Grinding wheel, grinding machine and method for dressing grinding wheel

Abstract

To provide a grinding wheel which is suitable for electrolytic corrosion dressing and which ensures a high surface quality that is not adversely affected by the electrolytic corrosion dressing.SOLUTION: A grinding wheel (24) has: a rotation axis (136); and an abrasive coating material (142) including a macroscopic matrix (154). The grinding wheel (24) can rotate about the rotation axis (136). The macroscopic matrix (154) is conductive, and embedded, therein, with abrasive grains (156). The abrasive grains (156) each have a conductive microscopic matrix (164), in which cutting particles (166) are embedded. A method using a grinding machine (10) is used for dressing such grinding wheel (24) by means of wire electrolytic corrosion.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention (hereinafter sometimes referred to as the "disclosure") relates to a grinding wheel, in particular suitable for electroerosion dressing, comprising a central hole defining an axis of rotation for rotating the grinding wheel and an abrasive coating comprising a macroscopic matrix in which abrasive grains are embedded, the macroscopic matrix being electrically conductive. The disclosure further relates to a grinding machine comprising such a grinding wheel, the grinding machine being provided with or coupled to an electroerosion dressing device, in particular for dressing the grinding wheel. The disclosure further relates to a method for dressing a grinding wheel by wire electroerosion. [Background technology]

[0002] From US Pat. No. 5,399,543 a grinding wheel for machining a workpiece is known, which comprises a base body rotatable about a rotation axis, a conductive tool face for removing material from the workpiece, and a functional surface electrically connected to the tool face for electrically contacting the tool face during rotation of the tool, the functional surface being arranged axially on an end face or radially on a step of the base body relative to the rotation axis.

[0003] From DE 10 200 03 133 A1 a device for dressing grinding wheels by wire erosion is known. From DE 10 200 03 133 A1 a wire guide for guiding a wire electrode during wire erosion is known.

[0004] During grinding, dressing ensures the correct concentricity and correct geometry of the grinding wheel. In addition, dressing can be used to profile and / or sharpen the grinding wheel. Dressing can also remove dirt from the grinding wheel. Furthermore, dressing can remove dull abrasive grains from the grinding body, which sharpens the grinding wheel.

[0005] The so-called wire erosion dressing is an electrochemical erosion method, which however does not concern itself with machining workpieces (see also the so-called electrochemical grinding), but instead with dressing the grinding wheel so that it can be used again for grinding workpieces.

[0006] Wire erosion dressing is based on wire erosion. A dressing device is provided which usually comprises a dressing wire and a drive for the dressing wire. The wire drive pulls the dressing wire, for example from a spool, feeds it via a power supply line and a thin wire guide disk with a circumferential groove and passes it past the grinding wheel, which rotates at a relatively high peripheral speed. The eroded areas are usually washed away with a dielectric cleaning medium. The respective previously used parts of the dressing wire are usually shredded and discarded.

[0007] Material removal from the grinding wheel is usually done contactlessly by very short, rapidly successive DC pulses which generate a discharge in the dielectric in the small gap between the electrode (dressing wire) and the grinding wheel. During the discharge, a tiny area of ​​the conductive binder material of the grinding wheel melts and is washed out of the gap as small fragments at the end of the spark discharge. The material removal forms a small crater on the surface of the grinding wheel. Continuous repetition results in continuous removal from the surface of the grinding wheel. The abrasive grains retain their morphology, unaffected by the erosion process.

[0008] That is, there is usually a discharge gap, so that there is no mechanical contact between the dressing wire and the abrasive grains or binder in the grinding coating of the grinding wheel. If the abrasive grains are exposed from the binder, they can separate or even fall off without the action of significant force.

[0009] It has been found that wire erosion dressing offers various advantages. This refers, for example, to the possibility of dressing the grinding wheel with a particularly hard abrasive (e.g. diamond- or boron-nitride-based abrasive). For the bonding of the abrasive grains in the abrasive coating, a conductive binder material is necessary as a prerequisite for wire erosion dressing. Apart from the wear of the dressing wire, the wear on the dressing device is not excessively large. Various profiles can be produced and dressed with the dressing device. The dressing device can be integrated into the grinding machine. External dressing devices are also conceivable.

[0010] Wire erosion dressing is suitable, for example, for grinding wheels for external grinding / external cylindrical grinding and for internal grinding / internal cylindrical grinding. Grinding wheels that can be dressed by wire erosion dressing can contain particularly hard abrasives / cutting materials. This makes them suitable, for example, for machining hard materials. This can include, for example, workpieces made of hardened steel, carbide metals, ceramic materials, etc.

