EP3157709B1 - Finishing tool - Google Patents

Description

AREA OF APPLICATION AND PRIOR ART

The invention relates to a finishing tool according to the preamble of claim 1, such as from JP S62 74964 U known. Finishing, also referred to as superfinishing, is a machining process using geometrically indefinite cutting edges. By finishing work surfaces of rotationally symmetric or non-rotationally symmetrical workpiece sections on workpieces such as crankshafts, camshafts, transmission shafts or other components for power and working machines can be edited to produce a desired surface fine structure. When finishing in the piercing process, a finishing tool with granular cutting agent is pressed against the peripheral surface to be machined. To produce the cutting speed required for the material removal, the workpiece is rotated about its workpiece axis. At the same time an oscillating relative to the workpiece axis relative movement between the workpiece and the voltage applied to the peripheral surface finish tool is generated. By combining the rotational movement of the workpiece and the superimposed oscillatory motion, a cross-cut pattern can be generated, whereby the machined workpiece surfaces are particularly suitable, for example as running surfaces for plain bearings or rolling bearings or the like. The workpiece section to be machined may, for example, be a main bearing or a crank bearing of a crankshaft or a camshaft bearing or a bearing of another shaft, eg a balancing shaft.
According to the type of finish tool used, two different finishing processes are distinguished, namely band finishing and finishing stone finishing. In band finishing, the cutting medium carrier is a flexible band coated with a relatively thin layer of granular cutting means. Finishing with finish stone uses a finishing tool having a rigid cutting means carrier to which is attached a more or less thick, relatively solid cutting pad having cutting agent grains distributed in a bond. The cutting medium carrier has, on its side facing the workpiece, a cutting surface which is intended to be pressed flat against the workpiece section during a finish machining operation. The cutting coating defines a longitudinal direction to be aligned substantially parallel to the workpiece rotation axis and a transverse direction perpendicular thereto. The cutting surface has a concave shape in the transverse direction, so that the cutting surface over a large area of the rotationally symmetrical workpiece section to be machined press on. The cutting surface is normally substantially cylindrically curved.

In contrast to grinding, finishing is a thermally neutral processing method in which no soft skin interspersed with microcracks or surface tensions arises. Finishing is often used after a grinding process as the last machining process of a process chain to remove the soft skin, re-exposing the original microstructure, increasing the supporting portion of the roughened surface structure, and increasing the component geometry in terms of roundness and short-wave defects in the axial direction

In the finishing machining of rotationally symmetrical bearing points, the preservation of the axial contour is usually in the foreground. An improvement in the form values on cylindrical bearings takes place mainly in the radial direction and is highly dependent on the pre-processing. For example, short-wave error components, e.g. with more than 15 waves on the circumference, are relatively reliably improved, while long-wave components, such as e.g. Ovals, triangles or quadrilaterals can not be positively influenced by finishing. The cutting volume through the finishing process is usually less than 10 μm. In order to obtain the best possible geometry, the material removal of the finishing process is normally adjusted to the pre-processing.

Grinding is usually the last shaping machining operation. This means that the contouring of a rotationally symmetrical bearing point essentially takes place through the grinding process preceding the finishing process. A continuous dressing of the grinding wheel is imperative for the shaping and design of the bearing. Depending on the requirement and the drawing tolerance of the bearing, the dressing cycle is reduced or extended. However, the grinding process is usually unable to achieve the achievable by the finish machining surface properties.

When machining bearing sections on shafts, the geometry requirements are often such that individual or all bearing sections should have a slightly spherical shape. A crowned (barrel-shaped, convex) shape of rotationally symmetric bearing sections can help to reduce bearing damage due to flight and form errors of the components interacting in the bearing. Corresponding, given by the customer final Mellellinienanforderungen regarding crowning usually expressed in diameter differences of a few micrometers between different axial positions of the (crowned) bearing section.

When grinding crankshaft bearing sections, a crowned macro-shape can be achieved by appropriate dressing of the circumferential surfaces of the grinding wheels used during grinding (cf. EP 1 181 132 B1 . Fig. 5 ).

