Method for Precision Machining a Workpiece Provided With Gearing

Abstract

For the precision machining of a workpiece (10) provided with gearing (11) and rotating about a rotation axis (Dw), teeth (3) of a gear-cutting tool (1) rotating about a rotation axis (Dz) are brought into engagement with teeth (12) of the workpiece (10), and the gear-cutting tool (1) and the workpiece (10) are moved relative to each other in a direction (AX+, AX−) parallel to the rotation axis (Dw). The thickness (dZ) of the teeth (3) of the gear-cutting tool (1) increases in the axial direction, starting from the respective front ends (4, 5) of the teeth, until a thickness maximum (dZmax) is reached. High material removal performances and long-term durability of the gear-cutting tool (1) are achieved in that, according to the invention, 2≤Bw/Bz≤20 applies (wherein Bw=width Bw of the teeth of the gearing (11) of the workpiece (10), Bz=width of the teeth (3) of the gear-cutting tool (1)), that the gear-cutting tool (1), before each pass of its teeth (3) through the tooth gaps (17) of the workpiece (10) in the respective axial directions (AX+, AX−), is positioned at a position (P1, P2) in which the thickness maximum (dZmax) of the teeth (3) of the gear-cutting tool (1) is situated outside the gearing (11) of the workpiece (10), and that as a consequence of the relative movement of the workpiece (10) and of the gear-cutting tool (1) in the axial direction (AX+, AX−), the teeth (3) of the gear-cutting tool (1) are each moved through the respective tooth gaps (17) of the gearing (11) of the workpiece (10) that are assigned to them, until the thickness maximum (dZmax) of each tooth (3) has exited the assigned tooth gap (17).

Claims

1. A method for precision machining a workpiece provided with gearing, in which teeth of a gear-shaped gear-cutting tool, which rotates about a rotation axis, are brought into rolling engagement with teeth of the gearing of the workpiece rotating about a rotation axis while the gear-cutting tool and the workpiece are being moved relative to each other in a direction parallel to the rotation axis of the workpiece, wherein the thickness of the teeth of the gear-cutting tool increases, in each case, starting from the end face of the teeth facing forward with respect to the corresponding movement in the axial direction, until a thickness maximum is reached, characterized in that, the following applies to the ratio Bw/Bz formed by the width Bw of the teeth of the gearing of the workpiece and the width Bz of the teeth of the gear-cutting tool:
2≤Bw/Bz≤20, that the gear-cutting tool, before each pass of its teeth through the tooth gaps of the gearing of the workpiece in the respective axial directions, is positioned at a position in which the thickness maximum of the teeth of the gear-cutting tool is situated outside the gearing of the workpiece, and that the teeth of the gear-cutting tool, as a consequence of the relative movement of the workpiece and of the gear-cutting tool in the axial direction, are each moved through the tooth gaps of the gearing of the workpiece assigned to them until the thickness maximum of each tooth has exited from the tooth gap assigned to it.

2. The method according to claim 1, characterized in that the workpiece is a gear rotating about a workpiece rotation axis during the precision machining.

3. The method according to claim 2, characterized in that the rotation axis of the gear-cutting tool is aligned at an axis intersection angle with respect to the rotation axis of the workpiece.

4. The method according to claim 2, characterized in that the gearing of the workpiece is an internal gearing and the gearing of the gear-cutting tool is an external gearing.

5. The method according to claim 1, characterized in that only the workpiece is moved in the axial direction.

6. The method according to claim 1, characterized in that the following applies to the ratio Bw/Bz:
2<Bw/Bz<20

7. The method according to claim 6, characterized in that the following applies to the ratio Bw/Bz:
2<Bw/Bz<5

8. The method according to claim 1, characterized in that the thickness of the teeth of the gearing of the gear-cutting tool increases continuously to the thickness maximum, starting from one of the end faces of the teeth.