[0011] However, it has been found that in some cases the surface quality after electrochemical dressing is still not sufficient for certain applications. The surface quality is, for example, influenced by the grain size of the abrasive grains used. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] DE 102015121316 [Patent Document 2] European Patent Application Publication No. 2607006 [Patent Document 3] DE 102015104405 A1 Summary of the Invention [Problem to be solved by the invention]

[0013] Against this background, the present disclosure is based on the task of identifying a grinding wheel that is particularly suitable for electrolytic dressing, which ensures a high surface quality that is not adversely affected by electrolytic dressing. When subsequently machining a workpiece with the grinding wheel, a good surface quality should be achievable. Nevertheless, the highest possible removal rate and / or service life of the grinding wheel should be achieved. A high dimensional accuracy is also required of the dressed grinding wheel. The grinding wheel should be as suitable as possible for machining materials that are considered problematic with regard to the grinding process. [Means for solving the problem]

[0014] According to a first aspect, the present disclosure relates to a grinding wheel, in particular a grinding wheel suitable for electrolytic dressing, comprising a rotation axis about which the grinding wheel can rotate and an abrasive coating comprising a macroscopic matrix in which abrasive grains are embedded, the macroscopic matrix being electrically conductive, the abrasive grains comprising an electrically conductive microscopic matrix in which cutting particles are embedded.

[0015] In this way, during electrolytic dressing, material removal can take place both in the macroscopic and in the microscopic matrix. Material removal in the microscopic matrix (within the abrasive grain) can, for example, allow a partial amount of cutting particles within the abrasive grain to separate from the surface of the grinding body of the grinding wheel.

[0016] Within the scope of this disclosure, the terms macroscopic and microscopic are not necessarily used in the narrow sense of the optical / physics field. Instead, what is important is that each microscopic matrix is ​​a component of an individual component of a macroscopic matrix. The individual components of the macroscopic matrix usually have a larger grain size than the individual components of the microscopic matrix. Thus, there is a hierarchy between macroscopic and microscopic matrices, mainly based on grain size. For example, there is an order of magnitude difference between an abrasive grain embedded in a macroscopic matrix and a cutting particle embedded in a microscopic matrix within an abrasive grain.

[0017] In this way, during electrolytic dressing, abrasive grains that would partially protrude from the surface of the grinding body in a conventionally designed grinding wheel can be partially removed by separating the individual cutting particles, improving the overall surface, and thus the surface quality when the workpiece is subsequently machined with the grinding wheel.

[0018] In conventionally designed grinding wheels that are dressed by electroerosion dressing, the abrasive grains are mainly or exclusively entirely detached from the abrasive dressing. This can lead to undesirable depressions on the surface of the abrasive dressing. However, this can also lead to individual grains protruding far beyond the desired target contour of the surface of the abrasive dressing. This is the case, for example, when electroerosion dressing has already removed some of the binder of the macroscopic matrix around the individual grains, but the grains themselves are not yet exposed enough to be separated from the abrasive dressing. Such (significantly) protruding grains can also cause streaks, scratches, etc., when the workpiece is subsequently machined with the grinding wheel, adversely affecting the surface quality. In this case, improvements can be achieved with the grinding wheel according to the present disclosure.

[0019] Therefore, within the scope of the present disclosure, it is proposed to design the abrasive coating of the grinding wheel such that dressing results in material removal in both the macroscopic matrix (binder for the abrasive grains) and the microscopic matrix (binder for the cutting particles within the abrasive grains).

[0020] Within the scope of this disclosure, a matrix refers to a material (binder) in which the abrasive is embedded. In a macroscopic matrix, the abrasive grains are embedded in the binder. Each abrasive grain has a microscopic matrix in which the cutting particles are embedded in the binder to form the abrasive grain. Thus, an abrasive grain comprises a multiplicity of cutting particles embedded in a microscopic matrix.

[0021] The grinding wheel has a central hole for connecting it to a grinding spindle. The grinding spindle allows the grinding wheel to rotate about its axis of rotation, which usually coincides with the longitudinal axis of the grinding spindle. At least the microscopic and macroscopic matrices are designed to be electrically conductive for the purposes of electrolytic dressing. The grinding wheel includes (electrical) contacts so that the desired pulses can be generated between the grinding wheel and the dressing wire.

[0022] According to an embodiment, the macroscopic matrix comprises an electrically conductive binder, in particular a metal bond or an electrically conductive hybrid bond, in which the abrasive grains are embedded. In other words, the grinding wheel is, for example, a grinding wheel comprising metal bonded abrasive grains. The matrix can be, for example, a sintered metal bond. So-called hybrid bonds are also conceivable, which are nevertheless electrically conductive. Hybrid bonds include, for example, synthetic resin metal bonds, ceramic metal bonds and / or carbide metal bonds.

[0023] According to another embodiment, the microscopic matrix within the abrasive grain comprises a plurality of cutting particles connected to one another by a conductive binder, such that there is a substructure within the abrasive grain that also comprises a conductive microscopic matrix, thereby allowing removal to occur within the grain as well.

[0024] According to another embodiment, the conductive binder of the microscopic matrix comprises a metal, a semi-metal or a transition metal. According to another embodiment, the conductive binder of the microscopic matrix comprises boron or cobalt. Boron is a so-called semi-metal. Cobalt is a so-called transition metal. The corresponding binder of the microscopic matrix can be designed to have sufficient conductivity for the purpose of galvanic dressing. According to another embodiment, the conductive binder of the microscopic matrix comprises bronze as a binder or as a component of the binder.