The EP 1 514 642 A2 describes a device for finish machining of shafts, in particular crankshafts and camshafts, with a tool carrier and an endless abrasive belt, which has a flexible carrier and an abrasive layer with hard material. The device is used for processing a rotating about its axis of rotation workpiece. A sanding belt drive continuously drives the sanding belt during workpiece machining. There is provided a clamping device for the grinding belt. The tool carrier has a machining head with two mutually spaced band deflections, which limit a working range of the machining head, wherein the grinding belt is guided over the tape deflections and passes in the work area on the peripheral surface of the workpiece to be machined. The circulating abrasive belt outside of the work area is associated with a device for dressing the abrasive layer, which has a deliverable during the workpiece processing against the abrasive layer of the belt at a speed adjusted to the workpiece processing belt speed adjustable dressing tool. In one embodiment, the dressing tool has a convex contour transverse to the direction of tape travel, which is transferred to the abrasive layer during dressing. As a result, a slightly convex contour can be produced on the machined workpiece section by means of band finishers.

The Utility Model JP S62 74964 U discloses a finish tool for finish machining a rotationally symmetric workpiece portion of a workpiece which rotates about a workpiece rotational axis during finish machining. The finish tool has a cutting agent carrier and a cutting pad mounted on the cutting medium carrier which has a cutting surface intended to be pressed flat against the workpiece portion in the finish machining. In one embodiment (FIGS. 13, 14), the longitudinal edges of the cutting coating to be aligned parallel to the workpiece rotation axis are concavely curved so that a waist shape of the cutting coating results. As a result, the effective width of the cutting coating in the central region between the longitudinal ends is minimal and increases continuously to the longitudinal ends on both sides.

The patent US 4,240,232 discloses a finishing stone for finish machining rotationally symmetrical workpiece sections of a workpiece. The finishing stone has a body of good machinable metal and a concave curved cutting surface on which an abrasive coating is applied. In the body of the finishing stone cooling channels are provided which through extend the body and through the abrasive coating. As a result, coolant can be flushed directly into the area between the cutting surface and the workpiece.
The EP 2 712 702 A1 relates to a belt finishing device with a pressing device for pressing a finishing strip against a workpiece surface. The pressing device comprises a pressing belt which is mounted on two bearing surfaces which are arranged at a distance from each other as seen in the running direction of the finishing belt. At least one of the bearing surfaces and / or the pressure belt has a profile which deviates from a straight course in the width direction of the finishing belt. In one embodiment (FIG. 32), a plurality of apertures are provided in the pressing region of the pressure band. In another embodiment (FIG. 29), a single diamond-shaped opening is provided in the pressing region of the pressing belt.
The EP 2 327 510 A1 discloses a belt finishing apparatus having a finish belt guide for pressing a finish belt against a workpiece surface. A guide body of the finishing belt guide has a cup-shaped guide surface along which the finishing belt can be guided. The guide surface is resiliently mounted in the radial direction. In one embodiment ( 5 and FIG. 5 ) is provided in the guide surface a diamond-shaped opening.
The FR 2 975 621 A3 discloses a belt finishing apparatus having pressing means for pressing a finishing belt against a workpiece surface. An embodiment ( FIG. 3 and FIG. 4 ) has a cup-shaped pressure shoe with a concave-cylindrical pressure surface, in which there are in the middle of a rhombus-shaped recess and at the ends of each triangular-shaped recesses.

TASK AND SOLUTION

It is an object of the invention to provide means for a finish process that allow not only to obtain and possibly slightly improve the resulting shape values of machined workpiece sections with the aid of the finish machining from a pre-machining, but also selectively influence them as required create or change.
To achieve this object, the invention provides a finishing tool having the features of claim 1. Advantageous developments are specified in the dependent claims.

The claimed invention provides a finishing tool, in use of which it is possible to control the axial contour of a workpiece section through the process of finishing, i. by a material-removing finish machining by means of geometrically indefinite cutting to influence in a simple manner targeted and, if necessary, to change targeted to a pre-processing. This new functionality can be achieved without making any changes to the finish machine itself.

