Cutting tools

Abstract

To provide a cutting tool that can stably reduce chatter vibrations, even in a range of high L / D (L: a protrusion length of the tool and D: an outer diameter of the tool).SOLUTION: A cutting tool (1) comprises a main body (10) having a containing space formed symmetrically around a rotary shaft and powder (P) contained in the containing space (101), which rotates with respect to a fixed work-piece. It is preferable that the powder has an average particle diameter of 1-250 μm and repose angles: 5°-40°. Further it is preferable that the powder has true densities: 4-23 g / cm3 and has degrees of circularity of 0.75 or higher of particles determined from an image analysis. The cutting tool (1), when using powder whose average diameter is comparatively small, can suppress large chatter vibrations generated therein. Further, the cutting tool (1), when using powder having excellent fluidity, can suppress small chatter vibrations generated therein.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to cutting tools and the like that have excellent vibration damping properties. [Background technology]

[0002] Machining is performed by moving a tool equipped with a cutting edge relative to the workpiece (material to be machined). There are mainly two types of machining: milling, where the workpiece is fixed and the tool is rotated, and turning, where the tool is fixed and the workpiece is rotated. However, milling (e.g., milling cuts, drilling, etc.) is usually used more frequently.

[0003] To ensure the quality (such as surface accuracy and roughness) and productivity of cutting processes (especially milling), it is necessary to suppress chatter vibrations that may occur in tools (e.g., end mills, shanks, holders, etc.). Various proposals have been made regarding the damping of chatter vibrations, and for example, there are descriptions related to the following patent documents. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Special Publication No. 2015-530268 [Patent Document 2] Japanese Patent Publication No. 2017-42863 [Patent Document 3] Japanese Patent Publication No. 2021-41498 [Overview of the project] [Problems that the invention aims to solve]

[0005] Patent Document 1 proposes a tool in which solid particles or hollow bodies are movably housed in a hollow structural element provided in the cavity of the tool body, thereby improving vibration damping characteristics. However, Patent Document 1 does not provide any specific description regarding the form (size, shape, etc.) or effects of the solid particles.

[0006] Patent Document 2 proposes a cutting tool holder in which a rod member and powder are housed in a hollow section. The particles constituting the powder are quite large (average particle size: 1 to 150 mm), and a spherical shape is preferred to improve packing efficiency (see

[0028] , etc.). However, Patent Document 2 does not provide any specific description regarding the vibration damping properties of the powder. Furthermore, since the rod member housed in the hollow section together with the powder changes its posture independently of the holder, it can become unbalanced during rotation, potentially becoming a new source of vibration. This tendency can become particularly pronounced when the tool rotation axis changes in various ways, from the vertical to the horizontal, such as in a machining center performing multi-axis machining.

[0007] Patent Document 3 proposes a cutting tool having wings that transport a fluid, filled in a hollow space (internal space) formed in the shank, to one end (the cutting tool side). The wings press the fluid against the cutting tool side, suppressing chatter vibration and rotational unbalance. Commercial powder used in powder bed fusion (particle size: 10-45 μm) is used as the fluid, and the shank is made of the same material as the powder (equivalent to SKD61) (see

[0068] , etc.). The particle shape of the powder is not described in Patent Document 3, but it is usually non-spherical.

[0008] This invention was made in view of these circumstances, and aims to provide cutting tools and the like with excellent vibration damping properties from a different perspective than conventional methods. [Means for solving the problem]

[0009] The inventors diligently researched how to solve this problem and discovered that by placing a specific powder in the hollow portion (internal space) of a cutting tool used for milling, vibration damping against chatter vibrations can be improved. Building upon this finding, the inventors completed the present invention described below.

[0010] 《Cutting tools》 (1) The present invention relates to a cutting tool that rotates relative to a fixed workpiece, comprising a body having a symmetrical internal space around a rotation axis and powder contained in the internal space, wherein the powder has an average particle size of 1 to 250 μm and an angle of repose of 5 to 40°.

[0011] (2) The cutting tool of the present invention (also simply called "tool") has excellent vibration damping properties and can suppress chatter vibrations that occur in the cutting tool during machining. For this reason, when using the tool of the present invention, good cutting (turning) is possible under a wide range of machining conditions, even in a high L / D (L: tool protrusion length, D: its outer diameter) range.

