US20220055177A1

US20220055177A1 - Honing tool and fine machining method using the honing tool

Info

Publication number: US20220055177A1
Application number: US17/428,905
Authority: US
Inventors: Florian Kranichsfeld; Joachim Weiblen
Original assignee: Elgan Diamantwerkzeuge GmbH and Co KG
Current assignee: Elgan Diamantwerkzeuge GmbH and Co KG
Priority date: 2019-02-05
Filing date: 2020-01-29
Publication date: 2022-02-24
Also published as: EP3921118A1; EP3921118C0; CN113474120B; DE102019201465A1; WO2020160983A1; EP3921118B1; CN113474120A

Abstract

A honing tool (100) for machining an inner face of a bore in a workpiece with the aid of at least one honing operation comprises a tool body (110) that defines a tool axis (112); a first cutting group (160-1), attached to the tool body, having a plurality of radially feedable first carriers (150-1) that are feedable radially with respect to the tool axis (112) by means of an associated first cutting group feeding system (170-1), wherein each first carrier covers, on its radial outer side, a circumferential angle range of at least 20° and carries, on its outer side (154), a single first cutting material body that is wide in the circumferential direction or a plurality of narrow first cutting material bodies (140-1), which are arranged in a manner spaced apart from one another; and a second cutting group (160-2), attached to the tool body, having a plurality of radially feedable second carriers (150-2) that are feedable radially with respect to the tool axis (112), independently of the first carriers (150-1), by means of an associated second cutting group feeding system (170-2), wherein each second carrier (150-2) carries, on its radial outer side (154), a single narrow second cutting material body (140-1, 140-2). All the cutting material bodies (140-1, 140-2) of the first and the second cutting group are arranged in an axially short cutting region (130) that has a length, measured in the axial direction, which is much less than an effective outside diameter of the cutting groups with the cutting material bodies fully retracted.

Description

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, and at the same time rotated in order to create a rotary movement superimposed on the reciprocating movement. The cutting material bodies attached 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 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.
With increasing demands being made of the economy and environmental friendliness of motors, 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 provide good sealing around the entire bore circumference.
DE 10 2013 204 714 A1 discloses honing tools that are suitable, inter alia, for machining rotationally symmetric bores that have bore portions with different diameters and/or forms. Thus, it is possible for, for example, rotationally symmetric bores having a bottle shape, a cone shape or a barrel shape to be machined and/or created. The honing tool has an annular expandable cutting group with a plurality of cutting material bodies which are distributed around the circumference of the tool body and the axial length of which, measured in the axial direction (parallel to the tool axis), is less than an effective outside diameter of the cutting group with the cutting material bodies fully retracted. The cutting group has a plurality of radially feedable carriers, which carry, on their radial outer sides, cutting material bodies in the form of honing segments, 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 creating an axial contour and/or for following a pre-existing axial contour of the bore. Moreover, short axial lengths of the cutting group may be advantageous in order to create sufficient surface pressure for machining. Since the cutting group has a plurality of radially feedable carriers, which each cover a circumferential angle range that is greater than the axial length of the cutting group, it is, inter alia, possible for, for example, cross bores in the wall of a cylinder running surface to be able to be bridged in the circumferential direction during honing, such that, in spite of an axially short cutting material body, 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.
The Applicant's DE 10 2014 212 941 A1 discloses similar honing tools with an annular cutting group which is relatively short in the axial direction and in which a large part of the circumference is provided with abrasive. A guide group with feedable guide strips is additionally provided. The annular cutting group has carriers that are relatively wide in the circumferential direction and can be radially fed jointly via a feeding system. In some exemplary embodiments, the outer sides of the carriers are provided with a shell-like full layer (honing segment). It is also possible for the outer sides each to carry cutting material bodies with axial longitudinal grooves such that the radially external cutting faces are interrupted multiple times in the circumferential direction. Variants are also described in which a plurality of relatively narrow honing strips are fastened to the outer side, curved in a circular-arc shape in the circumferential direction, of the rigid carriers, said honing strips being circumferentially spaced apart from one another such that groove-like gaps are formed between the honing strips. As a result of the grooves or gaps, efficient supply and discharge of cooling lubricant and discharging of abrasion dust is possible.
It has been observed that, in certain cases when machining non-cylindrical bores (for example rotationally symmetric 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, it is possible for, for example, oil consumption and blow-by to 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. In the vicinity of 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

