Method for shaping periodic structures, in particular gear teeth, and shaping machine designed therefor

Abstract

The present invention relates to a method for gear shaping of periodic structures, in particular teeth on a workpiece, in which the workpiece, rotating continuously about its axis of rotation, enters into material-removing machining engagement with a toothed shaping tool rotating about its axis of rotation in rolling contact with the workpiece rotation. After a machining stroke, the shaping tool is lifted off the workpiece in a lifting direction, and after a subsequent return stroke, the lifted shaping tool is returned to the workpiece for the next machining stroke. During the return stroke, the rolling contact is accompanied by a deflection movement of the shaping tool in the lifting direction against the incoming flank of the workpiece.

Description

[Technical field]

[0001] The present invention relates to a method for gear shaping of periodic structures, in particular teeth on a workpiece, in which the workpiece, rotating continuously about its axis of rotation, enters into material-removing machining engagement with a toothed shaping tool rotating about its axis of rotation in rolling contact with the workpiece rotation, after a machining stroke the shaping tool is lifted off the workpiece in a lifting direction and after a subsequent return stroke the lifted shaping tool is returned again to the workpiece for the next machining stroke and to a gear shaping machine controlled for this purpose. [Background technology]

[0002] Gear shaping is a technique for producing teeth, which has been known for a long time. It is a cutting method in which the main cutting motion is implemented by the linear oscillation of the tool. The machining removal of the workpiece material is only performed in the so-called machining stroke, the return stroke takes place in a lifted state to avoid the return stroke strip. The method principle of gear shaping is described, for example, in Thomas Bausch et al., "Innovative Zahnradproduktion", 3rd edition, p. 281, fig. 7.1-1, which document is otherwise referred to with respect to its basic technique. For example, rolling contact is merely a rotational motion of the tool and the workpiece cooperating with each other towards a rolling engagement, whereas in the case of machining helical teeth, a so-called screw guidance becomes necessary, which guidance can be implemented in a CNC-controlled manner via an additional rotation of the tool adapted to the stroke motion in order to maintain the rolling machining engagement during the axial movement (electronic screw guidance or simply electronic tilt). For the purposes of this application, the screw guidance required for machining helical teeth is part of the rolling contact.

[0003] An important advantage of gear shaping over other methods such as gear hobbing is that gear shaping can be used more generally for specific workpiece geometries such as internal teeth, and for workpieces with shoulders connected to the gear for which gear hobbing is poorly or not at all suitable.

[0004] Between the working stroke and the return stroke, the tool is typically not lifted out to such an extent that the tool teeth are completely radially out of the tool tooth gaps, but is lifted out a sufficient radial lift distance to avoid collisions on the return stroke (return stroke strip).

[0005] In a typical gear shaper, the lifting direction corresponds, for example, to the lifting direction provided by a lifting cam and usually also to the radial infeed axis of the gear shaper. In the case of gears, especially internal toothing, which are critical with respect to the risk of collision, the effective lifting direction (corresponding to the lifting angle in a plane perpendicular to the stroke direction) can also be changed by inducing lifting with a tangential lifting component by column offset or rotation of the radial machine axis, generating a new lifting vector (lifting direction), as the tool path occurs on the return stroke with a set tangential offset. This is disclosed in EP 2 368 660 (A1).

[0006] US2010 / 0290852(A1) also relates to gear shaping, and proposes discontinuous (time-step) tool rotation, as continuous tool spindle rotation causes interference problems in the workpiece. Summary of the Invention [Problem to be solved by the invention]

[0007] The invention is based on the object of further improving a method of the type mentioned at the beginning, in particular with regard to the integration of collision-free tool paths into the overall concept of the method. [Means for solving the problem]

[0008] From the point of view of process engineering, this object is achieved by the development of a method of the kind mentioned at the beginning, which is essentially characterized in that a flexing movement of the shaping tool running in the lifting direction against the incoming flank of the workpiece is superimposed on the rolling contact during the return stroke. According to the invention, the return stroke movement of the shaping tool is modified, in particular by taking advantage of the knowledge that the greatest risk of collision occurs in the region of the transition at the end of the return stroke, where the uncut material is still present in a relatively maximum amount. The flexing movement is necessarily an approaching movement against the other opposite flank, and therefore occurs in such a way that it coincides with the return stroke, where there is less destructive influence of the other flank between the teeth into which the shaping wheel teeth penetrate during the machining stroke.

