Grinding tool for machining gearwheels
Patent Information
- Application Number
- EP2023730789
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-06-03
- Filing Date
- 2023-06-05
- Publication Date
- 2025-04-09
Smart Images
Figure 1.1
Abstract
Description
[0001] Grinding tool for machining gears
[0002] The invention relates to a profiled grinding tool for the rotating machining of workpieces, in particular gears and / or transmission wheels, with a base body which has at least one device designed as a preferably hollow cylindrical formation for clamping onto a tool carrier, and with at least two grinding segments spaced apart from one another in the axial direction and acting in the circumferential direction, wherein the second grinding segment has a modulus of elasticity which is lower than the modulus of elasticity of the first grinding segment.
[0003] Gears are of high quality when they have both a precise geometry and a defined surface structure, given the appropriate material properties. During production, a distinction can be made between prefabrication and final processing.
[0004] Prefabrication can be achieved, for example, by gear or disc milling with subsequent case hardening. Important quality features such as a precise tooth profile or defined tip and core diameters are often not achieved during prefabrication, but only in a subsequent finishing process.
[0005] During final machining, prefabricated gears are machined with profiled grinding tools whose profile corresponds to the gear geometry. A distinction is made between several machining steps. First, machining takes place with a preferably vitrified-bonded grinding wheel, whereby the geometric properties, for example the tooth flank geometry, are to be adjusted through material removal. Because grinding processes with significant material removal tend to produce a rough surface, the surface is machined in a further machining step.
[0006] The key here is to modify the surface structure to meet the desired functionality. In many cases, this involves reducing the roughness depth and, if necessary, structuring the surface in a defined manner (removing roughness peaks), for example, to ensure adequate oil retention. The result is gears with smooth, vibration-free, and low-loss operation.
[0007] The individual processing steps of the final processing, the removal and the surface structuring, are carried out by a grinding tool according to the state of the art.
[0008] This tool has a cylindrical geometry with a profiled surface. It is divided axially into individual segments, each of which has a different composition. They can differ in terms of abrasive, grain size, and binder to ensure the desired functionality in the finishing process.
[0009] In typical designs, grinding tools consist of two segments, one with a ceramic and thus comparatively hard bond with coarser grain, and the other with a soft bond made of an organic polymer with finer grain. Both segments are permanently connected to one another and are clamped onto the corresponding machine shaft as a single unit.
[0010] In the interests of efficient production, but also to achieve the appropriate machining result, such tools are operated at higher working speeds, for example with a maximum working speed of 80 m / s.
[0011] Such maximum working speeds are common for mechanically strong, stable and low-elongation grinding tools such as grinding wheels with ceramic bonds, with synthetic resin bonds or with vulcanized fiber grinding wheels.
[0012] However, the desired results in the final finishing step can only be achieved with soft-bonded abrasive, with a polyurethane polymer often being used as the binder.
[0013] The segment with the soft-bonded abrasive must exhibit sufficient strength against centrifugal forces. Regardless of this, it also exhibits elastic deformability. This elastic deformability causes the segment to deform under centrifugal forces.
[0014] The grinding tool is typically slid onto a machine shaft and clamped to the front end by means of a flange. The clamping forces on the soft-bonded segment can deform it, which also impairs profile fidelity.
[0015] There are various attempts to solve these problems. For example, the hardness of the soft bond can be adjusted to avoid undesirable elastic deformations. However, because a soft, elastic bond can be crucial for the final machining result, this would lead to an undesirable limitation of the functionality of the grinding tool.
[0016] Another design features a special construction for the softer segment. This consists of an inner, harder ring and an outer, softer ring intended for machining. This design allows the clamping forces to be absorbed by the harder, inner ring without deforming the elastically bonded, outer ring. The disadvantages, however, are the high manufacturing costs and the requirement to connect both segments to one another at the end faces in a force-fitting and torsion-proof manner.
[0017] The use of base bodies with a high modulus of elasticity ( e . g . DE10104410A1 ) as well as the use of combination grinding bodies or grinding tools with two grinding zones in processes for producing a workpiece provided with a toothing or profiling ( e . g .
[0018] DE102019115294A1). For example, the two bodies are glued to a plastic tube.
