HONING TOOL AND FINE MACHINING METHOD USING THE HONING TOOL

FIELD OF APPLICATION AND PRIOR ART

The invention relates to a honing tool according to the preamble of claim 1 and to a fine machining method according to the preamble of claim 13. A preferred field of application is the fine machining of cylinder surfaces in the production of cylinder blocks or cylinder liners for reciprocating piston engines.

The cylinder surfaces in cylinder blocks (engine blocks) or cylinder liners of internal combustion engines or other reciprocating piston engines are exposed to high tribological stress during operation. Therefore, in the production of cylinder blocks or cylinder liners, it is necessary to machine these cylinder surfaces such that sufficient lubrication by a lubricant film is subsequently ensured under all operating conditions and the frictional resistance between parts that move relative to one another is kept as low as possible.

The quality-determining finishing of such tribologically stressable inner faces generally takes place with suitable honing methods, which typically comprise a plurality of successive honing operations. Honing is a metal cutting method with geometrically undetermined cutting edges. In a honing operation, an expandable honing tool is moved up and down or back and forth within the bore to be machined in order to create a reciprocating movement in the axial direction of the bore with a stroke frequency, and at the same time rotated in order to create a rotary movement, superimposed on the reciprocating movement, with a rotation frequency. The cutting material bodies applied to the honing tool are pressed against the inner face to be machined with a feeding force acting radially with respect to the tool axis via a cutting material body feeding system. During honing, a cross-hatch pattern that is typical for machining by honing and has intersecting machining lines, which are also known as “honing scores”, generally arises on the inner face.

In order to prepare the workpieces to be machined for honing, there can be a prior pre-machining operation by fine boring, which is sometimes also referred to as fine turning or fine spindling. Fine boring operations, which are carried out with fine boring tools with a geometrically determined cutting edge, generally serve to define the desired position and angular position of the bore, optionally also to create bore shapes that differ from a circular-cylindrical form. An essential object of the honing operation with a smaller allowance compared with fine boring is the creation of the required surface structure.

With increasing demands being made of the economy and environmental friendliness of engines, the optimization of the piston/piston rings/cylinder surface tribological system is of particular importance in order to achieve a low level of friction, a low level of wear and low oil consumption. The macroscopic form (macro shape) of the bores and the surface structure are accorded particular importance here.

In some fine machining methods, a bore shape that differs in a defined manner from the circular-cylindrical shape is created by means of fine boring and/or honing. Such bore shapes are generally asymmetric in the axial direction and/or in the circumferential direction, because the deformations of the cylinder block are generally not symmetric either. In the operating state, a circular-cylindrical shape that is as ideal as possible is usually intended to result, such that the piston ring set can seal off well around the entire bore circumference.

On account of a wide variety of demands, different honing tool types have been developed. They can be categorized as honing tools that are feedable during machining and honing tools that are presettable. Honing tools that are feedable during machining can be subdivided further into strip honing tools, such as one-strip honing tools, multi-strip honing tools and special tools, and into largely full-faced tools, such as shell tools and shank tools. The category of presettable honing tools includes what are known as mandrel tools or precidor honing tools.

One-strip honing tools are frequently used in the machining of high-precision small parts. Multi-strip honing tools are available in a wide variety of forms for a variety of possible uses. On account of the high abrasive capacity and the operating parameters thereof, high cutting efficiency is achievable during honing.

In the case of bores with large interruptions, the use of conventional strip honing tools can result in problems. Although the individually guided honing strips can ensure concentric widening and optimal roundness of the bore, when there are large interruptions, there is the risk that they will get caught in the workpiece. The shell tools, as they are known, were developed for this purpose, inter alia, in the case of which abrasives are arranged on a cutting material body carrier that is relatively wide in the circumferential direction. A shell tool can be constructed for example with only two cutting material body carriers (half shells), and optionally also with three or four or more cutting material body carriers of correspondingly smaller circumferential width.

Shell tools can be designed with different structures.

The laid-open application DE 1652074 describes a honing tool having shell segments that have been produced from one piece as a sintered part with a cutting coating and that can have, as carriers for the cutting coating, a multiplicity of outwardly protruding ribs.

DE 102013204714 A1 discloses honing tools designed for example as shell tools, which are suitable for machining rotationally symmetric bores that have bore portions with different diameters and/or forms. In that case, it is possible for bores with a bottle shape, cone shape or barrel shape, for example, to be machined and/or created. The corresponding honing methods are occasionally referred to as “contour honing”. The honing tool has an expandable annular cutting group with a plurality of cutting material bodies distributed around the circumference of the tool body, the axial length of said cutting material bodies as measured in the axial direction being less than an effective outside diameter of the cutting group with cutting material bodies fully retracted. The cutting group has a plurality of radially feedable cutting material body carriers, which each cover a circumferential angle range that is greater than the axial length of the cutting group.

On account of the relatively short axial length of the cutting group, such honing tools are particularly suitable for the creation of an axial contour and/or for following an already existing axial contour of the bore. Furthermore, small axial lengths of the cutting group can be advantageous in order to create sufficient surface pressure for machining Since the cutting group has a plurality of radially feedable cutting material body carriers, which each cover a circumferential angle range that is greater than the axial length of the cutting group, it is possible, inter alia, for cross bores, for example, in the wall of a cylinder running surface to be bridged in the circumferential direction during honing, such that, in spite of axially short cutting material bodies, there is no risk of irregular machining in the region of cross bores. When such honing tools are used, it is furthermore possible to work with a very small honing overrun at the axial ends of a bore, without problems with irregular cutting body wear arising. However, it has been found that, in certain cases, during the machining of non-cylindrical bores (for example bores with a bottle shape, cone shape or barrel shape), locally different surface structures can be created on account of different cutting depths. These can cause technical problems. In the case of undesired excessively high local roughness, oil consumption and blow-by, for example, can be increased. If too little material removal is created locally, it is possible, on account of inadequate remedying of material damage from upstream machining stages, for the risk of seizing during operation of a combustion engine to increase. Close to the axial ends of a bore, deviations of the grinding pattern from the grinding pattern in the rest of the bore can occur.