For this purpose, it is provided in a finishing tool according to the claimed invention that a measured in the transverse direction effective width of the cutting surface in the longitudinal direction of the cutting surface varies. The term "effective width" here refers to the width measured in the transverse direction over which cutting means can be in engagement with the workpiece surface to be machined during workpiece machining. The greater the effective width in a particular axial portion of the cutting pad during machining, the more cutting means is available within this axial portion for the material-removing machining. On the other hand, in those axial regions in which the effective width is smaller than in adjacent regions, less material removal takes place during the same processing time. Thus, if the effective width of the cutting surface varies in the longitudinal direction of the cutting surface, uneven material removal can be achieved in the region of the workpiece section on which the finishing tool engages, seen in the axial direction. As a result, the shape of the machined workpiece section or its generatrix line shape can be selectively changed. The extent of variation in the effective width between the minimum effective width and the maximum effective width and the distribution of the effective width in the longitudinal direction thereby substantially determine the shape of the workpiece section that can be achieved by finish machining.

The amount of effective width variation may be different in different embodiments. Preferably, the effective width in a minimum effective width axial section is between 20% and 80% of the effective width in a maximum effective width section. Stronger or weaker variations are also possible.

In some embodiments, the effective width of the cutting surface seen in the longitudinal direction is lowest in a central portion of the cutting surface and increases continuously or discontinuously toward the axial end portions. In the axial center, the smallest effective width may be present. The cutting agent portion can be viewed in the longitudinal direction mirror-symmetrical to a center plane of the cutting surface. By a reduced proportion of cutting agent or a reduced effective width in the central region of the cutting surface Depending on the design of the width profile, a desired crown on the workpiece section can be purposefully reduced or reinforced in order to obtain the desired generatrix line shape within the dimensional tolerances after completion of the finish machining.

In the claimed invention it is provided that the cutting coating has a recess which opens into the cutting surface, so that the effective width of the cutting surface is reduced in the region of the recess relative to a cutting surface without this recess. If such a recess is provided in the cutting surface, in the axial region of the recess the effective width is smaller than the width of the cutting surface measured between the longitudinal edges in the transverse direction. With the help of a recess, it is possible to make the cutting surface so that the cutting surface is limited in its outer side rectangular, yet the effective width varies in the longitudinal direction. The term "recess" here stands for a cutting agent-free area within the outer boundary of the cutting surface.

In the claimed invention, only a single recess is provided in the cutting pad, the shape of which is selected to provide the desired axial distribution of the effective width. Finish tools with a single recess are particularly easy to manufacture and are also characterized by particularly high mechanical stability.

In some embodiments, the recess has a parallelogram shape or a diamond shape, preferably in such a way that the recess in the axial center of the cutting surface has its maximum extent in the transverse direction, wherein the width of the recess in the transverse direction to the axial ends of the recess decreases linearly ,

It is also possible for the recess to have a lenticular shape, ie a biconvex shape whose width is greatest in the middle region of the cutting surface and gradually decreases to zero at the axial ends according to a non-linear function.

It is possible that the effective width varies over the entire length of the cutting surface. In some embodiments, on the other hand, it is provided that the effective width of the cutting surface seen in the longitudinal direction in the edge regions, ie in the axial end regions of the cutting surface, is constant over a certain axial length. For example, the areas of constant effective width may each be between 5% and 20% of the axial length of the cutting surface.

It is basically not necessary that a recess in the cutting surface leads through the entire cutting surface to the cutting medium carrier. For the reduction of the proportion of cutting agent in the cutting surface, it is sufficient if the cutting means is set back sufficiently far from the cutting surface.

In some embodiments, however, a further advantage of a configuration with a recess is utilized in that the cutting medium carrier has at least one coolant channel which opens into at least one recess in the cutting coating. As a result, it is possible to supply coolant lubricant during machining by the cutting means or the cutting coating with pinpoint accuracy to the processing site. As a result, despite the greatest possible cutting performance, a sufficient rinsing effect during finishing can be achieved.