[0019] The invention is based on the object of providing a profiled grinding tool of the type mentioned at the beginning, which remains stable even at high grinding speeds and achieves a high precision of the surface structures to be machined.
[0020] Based on the cited prior art, the problem is solved with the features of claim 1. Advantageous embodiments are given in the subclaims.
[0021] According to the invention, it is thus provided that the base body is formed integrally with the first grinding segment, and that the base body has at least one support section, axially spaced from the first grinding segment, to the periphery of which at least one second grinding segment is force-fitted. This force-fit connection is preferably permanent and cannot be removed or cannot be removed without damage. First, some terms used in the context of the invention will be explained.
[0022] The profiled grinding tool according to the invention is used to machine workpieces such as machine elements as components of gears or for power transmission, in particular gears and transmission wheels. The term gears can generally encompass machine elements as components of gears or for power transmission. The surface shape (profile) of the profiled grinding tool corresponds to the shape of the machine element to be machined. The grinding tool engages with the toothing, for example of the gear or transmission wheel. In the context of the present invention, the term profiled grinding tool also refers to a grinding tool that is profiled by the end user before use, i.e., is provided with the desired profile shape. A profiled grinding tool according to the invention is usually designed with a profile.
[0023] The base body is designed for force-fitting connection with a drive element; for this purpose, it usually has a hollow cylindrical shape.
[0024] The grinding tool has at least two grinding segments spaced apart in the axial direction and acting in the circumferential direction. The axial direction corresponds to the rotational axis of the tool. The grinding segments act in the circumferential direction, i.e., they are designed to machine the workpiece with its (profiled) circumferential surfaces.
[0025] The grinding segments have different moduli of elasticity, as defined in the patent claim. Together they form a two- or multi-zone grinding tool. A first zone, which is formed by the grinding surface of the first grinding segment, is used for the grinding process, which improves the required geometric accuracy. A second zone, which is formed by the grinding surface of the second grinding segment, is used during fine machining to specifically level the surface roughness with only very little material removal to achieve functional (structural or optical) target parameters. The modulus of elasticity of the second grinding segment is lower than the modulus of elasticity of the first grinding segment. By designing the grinding tool with at least two zones, both machining steps can take place continuously. This avoids interrupting the machining process to change the tools.
[0026] According to the invention, the base body is formed integrally with the first grinding segment. The base body, with its high modulus of elasticity and high strength, thus establishes, on the one hand, a force-fitting and dimensionally accurate connection with the tool carrier, and, on the other hand, its integral design with the first grinding segment ensures its strength and dimensionally accurate connection.
[0027] The base body has at least one support section, axially spaced from the first grinding segment, to the circumference of which at least one second grinding segment is force-fittingly connected. The force-fitting connection is permanent and can, for example, be a material connection. Permanent means that the force-fitting connection cannot be released or can only be broken with damage / destruction of the base body and / or the corresponding grinding segment. This second grinding segment with a lower modulus of elasticity is thus held and driven by the circumference of the corresponding support section of the base body by means of the permanently force-fitting connection. This means that according to the invention no force has to be introduced into the second grinding segment via its end faces.This has the particular advantage that a deformation of the second grinding segment caused, for example, by centrifugal forces is not influenced by a front-side connection, for example adhesive bonding, with the first grinding segment, whose modulus of elasticity is different.
[0028] Such deformation can lead to unsatisfactory machining results, particularly if the second grinding segment is glued to the first grinding segment on one end face (as is common in the prior art), while the second end face is open and not glued, whereby the second grinding segment can deform asymmetrically under the influence of centrifugal forces, with a loss of profile fidelity. According to the invention, however, the second grinding segment with comparatively higher elasticity can expand on both end faces due to centrifugal forces, unaffected by a face-face connection or glueing on one end face.
[0029] The comparatively solid base body absorbs the forces generated during clamping and thus prevents unwanted deformation of the comparatively more elastic second grinding segment due to clamping forces.
[0030] The core idea of the invention is that the base body and the integrally formed first grinding segment on the one hand and the second grinding segment (and optionally further grinding segments) permanently connected to the support section of the base body in a force-locking manner on the other hand form a grinding tool that is simple and cost-effective to manufacture, in which each segment has a high degree of dimensional accuracy during use and which is overall resistant to centrifugal force loads.
