Vibration damping tool holder for metal cutting tools

Abstract

A vibration damped tool holder (1) for a metal cutting tool (2), comprising a holder body (3) having an internal cavity (10) extending into the holder body (3) along a longitudinal axis (6) and having a first cavity end at a first holder body end (4). The damped tool holder further comprises an adjustment mass (15) movably disposed within the cavity (10), extending along the longitudinal axis (6) and having a first adjustment mass end at the first holder body end (4). The damped tool holder further comprises a damping medium (22) surrounding the adjustment mass (15) within the cavity (10) and a single primary spring element (18) positioned within the cavity (10). The outer spring element end (19) is fixedly secured to the first cavity end by its longitudinal axis (6) and the inner spring element end (20) is fixedly secured to the first tuning mass end by its longitudinal axis (6).

Description

[Technical field]

[0001] The present invention relates to a vibration dampened tool holder for a metal cutting tool. [Background technology]

[0002] A variety of cutting tools, e.g., rotary or non-rotary cutting tools, are used to machine metal workpieces. Such tools typically include an elongated body having a cutting head at a front end and a shank at a rear end for connecting the cutting tool to a machine tool. The cutting head includes a cutting edge that may be integral with the cutting head or located on a replaceable cutting insert.

[0003] As a cutting tool is operated, it is subjected to cutting forces that may vary in magnitude and / or direction, which can cause undesirable vibration or oscillation in the cutting tool, which can result in a poor surface finish on the machined workpiece or damage to the cutting tool or the workpiece.

[0004] U.S. Patent No. 3,598,498 shows an adjustable apparatus for damping vibrations of a boring bar. The apparatus comprises a conical damping mass located within a conical axial bore. A hollow pin is threaded into an axially extending recess of the damping mass and one end of an adjustable spring rod is inserted into the hollow pin. The other end of the adjustable spring rod is coupled to a wall of the bore via an adjustable sleeve. A damping fluid is provided within the bore.

[0005] A problem with this known device is that it is difficult to design the device to provide good and consistent attenuation over a desired frequency range and / or a desired amplitude range. Summary of the Invention

[0006] The object of the present invention is to alleviate the drawbacks of the prior art and to provide a vibration-damped tool holder which is easier to adjust. This object is achieved according to the present invention by a vibration-damped tool holder for metal cutting tools as claimed in claim 1.

[0007] The present invention relates to a vibration damped tool holder for metal cutting tools, comprising a holder body having a first holder body end, a second holder body end and a longitudinal axis extending from the first holder body end to the second holder body end. The holder body is provided with an internal cavity, the internal cavity being defined by an internal cavity surface, extending into the holder body along the longitudinal axis and having a first cavity end at the first holder body end. The damped tool holder further comprises an adjustment mass movably arranged within the cavity. In a neutral rest position, the adjustment mass extends along the longitudinal axis and has a first adjustment mass end at the first holder body end. The damping toolholder further comprises a damping medium surrounding the tuning mass within the cavity, and a single primary spring element positioned within the cavity and having an outer spring element end and an inner spring element end, the outer spring element end being fixedly secured to the first cavity end about its longitudinal axis, and the inner spring element end being fixedly secured to the first tuning mass end about its longitudinal axis.

[0008] The tool holder thus comprises a cavity in which the tuning mass, the primary spring element and the damping medium are arranged. These components constitute a mass-damper system in which the tuning mass corresponds to the oscillating mass and the primary spring element and the damping fluid provide the stiffness and damping. When designing a vibration-damped tool holder, the desired stiffness and the desired damping required for an optimized response to a selected induction frequency and / or amplitude are calculated. Thanks to the configuration of the primary spring element and the immovable connection of the primary spring element, very little damping is added to the system by the primary spring element. Furthermore, the damping medium, e.g. a fluid, can be selected such that very little stiffness is added to the system by the damping medium. The primary spring element and the damping fluid can therefore be selected independently to meet the calculated values.

[0009] In contrast, in prior art devices, including the device of U.S. Pat. No. 3,598,498, the spring components also inherently provide damping to the system due to their mounting and configuration. Thus, tuning the spring components of the prior art devices to meet a desired stiffness also affects the damping of the device. Thus, designing prior art tool holders to provide a desired response over a frequency range and amplitude is significantly more difficult than the vibration damped tool holder of the present invention.