[0012] The reason why the tool of the present invention has excellent vibration damping properties is thought to be as follows: The constituent particles of the powder contained within the vibrating tool (simply referred to as "particles") repeatedly experience friction and collisions with each other or with the constituent walls of the enclosed space (simply referred to as "inner walls"), which can produce a damping effect. This changes the vibration characteristics of the tool, and the vibration energy is converted into thermal energy and dissipated. In this way, the vibration damping properties of the tool containing the powder can be improved.

[0013] However, it was found that the vibration damping properties can vary greatly depending on the particle morphology (size, shape, etc.) and fluidity of the powder. For example, in powders consisting of particles that are too small or too large, or irregularly shaped (also simply called "irregularly shaped"), and having low fluidity, the damping effect described above may be insufficient, at least under certain processing conditions (tool rotation speed, depth of cut, feed rate, etc.).

[0014] Specifically, to suppress vibrations with small amplitude and acceleration, a smaller static friction coefficient acting on the particles is preferable as it increases responsiveness. Conversely, to suppress vibrations with large amplitude and acceleration, a larger dynamic friction coefficient acting on the particles is preferable as it increases damping. The powder according to the present invention, as a result of its particles possessing predetermined shapes and characteristics, exhibits excellent responsiveness and damping, and is thought to be able to reduce tool chatter vibrations under a relatively wide range of machining conditions.

[0015] As a result of the powder according to the present invention exhibiting the above-described characteristics, even in a state where only the powder is present in the enclosed space (a state where a块状 vibration damping piece or the like is not incorporated), the tool of the present invention can exhibit sufficient vibration damping performance. In that case, even if the rotation axis of the tool tilts during cutting, the amount of eccentricity between the rotation axis and the center of gravity of the tool including the powder is suppressed, and rotational imbalance, which is a cause of vibration, is also less likely to occur.

[0016] 《Others》 (1) The cutting tool referred to in the present invention may be, for example, only a shank (handle, shaft portion), may further have a cutting tool, or may include other elements. Note that the cutting tool (cutting edge) may be detachable from the shank or may be fixed (non-detachable) to the shank.

[0017] (2) Unless otherwise specified, "x to y" as referred to in this specification includes the lower limit value x and the upper limit value y. A new range such as "a to b" can be newly established by using any numerical value included in the various numerical values or numerical ranges described in this specification as a new lower limit value or upper limit value. Also, unless otherwise specified, "x to y μm" as referred to in this specification means x μm to y μm. The same applies to other unit systems (sec / 50g, g / cm 3 etc.).

Brief Description of the Drawings

[0018] [Figure 1] Vertical cross-sectional view and horizontal cross-sectional view of the test tool. [Figure 2] List showing the specifications of the test powder (First Embodiment). [Figure 3] Photograph showing the state of the cutting test. [Figure 4] List showing the results of the cutting test. [Figure 5] Example of the time waveform of the cutting dynamometer. [Figure 6] Observation image and particle size distribution of the test powder (Second Embodiment). [Figure 7] Schematic diagram of the vibration test apparatus. [Figure 8] Graph showing the relationship between acceleration and attenuation coefficient under each test condition. [Figure 9] This graph shows the relationship between the average particle size of the powder and the sum of the equivalent damping coefficients. [Modes for carrying out the invention]

[0019] One or more components, arbitrarily selected from this specification, may be added to the components of the present invention. The contents described herein apply not only to the cutting tools of the present invention but also to their manufacturing methods, etc., as appropriate. Even method-related components can also be components relating to objects.

[0020] 《Powder》 (1) Overview The powder may be a single type of powder, or a mixed powder containing multiple types of powders with different compositions (components), forms (average particle size, particle shape, etc.), and properties (angle of repose, density, etc.). The powder only needs to be contained within the internal space to the extent that it does not leak or scatter when the tool is used (during cutting). In addition to the powder, the hollow part (internal space) of the tool may contain or be mixed with liquids such as cutting oil (cutting fluid, coolant, etc.) and lubricating oil (silicone oil, etc.). The liquid does not have to remain in the hollow part (internal space), but may be guided (supplied, discharged) to the cutting tool, etc., through a separately provided flow path (oil passage, etc.) to cool or lubricate the cutting tool or tool.

