TOOL AND METHOD FOR MACHINING A WORKPIECE

Abstract

A power skiving tool comprising a shank that extends along a longitudinal axis of the tool, and a cutting head that is arranged at an end face of the shank. The cutting head comprises a plurality of circumferentially arranged teeth, wherein, when viewed in a cross-section orthogonal to the longitudinal axis, each of the teeth comprises a convexly rounded contour, which at a first end transitions either directly or via a first concave transition contour into the convexly rounded contour of a first adjacent tooth of the plurality of teeth and at a second end opposite the first end transitions either directly or via a second concave transition contour into the convexly rounded contour of a second adjacent tooth of the plurality of teeth. A width of each tooth of the plurality of teeth, measured in the cross-section as a distance between the first end and the second end, is greater than a height of the respective tooth, measured in the cross-section orthogonal to the width and centrally between the first end and the second end.

Claims

1. A power skiving tool, comprising a shank that extends along a longitudinal axis of the tool, and a cutting head that is arranged at an end face of the shank, wherein the cutting head comprises a plurality of circumferentially arranged teeth, wherein, when viewed in a cross-section orthogonal to the longitudinal axis, each of the teeth comprises a convexly rounded contour, which at a first end transitions either directly or via a first concave transition contour into the convexly rounded contour of a first adjacent tooth of the plurality of teeth and at a second end opposite the first end transitions either directly or via a second concave transition contour into the convexly rounded contour of a second adjacent tooth of the plurality of teeth, and wherein a width of each tooth of the plurality of teeth, measured in the cross-section as a distance between the first end and the second end, is greater than a height of the respective tooth measured in the cross-section orthogonal to the width and centrally between the first end and the second end.

2. The power skiving tool according to claim 1, wherein the width of each tooth of the plurality of teeth is more than twice the height of the respective tooth.

3. The power skiving tool according to claim 1, wherein the width of each tooth of the plurality of teeth is more than three times the height of the respective tooth.

4. The power skiving tool according to claim 1, wherein a first tangent applied in said cross-section to the first end of the convexly rounded contour and a second tangent applied in said cross-section to the second end of the convexly rounded contour intersect at an angle α, where 60°≤α≤140.

5. The power skiving tool according to claim 1, wherein each of the first concave transition contour and the second concave transition contour is a radius when viewed in said cross-section.

6. The power skiving tool according to claim 1, wherein each tooth of the plurality of teeth has a shape identical to the remaining teeth of the plurality of teeth.

7. The power skiving tool according to claim 1, wherein each of the plurality of teeth comprises a rake face at an end of the cutting head that is facing away from the shank, the rake face being inclined at an angle other than 90° with respect to the longitudinal axis.

8. The power skiving tool according to claim 7, wherein the rake faces of all the teeth of the plurality of teeth are arranged in a common conical surface that is rotationally symmetrical to the longitudinal axis.

9. The power skiving tool according to claim 7, wherein between the rake faces of two adjacent teeth of the plurality of teeth there is respectively arranged a transition face, which is also arranged at the front end of the cutting head and directly adjoins the rake faces of the two adjacent teeth.

10. The power skiving tool according to claim 1, wherein each of the plurality of teeth comprises a circumferentially arranged flank oriented skew to the longitudinal axis.

11. The power skiving tool according to claim 1, wherein the plurality of teeth comprises more than twelve teeth.

12. The power skiving tool according to claim 1, wherein the shank is made of steel and the teeth of the cutting head are made of carbide.

13. A method for machining a workpiece, comprising the steps of: providing a power skiving tool and the workpiece to be machined; producing an outer contour on the workpiece by means of the power skiving tool during power skiving machining, wherein the outer contour to be produced corresponds to a regular convex polygon in a cross-sectional profile of the workpiece, and wherein the power skiving tool and the workpiece are rotated with opposite directions of rotation to one another during the power skiving machining, wherein an axis of rotation of the power skiving tool is aligned at a defined axis cross angle with respect to an axis of rotation of the workpiece, and wherein the power skiving tool and/or the workpiece are simultaneously moved translationally to generate a feed motion.

14. The method of claim 13, wherein the power skiving machining comprises rotating the power skiving tool at a first speed and rotating the workpiece at a second speed, wherein the second speed is an integer multiple of the first speed.