A problem addressed by the present invention is to provide a honing tool of the type in question and a fine machining method that can be carried out therewith, these making it possible to machine bores with different forms such that the machined bore faces have a well-defined 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 of the claims is made part of the content of the description by reference.
The honing tool has a tool body that defines a tool axis. Directions parallel to the tool axis are denoted “axial direction”. Attached to the tool body are two cutting groups that are feedable independently of one another, specifically a first cutting group and a second cutting group. The first cutting group has a plurality of first carriers that are feedable radially with respect to the tool axis by means of an associated first feeding system. The first carriers each cover, on their radial outer side, a relatively wide circumferential angle range of at least 20°.
The circumferential angle range covered by a first carrier can be for example 25° or more or 30° or more. Preferably, the circumferential angle range is at most 120° or at most 90°.
The number of the first carriers can vary from embodiment to embodiment, for example depending on the circumferential width thereof. Preferably, three or more first carriers are provided, for example three, four, five or six first carriers, and optionally also only two first carriers.
The first carriers carry, on their relatively wide radial outer sides, either a single first cutting material body that is relatively wide in the circumferential direction, for example in the manner of a shell-like full layer with a continuous (uninterrupted) cutting face or a cutting face interrupted by grooves, or a plurality of narrow first cutting material bodies that are arranged in a manner spaced apart from one another (in the circumferential direction). Usually, all the first carriers have the same type of first cutting layer (full layer, optionally with grooves or a strip group with a plurality of narrow first cutting material bodies), this not necessarily having to be the case, though.
The second cutting group, likewise attached to the tool body, has a plurality of second carriers that can be fed radially with respect to the tool axis by means of an associated second feeding system. Each of the second carriers carries, on its radial outer side, in each case only a single narrow second cutting material body.
The term “cutting material bodies” describes the abrasive elements of the honing tools. In honing tools, a cutting material body, which can also be referred to as cutting layer, consists substantially of irregularly shaped cutting grains of different shapes and sizes that are bound within a bonding system. As a result of the selection of the type of cutting layer, a honing tool can be adapted particularly precisely to the desired machining task. Cutting grains can be for example diamond grains or grains of cubic boron nitride (CBN). Cutting grains can also consist of corundum and/or other types of ceramic materials, such as for example SiC. The bonding can consist for example of a ceramic material or of synthetic resin. Metal bonding systems, for example galvanically created bonds or sintered bonds, are also possible, and optionally also soldered bonds.
The term “narrow” means, in connection with cutting material bodies, that the width of the (narrow) cutting material bodies in the circumferential direction is much less than a length measured in the axial direction. An aspect ratio between the (axial) length and the width (measured in the circumferential direction) can be, for example, in the range of 5 or more, in particular in the range from 8 to 25. Narrow cutting material bodies are frequently also referred to as cutting strips or honing strips. Expressed in absolute terms, the narrow first cutting material bodies can have for example circumferential widths in the range from 1.5 mm to 5 mm, and optionally also thereabove or therebelow.
A first cutting material body that is relatively wide in the circumferential direction compared with the latter and can be designed for example in the manner of a shell-like full layer has preferably a much lower aspect ratio, which may be for example in the range of 3 or less, and optionally also 1 or below, such that the width in the circumferential direction can be greater than the axial length.
The optimal dimensions of the cutting material bodies are generally dependent on the effective diameter of the honing tool, or on the diameter of the bore to be machined.
The cutting material bodies of the first cutting group and of the second cutting group are arranged in an axially relatively short cutting region. The cutting region has a length, measured in the axial direction, that is much less than an effective outside diameter of the cutting groups with the cutting material bodies fully retracted. “Much less” means here that the axial length or extent of the cutting region is at most 80% of the effective outside diameter of the cutting groups. Put another way, “much less” thus means: at least 20% less. The axial length can be, for example, less than half the size of the effective outside diameter. The first cutting material bodies and the second cutting material bodies are thus arranged such that they are all entirely within a relatively short cutting region as seen in the axial direction. On account of the relatively short axial length of the cutting region, such honing tools are particularly suitable for creating bore forms with an axial contour, i.e. a different diameter in the axial direction. Alternatively or additionally, they can also be used to follow such a pre-existing axial contour of the bore.
The axial length or extent of the cutting region can be for example less than 40% of the effective outside diameter of the cutting groups and/or less than 20% of the bore length of the bore.
Investigations by the inventors have shown that the particular distribution of cutting material bodies on the first and second carriers affords particular advantages. Each of the first carriers covers, with the first cutting material bodies attached thereto (for example a wide full layer or a plurality of narrow, strip-like cutting material bodies per carrier), a certain, relatively wide circumferential region. It has been shown that, during machining by honing with the aid of the first cutting group, particularly good roundness values of the created bore can be achieved, among other things. In the variants with a plurality of narrow cutting material bodies per first carrier, on account of the multiplicity of first cutting material bodies, which are simultaneously engaged with the bore inner wall, good service lives arise even in the case of shaping involving heavy material removal. In the variants with relatively wide first cutting material bodies, relatively efficient material removal with low wear is likewise possible.
