Patent Application
20240042569
This disclosure relates to a honing strip, a method of producing such a honing strip and a honing tool comprising at least one such honing strip.
The manufacturing method honing is frequently used for the quality-determining finishing of tribologically stressable inner surfaces of bores. By way of example, cylinder running surfaces in cylinder blocks (cylinder crankcases) or cylinder liners, bearing surfaces for shafts, for example, in a crankshaft bearing bore, cylindrical inner surfaces in connecting-rod eyes, bearing surfaces on connecting rods, gearwheels or structural parts for other engines and working machines, for example, compressors, are often machined by honing.
Honing is a cutting machining method using geometrically undefined cutting edges carried out by a generally expandable honing tool. During a honing operation in the bore, the honing tool performs a working movement consisting of two components and leads to a characteristic surface structure of the machined inner surface. The working movement generally consists of an axially back and forth reciprocating movement and a rotary movement superposed thereon. The surface structure generally comprises criss-crossed machining traces.
The machining method honing operates using bound cutting grain with constant areal contact between the abrasive working surfaces of the honing tool and the bore surface. The working surfaces therefore usually have a curvature which is convex-cylindrical to a greater or lesser extent (or slightly conical). The cutting grains are bound in a bonding system (also “bond”) and form, together with the bonding system, a cutting layer. In that example, the function of the bonding system is to firmly hold the bound cutting grains until they are blunted by the cutting process. They are then intended to be released so that new cutting grains which are still sharp can come into engagement with the workpiece (self-sharpening effect). In this regard, the bond should be reset in relation to exposed parts of the cutting grains such that there is what is known as a grain protrusion.
A honing tool of the type considered herein has a tool body defining a tool axis about which the honing tool rotates during the honing machining. At least one radially feedable honing strip is arranged on the tool body and comprises, on an outer side, a cutting layer. The cutting layer comprises cutting grains bound within a bond and an abrasive working surface for engaging on the inner surface of the bore.
If honing tools in the newly produced state or in the context of subsequent maintenance or repair are equipped with fresh (newly produced or freshly processed) honing strips, they generally cannot immediately be used with the best abrasive removal performance, but rather a certain run-in phase is necessary to achieve a good areal adaptation between the working surfaces of the honing strips and the bore inner surfaces to be machined. The run-in phase requires time. Furthermore, it is usually not possible to produce any good parts in the run-in phase, and so scrap is produced.
To achieve favorable run-in behavior, a known method involves a tool body fitted with new honing strips, the thus assembled honing tool being clamped into a cylindrical grinding machine and being machined by cylindrical grinding with the aid of a grinding disk with rotation of the honing tool about its tool axis. In that example, the grinding machining generates a cylindrically curved macro shape of the abrasive working surfaces of the cutting layers. In that grinding operation, the cutting layer obtains the desired roundness or cylinder shape of the working surface, the curvature of which corresponds approximately to the curvature of the bore inner surface to be machined, and therefore an areal working engagement is possible. Furthermore, the cutting layer obtains the desired straightness parallel to the tool axis. In general, the bond can also be reset by cylindrical grinding such that the working surface has good cutting properties from the outset.
In EP 3 195 978 B1, alternative methods of producing tools for machining using geometrically undefined cutting edge are described, wherein the cutting grains are bound in a bond and the tool comprises at least one working surface. In the method, proceeding from a blank of the tool, the shape and/or the condition of the working surface is determined by a locally limited structural change of the bond. After the structural change has been generated, the subsequent working surface lies in the interior of the blank at the boundary between a peripheral zone which has changed with respect to the structure and the remaining structure of the cutting layer, which has not been changed. This is intended to make it possible to machine the generally sintered blank in one operation such that the working surface is formed and subsequent sharpening of the working surface is not required. Rather, the blank is intended to be able to be used without further machining.
It could therefore be helpful to provide a honing strip, the use of which makes it possible for a honing tool equipped therewith to already be able to generate bores of high honing quality after a short run-in phase as well as a method of producing such a honing strip, the method being able to be carried out efficiently with reasonable effort, and a honing tool equipped with at least one such honing strip.
We provide a honing strip for use in a honing tool for machining an inner surface of a bore, including a cutting layer carrier that carries, on an outer side, a cutting layer including cutting grains bound within a bond and an abrasive working surface that engages on the inner surface of the bore, wherein the honing strip defines a longitudinal direction (L) to be oriented parallel to a bore axis and the working surface extends in a width direction (B), perpendicular to the longitudinal direction, between a first side surface and a second side surface of the cutting layer, and the working surface has a generally convex macroscopic form with at least two macroscopically planar facets of different orientation which transition, along edges running in the longitudinal direction, to an adjacent facet or a side surface.