[0021] (2) Average particle size The average particle size of the powder can be, for example, 1-250 μm, 5-200 μm, 10-150 μm, 20-100 μm, or even 30-40 μm. Powders with an average particle size that is too small are difficult to handle, while powders with an average particle size that is too large may have reduced vibration damping properties.

[0022] In this specification, "average particle size" refers to the particle size (median diameter: Dv50) at which the volume distribution (cumulative distribution based on volume) obtained by measuring the size of each particle in the powder using the laser diffraction-scattering method becomes 50%. The measurement of the particle size distribution of the powder using the laser diffraction-scattering method is performed, for example, using a laser micronizer LMS-3000 manufactured by Seishin Corporation. When using commercially available powder, the nominal particle size (catalog value from the supplier (powder manufacturer), etc.) measured by a similar method may be used as the average particle size in this specification.

[0023] (3) Fluidity (angle of repose / flow rate) Powders should have excellent fluidity. Indicators of fluidity include the angle of repose and fluidity. The angle of repose for powders is, for example, 5°~40°, 10°~35°, 20°~33°, and even 24°~30°. The fluidity for powders is, for example, 0.4~2.3 sec / cm². 3 , 0.8~2.1 sec / cm 3 Furthermore, 1.2-1.9 sec / cm 3 That is the case.

[0024] The angle of repose was measured using the funnel injection method, with the following settings: funnel cone angle: 60°, orifice hole diameter: 2.6 mm, orifice length: 3.2 mm, height (distance from funnel tip to measuring platform): 33 mm, and measuring platform diameter: 34 mm. For the measuring device, for example, a bulk specific gravity meter manufactured by Tsutsui Chemical Machinery Co., Ltd. or an equivalent product may be used.

[0025] The fluidity is determined in accordance with JIS Z2502 (2012). However, since it is affected by volume and gravity due to true density, in this specification, the fluidity is expressed in terms of unit volume rather than unit mass.

[0026] (4) Circularity Each particle of the powder may be entirely or partially spherical. When viewed as a whole powder, the circularity obtained from image analysis is, for example, 0.75 - 1.00, 0.80 - 0.98, 0.83 - 0.95, or even 0.85 - 0.93. Incidentally, a circularity of 1.00 means that the particle shape appearing in the two-dimensional image is a perfect circle, and such particles are usually considered to be (substantially) spherical.

[0027] The circularity is obtained, for example, by processing an observation image (two-dimensional SEM image, etc.) of the powder with image analysis software (such as ImageJ). Specifically, it is as follows. In the observation image, binarization is performed at an arbitrary threshold from the grayscale information of each pixel to extract the contour of each particle. For each particle, its area (S) and perimeter (L) are acquired, and circularity = 4π×S / L 2 is calculated. The arithmetic mean value of the circularity calculated for about 70 (40 - 100) particles is adopted as the "circularity" of the powder referred to in this specification.

[0028] Incidentally, the circularity may also be obtained using the image processing function attached to the VHX-7000 manufactured by KEYENCE CORPORATION. In this case, it is advisable to use an observation image taken at a magnification of 400 times, a resolution of 2880×2160 pixels, and a pixel size of 0.26 μm / pixel.

[0029] (5) Density The tool itself to be vibration-damped is usually made of a high-specific-gravity metal (such as steel or cemented carbide). The mass ratio of the tool to the powder (total amount) can also affect the vibration characteristics and vibration-damping properties of such a tool. When using a powder with a large specific gravity (true density), the internal space for accommodating the powder can be made smaller, making it easier to ensure the (static) rigidity, strength, etc. of the tool, and increasing the degree of freedom in the shape of the tool. The true density of such powder (particles) is, for example, 4 - 23 g / cm 3 7 - 22 g / cm 3 13 - 21 g / cm 3 or even 18 - 20 g / cm 3 In any case, the true density of the powder should be equal to or greater than the true density of the main body (constituent material), and preferably even greater than that true density.