The second cutting group with individual, relatively narrow cutting material bodies affords other advantages according to the inventors' findings. Thus, it has been found that individual second cutting material bodies that are feedable individually in different radial directions tend to be able to bear more fully (better, more uniform surface contact) on a present surface than first cutting material bodies, which can be pressed in a common radial direction against the bore inner wall only jointly or in groups per second carrier. As a result, particularly high surface qualities are achievable.
The total cutting area of the second cutting group can be smaller than the total cutting area of the first cutting group. This can be favorable in particular when only relatively little substantial material removal is intended to be achieved with the second cutting group, for example when plateau honing or when smoothing a surface previously machined with coarser abrasive.
In terms of type and dimensioning of the cutting material bodies, the first and the second cutting group can be adapted to one another and to the honing process such that they wear away more or less equally greatly or equally quickly during the intended honing process. This is favorable, among other things, for economical refitting.
In many embodiments, the number of second cutting material bodies is greater than the number of first cutting material bodies, in order, among other things, to obtain comparable service lives and overlaps.
In the variants with a plurality of narrow cutting material bodies per first carrier, more than two first cutting material bodies are preferably attached to the radial outer side of a first carrier, for example three, four, five, six, seven or more first cutting material bodies. From experience, between three and seven first cutting material bodies per carrier are frequently advantageous.
The mutual spacing between immediately adjacent first cutting material bodies is, in some embodiments of these variants, in the order of the circumferential width of the cutting material bodies or therebelow. When the mutual spacing is less than the circumferential width of the first cutting material bodies, a relatively high surface proportion, as seen in the circumferential direction, of the abrasive material of the first cutting material bodies can be ensured, and so a high level of material removal with a simultaneously low level of wear is possible. Removed material chips can be discharged readily by means of cooling lubricant through the channels located between the first cutting material bodies, and so the risk of the abrasive outer faces of the cutting material bodies becoming clogged can be kept low.
Preferably, the first cutting material bodies carried by a first carrier cover as a whole, with their external cutting faces, a circumferential angle range that corresponds to at least 30% or at least 50% of the circumferential width of the carrier, such that, in the case of the first cutting group, as seen in the circumferential direction, a relatively large total cutting area can be used and thus optionally a relatively high removal capacity can be achieved with a long service life.
It may suffice for the second cutting group to have relatively few narrow second cutting material bodies that are feedable in different radial directions, for example four, six, eight or ten second cutting material bodies. The second cutting material bodies can be distributed symmetrically or asymmetrically around the circumference of the honing tool.
First carriers and second carriers and the associated cutting material bodies are, in some embodiments, arranged on the tool body alternately in the circumferential direction. The distribution in the circumferential direction can vary. Preferably, at least one second carrier is arranged between first carriers that are adjacent in the circumferential direction. It may be that exactly one second carrier with an associated second cutting material body is arranged between a pair of immediately adjacent first carriers. At another point on the circumference and/or in another embodiment, it may be the case that two or more second carriers are arranged between immediately adjacent first carriers, such that there are second carriers that are immediately adjacent in the circumferential direction. In this way, the density, as seen in the circumferential direction, of the second carriers and/or of the second cutting material bodies carried thereby can be optimized for any application.
A uniform distribution, as seen in the circumferential direction, of first and second carriers is possible. In many embodiments, however, the first carriers and the second carriers are arranged in a manner distributed irregularly in the circumferential direction, in particular such that circumferential angles in between vary.
Preferably, the arrangement is such that in each case pairs of the same type of carriers and cutting material bodies are arranged in diametrically opposite positions on the circumference, such that during feeding, on account of this symmetry, no transverse forces that result from the design arise, which may result in undesired deflection of the honing tool during machining.
The first cutting material bodies and the second cutting material bodies can have the same length in the axial direction. If, furthermore, all of them are arranged in the same axial portion, the axial length of the cutting region results from the axial length of the first and second cutting material bodies. The first and second cutting material bodies can also be axially offset slightly with respect to one another, such that the axial length of the cutting region can be somewhat greater than the axial length of the longest of the cutting material bodies.
In one embodiment, the first cutting material bodies are shorter in the axial direction than the second cutting material bodies. The axial length of the first cutting material bodies can be for example less than 80% or less than 70% of the axial length of the second cutting material bodies, but as a rule not less than 50% of this length. In this way, it is possible for the first cutting group, in the fed state, i.e. when machining the bore inner face, to act in an effective first cutting region that is shorter than the cutting region of the honing tool. In this way, it is possible for, for example, bore portions that have a relatively great change in diameter (small radii) in the axial direction to be machined particularly readily. It is also possible for second cutting material bodies to be shorter in the axial direction than first cutting material bodies.