The invention also relates to a method for finishing machining peripheral surfaces of rotationally symmetrical workpiece sections on workpieces. In the method, a finish tool is pressed with a pressing force against a workpiece portion of a workpiece to be machined. To produce material removal, the workpiece is rotated about a workpiece rotation axis and a parallel movement to the workpiece rotation axis oscillating relative movement between the workpiece and the finish tool is generated. The method uses a finish tool of the type proposed here. This makes it possible to achieve a targeted contouring of the machined workpiece section by means of finish machining without constructive changes to a finish machine solely by the design of the finish tool.

The invention also relates to a device for finish machining peripheral surfaces of rotationally symmetrical workpiece sections on workpieces, in which a finishing tool of the type described is or is used.

BRIEF DESCRIPTION OF THE DRAWINGS

• Fig. 1 eine Seitenansicht einer Bearbeitungssituation bei einem Ausführungsbeispiel eines Verfahrens zur Finish-Bearbeitung;
• Fig. 2 eine Ansicht der Bearbeitungssituation aus Fig. 1 in Richtung parallel zur Werkstückrotationsachse;
• Fig. 3 ein Ausführungsbeispiel eines Finish-Werkzeugs mit einer rautenförmigen Ausnehmung im Schneidbelag;
• Fig. 4 ein Ausführungsbeispiel eines Finish-Werkzeugs mit einer bikonvexen Ausnehmung im Schneidbelag; und
• Fig. 5 schematische Beispiele für unterschiedliche Finish-Werkzeuge und damit erzielbare unterschiedliche Mantellinienformen eines Werkstückabschnitts.

Further advantages and aspects of the invention will become apparent from the claims and from the following description of preferred embodiments of the invention, which are explained below with reference to the figures. Showing:

• Fig. 1 a side view of a processing situation in an embodiment of a method for finish machining;
• Fig. 2 a view of the processing situation Fig. 1 in the direction parallel to the workpiece rotation axis;
• Fig. 3 an embodiment of a finishing tool with a diamond-shaped recess in the cutting surface;
• Fig. 4 an embodiment of a finishing tool with a biconvex recess in the cutting surface; and
• Fig. 5 schematic examples of different finishing tools and thus achievable different generatrix shapes of a workpiece section.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Based on Figures 1 and 2 some of the context and terms helpful in understanding the invention will be explained. Fig. 1 11 shows a side view of a typical machining situation in one embodiment of a method for finish machining a peripheral surface 193 of a rotationally symmetrical workpiece section on a workpiece 190 which is rotated about a workpiece rotational axis 192 at a constant rotational speed by means of a rotator for producing rotational movement of the workpiece. The workpiece section to be machined may, for example, be a main bearing of a crankshaft or a bearing surface of another shaft, for example a camshaft or a balancing shaft.

In order to effect a material removal on the workpiece section by means of finishing, a finishing tool 100 is pressed by means of a pressing device of the finishing machine with a pressing force F acting essentially radially to the workpiece rotation axis on the peripheral surface to be machined or on the workpiece section to be machined. The removal of material is assisted by using an oscillation device of the finishing machine to generate an oscillating relative movement between the workpiece and the finish tool aligned parallel to the workpiece rotation axis (see double arrow OSZ). In the example, the oscillator is mounted on the side of the finish tool so that the finish tool is oscillated while the workpiece rotates only about the workpiece rotation axis 192. It is also possible to drive the workpiece or the workpiece clamping device axially oscillating, while the tool is not oscillated axially. The axial stroke or the amplitude of the oscillatory motion can, for example, in the range from 0.5 mm to 3 mm, possibly also above or below. Typical speeds of rotation of the workpiece may lie min ^-1, and possibly also above or below, for example in the range of 50 min ^-1 to 300 bar.