15. The method according to claim 13, wherein the power skiving tool comprises a shank that extends along a longitudinal axis of the tool, and a cutting head that is arranged at an end face of the shank, wherein the cutting head comprises a plurality of circumferentially arranged teeth, wherein, when viewed in a cross-section orthogonal to the longitudinal axis, each of the teeth comprises a convexly rounded contour, which at a first end transitions either directly or via a first concave transition contour into the convexly rounded contour of a first adjacent tooth of the plurality of teeth and at a second end opposite the first end transitions either directly or via a second concave transition contour into the convexly rounded contour of a second adjacent tooth of the plurality of teeth, and wherein a width of each tooth of the plurality of teeth, measured in the cross-section as a distance between the first end and the second end, is greater than a height of the respective tooth measured in the cross-section orthogonal to the width and centrally between the first end and the second end.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] FIG. 1 a perspective view of an embodiment of a power skiving tool;

[0051] FIG. 2 a side view of the power skiving tool shown in FIG. 1;

[0052] FIG. 3 a detailed view from FIG. 2;

[0053] FIG. 4 a top view from below of the power skiving tool shown in FIGS. 1 and 2;

[0054] FIG. 5 a detail from FIG. 4;

[0055] FIG. 6 the detail shown in FIG. 5 in a sectional view orthogonal to the longitudinal axis of the power skiving tool;

[0056] FIG. 7 a perspective view of the cutting head of the power skiving tool shown in FIG. 1;

[0057] FIG. 8 a detail from FIG. 7;

[0058] FIG. 9 a perspective view of the power skiving tool shown in FIG. 1 together with a workpiece to be machined; and

[0059] FIG. 10a-d several views illustrating a power skiving operation on a workpiece using the power skiving tool.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0060] FIG. 1 shows a perspective view of an embodiment of the power skiving tool. The power skiving tool is denoted therein in its entirety with the reference numeral 10.

[0061] The power skiving tool 10 comprises a shank 12 extending along a longitudinal axis 14. In the shown embodiment, the shank 12 is cylindrical. In principle, however, it can also have a different shape, for example a cuboid shape.

[0062] Furthermore, the power skiving tool 10 comprises a cutting head 16 which is arranged at a front end of the shaft. A plurality of teeth 18 are arranged on the cutting head 12, which teeth are distributed around the circumference of the cutting head 16.

[0063] As can be seen in particular in FIGS. 4-6, the teeth 18 comprise a convexly rounded contour. More specifically, the teeth 18 comprise this convexly rounded contour in a cross-section orthogonal to longitudinal axis 14, as shown in FIG. 6.

[0064] Unlike the teeth of conventional power skiving tools, the teeth 18 of the power skiving tool 10 are neither angular nor pointed. They have a much rounder design, which means that they have no corners or sharp edges. A further feature of the power skiving tool 10 can be seen in the fact that the teeth 18 are designed to be significantly flatter or less strongly curved than is the case with conventional power skiving tools which are used to produce gear teeth.

[0065] The teeth 18 comprise a rake face 20 at a front end of the teeth 18 facing away from the shank 12. As can be seen in particular from FIG. 4, the rake faces 20 of all teeth 18 lie in a common plane in the power skiving tool 10 according to the herein shown embodiment. This plane is a conical plane which extends all around at a constant angle relative to the longitudinal axis 14. Alternatively, however, it is also possible for the rake faces 20 of the individual teeth to be arranged in different planes, in which case a kind of step is formed between the rake faces 20 of two adjacent teeth 18 in each case.

[0066] The power skiving tool 10 according to the herein shown embodiment comprises a total of twenty-four such teeth 18. These twenty-four teeth 18 are evenly distributed around the circumference of the cutting head 16 and project in a star shape from the circumference thereof. However, as can be seen from the figures, the teeth 18 do not project from the circumference of the cutting head 16 exactly in a radial direction (orthogonal to the longitudinal axis 14).

[0067] On the circumferential side, each of the teeth 18 comprise a flank 22 representing the radially outermost part of each tooth 18 and thus also the radially outermost part of the cutting head 16. These flanks 22 are oriented skew with respect to the longitudinal axis 14, which can be seen in particular in FIG. 3.

[0068] FIGS. 5 and 6 illustrate the low curvature and the flat configuration of the teeth 18 characteristic of the power skiving tool 10. In this regard, FIG. 6 shows a detail of the cutting head 16 in a cross-section oriented orthogonally to the longitudinal axis 14. Additionally to the convexly rounded contour of each tooth 18, it is further apparent from FIGS. 5 and 6 that the teeth 18 merge directly into one another according to the herein shown embodiment. That is, in other words, each tooth 18 in the cross-section shown in FIG. 6 merges directly into the convexly rounded contour of an adjacent tooth 18′ at its first end 24 and merges directly into the convexly rounded contour of its second adjacent tooth 18″ at its second end 26 opposite the first end 24.

[0069] Instead of a direct transition of the convexly rounded contours of the individual teeth 18 into one another, concave transition contours can also be provided between the individual teeth 18, but these are comparatively small in comparison to the convexly rounded contours formed by the teeth 18 in the shown cross section. For example, radii may be considered as concave transition contours between the individual teeth 18.

