Patent Application
20250187134
This disclosure relates to a honing tool and a honing stone, which can be used to produce such a honing tool.
Honing is a machining process with geometrically indeterminate cutting edges in which a honing tool executes a cutting movement consisting of two components within a bore to be machined and there is constant surface contact between one or more cutting material bodies of the honing tool and the inner surface of the bore to be machined. The kinematics of an expandable honing tool are characterized by a superposition of a rotary movement, a stroke movement running in the axial direction of the bore, in most instances oscillating, and a feed movement, which leads to a change in the effective diameter of the honing tool. This results in a surface structure with intersecting machining tracks on the inner surface of the bore. Surfaces finished by honing can meet high requirements in terms of dimensional and shape tolerances, so that many highly stressed sliding surfaces in engines or engine components, e.g., cylinder running surfaces in engine blocks or bore inner faces in injection pump housings, are machined by honing.
Particularly when machining bores with relatively small diameters, for example, in the diameter range of 15 mm or less, honing tools are used that have an at least partially tubular tool body that has a cutting region with at least one honing stone receiving opening extending from the inside of the tool body outwards for receiving a honing stone. The tool body serves as a holder for one or more honing stones and at the same time as a guide for a feed element, which is used for the radial feed of the honing stones. The honing tool comprises a device for detachably attaching the honing tool to the work spindle of a honing machine.
The dimensions of the generally rectangular honing stone receiving opening and the corresponding cross-sectional dimensions of the honing stone are matched to each other in such a way that the honing stone is received between the delimiting surfaces of the honing stone receiving opening to be radially movable and substantially free of play in the circumferential direction of the tool body. An attempt is usually made to achieve a sliding fit by precisely machining the delimiting surfaces of the honing stone receiving opening and the corresponding side surfaces of the honing stone, so that the honing stone can just be inserted into the honing stone receiving opening by hand and is held there by static friction forces between the side surfaces of the honing stone and adjacent delimiting surfaces of the honing stone receiving opening.
The inner side of the honing stone, which projects into the interior of the tool body, generally has an oblique surface which interacts with a corresponding oblique surface on the feed element in the manner of a wedge drive in such a way that an axial displacement of the feed element towards the end of the tool body remote from the spindle causes a radial outward displacement of the honing stone.
For honing tools, restoring the honing stone is also very important. Restoring the honing stone involves a radial displacement of the honing stone inwards during an axial displacement of the feed element towards the end of the tool body close to the spindle. This makes it easier to pull the honing tool out of the machined bore and also prevents damage to the honing stone and/or the inner surface of the bore. Similar advantages can also result when inserting the tool into a new bore. To enable the honing stone to be restored, different honing stone restoring systems have been developed.
Honing stone restoring systems with so-called return springs are well known. These are usually designed as annularly closed worm springs or helical tension springs. Two return springs are usually provided, which are inserted into a ring groove in the tool body in the area of the axial ends of the honing stones and grip the axial ends of the honing stones. The return springs are intended to ensure that the honing stones are pushed back into the tool body at the end of machining when the feed cones retract.
Instead of return springs, elastic O-rings are occasionally used as restoring elements for honing tools with smaller diameters.
It could therefore be helpful to provide a generic honing tool which has a reliably functioning honing stone restoring system, which can be manufactured with relatively simple design measures and which is characterized by simple handling during manufacture and use.
I provide a honing tool that has an at least partially tubular tool body which includes a cutting region with at least one honing stone receiving opening which runs from the inside of the tool body outwards and receives a single honing stone. The dimensions of the honing stone receiving opening and of the honing stone in the circumferential direction and preferably also in the axial direction are matched to one another in such a way that the honing stone is received between delimiting surfaces of the honing stone receiving opening to be radially movable and substantially free of play in the circumferential direction of the tool body. The radial movability ensures that the honing stone can be fed in the radial direction with the aid of a feed element which is guided axially displaceably inside the tool body over cooperating oblique surfaces, when the feed element is axially displaced. The honing tool has a honing tool restoring system which includes at least one elastic restoring element. When the honing stone is installed, the elastic restoring element engages with the honing stone in such a way that a radial force acts from the outside inwards and presses the honing stone in the direction of the feed element.