We also provide a method of producing a honing strip for use in a honing tool for machining an inner surface of a bore, including providing a honing strip blank including a cutting layer carrier that carries, on an outer side, a cutting layer including cutting grains bound within a bond; generating an abrasive working surface on the cutting layer, the working surface adapted to engage on the inner surface of the bore, wherein the working surface defines a longitudinal direction (L) to be oriented parallel to a bore axis and extends in a width direction (B), perpendicular to the longitudinal direction, between a first side surface and a second side surface of the cutting layer, and the working surface is generated such that it obtains a generally convex form with at least two facets which transition, along edges running in the longitudinal direction, to an adjacent facet or a side surface.
We further provide a honing tool for machining the inner surface of a bore, including a tool body that defines a tool axis about which the honing tool rotates during the honing machining; at least one honing strip arranged on the tool body, the honing strip adapted to be fed radially with respect to the tool axis and including, on an outer side, a cutting layer including cutting grains bound within a bond and an abrasive working surface that engages on the inner surface of the bore, wherein the honing strip for use in a honing tool for machining an inner surface of a bore includes a cutting layer carrier that carries, on an outer side, a cutting layer including cutting grains bound within a bond and an abrasive working surface that engages on the inner surface of the bore, wherein the honing strip defines a longitudinal direction (L) to be oriented parallel to a bore axis and the working surface extends in a width direction (B), perpendicular to the longitudinal direction, between a first side surface and a second side surface of the cutting layer, and the working surface has a generally convex macroscopic form with at least two macroscopically planar facets of different orientation which transition, along edges running in the longitudinal direction, to an adjacent facet or a side surface.
Further advantages and aspects will emerge from the description of examples explained below on the basis of the figures.
Our honing strip is intended to be inserted into a honing tool and to be used in the honing tool for machining the inner surface of a bore. The honing strip comprises a cutting layer carrier that carries, on an outer side, a cutting layer comprising cutting grains bound within a bond and an abrasive working surface that engages the inner surface of the bore. The cutting layer contains a multiplicity of cutting grains generally distributed homogeneously within the bond.
The bond may, for example, be a metallic bond or a ceramic bond. Depending on the intended application of the honing strip, the cutting grains may be, for example, diamond grains or grains composed of cubic boron nitride, or also cutting grains composed of silicon carbide (SiC) or corundum (aluminum oxide). Typical mean grain sizes may be, for example, 5 μm to 251 μm, in particular 10 μm to 126 μm.
The honing strip defines a longitudinal direction, when the honing tool is in the mounted state ready for operation, oriented substantially parallel to the tool axis and the bore axis of the machined bore during the honing operation. Running perpendicular to the longitudinal direction is the width direction which, in the mounted state ready for operation, runs substantially perpendicular to the tool axis. The working surface, which during the intended use of the honing tool equipped with the honing strip is located on that side of the cutting layer which faces the bore inner wall, extends in the width direction between a first side surface and a second side surface of the cutting layer or a first and a second side periphery. The side peripheries are the linear regions in which the working surface transitions into the side surfaces. During the intended use of the honing strip incorporated into the honing tool, one of the side peripheries runs ahead of the other side periphery during the rotation of the honing tool. The side peripheries are thus offset in relation to one another in a circumferential direction of the bore.
In one example, the working surface has a generally convex macroscopic form in the sense that the middle region between the side surfaces or side peripheries protrudes outward, that is to say away from the cutting layer carrier, in relation to a common plane spanned by the side peripheries. The macroscopic form of the working surface is characterized by at least two macroscopically planar facets of different orientation which transition, along edges running in the longitudinal direction, into an adjacent facet or into a side surface at a side periphery. Adjacent facets form, at the enclosed edge, an interior angle of less than 180°. The interior angle may be, for example, 150° to 179°.
Such honing strips deliver a sufficiently good honing quality very soon after the run-in phase has begun since the macroscopic form of the working surface adjusts very rapidly to the curved shape of the inner surface of the bore on account of the faceted macro shape which is initially present. This surprising effect is understood as meaning that, during radial feed of the honing strip, the working surface, which is also faceted at the outset, initially comes into contact with the bore inner surface only along one or more longitudinally running edges. Owing to the more or less linear contact, a high surface pressure and correspondingly high wear on the cutting layer is produced in the region of the edges, and therefore the macro shape of the working surface, proceeding from the edges in both circumferential directions, adjusts very rapidly to the curved shape of the bore inner surface. As a result, complete areal contact between working surface and bore inner surface is produced rapidly over the entire width between the side peripheries.
