Lapping disk for a lapping machine, lapping machine and method for lapping a workpiece using a lapping machine

Abstract

The invention relates to a lapping disk for a lapping machine in which, in order to machine workpieces by material removal, a mixture of a liquid lapping agent and loose lapping particles is fed between the lapping disk and a workpiece to be machined into a working gap of the lapping machine and the lapping disk is rotationally driven by means of a rotary drive of the lapping machine, wherein: the lapping disk has a plurality of concentrically arranged annular grooves on its working surface which faces the workpiece during operation; adjacent annular grooves are connected to one another by connecting grooves; the connecting grooves are arranged in a plurality of groups which are spaced apart in the circumferential direction of the lapping disk; the connecting grooves of a group are arranged one behind the other along a direction of extension from the center of the lapping disk to the circumferential edge of the lapping disk; between connecting grooves of a group which are adjacent along the direction of extension, in each case at least two adjacent annular grooves are unconnected; and a connection between said annular grooves is provided by connecting grooves of at least one other group. The invention also relates to a lapping machine and a method for lapping a workpiece.

Description

[0001] Lapping disc for a lapping machine, lapping machine and method for lapping a workpiece with a lapping machine

[0002] The invention relates to a lapping disc for a lapping machine in which material-removing machining of workpieces takes place by feeding a mixture of a liquid lapping agent and loose lapping particles between the lapping disc and a workpiece to be machined into a working gap of the lapping machine, and the lapping disc is driven in rotation by a rotary drive of the lapping machine. The invention also relates to a lapping machine and a method for lapping a workpiece using a lapping machine.

[0003] Lapping is an abrasive machining process in which, in contrast to grinding, loose lapping particles, in particular abrasive lapping grit, are mixed with a liquid lapping compound and placed in a working gap to machine a workpiece. Unlike grinding compounds, the lapping wheels themselves do not have an abrasive incorporated into their working surface. In double-sided lapping machines, the workpieces to be machined are placed in an often annular working gap defined by the working surfaces of opposing lapping wheels. However, single-sided lapping machines are also known in which the working gap is formed between a lapping wheel and a counter-bearing element. The liquid lapping compound, together with the loose lapping particles it contains, is placed in this working gap between the working surfaces and the surfaces of the workpieces to be machined. At least one of the lapping wheels is driven in rotation for lapping.

[0004] To ensure even distribution and removal of the liquid lapping compound and its lapping particles, grooves are formed into the working surfaces of the lapping discs. Common grooves include spiral grooves extending from the center of the working surface to the outer edge of the working surface, or grooves formed in a waffle pattern, which define, for example, square working surface sections.

[0005] There is a growing desire to surface finish workpieces made of very hard materials that are difficult to machine, for example, those with a Mohs hardness of more than 8, such as silicon carbide or diamond wafers. Machining diamond wafers is practically only possible with lapping machines. Compared to silicon wafers, for example, the machining time per workpiece load is longer, at six to ten hours. At the same time, the lapping wheels are subject to considerable wear when machining such hard workpieces. The lapping wheels must be dressed practically after every machining process. This significantly increases the effort required.

[0006] Based on the prior art explained above, the object of the invention is to provide a lapping disc, a lapping machine and a method of the type mentioned at the outset, with which the effort required for machining even very hard workpieces can be reduced.

[0007] The invention solves this problem through the independent claims. Advantageous embodiments can be found in the dependent claims, the description, and the figures.

[0008] For a lapping disc of the type mentioned at the outset, the invention achieves the object in that the lapping disc has a plurality of concentrically arranged annular grooves on its working surface facing the workpiece during operation, in that adjacent annular grooves are connected to one another by connecting grooves, wherein the connecting grooves are arranged in a plurality of groups spaced apart in the circumferential direction of the lapping disc, wherein the connecting grooves of a group are each arranged one behind the other along a direction of extension from the center of the lapping disc to the circumferential edge of the lapping disc, wherein between connecting grooves of a group which are adjacent along the direction of extension there is no connection between at least two adjacent annular grooves, wherein a connection between these annular grooves is provided by connecting grooves of at least one other group.