[0009] In a preferred embodiment, the deflection movement is provided by an additional rotation of the shaping tool. This means that any additional machine axis provided separately can be dispensed with and the workpiece rotation can remain unchanged. The tool rotation combines the concurrent rolling contact (possibly including electronic tilting when cutting the helical tooth) with the deflection movement caused by the additional rotation. With respect to a reference system that only rotates the rolling contact, possibly with electronic tilting, the tool rotation position reference (e.g. the lowest point of the working shaping wheel tooth) moves in rotation in the stroke direction and also in the lift direction.

[0010] In a further preferred embodiment of the method, the deflection motion is performed over a large portion of the return stroke, thus extending the usable period and allowing the destructive access to the opposite flank to be conveniently shifted to higher return stroke levels.

[0011] In this connection, it is particularly preferred to provide that the deflection motion is controlled with respect to the rolling contact against a deviation, in particular a rotational angle deviation, which steadily increases on the return stroke, such deviation being therefore not yet fully available at the beginning of the return stroke, but only increasing on the return stroke.

[0012] In this regard, it is particularly preferred that the maximum deviation is at the end of the return stroke rather than at the beginning, preferably closer to the end than in the middle of the stroke, and in particular that the maximum deviation can be at the end of the return stroke or, depending on an optional phase shift between the linear vibration and the lift, at the transition where the tool lowest point of the machining shaping tooth is axially located in the stroke direction just above the upper tooth edge.

[0013] In a further preferred embodiment of the method, the deflection movement is controlled by the ratio of the shortest distance between the workpiece and the shaping tool, which ratio is in the interval [1 / 8;8], preferably [1 / 5;5], in particular [1 / 3;3], on the incoming flank to the ratio on the opposite flank. In short, the collision risk on both flanks is thus kept under a certain symmetry.

[0014] A further advantage of the design option offered by the method according to the invention is the reduction of the lifting amount of the lifting movement that would otherwise be required, in particular its radial component, which is predetermined by the machine axis. It is therefore preferable that the lifting amount is set lower than the first lifting criterion, provided that when set, the shaping tool is outside the safety distance to the return stroke strip without deflection movements. A standard value of the order of 0.05 is applied here as a safety margin. In this way, the shaping machine can be of low vibration design.

[0015] Moreover, it may be preferable to provide that the lifting and deflection movements are coordinated with each other to minimize the lifting amount. This can be seen and optimized, for example, through a prior simulation, in particular through repeated checking, of the penetration curves showing the collision of movements during the return stroke. To this end, the customary safety margins are respected.

[0016] For example, the lift amount can be in a range wider than R2+p(R1-R2) and narrower than R2+q(R1-R2), where R1 is a first lift criterion and R2 is a second lift criterion at which only a return stroke strip occurs despite the deflection movement, p is ≧0.1, preferably ≧0.2, and q is <0.9, preferably <0.8, in particular <0.7.

[0017] A further advantage of the method according to the invention is the wider design options, due to the collision risk reduction according to the invention, also with regard to the accelerations occurring in the tool path, so that it is preferable to provide that the switchover of the lifting component to the axial component of the tool path takes place without any curvature fluctuations.

[0018] Using electronic CNC control of the crank drive, the return stroke can also be accelerated relative to the working stroke in order to reduce the total stroke cycle time, and the rolling contact is adapted accordingly on the accelerated return stroke.

[0019] Preferably, multiple strokes are made per section of the workpiece toothing, i.e. the workpiece rotation occurs relatively slowly compared to the stroke movement, and preferably at least four, more preferably at least six, especially at least eight strokes are made before the workpiece rotation rotates further by a total of one section.

[0020] In a further preferred embodiment, the return movement occurs later than the lifting movement or the minimal reset, for example with a wider overflow than the required upper overflow, so that more time remains for the reversal of the deflection movement required to recover before the next working stroke, or for the reduction of the increased deviation of the return movement, already subjected to high acceleration by passing through the top dead center, so that the correct connection is achieved more smoothly and with satisfactory accuracy.