PROBLEM AND SOLUTION

The problem addressed by the present invention is to provide a honing tool of the type in question and a fine machining operation able to be carried out therewith, which make it possible to machine bores of different form such that the machined bore faces have a readily definable surface structure along the entire bore length.

To solve this problem, the invention provides a honing tool having the features of claim 1. Furthermore, a fine machining method having the features of claim 13 is provided. Advantageous developments are specified in the dependent claims. The wording of all the claims is made part of the content of the description by reference.

The expandable cutting group attached to the tool body has a plurality of radially feedable cutting material body carriers that each cover a circumferential angle range and are feedable radially with respect to the tool axis by means of a cutting group feeding system assigned to the cutting group. The circumferential angle range can be for example 30° or more, 40° or more, or about 60° or more, or even 90° or more. Each cutting material body carrier carries, on its radial outer side, a plurality of narrow cutting material bodies that are arranged at a mutual lateral spacing from one another and each cover only a fraction of the circumferential angle range. Therefore, intermediate spaces or gaps without cutting material remain between the cutting material bodies. As a result, even in the event of heavy material removal, reliable lubrication with cooling lubricant and sufficient discharge of machining residues can be ensured.

The cutting material bodies are configured as cutting material strips that are narrow in the circumferential direction and have a width in the circumferential direction that is small compared with the axial length of the cutting material strips. By means of cutting material strips, it is possible, if necessary, to achieve particularly uniform coverage along the entire bore length, even at the bore ends, where a honing overrun may be desired. An aspect ratio between the axial length and the width to be measured in the circumferential direction may be for example in the range from 4:1 to 20:1.

The cutting material bodies can consist entirely of abrasive or have a carrier that consists for example of metal and bears the abrasive. The abrasive can exhibit for example cutting grains made of diamond or cubic boron nitride (CBN), which are bound in a metallic or ceramic matrix.

The cutting group has cutting material bodies that have not been applied directly to the radial outer side of the associated cutting material body carrier and have not been rigidly or firmly connected thereto either. Rather, an elastically resilient intermediate layer is arranged in an intermediate space between a cutting material body and the cutting material body carrier carrying the cutting material body, said intermediate layer filling the intermediate space between the cutting material body and the cutting material body carrier.

Such an intermediate layer can be provided at all cutting material bodies of a cutting group. It is also possible for only some cutting material bodies of a cutting group to be carried by such an intermediate layer and for others to be connected rigidly to the cutting material body carrying them. Preferably, either all the cutting material bodies of a cutting material body carrier are connected to the associated cutting material body carrier in a resilient manner via an elastic intermediate layer or they are all fastened rigidly thereto, such that there is no mixture of rigidly and resiliently coupled cutting material bodies at one cutting material body carrier.

Each cutting material body carrier therefore carries a cutting material body group with two, three, four, five, six, seven, eight or more in each case relatively narrow cutting material bodies, between which gaps remain in the circumferential direction. The cutting material body group (group of cutting material bodies) is carried by the inherently substantially rigid cutting material body carrier such that all cutting material bodies of the cutting material body group are radially fed jointly when the cutting material body carrier is radially fed. The requirement of radial feedability of the cutting material body carrier means that the carrier has to be mounted in a movable manner with respect to the workpiece body, wherein especially movability in a radial direction is necessary. A certain amount of tilting of a cutting material body carrier, for example in the region of the honing overrun, cannot be completely ruled out, however, since uneven loading of the cutting material bodies and thus of the associated cutting material body carrier arises there as seen in the axial direction.

As a result of the elastically resilient intermediate layers between the cutting material bodies and the cutting material body carrier carrying them, there is, to a certain extent, individual flexibility or movability of the cutting material bodies with respect to the (rigid) cutting material body carrier carrying them and relative to other cutting material bodies of the cutting material body group. It has been found that, as a result, the adaptability of the honing tool or of the cutting material bodies to different orientations of the surface to be machined can be improved even further compared with conventional solutions.

Improvements can result in particular in the case of conical shapes and/or in the region of axial transitions between cylindrical and conical bore portions and/or in the region of axial transitions between portions of different cone angle. Furthermore, the cutting material bodies can better follow deviations, which may also be present, from the roundness of the bore in the case of oval bore shapes or higher-order roundness deviations. Potentially, there may be improvements even in the region of the turning point of the axially back and forth honing movement, i.e. where a tilting moment can arise on the arrangement of cutting material bodies and the carrying cutting material body carrier during the change in direction.

As a result of the intermediate layer, it is possible, inter alia, for a cutting material body to remain oriented largely parallel to the machined bore surface in spite of any tilting moment acting on the overall arrangement (cutting material body carrier with cutting material bodies), with the result that a readily definable uniform surface structure can be ensured even in axial transition regions of different surface orientation and as far as the axial bore ends. Since the intermediate layer fills the intermediate space between the cutting material body and the cutting material body carrier, no abrasion dust can pass between the cutting material body and cutting material body carrier and so the individual flexibility is maintained even in the event of heavy material removal throughout the honing process. Likewise, surface damage by scratches and/or scores, which can occur as a result of abrasion dust and/or course cutting grains or foreign bodies collecting in the cutouts of sprung strip carriers, can be prevented thereby.

