Process for machining the tooth flanks of bevel gear workpieces using the semi-completing single part process with a standardized gear cutting tool

Abstract

Method for milling or grinding the tooth flanks of a bevel gear workpiece in a semi-completing single part process using a gear cutting tool (100), which is a standardized gear cutting tool (100) with standardized tool profiles, which has a positive center distance (s a0 ) and for which at least two different tool flank angles are specified, wherein the following steps are carried out for machining the tooth flanks of a first bevel gear workpiece: - machining a convex tooth flank of the first bevel gear workpiece with an inner side (11.i) of the gear cutting tool (100) after setting a first machine setting, - machining a concave tooth flank of the first bevel gear workpiece with an outer side (11.a) of the gear cutting tool (100) after setting a second machine setting, wherein the first and the second machine settings differ at least by an inclination angle of the tool misalignment and by a rolling ratio, wherein the order of the two steps can also be reversed.

Description

Field of the invention

[0001] The subject matter of the invention is a method for machining the teeth of spiral-toothed bevel gears, referring here to spiral-toothed bevel gears with and without axial offset (so-called hypoid gears). It also involves the use of a corresponding milling or grinding tool. Documents DE 195 17 360 C1 and US Pat. No. 1,654,199 A disclose methods for manufacturing bevel gears.

[0002] This is a so-called semi-completing process. This is a single-part process used for grinding or milling bevel gears. The two opposite flanks of a tooth gap of the bevel gear to be machined are machined with the same tool but with different machine settings (with different tilt).

[0003] The semi-completing process of the invention is classified as a discontinuous process, as described, for example, in DE 195 17 360 C1. The semi-completing process of the invention is a discontinuous generating grinding or hobbing process. In this discontinuous process, the tooth profile on the work gear is ultimately created by rolling and moving the tool on the work gear. The inventive process also makes it possible to manufacture the ring gear, as is known, only by plunging and then to manufacture the pinion with adapted machine settings, so that the pinion and ring gear form a functioning pair.

[0004] It is known that it is advantageous for the production of spiral-toothed bevel gears to manufacture them on the basis of identical generating face gears. A prerequisite for this is that the tool's cutting radius for the pinion and ring gear flanks is identical. As is known from the prior art, small differences in these cutting radius radii are used to create crowning. Since a concave flank rolls off a convex flank, the requirement for an identical cutting radius cannot be reflected in a tool profile. To achieve a positive center distance on the tool, the cutting radius of the external cutting profile, which creates the concave bevel gear flanks, must be larger than the cutting radius of the internal cutting profile, which creates the convex bevel gear flanks.

[0005] Since a pair of spiral-toothed bevel gears always combines a concave flank with a convex flank, the difference in cutting radius mentioned in the previous section leads to a very large crowning. In addition to generating crowning by means of a radius difference, the use of a tool tilt is a well-known method for generating or influencing this. Depending on the orientation or direction of this tilt, it is possible to generate positive or negative crowning.

[0006] The crowning caused by the radius difference can be reduced to a desired level by adjusting the tool inclination. The required tool inclination varies for each gear design, so individual tool flank angles are required to generate the desired pressure angle on the bevel gear. Due to this fact, semi-completing has so far been mostly limited to grinding with dressable grinding wheels.

[0007] The object of the invention is to enable semi-completion with standardized tool profiles (on grinding wheels or cutter heads for milling) while simultaneously generating the required pressure angles on the tooth flank of the bevel gear. The method can be used for both soft and hard gear cutting in milling or grinding processes.

[0008] As mentioned above, a specific radius difference in each bevel gear pair results in a specific crowning angle. To achieve this to the desired level, a coordinated tool inclination is required. Those skilled in the art will know that this, in turn, requires an adjustment of the tool flank angle to create the specified pressure angle on the gearing. Using a tool flank angle that deviates from the actually required tool flank angle will result in a pressure angle error and thus a poor contact pattern on the gearing.

