A method for shaping teeth into a gear shape, a control program, and a gear shaping machine for carrying out this method.

Abstract

The present invention provides a method for producing a gear with a specified straight tooth angle module (m n The present invention relates to a method for gear shaping of teeth (55) having a specified stroke length (h), an action angle (α) and optionally a helix angle (β), in which a shaper cutter (40) moving in a stroke cycle having a specified stroke length (h) removes material from a workpiece in a number of working strokes in a rolling machining engagement to form a contact locus, and in which, for at least a first number of strokes, the contact locus on a partial circle at the stroke center extends at an angle (γ) to the tooth flank line (57), the cotangent of which is less than or equal to 40, preferably 33, in particular 25, a product of a constant and a geometry / process factor.

Description

[Technical Field] 【0001】 The present invention relates to a method for shaping teeth into a gear on a workpiece, wherein a shaping cutter moving in a stroke cycle having a specified stroke length forms a contact trajectory by removing material from the workpiece in multiple operating strokes in a rolling machining engagement. 【0002】 Such gear shaping is, on the one hand, a long-known technique for creating teeth. This technique is a cutting method in which the main cutting movement is achieved by the stroke movement of the tool, in which material removal of the workpiece material is performed in the so-called working stroke, and the return stroke is performed in a lifted position to avoid return stroke scratches. The principle of this method is explained, for example, in Thomas Bausch et al.'s "Innovative Zahnradfertigung [Innovative gear production]", 3rd edition, page 281, image C1-1. 【0003】 A key advantage of gear shaping over other methods such as gear hobbing is its broad applicability, particularly to workpieces with internal teeth or shoulders connected to teeth, where gear hobbing is largely or completely unsuitable. 【0004】 In addition to conventional feed rates, regressive helical feeds are now also used. However, regardless of the feed rate, especially at high stroke counts, and particularly for teeth with small helical angles leading to straight teeth, it can be observed that the risk of damage also increases when higher tool loads occur and high cutting forces become dominant. 【0005】 In view of this observation, the present invention aims to further develop the gear shaping method of the type described at the beginning, with respect to combining sufficiently rapid machining and process safety, while minimizing tool wear as much as possible. 【0006】 From a method perspective, this object is achieved by developing a method of the type described at the beginning, which essentially, with respect to at least a first plurality of strokes, has a contact locus on the pitch circle at the stroke center extending at an angle γ with respect to the tooth flank line, where the cotangent of this angle is less than or equal to the product of constants K1 and K2, K1 being equal to 40, preferably 33, particularly 25, and K2 being K2 = K h ·K m ·K α ·K β which is the geometric shape / process coefficient (second coefficient) of, K h = h [mm] / 20, K m = 3 / m n [mm], K α = sin20° / sinα, and K β = cosβ, where m n is the straight-tooth module, α is the pressure angle, β is an arbitrarily selectable helix angle of the teeth of the workpiece (β = 0 in the case of straight teeth), and h is the stroke length. 【0007】 For example, in the conventionally known gear hobbing, the type of chip formation results in chip compression, and furthermore, individual points on the cutting edge of the hob cutter are intensively stressed, and as a result, the wear of the hob cutter also increases, and points related to the direction of the contact locus have been found for these effects. 【0008】 According to the present invention, compared to the prior art, the contact trajectory extends over a larger area perpendicular to the tooth being machined, thereby mitigating the effects described above. These contact trajectories extend substantially parallel to each other and essentially uniformly across the tooth surface; however, when stroke movement is typically achieved via crank drive, the velocity profile is not constant across the stroke; therefore, for the definitions used in the characterization section of claim 1, refer to the stroke center and pitch circle. Furthermore, it has been found that an advantageous design exists when the angular conditions according to the present invention also depend on the geometry of the process and workpiece, which are further represented by a second coefficient K2 in the features characterized in claim 1, rather than employing a fixed angle independent of the workpiece and process. However, in conventional methods, the contact trajectory on the workpiece tooth surface extends substantially parallel to the tooth surface line, and even in the case of radial feed, a cotangent γ value of 70 or more is typically obtained in configurations where K2=1. 【0009】 K1 can preferably be further set to 20.5, but K1 can also be set to only 19.7, or even only 19.4. 【0010】 In a further preferred embodiment, the shaping cutter is fed through a first plurality of strokes, particularly with a constant helical feed, and the feed parameter, defined by the quotient of the radial feed per revolution of the workpiece and the lift of the shaping cutter between the working stroke and the return stroke in the first plurality of strokes, is specified to be less than 1.4. This is a significantly lower value compared to the prior art, and the surface removal of the material is shifting towards a flatter but wider material removal trend. Along with the contact trajectory adjustment according to the present invention, which reaches the full height of the tooth surface relatively quickly, this results in particularly tool-friendly chip formation and absorption of machining forces on the shaping cutter. Furthermore, a collision-free return stroke can be performed with high process reliability despite changes in the contact trajectory position. In this regard, it is also specified that the feed parameter may be less than 1.3, preferably less than 1.2, particularly less than 1.1, or even 1.0. 【0011】 In a further preferred configuration, the first and second sets of strokes are performed across feed regions that constitute the majority of the total feed for completing the tooth being machined, and the cotangent γ is specified to be greater than 40·K2, and especially greater than 60·K2, across subsequent further feed regions. This facilitates a smoother transition to the even higher values ​​described below, towards the end of machining. 【0012】 Therefore, a further preferred configuration is provided in which the cotangent γ is greater than 80·K2, and especially greater than 120·K2, during the final feed to reach the final feed depth of the tooth being shaped. This enables higher machining accuracy toward the end of the shaping process. In other words, shaping machining can be divided into several regions of about two or three different kinematics, gradually transitioning from high machining speed to high machining accuracy. 【0013】 The greatest effect of the embodiments of the present invention is achieved on straight teeth or teeth with a moderate twist angle. This method is particularly effective for tooth twist angles of less than 14°, more preferably less than 12°, and especially less than 10°. 