In some embodiments, the second cutting material bodies are mounted in an elastically resilient manner with regard to the tool body. As a result of being mounted in an elastically resilient manner, the capability of the second cutting material bodies to follow the contour without contact pressure peaks can be improved, this being able to have a positive effect on the quality of the achievable surfaces. The elastic resilience can be achieved in different ways. For example, it is possible to work within the second feeding system as far as the carrier without design-related resilience and to provide elastic resilience between the carrier and carried cutting material body. This can be achieved for example in that an elastically resilient intermediate layer is arranged in a gap between a cutting material body and the carrier carrying the cutting material body, said intermediate layer being able to be formed for example by a layer made of an elastomer. The intermediate layer may entirely fill the gap, in order to avoid the penetration of cutting material residues or abrasion dust. With regard to this partial aspect, reference is made to the Applicant's DE 10 2017 202 573 A, which describes possible realizations thereof. The disclosure of that document is, in this regard, made part of the content of the description by reference.
In some embodiments, the elastic resilience is achieved in that the second carriers have, close to or next to a second cutting material body, an elastically resilient portion with (carrier-material-free) cutouts and spring elements formed integrally with the carrier. Compared with likewise possible designs with separate springs within the feeding system, such variants with monolithically integrated spring elements are distinguished, among other things, by the fact that the spring force can be specified with great precision during the manufacture of the carriers. This solution is also extremely robust and durable.
In variants with separate springs for the resilient mounting of the second cutting material bodies and in variants with the cutouts in the carrier material, it may be possible for abrasion dust to pass into the spring region and impair the function. This is prevented, in some embodiments, in that the spring-material-free region is filled, between spring turns or in the cutouts, with an elastically resilient elastomer material or some other elastically resilient filling material. As a result, the spring action is maintained in the long run. As a result of the choice of suitable elastically resilient filling materials, the spring characteristic, for example the “hardness” of springing, can be set precisely. It is possible for some or all of the clearances in the spring region to be filled. These measures can be used independently of the other features of the invention, even in honing tools that are not according to the invention with elastic resilience in the honing tool.
In some embodiments, the honing tool has a guide group with a plurality of guide strips distributed around the circumference of the tool body. These can be attached fixedly to the tool body. Individual, a plurality of or all guide strips can extend at least partially into axial regions outside the cutting region. In some embodiments, the guide strips are arranged only within the cutting region. As a result, it is possible to ensure that, even in bore portions with a diameter that varies greatly axially, the guide strips do not come into undesired contact with the bore inner face. One, a plurality or all of the guide strips can be arranged immediately next to a second carrier, such that the adjacent second carriers are protected by the immediately adjacent guide strip.
A further contribution to achieving high surface qualities is achieved in some embodiments in that the honing tool has an integrated multiaxial joint for coupling the tool body, with limited movability, to a connection piece. Provision is preferably made for an axial spacing between the joint and the cutting region configured with cutting material bodies to be smaller than the effective outside diameter of the cutting groups with the cutting material bodies fully retracted. This results in an axially compact design. Moreover, any tilting moments when an inclined position of the tool axis with respect to the axis of rotation of the drive spindle occurs can be kept low, and the inventors' experience has shown that this can have a positive effect on the surface quality of the honed bore inner face. The axial spacing is measured, in the context of this application, between the plane of the articulation point and the axial end of the cutting region.
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. The fine machining method comprises at least one honing operation, in which an expandable honing tool is moved back and forth 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, wherein, during the honing operation, a honing tool according to the claimed invention is used.
According to one development, a honing operation is carried out as a multistage honing operation, wherein, in a first honing stage, the first cutting group is pressed against the bore inner face and a bore shape that differs from a circular-cylindrical shape and is preferably rotationally symmetric is created by means of the first cutting group, by means of axially irregular material removal, starting from an initial shape, and wherein subsequently, in a second honing stage, the second cutting group is fed and, by means of the second cutting group, a desired surface structure is created on the bore inner face substantially without changing the macro shape of the bore. The honing tool can thus in this case be used without an intermediate tool change both to change the bore shape by means of axially irregular material removal (first honing stage) and, subsequently, with the first cutting group retracted and second cutting group fed, to improve the surface structure of the bore inner face, substantially without further material removal or with at most very little material removal.
Since it is possible to dispense with a tool change between the two honing stages, the cycle time can be reduced considerably compared with methods with a tool change. Moreover, imprecisions that can be caused by a tool change can be avoided.
Preferably, work is carried out with path control in the first honing stage, in order to achieve the desired bore shape with a high level of precision. In the second honing stage, honing is preferably carried out with force control. In this case, provision is made in some variants for honing to be carried out with a substantially constant pressing force along the entire length of the bore, in order to achieve a surface structure that is largely uniform along the entire length.
In other variants, the bore is subdivided in terms of control into at least two adjacent axial bore portions (a first bore portion and at least a second bore portion) and the control is effected such that the honing parameters in the bore portions differ from one another, wherein, for example, honing is carried out with a greater pressure force in one of the bore portions than in another bore portion. As a result, the surfaces in the bore portions can be optimized with regard to different conditions during proper use (for example piston speed in reciprocating piston engines).