[0009] As explained, lapping wheels, unlike grinding wheels, do not have an abrasive agent, such as abrasive grain, incorporated into their working surfaces. Instead, they work with a loose abrasive that is mixed with a lapping fluid into the working gap. The lapping particles, such as grains, contained in the fluid roll between the working surface of the lapping wheel and the facing surface of the workpiece to be machined when the lapping machine is in operation, thereby removing material. As explained at the beginning, it is known for lapping wheels to distribute the lapping mixture applied via grooves cut into the working surface and to remove it from the working gap once used. Such grooves are also provided on the lapping wheel according to the invention.Unlike the prior art, the lapping disc according to the invention has a plurality of concentrically arranged annular grooves on its working surface. These grooves are therefore not designed in the form of a spiral groove running across the entire working surface, but are introduced into the working surface as individual, initially unconnected annular grooves with increasing radius. In order for the concentric annular grooves to be able to distribute the lapping mixture in the working gap as well as to remove used lapping mixture from the working gap, adjacent annular grooves are connected to one another by connecting grooves. The connecting grooves are arranged in several groups spaced apart in the circumferential direction of the lapping disc, with the connecting grooves of a group each being arranged one behind the other along a direction running from the center of the lapping disc to the circumferential edge of the lapping disc.The connecting grooves of a group can, for example, be arranged one behind the other along a straight line. The connecting grooves do not form a continuous groove from the inner to the outer edge of the work surface along the running direction. Rather, a group comprises a plurality of separate connecting grooves along the running direction from the inner to the outer edge of the work surface, so that there is no connection between at least two adjacent annular grooves between adjacent connecting grooves of a group along the running direction. These annular grooves not connected by a group of connecting grooves are connected to one another by connecting grooves of one or more other groups.In this way, for example, lapping compound picked up by an inner annular groove passes through a connecting groove into the next adjacent annular groove as the lapping disc rotates during operation. It then flows along the predetermined path of this next annular groove, initially to the next connecting groove of a different group, and then to the next outer annular groove. This next connecting groove is spaced apart from the first connecting groove in the direction of rotation. In this way, the lapping compound moves successively from the innermost annular groove to the outermost annular groove and can thus be removed from the working gap.

[0010] The invention is based on the finding that an interruption of the radial connection between the annular grooves offers advantages in terms of machining, as opposed to a radial connecting groove that runs continuous from the inner to the outer edge. This results in better distribution of the lapping agent in the working gap. It also prevents excessive amounts of lapping agent from being removed, as is the case with continuous connecting grooves. The lapping agent is kept in the working gap and thus in the process for longer, as direct flow away is not possible. This time can be varied by changing the number of connecting grooves (per direction of rotation). The more similarly oriented connecting grooves there are, the faster the lapping agent is removed. The overall machining result can be improved. This means that even harder workpieces can be machined better and with less effort.

[0011] The lapping disc according to the invention can have more than five annular grooves, preferably more than ten annular grooves, more preferably more than 15 annular grooves. The number of annular grooves depends on the size of the lapping disc. A sufficient number is advantageous for the distribution and removal of the lapping compound.

[0012] For particularly good removal of the lapping agent with the lapping particles during the rotation of the lapping disc, the direction of travel can run in a radial direction from the center of the lapping disc to the peripheral edge of the lapping disc.

[0013] According to a further embodiment, there can be no connection between exactly two adjacent annular grooves between connecting grooves of a group that are adjacent along the direction of travel. According to a further embodiment, the connecting grooves can each connect exactly two adjacent annular grooves. This achieves a particularly uniform distribution and removal of the lapping agent with the lapping particles in both directions of rotation.

