JP7847958B2 - cutting tools - Google Patents

Description

This invention relates to cutting tools and the like that exhibit excellent vibration damping properties.

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 rotates, and turning, where the tool is fixed and the workpiece rotates. However, milling (e.g., milling cuts, drilling) is more commonly used.

To ensure the quality (such as surface accuracy and roughness) and productivity of machining 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; for example, there are descriptions related to the following patent documents.

Special table 2015-530268 publication Japanese Patent Publication No. 2017-42863 Japanese Patent Publication No. 2021-41498

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 morphology (size, shape, etc.) or effects of the solid particles.

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 filling efficiency ([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 create an imbalance during rotation, potentially becoming a new source of vibration. This tendency can become particularly pronounced in machining centers that perform multi-axis machining, where the tool rotation axis varies considerably between the vertical and horizontal directions.

Patent Document 3 proposes a cutting tool having a wing portion that delivers a fluid, filled in a hollow space (internal space) formed in the shank's shaft, to one end (the cutting tool side). The wing portion presses the fluid against the cutting tool side, suppressing chatter vibration and rotational unbalance. The fluid used is a commercially available powder (particle size: 10-45 μm) used in powder bed fusion manufacturing, and the shaft is made of the same material as the powder (equivalent to SKD61) (e.g., [0068]). While the particle shape of the powder is not described in Patent Document 3, it is usually non-spherical.

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.

The inventors, through diligent research to solve this problem, have newly discovered that by filling the hollow portion (internal space) of a cutting tool used in milling, the vibration damping against chatter vibration can be improved. Building upon this finding, the inventors have completed the present invention described below.

《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°.

(2) The cutting tool of the present invention (also simply referred to as "tool") exhibits excellent vibration damping properties, and can suppress chatter vibrations generated in the cutting tool during machining. Therefore, using the tool of the present invention enables good cutting (turning) under a wide range of machining conditions, even in a high L/D (L: tool protrusion length, D: its outer diameter) range.

The reason why the tool of this invention exhibits excellent vibration damping 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 generate 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 powder-containing tool can be improved.

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 specific processing conditions (tool rotation speed, depth of cut, feed rate, etc.).

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 morphology and characteristics, exhibits excellent responsiveness and damping, and is considered capable of reducing tool chatter vibrations under a relatively wide range of machining conditions.

Furthermore, as a result of the powder exhibiting the characteristics described above, the tool of the present invention can exhibit sufficient vibration damping even when only powder is present in the internal space (without the inclusion of a block-shaped vibration damping piece, etc.). In this 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 containing the powder is suppressed, and rotational imbalance, which is a source of vibration, is less likely to occur.

"others"
(1) The cutting tool referred to in the present invention may consist only of a shank (handle, shaft), or it may also have a cutting tool, or it may have other elements. The cutting tool (cutting edge) may be detachable from the shank, or it may be fixed to the shank (not detachable).

(2) Unless otherwise specified, "x to y" in this specification includes the lower limit x and the upper limit y. Any numerical value included in the various numerical values or ranges described in this specification may be used to create new lower or upper limits, such as a range "a to b". Also, unless otherwise specified, "x to y μm" in this specification means x μm to y μm. The same applies to other unit systems (sec/50 g, g/ ^cm³ , etc.).

These are longitudinal and transverse cross-sectional views of the test tool. This is a table showing the specifications of the test powder (First Example). This is a photograph showing a machining test. This is a table showing the results of the machining tests. This is an example of a time waveform from a cutting dynamometer. The images show the observed appearance and particle size distribution of the test powder (second example). This is a schematic diagram of a vibration testing apparatus. This graph shows the relationship between acceleration and damping coefficient under various test conditions. This graph shows the relationship between the average particle size of the powder and the sum of the equivalent damping coefficients.

The components of the present invention may be modified by adding one or more components arbitrarily selected from this specification. The information described herein applies not only to the cutting tools of the present invention but also, as appropriate, to their manufacturing methods, etc. Even method-related components can also be components relating to physical objects.

《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, liquids such as cutting oil (cutting fluid, coolant, etc.) and lubricating oil (silicone oil, etc.) may be mixed into the hollow part (internal space) of the tool. 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.) and used for cooling and lubrication of the cutting tool or tool.

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

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 individual particle sizes of the powder using laser diffraction/scattering methods becomes 50%. The measurement of the powder particle size distribution using laser diffraction/scattering methods is performed, for example, using a Laser Micron Sizer 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.

(3) Fluidity (angle of repose/flow rate)
Powders should have excellent fluidity. Indicators of fluidity include the angle of repose and the degree of fluidity. The angle of repose of powders is, for example, 5° to 40°, 10° to 35°, 20° to 33°, and even 24° to 30°. The degree of fluidity of powders is, for example, 0.4 to 2.3 sec/ ^cm³ , 0.8 to 2.1 sec/ ^cm³ , and even 1.2 to 1.9 sec/ ^cm³ .

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, 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 is recommended.

The fluidity is determined according to JIS Z2502 (2012). However, because it is affected by volume and gravity due to true density, the fluidity is expressed in this specification on a per-unit volume basis, not per-unit mass.

(4) Circularity Each particle of the powder should be spherical in whole or in part. When viewed as a whole, the circularity obtained from image analysis is, for example, 0.75 to 1.00, 0.80 to 0.98, 0.83 to 0.95, and even 0.85 to 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 perfectly spherical.