【0014】 Furthermore, it is preferable that the tooth width is at least 60%, preferably at least 70%, and particularly at least 80% of the stroke length (or conversely, that the stroke length is adapted to the tooth width within these ratio limits). This enables a preferred overall configuration for the preferred use of the stroke length for machining, and it is specified that this ratio is preferably 96% or less, and particularly 92% or less, in order to achieve a sufficient cutting speed. 【0015】 In a further preferred configuration, the rolling position is specified to differ in each case in the tooth groove being shaped between two consecutive workpiece rotations. This ensures that not all tooth grooves are machined repeatedly at the exact same rolling position. For this purpose, the number of strokes per section should not be a strict integer, and within the scope of the present invention, a value of less than 1.4, more preferably less than 1.2, and particularly less than 1.1 is preferred. However, in this regard, values ​​of less than 1, and even less than 0.9, are conceivable, while on the other hand, these values ​​should preferably be less than 0.5, and more preferably less than 0.6. It will be understood that the number of strokes per workpiece rotation is also preferably not an integer. 【0016】 In a further preferred embodiment, the stroke rate is at least 30 double strokes per minute, preferably at least 100, and particularly at least 200 double strokes per minute. However, to achieve the highest possible machining speed, even higher values ​​can be used, such as 300 double strokes per minute, and even 400 or more double strokes per minute. 【0017】 The advantages of the method according to the present invention are particularly evident when the tooth width of the tooth to be shaped is greater than 15 mm, even when the tooth width is 20 mm or more, especially 35 mm or more, or even 50 mm or more. 【0018】 In a further preferred embodiment, for at least one of the first strokes, a consistent contact trajectory is specified to extend in the profile direction over an area of ​​at least 20%, preferably at least 30%, and particularly at least 40%, of the total profile height of the final geometric shape of the tooth being machined. This further facilitates chip formation and a certain degree of absorption of machining forces on the tool. 【0019】 The present invention further provides a control program, when executed on the controller of a gear cutting machine, that controls the gear cutting machine to carry out the method described in any one of the prior claims. 【0020】 From a device technology standpoint, the present invention provides a gear shaping machine having a controller equipped with the control program described in claim 12. A gear shaping machine equipped with NC control of the moving axis of the gear shaping machine is preferred, and its stroke movement is achieved via crank drive. However, with respect to the stroke, a hydraulic axis can also be used. Furthermore, the present invention is not limited to any particular detail with respect to the implementation of the gear shaping machine, and it is possible to use gear shaping machines that are well known to those skilled in the art and available on the market, and for exemplary designs of suitable gear shaping machines, it is possible to use the design described in German Published Patent No. 10 2019 004 299(A1), which is incorporated herein by reference. [Brief explanation of the drawing] 【0021】 Further features, details, and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings. [Figure 1] A schematic diagram of the machining engagement during gear shaping is shown. [Figure 2]Indicates the angle between the contact locus and the tooth flank line on the pitch circle at the stroke center. [Figure 3] Shows a qualitative comparison of the contact locus compared to the prior art. 【Best Mode for Carrying Out the Invention】 【0022】 In FIG. 1, it can be seen how the form milling cutter 40 engages with the workpiece for generating the tooth 55 on the workpiece 50. The situation during the working stroke at the start of the engagement is shown, from which it can be seen that while the form milling cutter 40 and the workpiece 50 are meshing and engaging with each other, the form milling cutter 40 is moved downward along the stroke axis Z, and for that purpose, Shape cutting machine cutter the rotational speed of 40 and the rotational speed of the workpiece 50 are synchronized in a known manner. In this exemplary embodiment, the stroke movement is carried out by a crank drive as in the prior art, and in the given exemplary embodiment, for example, for generating straight teeth on the workpiece, a stroke length of about 20 mm is set, the number of strokes is 500 double strokes (working stroke + return stroke) per minute, and the rolling speed is 0.95 strokes per section. However, it is understood that the present invention is not limited to a specific tooth type such as external teeth or internal teeth, and preferably internal teeth are also similarly generated. It is also understood that the present invention is not limited to a specific tooth width, the corresponding stroke length or pitch size, and in this exemplary embodiment, the tooth pitch (straight tooth angle module) is, for example, 3 mm and the teeth are straight teeth. However, the present invention can also be applied to helical teeth, but the helical teeth should preferably be less than 14° or the above value. 【0023】 Regarding the design of a suitable gear hobbing machine, designs already known from the prior art can be used, for example, the design shown in German Patent Publication No. 10 2019 004 299 (A1), in which the lifting movement for the return stroke is achieved by a rotary drive cam having a predetermined profile. The above-mentioned document is incorporated herein by reference with respect to an exemplary design of a hobbing machine. 【0024】 In FIG. 2 (for the purpose of illustration or definition, it is clear that the form of the gear shown in FIG. 2 is different from the form of the gear in FIG. 1), (in this exemplary embodiment, at the stroke center, which coincides with the center in the width direction of tooth 55), an angle γ is shown between the contact locus of the hobbing operation and the tooth flank line 57 on the pitch circle on tooth flank 56. This angle is extremely narrow even in the case of conventional gear hobbing with helical retrograde feed (as shown by reference numeral 58 in FIG. 1, during conventional gear hobbing, the typical machining locus extends substantially parallel to the tooth flank line). In the configuration according to the invention, respectively, this angle is quite large and its cotangent is quite small, but in an exemplary embodiment where the second coefficient K2 is 1 for the sake of simplification and no correction is provided, a value of about 20 is reached for cotangent γ. 【0025】 In FIG. 3, the differences between an exemplary embodiment of the invention (FIG. 3A) and the prior art (FIG. 3B) are again juxtaposed in a purely relative representation (shown in an overly distorted manner) without observing absolute values, and looking at the machining locus that extends in a clearly more oblique manner across tooth flank 56, which, despite not having a lower number of strokes, results in both good machining quality of the hobbed tooth 55 and material removal with less tool wear. 【0026】 It will be understood that the invention is not limited to the detailed features shown in the exemplary embodiments. Rather, the individual features of the above specification text and the following claims may be essential, individually and in combination, for the implementation of the invention in its various embodiments.