[0009] This problem is solved according to the invention as follows: - Determination of the crowning caused by the difference in radius, - Determining the required tool inclination to generate or reduce the crowning to a desired value, - Selecting a tool engagement angle (from a set of standardized tools) and determining the difference between the flank angle of the selected standard tool and the required flank angle, - Correction of the pressure angle error by modifying the rolling ratio.

[0010] For example, if the pressure angle is set to 20 degrees, a range of +2.5 degrees to -2.5 degrees can be covered by relative tilting (changing the machine settings). However, since the relative tilt shifts the contact pattern on the spiral tooth flanks to be machined on the workpiece, the rolling ratio of the machine is also adjusted when changing the machine settings to optimize the contact pattern.

[0011] To put it very simply, you accept a slightly unsuitable tool pressure angle, which results from the fact that you are selecting a tool from a set of standardized tools. The set of standardized tools only has a small number of different tools, which means that you have to make certain compromises in terms of tool pressure angle. You therefore accept a slightly "suboptimal" tool pressure angle in order to be able to use an existing or specified tool. You then make corrections to the gearing by changing the machine setting(s) in order to adapt the flank geometry. Changing the machine setting(s) therefore involves changing the pitch ratio.

[0012] According to the invention, an existing or predefined tool can be used to cut different workpieces. This allows for standardization of grinding and / or milling tools. Only the machine settings need to be adjusted accordingly.

[0013] According to the invention, standardized or conventional tools are used, in which the tool engagement angles are preferably specified in steps. For example, a first tool for use according to the invention can be designed for an engagement angle of 20 and 22 degrees. A second tool for use according to the invention can be designed for an engagement angle of 22 and 18 degrees, to give two specific examples.

[0014] The nominal radii of these standardized or conventional tools can be constant. For example, one tool can then machine a gear with a module of 4.5 to 5.5.

[0015] Despite the use of standardized or conventional tools, workpieces can be manufactured with the desired pressure angles and the required flank topography. The bevel gears machined according to the invention all have a circular arc as the longitudinal tooth line, meaning they are all circular-arc toothed workpieces. This refers to both arc-toothed bevel gears with and without axial offset (so-called hypoid gears).

[0016] The milling tools of the invention are preferably cutterhead tools with blades that have both an inner cutting edge for machining the convex flank and an outer cutting edge for machining the concave flank. Another possibility is the use of inner blades (IM) and outer blades (AM) arranged in groups to machine the convex and concave flanks of the teeth of a workpiece. Furthermore, these cutterheads can also have so-called leading or center cutters, which serve to relieve the load on the subsequent blades or cut part of the tooth gap base.

[0017] The grinding tools are preferably cup-shaped tools (called cup wheels). The inner cone of such a grinding tool is designed for grinding the convex tooth flanks, and the outer cone for grinding the concave tooth flanks.

[0018] Depending on the situation, the contact pattern of the gearing shifts due to the described conditions. The contact pattern typically shifts upwards or downwards along the tooth flank. To improve the contact pattern, according to the invention, when adjusting the machine setting, the pitch ratio of the machine is also adjusted in addition to the inclination angle, as explained.

[0019] According to the invention, the flanks of the bevel gear teeth can be optimized independently of each other.

[0020] Grinding is preferred for post-processing, as the workpieces involved are circular-geared. The flanks of such circular-geared workpieces are easily reworked and individually optimized using a grinding process.

[0021] The semi-completing process of the invention can be used for both hard and soft machining of bevel gear teeth.

[0022] The semi-completing method of the invention can be used for both milling and grinding of bevel gear teeth.

[0023] In particular, the following variants according to the invention are possible: 1. Variant: Soft milling followed by hard grinding 2. Variant: Soft grinding followed by hard grinding 3. Variant: Soft milling followed by hard milling 4th variant: Soft grinding followed by hard milling.

[0024] The semi-completing process of the invention is particularly suitable for small series, since one of the standardized or conventional tools can be used to machine a desired gear.