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.

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

FIG. 2 shows a view of the honing tool from FIG. 1 in the axial direction looking at the spindle-remote end;

FIG. 3 shows a side view of the honing tool from FIG. 1;

FIG. 4 shows a section, in a radial plane containing the tool axis, through individually feedable second cutting material bodies on the line IV-IV in FIG. 2;

FIG. 5 shows a section, in a radial plane containing the tool axis, through first carriers on the line V-V in FIG. 2;

FIG. 6 shows a section, in a radial plane containing the tool axis, through first carriers of another embodiment;

FIGS. 7 to 10 show different variants of strip-form second carriers, which are configured to be elastically resilient in the region close to the outer face for fastening a cutting material body by way of a pattern of recesses and integral spring elements.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 shows an oblique-perspective illustration of a honing tool 100 according to one embodiment of the invention. The honing tool is used for machining 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 also for 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 a diameter that continuously varies axially. The honing tool can, however, also be used to machine circular-cylindrical bores, i.e. rotationally symmetric bores without an axial contour profile.
The honing tool has a material body 110 manufactured from a steel material, which defines a tool axis 112, which at the same time is the axis of rotation of the honing tool during machining by honing. At the spindle-side end of the honing tool there 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 both rotatable about the spindle axis and movable back and forth in an oscillating manner parallel to the spindle axis. In FIG. 1, the coupling structure 120 is designed as a functional part of a bayonet joint. In exemplary embodiments for use on the working spindle of a machining center, it is possible to provide, for example, a coupling structure in the manner of a hollow shank taper or some other cone.
Located in the end portion of the tool body that is remote from the coupling structure 120 or the (not illustrated) working spindle is the cutting region 130 of the honing tool, in which all abrasive cutting material bodies (general reference sign 140) are attached. Arranged within the cutting region 130 are a large number of cutting material bodies that are distributed around the circumference of the tool body, said cutting material bodies having, in an axial direction extending parallel to the tool axis, an axial length LS which is a multiple smaller than a minimum effective outside diameter AD of the honing tool in the cutting region 130 equipped with cutting material bodies.
In the exemplary embodiment, all the cutting material bodies are in the form of cutting material strips that are narrow in the circumferential direction, the width BS, measured in the circumferential direction, of which is small compared with the axial length LS. An aspect ratio between length LS and width BS can be for example in the range from 4:1 to 25:1.
The honing tool has only a single cutting region 130. This is arranged more or less flush with the spindle-remote end of the tool body in the end portion of the tool body that is remote from the spindle, such that it is optionally also possible to machine blind bores down to the bore bottom.
The honing tool 100 in FIG. 1 is a honing tool with double expansion, which is distinguished by the fact that a first cutting group 160-1 and a second cutting group 160-2 that is feedable independently thereof are arranged on the tool body. The first cutting group 160-1 has a plurality of (in the case of the example exactly four) first carriers 150-1, which can be fed radially with respect to the tool axis 112 in associated radial directions by means of an associated first feeding system 170-1. The second cutting group 160-2 has a plurality of (in the case of the example a total of eight) second carriers 150-2, which can be fed radially with respect to the tool axis 112 in associated radial directions independently of the first carriers 150-1, for which purpose a second feeding system 170-2 is provided.
The carriers 150-1, 150-2 that carry the respective cutting material bodies 140-1 and 140-2 are each one-piece components produced from steel material, which are substantially rigid. Each of the first carriers 150-1 has a carrier portion 152-1 that is relatively wide in the circumferential direction and has a generally cylindrically curved outer side 154-1 and a substantially planar inner side, facing the tool body, a plate-like feeding portion 156-1 projecting inwardly from said inner side. Located on the inner side, facing away from the outer side 154-1, of the feeding portion are oblique faces that cooperate with a corresponding oblique face of an axially displaceable first feeding cone in the manner of a wedge drive, such that an axial movement of the feeding cone in the interior of the tool body results in a radial movement of the carrier. The feeding portion 156-1 of the carrier 150-1 fits in a radially movable manner in a substantially rectangular cutout in the tool body, such that a radial movement (radially with respect to the tool axis 112) is possible, but tilting movements in a transverse direction thereto are largely avoided. The carriers are preloaded into the inwardly retracted position with the aid of a plurality of encircling helical springs, such that the radial feeding takes place toward the outside counter to the force of these restoring springs.
The external carrier portions 152-1 are wide enough in the circumferential direction that the first carriers each cover a circumferential portion of more than 20° of circumferential width, and in the example more than 30°, specifically about 35° of circumferential width. In the event of feeding in the radial direction with respect to the workpiece axis, only the central region, as seen in the circumferential direction, of this carrier portion is fed exactly radially with respect to the tool axis. The regions located further out are fed parallel to this central radial direction, such that there is a small angle deviation between the local radial direction and the actual feeding direction. Therefore, in many embodiments, the circumferential width is no more than 45° or no more than 60° or no more than 90°.
The second carriers 150-2 are much narrower in the region of their radial outer sides 154-2 than the wide carrier portions 152-1. In the case of the example, they each cover a circumferential angle range of less than 10°, wherein, in the case of the example, the circumferential angle range is about 5° to 7°. As seen in absolute terms, the widths can be for example in the range from 1.5 mm to 4.0 mm. The second carriers, like the first carriers, have a plate-like feeding portion, which projects inwardly and has, on its narrowed inner side, oblique faces for cooperating with an axially displaceable feeding cone of a second feeding system 170-2. Here too, the feeding portions fit in a radially movable manner, but so as to be substantially immovable in a transverse direction thereto, in a rectangular cutout in the tool body, such that radial displacement is possible and displacements transversely thereto are prevented.