I also provide a honing tool that is characterized in that the elastic restoring element is C-shaped and partially surrounds the outer side of the tool body in the circumferential direction. “Partially” means in particular that the restoring element does not completely surround the outer side of the tool body, but leaves a certain circumferential portion free. The elastic restoring element can be attached to the outer side of the tool body with elastic deformation. The partially open, C-shaped design ensures, among other things, that the elastic restoring element is easy to mount on the tool body. When attached, the resilience of the restoring element allows it to hold onto the tool body automatically. It is also easy to remove the elastic restoring element, especially when changing the honing stone. The restoring element can be attached laterally of the tool body for assembly and removed laterally for disassembly. The term “laterally” refers here in particular to a direction transverse to the tool axis.
Further advantages and aspects of the invention can be found in the description of examples which are explained below with reference to the figures.
In particular, no tools are required for assembly, and possibly also for disassembly. Pliers, a screwdriver or a comparable object can be used for simple, convenient disassembly of the restoring element. Handling is simple, as a fitter can hold the honing tool in one hand and grip the restoring element with the other hand and push it on or pull it off.
The C-shaped elastic restoring element has an opening angle of more than 90° and less than 180° in a relaxed state. The opening angle refers to the angle measured in the circumferential direction between the free ends of the C-shape. This represents a structurally and functionally advantageous realization for the honing stone restoring system. With an opening angle in this range, the elastic restoring element is easy to assemble and disassemble because the C-shape is open over at least a quarter of its circumference, and the restoring element is securely and reliably held or attached to the tool body because it grips the workpiece body around more than half of its circumference. The elastic restoring element can be attached to the tool body under elastic deformation by “clipping on” laterally. When attached, the restoring element is automatically held captive on the tool body. “Captive” means in particular that the restoring element cannot detach or fall off the tool body on its own, e.g., under the effect of gravity.
In the assembled state, the elastic restoring element preferably surrounds the outer side of the tool body by more than 180° and less than 270°, in particular by around 225°. This represents a constructively and functionally advantageous realization for the honing stone restoring system. In this example, the elastic restoring element is on the one hand easy to assemble and disassemble and on the other hand securely and reliably held or attached to the tool body.
The elastic restoring element is a bent wire part, preferably made of spring steel. Bent wire parts can be produced quickly and inexpensively and with precisely maintained dimensions. Spring steel is very elastic and has, among other things, a tensile strength that is favorable for the application and a high elongation at break. This means that large elastic restoring forces can be generated during elastic deformation. The elastic restoring element is designed in such a way that it can bend up to the elasticity limit and return to its original form after being relieved without being permanently deformed. Alternatively, an elastic element can also be manufactured as a stamped part, for example.
In alternative examples, the elastic restoring element is formed from an elastomer material. The elastomer material can have similar material properties to the spring steel.
The C-shaped restoring element can substantially have the shape of a circular arc or an elliptical arc with uniform or only slightly varying curvature up to the ends.
An end portion of the elastic restoring element facing the honing stone is bent, wherein the restoring element is connectable to the honing stone via this bent end portion. “Connectable” means in particular that the restoring element can engage with the honing stone for force transmission and is detachably attached to the honing stone. In this example, a further end portion of the elastic restoring element facing away from the bent end portion surrounds the tool body and rests at least partially against it.
Preferably, the end portion of the elastic restoring element facing the honing stone is bent radially inwards. It then lies in the plane defined by the C-shape. In alternative examples, the end portion of the restoring element facing the honing stone can be bent in an axial direction, for example. This means that the bent end portion protrudes from the plane defined by the C-shape, in particular substantially perpendicular thereto. The bent end portion of the restoring element runs parallel to the tool axis.