9. The method according to claim 8, characterized in that the increase of the thickness follows a circular function.

10. The method according to claim 8, characterized in that the increase of the thickness follows an elliptical function.

11. The method according to claim 1, characterized in that the axial relative movement between the workpiece and the gear-cutting tool is effected in a periodically changing direction, that the thickness maximum (dZmax) of the teeth of the gearing of the gear-cutting tool is situated between the end faces of the teeth of the gearing in each case, and that the thickness of the teeth of the gear-cutting tool increases to the thickness maximum of the tooth concerned, starting from each of the end faces thereof.

12. The method according to claim 11, characterized in that the thickness maximum is formed in the center between the end faces of the teeth of the gear-cutting tool.

13. The method according to claim 1, characterized in that the relative movement in the axial direction is completed in two or more passes.

14. The method according to claim 13, characterized in that an infeed in the radial direction is effected after each pass.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In the following, the invention will be explained in more detail, with reference to a drawing depicting an exemplary embodiment. Shown schematically in each case are:

[0034] FIG. 1 a gear-cutting tool with external gearing in engagement with the internal gearing of a workpiece, in a perspective view;

[0035] FIG. 2 an enlarged detail A from FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] The gear-cutting tool 1 produced from a material typically used in the prior art is held in a tool holder, which is not shown here for the sake of clarity and which in turn is coupled in a manner known per se to a rotary drive, via which the gear-cutting tool 1 in use is driven to rotate about a tool rotation axis Dz.

[0037] The gear-cutting tool 1 has an external gearing 2 configured as spur gearing, which is formed in standard fashion by a multiplicity of teeth 3 distributed at uniform angular distances about the tool rotation axis Dz. The teeth 3 are each aligned in an axis-parallel manner to the tool rotation axis Dz, and extend over the width Bz of the gear-cutting tool 1, between the end faces 4, 5 of the gear-cutting tool 1.

[0038] Each tooth 3 has tooth flanks 6, 7, one of which in each case is assigned to the tooth gaps 8, 9 of the gearing 2 of the gear-cutting tool 1, which are bordered on one of their sides by the corresponding tooth 3. The tooth flanks 6, 7 are curved outwards toward the corresponding tooth gap 8, 9. The tooth trace of the tooth flanks 6, 7 thus describes a circular arc, in other words it follows a circular function such that the teeth 3 each have a minimum thickness dZmin at each of their ends assigned to the end faces 4, 5, and such that the thickness dZ of the teeth 3 continuously increases in the axial direction with respect to the tool rotation axis Dz, starting from the minimum thickness dZmin of the teeth 3, until a thickness maximum dZmax is reached, which is situated exactly in the center of the teeth 3 with respect to the width Bz.

[0039] The workpiece 10 that is to be precision machined in a manner according to the invention is a standard gear provided with internal gearing 11 configured as helical gearing, which was formed from a blank by material-removing machining and then tempered.

[0040] The workpiece 10 is clamped in a workpiece holder, which is not shown here for the sake of clarity and which is coupled to a rotary drive, which is also not shown here and which drives the workpiece 10 to rotate about a rotation axis Dw in use. The rotation axis Dw is aligned in standard fashion at an axis intersection angle E with respect to the rotation axis Dz of the gear-cutting tool 1.

[0041] Furthermore, the workpiece holder is mounted on a positioning drive, not shown, which is provided for moving the workpiece holder with the workpiece 10, in use, back and forth in an oscillating manner between two reversing positions P1, P2 in the axial direction AX+, AX− with respect to the workpiece rotation axis Dw, wherein the axial direction in the forwards movement is designated by “Ax+” and the opposite axial direction in the backwards movement of the workpiece 10 is designated by “Ax-”. By means of the positioning mechanism, further movements about additional axes (e.g., an infeed in the radial direction R) can be superimposed on the movements of the workpiece 10 in the axial direction AX+, AX− if, in addition to removing material in linear fashion from the tooth flanks, specific form elements (such as a crowning) are to be reproduced on them as well.

[0042] In contrast to the workpiece 10, the gear-cutting tool 1 is only rotated about its rotation axis Dw and not moved in axial direction AX+, AX− during the machining of the workpiece 10.

[0043] The teeth 12 of the internal gearing 11 of the workpiece 10 each extend between the end faces 13, 14 of the workpiece 10 over a width Bw and have a constant thickness dW over the width Bw. Adjacent teeth 12 in each case delimit a tooth gap 17 between themselves with their tooth flanks 15, 16.