[0010] The primary spring element is fixedly secured with its outer spring element end to the first cavity end and with its inner spring element end to the first tuning mass end. Thereby, there is no relative movement between the outer spring element end and the first cavity end, and between the inner spring element end and the first tuning mass end. In other words, there is no relative translation or rotation between each end of the primary spring and the associated end to which it is connected. The connection at both ends of the primary spring element can be described as rigid. Thereby, damping in the connection itself, caused for example by friction, can be neglected.

[0011] The tuning mass is movably disposed within the cavity such that vibrations of the toolholder during operation cause the tuning mass to move, e.g., oscillate, within the cavity. When the tuning mass is in a neutral rest position, the tuning mass extends along a longitudinal axis of the holder body. This may be an equilibrium state when the vibration damped toolholder is not in operation or at rest.

[0012] According to one embodiment, the damping of the primary spring element is structural damping. This should be understood as any other form of damping that may come from the primary spring element during normal operation of the vibration damping tool holder is so small that it can be neglected compared to the structural damping. Other forms of damping other than the structural damping coming from the spring element are smaller in magnitude and do not affect the vibration damping tool holder during normal operation of the vibration damping tool holder. Structural damping should be understood as the damping in the material of the primary spring element when it operates, e.g. when it bends or flexes. Since the structural damping of the spring element is low, this ensures that almost all the damping added to the system comes from the damping medium. This allows the desired damping of the vibration tool holder to be achieved by selecting a suitable damping medium without considering the damping of the primary spring element.

[0013] Optionally, the tuning mass is suspended only by the primary spring element. The primary spring element is the only component that defines the position of the tuning mass when the tuning mass is in equilibrium and in the rest position, since the damping medium yields to any force of the tuning mass. Thereby, advantageously, the vibration-damped tool holder is devoid of components that may add damping or stiffness of the damping medium or the primary spring element, respectively. Optionally, except for the damping medium, the primary spring element is the only component that contacts the tuning mass in the rest position or in all its positions.

[0014] Preferably, the tuning mass is pivotally arranged in the cavity. According to one embodiment, the tuning mass is pivotable around the axis of the primary spring element. The tuning mass is, for example, pivotable over an angle α around several different axes perpendicular to the longitudinal axis. Preferably, the tuning mass is pivotable around each axis perpendicular to the longitudinal axis. For each pivot axis of the tuning mass, the primary spring element can function as or similar to a cantilever spring, one end of which is fixed and the other end of which carries a mass in the form of the tuning mass. The inertia that the pivoting tuning mass provides to the system depends on the length of the tuning mass. When pivoting in the limited space of the cavity, a long tuning mass can provide more inertia to the system than a conventional mass of the same size suspended for translational motion. Thereby, advantageously, the tuning mass can be lighter than a conventional translational mass and still achieve the same or better damping results. Thus, the tuning mass of the vibration damped tool holder according to the present embodiment advantageously adds less weight to the tool holder than the translational mass of a prior art tool having the same dimensions.

[0015] Preferably, the first cavity end comprises a first cavity end face and the first tuning mass comprises a first tuning mass end face. Preferably, both end faces are flat at the connection with the associated end of the primary spring element and both end faces contact or are integral with the periphery of the associated end of the primary spring element. This allows the primary spring element to protrude from both of the respective planes. Such a design allows the tuning mass to pivot freely and at a maximum distance relative to the pivot axis of the primary spring element. Furthermore, it is ensured that the first cavity end and the first tuning mass end have as little influence as possible on the stiffness of the primary spring element. Optionally, both end faces extend in a plane perpendicular to the longitudinal axis.

[0016] The primary spring element may be of any suitable type having an elongated extension between two opposing ends. Preferably, the primary spring element is arranged and configured to bend in response to an excitation from the adjustment mass. Thus, the primary spring element is bendable and the adjustment mass is pivotable by bending of the primary spring element. Preferably, when the adjustment mass is in a neutral rest position, the primary spring element extends along the longitudinal axis of the holder body. This may be an equilibrium state when the vibration damped tool holder is non-operated or at rest. For example, the primary spring element is a separate component in the form of a rod, tube or helical screw attached to the first cavity and the first adjustment mass end. Preferably, the primary spring element is a solid rod.