In a development, the honing stone has a support strip and a cutting coating applied to a radial outer side of the support strip. The cutting coating can be sintered or soldered onto the support strip, for example. The radial outer side of the support strip is opposite the oblique surface of the support strip. In this example, the elastic restoring element can be connected to the support strip. The restoring element can therefore engage in a portion that is not provided with a cutting coating. “Connectable” also means in particular that the restoring element is detachably attached to the support strip. This represents a constructively and functionally advantageous realization for the honing stone restoring system.
The honing stone has a recess on an outer side into which one end of the elastic restoring element can be hooked. The recess is preferably a radial bore, in particular a blind bore, which is made in the honing stone in such a way that it is directed towards the tool axis when the honing stone is installed. The recess can provide a locally defined position for the force-transmitting contact with the restoring element and can also serve as a latching recess into which one end of the restoring element can latch during assembly.
In alternative examples, the bore on the outer side of the honing stone does not run radially, e.g., the bore can run through the honing stone in the circumferential direction of the tool body.
The elastic restoring element has an inner diameter which, in a relaxed state, is smaller than the outer diameter of the outer side of the tool body against which the elastic restoring element at least partially rests. The inner diameter of the elastic restoring element describes the diameter measured from inner side to inner side, wherein the inner side faces the tool body when the restoring element is installed. The outer diameter of the outside of the tool body corresponds to the diameter measured from outer side to outer side. If the elastic restoring element is attached to the honing stone inserted in the honing stone receiving opening of the tool body and to the tool body, a certain force already acts on the honing stone in the restored state or in the initial state of the honing stone due to the preload or deformation of the elastic restoring element. This force has a radial component that acts from the outside inwards and presses the honing stone against the feed element. This represents a constructively and functionally advantageous realization for the honing stone restoring system.
In some examples, the outer side of the tool body has an annular groove or a ring groove for receiving the elastic restoring element in the circumferential direction. If this is the situation, the inner diameter of the elastic restoring element in a relaxed state is smaller than the outer diameter of the tool body measured at the base of the groove.
In a development, the honing tool has at least one fluid supply channel in the tubular tool body for supplying coolant and/or lubricant to the cutting region. The fluid supply channel opens out into a cavity in which the honing stone and the feed element are also located. The inner coolant supply is particularly advantageous for long bores, as the coolant can be brought directly to the cutting region for cooling, lubrication and chip removal. This leads to better surface finishes, material removal rates, tool life and thermal stabilization of the machining process.
The elastic restoring element and the associated restoring forces are particularly important for honing tools with an internal fluid supply. This is because fluid supply creates fluid forces in the cavity, which also act on the honing stone, in particular on the support strip. This sits radially displaceably in its honing stone receiving opening and can be pressed outwards by the fluid pressure in a similar way to a piston and lifted off the feed element.
I have found that this effect is often difficult or impossible to suppress with the restoring forces of conventional worm springs or O-rings. In addition, even in the initial position, in which the worm springs or O-rings are still practically unable to bring about a restoring effect, high forces can already be achieved with the elastic, C-shaped restoring element. The restoring forces or the pressing forces of the elastic restoring element can be so great that fluid pressure-induced lifting of the honing stone from the feed element is avoided.
In alternative embodiments, the coolant and/or lubricant is supplied exclusively from the outside or from the outside and inside. Alternatively, the honing process can be carried out dry, without coolant and/or lubricant.
The honing tool is a single-stone honing tool, i.e., has only a single honing stone. In this instance, two guide strips made of hard metal, sintered metal or another hard material, for example ceramic, can be attached to the outer side of the tool body opposite the honing stone receiving opening, e.g., offset circumferentially by approximately 90° relative to one another. If there is only a single honing stone, the restoring element is particularly easy to attach.
In some examples, the honing stone restoring system has two elastic restoring elements per honing stone. The elastic restoring elements can each be connected or attached to the honing stone at an axial end region. This makes it possible to create a uniform distribution of restoring force in the axial direction, which counteracts unwanted tilting of the honing stone. The two elastic restoring elements can be attached from the same side or from two opposite sides.