[0030] (6) Filling rate The filling density of powder within the enclosed space is, for example, 10-65%, 15-50%, and even 20-35%. The filling density of powder is determined as the ratio (Vp / Vs) of the total volume of powder contained within the partitioned enclosed space (Vs) to the total volume (Vp) within that space, as shown in the following formula. Vp is the sum of the volumes of each particle that makes up the powder, and can be calculated by dividing the total mass of the powder by the true density of that powder (particle). Filling rate (%)=(Vp / Vs)×100

[0031] (7)Material The powder may be, for example, metal powder or ceramic powder. The metal powder may consist of, for example, various types of steel (tool steel, structural steel, stainless steel, etc.), heavy metals with a higher specific gravity than steel (tungsten, cemented carbide, etc.), or light metals with a lower specific gravity than steel (aluminum, etc.). The powder may be a mixture of multiple powders with different materials (compositions). Also, if there are multiple enclosed spaces, the powder placed in each enclosed space may be the same or different type.

[0032] 《Internal Space》 The internal space is the space formed within the body of the tool (e.g., the shank). To avoid rotational imbalance, the internal space is preferably symmetrical about the axis of rotation of the tool. For example, the internal space may be axially symmetric (circular) with a constant outer shape in its cross-section (a cross-section perpendicular to the axial direction), or it may be rotationally symmetric, overlapping every 2π / n rotations (n: a natural number).

[0033] The enclosed space may be a sealed, closed space or an open space that communicates with the outside. The enclosed space containing the powder is preferably biased (its volume is larger) towards the tool side (one end) that cuts the workpiece than towards the gripping side (other end) of the machine tool. In other words, in a position where the rotation axis of the tool coincides with the direction of gravity, it is preferable that the volume (mass) of the powder be larger on the tool side than on the gripping side. This suppresses the reduction in static rigidity and efficiently suppresses chatter vibrations on the tool side.

[0034] The internal space may be a single unit or there may be two or more. If there is only one internal space, it is preferable that it be positioned closer to the cutting tool than to the gripping side. If the internal space extends axially, it may have a shape that expands closer to the cutting tool than to the gripping side (e.g., teardrop shape). If there are multiple internal spaces, the internal space closer to the cutting tool may be made larger, or powder may be contained only in the internal space closer to the cutting tool.

[0035] 《Cutting tools》 The body (shank) of a cutting tool is typically equipped with a cutting tool at its tip (one end) and gripped by a machine tool (chuck, etc.) at its base (the other end). The cutting tool may be replaceable or integrally mounted. In the case of a replaceable tool, a holder (part) for attaching the cutting tool is provided at the tip of the body. The holder may be integrally molded with the body, or it may be a head joined to the tip of the body by welding, brazing, etc. The head may be made of a different material from the body. For example, the body may be made of cemented carbide and the head may be made of steel.

[0036] The powder is filled into the internal space through an opening in the main body, for example, and then sealed by closing the opening with a lid or the like. The lid or the like is fastened to the opening (with screws, etc.), joined (welding, brazing, bonding, press-fitting (including shrink-fitting), etc.).

[0037] Cutting tools may be manufactured, for example, by powder bed fusion (PBF), directed energy deposition (DED), etc. If the raw material powder satisfies the desired form (average particle size, roundness, etc.) and properties (fluidity, density, etc.), the formation of the internal space and the containment of the powder may occur simultaneously. [Examples]

[0038] [First Embodiment] The present invention will be described in more detail while specifically evaluating the vibration damping properties of cutting tools.

[0039] 《Test tool》 As cutting tools (referred to as "test tools" as appropriate), we prepared end mill 1 and end mill 2, as shown in Figure 1.

[0040] (1) The end mill 1 has an elongated cylindrical shank 10 (main body), a holder 11 at its tip side (cutting edge side), and a cap 12 at its base side (gripping side).

[0041] The holder 11 has a head 111 at its tip that holds a throwaway tip c (simply referred to as "tip c"), which is a cutting tool, and a female thread 112 (threaded portion) into which a bolt (screw) that fixes tip c to the head 111 is screwed. The head 111 is joined to an opening at the tip of the shank 10, closing the tip of the shank 10.

[0042] The cap 12 can be screwed onto the opening on the gripping side of the shank 10 to close the gripping side of the shank 10.