The finishing tool 100 mounted on the free end of a tool holder 180 comprises a cutting means carrier 110 made of tool steel or other metallic material and comprising means for mounting the finishing tool to the tool holder 180 on its rear side. On the front of the cutting medium carrier, a cutting pad 120 is attached, for example, by means of an adhesive or by means of screws. The cutting material consisting of a sintered material contains a plurality of cutting agent grains, which in the example are distributed homogeneously within a metallic matrix. Cutting agent grains may be, for example, diamond grains or cubic boron nitride (CBN) grains. Typical average grain sizes may be used in the applications described herein, e.g. in the range of 10 microns to 50 microns, in particular in the range of 15 microns to 40 microns.

The cutting coating has a rectangular cross-section at its base side facing the cutting medium carrier. By definition, the longitudinal direction L of the cutting pad is the direction parallel to the workpiece rotational axis during the finish machining. Perpendicular to the longitudinal direction L, the transverse direction Q is such that the longitudinal direction and transverse direction are in a plane perpendicular to the pressing direction, i. perpendicular to a radial direction of the workpiece rotation axis.

On the side facing away from the cutting medium carrier, the cutting coating forms an abrasive cutting surface 125, with which the cutting coating rests more or less extensively on the peripheral surface to be processed during the finish machining. As in Fig. 2 As can be clearly seen, the cutting surface has a concave-cylindrical shape whose radius of curvature substantially corresponds to the desired radius of curvature of the workpiece section to be machined at the end of the finish machining. The curvature runs in the transverse direction Q.

A special feature of the finish tool 100 is that within the cutting pad 120, a single central recess or recess 160 is formed, which extends from the base surface of the cutting pad (on the cutting medium carrier 110) to the cutting surface 125 with a constant cross-sectional shape. Examples of possible forms of such a recess are in the Fig. 3 to 5 shown. The recess 160 is a cutting agent-free area inside the cutting pad. The recess can already be produced during sintering by appropriate shaping of the sintering mold or subsequently created, for example by means of spark erosion or in another way. In the region of the recess 160 is thus on the side of the concave-cylindrical curved cutting surface no cutting means, so that no material removal takes place in this area. In the axial end portions E1, E2 of the cutting pad (longitudinally in front of and behind the recess), on the other hand, cutting means are present over the entire width of the cutting pad measured in the transverse direction Q. It can be seen that due to the recess 160, a transversely measured effective width of the cutting surface in the longitudinal direction L of the cutting surface 125 varies, in such a way that the (effective for material removal) width of the cutting surface in the axial end portions E1 and E2 larger is than in the region of the recess 160.

The finish tool 100 allows for internal coolant lubrication, i. a supply of cooling lubricant to the processing point through the finishing tool or through the cutting surface. For this purpose, a coolant channel 170 is provided in the cutting medium carrier 110, which passes from the back of the cutting medium carrier facing the workpiece holder 180 to the front side and opens into the region of the recess 160. Formed in the tool holder 180 is a corresponding coolant channel section 182, which is connected via coolant lines to a coolant pump 175 and which, when the finishing tool is completely assembled, opens into the coolant channel 170 of the finishing tool. Thus, the finish tool can be rinsed from the inside with coolant during the finish machining, so that even with high cutting performance, the removed material can be transported away from the processing point extremely efficiently.

By using this finish tool, a material removal that varies in the axial direction of the workpiece portion (direction parallel to the workpiece rotation axis 192) is achieved only on the workpiece portion being machined due to this configuration of the finish tool. In this case, in those sections, which are mainly or exclusively processed by the axial end sections E1 and E2 during the oscillation of the finishing tool, a stronger material removal tends to be generated than in that intermediate section which lies in the region of the recess 160. This is caused by that in the axial end regions E1, E2 over the entire width of the cutting pad cutting means is in engagement with the workpiece outside, while in the middle section, i. in the region of the recess 160, a material removal takes place only in the lateral edge regions of the cutting surface (in the transverse direction next to the recess). Within the region with recess, the effective width again varies in a complementary manner to the width of the recess in the transverse direction.