[0025] According to another embodiment, the abrasive grains are designed as polycrystalline grains. In other words, the abrasive grains consist of many or several small cutting particles. Polycrystalline grains can also be called microcrystalline grains. The cutting particles are embedded in an electrically conductive microscopic matrix, which allows the individual or several cutting particles to be separated when the material of the microscopic matrix is ​​removed by electroerosive dressing.

[0026] According to another embodiment, the abrasive grains are designed as polycrystalline diamond grains, natural diamond and / or polycrystalline cubic boron nitride grains. Polycrystalline diamond grains (PKD; Polykristallines Diamantkorn) or polycrystalline cubic boron nitride grains (PCBN) are suitable abrasives. Corresponding cutting particles can be embedded in a microscopic matrix to form the abrasive grains, which are also embedded in a macroscopic matrix.

[0027] According to another embodiment, the abrasive grains in the macroscopic matrix have a first grain size and the cutting particles within the abrasive grains have a second grain size, the first grain size being greater than the second grain size. According to another embodiment, the first grain size is at least three times the second grain size.

[0028] The term "grain size" is well known to those skilled in the art of abrasives. For example, the grain size designation of the Federation of European Producers of Abrasives (FEPA) is used, and the grain size of the abrasive body is called FEPA F. The term "grain size" refers to the largest grain of a given grain size, for example in micrometers (microns). In other words, grains of a certain grain size can be up to the above-mentioned grain size. In addition, there are grain size designations that refer to a certain density of sieve meshes through which the grains to be processed can fall. Such designations refer, for example, to the number of sieve meshes per 1.0 inch (25.4 mm) length. Tables are known to those skilled in the art that allow the conversion of the size designations of abrasive grains. A range can also be specified for the grain size, i.e. a maximum size and a minimum size. In that case, the grains of the grain size are located within a size range.

[0029] According to another embodiment, the first grain size has a grain size of at least 20 micrometers (microns, μm), preferably at least 35 micrometers (microns, μm), more preferably at least 50 micrometers (microns, μm). This refers to the maximum grain size of the grinding wheel, respectively. Since the grain size designation refers to the maximum grain size, when the grain size is at least 20 μm, for example, the abrasive grains are in the size range of 10-20 μm. Thus, when the grain size is at least 35 μm, for example, the abrasive grains are in the size range of 25-35 μm. Thus, when the grain size is at least 50 μm, for example, the abrasive grains are in the range of 40-50 μm. The first grain size can also be called macro grain size.

[0030] According to another embodiment, the second grain size has a grain size of up to 10 micrometers (microns, μm), preferably a grain size of up to 5 micrometers (microns, μm), more preferably a grain size of up to 3 micrometers (microns, μm). In the case of a grain size of up to 10 μm, for example, the cutting particles are present in a size range of 6 to 10 μm. In the case of a grain size of up to 5 μm, for example, the cutting particles are present in a size range of 1 to 5 μm. In the case of a grain size of up to 3 μm, for example, the cutting particles are present in a size range of 0.5 to 3 μm. The second grain size, i.e. the grain size of the cutting particles embedded in the second matrix, can also be called micrograins.

[0031] According to another embodiment, the volume fraction of the abrasive grains in the macroscopic matrix is ​​at least 30% by volume, preferably at least 50% by volume, thereby achieving good suitability for dressing and high grinding performance.

[0032] According to another embodiment, the volume fraction of cutting particles in the microscopic matrix is ​​at least 50% by volume, preferably at least 70% by volume, thereby achieving good suitability for dressing and high grinding performance.

[0033] According to another aspect, the present disclosure relates to a grinding machine, in particular a cylindrical grinding machine, comprising a work spindle rotatable about a longitudinal axis for accommodating a workpiece and a grinding spindle rotatable about a rotation axis, the tool spindle being fitted with a grinding wheel according to at least one of the embodiments described herein that is suitable for electrolytic dressing.

[0034] According to another aspect, the present disclosure relates to the use of a grinding wheel suitable for electrolytic dressing according to at least one of the embodiments described herein for grinding with a grinding machine. The grinding may be exemplarily external / external cylindrical grinding, internal / internal cylindrical grinding, and / or non-cylindrical grinding. By way of example, the grinding wheel can be used for grinding hard metal materials, cemented carbide, ceramic materials, titanium materials, etc., thereby allowing processing of potentially problematic materials from the standpoint of the grinding process with high removal rates, high dimensional accuracy and high surface quality.

[0035] According to an embodiment, the grinding machine further comprises an electroerosion dressing device for dressing the grinding wheel, which is especially designed as a wire electroerosion dressing device. In this way, the grinding machine is upgraded with a dressing capability. If the dressing device is integrated in the grinding machine, the motion axis of the grinding machine can be configured to generate a relative movement between the grinding wheel and the dressing wire (passing by it) in order to create the desired profile on the surface of the grinding coating.

[0036] Of course, the electroerosion dressing device can also be integrated into the grinding machine in other ways. This includes, for example, a design in which a separate kinematics for the electroerosion dressing device is provided, for example a separate cross slide, independent of the mechanical kinematics of the grinding machine. According to another embodiment, the electroerosion dressing device is designed as a separate device that can be coupled to the grinding machine or its grinding wheel as required. In some cases, the grinding wheel is separated from the grinding machine and dressed with the dressing device.

