CONDITIONING OF A SUPERABRASIVE GRINDING TOOL

Abstract

In a method of machining workpieces in a gear grinding machine with a grinding tool having vitrified-bonded abrasive grains made of a superabrasive material. The grinding tool is first dressed. Subsequently, the dressed grinding tool is conditioned such that a desired wear condition is produced. Thereafter, pre-toothed workpieces are machined using the dressed and conditioned grinding tool. Conditioning prevents undesirable grinding-in behavior of the grinding tool, which can cause thermal damage to the edge zone of the workpiece. Conditioning is performed with a conditioning kinematics, which is different from the machining kinematics and may correspond to a dressing kinematics. For conditioning, a conditioning tool is used which has a basic shape that is different from the basic shape of the workpieces.

Claims

1. A method for machining pre-toothed workpieces in a gear grinding machine using a grinding tool comprising vitrified-bonded abrasive grains made of a superabrasive material, comprising the steps: a) dressing the grinding tool using a dressing tool, wherein the gear grinding machine executes a dressing kinematics for moving the dressing tool relative to the grinding tool during the dressing of the grinding tool; b) conditioning the dressed grinding tool using a conditioning tool such that a desired wear condition of the grinding tool is produced, wherein the gear grinding machine executes a conditioning kinematics for moving the conditioning tool relative to the dressed grinding tool during the conditioning of the dressed grinding tool; and c) machining the pre-toothed workpieces using the dressed and conditioned grinding tool, wherein the gear grinding machine executes a machining kinematics for moving the dressed and conditioned grinding tool relative to the pre-toothed workpieces during the machining of the pre-toothed workpieces, wherein the conditioning kinematics is different from the machining kinematics.

2. The method of claim 1, wherein the conditioning kinematics corresponds to the dressing kinematics.

3. The method of claim 1, wherein the gear grinding machine comprises a conditioning device on which the conditioning tool is clamped, wherein the gear grinding machine comprises a workpiece spindle on which the workpieces are clamped in step c), and wherein the conditioning device is different from the workpiece spindle.

4. The method of claim 3, wherein the conditioning tool has a basic shape that is different from a basic shape of the workpieces.

5. The method of claim 4, wherein the basic shape of the conditioning tool corresponds to a basic shape of the dressing tool.

6. The method of claim 1, wherein a portion of the conditioning tool that is in contact with the grinding tool during conditioning is made of a metal.

7. The method of claim 1, wherein the grinding tool rotates during the step of conditioning and the conditioning tool is stationary during the step of conditioning.

8. The method of claim 1, wherein the grinding tool rotates during the step of conditioning and the conditioning tool rotates during the step of conditioning.

9. The method of claim 8, wherein the conditioning tool has a basic shape of a dressing roll.

10. The method of claim 1, wherein the conditioning tool is in line contact with the grinding tool during the step of conditioning.

11. The method of claim 1, wherein the conditioning kinematics comprises a relative movement between the grinding tool and the conditioning tool such that a contact position between the conditioning tool and the grinding tool changes along a profile of the grinding tool during conditioning.

12. The method of claim 1, wherein all workpieces in step c) are machined with identical machining parameters, wherein the machining parameters are selected such that thermal edge zone damage would occur during machining of at least a first workpiece in step c) if step b) were not performed, and wherein in step b) the conditioning is carried out in such a way that no thermal edge zone damage occurs during the machining in step c).

13. The method of claim 1, wherein the step b) of conditioning is carried out several times with the same conditioning tool.

14. The method of claim 1, wherein the grinding tool is a grinding worm.

15. A gear grinding machine, comprising: a tool spindle on which a grinding tool can be clamped; at least one workpiece spindle on which a workpiece can be clamped; a dressing device on which at least one dressing tool can be clamped; a conditioning device on which at least one conditioning tool can be clamped; a plurality of machine axes for driving the tool spindle, the workpiece spindle and the dressing device and moving them relatively to each other; and a control unit for controlling the machine axes, the control unit being configured to control the machine axes such that the machine tool performs the method according to claim 1.

16. The method of claim 6, wherein the portion of the conditioning tool that is in contact with the grinding tool during conditioning is made of steel.

17. The method of claim 9, wherein the conditioning tool corresponds to a metallic base body of a dressing roll without hard material coating.

18. The method of claim 1, wherein the conditioning tool is in point contact with the grinding tool during the step of conditioning.