[0014] According to a further embodiment, connecting grooves of at least some groups adjacent in the circumferential direction of the lapping disc can connect different annular grooves to one another. This achieves a particularly even distribution of the lapping agent. According to a further embodiment, connecting grooves of at least some adjacent groups can be oriented in different directions, in particular such that lapping agent can flow through the different connecting grooves when the lapping disc rotates in different directions. This embodiment makes it possible to use a lapping disc in both directions of rotation and to achieve optimal distribution and removal of the lapping mixture in both directions of rotation. It has been found that this improves the machining result and, in particular, can increase the stock removal rate for hard materials such as diamond, silicon carbide, CBN or sapphire.In addition, this method can significantly reduce wear on the lapping wheel compared to the state of the art, where the design of the grooves in the lapping wheel usually dictates a specific direction of rotation. The wheel geometry, which is crucial for the machining result, can also be better maintained with alternating direction of rotation operation than with the state of the art. Dressing of the lapping wheels between machining processes is required less frequently than with the state of the art. Furthermore, changing the direction of rotation can increase process variability. Changing the direction of rotation is even possible within a single workpiece machining process. Alternatively or additionally, it is also possible to change the direction of rotation between different workpiece machining processes.In a simplified embodiment, rotation in both directions would also be possible if all connecting grooves are oriented in the same direction, namely in particular with a longitudinal direction in the radial direction of the lapping disc.

[0015] According to a further embodiment, the connecting grooves of each pair of two adjacent groups can be oriented in the same direction in the circumferential direction of the lapping disc, with the orientation of the connecting grooves changing between adjacent pairs of groups. The groups are thus oriented alternately in pairs. Especially when the connecting grooves of adjacent groups connect different annular grooves, this ensures optimal distribution and removal of the lapping compound in both directions of rotation.

[0016] According to a further embodiment, the connecting grooves can each have an elongated shape with a longitudinal direction, wherein the longitudinal directions of the connecting grooves extend at an angle of between 0° and 90°, preferably between 30° and 60°, to a straight line running in the radial direction from the center of the lapping disc to the peripheral edge of the lapping disc. In particular, the longitudinal directions of differently oriented connecting grooves can be arranged symmetrically with respect to a straight line running in the radial direction from the center of the lapping disc to the peripheral edge of the lapping disc. This embodiment achieves a further improvement in the distribution and removal of the lapping agent with the lapping particles in both directions of rotation.

[0017] As already explained, the connecting grooves of different groups, for example, neighboring groups, can each connect different pairs of annular grooves. This achieves an even better distribution of the lapping compound.

[0018] It is also possible for different groups to have a different number of connecting grooves. For example, between each two groups of connecting grooves extending over the entire radial extent of the lapping disc, a group of connecting grooves can be provided which extends only over an outer section of the radial extent of the lapping disc. In this way, a more uniform density of connecting grooves can be achieved in the radial direction of the lapping disc. According to a further embodiment, the lapping disc can also have several feed openings for feeding a mixture of a liquid lapping agent and loose lapping particles. In a double-sided lapping machine, it is also possible for only one of the lapping discs, for example the upper lapping disc, to have such feed openings. The feed openings can generally be distributed over the work surface in the radial and / or rotational direction.

[0019] The lapping disc can also be ring-shaped or have a ring-shaped working surface. A rotary drive can be mounted centrally to rotate the lapping disc.

[0020] The invention also achieves the object by a lapping machine comprising a lapping disc according to the invention and a counter-bearing element arranged opposite the lapping disc, which form a working gap between them for receiving one or more workpieces to be machined, further comprising a rotary drive for rotating the lapping disc and / or the counter-bearing element, and comprising a feed device for feeding a mixture of a liquid lapping agent and loose lapping particles between the lapping disc and the workpiece to be machined into the working gap. The rotary drive can be designed to rotate the lapping disc and / or the counter-bearing element in opposite directions of rotation. The counter-bearing element can also be a lapping disc. It can therefore be a single-sided or double-sided lapping machine.

[0021] The lapping machine according to the invention can further comprise one or more carrier discs arranged in the working gap, into which workpieces to be machined can be inserted. The carrier discs are driven in rotation during operation, for example, by inner and / or outer pin rings, so that workpieces accommodated therein move along cycloidal paths through the working gap. This achieves particularly uniform surface finishing.