[0037] According to another aspect, the present disclosure relates to the use of an electroerosion dressing device, in particular designed as a wire electroerosion dressing device, for dressing a grinding wheel according to at least one of the embodiments described herein. The electroerosion dressing device can be integrated into the grinding machine or can be designed as a stand-alone device independent of the grinding machine.

[0038] According to another aspect, the disclosure relates to the use of a grinding wheel suitable for electroerosion dressing according to at least one of the embodiments described herein for electroerosion dressing in a grinding machine in which an electroerosion dressing device is integrated. In this way, the grinding of the workpiece and the highly accurate dressing of the contour / surface of the abrasive coating of the grinding wheel can be performed in one clamping. The dressing advantageously results in material removal in the macroscopic matrix and in material removal in the microscopic matrix.

[0039] According to another aspect, the present disclosure relates to a method of dressing a grinding wheel by wire electroerosion, comprising the steps of: providing a grinding wheel according to at least one of the embodiments described herein; providing a wire electroerosion dressing apparatus including a dressing wire and a wire guide; providing a dielectric between the grinding wheel and the dressing wire; moving the dressing wire from a wire supply along the grinding wheel; rotating the grinding wheel; generating a voltage pulse between the grinding wheel and the dressing wire for the purpose of removing material from the grinding wheel; and generating a relative motion between the grinding wheel and the dressing wire to create a desired profile of the grinding wheel by electroerosion removal, the electroerosion removal comprising separating a portion of individual abrasive cutting particles from the grinding wheel.

[0040] Within the scope of this method, i.e. by advantageous design of the grinding wheel with macroscopic and microscopic matrices, it is possible to remove material of the microscopic matrix within the abrasive grain embedded in the macroscopic matrix in order to separate individual cutting particles from the abrasive grain, i.e., in other words, not only the entire abrasive grain can be separated from the abrasive coating, but also a portion of the inner region of the abrasive grain can be removed precisely, i.e., the cutting particles can be separated, possibly indirectly, by electrolytic removal. Mainly, the binder of the microscopic matrix is ​​removed directly, which allows the cutting particles to be taken out of the microscopic matrix.

[0041] During dressing, the dressing wire can, for example, be unwound from a spool and guided so that it passes precisely over the surface of the abrasive coating of the grinding wheel during the movement. Furthermore, the grinding wheel is rotated. Then, by means of a suitable movement drive, an (additional) relative movement is generated between the grinding wheel and the dressing wire, so that the current "effective area" of galvanic corrosion removal moves over the contour of the surface of the abrasive coating. In this way, the desired grinding wheel contour can be created, which may also include profiling. Furthermore, in this way, the grinding wheel can be sharpened to generate the desired grain exposure. The moving dressing wire passes over the contour of the grinding wheel.

[0042] It goes without saying that the features mentioned above, and those further described below, can be used not only in the respective combinations described, but also in other combinations or alone, without departing from the scope of the present disclosure.

[0043] Further features and advantages of the invention will become apparent from the following description and explanation of several embodiments with reference to the drawings. [Brief description of the drawings]

[0044] [Figure 1] FIG. 1 is a schematic diagram showing one embodiment of a grinding machine equipped with a dressing device. [Diagram 2] FIG. 2 is a simplified schematic diagram of a dressing device showing the process of electrolytic dressing by wire electrolytic corrosion. [Diagram 3] FIG. 2 is a side view showing a grinding wheel suitable for electrolytic dressing. [Figure 4] 4 is an enlarged partial cross-sectional view of the grinding wheel according to FIG. 3, showing an abrasive coating including a macroscopic matrix. [Diagram 5] 5 is a schematic diagram based on FIG. 4 of an enlarged abrasive grain showing the respective microscopic matrix within the abrasive grain. [Figure 6] 6 is an enlarged partial cross-sectional view based on FIGS. 3 to 5 of a grinding wheel in which cutting particles in a microscopic matrix at the surface of an abrasive coating are dressed by material removal. FIG. [Figure 7] FIG. 7 is an enlarged partial cross-sectional view showing a form of a grinding wheel different from those in FIGS. 3 to 6, in which only a macroscopic matrix and abrasive grains embedded therein are shown. [Figure 8] FIG. 1 is a simplified schematic flow block diagram illustrating an embodiment of a method for dressing a grinding wheel by wire erosion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] Figure 1 shows in a schematic diagram an embodiment of a grinding machine, generally designated 10. Needless to say, the grinding machine can be of a different design than that shown in Figure 1. The illustration of the grinding machine 10 in Figure 1 is of an exemplary nature and should therefore not be understood as limiting. The grinding machine 10 is here designed as a cylindrical grinding machine.

[0046] In FIG. 1, a Cartesian coordinate system X, Y, Z is shown, only the Y and Z axes being explicitly shown. The X axis is oriented perpendicular to the drawing plane of FIG. 1. The Z axis is parallel to the longitudinal axis of the workpiece or of a possibly present workpiece spindle. The Y axis is oriented vertically in FIG. 1 and denotes a height extension perpendicular to the Z axis. The X axis is oriented horizontally (perpendicular to the drawing plane) in FIG. 1 and denotes a depth extension (infeed direction). Rotation about the X axis is assigned to the rotation A axis. Rotation about the Y axis is assigned to the rotation B axis. Rotation about the Z axis is assigned to the rotation C axis. In the following, the coordinate system X, Y, Z is used in particular to illustrate the embodiments and features and is not to be understood as limiting. The skilled person will have no problem making any necessary modifications, if necessary.