The first carriers 150-1 each carry, on their radial outer sides, six relatively narrow first cutting material bodies 140-1 in the form of cutting strips, which are fastened, with a mutual circumferential spacing, to the outer side of the carrier portion, for example by adhesive bonding, soldering, screw-fastening or the like. Between the cutting material bodies there are groove-like, axially parallel gaps, the circumferential width of which is less than the circumferential width of the respectively adjacent cutting material bodies. The cutting material bodies cover overall, with their external cutting faces, a circumferential angle range of about half or somewhat more of the circumferential width of the carrier portion, such that there is a relatively high surface density of abrasive cutting faces in the circumferential direction, but interrupted by longitudinally extending gaps, which favor the supply and discharge of cooling lubricant and optionally abrasion dust.
Each of the second carriers 150-2 carries, by contrast, on its outer side only a single relatively narrow cutting material body 140-2, the axial length of which determines the axial length of the cutting region. The circumferential width amounts to only about 20% of the length, but in the example is greater than the circumferential width of the many narrower first cutting material bodies of the first cutting group.
In the example in FIG. 1, the first cutting material bodies 140-1 are only about half as long as the second cutting material bodies (approximately between 40% and 70% of this length) and end, on the side remote from the spindle, at the same height as the second cutting material bodies 140-2. The first cutting material bodies as a result define an effective first cutting region, which is only about half as long as the cutting region 130 the length of which is defined by the length of the second cutting material bodies.
The shorter first cutting material bodies can, in other embodiments, also be arranged approximately in the middle of the cutting region or at an upper end, facing the coupling portion, of the cutting region.
The first cutting material bodies are very wear-resistant and have preferably diamond cutting grains in metal bonding. The second cutting material bodies can be constructed differently, for example with ceramic bonding or synthetic bonding.
The honing tool furthermore has a guide group with a plurality of non-cutting guide strips 180, which are distributed around the circumference of the tool body and are each attached fixedly to the tool body, i.e. are not feedable, in predefined positions. The guide strips, which are oriented parallel to the tool axis, have an axial length that corresponds to approximately the length of the cutting region, and are arranged only within the cutting region 130. The guide strips manufactured for example from hard metal are axially not longer than the cutting material bodies, such that guiding in the axial direction is restricted to that region in which material removal can also take place. There are no guide strips arranged outside the cutting region 130. The guide group has six guide strips, which are distributed uniformly at 60° intervals around the circumference of the tool body 110. The arrangement is such that each of the guide strips 180 is arranged immediately next to an individual second cutting material body 140-2, i.e. an individually feedable cutting material body of the second cutting group. The spacing in the circumferential direction is smaller than the guiding width, measured in the circumferential direction, of the respective guide strips.
Two diametrically opposite guide strips 180-M are designed as measurement strips. In their middle, i.e. half way up the cutting region, they have measurement nozzles 185 of a pneumatic diameter measurement system. These can also be located above or below the middle depending on the application.
Some special features of the honing tool that are not discernible from the outside are discernible from the sectional illustrations in FIGS. 4 and 5. Here, FIG. 4 shows a section through a radial plane that passes through carriers and cutting strips of the second cutting group (with individual strips), while FIG. 5 shows a section through first carriers 150-1 and first cutting strips 140-1 of the first cutting group.
The first feeding system 170-1 has a first feeding element 172-1 in the form of a tube, which is mounted so as to be axially displaceable in the tool body and has, at the end remote from the spindle, two conical portions that are arranged in a manner axially offset from one another. The first carriers 150-1, operatively connected thereto, of the first cutting group have two oblique faces that are axially offset from one another and cooperate with the conical portions in the manner of a wedge drive. As a result, each first carrier is supported on the associated feeding element in two regions that are axially spaced apart from one another, such that tilting of the first carriers is reliably avoided.
Feeding is solved in an analogous manner in the case of the second cutting group. The second feeding system has a second feeding element 172-2 in the form of a rod, which is guided inside the tube (first feed element) so as to be movable relative thereto in an axially displaceable manner. Two conical portions are located in an axially spaced-apart manner at the end of the rod. The second carriers 150-2 have, in a manner corresponding thereto, two axially offset oblique faces on their radial inner side, which cooperate with the corresponding cone faces. As a result, here too, tilting of the second carriers during feeding is reliably avoided in this respect.
As shown in FIG. 6, alternative solutions are also possible, in which for example the first carriers have, on their radial inner sides, only a single oblique face, which cooperates with a cone attached to the feeding element. A similar situation is also possible for the second carriers.