[0022] The invention also achieves the object by a method for lapping a workpiece using a lapping machine according to the invention. The lapping machine according to the invention can be designed accordingly to carry out the method according to the invention. With the method according to the invention, in particular wafers can be machined as workpieces, for example wafers made of a hard material such as diamond, ceramics, silicon carbide, cubic boron nitride (CBN), or sapphire. In the method according to the invention, the lapping disc and / or the counter-bearing element can be driven in opposite directions of rotation during the machining of a workpiece.

[0023] Embodiments of the invention are explained in more detail below with reference to the figures. They show schematically:

[0024] Figure 1 shows a lapping machine according to the invention in a perspective view,

[0025] Figure 2 shows a lapping disc of the lapping machine shown in Fig. 1 in a plan view,

[0026] Figure 3 shows section A from Fig. 2 in an enlarged view,

[0027] Figure 4 shows a lapping disc of the lapping machine shown in Figure 1 according to a further embodiment in a plan view, and Figure 5 shows section B from Figure 4 in an enlarged view.

[0028] Unless otherwise stated, the same reference symbols in the figures refer to the same objects.

[0029] Figure 1 schematically shows a lapping machine 10 according to the invention, in the example shown a double-sided lapping machine 10, with planetary kinematics. The lapping machine 10 has an upper pivot arm 12, which can be pivoted about a vertical axis via a pivoting device 16 mounted on a lower base 14. An upper lapping disk 18 is held on the pivot arm 12 and can be driven in rotation by a drive motor (not shown in detail). On its underside, not shown in Figure 1, the upper lapping disk 18 has an annular working surface 20 (see Figure 2). The lower base 14 has a trough 22 that supports a lower lapping disk 24, which has, on its upper side facing the upper lapping disk 18, a likewise annular working surface 26 corresponding to the working surface 20 of the upper lapping disk 18. The upper lapping disc 18 can be aligned coaxially to the lower lapping disc 24 via the swivel arm 12.In the example shown, the lower lapping disc 24 can also be driven in rotation via a drive motor (not shown), in particular in the opposite direction to the upper lapping disc 18. Of course, it is also possible to design only one of the lapping discs 18, 24 to be driven in rotation.

[0030] In the example shown, several carrier disks 28 are arranged on the working surface 26 of the lower lapping disk 24, each of which has recesses for workpieces 30 to be machined, for example wafers 30, in particular diamond, carbide, or sapphire wafers 30. For the sake of clarity, only one of the carrier disks 28 shows workpieces 30. It is understood that during operation, all of the recesses of the carrier disks 28 can be equipped with workpieces 30 to be machined. The carrier disks 28 each engage with an external toothing in an inner pin ring 32 and an outer pin ring 34. In this way, a rolling device is formed, wherein the carrier disks 28 are also set in rotation when the lower lapping disk 24 rotates.The workpieces 30, which are mounted, for example, floatingly in the recesses of the carrier disks 28, then move along cycloidal paths through the annular working gap formed between the upper lapping disk 18 and the lower lapping disk 24. During operation of the lapping machine 10, a mixture of a liquid lapping agent and loose lapping particles is also introduced into the working gap via a feed device integrated, for example, in the pivoting arm 12. As explained in more detail below, the upper lapping disk 18 and, if applicable, also the lower lapping disk 24 can have corresponding feed openings for this purpose. If the mixture of lapping agent and lapping particles is also fed via the lower lapping disk 24, a corresponding feed device can also be integrated into the base 14.

[0031] The design of the upper lapping disc 18, in particular its working surface 20, will be explained in more detail with reference to Figures 2 and 3. The lower lapping disc 24, including its working surface 26, can be designed identically to the upper lapping disc 18. However, it is also possible, for example, that the supply openings of the upper lapping disc 18 explained below are not provided on the lower lapping disc 24, or vice versa.