[0043] The shank 10 has a tapered internal space 101 that expands towards the tip. Powder p is filled into this internal space 101 from an opening at the base of the shank 10. After filling, the opening is closed with a cap 12, and the powder p is sealed inside the internal space 101.

[0044] The tip c is attached to the holder 11, and the gripping side of the shank 10 is clamped to the collet chuck (simply called "chuck") of the machine tool. When the machine tool is operated, the end mill 1 rotates, and the workpiece (material to be cut), which is the test piece, can be milled by the tip c.

[0045] When the shank 10 is mounted on the chuck, the distance (L) from the tip surface of the chuck to the cutting edge of the tip c (or the tip of the holder 11) becomes the protrusion length. The L / D ratio, which is used as a guideline for the occurrence of chatter vibration, is defined by this distance (L) and the outer diameter of the shank 10 (shank diameter: D).

[0046] (2) The end mill 2 has a solid cylindrical shank 20 and a holder 11 and tip c similar to those of the end mill 1 on its tip side. Parts and components common to the end mill 1 are denoted by the same reference numerals, and detailed descriptions thereof have been omitted.

[0047] (3) The specific specifications of end mills 1 and 2 are as follows: End mills 1 and 2 are based on the basic shape (φ19.5mm x 160mm) of a commercially available tool (ARPF20S20 manufactured by MOLDINO Co., Ltd.), with an overall length of 253mm for end mill 1, an overall length of 248mm for end mill 2, and an outer diameter of φ20mm for shanks 10 and 20.

[0048] Shanks 10 and 20 are made of carbide (equivalent to ISO K10, true density: 15.0 g / cm³). 3 The holder 11 is made of pre-hardened steel (NAK55, true density: 7.8 g / cm³). 3 The shanks 10 and 20 and the holder 11 (head 111) were manufactured using conventional methods (such as cutting and grinding). The shanks 10 and 20 and the head 111 were joined by brazing. The shanks 10 and 20 and the holder 11 may also be manufactured using additive manufacturing methods such as powder bed fusion (PBF).

[0049] 《Test powder》 As powders to be filled into the internal space 101 of the end mill 1 for evaluation of vibration damping properties (referred to as "test powders" as appropriate), spherical powder (Spherical Tungsten Powder, Particle Size 15~53 μm, manufactured by Stanford Advanced Materials) and irregularly shaped powder (W-U250, particle size 23~28 μm, manufactured by Allied Materials) were prepared as shown in Figure 2. The observed images (SEM images), specifications, and characteristics of each powder are summarized in Figure 2.

[0050] The particle sizes Dv10, Dv50, and Dv90 shown in Figure 2 represent the particle sizes at which the volume distribution (cumulative distribution based on volume), obtained by measuring each constituent particle of the powder using laser diffraction and scattering methods, is 10%, 50%, and 90%, respectively.

[0051] Both spherical and irregularly shaped powders contain tungsten (true density: 19.25 g / cm³). 3 The product was manufactured using a specific method, and 57.2g of each powder was packed into the internal space 101 of end mill 1. The ratio of the total volume of the packed powder (Vp) to the volume of the internal space 101 (Vs) (packing rate: Vp / Vs) was 26.6%.

[0052] Machining Test Using the test tools and powders described above, the following cutting (milling) tests were performed.

[0053] (1) Cutting tool For the cutting tool (tip c), we used the ZCFW200-R2.0-PTH08M manufactured by MOLDINO Corporation. Although this tool originally has two blades, one of the blades was slightly machined to eliminate the influence of assembly errors on vibration measurements. Therefore, the workpiece (test piece) was processed using only one blade per rotation of each test tool (end mill). Cutting was performed only by the straight portion of the cutting edge on the outer circumference of the tool. The cutting test was conducted under these conditions.

[0054] (2) Equipment A machining center (VERTEX550-5X, manufactured by Mitsui Seiki Co., Ltd.) was used as the machine tool. The base of each end mill was clamped to the collet chuck at a position where L / D (projection length / shank diameter) = 11. The collet chucks used were BBT40-MEGA200-90 and NBC20-20AA, manufactured by Daishowa Seiki Co., Ltd.