[0031] A force-fitting connection within the meaning of the invention can, for example, have a positive connection, a material connection or combinations thereof. Force-fitting means that the forces occurring when the tool is used can be introduced without the connection becoming loose or the second grinding segment becoming noticeably twisted relative to the base body. The force-fitting connection is permanent and therefore non-detachable. This means that the base body and second grinding segment cannot be separated without damage. It can, for example, be a connection in which either an adhesive and / or a polymer material of the second (or further) grinding segment itself infiltrates into the base body, which is preferably made of a ceramic material.Such infiltration creates a positive connection between the infiltrated material and the pores, and any bonding creates a material bond between the bonded materials. If the second or further grinding segment is cured upon application to the base body (e.g., an organically bonded grinding segment), shrinkage during application can lead to the development of an (additional) adhesive friction force between the grinding segment and the base body, which creates or reinforces the frictional connection.
[0032] In one embodiment of the grinding tool according to the invention, the first grinding segment and the second grinding segment have no force-fitting connection in a radial section facing the outer circumference and taking up at least a quarter of the grinding tool radius. This means that the two segments have no connection in the axial direction, in particular no end-to-end connection or adhesive bond, in a radial section facing the outer circumference. At least in this area, the two segments can deform independently of one another under the influence of centrifugal forces or contact pressure, so that the different moduli of elasticity do not result in the deformation of one segment influencing the dimensional accuracy of the other segment due to an end-to-end connection in the corresponding section.
[0033] It is preferred if the first and second grinding segments do not have a front-end connection over the entire radial section which extends from the outer circumference of the support section to the outer circumference of the entire tool, so that the second segment with the lower modulus of elasticity does not experience any force input from the front side.
[0034] According to the invention, a gap or slit can be provided between the end faces of the first grinding segment and the second grinding segment. This slit ensures that both grinding segments can expand largely freely due to centrifugal forces without being influenced by the other segment.
[0035] In one embodiment, a first axial section of the base body with a larger radius is designed as a grinding segment. A second axial section of the base body with a smaller radius is designed as a support section.
[0036] Preferably, the first and second axial sections are substantially cylindrical. Substantially cylindrical also includes embodiments in which the surface shape of the grinding segment is profiled. The abrasive surfaces can be complementary to the gear profile to be machined. The profile of the segments can be machined using a profiling machine. This allows the grinding tool to be given the profile suitable for the grinding task. The profiling machine can also be used to dress the profile after the grinding tool has worn down. The first and second grinding segments can, if necessary, be machined in a single pass through the profiling machine. Using the tool according to the invention, a gear can be shaped and surface-machined by grinding in one machining operation, for example generating grinding.Through continuous generating grinding, a high pitch accuracy and / or concentricity can be achieved.
[0037] The first and second axial sections of the base body are preferably jointly hollow and cylindrical, thus preferably forming a uniform hollow space which can be designed for clamping onto a drive element.
[0038] In one embodiment, the support element penetrates the entire second grinding segment in the axial direction, thus protruding (preferably only slightly) from the second grinding segment in the axial direction facing away from the first grinding segment. This enables the tool according to the invention to be clamped without the second segment being deformed by the action of clamping forces.
[0039] The axial length of the first grinding segment can, for example, be in a ratio of between 115:45 and 100:60 to the length of the second grinding segment.
[0040] Preferably, the second grinding segment is substantially hollow and cylindrical. Preferably, the frictional connection between the support section and the second grinding segment occurs exclusively via the permanently frictionally connected circumferential surfaces.
[0041] The base body and the first grinding segment are preferably made of ceramic and can, for example, contain a ceramic binder. In the first grinding segment, abrasive grain such as corundum is preferably bound in the ceramic material. The surface of the first grinding segment can therefore be suitable for rough machining of gears, whereby a high chip volume can be achieved in a short time. The second grinding segment can have a polymer matrix with abrasive material embedded therein, for example abrasive grain or micro grinding balls, for example made of glass. For example, it can have polyurethane as the matrix material in which corundum or another abrasive grain or polishing agent is bound.