The honing tool can also be a multi-stone honing tool. In these instances, the honing stone restoring system can have several axially offset restoring elements in each axial end region of the cutting region equipped with honing stones.
Particularly preferred are embodiments in which the outer side of the tool body, in particular at an axial end region of the honing stone receiving opening, has an annular groove in the circumferential direction for receiving the elastic restoring element.
The honing stone is suitable and intended for use in a honing tool which has a tool body which is at least partially tubular and which has a cutting region with at least one honing stone receiving opening which runs from the inside of the tool body outwards for receiving a honing stone. The dimensions of the honing stone and the dimensions of the honing stone receiving opening are matched to one another in such a way that the honing stone can be received between delimiting surfaces of the honing stone receiving opening to be radially movable and substantially without play in the circumferential direction of the tool body and has an oblique surface on an inner side projecting into the interior of the tool body.
A honing stone is characterized in that the honing stone has a recess, in particular a radial bore, on an outer side. Preferably, such a recess is formed at each end portion of the support strip in the extension of the elongate cutting coating. The honing stone is thus particularly adapted to interact with a honing tool of the type, which has a honing stone restoring system with an elastic, C-shaped restoring element. In the installed state of the honing stone, the restoring element is configured to partially surround an outer side of the tool body in the circumferential direction and to act on it with a pressure force generated by expansion in such a way that the honing stone is held in the honing stone receiving opening. An inwardly bent end portion of the C-shaped restoring element can engage in the recess.
Existing honing tools (new tools or already used tools) can be easily retrofitted, if necessary, to take advantage of this disclosure. For this purpose, I also provide a retrofit kit comprising at least one honing stone of the above-mentioned type and a suitable number of matching C-shaped restoring elements, for example two, three, four, five, six or more per honing stone.
The honing tool 100 is embodied as a single-stone honing tool, i.e., it has only a single radially adjustable honing stone 200 in its cutting region. The honing tool 100 has a tool body 110 which has approximately the form of a tube open on both sides with a relatively large wall thickness, wherein the outer diameter of the tube varies in portions in the axial direction.
The end portion 180 of the tool body 110 shown on the right in
The honing stone receiving opening 120 is bounded by four planar delimiting surfaces parallel to one another in pairs. Two planar delimiting surfaces acting in the circumferential direction are provided parallel to the axial direction, namely a first delimiting surface 121 and a second delimiting surface 122 parallel thereto. The delimiting surfaces 121, 122 are each flat and extend parallel to a plane which is spanned by the tool axis 101 and a radial direction running centrally between the lateral delimiting surfaces 121, 122. In the axial direction, the honing stone receiving opening 120 is bounded by an upper delimiting surface and a lower delimiting surface, each of which lies in a plane normal to the tool axis 101.
Two guide strips 160, 170 made of hard metal, sintered metal or another hard material, for example ceramic, are attached to the tool on the side opposite the honing stone receiving opening 120 and are circumferentially offset from each other by approximately 90°. These are supported with their smoothly polished, curved outer surfaces on the inner wall of the bore to be honed. The guide rails can have a coating made of diamond, for example, which forms a wear-resistant outer surface.
The honing stone 200 is plate-shaped overall and has a plate-shaped support strip 210 made of steel. A cutting coating 220 is applied to the radial outer side 212 of the support strip 210 and contains the cutting material grains bound in a bond. The cutting coating 220 can be sintered directly onto the flat outer side of the support strip 210, but it can also be glued or soldered on or attached to the support strip 210 by rivets or screws. It is also possible that a flat base 222 supporting the cutting coating 220 is located between the cutting coating 220 and the support strip 210.
A planar oblique surface 211 is formed on the radially inner side of the support strip 210 and interacts with a complementary planar oblique surface 131 at the lower end of a feed element 130 guided in the tool body 110 in the manner of a wedge drive in such a way that the honing stone 200 is pressed radially outwards within the honing stone receiving opening 120 when the feed element 130 is pressed in the direction of the cutting region of the honing tool 100 by the feed drive accommodated in the honing machine 100.