The sectional illustrations in FIGS. 4 to 6 also make a further special feature readily apparent. The honing tool 100 has an integrated joint 190, with the aid of which the tool body 110 is coupled, with limited movability, to the connection piece which serves for connecting to the working spindle of the machine tool. In the case of the example, the joint 190 is in the form of a ball joint, in which the joint ball 192 is formed at the lower end of the connection piece while the corresponding bearing elements having concave spherical bearing surfaces are attached inside the tool body 110. As a result, limited movability of the tool body with respect to the connection piece in an infinite number of directions extending transversely to the tool axis is possible, with the result that the honing tool, in particular when finishing bore inner faces in order to improve the surface quality, can follow the surfaces particularly well. The axial spacing AB between the articulation point (at the center of the joint ball) and the plane, defined thereby, orthogonal to the tool axis and the spindle-remote end of the cutting region 130 equipped with cutting material bodies is smaller than the effective outside diameter AD of the cutting groups with cutting material bodies fully retracted. As a result, the tilting moments that may arise in the event of an offset between the spindle axis and bore axis can be reduced compared with conventional constructions with a larger spacing, this having a positive effect on machining quality.
The second carriers 150-2, which carry the individual cutting material bodies of the second cutting group, can be manufactured entirely as inherently rigid components made of solid material, for example of steel. In particular for tracking non-circular-cylindrical bore inner faces when improving the surface quality by means of the second cutting group, it may be advantageous to incorporate a certain resilience in the force flow in the event of contact pressure of the second cutting material bodies, such that pressure force peaks can be avoided.
In the exemplary embodiments that are illustrated in FIGS. 7 to 10, this is solved in each case in that the plate-like, narrow strip-form second carriers have, in the vicinity of or at the radial outer side that is provided for carrying a narrow cutting material body, an elastically resilient portion 150-2E. The elastic resilience is achieved in these embodiments in that cutouts A of suitable shape, size and distribution are worked out of the initially monolithic carrier by means of electrical discharge machining or in some other way, such that the material adjoining the cutout acts elastically under external load in the manner of a spring, with the result that the outer portion 150-2E as a whole is elastically resilient in the radial direction of the carrier. This solution with integrally formed spring elements FE has proven to be particularly robust and durable. The spring force can be set by suitable dimensioning of the cutouts or remaining spring elements.
A variant of this design is explained with reference to FIG. 8. In this exemplary embodiment, the carrier-material-free cutouts A are not empty but filled entirely with an elastically resilient elastomer material EL. As a result, it is possible to prevent abraded material from getting into the cutouts. Moreover, the spring characteristic can be set precisely by suitable choice of the elastic filling material (elastomer material EL) and damping of any vibrations can be achieved. It is possible, as illustrated, for all cutouts or only some of the cutouts to be filled.
The honing tool can be used for a large number of fine machining methods for machining the inner face of a bore in a workpiece. In a method variant, provision is made to use the honing tool for the fine machining of cylinder surfaces in the production of cylinder blocks or cylinder liners for reciprocating piston engines, in which, starting from a bore with a, for example, circular-cylindrical initial shape, a preferably rotationally symmetric bore having an axial contour profile is intended to be produced, i.e. a bore which has different diameters in different axial portions, these diameters transitioning more or less continuously into one another. The bore shape can be for example a conical bore shape or a bottle-shaped bore shape or barrel-shaped bore shape.
To this end, the honing tool is coupled to the working spindle of a machine tool. The initial shape is circular-cylindrical in the case of the example and can be produced by means of honing or by means of fine machining with a defined cutting edge, for example precision turning. In a first honing stage, the first cutting group is used. After the honing tool has been introduced into the bore with the aid of the first feeding system, said first cutting group is pressed against the bore inner face. By means of the first cutting group, starting from the initial shape, a rotationally symmetric bore shape that differs from the circular-cylindrical shape is then created by axially irregular material removal. To this end, it is possible for example to vary the pressure force depending on the stroke position of the honing tool in the bore by means of the controller such that more material is removed in regions with a higher pressure force, such that larger inside diameters arise than in other regions. Alternatively or additionally, by varying the stroke length of the machining strokes, axially irregular material removal can be created, for example by reducing the axial height of the upper reversal point of the stroke movement while the lower reversal point remains the same.
If the desired rotationally symmetric bore shape has been achieved in the scope of the specification provided for this first honing stage (can be determined for example by means of pneumatic diameter measurement), the first cutting group is retracted and the second cutting group is fed. In the following second honing stage, with the aid of the individual strips, fed individually in different radial directions, of the second cutting group, only little material removal, or almost no material removal, is carried out, and so the macro shape of the bore does not change or does not change substantially, but rather only the desired surface structure arises.
In many cases, the fine machining method is used to create a rotationally symmetric bore shape with an axial contour profile, i.e. axially different diameters, and to generate the suitable surface structure or surface structure distribution thereon without an interim tool change. In principle, it is also possible to use the honing tool to create and/or to machine bore shapes that have a cross-sectional shape other than a circular shape in the at least one bore portion. A bore can, for example, have an oval bore shape or a trefoil shape in at least one portion. Honing tool embodiments that are suitable for this purpose have, preferably, in the first cutting group, i.e. in the one having the first carriers that are relatively wide in the circumferential direction, only a single pair of diametrically opposite first carriers with corresponding first cutting material bodies (for example full layer or a plurality of spaced-apart individual strips). The circumferential width is in this case preferably less than 90 or less than 60°. During the creating of this bore shape, it is possible, for example, for the pressure force to be varied depending on the rotational position of the honing tool, in order to create regions with a larger diameter by increasing the contact pressure in phases and to create regions with a smaller diameter by reducing the contact pressure. If appropriate, methods according to EP 1 815 943 A1 can also be used, applying vibratory movements.