[0042] According to the invention, the support element can have an infiltration of the polymer material of the second grinding segment in its axial section, to whose circumference the second grinding segment is permanently and force-fit connected. Thus, the second grinding segment is permanently and force-fit radially connected to the support element by infiltration. The radial penetration depth of the infiltration can be at least 0.5 mm, preferably at least 1.5 mm. The material of the base body and thus of the support element is preferably porous and preferably has a pore content of 30% to 60% by volume. The material of the second grinding segment can penetrate into the pores of the support element.
[0043] The elastic modulus of the second grinding segment is lower than the elastic modulus of the first grinding segment. Preferably, the elastic modulus of the second grinding segment can be 25%, 10%, or 5% of the elastic modulus of the first grinding segment.
[0044] In a preferred embodiment, the elastic modulus of the first grinding segment is 20 to 70 GPa, preferably 20 to 40 GPa. The elastic modulus of the second grinding segment can be 1 to 5 GPa, preferably 2 to 4 GPa, more preferably 2 to 3 GPa. The density of the first grinding segment can be 1.0 to 2.5 g / cm 3 preferably 1.7 to 1.9 g / cm 3 , and the density of the second grinding segment can be 0.95 to 1.87 g / cm 3 preferably 1.11 to 1.45 g / cm 3 The porosity of the first grinding segment can be 30 to 60%, preferably 45 to 50%. The porosity of the second grinding segment can be 20 to 50%.
[0045] The second grinding segment can have macropores with a pore size of 200 to 500 pm and micropores with a pore size of 3 to 6 pm.
[0046] The polymer matrix material can be selected from the group consisting of polyurethanes, epoxy resins, phenolic resins, and composites. The first and / or second grinding segment can contain embedded abrasive grains or other grinding media, such as glass beads, preferably corundum abrasive grains.
[0047] In a preferred embodiment, the grinding body has a minimum fracture speed or fracture peripheral speed of at least 40 m / s.
[0048] The invention also encompasses a method for producing a grinding tool according to the invention. The method comprises the following steps: a. providing the base body with the support element and the first grinding segment; b. providing a curable material for producing the second grinding segment; c. molding the curable material for producing the second grinding segment onto the support section; d. curing the curable material for producing the second grinding segment.
[0049] First, a base body is manufactured, comprising a support section and a first grinding segment. A curable material is provided and molded to the support section in such a way that a second grinding segment is produced from the curable material. Finally, the curable material is cured.
[0050] In a preferred variant of the method, the molding (step c) of the hardenable material for producing the second grinding segment onto the support element can be carried out by mold casting.
[0051] In this variant of the process, for example, the second grinding segment can be manufactured by mold casting around the support section. The second grinding segment can be cast radially around the support section, which encloses the rotational axis of the grinding tool. A mold can be used that encloses the second grinding segment.
[0052] The molding process may also involve foaming or spraying the material of the second grinding segment. The pouring process may also involve dipping the support section into a curable material of the second grinding segment. The material may be suitable for pouring or foaming. For example, it may be polyurethane with embedded abrasive grain. Pouring can prevent tilting, which can occur when joining two existing grinding segments.
[0053] In a variant of the method, the curable material for producing the second grinding segment can have a viscosity that enables infiltration into the support section. The material of the second grinding segment, which is poured onto the support section, can infiltrate the support section and thus form a circumferential connection with the support section. While the material of the second grinding segment is being poured on, the facing end face of the first grinding segment can be covered. The cover can be made of a paper material or polymer material, for example with a thickness of 0.2 mm to 1 mm. The cover can be removable after production. When the cover is removed, an axial gap can remain between the end faces of the first and second grinding segments.Alternatively, it is possible to coat the facing end face of the first grinding segment with a release agent, which prevents the materials of the first and second grinding segments from bonding. In this case, there is no axial gap between the end faces of the first and second grinding segments, but the release agent prevents a frictional connection between the end faces.
[0054] A tool according to the invention can have more than two grinding segments. In particular, it is possible, for example, for second and third grinding segments to be arranged on both axial sides of the first grinding segment which is integrally connected to the base body, each of which is permanently and force-fittingly connected to an associated support section. It is also possible for a grinding segment to have regions with different grinding properties, preferably in the axial direction, for example to be provided with different abrasive grains. According to a further aspect, a second grinding segment can have different materials, particularly in the radial direction. For example, a preferably solid, polymeric region can extend around the support section, and an elastic coating with an abrasive, for example, can be applied to the outer circumference of this polymer body.