Using the Finish tool 300 in Fig. 3 a possible embodiment of a finishing tool with a central recess 360 is explained. The finish tool 100 in Fig. 1 and 2 may be identical to this or have a different shape of the recess.

In the finishing tool 300, the recess 360 in the cutting pad 320 has the shape of a rhombus whose length in the longitudinal direction L is about twice as large as their (maximum) width in the transverse direction Q. The recess 360 extends from the cutting surface 325 to the cutting agent carrier 310 over the entire thickness of the cutting surface. In the area of the axial end sections E1 and E2, the effective width of the cutting surface for material removal in the transverse direction Q corresponds to the geometric width of the cutting surface, measured in the transverse direction. In the axial center M of the cutting surface, i. at the location of the largest width of the recess in the transverse direction, the measured in the transverse direction effective width of the cutting surface is only between 40% and 60% as large as in the axial end portions, since there is no cutting means in the region of the recess. From the axial location of minimum effective width in the median plane M, the effective width in the axial direction toward both ends increases linearly and symmetrically towards the center due to the diamond shape of the recess and reaches the maximum present in the end regions in the region of the axial peaks of the recess. The effective width is thus constant in the areas of the axial end portions and has symmetrical to the center plane a V-shaped curve with minimum in the axial center of the cutting pad.

It will be readily apparent that using such a finish tool in the area in which the recess moves during the oscillatory motion, the material removal per unit time is less than in the axial end areas in which the finish tool is over the full geometric width the cutting surface is in abrasive engagement with the workpiece surface. As a result, more material is removed in the axial end regions than in the middle region, resulting in a total crowned shape with a convexly curved generatrix line of the machined workpiece section.

In the variant of a finish tool 400 in Fig. 4 the recess 460 has a biconvex lens shape in the cutting surface 420 fixed to the cutting medium carrier 410, whose length in the longitudinal direction L is about two to three times as large as the measured in the transverse direction Q maximum width in the axial center of the recess. The fully eroded axial end portions E1 and E2 of the cutting surface 425 are narrower here than in the case of the embodiment of FIG Fig. 3 (between about 10% and about 5% of the axial length of the cutting pad). In the region of the recess, the effective width varies between a maximum value in the axial end regions and a minimum value in the axial center corresponding to a smooth profile with a local minimum in the axial center.

Based on Fig. 5 is exemplified, in which way by different interpretation of the dimensions of a single recess 560 in the center of a cutting pad (left part of figures) in the processing of a workpiece section different convex generatrix lines (right sub-figures) can be achieved. Fig. 5A This corresponds approximately to the variant Fig. 3 in that the effective width of the cutting surface in the center of the cutting surface, ie at the location of the largest width of the diamond-shaped recess, is only about 30% to 40% of the maximum effective width in the end regions. As a result, a relatively large crown with more or less consistently convex curved generatrix shape can be produced by finish machining.

In the variant of Fig. 5B For example, the recess 560 is narrower in the central region so that the effective width in the center is between about 40% and 50% of the effective width of the cutting surface in the axial end regions. As a result, with a corresponding adaptation of the dimensions to the oscillation stroke (deflection of the oscillation movement), a likewise convex generatrix line with a shallow central region can be achieved.

A further flattening of the central region of a fundamentally crowned shape of the machined workpiece section can then result if an even smaller variation of the effective width in the longitudinal direction is produced, as for example in FIG Fig. 5C is shown schematically. There, the effective width in the axial center region is about 60% to 80% of the maximum effective width in the axial end regions. In this way, optionally, a generatrix line shape can be achieved which is more or less cylindrical in its central region and is convexly curved only in the axial end regions of the machined workpiece section.

Finish tools of the type shown here and the variants described in this application make it possible to influence rotationally symmetrical, possibly initially more or less cylindrical, workpiece sections in their axial contours in a targeted manner. It is possible to better correct long-axial defects in the axial direction with the aid of such rigid finishing tools than with conventional finishing tools.