19. The method of claim 1, wherein the grinding tool is a profile grinding wheel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Preferred embodiments of the invention are described in the following with reference to the drawings, which are for explanatory purposes only and are not to be construed in a limiting manner. In the drawings,

[0041] FIG. 1 shows a gear grinding machine according to an embodiment example in a perspective view;

[0042] FIG. 2 shows a section of the gear grinding machine of FIG. 1 in the area of the dressing device, wherein parts of the gear grinding machine are not shown for simplification;

[0043] FIG. 3 shows the section of FIG. 2, wherein a profile grinding wheel is provided as the grinding tool instead of a grinding worm;

[0044] FIG. 4 shows a sketch showing a grinding worm in engagement with a workpiece;

[0045] FIG. 5 shows a sketch showing a profile grinding wheel in engagement with a workpiece; and

[0046] FIG. 6 shows a flow chart for a method according to the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Design of an Exemplary Machine Tool

[0047] FIG. 1 shows an example of a machine tool for hard finishing of gears by generating gear grinding. Horizontal spatial directions are denoted by X and Y, and the vertical spatial direction (direction of gravity) is denoted by Z. The machine has a machine bed 100 on which an infeed slide 210 is arranged to be movable along an infeed direction X1. The infeed direction X1 corresponds to the horizontal spatial direction X. A tower-like tool carrier 200 is mounted on the infeed slide 210 so as to be pivotable about a vertical pivot axis C1, hereinafter referred to as the C1 axis. A feed slide 220 is arranged on the tool carrier 200 so as to be movable along an axial feed direction Z1. The feed direction Z1 corresponds to the vertical spatial direction Z. The feed slide 220 carries a tool head 300 which is pivotable relative to the feed slide 220 about a horizontal pivot axis A1, hereinafter referred to as the A1-axis. The A1-axis is parallel to the infeed direction X1. A tool spindle 310 is arranged on the tool head 300 so as to be movable along a shift direction Y1. The shift direction Y1 is perpendicular to the A1-axis and at an angle to the axial feed direction Z1, which depends on the pivot angle of the tool head 300 about the A1 axis. A grinding tool 320 in the form of a grinding worm is clamped on the tool spindle 310 to rotate about a tool spindle axis 1 (see FIGS. 2 to 5). The tool spindle axis 1 is parallel to the shift direction Y1.

[0048] A dressing device 400 is arranged on the machine bed 100. On a side of the tool carrier 200 facing away from the dressing device 400, a workpiece spindle 500, which is only partially visible in FIG. 1, is arranged on the machine bed 100 to rotate a workpiece 510 clamped thereon about a vertical workpiece spindle axis C (see FIGS. 4 and 5). The tool carrier 200 is pivotable 180 about the C1 axis between a machining position and a dressing position. In the machining position of the tool carrier 200, the grinding tool 320 can be brought into engagement with the workpiece 510 (see FIGS. 4 and 5). In the dressing position, the grinding tool 320 can be brought into engagement with dressing tools of the dressing device 400 described in more detail below (see FIGS. 2 and 3). In FIG. 1, the tool carrier 200 is shown in the dressing position.

[0049] A machine control 600, shown only symbolically, receives signals from sensors in the machine and controls the linear and pivot axes of the machine, the tool spindle, the workpiece spindle and the dressing device.

[0050] A machine concept according to FIG. 1 is disclosed in U.S. Pat. No. 5,857,894A. Corresponding machines are available under the designation RZ 400 from Reishauer A G, Wallisellen, Switzerland.

Dressing and Conditioning Device

[0051] In FIG. 2, a section of the machine in FIG. 1 is illustrated from a different viewing direction. Parts of the machine have been omitted in order to achieve a clearer representation.

[0052] The grinding tool 320 is illustrated in FIG. 2 as being free-floating. However, it will be understood that the grinding tool is still clamped to the tool spindle 310 as illustrated in FIG. 1. For the discussion below, it is assumed that the grinding tool 320 comprises an abrasive body made of vitrified-bonded cBN.

[0053] In particular, FIG. 2 shows the structure of the dressing device 400. The dressing device 400 comprises a first dressing spindle 410 which is pivotable relative to the machine bed about a vertical axis C_P1 as well as linearly movable along two orthogonal horizontal directions X_P, Y_P. A pivot drive 411, a first linear drive 412 and a second linear drive, which is not visible in FIG. 2, serve this purpose. A disk-shaped dressing tool 415 is clamped on the first dressing spindle 410 for rotation. The dressing device 400 further comprises a second dressing spindle 420, which is pivotable relative to the machine bed about a vertical axis C_P2 by means of a pivot drive 421. A second disk-shaped dressing tool can be clamped on the second dressing spindle 420 for rotation.