[0032] A plurality of concentric annular grooves 36 are formed on the working surface 20 of the upper lapping disk 18. Adjacent annular grooves 36 are each equidistant. Furthermore, adjacent annular grooves 36 are connected to one another by connecting grooves 38, wherein the connecting grooves are arranged in several groups spaced apart in the circumferential direction of the lapping disk. For illustrative purposes, three groups are circled by dashed lines in Figure 3 and designated Gl, G2, G3. The connecting grooves of a group Gl, G2, G3 are each arranged along a direction in the radial direction from the center of the lapping disk 18 to the circumferential edge of the lapping disk 18. In particular, the connecting grooves 38 of a group Gl, G2, G3 are arranged one behind the other along a straight line radially from the center of the lapping disk 18 to the circumferential edge of the lapping disk 18.In the example shown, twelve such groups G1, G2, G3 of connecting grooves 38 are provided over the circumference of the working surface 20 of the lapping disc 18. Adjacent groups G1, G2, G3 are each spaced equally apart in the circumferential direction.

[0033] As can be seen particularly in the enlarged view of Figure 3, the connecting grooves 38 each connect exactly two adjacent annular grooves 36 to one another and there is no connection between exactly two adjacent annular grooves 36 along the direction of each group Gl, G2, G3.

[0034] It can also be seen that the connecting grooves 38 of adjacent groups Gl and G2 or G2 and G3 each connect different pairs of annular grooves 36 to one another. Furthermore, it can be seen that the connecting grooves 38 of groups Gl, G2, G3 adjacent in the circumferential direction of the lapping disk 18 are each alternately oriented in different directions. The connecting grooves 38 of every second group Gl, G2, G3 in the circumferential direction of the lapping disk 18 are oriented the same in the example shown. In the example shown, the connecting grooves 38 each have an elongated shape with a longitudinal direction, wherein the connecting grooves 38 of adjacent groups Gl, G2, G3 are each formed symmetrically with respect to a straight line running in the radial direction from the center of the lapping disk 18 to the circumferential edge of the lapping disk 18.In this way, the connecting grooves 38 of every second group G1, G2, G3 are tilted in the circumferential direction in a first direction relative to the radial direction, and the connecting grooves 38 of the groups G1, G2, G3 arranged between them are tilted in a second direction relative to the radial direction. Finally, it can be seen, particularly in Figure 3, that several feed openings 40 are formed in the working surface 20, distributed radially and circumferentially, for feeding the mixture of the liquid lapping agent and the loose lapping particles.

[0035] Figure 4 shows a further embodiment of an upper lapping disc 118 according to the invention, for example, with a working surface 120. Again, an associated lower lapping disc can be designed identically to the upper lapping disc 118.

[0036] On the working surface 120 of the upper lapping disk 118, a plurality of concentric annular grooves 136 are formed. In the example shown, adjacent annular grooves 136 are each spaced equally. Of course, the spacing between some or all of the adjacent annular grooves could vary in all embodiments. For example, as the radius of the annular grooves increases, the spacing between adjacent annular grooves could decrease. Furthermore, adjacent annular grooves 136 are connected to one another by connecting grooves 138, wherein the connecting grooves are arranged in several groups spaced apart in the circumferential direction of the lapping disk. For illustrative purposes, six groups are circled by dashed lines in Figure 5 and labeled GL, G2', G3', G4', G5', G6'.The connecting grooves of a group GL, G2', G3', G4', G5', G6' are each arranged along a radial direction from the center of the lapping disc 118 to the peripheral edge of the lapping disc 118. In particular, the connecting grooves 138 of a group GL, G2', G3', G4', G5', G6' are arranged one behind the other along a straight line radially from the center of the lapping disc 118 to the peripheral edge of the lapping disc 118.