[0017] According to one embodiment, the first cavity end, the first tuning mass end, and the primary spring element are integral and made from a single workpiece. This advantageously ensures that the two primary spring element ends are immovably connected to the first cavity end and the first tuning mass end, respectively. For example, the primary spring element is a rod extending from the first cavity end to the first tuning mass end, the rod being integral with both the first cavity end and the first tuning mass end.

[0018] A preferred method of manufacturing the tuning mass, the first cavity end and the primary spring element is to provide a solid blank having the shape of the tuning mass. Material is then removed from the solid blank near one end thereof until the desired shape of the primary spring element is obtained. The primary spring element can have a minimum cross-sectional area that is smaller than the average cross-sectional area of ​​the tuning mass. For example, a solid cylindrical blank can be turned to form the primary spring element between the remaining material at the outer end that forms the cavity end and the remaining material at the inner end that forms the tuning mass. Preferably, the cavity, the tuning mass and the primary spring element have a circular cross-section.

[0019] Optionally, the tuning mass comprises tungsten, tungsten carbide, tungsten alloy, cemented carbide, steel or steel alloy. Optionally, the primary spring element comprises tungsten, tungsten carbide, tungsten alloy, cemented carbide, steel or steel alloy. In embodiments where the first cavity end, the first tuning mass end and the primary spring element are integral and made from a unitary workpiece, the unitary workpiece comprises a material from this list, preferably cemented carbide or steel. Preferably, the cavity is formed in a body comprising a material from this list.

[0020] The tuning mass can have any suitable shape. The shape of the tuning mass can be selected depending on the desired weight and / or inertia. Since a pivoting tuning mass has a larger movement than a corresponding conventional translating mass, the tuning mass provides a larger inertia to the system than when it translates. It is advantageous to provide a cavity that extends over the entire available length of the toolholder body and to place the tuning mass as long as possible in the cavity so that the inertia of the pivoting tuning mass is as large as possible. Thus, the tuning mass can extend all the way from the primary spring element at the first cavity end to the opposite end of the cavity. To further increase the inertia, the mass of the tuning mass may be concentrated at an end that is distal to the first tuning mass end.

[0021] Preferably, the tuning mass has only a circular cross section, so that the tuning mass has equal quality in all directions perpendicular to the longitudinal axis along which it pivots. Optionally, the tuning mass is cylindrical, conical or spherical. Optionally, the tuning mass is solid or hollow.

[0022] The outer surface of the tuning mass can be selected for a desired interaction with the damping medium. Optionally, the outer surface of the tuning mass is smooth, rough or includes protruding elements such as fins.

[0023] The primary spring element adds stiffness to the vibration damping tool holder. The minimum cross-sectional area of ​​the primary spring element determines the stiffness of the primary spring element. According to one embodiment, the primary spring element has a cross-sectional area that increases in both directions toward the respective ends from a minimum cross-sectional area at a distance from both the outer spring element end and the inner spring element end. Such a design allows for an accurate selection of stiffness while reducing the risk of crack formation. The primary spring element is, for example, a solid component with a circular cross-section, and the minimum cross-sectional area of ​​the primary spring element is, for example, in the middle between the ends. In other embodiments, the cross-sectional area of ​​the primary spring element is constant along a portion, for example a main portion, or along the entire longitudinal length of the primary spring element.

[0024] Preferably, the damping medium is a fluid, more preferably a liquid. The damping medium may also be a combination of several materials and / or a combination of fluids, gases or solids. If the damping medium is a fluid, the cavity is closed, preferably sealed to tightly retain the fluid and prevent leakage.

[0025] The damping medium is located within the cavity and surrounds the tuning mass. The damping medium can be selected to achieve the desired damping given the selected tuning mass, primary spring element and / or internal cavity. For example, by first selecting an appropriate density and geometry for the tuning mass, and an appropriate geometry for the cavity, and then selecting an appropriate type of damping medium, and / or an appropriate distribution of the damping medium within the cavity, the desired damping of the vibration damped toolholder is achieved.

[0026] For example, the damping medium is distributed along the tuning mass in the longitudinal and circumferential directions. Optionally, the damping medium fills part or all of the cavity, being distributed uniformly or non-uniformly. In this case, the tuning mass may be only partially surrounded by the damping medium. The damping medium may be concentrated, for example, at an end in the cavity opposite the first cavity end. This allows the damping characteristics of the tool holder to be designed for a particular damping characteristic.