Claims

[Claim 1] On the workpiece, the specified tooth perpendicular module (m n A method for shaping a gear tooth having a pressure angle (α) and optionally a helix angle (β), wherein a shaping machine cutter moving in a stroke cycle having a specified stroke length (h) removes material from the workpiece in a plurality of operating strokes in a rolling machining engagement, thereby forming a trajectory for the shaping machine cutter as it moves along the tooth surface, A first set of strokes are performed across a first feed region of the entire feed for completing the tooth being shaped, and the first feed region further comprises a subsequent feed region. With respect to at least the first plurality of strokes, the trajectory on the pitch circle at the stroke center extends at an angle γ with respect to the tooth surface line, and the cotangent of the angle γ is a constant K 1 and K 2 It is less than or equal to the product of, K 1 is equal to 40, K 2 is K 2 = K h · K m · K α · K β is the geometric shape / process coefficient of, K h = h [mm] / 20, K m = 3 / m n [mm], K α = sin20° / sinα, and K β = cosβ, characterized by a method. [Claim 2] The method according to claim 1, wherein the shaping cutter is fed through a first plurality of strokes, and the feed parameter, defined by the quotient of the radial feed per revolution of the workpiece and the amount the shaping cutter is lifted between the operating stroke and the return stroke in the first plurality of strokes, is less than 1.

4. [Claim 3] The method according to claim 2, wherein the feed parameter is less than 1.

3. [Claim 4] The subsequent feed region is such that the cotangent γ is 40·K 2 The method according to any one of claims 1 to 3, which is greater than [Claim 5] During the final feed to reach the final feed depth of the tooth being machined, the cotangent γ is 80·K 2 The method according to any one of claims 1 to 4, which is greater than [Claim 6] The method according to any one of claims 1 to 5, wherein the tooth is a straight tooth or a tooth whose helix angle is less than 14°. [Claim 7] The method according to any one of claims 1 to 6, wherein the tooth width is at least 60% of the stroke length. [Claim 8] The method according to any one of claims 1 to 7, wherein in two consecutive workpiece rotations, the rolling position of the first workpiece rotation differs from the rolling position of the subsequent second workpiece rotation in the tooth groove being machined. [Claim 9] The method according to any one of claims 1 to 8, wherein the number of strokes is at least 30 double strokes per minute. [Claim 10] The method according to claim 7, wherein the tooth width is greater than 15 mm. [Claim 11] The method according to any one of claims 1 to 10, wherein, with respect to at least a first plurality of strokes, the continuous trajectory extends over an area of ​​at least 20% of the total profile height of the final geometric shape of the tooth being machined, when viewed in the height direction of the tooth. [Claim 12] A control program, which, when executed on the controller of a gear cutting machine, controls the gear cutting machine to carry out the method according to any one of claims 1 to 11. [Claim 13] A gear cutting machine comprising a controller equipped with the control program described in claim 12.

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