Honing tools according to the invention are particularly suitable for honing bores with an axial contour. The individually flexibly or resiliently mounted cutting material bodies can adapt particularly readily to inclinations of the bore inner face that change in the axial direction of the bore, for example at the transition between a circular-cylindrical bore portion and a conical bore portion. Honing operations in which the cutting material bodies are intended to track the contour of the bore as well as possible, without changing the macroscopic form of the bore, are also referred to as “tracking honing” here. The advantages of honing tools according to the invention can be used in the machining by honing of non-round bore shapes with deviations from the rotational symmetry, too.

Numerous tests have shown that it is generally favorable for the intermediate layer to have a layer thickness in the range from 0.1 mm to 2 mm, in particular in the range from 0.5 mm to 1.5 mm At layer thicknesses that are significantly below the lower limit, the tiltability of the cutting material bodies with respect to the cutting material body carrier element that is achievable thereby is generally insufficient for it to be possible to compensate for all misorientations that occur. At layer thicknesses that are significantly above the upper limit, it is harder to obtain sufficient stability of the cutting material strips with respect to transverse loads.

In order to allow a good compromise between sufficient stability of the intermediate layer with respect to transverse loads and sufficient flexibility for compensating for misorientations, it has been found to be advantageous for a Shore hardness of the intermediate layer to be in the range from 70 Shore A to 95 Shore A. At greater hardnesses, there is generally no longer sufficient resilience. At significantly lower hardnesses, the arrangement of the cutting material strips on the cutting material body carrier element can become too unstable, and so sufficient machining forces can no longer be applied to the surface to be machined during machining by honing.

In preferred embodiments, the intermediate layer has an elastic layer made of an elastomer, in particular of a rubber-elastic polyurethane elastomer. The term “elastomer” stands here for dimensionally stable but elastically deformable plastics, the glass transition point of which is below the application temperature. An elastomer can deform elastically under tensile and compressive load but then returns to its original undeformed shape. Such elastomers can be produced for example by vulcanization of natural rubber or silicone rubber. Adhesive elastomers are particularly good to use. An advantage of polyurethane elastomers is the particularly high resistance of the material properties to the influence of typical cooling lubricants.

In some embodiments, the intermediate layer has been vulcanized directly onto a contact face on the cutting material body or the outer face of the cutting material body carrier element. In this case, in order to establish the connection between the intermediate layer and the element adjoining the latter, no further material (for example an adhesion promoter or an adhesive) is required. The extensive connection to the other element (cutting material body or outer face of the cutting material body carrier element) can be realized for example by a thin adhesive layer.

In some embodiments, the intermediate layer has a multi-ply or multilayer structure. In particular, the intermediate layer can have been constructed such that it has a first layer and at least one second layer connected extensively thereto, wherein the first layer is a layer made of an elastomer and the second layer is an adhesive layer connected extensively to the first layer.

Although it is possible for the adhesive layer (second layer) to be thicker than the elastomer layer (first layer), it is preferable for the layer thickness of the first layer to be greater than the layer thickness of the second layer. As a result, it is possible for the essential contribution to the desired elasticity or flexibility of the cutting material body with respect to the cutting material body carrier element to be determined by the properties of the first layer (elastomer layer).

It is possible for a potentially relatively small contribution to the overall elasticity of the intermediate layer to be made by the adhesive layer. This can be achieved in that the adhesive layer itself is inherently elastically deformable. In order to produce the adhesive layer, it is possible to use for example viscoplastic adhesives, for example an acrylate-based viscoplastic two-component plastic adhesive. When selecting the material for the adhesive layer, care should preferably be taken to ensure good adhesive strength with respect to the material of the cutting material bodies and/or with respect to the material of the outer side of the cutting material body carrier element.

In order to improve the adhesive strength at an adhesive joint, at least one of the faces adjoining the adhesive layer can be roughened by sand blasting or sanding or in some other way prior to application of the adhesive. Preferably, the average roughness depth R_zof a face, adjoining the adhesive layer, of a cutting material body carrier produced for example from steel and/or of the cutting material body is in the range from R_z=10 μm to R_z=30 μm. As a result, high adhesive strengths are achievable in a long-lasting manner The face of the intermediate layer material (for example plate or strip made of polyurethane elastomer) that comes into contact with the adhesive can also be roughened beforehand. In this case, average roughness depths in the range from R_z=15 μm to R_z=40 μm have been found to be particularly favorable.

The invention can be used in different types of honing tool. For example, the cutting material body carriers can be longer in the axial direction than in the circumferential direction. In many embodiments, the cutting group has, by contrast, an axial length, measured in the axial direction, that is less than an effective outside diameter of the cutting group with cutting material bodies fully retracted. Such a cutting group can be referred to as an annular cutting group. In the case of an annular cutting group, too, cutting material bodies can be configured as cutting material strips that are narrow in the circumferential direction and have a width in the circumferential direction that is small compared with the axial length of the cutting material strips.

The honing tool has preferably exactly one annular cutting group. An annular cutting group can be designed such that, in the axial portion covered by the annular cutting group, substantially more contact area can exist between cutting material bodies and bore inner face than in a comparatively narrow axial portion of a conventional honing tool with relatively narrow honing strips.