[0021] If there is already a collision risk during the lifting movement, provisions can also be made to change the effective lifting direction during lifting by using a parallel movement running across the machine axis causing the lifting and / or by using off-center machining (column offset), preferably also by using an additional tool rotation, provided that in this case the majority of the increased total offset does not increase until the return stroke.

[0022] In principle, the invention is suitable for various machine-side implementations of periodic tool paths, but is preferably used in the variant in which a lifting cam is used in a shaping head with a crank drive.

[0023] A control program resulting in the execution of a method according to one of the previously described aspects is also covered by the present invention, as is a gear shaper equipped with a controller for controlling said gear shaper in executing a method according to one of the previously described aspects. The advantages of the gear shaper according to the present invention result from the advantages of the method according to the present invention.

[0024] Preferably, disc cutting wheels are used as shaping tools, but depending on the configuration of the workpiece, bell cutting wheels, shank cutting wheels or hollow bell cutting wheels may also be used.

[0025] Regarding the infeed strategy, the invention is not subject to any particular restrictions, for example radial infeed with roller feed, or spiral with regressive radial infeed, or other kinds of infeed may be selected. From the mechanical engineering point of view, the electronic tilt guidance, and preferably the deflection movement, is implemented by means of a CNC-controlled direct drive.

[0026] Further features, details and advantages of the invention can be found in the following description, with reference to the accompanying drawings. [Brief description of the drawings]

[0027] [Figure 1]The tool path during gear shaping is shown. [Diagram 2] 1 shows a schematic of a lift cam profile. [Diagram 3] FIG. 1 is a partially cut-away cross-sectional view of a shaping head with a crank drive and lifting cam. [Figure 4] (a) shows the stroke position as a function of time, (b) shows the rotational position as a function of time, and (c) shows the relationship between rotational position and stroke position. [Diagram 5] A highly exaggerated representation of the deflection motion is shown in the rotation position / stroke position diagram. [Figure 6] FIG. 1 is a schematic diagram of a gear shaper and its NC machine axes. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] 1 shows the tool path during a shaping stroke in an embodiment of the invention in which a shaping head with a crank drive is used, the lifting motion being caused by a lifting cam which in turn is coupled to the movement of the stroke spindle. The tool path is shown in projection onto a plane spanning the stroke direction and the lifting direction and more precisely represents the path travelled by the tip 4 of the working tooth of the shaping wheel 8 over the entire stroke.

[0029] The tool path runs through four sections AB, BC, CD and DA, the tool is positioned to abut against the roller interface teeth 2 in the machining stroke AB. In the area of ​​lower lift (BC) the tool is pulled back to the lifted position and in upper lift (DA) it is pulled back or positioned to abut. The return stroke (CD) occurs with the tool in the lifted state.

[0030] The overflow path of the up and down shaping stroke of the tooth caused by the lifting area of ​​the cam is shown in Figure 1. UB and O LBThe additional overflow path determined by the cutting tool, which occurs during the grinding process when the cutting wheel is grounded and the helical tooth is shaped, is shown in Fig. 1 as O. LC and O LB In this way, the so-called cutting length S Cut is the sum of the tooth width b2 of the workpiece tooth 2 and the upper and lower overflows of the shaping wheel 8, while the axial length of the lifting movement BC is given due to the overflow of the lower lifting, and the axial length of the return movement is given due to the overflow of the upper lifting, as can be seen from FIG. 1. As can be seen from FIG. 1, the total stroke length S stK The upper and lower overflows and cutting length S cut It is the sum of.

[0031] FIG. 2 shows a schematic of the lifting cam profile associated with the tool path of FIG. 1 (in practice, the transitions A, B, C, and D are designed to be smooth movements). The lifting cam has a constant radius r cam can be observed in both the cutting and constant regions, but has a smaller radius in the return stroke region. However, the return stroke is not limited to linear motion.

[0032] The tool path in the return stroke area CD in FIG. 1 does not run parallel to the machining stroke, but at an angle, since in this embodiment the lifting, as in the case of a shaping head with a crank drive, occurs due to the tilting movement of the spindle guide. This can be seen well in FIG. 3, which shows the shaping head, with the mount of the shaping head indicated at 20, the connecting rod at 23, the pivot point at 21 and the spindle guide at 22. The spindle guide is pushed forward during cutting by the lifting cam 24, which is in contact with the pressure roller 26, and is left behind during the return stroke. As a result of this tilting, the lifting of the tool depends on the stroke position, and the ratio of the lifting of the cutting wheel to the lifting of the cam is equal to the ratio from the difference between the distance from the center M of the stroke between the top dead center OT and the bottom dead center UT to the stroke position relative to the center of the stroke and the axial distance from the center of rotation of the lifting cam to the pivot point 21. Thus, the lifting can be influenced by the selected design of the shaping head.