These advantages in the run-in behavior can be obtained in a relatively simple and correspondingly cost-effective manner since the generation of macroscopically planar facets on a cutting layer can be implemented in terms of manufacturing in a simpler and more cost-effective manner than, for example, the generation of cylindrically curved working surfaces in cylindrical grinding.
A further advantage is that the diameter range around a nominal diameter for which a honing strip with faceted working surface can be used is relatively greater than the diameter range that can readily be covered by a working surface that has already been pre-machined in a cylindrically curved manner. Our honing strips are thus distinguished by relatively simple and cost-effective producibility, a rapid adaptation to the bore surface to be machined and a certain tolerance with regard to the bore diameter.
It may suffice for the working surface to have only exactly two facets between the side surfaces or the side peripheries such that the working surface assumes a roof shape. Preferred examples have more than two facets, for example, three, four, five or six facets. This makes it possible to better approximate a continuously curved surface.
It is particularly advantageous for the working surface to comprise exactly three facets. This number constitutes a good compromise between, on the one hand, a good adaptability to the bore inner diameter, and, on the other hand, simple manufacture.
In some examples, the facets have substantially identical widths. A “substantially identical width” is present if the comparative widths of the facets differ by no more than ±20%. This results in particularly uniform distributions of the contact pressures in the edge regions and a corresponding uniform adjustment during the run-in phase.
In one example, the facets are dimensioned such that the side peripheries and the at least one edge between facets lie on a common cylinder surface having a radius of curvature corresponding substantially to a nominal radius of the bore to be subsequently machined. What can be achieved by this is that, from the very beginning, both the edges formed at the side peripheries between side surface and lateral facet and the intermediate edges (one or more) bear against the bore inner wall more or less simultaneously under similar pressing conditions, as a result of which the dimensional change in the run-in phase is favorably distributed over all the edges from the beginning.
In preferred examples, on the working surface, the bond is reset in relation to exposed parts of the cutting grains such that there is a grain protrusion. The facets thus have good cutting properties from the outset, even during the run-in phase.
In a method of producing such a honing strip, a honing strip blank is first provided, comprising a cutting layer carrier that carries, on an outer side, a cutting layer comprising cutting grains bound within a bond. An abrasive working surface which is intended to engage on the inner surface of the bore is then generated on the cutting layer. As mentioned above, the working surface extends, as viewed in the width direction, between a first and a second side periphery or between the side surfaces of the cutting layer. The working surface is generated such that it obtains a generally convex form with at least two facets which transition, along edges running in the longitudinal direction, to an adjacent facet or a side surface.
The facets may have already been generated during the production of the cutting layer, for example, during the sintering of a sintered cutting layer by corresponding shaping in a mold.
However, proceeding from a raw state of the cutting layer, the facets are preferably generated by local removal of material. Blanks, in which a cutting layer of constant thickness has been applied to a planar outer side of the cutting layer carrier, are usually used such that the honing strip blank has a rectangular cross-sectional shape overall, before the facets are generated on the cutting layer by locally unequal removal of material.
In preferred examples, the facets on the cutting layer of the honing strip blank are generated by surface grinding, in particular face grinding. In face grinding, particularly uniform wear of the face grinding tool is produced, and therefore high unit quantities can be machined without renewed dressing of the grinding tool. The grinding tool used may be, for example, a cup wheel.
In many situations, for the generation of the facets, a surface grinding tool comprising diamond cutting grains is used, the cutting grains possibly being bound, for example, in a metallic matrix. Such grinding tools are distinguished, inter alia, by long service lives and can perform material-removing machining of many different types of cutting layer.
Preferably, production of the honing strip also comprises resetting of the bond on the working surface on the facets. In this example, the working surface is preferably generated in two successive stages. This involves, in a first step, generating substantially planar facets without grain protrusion, before then, in a second step, resetting the bond on the facets in relation to the cutting grains in a resetting operation.
For the resetting operation, use may be made of a surface grinding tool comprising a cutting layer whose cutting grains are harder than the bond of the cutting layer of the honing strip but are unable to cut the cutting grains of the cutting layer of the honing strip.
We also provide a honing tool comprising at least one honing strip of the type described here.
In the following description of examples, for the sake of clarity, identical or similar features are each denoted by the same reference designations in all examples shown.