The axial length of the cutting material bodies can be for example less than 40% or less than 30% of the effective outside diameter of the honing tool, in particular between 15% and 30% of this outside diameter. In honing tools for machining typical cylinder bores in engine blocks for passenger cars or trucks, the axial length can be for example in the range from 5 mm to 40 mm, in particular 10 mm to 35 mm With regard to the bore length of a bore to be machined, the axial length can be for example less than 20% or less than 10% of this bore length. With regard to the bore diameter of a bore to be machined, the axial length can be for example in the range from 20% to 50% of the bore diameter.

Since, in such an annular cutting group, the cutting material bodies are relatively short in the axial direction compared to conventional honing strips, it is possible, even in the case of stable intermediate layers with a relatively small thickness (for example 0.5 mm to 1.5 mm), for sufficiently large inclination angles to be established between the cutting material body and tool axis, with the result that a particular contour-following capability is favored.

If at least three cutting material body carriers are provided in the cutting group, the machining forces over the entire effective outside diameter, available by expansion, of the honing tool can be distributed well and relatively uniformly around the circumference of the cutting group. It is possible for example for exactly three, exactly four, exactly five, exactly six, exactly seven or exactly eight cutting material body carriers of the same or different circumferential width to be provided in the cutting group. Although more than eight cutting material body carriers within a cutting group are possible, they make the construction more complicated and are generally not required. In some cases, it may even be sufficient for the honing tool to have only two cutting material body carriers.

There are exemplary embodiments in which all the cutting material body carriers or all the cutting material bodies of the honing tool can be radially fed with a single common feed. Such honing tools are referred to as honing tools with single expansion. Other embodiments are characterized in that the honing tool is designed as a honing tool with double expansion. In such honing tools, the cutting group comprises a first group of cutting material body carriers and a second group of cutting material body carriers that is separate therefrom, wherein the first group and the second group are feedable independently of one another. When a honing tool with double expansion is used, fine machining methods are possible in which in each case the cutting body material carriers of one group are radially fed and retracted jointly. As a result, it is possible for example for one of the groups to be taken out of engagement with the bore inner face by retraction, such that the bore inner face is machined only by the other group. It is also possible to machine the bore inner face simultaneously with all cutting material bodies of the first and the second group.

The use of a honing tool with double expansion provides potential for shortening cycle times, since tool changes between successive different honing operations can potentially be dispensed with. In some embodiments, a prior first honing operation is first of all carried out with the first group, this first group is then retracted, the other group (second group) is radially fed outwards, preferably at the same time as the retraction of the first group, and then a following second honing operation is carried out with the cutting material bodies of the second group.

Overall, the cutting material bodies of the first and the second group can have different removal characteristics or other properties intended for material removal. For example, the cutting material bodies of the two groups can have different widths and/or have been applied to the respectively associated cutting material body carriers with different circumferential spacings and/or a different pitch. Alternatively or additionally, it is also possible for the cutting material bodies of one of the groups to be provided with coarser grain for rougher machining and the cutting material bodies of the other group to be provided with finer grain for finer machining Therefore, it is possible, for example, to carry out a pre-honing operation with substantial material removal and a following finish-honing operation with less or almost no material removal, mainly to smooth the previously structured surface, one after the other with the same honing tool.

Some embodiments of honing tools with double expansion are distinguished by the fact that, in the first group, the cutting material bodies are fastened directly to the associated cutting material body carrier without interposition of an elastic intermediate layer and as a result are connected rigidly to the cutting material body carrier, whereas, in the second group, the cutting material bodies are fastened to the associated cutting material body carrier in an individually elastically resilient manner via an elastically resilient intermediate layer. With the double expansion, it is possible, for example, to use the first group first of all in order to carry out a first honing operation, which is designed as a contour honing operation, in order to change the axial contour of the bore in a targeted manner starting from a prior machining operation. Then, the first group can be taken out of engagement and the second group put into engagement with the bore inner face, in order to carry out a second honing operation in the form of a tracking honing operation with the second group, in which only weakly abrasive cutting material bodies that are held in an elastically resilient manner substantially track the previously created contour and primarily improve the surface structure.

The invention also relates to a fine machining method for machining the inner face of a bore in a workpiece, in particular for fine machining cylinder surfaces in the production of cylinder blocks or cylinder liners for reciprocating piston engines. In the course of the fine machining method, at least one honing operation is carried out in which an expandable honing tool is moved up and down within the bore in order to create a reciprocating movement in the axial direction of the bore and at the same time is rotated in order to create a rotary movement superimposed on the reciprocating movement. In this honing operation, a honing tool according to the claimed invention is used. This honing operation is preferably the last fine machining operation of a multistage fine machining method and determines substantially the surface structure of the end product.

Before the start of the honing operation, a bore shape that differs significantly from a circular-cylindrical shape can be created by fine boring (with a geometrically determined cutting edge), honing (with geometrically undetermined cutting edges) or by a combination of both fine machining methods (for example first fine boring, then honing). The bore can be premachined for example such that, before the start of the honing operation, it is given an axial contour profile (for example barrel shape, bottle shape or cone shape) and/or one or more portions with a deliberately non-round shape (for example oval shape or trefoil shape). The honing operation can then be carried out in a substantially shape-maintaining way such that the finally desired surface structure is created at the bore inner face, using the honing tool, substantially without changing the macro shape of the bore. In the process, the cutting material bodies track the previously defined surface form or follow the latter, wherein the individually resilient mounting of the individual cutting material bodies results in a particularly good suitability for tracking.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG. 1 shows an oblique perspective schematic view of one embodiment of a honing tool according to the claimed invention;

FIG. 2 shows a schematic sectional illustration through a part of a cutting material body carrier, on the outer side of which a plurality of cutting material strips are fastened in each case with interposition of an elastically resilient intermediate layer;