[0033] The examples described so far are mainly used for machining the external toothing, but the invention also relates to the machining of the internal toothing. For this reason, as the skilled person knows, when machining the internal toothing on the side facing the main column, an internal cam is used, in which the lifting occurs in the opposite direction to the lifting cam described above. However, the internal toothing can alternatively be machined on the side opposite the main column, with the same conditions being applicable as for the external toothing. It is also possible to reverse the connection between the stroke spindle and the lifting cam rotation axis so that when the internal toothing is pressed by an external lifting cam on the side facing the main column, the cutting occurs in the return stroke area of ​​the lifting cam.

[0034] Lifting cams have previously been used in crank-driven shaping heads, but the invention can also be used in various types of shaping heads, such as hydraulic shaping heads, in which case the entire main column is radially retracted during lifting, thereby allowing the amount of lift to be freely selected.

[0035] In the following, the simultaneous deflection is illustrated in an embodiment with reference to Figs. 4 and 5, which in this embodiment corresponds to a stroke position δA during the return stroke C-D. Z is implemented by an additional rotation δC8 of the shaping tool 8 as a function of the change in

[0036] For this purpose, a stroke motion A, which corresponds to the axial projection of the successively traversed tool path of FIG. Z is shown alone in Fig. 4a as a function of time. The periodically repeating shaping strokes can be seen. In Fig. 4b below, the rotational position C8 of the shaping wheel is recorded, which is determined, for example, by a rotary encoder, and the recording is taken at the time of the rolling contact. The curve shown in Fig. 4b is the result of the superimposition of a linear rise, which reproduces the superimposition of the rolling contact with a supposed straight tooth and thus the coupling of the tool rotation to the workpiece rotation, which is superimposed by electronic tilting, slower than the frequency of the shaping stroke (multiple strokes per section), as explained at the beginning. This is reflected in the vibration components in Fig. 4b, which are adapted to the frequency of the stroke axis. During the machining stroke AB, the tilt is corrected by tracing the tool rotation, and during the return stroke CD, the tilt must be restored again so that the correct rolling contact is again achieved in the next machining stroke.

[0037] In Figure 4c the stroke motion and rotational position are plotted against each other. Without the linear component of rolling contact in Figure 4b there would be only one line running in opposite directions on the return stroke and the linear component of rolling contact in Figure 4b results in the relationship shown in Figure 4c where the trajectory is distorted and diverges like an accordion due to the distortion caused by changing C8 position on successive strokes.

[0038] The additional amount ΔC8 accompanying this illustrated movement is much smaller than the electronic tilt, which is not visible in FIG. 4 and is therefore shown greatly exaggerated in FIG. 5 for one return stroke (in reality, in typical applications, a change of about 30 μm on the pitch circle of the tool 8 corresponds to a rotational position difference of 0.02° on the C8 axis). In FIG. 5, the straight line UT-OT shows the relationship between stroke and tool rotation during the return stroke, and the greatly exaggerated curved path that deviates from the straight line is the function ΔC8 / ΔA of the stroke motion. Z It can be seen that in the region of the return stroke, for the same stroke movement position, the rotational position steadily increases relative to the linear path until it reaches a maximum near the upper workpiece edge, while in the region of the upper overflow, the deviation previously caused by the additional rotation is reset to zero by the reversal of the additional rotation.

[0039] As can be seen in particular from figure 5, this additional angular deviation only increases slowly on the return stroke, so that in each case the deviation occurs less in the region of the lower workpiece edge than in the region of the upper workpiece edge. In this way, deflection occurs on the return stroke of the incoming flank of the workpiece toothing, but the position of maximum deflection is not suddenly reached, so that the impact distance to the opposite flank remains short, especially in the region close to the lower tooth edge of the workpiece toothing 2. As already explained above, this allows a design for an overall low (radial) lift, i.e. a short distance between the working stroke path and the return stroke path in figure 1, which allows design options in the low-vibration design of the gear shaper.