The honing tool 100 has a tool body 110 manufactured from steel or hard metal in the form of a tube open on both sides and having a relatively large wall thickness. An end portion of the tool body is introduced into a cylindrical receiving opening of a tool shaft 120 in a rotationally fixed manner and fixed there with the aid of a retaining screw 122. The tool shaft 120 couples the honing tool to the honing spindle of a machine tool. Tool shaft and tool body may also be connected to one another releasably or non-releasably in some other way, for example, by clamping, soldering or the like.
Located in a free end portion of the tool body, the end portion lying opposite the tool shaft, is the cutting region of the honing tool, the cutting region being introduced, for the honing machining, into the interior of a bore 195 to be machined in a workpiece 190 to hone the bore inner surface 192. The bore has a nominal diameter D, which may be, for example, 10 mm to 40 mm, but may also be above or below that.
In the cutting region, the tool body 110 comprises a rectangular honing strip receiving opening 140 which is continuous from the interior of the tool body to the outside and in which the honing strip 200 is received with an accurate fit and in a radially displaceable manner in the assembled honing tool.
The honing strip 200 has, in its longitudinal direction L running parallel to the tool axis 112, a length greater than the width measured in the width direction B running perpendicular to the longitudinal direction L and the radial direction R. It is also possible for the axial length of a honing strip to be shorter than the width measured in the circumferential direction or width direction.
On the side opposite the honing strip receiving opening 140, two guide strips 180, 181 that are circumferentially offset in relation to one another by approximately 90° and composed of hard metal, sintered metal or another hard, for example, ceramic material are attached to the tool body. These guide strips are designed to be supported with their smooth polished, curved outer surfaces on the inner wall of the bore to be honed. The guide strips may carry a coating consisting of, for example, diamond and which forms a wear-resistant outer surface.
The honing strip 200, which is plate-shaped overall, has a plate-shaped cutting layer carrier 202 composed of steel, often also referred to as supporting strip and having attached to its planar, radial outer side 204 a cutting layer 210 that holds the cutting grains 215 bound in a bond 213. The cutting layer of the example comprises diamond cutting grains bound in a metallic bond (for example, composed of a bronze alloy). In the example, the cutting layer 210 is sintered onto the cutting layer carrier 202, but in other examples may also be adhesively bonded onto, or soldered onto, or fastened by rivets or screws to, the cutting layer carrier. A honing strip may also be formed by a one-piece sintered body. Located on the radial outer side of the cutting layer 210 is an abrasive working surface 220 that engages the inner surface of the bore.
The radial inner side of the cutting layer carrier 202 has a planar oblique surface 216 cooperating with a complementary planar oblique surface at the lower end of a feed rod 130, guided in the tool body, in the manner of a wedge-type drive such that the honing strip 200 is pushed radially outward within the honing strip receiving opening 140 when the feed rod is pushed in the direction of the cutting region of the honing tool by the feed drive accommodated in the honing machine.
During the honing machining, the honing tool 100 is intended to be in constant areal contact with the inner surface 192 of the bore 195 by way of the abrasive working surface 220. In a satisfactorily run-in honing tool, the abrasive working surface is therefore curved in a substantially cylindrical manner and has a radius of curvature corresponding substantially to the inner radius of the machined bore.
However, this does not apply to the honing tool 100. It is a honing tool equipped with a newly produced or newly reprocessed honing strip 200 not yet having been used to carry out a honing operation. The honing tool may thus be a new tool or a used honing tool fitted with a new or fresh honing strip 200.
The honing strip 200 is distinguished by particular features making it possible for the honing tool to already be able to generate good parts with high honing quality of the bore inner surface after a very short run-in phase. For illustration purposes,
There are also configurations in which the cutting layer carrier is wider than the cutting layer. By way of example, a narrower groove in which the cutting layer is received may be milled centrally or eccentrically into the wide outer side of the cutting layer carrier or be generated in some other way. Support edges composed of the material of the cutting layer carrier are then located on both sides of the cutting layer.
The working surface 220 has a generally convex macroscopic form such that the middle region of the working surface is bulged outward in a radial direction R in relation to the peripheral regions on the side surfaces. However, the convex form is not rounded, but rather faceted. Specifically, the working surface 220 has three macroscopically planar facets 230-1, 230-2, 230-3 which transition, along edges running in the longitudinal direction L (longitudinal edges), to an adjacent facet or a side periphery or a side surface. The first facet 230-1 adjoining the side surface 212-1 visible on the left encloses, together with this side surface, an angle of more than 90° at the side periphery and forms a first edge 235-1 therewith. A second facet 230-2, running parallel to the planar outer side 204 of the cutting layer carrier 202, encloses, together with the first facet 230-1, an interior angle IW of less than 180° and forms, together with the first facet, a second edge 235-2 at the transition. Located on the side visible on the right is a third facet 230-3 which transitions, in the region of a third edge 235-3, to the second facet and encloses, together with the second facet, an interior angle of less than 180°. The third facet transitions, along a fourth edge 235-4, into the right-hand side surface 212-2 or the right-hand side periphery.