[0037] As can be seen particularly in the enlarged view of Figure 5, the connecting grooves 138 each connect exactly two adjacent annular grooves 136 to one another. In the example shown, the connecting grooves 138 each have an elongated shape with a longitudinal direction, wherein the connecting grooves 138 of every second group GL, G2', G3', G4', G5', G6' are tilted in the circumferential direction in a first direction to the radial, and the connecting grooves 138 of the groups GL, G2', G3', G4', G5', G6' arranged between them are tilted in a second direction relative to the radial direction. The connecting grooves 138 of adjacent groups GL, G2', G3', G4', G5', G6' are each tilted symmetrically with respect to a straight line running in the radial direction from the center of the lapping disk 118 to the circumferential edge of the lapping disk 118.The groups GL, G2', G3', G4', G5', G6' can be repeated over the circumference of the lapping disk 118, so that, for example, the group shown on the far left in Figure 5 again corresponds to the group G6'. As can be seen particularly in Figure 5, some adjacent groups GL, G2' of connecting grooves 138 connect the same annular grooves 136 with one another, while other groups G3', G4', G5' connect other annular grooves 136 with one another. In the example shown, the groups GL and G2' as well as the groups G3' and G6' as well as the groups G4' and G5' are each of the same design except for the different tilting of the longitudinal directions of the connecting grooves 138.

[0038] The inventive design of the annular grooves 36, 136 and the connecting grooves 38, 138 ensures, on the one hand, optimal distribution of the mixture of the liquid lapping agent and the loose lapping particles and optimal removal of used mixture from the working gap. Furthermore, the lapping disk 18, 118 can be operated in both directions of rotation, whereby the mixture of the liquid lapping agent and the loose lapping particles can flow from one annular groove 36, 136 into the next annular groove 36, 136 via the connecting grooves 38, 138 of a group Gl, G2, G3, GL, G2', G3', G4', G5', G6' or the connecting grooves 38, 138 of an adjacent group Gl, G2, G3, Gl', G2', G3', G4', G5', G6', depending on the direction of rotation. This reduces wear and dressing of the lapping wheels 18, 118, 24 is required less frequently, especially when machining hard workpieces, as explained above.Furthermore, especially with hard materials, changing the direction of rotation can increase the removal rate and enhance process variability. Finally, the wheel geometry is better preserved than with the current technology due to the ability to change the direction of rotation.

[0039] List of reference symbols

[0040] 10 Lapping machine

[0041] 12 swivel arm

[0042] 14 bases

[0043] 16 Swivel device

[0044] 18 Upper lapping disc

[0045] 118 Upper lapping disc

[0046] 20 work surface

[0047] 120 work surface

[0048] 22 tub

[0049] 24 Lower lapping disc

[0050] 26 work surface

[0051] 28 Rotor disc

[0052] 30 workpiece

[0053] 32 inner pin ring

[0054] 34 outer pin ring

[0055] 36 ring grooves

[0056] 136 ring grooves

[0057] 38 connecting grooves

[0058] 138 connecting grooves

[0059] 40 feed openings

[0060] Gl Group

[0061] Gl ' Group

[0062] G2 Group

[0063] G2' group

[0064] G3 Group

[0065] G3 ' Group

[0066] G4' Group

[0067] G5' Group

[0068] G6' Group

Claims

Claims 1. Lapping disc for a lapping machine (10), in which a material-removing machining of workpieces (30) takes place by feeding a mixture of a liquid lapping agent and loose lapping particles between the lapping disc (18, 118, 24) and a workpiece (30) to be machined into a working gap of the lapping machine (10), and the lapping disc (18, 118) is driven in rotation by means of a rotary drive of the lapping machine (10), characterized in that the lapping disc (18, 118, 24) has a plurality of concentrically arranged annular grooves (36, 136) on its working surface (20, 120, 26) facing the workpiece (30) during operation, that adjacent annular grooves (36, 136) are connected to one another by connecting grooves (38, 138), wherein the connecting grooves (38, 138) are arranged in several, in the circumferential direction of the lapping disc (18, 118) spaced groups (Gl, G2, G3, GL, G2', G3', G4', G5', G6') are arranged, wherein the connecting grooves (38, 138) of a group (Gl, G2, G3, GL, G2', G3',G4', G5', G6') are each arranged one behind the other along a direction of extension from the center of the lapping disc (18, 118, 24) to the peripheral edge of the lapping disc (18, 118, 24), wherein between connecting grooves (38, 138) of a group (Gl, G2, G3, GL, G2', G3', G4', G5', G6') adjacent along the direction of extension there is no connection between at least two adjacent annular grooves (36), wherein a connection between these annular grooves (36, 136) is provided by connecting grooves (38, 138) of at least one other group (Gl, G2, G3, GL, G2', G3', G4', G5', G6').