FIG. 3 shows a schematic illustration of a machining situation in the region of a transition between a cylindrical and a conical portion of a rotationally symmetric bore with an axial contour profile;

FIG. 4 shows an axial view of another embodiment of a honing tool;

FIG. 5 shows a schematic sectional illustration through a part of a cutting material body carrier, on the outer side of which an elastically resilient layer has been applied, which carries a plurality of cutting material bodies, and an enlarged detail;

FIG. 6 shows, in 6A and 6B, a first exemplary embodiment with a laterally inhomogeneous intermediate layer; and

FIGS. 7-9 show further exemplary embodiments with a laterally inhomogeneous intermediate layer.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The schematic FIG. 1 shows an oblique perspective illustration of a honing tool 100 according to one embodiment of the invention. The honing tool serves to machine an inner face of a bore in a workpiece by means of honing and, in the case of the example, is designed to hone cylinder surfaces in the production of cylinder blocks or cylinder liners for reciprocating piston engines. The honing tool is particularly suitable for also machining rotationally symmetric bores that have bore portions with different diameters and/or different forms, for example bottle-shaped bores, barrel-shaped bores and/or bores that have at least one conical bore portion with an axially continuously changing diameter. However, the honing tool can also be used to machine circular-cylindrical bores, i.e. rotationally symmetric bores without an axial contour profile.

The honing tool has a tool body 110, manufactured from a steel material, that defines a tool axis 112, which is at the same time the axis of rotation of the honing tool during machining by honing. Located at the spindle-side end of the honing tool is a coupling structure 120 for coupling the honing tool to a drive rod or a working spindle of a honing machine or some other machine tool that has a working spindle which is rotatable about the spindle axis and is also movable back and forth in an oscillating manner parallel to the spindle axis.

In exemplary embodiments, for use on the working spindle of a machining center, it is possible for example for a coupling structure in the manner of a hollow shank taper or a cone of some other type to be provided.

Located in the end portion of the tool body that is remote from the spindle is an expandable annular cutting group 130 having a multiplicity of cutting material bodies 140-1, 140-2 etc. that are distributed around the circumference of the tool body and have an axial length LS, measured in the axial direction, that is smaller by a multiple than an effective outside diameter AD of the cutting group 130 with cutting material bodies fully retracted in the radial direction. The cutting material bodies 140-1 etc. are in the form of cutting material strips that are narrow in the circumferential direction and have a width BS, measured in the circumferential direction, that is small compared with the axial length LS of the cutting material strips. An aspect ratio between length LS and width BS can be for example in the range from 4:1 to 20:1. Expressed in absolute terms, the length can be for example in the range from 10 mm to 20 mm and the width in the range from 2 mm to 5 mm.

The honing tool has only one annular cutting group 130. The latter is arranged more or less flush with the end of the tool body remote from the spindle, such that it is also possible, if required, to machine blind bores right to the bottom of the bore. Illustrated by dashed lines is an optionally present slender coupling portion at the end of the honing tool remote from the spindle. This coupling portion can be used as a coding element for example during an automatic tool change.

The cutting group or the cutting material bodies of the cutting group are feedable radially with respect to the tool axis by means of a cutting group feeding system assigned to the cutting group. Since this functionality, which is typical for honing tools, is known per se, the components (for example feeding rod(s), expansion cone etc.) provided for this purpose are not described in more detail here.

The expandable annular cutting group 130 comprises a plurality of radially feedable cutting material body carriers 150-1, 150-2 etc., which each cover a circumferential angle range that is greater than the axial length LS of the cutting material bodies or of the cutting group. In the case of the example in FIG. 1, six cutting material body carriers 150-1 to 150-6 are provided, which each cover a circumferential angle range of between 45° and 60° and are arranged regularly around the circumference of the honing tool.

Between directly adjacent cutting material body carriers, respective non-cutting guide strips 115-1 etc. are fastened to the tool body. FIG. 1 shows the honing tool 100 with retracted cutting material bodies, such that the outer faces, serving as guide faces, of the guide strips project beyond the abrasive outer faces of the cutting material bodies in a radial direction. Before and/or during the machining by honing, the cutting material body carrier elements are fed radially outward, such that they pass into engagement with the inner face to be machined of the bore.

The cutting material body carriers are, in the case of the example, produced in one piece from a steel material and are therefore inherently substantially rigid. Each cutting material body carrier has a carrier portion 152-1 etc. that is relatively wide in the circumferential direction and has a cylindrically curved outer side 154 and a substantially planar inner side, facing the tool body, from which a plate-form feeding portion 156 projects inwardly. Located on the inner side, remote from the outer side 154, of the feeding portion is a sloping surface that cooperates with a corresponding sloping surface of an axially displaceable feeding cone in the manner of a wedge drive, such that an axial movement of the feeding rod in the interior of the tool body causes a radial movement of the cutting material body carrier. The feeding portion 156 of the cutting material body carrier sits in a radially movable manner in a substantially rectangular cutout in the tool body, such that a radial movement is possible but tilting movements in a transverse direction thereto are largely avoided. The cutting material body carriers are pretensioned into the inwardly retracted position with the aid of a plurality of encircling coil springs, such that the radial outward feeding takes place counter to the force of these restoring springs.

There are exemplary embodiments in which all of the cutting material body carriers or all of the cutting material bodies of the honing tool can be fed radially with a single common feed (honing tools with single expansion).

The exemplary embodiment of the honing tool 100 in FIG. 1 is a honing tool with double expansion. The annular cutting group 130 has two mutually independently feedable groups of cutting material body carriers, wherein the three cutting material body carriers of one group are each circumferentially offset through 120° with respect to one another such that, between two adjacent cutting material body carriers of one of the groups, a cutting material body carrier of the other group is arranged.