[0047] The grinding machine 10 comprises a base 12, which may also be referred to as a frame. The base 12 carries a grinding spindle unit 18 with a headstock 20 including a grinding spindle 22. A grinding wheel 24 is accommodated in the grinding spindle 22. The grinding wheel 24 can be driven in rotation by the grinding spindle 22. In FIG. 1 a hood 26 for the grinding wheel 24, which may also be referred to as a protective hood, is further shown. A workpiece can be machined by the grinding wheel 24 in the working space 16 of the machine tool 10. The machine tool 10 typically comprises a housing enclosing the working space 16 and possibly other components, which is not shown in FIG. 1.

[0048] The workpiece 34 can be machined by the grinding wheel 24. In an embodiment, the grinding spindle unit 18 including the grinding wheel 24 can be moved relative to the workpiece 34 in the plane formed by the axes X and Z. This can be done, for example, via a cross slide, a T slide or in a similar manner. In this way, infeed movements, feed movements, drilling movements, etc. are possible. In an embodiment, the grinding spindle unit 18 including the grinding wheel 24 can additionally be swiveled about the Y axis. This function is called the B axis. In this way, the grinding wheel 24 can be applied obliquely to the workpiece 34, if necessary. These axis configurations and the associated degrees of freedom of movement are used only to illustrate possible embodiments and should not be understood as limiting. In another embodiment, an inclination is provided between the so-called A axis, i.e. the axis of rotation of the grinding wheel 24 and the workpiece 34 or its longitudinal axis Z. Such an inclination makes it possible, for example, to machine pitches, for example on threads and similar parts.

[0049] The grinding machine 10 further comprises a work spindle unit 40. The work spindle unit 40 comprises a headstock 42 which accommodates a work spindle 44. The work spindle 44 is rotatably driveable about a longitudinal axis 46. The rotational movement of the work spindle 44 can on the one hand comprise rotations at a certain number of revolutions. Furthermore, the work spindle 44 can also be precisely positioned in a certain rotational orientation about the longitudinal axis 46 (C-axis).

[0050] The workpiece spindle 44 carries a workpiece holder 50. In the embodiment according to FIG. 1, the workpiece holder 50 comprises a chuck 54. The chuck 54 exemplarily has clamping jaws or the like for gripping and holding the workpiece 34. In the embodiment, the workpiece 34 is held in the workpiece holder 50 such that its axis of rotation coincides with the longitudinal axis 46. The chuck 54 is exemplarily designed as a compensation chuck or a centering chuck. In principle, other designs of the workpiece holder 50 are also conceivable, for example as a driven tip or as a fixed tip with a separate driver.

[0051] In the embodiment shown in FIG. 1, a tailstock 60 or another workpiece holder 62, which can also be a component of a counter spindle, is arranged opposite the workpiece spindle 44 containing the workpiece holder 50. The tailstock is mainly used for centering, support and bearing. The counter spindle can be equipped with its own drive. Like the workpiece holder 50, the workpiece holder 62 can also be designed as a tip, chuck or the like. The workpiece holder 50 and the workpiece holder 62 face each other and hold the workpiece 34, clamping it between them. Depending on the specific application and processing purpose, a fixed or rotating tip for the accommodation of the workpiece 34 is basically conceivable. The fixed tip does not rotate when the workpiece 34 rotates. The rotating tip moves together with the workpiece 34.

[0052] Of course, the opposing work holder 62 may be omitted, especially if the workpiece 34 is short (having a small length-to-diameter ratio). The illustration in FIG. 1 is used for illustrative purposes only and should not be understood as limiting.

[0053] In the embodiment, a Z-guide 66 formed on the base 12 is further shown. The base 12 carries a Z-slide 68 for the tailstock 60. The Z-slide 68 is movable in the Z direction on the Z-guide 66. In this way, the distance between the workpiece holder 50 and the workpiece holder 62 can be changed. In the embodiment, the grinding spindle unit 18 is also arranged to be movable in the Z axis via a Z-slide 70. In the illustration according to FIG. 1, the Z-slide 70 is also arranged on the Z-guide 66. Alternatively, a parallel Z-guide spaced apart from the Z-guide 66 can also be arranged on the base 12.

[0054] The Z-slide 70 is connected to an X-slide 72 in the embodiment. In the embodiment according to FIG. 1, the X-slide 72 is relatively movable in a direction perpendicular to the Z-slide 70 with respect to the drawing plane. The X-slide 72 and the Z-slide 70 together form a cross-slide. Besides the cross-slide type, a design using a so-called T-bed is also conceivable, by way of example. In the case of a T-bed, the Z-axis is the axis of the workpiece. That is to say, in a T-bed, the workpiece 34, and not the grinding wheel 24, is moved along the Z-axis during the Z-motion. This should not be understood as limiting. Other machine kinematics are also conceivable.