The dimensions of the honing stone 200 and the honing stone receiving opening 120 are matched to each other in such a way that the honing stone 200 can move radially, but is received substantially free of play in the circumferential direction of the tool body 110 between the lateral delimiting surfaces 121, 122. In the axial direction, i.e., between the upper and lower delimiting surfaces, there may be a small amount of play, wherein a play-free fit is also provided here as far as possible.
When manufacturing the honing stone 200 and the tool body 110, care is taken to ensure that the clear distance between the front and rear delimiting surfaces 121, 122 of the honing stone receiving opening 120 is only minimally greater than the width of the honing stone 200 measured between a front side surface 201 and a rear side surface 202 of the honing stone 200 or the support strip 210. In the most favorable instance, a relatively tight sliding fit should result, so that the honing stone 200 can be manually pushed into the honing stone receiving opening 120 from the outside during assembly, but cannot fall out of the honing stone receiving opening 120 on its own. However, the honing stone 200 should be able to be displaced radially outwards under the action of the downwardly pressed feed element 130.
The honing tool can be used with an internal coolant supply. The internal coolant supply is particularly advantageous for long bores, as the coolant can be brought directly to the cutting edge for cooling, lubrication and chip transport. This leads to better surface finishes, material removal rates, tool life and thermal stabilization of the machining process.
To enable an internal coolant supply, the honing tool 100 has at least one fluid supply channel 140 in the tubular tool body 110 for supplying coolant and/or lubricant to the cutting region. The fluid supply channel 140 opens out into a cavity 150, in which the honing stone 200 and the feed element 130 are also located. The coolant and/or lubricant passes from the cavity 150 into the cutting region via two radial holes 141, 142 on an outer side 113 of the tool body 110 and an axial hole 143 on an end face 114 of the tool body 110, as can be seen in
With an internal fluid supply, fluid forces can be generated in the cavity 150, which, among other things, also act on the support strip 210 of the honing stone 200 and act on it radially outwards.
It has been found that, especially when using an internal coolant supply which is fed inside the tool body up to the exit bore at the engagement point of the honing stone, the coolant pressure can be sufficient to lift the support strip from the cone or the oblique surface of the feed element at exposed points of the support strip, thereby generating a “hydraulic” feed force on the entire rear surface. This is difficult or impossible to suppress with the restoring forces of conventional worm springs or O-rings.
To avoid such problems, the honing tool 100 is equipped with a honing stone restoring system 300 which, when the honing stone 200 is installed, acts on the honing stone 200 in such a way that a radial force acts from the outside inwards and presses the honing stone 200 in the direction of the feed element 130.
In the example shown, the honing stone restoring system 300 has two elastic, C-shaped restoring elements 310 of identical shape, which are explained in greater detail below with reference to the restoring element 310. An elastic restoring element 310 is attached to each of the two axial end regions 203, 204 of the honing stone 200.
An elastic restoring element 310 is a bent wire part made of spring steel. Spring steel has favorable properties for the application, among other things because large elastic restoring forces can be generated when the elastic restoring element 310 is elastically deformed. The spring steel can, for example, have a strength of between approximately 600 and 1800 N/mm2. The elastic restoring element 310 made from a round wire substantially has the shape of a non-closed circle arc with an end portion 311 bent radially inwards. In alternative examples, the elastic restoring element 310 can also be made from a profiled wire which is not round in cross-section but, for example, polygonal.
The unclosed circular arc portion of the elastic restoring element 310 defines an opening angle α, wherein the center of the elastic restoring element 310 is the apex of the opening angle α. The first leg of the opening angle α extends from the apex to a central axis of the radially inwardly bent end portion 311 of the elastic restoring element 310; the second leg of the opening angle α extends from the apex to an end point at the other end portion 312 of the elastic restoring element 310. In the inserted state of the elastic restoring element 310 in the honing stone 200 or on the tool body 110, the opening angle α increases due to the deformation of the elastic restoring element 310, wherein the first leg also runs through the center axis of the radial bore 231.