[0044] The width Bw of the teeth 12 of the gearing 11 of the workpiece 10 is significantly greater than the width Bz of the gear-cutting tool 1. In the example shown here, the ratio Bw/Bz is thus ca. 6:1.

[0045] The workpiece 10 is moved into the first reversing position P1 for the precision machining of the teeth 12 of the internal gearing 11. This position is situated outside the external gearing 2 of the gear-cutting tool 1 such that in this position P1, the front end face 13 of the workpiece 10 in the axial direction AX+ is arranged immediately adjacently to the end face 13 of the gear-cutting tool 1.

[0046] The gear-cutting tool 1 is fed in to the internal gearing 11 in a radial direction R, to an extent that corresponds to the depth over which material is to be removed from the tooth flanks 15, 16 of the teeth 12 in the next pass completed by the teeth 3 of the gear-cutting tool 1 through the tooth gaps 17 of the workpiece 10.

[0047] By the workpiece 10 being continuously advanced axially along its rotation axis Dz in the axial direction AX+ relative to the gear-cutting tool 1, the gearings 2, 11 of the gear-cutting tool 1 and of the workpiece 10 driven in codirectional rotation about their respective rotation axes Dz, Dw are brought into rolling engagement.

[0048] As a consequence of the rolling engagement and of the radial infeed, the teeth 3 of the gear-cutting tool 1 now remove material from the tooth flanks 15, 16 of the teeth 12. In this process, the less thick region of the teeth 3 of the gear-cutting tool 1, which abuts on the rear end face 4 of the gear-cutting tool 1 (with respect to the present direction AX+ of the axial movement), first comes in engagement with the assigned teeth 12 of the workpiece 10 in such a way that removal of material starts immediately on the tooth 12 of the workpiece 10 that comes in contact with the corresponding tooth 3 of the gear-cutting tool 1. With continued movement of the workpiece 10 in the axial direction AX+, the teeth 3 of the gear-cutting tool 1, which increase in thickness from the end face 4 on, penetrate deeper and deeper into the material of the teeth 12 of the workpiece 10, such that more and more material is removed from the teeth 12 until the thickness maximum dZmax of the teeth of the gear-cutting tool 1 is reached.

[0049] Due to the movement in the axial direction AX+, the rear end face 14 of the workpiece 10 (with respect to the axial direction AX+) approaches the front end face 5 of the gear-cutting tool 1 (with respect to the axial direction AX+), whereas the front end face 13 of the workpiece 10 (with respect to the axial direction AX+) moves away from the rear end face 4 of the gear-cutting tool 1 (when viewed in the axial direction AX+).

[0050] The advancing movement of the gear-cutting tool 1 in the axial direction AX+ is continued until the place where the teeth 3 have their greatest thickness dZmax is situated outside the gearing 11 of the workpiece 10. In this position, the workpiece 10 has reached the second reversing position P2 of its axial movement. The first pass of the teeth 3 of the gear-cutting tool 1 through the teeth 12 of the gearing 11 of the workpiece 10 is thus completed.

[0051] If the material removal on the teeth 12 of the workpiece 10 effected by the first pass is insufficient for providing the gearing 11 of the workpiece 10 with the required final geometry, a second pass can now be made. To this end, the gear-cutting tool 1, if need be after a further infeed in the radial direction R, is moved from the reversing position P2 in the opposite axial direction AX− back through the gearing 11 of the workpiece 10 until the reversing position P1 is reached and the second pass is completed.

[0052] If required, further passes in the manner explained above are made until the teeth 12 of the workpiece 10 have the required final geometry.