[0055] In Fig. 1, furthermore, a so-called B-axis is indicated with the reference number 74. The B-axis enables a pivoting movement of the headstock 18, and thus the grinding wheel 24, about the Y-axis. In this way, the grinding wheel 24 can be oriented obliquely relative to the workpiece 34. The embodiment shown in Fig. 1 enables the necessary infeed, drilling and feed movements of the grinding wheel 24 relative to the workpiece 34 clamped between the workpiece holders 50, 62.

[0056] Furthermore, a control unit for controlling the grinding machine 10 is indicated at 80. In particular, the control unit 80 is a unit for NC-based or CNC-based control of the grinding machine 10. Next to it, an operator interface is exemplarily provided, indicated at 82. The operator interface 82 comprises input and output elements. It goes without saying that the grinding machine 10 can also be controlled via an external control unit. Furthermore, embodiments with distributed control are known, in which certain control tasks of the units integrated in the grinding machine 10 and other control tasks are carried out by an external unit.

[0057] In Fig. 1, a dressing device 100 integrated into a machine tool 10 is shown in dashed lines. The dressing device 100 is in particular an apparatus for dressing by wire electroerosion. If the dressing device 100 is structurally integrated into the machine tool 10, the degrees of freedom of movement (axis of movement) of the machine tool 10 can be used to generate the desired relative movement between the dressing device 100 and the grinding wheel 24 during dressing. The grinding wheel 24 can be dressed in the same operation in which the workpiece 34 is machined.

[0058] FIG. 2 shows the function of the dressing device 100 in a schematic simplified view. In FIG. 2, only the periphery of the grinding wheel 24 is shown in cross section to show the dressing by electrolytic removal of the surface 124 of the grinding wheel 24. The dressing device 100 uses a dressing wire 102. The dressing wire 102 is used as an electrode. The dressing wire 102 is provided in a wire source 104, for example a wire spool. The arrow indicated at 108 shows the movement of the dressing wire 102 away from the wire source 104 along the grinding wheel 24. The dressing wire 102 is guided along a wire guide 110, which possibly has a recess adjacent to the grinding wheel 24, in which the dressing wire 102 can move freely along the grinding wheel 24. The movement of the dressing wire 102 along the grinding wheel 24 is performed while maintaining a small clearance. That is, typically there is no direct contact between the grinding wheel 24 and the dressing wire 102 .

[0059] In FIG. 2, a nozzle for supplying a dielectric cleaning medium is shown diagrammatically at 112. Dressing by wire erosion requires, for example, the provision of a dielectric 114 by supplying a dielectric cleaning medium via the nozzle 112. During dressing, the grinding wheel 24 is driven in rotation, see the arrow at 118 in FIG. 2. Via a power supply 120, a pulse (current pulse) is generated between the grinding wheel 24 and the dressing wire 102. A spark discharge occurs between the grinding wheel 24 and the dressing wire 102, which removes material from the surface 124 of the grinding wheel 24. This usually corresponds to the conductive binder in which the abrasive grains are embedded; in other words, the abrasive grains are usually not removed directly. The abrasive grains can be separated from the surface 124 of the grinding wheel 24 when the surrounding material is removed.

[0060] In the embodiment according to FIG. 2, the used dressing wire 102 is fed to a wire waste disposal unit 126 which includes, for example, a wire cutter 128 for chopping the used dressing wire 102 .

[0061] 3 shows in side view a grinding wheel designated 24. The grinding wheel 24 is used, for example, for cylindrical grinding, in particular for external cylindrical grinding of a workpiece, although this should not be understood as limiting.

[0062] The grinding wheel 24 has a central bore 134 for receiving the grinding spindle 22. The grinding wheel 24 can be driven in rotation about a rotation axis 136. The grinding wheel comprises a base body 140 carrying an abrasive coating 142. The actual machining is performed by this abrasive coating 142. The abrasive coating 142 is dressed by a dressing device 100 (see FIG. 2). This can be used on the one hand to create a desired contour on the surface 124 of the grinding wheel 24. In other words, the grinding wheel 24 can be profiled. However, dressing can also be required if the grinding wheel 24 has to be sharpened again after a certain service life.

[0063] The grinding wheel 24 further includes a contact 148 capable of closing an electrical circuit by sliding contact, for example to generate a spark discharge. The contact 148 is conductively connected to the abrasive coating 142 so that material on the surface 124 of the abrasive coating 142 can be removed by wire erosion dressing.

[0064] FIG. 4 shows a partial enlarged view of the grinding wheel 24 according to FIG. 3. The abrasive coating 142 on the substrate 140 is shown in cross section. The abrasive coating 142 comprises a macroscopic matrix 154 in which a number of abrasive grains 156 are embedded. The macroscopic matrix 154 comprises a conductive binder 158 that fills the gaps between the abrasive grains 156. In the case of electroerosion dressing with the dressing wire 102 (FIG. 2), material of the binder 158 is removed, which allows the (outerly located) abrasive grains 156 to gradually separate from the abrasive coating 142. In this way, the grinding wheel 24 can be resharpened or profiled. Furthermore, a desired profiling and / or a desired shape of the grinding wheel 24 can be produced.

