Tool, method and machine for producing a tooth profile on a workpiece by skiving

Abstract

A tool, a method and a machine for producing a tooth profile by performing a coupled skiving movement between a skiving tool and the workpiece, by rotating the tool about a tool axis of rotation and rotating the workpiece about a workpiece axis of rotation. The tool includes a crown gear, on the front of which a tooth system with a cutting profile is located, which when in use reproduces the tooth profile on the workpiece.

Claims

1. A method for producing a tooth profile on a workpiece comprising the steps of performing a coupled skiving movement between a skiving tool and the workpiece, rotating the tool about a tool axis of rotation and rotating the workpiece about a workpiece axis of rotation, wherein the tool comprises a crown gear on the front of which a tooth system with a cutting profile is provided which when in use reproduces the tooth profile on the workpiece, wherein the tool axis of rotation and the workpiece axis of rotation are aligned intersecting each other at an axis intersection angle and wherein an offset is provided between the workpiece axis of rotation and the tool axis of rotation, in order to achieve a cutting speed component in the tooth gap direction of the tooth profile to be created between the workpiece and the tool.

2. The method according to claim 1, wherein the axis intersection angle between the tool axis of rotation and the workpiece axis of rotation is 85-95°.

3. The method according to claim 2, wherein the axis intersection angle between the tool axis of rotation and the workpiece axis of rotation is 90°.

4. The method according to claim 1, wherein the workpiece is moved relative to the tool in a movement direction directed parallel to the workpiece axis of rotation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 a tool and a cylindrical workpiece in the skiving operation as a top view;

(2) FIG. 2 the tool and the workpiece according to FIG. 1 in a side view;

(3) FIGS. 3a-3j snapshots of the engagement of a cutting edge in the production of a tooth profile on a workpiece through skiving in a side view.

DETAILED DESCRIPTION OF THE INVENTION

(4) FIGS. 1 and 2 show a simplified representation of a tool 1 modelled as a crown gear and a cylindrical workpiece 2 in a snapshot of the skiving method according to the invention.

(5) To illustrate the engagement relationships and the relative axis positions, a three-dimensional Cartesian coordinates system (x, y, z) is introduced, wherein the tool axis of rotation WZ is aligned coaxially to the x-coordinate. The workpiece axis of rotation WS on the other hand runs parallel to an auxiliary plane H spanning the x and z-axis and is positioned with an offset a to this auxiliary plane H. In the example described here, the offset a corresponds to approximately one quarter of the tool radius WR.

(6) In the example shown here, on the workpiece 1 a spur toothing is created by skiving. Here, the tooth gap direction ZR runs parallel to the workpiece axis of rotation WS.

(7) The tool 1 and the workpiece 2 perform a continuous division movement in relation to one another. Here, the tool rotation ω.sub.WZ about the x-axis and the workpiece rotation ω.sub.WS about the tool axis of rotation WS are coupled according to the tooth ratio of tool 1 and workpiece 2.

(8) The speed vectors shown in FIG. 1 v.sub.c, v.sub.WZ, v.sub.WS illustrate schematically how, as a result of the offset a between the workpiece 2 and the tool 1, or their respective axes of rotation WS, WZ, a cutting speed component v.sub.c results along the tooth gap direction ZR of the tooth profile VP to be produced. Here, the speed vectors v.sub.c, v.sub.WZ, v.sub.WS for example reproduce the respective circumferential speeds of the tool v.sub.WZ and the workpiece v.sub.WS in a point of contact B between a tool cutting edge 3 and a tooth flank.

(9) Were there to be no offset a (a=O) between the tool 1 and the workpiece 2, then in the point of contact B.sub.o the circumferential speed v.sub.W2,0 of the tool 1 and the circumferential speed v.sub.WS,0 of the workpiece 2 would be the same. Then no relative movement v.sub.c in tooth gap direction ZR between tool 1 and workpiece 2 would result.

(10) The cutting conditions arising during skiving with, according to the invention, a tool 1 and workpiece 2 offset with an offset a can be illustrated using the contact point B.sub.a. The circumferential speed v.sub.WS,a, v.sub.WZ,a of workpiece 2 and tool 1 are in this case not congruent, so that here a cutting speed component v.sub.c,a along the tooth gap direction ZR results.

(11) From the contact point B.sub.x that lies in the direction of rotation of the tool 1 before the contact point B.sub.a it is clear that the proportion which is converted from the circumferential speed v.sub.WZ at a cutting point into a feed movement or a cutting speed v.sub.c in the tooth gap direction ZR, grows as the offset a increases. Here, the maximum permitted offset a is limited by the necessary clearance and rake angle in the area of the tool cutting edge 3.