[0055] A machining center with an end mill fitted with a cutting tool was operated to cut the side surface of a workpiece (made of pre-hardened steel (NAK55), 40mm wide x 5mm thick) placed on a cutting dynamometer (Kistler Japan Co., Ltd. 9257A). This process is shown in Figure 3.

[0056] (3) Conditions For each test tool, the spindle (end mill) rotation speed (5 levels) and depth of cut (8 levels) were changed, resulting in a total of 40 machining conditions (5 x 8 conditions). The 5 spindle speed levels were 3680 rpm, 3900 rpm, 4155 rpm, 4280 rpm, and 4500 rpm. The 8 depth of cut levels were 0.10 mm, 0.15 mm, 0.20 mm, 0.25 mm, 0.30 mm, 0.35 mm, 0.40 mm, and 0.45 mm. The feed rate per tooth was 0.2 mm / rev (down cut), and machining was performed in a dry atmosphere without cutting fluid. Under these machining conditions, the theoretical surface roughness (maximum height Rz / JIS B 0601:2001) was 0.50 μm.

[0057] (4) Measurement The surface roughness of the machined surface of the workpiece obtained under each condition was measured using a small surface roughness measuring instrument (Mitutoyo SJ-310 (0.75mN type)). The measurement was performed near the center of the workpiece end face (width 40mm x thickness 5mm) along the feed direction during machining. Surface roughness was measured according to the JIS standard (B 0601:2001), with the maximum height (Rz / μm) measured at a measurement length of 4.8mm. For each condition, machining and measurement were repeated three times, and the presence or absence of chatter vibration was determined from the average value.

[0058] The measurement results are summarized in Figure 4. In Figure 4, Test 1: Test using end mill 1 filled with spherical powder, Test 2: Test using end mill 1 filled with irregularly shaped powder, and Test 3: Test using solid end mill 2 without powder. In the results in Figure 4, good judgment is indicated by ○ and bad judgment by ×.

[0059] A negative rating (×) was given if the measured surface roughness of the machined surface was more than twice the theoretical finished surface roughness (Rz: 0.50 μm), or if two or more impact forces were detected during one rotation in the time waveform of the cutting dynamometer (see Figure 5). In all other cases (measured surface roughness is less than twice the theoretical value and there is only one impact force during one rotation), a good rating (〇) was given.

[0060] As shown in Figure 5, the reason why impact forces appear more than once per rotation in the time waveform of the cutting dynamometer is that a cutting edge, or the outer diameter of the head, which has been pre-cut and should not contribute to machining, unintentionally comes into contact with (collides with) the workpiece. This phenomenon can occur when the amplitude of chatter vibration is large.

[0061] Figure 4 also shows, for each of the three tests (1-3), the number of good results (number of circles) relative to the total number of tests (40 conditions), and the percentage increase or decrease in the number of good results relative to Test 3 (the baseline) (vibration damping / vibration resistance).

[0062] "evaluation" As is clear from Figure 4, by using a tool containing spherical powder, chatter vibration of the cutting tool was significantly suppressed even in the high L / D range, and good surface roughness was obtained even when cutting under various conditions.

[0063] From the above, it has been confirmed that the cutting tool of the present invention ensures high vibration damping and enables high-precision machining (including surface roughness) even in the high L / D range.

[0064] [Second Example] Based on the first embodiment, the relationship between the particle size of the spherical powder and its vibration damping properties (damping coefficient) was investigated as follows.

[0065] 《Test powder》 As shown in Figure 6, four types of zirconia powder with different particle sizes were used as test powders (YTZ balls manufactured by Tosoh Corporation / true density: 6.09 g / cm³). 3 A sample was prepared. The average particle size (Dv50) obtained by image processing of approximately 100 observed particles of each powder was 54 μm, 102 μm, 221 μm, or 415 μm. Incidentally, the nominal particle size of each powder was 50 μm, 100 μm, 200 μm, or 400 μm, as shown in Figure 6, and there was no significant difference from the average particle size (Dv50). Furthermore, as is clear from Figure 6, each powder consisted of uniform spherical particles with a narrow particle size distribution, and the circularity of the powders with nominal particle sizes of 50 μm, 100 μm, 200 μm, and 400 μm was 0.79, 0.85, 0.87, and 0.88, respectively.