2. Lapping disc according to claim 1, characterized in that the direction of extension runs in the radial direction from the center of the lapping disc (18, 118, 24) to the peripheral edge of the lapping disc (18, 118, 24).

3. Lapping disc according to one of the preceding claims, characterized in that between connecting grooves (38, 138) of a group (G1, G2, G3, G1', G2', G3', G4', G5', G6') which are adjacent along the direction of extension, there is no connection between exactly two adjacent annular grooves (36, 136).

4. Lapping disc according to one of the preceding claims, characterized in that the connecting grooves (38, 138) each connect exactly two adjacent annular grooves (36, 136) to one another.

5. Lapping disc according to one of the preceding claims, characterized in that connecting grooves (38, 138) of at least some groups (G1, G2, G3, G1', G2', G3', G4', G5', G6') adjacent in the circumferential direction of the lapping disc (18, 118, 24) connect different annular grooves (36, 136) to one another.

6. Lapping disc according to one of the preceding claims, characterized in that connecting grooves (38, 138) of at least some adjacent groups (Gl, G2, G3, GL, G2', G3', G4', G5', G6') are oriented in different directions.

7. Lapping disc according to claim 6, characterized in that, viewed in the circumferential direction of the lapping disc (18, 118, 24), connecting grooves (38, 138) of each pair of two adjacent groups (Gl, G2, G3, GL, G2', G3', G4', G5', G6') are oriented in the same direction, wherein the orientation of the connecting grooves (38, 138) changes between adjacent pairs of groups (Gl, G2, G3, GL, G2', G3', G4', G5', G6').

8. Lapping disc according to one of the preceding claims, characterized in that the connecting grooves (38, 138) each have an elongated shape with a longitudinal direction, and that the longitudinal directions of the connecting grooves (38, 138) run at an angle between 0° and 90°, preferably between 30° and 60°, to a straight line running in the radial direction from the center of the lapping disc (18, 118, 24) to the peripheral edge of the lapping disc (18, 118, 24).

9. Lapping disc according to claim 8, characterized in that the longitudinal directions of differently oriented connecting grooves (38, 138) are arranged symmetrically with respect to a straight line running in the radial direction from the center of the lapping disc (18, 118, 24) to the peripheral edge of the lapping disc (18, 118, 24).

10. Lapping disc according to one of the preceding claims, characterized in that it further comprises a plurality of feed openings (40) for feeding a mixture of a liquid lapping agent and loose lapping particles.

11. Lapping disc according to one of the preceding claims, characterized in that it is annular.

12. Lapping machine, comprising a lapping disc (18, 118, 24) according to one of the preceding claims and a counter-bearing element arranged opposite the lapping disc, which form a working gap between them for receiving a workpiece (30) to be machined, further comprising a rotary drive for rotatingly driving the lapping disc (18, 118, 24) and / or the counter-bearing element, and comprising a feeding device for Feeding a mixture of a liquid lapping agent and loose lapping particles between the lapping disc (18, 118, 24) and the workpiece (30) to be machined into the working gap.

13. Lapping machine according to claim 12, characterized in that the rotary drive is designed to drive the lapping disc (18, 118, 24) and / or the counter-bearing element in opposite directions of rotation.

14. Lapping machine according to one of claims 12 or 13, characterized in that the counter-bearing element is also a lapping disc (18, 118, 24).

15. A method for lapping a workpiece (30) with a lapping machine (10) according to one of claims 12 to 14.

16. The method according to claim 15, characterized in that the lapping disc (18, 118, 24) and / or the counter-bearing element is driven to rotate in opposite directions of rotation during the machining of a workpiece (30).

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