Claims (11)

1. Finishing tool (100, 300, 400) for the finish-machining of a rotationally symmetrical workpiece portion of a workpiece (190) which rotates about an axis of rotation (192) of the workpiece during the finish-machining, having:

   an abrasive carrier (110, 310, 410),

   a cutting layer (120, 320, 420), which is fastened on the abrasive carrier and has a cutting surface (125, 325, 425), which is provided in order to be pressed onto the workpiece portion, with surface contact, during finish-machining, wherein the cutting layer defines a longitudinal direction (L), which is to be oriented essentially parallel to the axis of rotation of the workpiece, and a transverse direction (Q), which runs perpendicularly to the longitudinal direction, and the cutting surface (125, 325, 425) is of a shape which is concave in the transverse direction, and wherein an effective width of the cutting surface, as measured in the transverse direction (Q), varies in the longitudinal direction (L) of the cutting surface,

   characterized in that

   the cutting layer has a single aperture (160, 360, 460, 560) which opens out into the cutting surface (125, 325, 425) such that the effective width of the cutting surface in the region of the aperture is reduced in relation to a cutting surface without any aperture, wherein the shape of the aperture is selected such that the desired axial distribution of the effective width of the cutting surface is obtained.
2. Finishing tool according to claim 1, characterized in that the effective width in an axial portion of minimum effective width is between 20% and 80% of the effective width in a portion of maximum effective width.
3. Finishing tool according to claim 1 or 2, characterized in that, as seen in the longitudinal direction (L), the effective width of the cutting surface is smallest in a central portion of the cutting surface, in particular in the axial center (M) of the cutting surface, and increases in the direction of axial end portions (E1, E2) of the cutting surface.
4. Finishing tool according to any of the preceding claims, characterized in that, as seen in the longitudinal direction (L), an abrasive fraction of the cutting surface (125, 325, 425) runs in a mirror-symmetrical manner in relation to a center plane (M) of the cutting surface.
5. Finishing tool according to any of the preceding claims, characterized in that the cutting surface (125, 325, 425) is bounded in rectangular form.
6. Finishing tool according to any of claims 1 to 5, characterized in that the aperture (360, 560) is of a diamond shape, preferably such that the aperture has its maximum extent in the transverse direction (Q) in the axial center of the cutting surface, wherein the width of the aperture in the transverse direction decreases linearly to the axial ends of the aperture.
7. Finishing tool according to any of claims 1 to 5, characterized in that the aperture (460) is in the form of a lens, of which the width is greatest in the central region of the cutting surface and decreases gradually, in accordance with a non-linear function, towards the axial ends.
8. Finishing tool according to any of the preceding claims, characterized in that, as seen in the longitudinal direction (L), the effective width of the cutting surface (125, 325, 425) is constant in axial end regions (E1, E2) of the cutting surface.
9. Finishing tool according to any of the preceding claims, characterized in that the abrasive carrier (110) has at least one coolant channel (170), which opens out in the aperture (160) in the cutting layer (120).
10. Method for the finish-machining of circumferential surfaces of rotationally symmetrical workpiece portions on workpieces, in the case of which a finishing tool is pressed by way of a pressure-exerting force onto a circumferential surface which is to be machined and, for material-removal purposes, the workpiece is rotated about a workpiece axis and a relative movement with oscillation parallel to the workpiece axis is generated between the workpiece and the abrasive, characterized in that use is made of a finishing tool according to any of the preceding claims.
11. Apparatus for the finish-machining of circumferential surfaces of rotationally symmetrical workpiece portions on workpieces, having:

    a rotating device for generating a rotary movement of the workpiece (190) about a workpiece axis of rotation (192);

    a pressure-exerting device for pressing a finishing tool (100, 300, 400) onto a circumferential surface which is to be machined, such that the finishing tool is pressed onto the circumferential surface by way of a pressure-exerting force (F); and

    an oscillation device for generating an oscillating relative movement between the workpiece (190) and the finishing tool, said relative movement being oriented parallel to the axis of rotation of the workpiece,

    characterized in that the finishing tool is designed according to any of claims 1 to 9.

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