For the honing tool, particular design precautions are taken, which can help to optimize the machining result on the bores machined with the honing tool, such that the desired surface structure can be created with relatively uniform quality along the entire bore length, in particular including in the region of transitions between bore portions of different form and/or in the region of turning points of the axial honing movement.

As is apparent from FIG. 1, each cutting material body carrier has, on its radial outer side 154, a plurality of cutting material bodies in the form of cutting material strips, which are arranged at a mutual circumferential spacing from one another. These cutting material body groups or strip groups of cutting material strips applied jointly to a cutting material body carrier can consist for example of between three and ten cutting material strips. In the case of the example, seven cutting material strips are arranged at a uniform circumferential spacing from one another on each cutting material body carrier. The circumferential spacing in the case of the narrower cutting material strips is approximately of a similar size to or greater than the width of the cutting material strips, and in the case of the wider cutting material strips is approximately the same size as or less than the width of the cutting material strips.

The cutting material bodies are not connected rigidly to the cutting material body carriers carrying them. Rather, between each of the cutting material strips and the cutting material body carrier carrying the cutting material strip, there is an intermediate space in which an elastically resilient intermediate layer 160 is arranged, which fills the intermediate space between the cutting material strip and the cutting material body carrier element substantially completely. The elastically resilient intermediate layer has the effect that the cutting material bodies, when externally loaded, can move to a limited extent relative to the cutting material body carrier and to a limited extent counter to the restoring force by the intermediate layer. The cutting material strips in this case each have individual flexibility, in other words can each move slightly, independently of the adjacent cutting material strips.

In the case of the example, the intermediate layer has a layer thickness SD of about 1 mm, with the result that a good compromise between sufficient resilience and sufficient stability of the cutting material bodies to transverse forces is achievable. The intermediate layer consists substantially of a rubber-elastic polyurethane elastomer with a hardness in the hardness range of between 75 and 85 Shore A. Suitable elastic polyurethane plastics are commercially available for example under the trade names Vulkollan® or Urepan®. The intermediate layer material is pore-free, i.e. impermeable, and so no cooling lubricant can penetrate and the elastic properties are maintained in a long-lasting manner The material is also chemically resistant to cooling lubricants and also sufficiently mechanically resistant, in the harsh machining environment, to the abrasion caused by the machining by honing.

It is possible, in the production of the honing tool, to first of all stick prefabricated narrow thin strips of the intermediate layer material to the outer side of the cutting material body carrier and then to stick on the strip-form cutting material bodies (cutting material strips), provided therefor, with a suitable adhesive.

In one variant of the production, there is no adhesion promoter between the intermediate layer material and the cutting material bodies. In this variant, first of all a plate made of cutting material body material is produced. Then, a layer made of the precursor of the finished intermediate layer material is vulcanized onto the side intended to be the fastening side (contact side), such that, as a result of the vulcanization, mechanically firm adhesive contact arises between the cutting material body material and the intermediate layer material. Subsequently, the individual cutting material bodies, each provided with an intermediate layer, can be produced by dividing up the coated cutting material body plate. It would also be possible to provide individual cutting material strips in each case on one side with a vulcanized-on elastomer layer and then to stick them to the cutting material body carrier element.

It is also possible to first of all coat the outer side of a cutting material body carrier element with a layer of intermediate layer material more or less over its entire surface (for example by sticking it on) and then to fasten the cutting material strips at the points provided therefor by adhesive bonding. The intermediate layer material is then exposed between adjacent cutting material strips (cf. FIG. 5).

For the production of an extensive adhesive bond between a cutting material body and a strip made of elastic intermediate layer material and/or an adhesive bond between an intermediate layer made of polyurethane plastic and the outer side of the cutting material body carrier element, in preferred embodiments, an acrylate-based viscoplastic two-component construction adhesive is used. The adhesion that is obtainable as a result is distinguished by high adhesive strength. Furthermore, the adhesive layer is inherently slightly elastic, such that a multilayer elastically resilient intermediate layer is produced, which affords good adhesion even after long-term alternating stress.

An improvement in the adhesive strength can be achieved when those faces of the intermediate layer material, of the cutting material body carrier and/or of the cutting material body that come into contact with the adhesive have a relatively rough surface structure. The surfaces can potentially be roughened before adhesive application by sanding, sand blasting or in some other way, for example to average roughness depths in the range from R_z=15 μm to R_z=30 μm.

As a result of the interposition of an elastically resilient intermediate layer between the cutting material strips and the cutting material body carrier elements, the contour-following capability of the honing tool during machining and/or the creation of bores with an axial contour profile can be generally improved, since the cutting material strips align themselves to some extent with the rigid cutting material body carrier element and can thus achieve more uniform contact pressure with the bore inner face.

A particular phase of the machining is schematically illustrated in FIG. 3. A detail of a workpiece 300 in the form of an engine block (crankcase) for an internal combustion engine can be seen. The bore 320 to be machined is delimited by a bore inner face 322. The bore inner face is the workpiece surface to be machined during the machining by honing. The bore 320 is rotationally symmetric with respect to its bore axis (not illustrated) and extends along a bore length from the illustrated bore inlet 314, facing the cylinder head in the installed state, to an axially opposite bore outlet. The bore can be subdivided into a plurality of bore portions of different function that axially adjoin one another and transition into one another seamlessly, i.e. without forming steps or edges. Directly at the bore inlet 314 there begins a first bore portion 322, which, after completion of machining, is intended to have a substantially circular-cylindrical form, i.e. not to have an axial contour profile. This circular-cylindrical bore portion is adjoined in the direction of the opposite bore end by a conical second bore portion 324, in which the bore diameter increases continuously from the inlet side in the direction of the outlet side. The conical bore portion can extend as far as the bore outlet. It is also possible for a further substantially circular-cylindrical portion to adjoin the conical bore portion, said substantially circular-cylindrical portion then having a larger diameter than the inlet-side first bore portion 322. In such a case, the bore would then at least approximately have a bottle shape. The transition regions between the bore portions are (unlike in the schematic drawing) continuously curved. There can be convex or concave transition regions.