[0065] The schematic diagram of Fig. 5 shows an individual abrasive grain 156 of the abrasive coating 142 of the grinding wheel 24 according to Fig. 3, firstly in a view roughly corresponding to Fig. 4 and additionally in an enlarged cross-sectional view showing the internal structure of the abrasive grain 156, respectively. In other words, in Fig. 5 the abrasive grain 156 is shown at two different scales (and uncut and cut). The magnification is approximately 3:1.

[0066] 5 shows that the abrasive grains 156 shown in FIG. 4 embedded in the macroscopic matrix 154 of the abrasive coating 142 also include a matrix 164, referred to as the microscopic matrix. In other words, each abrasive grain 156 includes a plurality or number of cutting particles 166. These cutting particles 166 ultimately result in material removal at the workpiece 34 during grinding by the grinding wheel 24 (see FIG. 1).

[0067] The cutting particles 166 are embedded in a binder 168 of the microscopic matrix 164. The binder 168 fills the interstices between the individual cutting particles 166 within the abrasive grain 156. The abrasive grain 156 may be referred to as, for example, a polycrystalline abrasive grain 156, depending on its internal structure.

[0068] The abrasive grains 156 have a first grain size, which may also be referred to as a macroscopic grain size. The cutting particles 166 within the abrasive grains 165 have a second grain size, which may also be referred to as a microscopic grain size. The grain size of the abrasive grains 156 is many or several times larger than the grain size of the cutting particles 166. In other words, multiple or numerous cutting particles 166 are required to form the abrasive grains 156.

[0069] The binder 168 of the microscopic matrix 164 is electrically conductive. In this way, material can be removed even within the abrasive grains 156 during electroerosive dressing. In that case, when the binder 168 is removed around each of the cutting particles 166 in the microscopic matrix 164, each of the cutting particles 166 in the matrix 164 can be separated.

[0070] The abrasive grains 156 occupy a certain volume fraction in the macroscopic matrix 154. The remaining volume is typically filled by a (macroscopic) binder 158. The cutting particles 166 occupy a certain volume fraction in the microscopic matrix 164. The remaining volume is typically filled by a (microscopic) binder 168.

[0071] FIG. 6 shows a close-up of a portion of the grinding wheel 24 with individual abrasive grains 156 embedded in a macroscopic matrix 154 and arranged on the surface 124 of the abrasive coating 142. FIG. 5 shows the grains 156 in their original state. FIG. 6 then shows the state in which each of the cutting particles 166 has been separated. This may possibly result in (microscopic) voids 172 in the microscopic matrix 164. Overall, the abrasive grains 156 fit very well to the surface 124 of the grinding wheel 24 obtained by dressing. In particular, a state in which the individual abrasive grains protrude significantly above the (target) surface 124 of the grinding wheel 24 is avoided. The design of the grinding wheel 24 shown in FIGS. 3 to 6 allows a high surface quality to be achieved during processing.

[0072] In contrast, FIG. 7 shows, as a comparative example, a partial view of a grinding wheel designated 224 in which there is a macroscopic matrix 354 in which abrasive grains 356 and conductive binder 358 are embedded, but in which the individual abrasive grains 356 do not have a microscopic matrix containing a conductive binder.

[0073] Thus, the abrasive grains 356 can only remain individually and entirely in the grinding wheel 224 during electroerosion dressing or can separate to form voids 360. However, this leads to a much larger deviation from the desired target geometry compared to the design of the grinding wheel 24 according to Figure 6, which in turn leads to a reduced surface quality when a workpiece is machined with the grinding wheel 224.

[0074] 8 shows, by means of a schematic block diagram, an embodiment of the method for dressing a grinding wheel by wire erosion. The method starts with step S10.

[0075] Step S12 involves providing an abrasive coating having a macroscopic matrix with a conductive binder and abrasive grains embedded therein, and a grinding wheel designed according to the present disclosure having, at the level of the abrasive grains, a microscopic matrix with a conductive binder and (micro)cutting particles embedded therein. Such a grinding wheel can illustratively be mounted on the grinding spindle of a grinding machine.

[0076] Step S14 concerns providing a dressing device designed for electroerosion dressing, for example by wire electroerosion. In this embodiment, the dressing device is structurally integrated into the grinding machine. In an alternative embodiment, the dressing device may not be directly integrated into the grinding machine but may be designed as a stand-alone device. The dressing device exemplarily has a wire supply for the dressing wire and a wire guide along which the dressing wire can be moved. During this guided movement, the dressing wire is brought close to the grinding wheel, where material is removed by spark discharge.

[0077] Step S16 involves providing a dielectric, such as a dielectric cleaning medium, that is applied via a nozzle, the dielectric being necessary for the desired material removal.

[0078] Step S18 involves moving the dressing wire from a wire supply along the grinding wheel in close proximity to the grinding wheel such that only a small gap remains between the dressing wire and the grinding wheel. During this movement, the dressing wire is typically guided by a wire guide. Step S20 involves driving the grinding wheel in rotation.