[0066] Vibration Test (1) The vibration characteristics of each powder were evaluated using the test apparatus shown in Figure 7. The test apparatus consists of a container with a cubic space (1 cm on each side) for holding each powder, an impedance head (PCB PIEZOTRONICS 288D01), and a vibrator (The Modal Shop K2004E01), all directly connected in sequence.

[0067] In the vibration tests, various sinusoidal vibrations were applied to containers holding each powder (3.76g), and the damping coefficient for each powder under each condition was determined. The vibration frequencies were set to six levels: 300Hz, 400Hz, 500Hz, 600Hz, 700Hz, and 800Hz. The effective voltage used to control the vibration intensity was set to five levels: 0.10V, 0.25V, 0.50V, 0.75V, and 1.00V. Thus, a total of 30 (=5×6) vibration conditions were applied to each powder, and the damping coefficient under each condition was determined. The results, organized by vibration frequency, are summarized in Figure 8.

[0068] The reason for selecting the above six levels as vibration frequencies is as follows: In cutting processes, chatter vibration caused by the tool often occurs when L / D ≥ 6. Also, from the standpoint of static rigidity and strength of the tool, L / D is usually set to ≤ 11. In this range (6 ≤ L / D ≤ ​​11), the natural frequency of the tool's primary bending mode becomes the main cause of chatter vibration, and this natural frequency is approximately 300 to 800 Hz. For example, when end mills 1 and 2 shown in the first embodiment were mounted with L / D = 11 and a hammering test was performed, their primary natural frequencies were 310 to 340 Hz. Therefore, since chatter vibration caused by the tool in cutting processes only needs to be considered in the range of 300 to 800 Hz, the above six levels were selected.

[0069] (2) In a cutting test different from that of the first embodiment, the effective acceleration (Grms / simply referred to as "acceleration") generated near the cutting edge during stable cutting without chatter vibration was measured, and the maximum value was approximately 13 Grms. Furthermore, when a cutting test was performed with a very shallow depth of cut (0.025 mm), which is not performed in normal cutting, the acceleration generated near the cutting edge was approximately 2 Grms. Therefore, considering stable cutting conditions without chatter vibration, the acceleration generated near the cutting edge can be said to be between 2 and 13 Grms.

[0070] Applying these findings to the results shown in Figure 8, the sum of the damping coefficients (equivalent damping coefficients) obtained for each powder with different particle sizes in the range where the acceleration is 2 to 13 Grms was calculated. The results are summarized in Figure 9. Note that Figure 8 shows the nominal particle size, while Figure 9 shows the corresponding average particle size (Dv50).

[0071] "evaluation" As can be seen from Figure 8, under normal cutting conditions (acceleration of 5Grms or more), the smaller the powder particle size, the larger the damping coefficient, indicating superior vibration damping against chatter vibrations. Furthermore, as can be seen from Figure 9, chatter vibrations can be effectively suppressed by setting the average particle size of the powder used to fill the tool to 300 μm or less, 250 μm or less, and even 200 μm or less.

[0072] From the above, it was confirmed that chatter vibration can be effectively suppressed when the powder contained within the tool consists of spherical particles with an average particle size within a predetermined range. [Explanation of symbols]

[0073] 1. End mill (cutting tool) 10 Shank (Main body) 11 holder 12 caps 101 Integral space p powder

Claims

1. A body having an enclosed space symmetrical around the axis of rotation, The enclosed space contains powder, A cutting tool that rotates relative to a fixed workpiece, The aforementioned powder has an average particle size of 1 to 250 μm and an angle of repose of 5° to 40°. The main body is made of cemented carbide, The powder consists of tungsten, A cutting tool in which the true density of the powder exceeds the true density of the main body.

2. The cutting tool according to claim 1, wherein the powder comprises particles having a circularity of 0.75 to 1.

00.

3. The cutting tool according to claim 2, wherein the powder comprises spherical particles.

4. A cutting tool according to any one of claims 1 to 3, wherein the packing rate (Vp / Vs), which is the ratio of the volume of the powder (Vp) to the volume of the enclosed space (Vs), is 10 to 65%.

5. The cutting tool according to any one of claims 1 to 4, wherein the enclosed space is biased toward the cutting tool side that cuts the workpiece rather than the gripping side by the machine tool.

Images