[0027] Typically, when establishing the stiffness and damping of a structure, the Frequency Response Function (FRF) of the structure is obtained, for example using impact hammer or shaker tests. If the FRF is calculated in the frequency domain, the corresponding curve can be plotted as frequency versus magnitude. The target natural frequency, which is the natural frequency related to the desired application, can be seen as the peak of the curve. The location of the peak, i.e. the natural frequency, is an indication of the stiffness of the structure at this frequency. The width of the curve at the peak is an indication of the damping at this frequency.

[0028] In general, stiffness and mass are the two main factors that determine the natural frequency of a structure. When adding a damping medium to a vibration damped tool holder, the mass of the damping medium can be neglected compared to the holder body and the adjusting mass. However, when comparing the FRF curves obtained for a damped vibration tool holder without and with a damping medium, the peak natural frequency is different. This change indicates the stiffness added to the vibration damped tool holder by the damping medium.

[0029] According to one embodiment, the damping medium in the form of a damping fluid is selected and distributed within the internal cavity such that the target natural frequency of the vibration-damped tool holder is reduced by at most 15%, preferably at most 10%. The small portion of stiffness coming from the damping fluid further contributes to ensuring that nearly all stiffness added to the system is provided by the primary spring element. Furthermore, due to the low damping of the primary spring element, nearly all damping of the system is provided by the damping medium. Thus, the primary spring element and the damping fluid can be independently selected to meet the desired characteristics of the vibration-damped tool holder.

[0030] The combination of a pivoting adjustable mass, a primary spring element providing precisely selectable stiffness, and a separate damping medium providing precisely selectable damping advantageously achieves high independence of the vibration damped tool holder from the amplitude of induced vibrations. Thus, embodiments of the vibration damped tool holder have improved efficiency for low amplitudes compared to prior art devices comprising a translating mass suspended by a component having both stiffness and damping properties.

[0031] Optionally, the vibration damped toolholder further comprises an auxiliary resilient element disposed in the cavity, the auxiliary resilient element positioned and configured to be excited by the tuning mass only when the tuning mass pivots beyond a threshold angle α. The resilient element primarily adds stiffness to the system, but also has inherent damping. The inherent damping may result from the shape of the resilient element and / or the selected resilient material.

[0032] Preferably, the auxiliary elastic element comprises a polymer, such as, for example, nitrile, silicon or polyethylene. In general, the advantage of elastic polymer elements in a damping system is that they work well for high amplitudes. Thus, in one embodiment of a damped vibration tool holder, the arrangement of a polymer elastic element that only operates when the induced vibration has a high amplitude makes it possible to improve the efficiency of the tool holder for high amplitudes without affecting the already good results at low amplitudes.

[0033] Preferably, the tuning mass is maximally pivotable at a maximum angle α, with the threshold angle being at least 20% of the maximum angle. The maximum angle α may be determined by the maximum arc length the tuning mass may pivot without contacting the cavity wall. In an embodiment having a cylindrical tuning mass and cavity, the threshold angle may correspond to a radial movement of the distal end of the tuning mass of 20% of the difference in diameter between the tuning mass and the cavity. The distal end of the tuning mass is the end opposite the first end and proximate to the second holder body end.

[0034] According to one embodiment, the vibration damping tool holder further comprises a secondary auxiliary elastic element arranged in the cavity for damping longitudinal vibrations. The secondary auxiliary elastic element may for example be arranged between the distal end of the adjustment mass and the cavity wall at the second holder body end. Preferably, the influence of the secondary auxiliary elastic element is negligible for pivotal movements of the adjustment mass below a threshold angle.

[0035] Optionally, the auxiliary resilient element is configured to compress or stress in response to an excitation from the tuning mass.

[0036] According to a preferred embodiment, the first holder body end is the front end having a contact surface for supporting the cutting head. This positions the spring element closer to the cutting head where vibrations are induced during operation. Furthermore, the counterforce from the pivoting adjustment mass acts on the spring element and therefore closer to the cutting head. Another advantage is that most of the damping takes place at the distal end of the adjustment mass, i.e. the end located furthest from the primary spring element and the cutting head where heat is generated during operation. Since many damping media are heat sensitive or change their damping characteristics in response to heat, the damping characteristics of this embodiment of the vibration damping tool holder are therefore less heat sensitive.