[0079] In step S22, an electrical pulse is precisely generated between the dressing wire (electrode) and the grinding wheel to remove the material therein by spark discharge.

[0080] Step S24 shows the generation of a relative motion, which is usually superimposed on step S22. In this way, an infeed and feed motion can be generated between the dressing wire and the grinding wheel, which creates the desired profile by electrolytic removal when dressing the grinding wheel.

[0081] The method ends in step S26. Overall, the method allows for high-precision dressing, since material is removed by wire erosion not only at the level of the macroscopic matrix, but also at the level of the microscopic matrix. This reduces the possibility of individual abrasive grains protruding too far above the surface of the grinding wheel. Overall, this improves the surface quality when the grinding wheel is subsequently used to machine the workpiece.

[0082] It goes without saying that embodiments of the grinding wheel, the dressing device and the grinding machine described within the scope of the present disclosure can be considered in further embodiments of the method according to the present disclosure. This is also true for the embodiments of the dressing method described within the scope of the present disclosure, which can also be considered in the embodiments of the grinding wheel, the dressing device and the grinding machine. The fact that specific embodiments have been described in the context of a device or a method does not preclude their application in the respective other categories. Such combinations are expressly encompassed by the present disclosure.

Claims

1. A grinding wheel (24), in particular a grinding wheel (24) suitable for electrolytic dressing, comprising: the grinding wheel (24) having a central axis (136) about which it is rotatable, and an abrasive coating (142) having a macroscopic matrix (154) in which abrasive grains (156) are embedded; the macroscopic matrix (154) is electrically conductive; The abrasive (156) comprises a conductive microscopic matrix (164) having cutting particles (166) embedded therein.

2. 2. Grinding wheel according to claim 1, wherein the macroscopic matrix (154) comprises a conductive binder (158), in particular a metallic bond or a conductive hybrid bond, in which the abrasive grains (156) are embedded.

3. 2. The grinding wheel of claim 1, wherein the microscopic matrix (164) within the abrasive grain (156) comprises a plurality of cutting particles (166) connected to one another by a conductive binder (168).

4. The grinding wheel of claim 3, wherein the conductive binder (168) of the microscopic matrix (164) comprises a metal, a metalloid, or a transition metal.

5. 5. The grinding wheel of claim 3 or claim 4, wherein the conductive binder (168) of the microscopic matrix (164) comprises boron or cobalt.

6. The grinding wheel of claim 1 , wherein the abrasive grains (156) are formed as polycrystalline grains.

7. The grinding wheel of claim 6, wherein the abrasive grains (156) are formed as polycrystalline diamond grains and / or polycrystalline cubic boron nitride grains.

8. 2. The grinding wheel of claim 1, wherein the abrasive grains (156) in the macroscopic matrix (154) have a first grain size and the cutting particles (166) in the abrasive grains (156) have a second grain size, the first grain size being larger than the second grain size, in particular the first grain size being at least three times the second grain size.

9. 9. The grinding wheel of claim 8, wherein the first grain size has a grain size of at least 20 micrometers, preferably at least 35 micrometers, and more preferably at least 50 micrometers.

10. 10. Grinding wheel according to claim 8 or claim 9, wherein the second grain size has a grain size of up to 10 micrometers, preferably a grain size of up to 5 micrometers, more preferably a grain size of up to 3 micrometers.

11. 2. Grinding wheel according to claim 1, wherein the volume fraction of said abrasive grains (156) in said macroscopic matrix (154) is at least 30% by volume, preferably at least 50% by volume.

12. Grinding wheel according to claim 1 or 11, wherein the volume fraction of the cutting particles (166) in the microscopic matrix (164) is at least 50% by volume, preferably at least 70% by volume.

13. 1. A grinding machine (10), in particular a cylindrical grinding machine, having a workpiece spindle (44) rotatable about a longitudinal axis (46) for receiving a workpiece (34) and a grinding spindle (22) rotatable about an axis of rotation (136), on which a grinding wheel (24) according to claim 1 suitable for electroerosion dressing is mounted.

14. 14. Grinding machine according to claim 13, further comprising an electroerosion dressing device (100) for dressing the grinding wheel (24), in particular designed as a wire electroerosion dressing device.

15. 2. Use of an electroerosion dressing device (100), in particular designed as a wire electroerosion dressing device, for dressing a grinding wheel (24) according to claim 1.

16. A method for dressing a grinding wheel (24) by wire electroerosion, comprising the steps of: Providing a grinding wheel (24) according to claim 1; Providing a wire electroerosion dressing device (100) having a dressing wire (102) and a wire guide (110); providing a dielectric between the grinding wheel (24) and the dressing wire; moving the dressing wire (102) from a wire supply (104) along the grinding wheel (24); Rotating the grinding wheel (24); generating a voltage pulse between the grinding wheel (24) and the dressing wire (102) for the purpose of removing material from the grinding wheel (24); generating relative motion between the grinding wheel (24) and the dressing wire (102) to create a desired profile of the grinding wheel (24) by electrolytic removal; The method, wherein the electrolytic removal comprises separating a portion of the cutting particles (166) of individual abrasive grains (156) from the grinding wheel (24).

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