[0055] The tool according to the invention can be manufactured easily and cost-effectively; it merely requires direct joining of the second grinding segment to the support section of the base body; the first grinding segment is already formed integrally with the base body. The method according to the invention enables good, permanent force-fitting and form-fitting anchoring of the second grinding segment to the support section of the base body. The end faces of the two grinding segments are not connected to one another and have no force connection; therefore, shear stresses at the interface between the two segments do not occur. This improves dimensional accuracy during grinding and increases the minimum breaking speed of the tool. According to the invention, the minimum breaking speed is at least 40 m / s, preferably at least 80 m / s, more preferably at least 100 m / s. Exemplary achieved minimum breaking speeds are 115 and 125 m / s.
[0056] An embodiment of the invention is described below with reference to the drawings, in which:
[0057] Fig. 1 is a side view of an embodiment of the grinding tool (7) according to the invention, and
[0058] Fig. 2 is a plan view of an embodiment of the grinding tool (7) according to the invention from the side of the second grinding body.
[0059] In the embodiment in Fig. 1, the base body has a grinding segment (1) and a support section (2) which enclose the axis of rotation (4) of the grinding tool (7) in a rotationally symmetrical manner. A second grinding segment (3) is arranged rotationally symmetrically around the support section (2) of the base body. The support section (2) has an end face (5) of a hollow cylindrical bore (6) which serves to fasten or clamp the grinding tool (7). In the plan view of the grinding tool (7) in Fig. 2, the axis of rotation (4) is in the center of the bore (6). The bore is delimited by the end face (5) of the support section (2) and extends through the entire length of the base body comprising the first grinding segment (1) and the support section (2).
[0060] In one embodiment, the outer diameter can be between 275 and 280 mm. The width is preferably 160 mm. The inner diameter of the hollow cylindrical bore for accommodating the tool holder depends on the tool holder used and can, for example, be between 115 and 160 mm. The outer diameter of the support element can be, for example, 210 mm.
[0061] The elastic modulus of the ceramic base body and the first grinding segment can, for example, be between 22 and 38 GPa. The elastic modulus of the second grinding segment can, for example, be between 2 GPa and 3 GPa. The density can, for example, be approximately 1.42 g / cm 3 preferred ranges are 1.12 - 1.45 g / cm 3 . A lower density at the lower end of this range can be used, especially when a high porosity is chosen.
[0062] In a preferred variant of the method for producing the grinding tool (7) shown in Figs. 1 and 2, the material of the second grinding segment (3) is molded, cast, or foamed onto the support section (2) in a ring shape. For this purpose, an annular mold can be used that at least radially encloses the grinding tool (7). According to the invention, the Rencast system from Huntsman, for example, can be used.
[0063] In one embodiment, the material of the base body is a vitrified corundum material (e.g., 3SK3), grain size F120, low hardness H, porous structure 12, and a bond V09 made of frit, clay, and flux. From this base body, the supporting section is turned as a section with a reduced diameter. The end face of the first grinding segment facing the supporting section is covered or coated with a release agent (e.g., EWOmold 5716 from Eckert & Woelk GmbH). The base body prepared in this way is placed in an aluminum mold whose inner radius is flush with the outer radius of the first grinding segment and whose height essentially corresponds to the axial length of the base body. The following mixture is used to produce the second grinding segment:
[0064] Polyol: 21% by weight Huntsman Rencast® FC 52 / 53
[0065] Isocyanate: 21% by weight Huntsman Rencast® FC 52
[0066] Grain: 58% EKW (grain: F800)
[0067] Foaming agent: 0.5 wt% water
[0068] The mixture is homogenized for 2-3 minutes, poured into the mold, and left in the mold for at least 20 minutes. The grinding tool is then removed from the aluminum mold. A subsequent heat treatment, preferably at 80°C for 14 hours, contributes to the complete crosslinking of the polyurethane system. The grinding tool is machined to the desired geometric dimensions, removing any protruding polyurethane edges and the polyurethane skin.