FIG. 3 shows a phase of the machining by honing, in which the annular cutting group 330, for example during a downward movement from the bore inlet 314 in the direction of the bore outlet, is located at the level of a transition portion 323 between the circular-cylindrical first bore portion 322 and the downwardly following conical second bore portion 324. The transition portion generally has a slight rounding with a suitable transition radius, i.e. is not sharp-edged. A leading part of the cutting material bodies 140, coming from the cylindrical bore portion, has already reached the conical bore portion, in which the bore is widened and the lateral surface of the bore is at an angle or inclined with respect to the bore axis. Here, axially irregular loading can occur and this can result in a tilting moment and potentially slight tilting of the cutting material carrier 150. The elastically resilient intermediate layer 160 can compensate for some of this tilting in that the upper part is compressed more greatly than the leading lower part towards the bore end. As a result, even during the machining by honing of the conical bore portion, relatively uniformly distributed machining forces can arise, and so the surface structure can remain relatively uniform along the entire bore length, i.e. including both the cylindrical bore portion and the conical bore portion and the transition portion.

On account of the elastically resilient intermediate layer, the cutting material bodies are tiltable with respect to the cutting material body carrier in an axial direction (about a tilting axis extending tangentially to the honing tool), as is schematically shown in FIG. 3. Moreover, tilting in the circumferential direction is also possible to a certain extent. This tilting movement can take place for example about a substantially axially parallel tilting axis. As a result, the cutting material bodies can follow the bore inner face almost without constraining forces even when the macroscopic form of the bore inner face differs significantly from a rotationally symmetric form in the machined portion. Thus, it is possible for example for bore portions with an oval form or with a trefoil shape or higher-order non-roundness or having irregular non-rotationally symmetric shapes to be machined by means of honing, by virtue of the individual flexibility of the cutting material bodies, such that a relatively uniform surface structure can be achieved around the entire circumference and/or along the entire length of the bore. This is achieved, inter alia, in that the cutting material bodies can track the defined surface form to a certain extent on account of the elastically resilient intermediate layer, such that contact pressure force peaks, as could occur in the case of cutting material bodies fastened rigidly to the cutting material body carrier, are alleviated or avoided. Thus, in spite of a non-round bore and/or axial bore contour, a relatively uniform cutting depth can be achieved over the entire bore inner face. This can be favorable both for largely smooth final surfaces and for surfaces with a plateau structure. In this connection, it is also worth mentioning that the expansion force is generally a multiple of the “spring force” of the intermediate layer. This results in a relatively uniform cutting depth even at “bulges”, which generally represent only radial deviations of a few μm.

In the honing tool 100 with double expansion, the three cutting material body carriers of one group are each circumferentially offset through 120° with respect to one another. The cutting material bodies of one group are preferably identical to one another. The cutting material bodies of a first group differ preferably from the cutting material bodies of a second group. For example, the cutting material bodies of the two groups can have different widths and/or they can have been attached to the cutting material body carriers with different circumferential spacings and/or a different pitch. It is possible for the cutting material bodies of one of the groups to be provided with coarser grain for rougher machining and for the cutting material bodies of the other group to be provided with finer grain for finer machining It is also possible for not all cutting material bodies of an annular cutting group to have been fastened to the associated cutting material body carriers by means of an elastically resilient intermediate layer. It may for example be the case that, in a first group, the cutting material bodies sit directly on the cutting material body carrier without interposition of an elastic intermediate layer and are thus rigidly connected thereto, while, in the other group, the cutting material bodies have been fastened to the cutting material body carrier in an individually resilient manner via an elastic intermediate layer. For example, a first group can be provided, which is provided for contour honing and has cutting strips connected rigidly to the cutting material body carriers, while the second group is provided for a following finishing honing process and is provided with cutting material bodies that are fastened in an elastically resilient manner relative to the cutting material body carrier. In another process chain, it is also possible to configure a first group for an intermediate honing process and the second group for the following finishing honing process, wherein the cutting material bodies of the two cutting groups are fastened to the associated cutting material body carriers in an elastically resilient manner

With reference to FIG. 4, a honing tool 400 according to another exemplary embodiment is explained. FIG. 4 shows the honing tool in an axial view from the end that is remote from the spindle. The honing tool has a single annular cutting group 430, which is arranged in the end region of the tool body remote from the spindle and has a total of eight cutting material body carriers 450-1 to 450-8 that are each feedable radially with respect to the tool axis 412 and each cover a circumferential angle range that is greater than the axial length of the cutting material bodies or of the cutting group. Each of the cutting material body carriers covers a circumferential range of about 40°.

The cutting material body carriers 450-1 and 450-2, together with the respectively diametrically opposite cutting material body carriers 450-5 and 450-6, form a first group of cutting material body carriers that carry relatively narrow cutting strips 440-1. The cutting material body carriers 450-3, 450-4, 450-7 and 450-8 belong to a second group of cutting material body carriers, the cutting material body carriers of which each carry cutting strips 440-2 with a somewhat greater circumferential width. Fastened between directly adjacent pairs of cutting material body carriers are in each case non-cutting guide strips 415-1 etc. Thus, directly adjacent cutting material body carriers of the same group are located next to one another in the circumferential direction without an interposed guide strip, while in each case one of the guide strips is arranged between adjacent cutting material body carriers of different groups.