[0054] In the context of the present invention, a disk-shaped first conditioning tool 425 is clamped on the second dressing spindle 420 in lieu of a dressing tool. Additionally or alternatively, a stationary second conditioning tool 416 may be provided. The stationary conditioning tool 416 is held in a holder 417, which in the example of FIG. 2 is stationarily arranged on the housing of the first dressing spindle 410.

[0055] Thus, in the context of the present invention, the dressing device 400 performs the function of a combined dressing and conditioning device. Strictly speaking, only the first dressing spindle 410 with the dressing tool 415 clamped thereon forms the actual dressing device, while the second dressing spindle 420 with the conditioning tool 425 clamped thereon and the holder 417 with the stationary conditioning tool 416 form a conditioning device.

[0056] Using NC axes to generate movements with respect to X1, Y1, Z1, A1, X_P, Y_P, C_P1, and C_P2, the grinding tool 320 can be selectively brought into engagement with each of the three dressing or conditioning tools 415, 416, and 425.

Grinding Tool in the Form of a Profile Grinding Wheel

[0057] While the grinding tool 320 in FIG. 2 is a grinding worm, FIG. 3 illustrates the use of a grinding tool 321 in the form of a profile grinding wheel. All the considerations described here also apply mutatis mutandis to this type of grinding tool. When profile grinding wheels are used, the term tangential feed direction is usually used for the direction Y1 instead of the term shift direction.

Dressing and Conditioning Process

[0058] To dress the grinding tool 320 or 321, the rotating grinding tool 320, 321 is first brought into engagement with the dressing tool 415, which is also rotating. This produces or restores the desired outer contour of the grinding tool 320, 321 and the grinding tool 320, 321 is sharpened.

[0059] In order to avoid or at least reduce the undesirable grinding-in behavior of the grinding tool 320, 321 dressed in this way, as described above, the rotating grinding tool 320, 321 is then brought into engagement with the rotating conditioning tool 425 and/or with the stationary conditioning tool 416. Conditioning is carried out until it is ensured that no thermal damage occurs to the edge zone of the workpieces during subsequent workpiece machining, even if machining is carried out with the same technological parameters for all workpieces.

Dressing and Conditioning Tools

[0060] Instead of a dressing tool and a conditioning tool of the type shown in FIGS. 1 to 3, other types of dressing and conditioning tools may be used. Accordingly, the dressing and conditioning device may be configured differently.

[0061] The dressing tool 415 may be any dressing tool suitable for dressing an abrasive body made of vitrified-bonded cBN. Such dressing tools are known in the prior art in a variety of embodiments. They can be used for dressing in various ways.

[0062] For example, it is known that the dressing of a grinding worm can be performed in line contact between the dressing tool and the grinding tool in order to map the profile of the dressing tool onto the profile of the grinding tool. This is referred to as profile dressing. If the dressing tool rotates, it is referred to as a profile roll. Depending on the dressing tool and dressing device, each flank of a worm start can be dressed individually during profile dressing, both flanks of a worm start can be dressed simultaneously, or the flanks of two or more worm starts of a multi-start grinding worm can be dressed simultaneously. In addition to the flanks, it is also possible to dress the head and/or foot areas of the worm starts simultaneously or successively. The same dressing tool or another dressing tool can be used for this purpose (cf. e.g. U.S. Pat. No. 6,234,880B1).

[0063] It is also known to dress a grinding worm in point contact, whereby the dressing tool is then guided line by line along the flanks of the grinding worm. This is referred to as form dressing. If the dressing tool rotates, it is referred to as a form roll.

[0064] Mixed forms are also known, in which parts of the profile are dressed in line contact and other parts in point contact, either with different dressing tools or with different areas of the same dressing tool (see e.g. U.S. Pat. No. 6,012,972A).

[0065] Accordingly, there are a large number of designs of dressing tools. For example, disc-shaped dressing tools (dressing rolls) are known which are driven to rotate about a dressing tool axis for dressing, as is the case with the dressing tool 415. The dressing tool then often has a disc-shaped base body made of steel on which an abrasive coating, for example of diamond grains, is applied. Other types of dressing tools, on the other hand, are configured to be stationary. Such dressing tools may also have a base body of steel which is coated with abrasive material.

[0066] Different types of dressing methods and corresponding dressing tools are also known for dressing profile grinding wheels. In particular, a profile grinding wheel can also be dressed in line contact or in point contact. This can again be done with a rotating, disc-shaped dressing tool of the type of dressing tool 415 or with a stationary dressing tool, wherein the dressing tool may have a base body made of steel and an abrasive coating.