On the facet surfaces, the cutting grains protrude beyond the level of the bond, that is to say there is a grain protrusion such that the freshly prepared, faceted working surface has good cutting properties in particular also in the region of the longitudinal edges 235-1 and the like.
The size ratios are not illustrated to scale. Depending on the nominal diameter for which the honing strip is controlled, and also depending on the number of facets, the interior angle IW may be, for example, on the order of magnitude between 170° and 179°, possibly also above or below that. The widths of the facets, the widths being measured in the width direction B, are of approximately equal size and preferably differ by no more than ±20%. In an uneven number of facets, a middle facet (here the second facet 230-2) is preferably provided, the facet surface of which runs parallel to the outer surface 204 of the cutting layer carrier. The second facet may be formed by the original surface of the cutting layer which is initially applied with uniform layer thickness DS, or may already be machined by parallel resetting in relation thereto.
The number of facets and the width of the facets are preferably matched to one another such that the edges consisting of cutting material lie substantially on a common cylinder surface Z (illustrated by dashed lines), the radius of curvature of which corresponds to the nominal radius of the bore to be machined. This ensures that the fresh honing strip, when fed in the direction of the bore inner wall for the first time, bears against the bore inner wall at all edges (longitudinal edges) simultaneously. By contrast, in the regions between the longitudinal edges, as seen in the radial direction, there is a more or less large gap between facet and bore inner wall.
The faceted geometry of the abrasive working surface 220 enables short run-in times before the honing strip is in full large-area engagement, at its working surface, with the bore inner wall. In this example, at the beginning of the run-in phase, only the longitudinal edges are in contact with the bore inner wall. On account of the great surface pressure resulting therefrom, the wear on the cutting layer is greatest in the edge regions such that the edges are rapidly rounded and the rounded regions of adjacent edges rapidly approximate one another until the facets disappear and a working surface of continuously substantially cylindrical curvature is produced. Honing tools equipped with such honing strips are thus able to operate productively after the shortest time such that no or barely any scrap on the machined workpiece is produced.
Fresh honing strips of the type described here can be produced with a precise predefinable geometry in a production process which can be implemented in a relatively simple and cost-effective manner. An exemplary production process is explained on the basis of
A honing strip blank is first produced, when a cutting layer 220 with constant layer thickness is applied, for example, by sintering, to the planar outer side of a plate-shaped cutting layer carrier 202. Proceeding from the more or less planar outer surface of the cutting layer, facets that lead to the desired faceted macro shape are then introduced. In this regard, in the example, use is made of a surface grinding method with the aid of a cup wheel 300 driven to rotate about an axis of rotation 302 and is fitted with diamond cutting means. The end surface 305 which is oriented perpendicularly with respect to the axis of rotation is in grinding engagement with the cutting layer (face grinding). In the grinding into thirds described here, one of the lateral facets (first or third facet) is first generated, then the grinding tool and honing strip are tilted relative to one another such that the other facet surface (third or first facet) is generated by surface grinding. Depending on the preliminary machining quality, the middle facet (second facet) may remain non-machined or may alternatively likewise be subsequently machined by surface grinding such that all the facets have substantially the same surface quality.
In the example, the cutting grains of the surface grinding tool 300 are harder than the cutting grains 215 in the cutting layer of the honing strip such that cutting grains of the cutting layer are at least partially also abraded and a macroscopically planar grinding surface with partially incipiently cut cutting grains is produced.
In a second process step, the bond is then mechanically reset in relation to the cutting grains (cf.
There are numerous configurations. The number of facets is not restricted to three. It is, for example, also possible for only two facets to be provided such that the abrasive working surface initially has a roof shape. It is also possible to provide more than three facets, for example, four or five facets. This may be advantageous in obtaining an even more rapid run-in phase, but must be weighted against a somewhat longer production process. Furthermore, it is not absolutely necessary for the facets to all have substantially the same width. Facets with unequal widths can also be provided. In general, however, the faceted surface is substantially mirror symmetrical with respect to a plane of symmetry which lies between the wide sides of the honing strip in the width direction.
Our concepts can be used for different types of cutting layer, for example, cutting layers with metallic bond or ceramic bond or with synthetic resin bond.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2021 201 070.9 | Feb 2021 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/050887 | 1/17/2022 | WO |