The four cutting material body carriers of one group can each be radially fed and retracted jointly, and the two groups can be radially fed and retracted independently of one another. Thus, it is possible, with a first group, to carry out a prior first honing operation, then to retract this group, to radially feed the other group, and then to carry out a following second honing operation with the cutting material bodies of the second group.

With reference to FIG. 5, another possible way of fastening individual strip-form cutting material bodies 540-1 etc. to a common cutting material body carrier 552 is explained. In this exemplary embodiment, a thin flexible plate 560′ made of an elastomer (thickness about 1 mm) has been vulcanized or adhesively bonded onto the cylindrically curved outer side 554 of the metal cutting material body carrier 552. The individual cutting material bodies 540-1 etc. are then adhesively bonded onto the outer side of the elastomer layer. To this end, first of all the outer side 562 is roughened by sand blasting, sanding or in some other way to an average roughness depth of e.g. 20 to 40 μm. Furthermore, the rear side 542 of the cutting material body, which is intended to be connected to the elastic intermediate layer, is likewise roughened by means of sand blasting, sanding or in some other way, wherein typical roughness depths are usually in the range between 10 μm and 20 μm. The adhesive for the adhesive layer 565 can be applied on one side or both sides before the respective cutting material body is pressed at the intended point onto the outer side of the elastomer plate until the adhesive has cured. As a result of the surfaces of the cutting material body and of the elastomer plate that adjoin the adhesive layer 565 being roughened, the long-term adhesive strength can be increased considerably compared with surfaces that have not been roughened. This flexible plate 560′ forms an elastomer layer that forms a multilayer intermediate layer 560 with an (or at least one) adjoining adhesive layer 565.

In the region between the cutting material body carrier and the cutting material body carried by the intermediate layer, the intermediate layer can have spatially homogeneous elasticity properties, this being able to be achieved for example in that an intermediate layer made of homogeneous elastic material completely fills the intermediate space. It is also possible for the intermediate layer to be designed such that, in that region that carries a cutting material body, it is designed in a spatially inhomogeneous manner and/or has inhomogeneous elasticity properties, i.e. elasticity properties that can change from place to place over the face used for carrying a cutting material body.

By way of example, FIGS. 6A and 6B and FIG. 7 to FIG. 9 show a number of variants of exemplary embodiments with spatially, in particular laterally inhomogeneous intermediate layers. The intermediate layer 660, which is shown in FIG. 6A in vertical section and in FIG. 6B in plan view, was manufactured from a flat plane-parallel piece of elastomer material, into which blind bores 662 of different depth and/or size were introduced at a defined pitch from the side intended for carrying a cutting material body 640, for example by mechanical boring or by laser machining The holes can be distributed regularly or irregularly. They can also all have the same depth and/or the same diameter. The cutting material body 640 is adhesively bonded to the multiply perforated free surface and closes the holes off from the outside such that the intermediate layer is protected circumferentially and from above and below from the penetration of honing sludge or the like into the cavities.

FIG. 7 shows a plan view of a flat intermediate layer 760 manufactured from elastomer material, which is configured in the manner of a circumferentially closed frame with a single long inner cavity 762. After the associated cutting material body has been stuck on, this cavity is also closed off on all sides.

In the variant of the intermediate layer 860 in FIG. 8, obliquely extending slots 862 have been introduced into the original flat material made of elastomer, these slots 862, in a similar manner to the bores in FIG. 6A, being circumferentially closed and thus protected from the penetration of honing sludge etc. after the carried cutting material body has been stuck on.

These are a number of examples of intermediate layers that have more or less large cavities of different and/or identical shape and/or size and as a result tend to be more elastically resilient than the corresponding solid elastomer material, into which the cavities (bores, slots or the like) have been introduced. Intermediate layers made of closed-pore elastomer material are also possible, i.e. elastomer material in which there are already cavities that are enclosed on all sides (closed pores) after manufacturing.

In an embodiment in FIG. 9, the elastomer material of the intermediate layer 960 completely fills the intermediate space between the cutting material body carrier and cutting material body 940. The elastomer material is laterally structured and has a sequence of mutually adjacent strips 964-1 made of a relatively softer elastomer material and 964-2 made of a relatively harder elastomer material.

The examples in FIGS. 6 to 9 illustrate that there are different possible ways of adapting the elasticity properties of the intermediate layer exactly to the intended use of the honing tool provided therewith by way of simple means. In the examples, to this end, in each case one layer of elastomer material that has been laterally structured by means of cavities and/or irregular material distribution is provided. The layer thicknesses that determine the spacing between the cutting material body carrier and cutting material body in the unloaded state are usually in the range from 0.1 to 2 mm, in particular in the range from 0.5 to 1.5 mm.

The advantages of honing tools according to the invention can be achieved regardless of the type of pre-machining of the bore to be honed. Before the start of the honing operation in which the honing tool is used, a bore shape that differs significantly from the circular-cylindrical shape can be created by fine boring and/or by honing. With the aid of the honing operation, it is then possible, on account of the use of a honing tool with individually elastically resilient cutting material bodies, to produce the surface structure desired on the bore inner face, substantially without changing the previously defined macro shape of the bore.

HONING TOOL AND FINE MACHINING METHOD USING THE HONING TOOL

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