The radially inwardly bent end portion 311 of the elastic restoring element 310 preferably has a length that can be between 10% and 40% of the outer diameter of the elastic restoring element 310 and/or between one to three times the wire diameter or the wire thickness of the elastic restoring element 310. The wire diameter or the wire thickness of the elastic restoring element 310 can, for example, be in the range between 5% and 20% of the diameter of the tool body 110.
The tool body 110 also has an annular groove 112 for each elastic restoring element 310, which groove is provided on the outer side 113 of the tool body 110. The groove 112 runs over the entire circumference of the tool body 110 and can be produced, for example, by turning. In each instance, an annular groove 112 runs at an axial end region 203, 204 of the honing stone 200 or honing stone receiving opening 120. Furthermore, a groove runs over the radial outer side 212 of a cutting-coating-free end portion 213, 214 of the support strip 210 and runs in the extension of the annular groove 112 in the retracted state of the honing stone 200. Alternatively, the radial outer side 212 of a cutting-coating-free end portion 213, 214 of the support strip 210 may have a shoulder. The cutting-coating-free end portions 213, 214 of the support strip 210 each have a radial bore 231 in this groove. The radial bore 231 is made in the support strip 210 in such a way that, when the honing stone 200 is installed, it points in the direction of the tool axis 101.
The arrangement of the elastic restoring element 310 on the tool body 110 is described below. This applies analogously to the second elastic restoring element 310.
The elastic restoring element 310 is arranged or suspended in the radial bore 231 with its radially inwardly bent end portion 311 and partially surrounds an outer side or a groove base 111 of the annular groove 112 in the circumferential direction with the C-shaped part. The elastic restoring element 310 has an inner diameter which, in a relaxed state, is smaller than the outer diameter of the annular groove 112 measured at the groove base 111.
To assemble the restoring element 310, the bent end portion 311 of the elastic restoring element 310 is inserted into the radial bore 231 and, with elastic deformation of the elastic restoring element 310, the other end portion 312 of the elastic restoring element 310 is placed or attached in the annular groove 112 around the tool body 110. Due to the partially open, C-shaped form of the elastic restoring element 310, it is easy to install on the tool body 110. When pushed on sideways, the C-shape expands elastically temporarily until the restoring element is then clipped onto the circumference and holds onto the tool body under elastic clamping force.
In the example shown, the elastic restoring element 310 surrounds the outer side 111 of the annular groove 112 or the tool body 110 by approximately 225° in the assembled state and thus leaves a certain circumferential portion free (cf.
Due to the elastic pretension of the clipped-on restoring element, a certain force already acts on the honing stone 200 in the restored state or in the initial state of the honing stone 200 due to the deformation or elasticity of the elastic restoring element 310, which acts from the outside inwards and presses the honing stone 200 against the feed element 130. In addition, the elastic restoring element 310 thereby automatically holds onto the tool body 110 in the attached state.
Due to the higher restoring forces, which act directly in the radial direction, it is now possible to prevent any “hydraulic” closing of the honing stone 200, as the mechanical contact between the oblique surface 211 or rear surface of the support strip 210 and the oblique surface 131 or the expansion cone of the closing element 130 remains and is not hydraulically undermined. This mechanical contact between the honing stone 200 and the feed element 130 would often be difficult or impossible to maintain if conventional worm springs were used as restoring elements 310 due to their low restoring forces.
As the examples shown and the further examples mentioned above make clear, I provide a honing tool and a honing stone which can be used to manufacture such a honing tool and which offer advantages over conventional honing tools and honing stones, in particular with regard to functionality, operational reliability, structure and/or handling.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2022 202 426.5 | Mar 2022 | DE | national |
This application is a US national stage filing under 35 U.S.C. § 371 of International Application No. PCT/EP2023/055041, filed Feb. 28, 2023, which claims priority to German Patent Application No. 10 2022 202 426.5 filed Mar. 10, 2022, each of which is incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2023/055041 | 2/28/2023 | WO |