[0053] With the invention, a method is provided for the precision machining of a workpiece 10 having gearing 11, wherein teeth 3 of a gear-cutting tool 1 rotating about a rotation axis Dz are brought into rolling engagement with teeth 12 of the gearing 11 of the workpiece 10 rotating about a rotation axis Dw, and wherein the gear-cutting tool 1 and the workpiece 10 are moved relative to each other in an axial direction AX+, AX− parallel to the rotation axis Dw of the workpiece 10. The thickness dZ of the teeth 3 of the gear-cutting tool 1 increases from a front end face 4, 5 of the teeth (with respect to the corresponding movement in axial direction AX+, AX−) to a thickness maximum dZmax. In order to achieve further enhanced removal performances along with long-term durability, according to the invention the following applies to the ratio Bw/Bz formed by the width Bw of the teeth 12 of the workpiece 10 and the width Bz of the teeth 3 of the gear-cutting tool 1: 2≤Bw/Bz≤20. Before each pass of its teeth 3 through the tooth gaps 17 of the workpiece 10 in the respective axial directions AX+, AX−, the gear-cutting tool 1 is in each case positioned at a position P1, P2 in which the thickness maximum dZmax of the teeth 3 of the gear-cutting tool 1 is situated outside the gearing 11 of the workpiece 10. As a result of the relative movement of the workpiece 10 and of the gear-cutting tool 1, the teeth of the gear-cutting tool 1 then travel in the axial direction AX+, AX− until the thickness maximum dZmax of each tooth 3 of the gear-cutting tool 1 exits its assigned tooth gap 17 of the gearing 11 of the workpiece 10.

[0054] According to the invention, for the precision machining of a workpiece 10 provided with gearing 11 and rotating about a rotation axis Dw, teeth 3 of a gear-cutting tool 1 rotating about a rotation axis Dz are thus brought into engagement with teeth 12 of the workpiece 10, and the gear-cutting tool 1 and the workpiece 10 are moved relative to each other in a direction AX+, AX− parallel to the rotation axis Dw. The thickness dZ of the teeth 3 of the gear-cutting tool 1 increases to a thickness maximum dZmax, starting in each case from the front end faces 4, 5 of the teeth (in the axial direction AX+, AX−). A high removal performance and long-term durability of the gear-cutting tool 1 are achieved in that, [0055] according to the invention, the following applies:

2≤Bw/Bz≤20

wherein BW=width Bw of the teeth of the gearing 11 of the workpiece 10, [0056] Bz=width of the teeth 3 of the gear-cutting tool 1, [0057] that the gear-cutting tool 1 is positioned, before each pass of its teeth 3 through the tooth gaps 17 of the workpiece in the respective axial directions AX+, AX−, at a position P1, P2 in which the thickness maximum dZmax of the teeth 3 of the gear-cutting tool 1 is situated outside the gearing 11 of the workpiece 10, and [0058] that the teeth 3 of the gear-cutting tool 1 are moved as a result of the relative movement of the workpiece 10 and of the gear-cutting tool 1 in the axial direction AX+, AX− through their assigned tooth gaps 17 of the gearing 11 of the workpiece 10, until the thickness maximum dZmax of each tooth 3 has exited the assigned tooth gap 17.

REFERENCE SYMBOLS

[0059] 1 Gear-cutting tool [0060] 2 External gearing of the gear-cutting tool 1 [0061] 3 Teeth of the external gearing 2 [0062] 4,5 End faces [0063] 6,7 Tooth flanks of the teeth 3 [0064] 8,9 Tooth gaps of the gearing 2 [0065] Workpiece (gear with internal teeth) [0066] 11 Internal gearing of the workpiece 10 [0067] 12 Teeth of the internal gearing 11 [0068] 13,14 End faces of the workpiece 10 [0069] 15,16 Tooth flanks of the teeth 12 [0070] 17 Tooth gaps of the workpiece 10 [0071] AX+, AX− Axial direction [0072] Bw Width of the workpiece 10 [0073] Bz Width of the gear-cutting tool 1 [0074] Dw Rotation axis of the workpiece 10 [0075] Dz Tool rotation axis [0076] dZ Thickness of the teeth 3 [0077] dZmin Minimum thickness of the teeth 3 of the gear-cutting tool 1 [0078] dZmax Maximum thickness of the teeth 3 of the gear-cutting tool 1 [0079] dW Thickness of the teeth 12 [0080] P1, P2 Reversing positions [0081] R Radial direction [0082] Σ Axis intersection angle