[0070] The flat or slightly curved configuration of the individual teeth can be characterized in particular by the following features: A width b of each tooth 18 measured in the cross-section shown in FIG. 6 as a distance between the first end 24 and the second end 26 is significantly greater than a height h of the respective tooth 18 measured in the cross-section orthogonal to the width b and centrally between the first end 24 and the second end 26. As indicated in FIG. 6, the height is measured as a distance from a point 28 on the contour of the tooth 18 to a connecting line 30 between the first and second ends 24, 26. The length of the connecting line 30 corresponds to the width b of the tooth 18. The point 28 is a point at the zenith of the tooth that has an equal distance from the first end 24 and the second end 26.

[0071] Preferably, there is a ratio between the width b and the height h of at least 2:1, preferably at least 3:1 or even at least 5:1.

[0072] A first tangent 32 applied to the first end 24 of the convexly rounded contour of tooth 18 in the cross-section shown in FIG. 6 and a second tangent 34 applied to the second end 26 of the convexly rounded contour of tooth 18 in the cross-section intersect at an angle α, which is preferably in the range of 60°≤α≤140°. As can be seen from FIG. 6, the angle α is an interior angle measured at the intersection of the two tangents 32, 34 within the imaginary triangle the three corners of which are the intersection 36 of the two tangents 32, 34, the first end 24 and the second end 26.

[0073] The individual teeth 18 preferably all have an identical shape corresponding to the previously mentioned shape. The teeth 18 are preferably made of carbide, while the shank 12 is preferably made of steel.

[0074] The power skiving tool 10 is particularly suitable for producing an outer contour which, in the cross-sectional profile of the workpiece, corresponds substantially to a regular convex polygon. The term “substantially”, which is associated with the term “regular convex polygon”, is intended to clarify at this point that the contour to be produced on the workpiece is a regularly polygonal cross-sectional profile in the overall view, which however does not necessarily correspond exactly to a regular polygon at the microscopic level or already in the detailed view due to manufacturing inaccuracies. For example, individual roundings may occur in the corners of the polygonal profile.

[0075] FIG. 9 illustrates in a very generally the way in which the power skiving tool 10 interacts with a workpiece 38. During power skiving machining, both the power skiving tool 10 and the workpiece 38 are rotated. However, the power skiving tool 10 and the workpiece 38 are rotated with contrary or opposite directions of rotation with respect to each other. In the example shown in FIG. 9, the workpiece 38 is rotated clockwise and the power skiving tool 10 is rotated counterclockwise.

[0076] The power skiving tool 10 is rotated about its longitudinal axis 14. The longitudinal axis of the workpiece 38 serves as the axis of rotation 40 of the workpiece 38. Although this is not clearly evident in FIG. 9, the two axes of rotation 14, 40 are not parallel, but are oriented transversely to each other at a so-called axis cross angle. This oblique arrangement of the rotational axes 14, 40 relative to each other is characteristic for power skiving. The crossed axis arrangement results in a relative speed between the power skiving tool 10 and the workpiece 38.

[0077] During the power skiving machining, the individual teeth 18 slide on the workpiece 38, lifting chips from the workpiece 38. This can be seen, for example, in the sequence of figures schematically indicated in FIGS. 10a-10d, which serves to illustrate the power skiving process.

[0078] In addition to the rotation of the workpiece 38 and the tool 10, the tool 10 and/or the workpiece 38 are also moved translationally during power skiving. In this way, a kind of screwing movement is created by which the chip lifted from the workpiece 38 is “peeled out”.

[0079] In the present case, an outer contour is produced on the workpiece 38 by means of the power skiving tool 10 in the mentioned manner, which outer contour corresponds to a regular hexagon when viewed in cross-section. Such an outer contour corresponds, for example, to the outer contour of a hexagon on a screw or bolt.

[0080] As can be seen in particular from the sequence of figures shown schematically in FIGS. 10a-10d, the flat surfaces of the hexagonal profile are produced with the aid of the teeth 18, which have the flat and comparatively slightly curved, convexly rounded contour described above. The corners of the hexagonal profile, on the other hand, are created with the aid of the transition contours between the teeth 18 or with the tooth spaces, resulting in more or less exact corners on the workpiece 38.

[0081] During the power skiving operation, the workpiece 38 is preferably rotated at a higher speed than the power skiving tool 10. For example, a speed ratio of 3:1 may be provided to produce the exemplary hexagonal profile on the workpiece 38. For example, the power skiving tool 10 may be rotated at a speed in the range of 3,000 rpm while the workpiece 38 is rotated at a speed in the range of 12,000 rpm. The axis cross angle R, shown only schematically in FIG. 9, can be 25°, for example. The cutting speed may be set to 100 m/min.

[0082] In this way, it is very easy, inexpensive and extremely fast to create an outer contour on a workpiece 38 which corresponds in cross-section to a regular convex polygon course.