[0025] The invention makes it possible to simplify the tool range, as one tool can be used to machine several slightly different workpieces. Slightly different workpieces, as defined by the invention, are workpieces whose module differs only slightly from one another. For example, a standard knife with a knife module of 4 is suitable for gears with a module of 3.5 to 4.5 mm.

[0026] The invention enables flexible, complete production of spiral-toothed bevel gears, allowing a certain range of different gear geometries to be machined using one and the same tool. This requires, on the one hand, the cutter module to be suitable (see example above), and, on the other hand, the cutter head cutting radius to be reasonable. DRAWINGS

[0027] An embodiment of the invention is described in more detail below with reference to the drawings. Fig. 1A shows a sectional view of a first tool according to the invention; Fig. 1B shows another sectional view of the first tool after Fig. 1A; Fig. 1C shows a top view of the first tool after Fig. 1A.

[0028] An exemplary, standardized gear cutting tool 100 is shown in the Fig. 1A, Fig. 1B and Fig. 1C. In addition to such an embodiment with bar knives, other embodiments of cutter heads are also possible. The gear cutting tool 100 comprises a base body 101 for receiving bar knives 10. One of the bar knives 10 is shown. This is a bar knife with two main cutting edges (17A and 17B), one for the concave and one for the convex tooth flank. Each of the bar knives 10 has a positive center width s. a0 , which, as can be seen in Fig. 1B, corresponds to the head width of the knife. The base body 101 together with the bar knives 10 rotates about a tool axis RW. Each bar knife 10 has a shank with dimensions a0 × b0 and an active (cutting or grinding) area with a profile height h.

[0029] The following additional sizes are available in the Fig. 1A, Fig. 1B and Fig. 1C: a0 is the shaft thickness; b0 is the shaft width; δ is the angle of inclination of the knife grooves for receiving the bar knives 10 in the base body 101; the head clearance angle is denoted by γ K and is 19.5° here, for example; the rake face is marked 12; γ A is the clearance angle with respect to the convex tooth flank of the workpiece; γ B is the clearance angle with reference to the concave tooth flank of the workpiece (the rake angles in this example are 0 degrees for both sides); the tip rounding radii of the bar blade 10 are in the Fig. 1B with ρ a0v and ρa0x designated; α Fx is the knife flank angle with respect to the convex tooth flank of the workpiece; α Fv is the knife flank angle with respect to the concave tooth flank of the workpiece; a H the cutting edge position is radial; h D corresponds to the height of the deeded property; H m the height of the cutter head body; H W0 The reference height of the cutter head; 14 denotes the head clearance surface; 15A is the first clearance surface and 15B the second clearance surface; 16 is the head cutting edge; 17A is the first cutting edge and 17B the second cutting edge. Reference numerals or symbols with a v in the subscript denote a cutting edge for producing the concave tooth flank, and reference numerals or symbols with an x ​​in the subscript denote a cutting edge for producing the convex tooth flank.

[0030] When machining gear teeth into solid material, both cutting edges cut during the first cut with the first machine setting, whether on a grinding wheel or a cutter head with internal and external blades, or a cutter head with a blade with internal and external cutting edges. Depending on the selected machine setting, the specified geometry of the concave or convex tooth flank is created first. In the next cut, after adjusting the machine settings to the respective convex or concave tooth flank, the tooth flank is machined. Only one cutting edge of the profile or cutter group then cuts, while the other moves in the existing gap.

[0031] If prefabricated tooth flanks are being machined, such as in the hard machining of hardened bevel gears, only one cutting edge of the profile cuts at a time, regardless of the machine setting. Since this is a single-part process, various machining sequences are possible. For example, first completing all concave or convex flanks and then completing all corresponding convex or concave flanks. Another option is to first machine both tooth flanks one after the other for each tooth gap and then divide them into the next tooth gap. It is also possible to vary the first cut, concave or convex flank, from component to component in order to achieve more even wear on the tool cutting edges. The machine settings differ at least in the tilt angle and the rolling ratio.Due to the different positions of the first and second cutting edges 17A and 17B on the bar blades 10 of the gear cutting tool 100, slightly different cutting circle radii result. The undesirable portion of the radius difference can be compensated for by setting an appropriate tilt angle for the first and second machine settings.