[0040] The machine axes of a gear shaper that may be used for this purpose are again shown with reference to FIG. 6 for an exemplary gear shaper 100 with a controller 99 for CNC control of the machine axes of the gear shaper 100.

[0041] The standard NC axes of the gear shaper 100 shown in FIG. 6, in the case of the preferred embodiment of the gear shaper 100 with lifting cam, are the radial axis X used for the infeed, the axis Z for the stroke position, the axis C for the workpiece rotation, the axis C2 for the tool rotation, the axis A for the stroke movement of the shaping spindle. Z , and axis A2 for cam rotation / lifting. Further NC axes such as axis Z2 for stroke length adjustment, axis B for adjustable column tilt, and tangential axis Y for column side offset can also be provided, either individually or in combination, to enable off-center gear shaping. A direct drive 70 for the rotation axis C8 is also shown on the shaping head.

[0042] Moreover, the invention is not limited to the embodiments shown on the basis of the figures, but rather individual features of the above description and the following claims may be essential both individually and in combination for implementing the invention in its various embodiments.

Claims

1. A method for gear shaping teeth (2) on a workpiece which is a periodic structure, in which the workpiece, rotating continuously about its axis of rotation (C2), enters into material-removal machining engagement with a toothed shaping tool (8) rotating about its axis of rotation (C8), the workpiece is in rolling contact with the toothed shaping tool (8), after a machining stroke (tool path A-B) the shaping tool is lifted off the workpiece in a lifting direction (A2) (tool path B-C) ​​and after a subsequent return stroke (tool path C-D) the lifted shaping tool is returned back to the workpiece again for the next machining stroke (tool path D-A), The deflection movement (δC8 / δA Z ) occurs simultaneously with said rolling contact during said return stroke (tool path CD).

2. The method of claim 1 , wherein the deflecting motion is provided by an additional rotation of the shaping tool.

3. The method according to claim 1 or 2, wherein the deflection movement is performed over the majority of the return stroke (tool path CD).

4. 10. The method according to any one of the preceding claims, wherein the deflection is controlled relative to a deviation, in particular the deviation (ΔC8) of the nominal rotation angle of the toothing of the toothed shaping tool (8) relative to the rolling contact, the deviation steadily increasing on the return stroke.

5. 5. The method of claim 4, wherein the maximum deviation is at the end (D) of the return stroke rather than at the beginning (C).

6. 10. A method according to any one of the preceding claims, wherein the deflection movement is controlled by the ratio of the shortest distance between the teeth (2) on the workpiece and the shaping tool (8), said ratio being in the interval [1 / 8;8] at the incoming flank of the workpiece to the ratio at the opposite workpiece flank.

7. 10. The method according to claim 9, wherein the lift amount is set lower than a first lift reference, and at said setting, the toothed shaping tool (8) is outside a safety distance relative to the return stroke strip without said deflection movement.

8. With respect to minimizing the lifting direction (A2), the lifting direction (A2) and the deflection movement (δC8 / δA Z 10. The method according to claim 9, wherein the first and second inputs are in coordination with each other.

9. 10. The method according to any one of the preceding claims, wherein the changeover of the lifting direction (A2) to the axial component of the tool path occurs without bending pressure.

10. 10. A method according to any one of the preceding claims, wherein a number of strokes are performed for each section of the toothing (2) on the workpiece.

11. 10. A method according to any one of the preceding claims, wherein the return stroke is accelerated more than the working stroke.

12. 10. A method according to any one of the preceding claims, in which the return movement is retarded.

13. 10. The method according to claim 9, wherein the effective lifting direction is already changed during lifting in the event of a collision risk by a simultaneous movement running in the direction of the machine axis causing the lifting and / or by misaligned machining.

14. A method according to any one of the preceding claims, wherein in the case of a shaping head with a crank drive, said tool path (ABCD) is also determined by a lifting cam (24).

15. A control program which, when implemented in a controller (99) of a gear shaper (100), controls said gear shaper (100) to perform the method according to any one of the preceding claims.

16. A gear shaping machine (100) comprising a lifting cam (24) on a shaping head with a crank drive, and a controller (99) for controlling the gear shaping machine in at least one operating mode to perform the method described in claim 14.

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