a circular grinding hob, at the periphery of a disk-or shaft-shaped workpiece blank. The tooth flanks remain set to their final dimensions in view of their convexity and hardened deformation. In other words, the flanks 12 have been made to final dimensions. Axially, it is limited by a sharp end edge 14. These end edges have burrs which are not represented in particular in the schematic illustration in fig. 1.

The burr of the end edge 14 is removed in a subsequent press deburring step. In this case, the tooth-making tool, which is designed specifically for the application case and depends on the geometry, is driven under pressure into the coarse tooth of the workpiece to be deburred, so that the intermediate state represented in fig. 1b results. The desired chamfering occurs at the tooth edges 14 during the deformation process that occurs in the hobbing movement that follows at this time. In this case, the workpiece material is plastically compressed in the region of the tooth edge 14 by the pressure of the hobbing movement and a chamfered edge 141 is formed. The plastic deformation of end edge 14/141 and the deburring associated therewith however lead to material displacement. In particular, in the region of the tooth flank 12 in the vicinity of the end edge, a secondary burr 16 in the form of a ridge parallel to the edge is turned up. Such secondary burrs also occur on the end face 15 and in the region of the protective chamfers 17, which are not shown in the figures for reasons of clarity.

This secondary burr 16 is almost completely removed in a subsequent second machining step, as is represented in fig. 1 c. In this connection, the coarse-toothed and press-deburred workpiece is subjected to cutting again while maintaining the workpiece stress and using the cutting tool, in particular a circular grinding hob, which has already been used in the first cutting step. However, the relative adjustment of the tool with respect to the workpiece is slightly changed here. In particular, the cutting tool, in particular a round grinding hob, is set back by a few microns from the flank 12 which has maintained the final dimensioning in view of its convexity and hardening deformation. The cutting interaction is thus only achieved in the region of the secondary burr 16. The secondary burr is removed up to the seat 161, which has the height of the said relief. A final-dimensioned end-toothed workpiece is produced with secondary burr seats 161 which are negligible in practice, in particular in the further machining steps which usually follow, such as hardening and/or tooth honing, and which are in the dimensional range marked by the feed of the milling operation.

In contrast, fig. 2 shows a corresponding intermediate stage in the case of the production of an end toothing according to the prior art. Here, as represented in fig. 2a, the coarse toothing is made overdose (or overdimensioned, Ü berma β) in a first cutting process step. The resulting tooth sizing is presented in dashed lines in fig. 2 a. The respective excess flanks, which are present as a result of the first cutting machining step, are marked with reference numeral 121 in fig. 2. The tooth flank which has not yet been realized in the first cutting process step and is finally dimensioned has the reference symbol 12 as in fig. 1.

In a subsequent press deburring step, the chamfered end edge 141 and the secondary bulge 16 occur, as already explained in the context of fig. 1.

In a subsequent step, the rough-toothed and deburred spur gear is subjected to a cutting machining step again. In particular, it is subjected to machining by the above-mentioned cutting tool, in particular by a circular grinding hob. In contrast to the present invention, the relative orientation of the tool and the workpiece is changed in the opposite direction. The tool is fed in response to the excess in the first cutting process step, i.e. is moved closer to the workpiece. The feed or initial excess is typically a few 100 μm. Together with the excess material of the flanks 121, the secondary hump 16 is removed by a scraping interaction between the cutting tool and the workpiece. The results are presented in fig. 2 c. In contrast to the spur gear according to the invention, the resulting tooth flank 12, which is dimensioned to the end, does not have a secondary burr seat near the end edge.

Naturally, the embodiments discussed in the specific description and shown in the figures are only illustrative examples of the invention. A wide range of variant possibilities is provided for use by those skilled in the art in light of the disclosure herein.

Claims

1. A method for manufacturing a workpiece having spur gear teeth with a predetermined final side-sized tooth section, comprising the steps of:

a) providing a workpiece blank, and preparing a workpiece blank,

b) machining the workpiece blank by means of a cutting tool for producing a coarse toothing on the circumference of the workpiece blank,

c) pressing the end-side tooth edges of the coarse teeth by means of a pressing tool to remove the burrs, and

d) machining the press-deburred coarse toothing by means of the cutting tool of step b for removing secondary burrs (16) which occur in the region of the coarse toothing flanks (12;121) in the vicinity of the end edges in the case of the press-deburring of step c for producing a toothing (12) of final defined dimensions,

it is characterized in that the preparation method is characterized in that,

the flank dimensioning of the coarse toothing produced in step b corresponds to the final flank dimensioning and the cutting operation in step d is carried out with a tool withdrawal of the cutting tool of 5 to 20 micrometers.

2. The method of claim 1, wherein the machining in step d is performed with the cutting tool retracted by 8 to 12 microns.

3. The method according to any one of the preceding claims, wherein the cutting tool is configured as a circular grinding hob.

4. Method according to claim 1 or 2, characterized in that the surface of the spur gear manufactured according to steps a to d is subjected to a hardening step.

5. A workpiece with spur gear teeth obtained by the method according to any of the preceding claims.