[0069] When using the grinding tool (7) shown in Figs. 1 and 2, the grinding tool (7) can be clamped onto a drive element and / or flanges. Fig. 2 shows the end face (5) of the support section (2), to which a flange can be applied. This prevents crushing of the elastic second grinding segment (3).
Claims
Claims Profiled grinding tool (7) for rotating machining of workpieces, in particular gears and / or transmission gears, with a base body having at least one device designed as a preferably hollow cylindrical shape (6) for clamping onto a tool carrier, and with at least two grinding segments (1, 3) spaced apart from each other in the axial direction and acting in the circumferential direction, wherein the second grinding segment (3) has a modulus of elasticity that is less than the modulus of elasticity of the first grinding segment (1), characterized in that the base body is formed integrally with the first grinding segment (1), and that the base body has at least one support section (2) spaced axially apart from the first grinding segment (1), with the circumference of which at least one second grinding segment (3) is permanently force-fitted.Grinding tool according to claim 1, characterized in that the first grinding segment (1) and the second grinding segment (3) do not have a force-fit connection to each other in a radial section comprising at least one quarter of the grinding tool radius. Grinding tool according to claim 1 or 2, characterized in that the base body has a first axial section of larger radius designed as a first grinding segment (1) and a second axial section of smaller radius designed as a support section (2). Grinding tool according to claim 3, characterized in that the first and second axial sections are substantially cylindrical. Grinding tool according to claim 4, characterized in that the first and second axial sections are hollow cylindrical, wherein the cylindrical cavity (6) is designed for clamping onto a tool holder. Grinding tool according to claim 4 or 5, characterized in that the second grinding segment (3) is substantially hollow cylindrical, wherein the force-fit between the support section (2) and the second grinding segment (3) preferably occurs exclusively via the force-fit connected circumferential surfaces. Grinding tool according to any one of claims 1 to 6, characterized in that the base body is ceramically bonded. Grinding tool according to any one of claims 1 to 7, characterized in that the second grinding segment (3) comprises a polymer matrix with abrasive material embedded therein.Grinding tool according to claim 8, characterized in that the base body, in its axial section to which the second grinding segment (3) is permanently and force-fit connected, has an infiltration of the polymer material of the second grinding segment. Grinding tool according to any one of claims 1 to 9, characterized in that the modulus of elasticity of the second grinding segment (3) is at most 25%, preferably at most 10%, more preferably at most 5% of the modulus of elasticity of the first grinding segment (1). Grinding tool according to one of claims 1 to 10, characterized by one or more of the following features: a. the modulus of elasticity of the first grinding segment (1) is 20 to 70 GPa, preferably 20 to 40 GPa, b. the modulus of elasticity of the second grinding segment (3) is 1 to 5 GPa, preferably 2 to 4 GPa, more preferably 2 to 3 GPa, c. the density of the first grinding segment (1) is 1.0 to 2.5 g / cm³3 , preferably 1.7 to 1.9 g / cm³ 3 , d. the density of the second grinding segment (3) is 0.95 to 1.87 g / cm³ 3 , preferably 1.11 to 1.45 g / cm³ 3 e. the porosity of the first grinding segment (1) is 30 to 60%, preferably 45 to 50%, f. the porosity of the second grinding segment (3) is 20 to 50%, g. the material of the polymer matrix is selected from the group consisting of polyurethanes, epoxy resins, phenolic resins and composites, h. the first and / or second grinding segment (1, 3) contain embedded abrasive grains or polishing compound, preferably corundum abrasive grains. Grinding tool according to any one of claims 1 to 11, characterized in that it has a minimum fracture velocity of at least 40 m / s. Method for manufacturing a grinding tool according to any one of claims 1 to 11, characterized by the steps: a. providing the base body with support section (2) and first grinding segment (1), b. providing a curable material for producing the second grinding segment (3), c. forming the curable material for producing the second grinding segment (3) onto the support section (2), d. curing the curable material for producing the second grinding segment (3).
14. Method according to claim 13, characterized in that the forming of the curable material for producing the second grinding segment (3) onto the support element is carried out by injection molding.
15. Method according to claim 14, characterized in that the curable material for producing the second The grinding segments (3) have a viscosity that allows infiltration into the support section (2).