Claims

1. A honing tool for machining an inner face of a bore in a workpiece with the aid of at least one honing operation, in particular for honing cylinder surfaces in the production of cylinder blocks or cylinder liners for reciprocating piston engines, comprising:

a tool body that defines a tool axis;

a first cutting group, attached to the tool body, having a plurality of radially feedable first carriers that are feedable radially with respect to the tool axis by means of an associated first cutting group feeding system, wherein each first carrier covers, on its radial outer side, a circumferential angle range of at least 20° and carries, on its outer side, a single first cutting material body that is wide in the circumferential direction or a plurality of narrow first cutting material bodies that are arranged in a manner spaced apart from one another; and

a second cutting group, attached to the tool body, having a plurality of radially feedable second carriers that are feedable radially with respect to the tool axis, independently of the first carriers, by means of an associated second cutting group feeding system, wherein each second carrier carries, on its radial outer side, a single narrow second cutting material body,

wherein all the cutting material bodies of the first and the second cutting group are arranged in an axially short cutting region that has a length, measured in the axial direction, which is much less than an effective outside diameter (AD) of the cutting groups with the cutting material bodies fully retracted.

2. The honing tool as claimed in claim 1, wherein, in the case of a first cutting material body that is wide in the circumferential direction, an aspect ratio between the axial length and the width measured in the circumferential direction is 3 or less, in particular less than 1, and/or in that, in the case of a narrow first cutting material body and/or in the case of a narrow second cutting material body, an aspect ratio between the axial length and the width measured in the circumferential direction is 5 or more, in particular in the range from 8 to 25.

3. The honing tool as claimed in claim 1, wherein the first cutting material bodies attached to a first carrier cover, with their external cutting faces, a total circumferential angle range that corresponds to at least 30% or at least 50% of the circumferential width of the outer side of the first carrier.

4. The honing tool as claimed in claim 1, wherein each first carrier carries more than two first cutting material bodies on its radial outer side, preferably three, four, five, six or seven first cutting material bodies, and/or in that a mutual spacing between immediately adjacent first cutting material bodies lies in the order of the circumferential width of the first cutting material bodies or less.

5. The honing tool as claimed in claim 1, wherein at least one second carrier is arranged between first carriers that are adjacent in the circumferential direction.

6. The honing tool as claimed in claim 1, wherein the first carriers and the second carriers are arranged in a manner distributed irregularly in the circumferential direction.

7. The honing tool as claimed in claim 1, wherein the first cutting material bodies are shorter in the axial direction than the second cutting material bodies, wherein preferably an axial length of the first cutting material bodies is less than 80% and/or more than 50% of the axial length of the second cutting material bodies.

8. The honing tool as claimed in claim 1, wherein the honing tool has an integrated joint for coupling the tool body, with limited movability, to a connection piece, wherein preferably an axial spacing (AB) between an articulation point of the joint and a spindle-remote end of the cutting region is smaller than the effective outside diameter (AD) of the cutting groups with the cutting material bodies fully retracted.

9. The honing tool as claimed in claim 1, wherein the second cutting material bodies are mounted in an elastically resilient manner with regard to the tool body, wherein preferably the second carriers have, close to or next to a second cutting material body, an elastic portion with cutouts (A) and spring elements (FE) formed integrally with the carrier.

10. The honing tool as claimed in claim 1, comprising a guide group having a plurality of guide strips distributed around the circumference of the tool body, wherein preferably the guide strips are arranged only within the cutting region.

11. The honing tool as claimed in claim 10, wherein one, a plurality or all of the guide strips are arranged immediately next to a second carrier, wherein preferably a circumferential spacing between a second carrier and the guide strip is less than the width of the guide strip in the circumferential direction.

12. The honing tool as claimed in claim 1, wherein the first cutting group feeding system and/or the second cutting group feeding system has an axially displaceable feeding element, which has a first conical portion and a second conical portion axially offset therefrom, wherein the first carriers and/or the second carriers have, on their radial inner side, two axially offset inclined faces that are configured to cooperate with the first and the second conical portion.

13. 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,

wherein the fine machining method comprises at least one honing operation, in which an expandable honing tool is moved back and forth 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,

wherein,

during the honing operation, a honing tool having the features of at least one of the preceding claims is used.

14. The fine machining method as claimed in claim 13, wherein a honing operation is carried out as a multistage honing operation, wherein, in a first honing stage, a first cutting group is pressed against the bore inner face and a bore shape that differs from a circular-cylindrical shape and is preferably rotationally symmetric is created by means of the first cutting group, by means of axially irregular material removal, starting from an initial shape, and in that subsequently, in a second honing stage, a second cutting group is fed and, by means of the second cutting group, a desired surface structure is created on the bore inner face substantially without changing the macro shape of the bore.

15. The fine machining method as claimed in claim 14, wherein honing is carried out with path control in the first honing stage and/or is carried out with force control in the second honing stage.