[0037] The vibration-damped tool holder according to the invention may be included in a metal cutting tool, such as, for example, a turning, milling, drilling or boring tool. Preferably, the metal cutting tool is a non-rotating metal cutting tool, such as, for example, a drilling tool. Drilling tools are particularly susceptible to vibrations when used to drill deep holes, due to the large required length of the tool holder. Thanks to the adjustment mass of the embodiment of the vibration-damped tool holder, which as described above relies mainly on inertia, long adjustment masses with small diameters can be used. This is advantageous in long boring bars intended for deep holes with small diameters.

[0038] According to one embodiment, a non-rotating metal cutting tool, such as a boring bar, comprises an elongated body including a vibration-damped tool holder and a cutting head. According to a preferred embodiment, the holder body comprises a contact surface at a first holder body end, the front end, for releasably connecting the cutting head to the vibration-damped tool holder. In another embodiment, the cutting head is integral with the holder body. The cutting head comprises a cutting edge, which may be integral with the cutting head or located on an exchangeable cutting insert. At a second holder body end, the rear end, a shank is provided for connecting the cutting tool to a machine tool. Optionally, the shank is provided with a coupling, such as, for example, a Coromant Capto© coupling.

[0039] Exemplary embodiments will now be described in more detail and with reference to the accompanying drawings. [Brief description of the drawings]

[0040] [Figure 1] FIG. 1 is a perspective view of a first embodiment of a non-rotating metal cutting tool comprising a vibration damped tool holder in the form of a boring bar. [Diagram 2] FIG. 2 is a perspective view of the vibration dampened toolholder shown in FIG. 1 showing only the tuning mass and the front / first end of the cavity. [Figure 3a] 3 is a side view of the boring bar shown in FIG. 1, showing in schematic longitudinal section the vibration-damped tool holder of FIG. 2; [Figure 3b] 3 is a side view of the boring bar shown in FIG. 1, showing in schematic longitudinal section the vibration-damped tool holder of FIG. 2; [Figure 4] FIG. 13 is a longitudinal cross-sectional view of an alternative embodiment of a vibration damped tool holder. [Diagram 5] FIG. 13 is a longitudinal cross-sectional view of an alternative embodiment of a vibration damped tool holder. [Figure 6] FIG. 13 is a longitudinal cross-sectional view of an alternative embodiment of a vibration damped tool holder. [Figure 7] FIG. 13 is a longitudinal cross-sectional view of an alternative embodiment of a vibration damped tool holder. [Figure 8]FIG. 13 is a longitudinal cross-sectional view of an alternative embodiment of a vibration damped tool holder. [Figure 9] FIG. 13 is a longitudinal cross-sectional view of an alternative embodiment of a vibration damped tool holder. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] All figures are schematic, not necessarily to scale, and generally show only the parts necessary to elucidate the respective embodiment, while other parts may be omitted or merely suggested. Unless otherwise indicated, like reference numbers refer to like parts in different figures.

[0042] With reference to figures 1 to 3, a first embodiment of a vibration damped tool holder 1 is shown. The tool holder 1 is a tool holder for a non-rotating metal cutting tool in the form of a boring bar 2. The tool holder comprises a holder body 3 having a first holder body end in the form of a front end 4 and a second holder body end in the form of a rear end 5. The holder body has a longitudinal extension along a longitudinal axis 6 from the front end 4 to the rear end 5. In the metal cutting boring tool 1 of figure 1, a cutting head in the form of a drilling head 7 is connected at the front end 4 to the holder body 3 of the tool holder 1. As can be seen in figure 2, the holder body 3 is provided with a contact surface in the form of a coupling, in particular a Coromant Capto (copyright) coupling, for receiving a corresponding coupling (not shown) at the cutting head 7. The cutting head 7 is fitted with a replicable cutting insert 8 having a cutting edge 9.

[0043] 3, the holder body 3 is provided with an internal cavity 10 defined by a cavity surface 11. The cavity 10 extends into the holder body 3 along a longitudinal axis 6 from a first cavity end in the form of a front end. The cavity 10 has a front end face 12 at the front end and a rear end 13 at an opposite end closer to the second holder body end 5. At the rear end 13 a duct 14 is in fluid communication with the cavity for connecting the cavity 10 with the outside of the holder body 3 at the rear end 5.