[0032] In order to compensate or correct pressure angle errors resulting from the use of standardized gear cutting tools 100, the rolling ratio will be set differently when machining the concave tooth flanks of a workpiece than when machining the convex tooth flanks of the workpiece.

[0033] According to the invention, the bar knives 10, or the standardized gear cutting tools 100, can be designed, for example, so that they are offered / provided in three different variants. The bar knives 10, or the standardized gear cutting tools 100, are designed so that in h D = 1.25 × m0 for all three variants, the same cutting circle radii are given (m0 is the module on the tool in the part plane). The bar knives 10 can, for example, be graded with the following three correction angles Δα: 1 0 , 2.5 0 , 4 0 The knife flank angles are then: α Fx = 20° + Δα and α Fv = 20° - Δα.

[0034] Changing the pitch ratio, which is used here to compensate for the flank angle errors, creates a helix angle error. This helix angle error can also be compensated for if necessary by adjusting the machine settings.

[0035] What has been written so far can also be applied to grinding tools. The invention can also be applied to solid tools and cutter heads with so-called relief-ground blades (profile blades), and not just to bar cutter heads.

Claims

[1] Method for milling or grinding the tooth flanks of a bevel gear workpiece in the semi-completing single part process with a gear cutting tool (100), which is a standardized gear cutting tool (100) with standardized tool profiles, which has a positive center distance (s a0 ) and for which at least two different tool flank angles are specified, wherein the following steps are carried out for machining the tooth flanks of a first bevel gear workpiece: - machining a convex tooth flank of the first bevel gear workpiece with an inner side (11.i) of the gear cutting tool (100) after setting a first machine setting, - machining a concave tooth flank of the first bevel gear workpiece with an outer side (11.a) of the gear cutting tool (100) after setting a second machine setting, wherein the first and the second machine settings differ at least by an inclination angle of the tool misalignment and by a rolling ratio, wherein the order of the two steps can also be reversed. [2] Method according to claim 1, characterized by that the tooth flanks of a second bevel gear workpiece are machined with the same standardized gear cutting tool (100), wherein the first bevel gear workpiece has a different component geometry than the second bevel gear workpiece, characterized by the following steps that are carried out to machine the tooth flanks of the second bevel gear workpiece: - machining a convex tooth flank of the second bevel gear workpiece with the inner side (11.i) of the gear cutting tool (100) after setting a third machine setting, - machining a concave tooth flank of the second bevel gear workpiece with the outer side (11.a) of the gear cutting tool (100) after setting a fourth machine setting, wherein the third and the fourth machine settings differ at least by an inclination angle of the tool misalignment and by the rolling ratio, wherein the order of the two steps can also be reversed. [3] Method according to claim 2, characterized by that the first bevel gear workpiece has a different module than the second bevel gear workpiece. [4] Method according to claim 1, 2 or 3, characterized by that it is used for pre-toothing a bevel gear workpiece and / or for remachining an already pre-toothed bevel gear workpiece. [5] Method according to claim 1, 2, 3 or 4, characterized by that a milling tool is used and that it is a process for milling the tooth flanks of bevel gear workpieces. [6] Method according to claim 5, characterized by that at least two different milling tools with bar knives (10) are provided, wherein these milling tools differ in that they have different correction angles (Δα). [7] Method according to claim 1, 2, 3 or 4, characterized by that a grinding tool is used and that it is a process for grinding the tooth flanks of bevel gear workpieces. [8] Use of a standardized gear cutting tool (100) that has a positive center distance (s a0) for machining the tooth flanks of at least two bevel gear workpieces according to a method according to claim 2, wherein the machine settings differ when machining the tooth flanks of the at least two bevel gear workpieces.

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