(12) In order to machine the workpiece 2 across its full tooth width BZ or the workpiece length an axial feed z.sub.v axially-parallel to the workpiece axis of rotation WS and parallel to the auxiliary plane H is provided. The direction of the axial feed z.sub.v is arbitrary, and can therefore also be reversed in respect of the axial feed z.sub.v shown in the Figure.

(13) As indicated in FIG. 1, the tool 1 modelled as a crown gear with a tooth system SP with teeth 3, which in an edge region bordering the outer circumference of the face 4 of the tool 1 runs in a circular manner about the face 4.

(14) With its front sides on the outer circumference of its teeth 3 the tooth system SP forms a cutting profile, to which each tooth on is front side contributes a cutting surface.

(15) As also illustrated in a simplified manner in FIG. 1, the teeth 3 of the tooth system SP have the flank form typical of a crown gear with an “engagement angle” that reduces from the outside to the inside, wherein the flanks in this case represent the open spaces of the tool 2. Here, the teeth 3 are merely implied and on the tool 1 naturally arranged with a distribution across the entire tool.

(16) In order to provide the clearance angle necessary for the skiving process, the tooth system SP in the radial direction has a helix angle β in the manner of a helical gearing. The helix angle β must be formed taking into account the predetermined offset a so that during chip removal a collision does not occur between the tool 1 and the workpiece 2 in the area of the free spaces. The helix angle β can be formed so that the tooth system SP of teeth 3 across its profile width during skiving at at least one point in time is aligned along the tooth gap direction ZR. Thus, the helix angle β can, for example, correspond to the angle enclosed by the speed vectors of workpiece v.sub.WZ,a and tool v.sub.WS,a.

(17) In addition, the teeth 3 of the tooth system SP starting from their front face cutting surface associated with the outer circumference have a reducing taper over the profile width in the radial direction on the tool axis of rotation WZ. At the same time, both the profile height and the profile thickness of the teeth 3 reduce from the outer circumference of the tool in the direction of the tool axis of rotation WZ.

(18) The axis intersection angle Σ between the workpiece axis of rotation WS and the tool axis of rotation WZ in the embodiment described here is set in a fixed manner at 90°. In order during the skiving to generate a kinematic clearance angle relative to the open spaces of the tool 1, the axis intersection angle Σ may differ from 90°, resulting in an inclination between the tool 1 and the workpiece 2. Preferably, however, such an inclination is dispensed with. Where an axis intersection angle Σ of different from 90° is provided for, this should be low. Such a low inclination of the tool 1 or the workpiece 2 counter to its 90° orientation has no significant influence on the cutting speed v.sub.c of the tool 1, however, in tooth gap direction ZR. The inclination merely concerns the change in the axis intersection angle Σ, so that the workpiece axis of rotation WS continues to be extended parallel to the auxiliary plane H.

(19) FIGS. 3a-3j by means of the tooth Zl of the tooth system profile VP to be produced on the workpiece 2 provide an understanding of how this tooth Zl is produced by the cutting profile 5 present on the tool 1, formed by the teeth 3 of the tooth system SP.

(20) Here, production of the tooth profile VP takes place in a number of passes, wherein the tool 1 after each pass is fed in the direction of the workpiece axis of rotation WS along a feed axis, which is aligned coaxially to the workpiece axis of rotation WZ, until the tooth profile VP has been fully completed.

KEY

(21) 1 Tool 2 Workpiece 3 Tooth of tooth system SP 4 Face 5 Cutting profile on the tooth system SP β Helix angle ω.sub.WS Workpiece rotation ω.sub.WZ Tool rotation a Offset B,B.sub.a,B.sub.o,B.sub.x Contact points BZ Tooth width H Auxiliary plane SP Tooth system v.sub.c Cutting speed component along the tooth gap direction ZR v.sub.c,a Cutting speed along the tooth gap direction ZR in contact point B.sub.a v.sub.c,x Cutting speed along the tooth gap direction ZR in contact point B.sub.x VP Tooth system profile v.sub.WS Circumferential speed of workpiece 2 v.sub.WZ Circumferential speed of tool 1 v.sub.WZ,0 Circumferential speed of tool 1 in contact point B.sub.0 v.sub.WS,0 Circumferential speed of workpiece 2 in contact point B.sub.0 v.sub.WZ,a Circumferential speed of tool 1 in contact point B.sub.a v.sub.WS,a Circumferential speed of workpiece 2 in contact point B.sub.a v.sub.WZ,x Circumferential speed of tool 1 in contact point B.sub.x v.sub.WS,x Circumferential speed of workpiece 2 in contact point B.sub.x WR Tool radius WS Workpiece axis of rotation WZ Tool axis of rotation Zl Tooth ZR Tooth gap direction z.sub.v Axial feed