[0044] The tool holder 1 further comprises an adjustment mass 15. The adjustment mass 15 is movably arranged in the cavity 10 and extends along the longitudinal axis 6 in a neutral rest position shown in FIG. 3. The adjustment mass 15 has a first adjustment mass end in the form of a front end 16 at the front end face 12 of the cavity 10. The adjustment mass 15 has a rear end face 17 at an opposite end closer to the rear end 5 of the holder body 3.

[0045] A single primary spring element 18 is positioned within cavity 10. The primary spring element has a longitudinal extension from an outer spring element end 19 to an inner spring element end 20.

[0046] The front end with front end face 12 of cavity 10, the adjustment mass 15 with a front end with front end face 16, and the primary spring element are integral, made from a unitary workpiece and comprise cemented carbide. In an exemplary embodiment, the weight of the integral components is 0.44 kg. This immovably fixes the two primary spring element ends 19, 20 to the front end face 12 of cavity 10 and the front end face 16 of the first adjustment mass 15, respectively.

[0047] The tuning mass 15, as well as the primary spring element, cavity 10 and duct 14, all have circular cross-sections along their entire lengths. The tuning mass 15, as well as the primary spring element 18 and the main chamber of cavity 10 which houses the tuning mass 15, are cylindrical. In the exemplary embodiment, the tuning mass 15 is 90 mm long from the longitudinal center to the distal end of the primary spring element 18 and has a diameter of 23 mm.

[0048] The primary spring element 18 has a cross-sectional area that increases in both directions from a minimum cross-sectional area 23 midway between the outer spring element end 19 and the inner spring element end 20 toward the respective ends 19,20.

[0049] The tool holder 1 further comprises an auxiliary elastic element 21 in the form of a polymer O-ring. The O-ring 21 is located in a slot in the circumferential surface of the rear end adjustment mass 15.

[0050] 20mm 2 A damping medium 22 in the form of an oil having a viscosity of 1 / s fills the remaining space within the cavity 10 .

[0051] In Fig. 3a, the tool holder 1 is inactive and at rest. The primary spring element 18 is in an equilibrium rest position and extends along the longitudinal axis 6 of the holder body 3 and the adjustment mass 15. In the illustrated rest position, the O-ring 21 does not contact the cavity surface 11, so that the adjustment mass 15 is suspended only by the primary spring element 18.

[0052] During operation, varying cutting forces from the cutting edges 9 of the cutting inserts 8 act on the boring bar, which causes the holder body 3 to oscillate and vibrate by pivoting about an axis at the primary spring element 18. Inertia from the tuning mass 15 causes the primary spring element 18 to flex, which in turn causes the tuning mass 15 to pivot about an axis perpendicular to the longitudinal axis 6 at the primary spring element 18.

[0053] A damping medium in the form of a damping liquid is selected and distributed within the internal cavity such that the target natural frequency of the vibration-damped tool holder is thereby reduced by up to 10%. This is verifiable by experiment in the form of impact hammer tests and by calculating the frequency response functions (FRFs) in the frequency domain of the vibration-damped tool holder with and without the damping medium. Essentially all of the stiffness added to the system therefore comes from the primary spring element. Thus, by providing the primary spring element 18 with an appropriate cross-sectional area along its length, a desired spring constant can be obtained.

[0054] In a first exemplary embodiment, the damping medium is a liquid. A damping liquid that works well with the pivoting mass and primary spring element of the first embodiment of the vibration damping tool holder is a liquid having a low viscosity, e.g. 2 / s, preferably less than 20 mm 2 It is an oil having a viscosity of less than 1 / s.

[0055] In the first exemplary embodiment, the damping of the primary spring element 18 is structural damping and all other forms of damping coming from the primary spring element, including its ends 19 and 20, can be neglected. Thus, essentially all damping added to the system comes from the damping medium 22.

[0056] By appropriately adjusting the stiffness of the primary spring element 18, the damping of the damping medium 22 and the weight / inertia of the tuning mass 15, the movements of the tuning mass will act against the movements of the holder body 3, thus damping its vibrations. The tuning mass 15 will move with a different phase and / or frequency.

[0057] Thanks to the design with the primary spring element 18 and the pivoting mass, the vibration-damped tool holder according to the first embodiment is more sensitive to low amplitudes than prior art devices with a translating mass. The vibration-damped tool holder therefore has similar damping properties for a wider range of amplitudes. In other words, the vibration-damped tool holder is less amplitude-dependent.