[0067] An equally large variety of configurations is possible for the conditioning process and the conditioning tool used for this purpose. The conditioning of the grinding tool can also be carried out in line contact or in point contact. The conditioning tool may be configured to be rotating or stationary. In particular, it may be formed by the steel base body of a dressing tool in which the abrasive coating has been omitted, so that the grinding tool is conditioned directly with the steel of the base body.

[0068] The conditioning tool may be of the same type as the dressing tool. For example, both the dressing tool and the conditioning tool may be a disc-shaped tool that is rotated during dressing or conditioning. However, the conditioning tool may also be different from the dressing tool. For example, the dressing tool may be rotating while the conditioning tool is stationary.

[0069] The decisive factor is that conditioning is not performed with a sacrificial workpiece that is clamped on the workpiece spindle for conditioning, but with a separate conditioning tool. The conditioning tool is not clamped on the workpiece spindle, and conditioning is not performed with a kinematics that correspond to the kinematics used in workpiece machining, but rather conditioning is performed with a kinematics that correspond to the kinematics of a typical dressing operation. While the kinematics used in conditioning may be different from the actual kinematics used in dressing (e.g., because the dressing tool and the conditioning tool are not the same), it is nonetheless a kinematics such as might be used in dressing.

[0070] In the examples of FIGS. 1 to 3, the same movement axes can be used for conditioning that can also be used for dressing. These include the axes X_P, Y_P, C_P1 and/or C_P2. These axes are purely dressing and conditioning axes that are not relevant for workpiece machining. The movement sequences during conditioning in the examples of FIGS. 1 to 3 are therefore obviously completely different from those during workpiece machining.

Workpiece Machining

[0071] After conditioning, the machining of workpieces takes place. For the sake of completeness, this is illustrated in FIG. 4 for the example of continuous generating gear grinding and in FIG. 5 for the example of discontinuous profile grinding.

[0072] In the example of FIG. 4, the grinding tool 320 is a grinding worm that is in rolling engagement with the workpiece 510. At the same time, the workpiece 510 rotates about the workpiece spindle axis C at a rotation speed that has a predetermined rotation speed ratio to the rotation speed of the grinding tool 320. This rolling engagement is established electronically by the machine control 600. The grinding tool 320 is simultaneously advanced continuously along the feed direction Z1 over the entire width of the workpiece and, if necessary, shifted along the shift direction Y1. It is apparent that this kinematics is significantly different from the kinematics used in dressing and conditioning.

[0073] In the example of FIG. 5, the grinding tool 321 is a profile grinding wheel. The rotating grinding tool 321 is sequentially inserted into each tooth gap of the workpiece 510 to machine the same. During the machining of a tooth gap, the workpiece 510 is stationary and the grinding tool 321 is continuously advanced along the feed direction Z1 over the entire width of the workpiece. Subsequently, the workpiece is rotated for machining the next tooth gap. It is obvious that this kinematics also differs significantly from the kinematics during dressing and conditioning.

Flowchart

[0074] The method described above is summarized in the form of a flow chart in FIG. 6. In step 701, the grinding tool is dressed. In step 702 it is conditioned. Then, in step 703, workpieces are machined. When the grinding tool is worn to the extent that it needs to be reprofiled and/or resharpened, steps 701 and 702 are carried out again.

Other Variations

[0075] The invention is not limited to the above embodiments, and further variations are possible. In particular, the invention is not limited to any particular machine design, but can be used with any gear grinding machine that allows both dressing and conditioning.

LIST OF REFERENCE SIGNS

[0076] 100 machine bed [0077] 200 tool carrier [0078] 210 infeed slide [0079] 220 feed slide [0080] 300 tool head [0081] 310 tool spindle [0082] 320, 321 grinding tool [0083] 400 dressing device [0084] 410 dressing spindle [0085] 411 pivot drive [0086] 412 linear drive [0087] 415 dressing tool [0088] 416 conditioning tool [0089] 417 holder [0090] 420 dressing spindle [0091] 421 pivot drive [0092] 425 conditioning tool [0093] 500 workpiece spindle [0094] 510 workpiece [0095] 600 machine control [0096] 701-703 procedural steps [0097] X, Y, Z coordinates [0098] X1 infeed direction [0099] Y1 shift direction [0100] Z1 axial feed direction [0101] A1 pivot axis of tool head [0102] C1 pivot axis of tool carrier [0103] C workpiece spindle axis [0104] X_P, Y_P displacement directions dressing/conditioning [0105] C_P1, C_P2 pivot axes dressing/conditioning