[0058] The tuning mass 15 pivots through a larger angle α in response to an increase in the amplitude. When the angle α reaches a threshold value, the O-ring 21 contacts the cavity wall 11 (see FIG. 3b). The O-ring 21 is excited by the tuning mass 15 pressing it against the cavity wall 11 and is thereby compressed. Thanks to the arrangement of the O-ring 21 in the first embodiment of the damped vibration tool holder such that it only operates when the induced vibration has a high amplitude, the efficiency of the tool holder for high amplitudes is improved without affecting the already good results at low amplitudes.

[0059] In the first exemplary embodiment, the maximum angle α that the tuning mass 15 can pivot within the available space in the cavity 10 is 1.3°. The threshold angle α is 0.26°.

[0060] In figures 4 to 9 alternative embodiments of the vibration damped tool holder 1 are shown. These embodiments differ from the first embodiment described above mainly by the design of the adjustment mass 15, the primary spring element 18 and the auxiliary elastic element 21, which is why the description of the embodiment in figures 4 to 11 focuses on these components.

[0061] In one embodiment of the vibration damped tool holder 1, shown in Figure 4, the primary spring element 18 is in the form of a long rod with a small circular cross section. The primary spring element 18 in the form of a rod and the adjustment mass 15 have the same constant cross section over their entire length. The long pivoting adjustment mass 15 of this embodiment provides sufficient inertia for the damping system without being large and heavy. This embodiment is advantageous for applications where the tool holder is to be inserted into a small diameter hole where it cannot have a large cross section.

[0062] In FIG. 5 an embodiment of the vibration damping tool holder 1 is shown, where the adjustment mass 15 comprises three sections. The first section 15a, closest to the primary spring element, is cylindrical with a cross section maximized to fit into the cavity while leaving a suitable clearance to allow pivoting. Section 15a is similar to the adjustment mass 15 of the first embodiment. The third section 15c extends into the duct 14 and is formed as a cylindrical rod with a constant small cross section similar to the adjustment mass 15 of the embodiment of FIG. 4. The second intermediate section 15b is located between the first section 15a and the third section 15c and forms a conical transition. The extension of the adjustment mass 15 into the duct allows the adjustment mass 15 to be longer so as to provide a larger inertia to the damping system. The conical section 15b ensures that no new spring elements are introduced in the transition from the first section 15a with a larger cross section to the third section 15c with a smaller cross section.

[0063] In figures 6a, 6b an embodiment of a vibration damped tool holder 1 is shown, where the adjustment mass 15 and the primary spring element 18 are similar to the embodiment of figure 4. The embodiment has a different kind of auxiliary elastic element 21 in the form of an O-ring arranged around the primary spring element 18. In figure 6a the tool holder 1 is inactivated and at rest.

[0064] The primary spring element 18 is in an equilibrium rest position and extends along the longitudinal axis 6 of the holder body 3 and the adjustment mass 15. In the illustrated rest position, the O-ring 21 is in contact with the front end face 16 of the adjustment mass 15 but not with the front end face 12 of the cavity 10. In the rest position of FIG. 6a, the adjustment mass 15 is suspended only by the primary spring element 18.

[0065] In Fig. 6b, the adjustment mass 15 has been pivoted through an angle α greater than the threshold value. The O-ring 21 contacts the front end face 12 of the cavity 10 and is excited and compressed against the front end face 12 of the cavity 10 by the front end face 16 of the adjustment mass 15. Thereby, the O-ring 21 of the embodiment of Figs. 6a, 6b improves the efficiency of the tool holder for high amplitudes without affecting the already good results at low amplitudes.

[0066] The embodiment of the vibration-damped tool holder 1 shown in Figure 7 is similar to the embodiment of Figure 3. In the embodiment of Figure 7, a shaft 24 is arranged in the duct 14. An auxiliary elastic element 21 in the form of an O-ring is arranged around the shaft 24 and interacts with an internal recess wall 25 of the adjustment mass 15 during an oscillation to pivot beyond a threshold angle α.

[0067] In Fig. 8 an embodiment of the vibration damping tool holder 1 is shown, where the tuning mass 15 comprises spherical balls 25. In this embodiment, it is possible to design the weight and weight distribution of the tuning mass 15 by selecting the appropriate balls and their positions within the tuning mass 15. The balls 25 can have the same or different weights. The cavity can comprise several compartments for holding the selected balls to ensure that the desired weight distribution is maintained.

[0068] In Fig. 9, an embodiment of the vibration damping tool holder 1 is shown, where the tuning mass 15 comprises two sections. The first section 15d, closest to the primary spring element, is a cylindrical rod with a small cross section similar to the rod of the embodiment of Fig. 4. The second section 15d comprises a spherical ball with a diameter maximized to fit in the cavity while leaving adequate clearance to allow pivoting. This design of the tuning mass 15 is advantageous in providing high inertia within the limited space of the cavity 10.

Claims

1. A vibration damping tool holder (1) for a metal cutting tool (2), the vibration damping tool holder (1) comprising a holder body (3), the holder body (3) having a first holder body end (4), a second holder body end (5), and a longitudinal axis (6) extending from the first holder body end (4) to the second holder body end (5), the holder body (3) being provided with an internal cavity (10), the internal cavity (10) being defined by an internal cavity surface (11), extending into the holder body (3) along the longitudinal axis (6) and having a first cavity end at the first holder body end (4), the damping tool holder being a tuning mass portion (15) which is disposed movably within the cavity (10), extending along the longitudinal axis (6) in a neutral rest position and having a first tuning mass end at the first holder body end (4), a tuning mass portion (15), a damping medium (22) surrounding the tuning mass portion (15) within the cavity (10), and a single primary spring element (18) positioned within the cavity (10) and having a longitudinal extension from an outer spring element end (19) to an inner spring element end (20), the vibration damping tool holder (1) further comprising: the outer spring element end (19) being fixedly immovable at the first cavity end on the longitudinal axis (6), and the inner spring element end (20) being fixedly immovable at the first tuning mass end on the longitudinal axis (6), characterized in that the vibration damping tool holder (1).

2. The vibration damping tool holder according to claim 1, wherein the damping of the primary spring element (18) is structural damping.

3. The vibration damping tool holder according to claim 1 or 2, wherein the tuning mass portion (15) is suspended only by the primary spring element (18).

4. The vibration damping tool holder according to claim 1 or 2, wherein the primary spring element (18) is bendable, and the tuning mass portion (15) is pivotable through an angle α about an axis of the primary spring element (15) perpendicular to the longitudinal axis (6) by bending of the primary spring element (18).

5. The vibration damping tool holder according to claim 1 or 2, wherein the first cavity end, the first tuning mass end, and the primary spring element (18) are integral and are made from a single workpiece.

6. The vibration damping tool holder according to claim 1 or 2, wherein the cavity (10), the adjustment mass part (15), and preferably the primary spring element (18) have a circular cross section.

7. The vibration damping tool holder according to claim 1 or 2, wherein the primary spring element (18) has a cross-sectional area that increases in both directions from a minimum cross-sectional area spaced from both the outer spring element end (19) and the inner spring element end (20) toward the respective ends (19, 20).

8. The vibration damping tool holder according to claim 1 or 2, wherein the damping medium (22) is a fluid, preferably a liquid.

9. The vibration damping tool holder according to claim 8, wherein the damping medium (22) in the form of a damping fluid is selected such that the target natural vibration frequency of the vibration damping tool holder is reduced by a maximum of 15%, preferably a maximum of 10%, and is distributed within the internal cavity.

10. The vibration damping tool holder according to claim 1 or 2, further comprising an auxiliary elastic element (21) disposed within the cavity (10), the auxiliary elastic element (21) being arranged and configured to be excited only by the adjustment mass part (15) when the adjustment mass part (15) pivots beyond a threshold angle.

11. The vibration damping tool holder according to claim 10, wherein the auxiliary elastic element (21) includes a polymer.

12. The vibration damping tool holder according to claim 10, wherein the auxiliary elastic element (21) is an O-ring disposed around the adjustment mass part (15) or the primary spring element (21).

13. The vibration damping tool holder according to claim 10, wherein the adjustment mass part (15) is pivotable maximally at a maximum angle, and the threshold angle is at least 20% of the maximum angle.

14. The vibration damping tool holder according to claim 1 or 2, wherein the first holder body end (4) is a front end for supporting a cutting head (7).

15. A drilling tool (2) comprising the vibration damping tool holder according to claim 1 or 2.

16. The drilling tool (2) according to claim 15, further comprising a cutting head (7), the cutting head (7) being connected to the holder body (3) at the first holder body end (4).

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