The circularity can be determined, for example, by processing an observation image of the powder (such as a two-dimensional SEM image) with image analysis software (such as ImageJ). Specifically, the process is as follows: In the observation image, the grayscale information of each pixel is binarized at an arbitrary threshold to extract the contour of each particle. For each particle, its area (S) and circumference (L) are obtained, and the circularity is calculated as 4π × S/ ^L² . The arithmetic mean of the circularity obtained for about 70 (40 to 100) particles is adopted as the "circularity" of the powder as referred to in this specification.

The circularity can also be determined using the image processing function included with the VHX-7000 camera manufactured by Keyence Corporation. In this case, it is recommended to use an observation image captured at a magnification of 400x, a resolution of 2880 x 2160 pixels, and a pixel size of 0.26 μm/pixel.

(5) Density The tool itself, which is the target of vibration damping, is usually made of a high-density metal (steel, cemented carbide, etc.). The vibration characteristics and vibration damping performance of such a tool can also be affected by the mass ratio of the tool to the powder (total amount). Using powder with a high specific gravity (true density) makes it possible to reduce the internal space that contains the powder, making it easier to ensure the (static) rigidity and strength of the tool, and also increases the degree of freedom in the shape of the tool. The true density of such powder (particles) is, for example, 4 to 23 g/ ^cm³ , 7 to 22 g/ ^cm³ , 13 to 21 g/ ^cm³ , and even 18 to 20 g/ ^cm³ . In any case, it is desirable that the true density of the powder be greater than or equal to the true density of the main body (constituent material), and even greater than the true density of the main body (constituent material).

(6) Packing Ratio The packing ratio of powder in the enclosed space is, for example, 10-65%, 15-50%, and even 20-35%. The packing ratio of powder is determined as the ratio (Vp/Vs) of the total volume of powder contained in the partitioned enclosed space (Vs) to the total volume (Vp) of the enclosed space, as shown in the following formula. Vp is the sum of the volumes of each particle that makes up the powder, but it is sufficient to obtain this by dividing the total mass of the powder by the true density of the powder (particles).
Filling rate (%) = (Vp/Vs) x 100

(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 types of powders with different materials (compositions). Also, if there are multiple enclosed spaces, the powders placed in each enclosed space may be the same or different types.

《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).

The enclosed space can be either a sealed, closed space or an open space communicating with the outside. The enclosed space containing the powder should ideally be more concentrated (volume-enlarged) on the tool side (one end) that cuts the workpiece than on the gripping side (the other end) of the machine tool. In other words, in a position where the tool's rotation axis aligns with the direction of gravity, the volume (mass) of the powder should be greater on the tool side than on the gripping side. This suppresses the reduction in static rigidity and efficiently reduces chatter vibration on the tool side.

The internal space may be a single space or two or more spaces. If there is only one internal space, it is preferable to position it closer to the cutting tool than the gripping side. If the internal space extends axially, it may have a shape that expands closer to the cutting tool than 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.

《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.

The powder is filled into the internal space through an opening in the main body, and then the opening is closed with a lid or similar device to seal it. The lid or similar device may be fastened to the opening (with screws, etc.), joined (welded, brazed, bonded, press-fitted (including shrink-fitted), etc.).

Cutting tools may be manufactured, for example, by powder bed fusion (PBF), directed energy deposition (DED), etc. If the raw material powder meets 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.

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

《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.

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

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

The cap 12 can be screwed onto the opening on the gripping side of the shank 10, thereby closing the gripping side of the shank 10.

The shank 10 has a tapered internal space 101 that expands towards the tip. Powder p is filled into this internal space 101 through an opening at the base of the shank 10. After filling, the opening is closed with the cap 12, sealing the powder p within the internal space 101.

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

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).

(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 at its tip. Parts and components common to both the end mill 1 and the end mill 2 are denoted by the same reference numerals, and their detailed descriptions have been omitted.

(3) The specific specifications of end mills 1 and 2 are as follows. End mills 1 and 2 are based on the basic shape (φ19.5 mm x 160 mm) of a commercially available tool (ARPF20S20 manufactured by MOLDINO Co., Ltd.). The total length of end mill 1 is 253 mm, the total length of end mill 2 is 248 mm, and the outer diameter of shanks 10 and 20 is φ20 mm.

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

《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 observation images (SEM images), specifications, and characteristics of each powder are summarized in Figure 2.

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.

Both the spherical powder and the irregularly shaped powder were made of tungsten (true density: 19.25 g/ ^cm³ ), and 57.2 g of each powder was packed into the internal space 101 of the 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%.

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

(1) Cutting tool The cutting tool (tip c) used was ZCFW200-R2.0-PTH08M manufactured by MOLDINO Corporation. This cutting tool originally has two blades, but in order to eliminate the influence of assembly errors on vibration measurements, one of the blades was slightly machined. Therefore, the workpiece (test piece) was processed by 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 cutting tool. Cutting tests were conducted under these conditions.

(2) Apparatus A machining center (VERTEX550-5X manufactured by Mitsui Seiki Co., Ltd.) was used as the machine tool. The root end of each end mill was clamped to its 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.

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) / 40 mm wide x 5 mm thick) placed on a cutting dynamometer (Kistler Japan Co., Ltd. 9257A). This process is shown in Figure 3.

(3) Conditions For each test tool, the spindle (end mill) rotation speed (5 levels) and depth of cut (8 levels) were changed, and a total of 40 conditions (5 x 8 conditions) of machining tests were performed. The 5 levels of spindle rotation speed were 3680 rpm, 3900 rpm, 4155 rpm, 4280 rpm, and 4500 rpm. The 8 levels of depth of cut 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 using cutting fluid. The theoretical surface roughness (maximum height Rz/JIS B 0601:2001) under these machining conditions was 0.50 μm.

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

The measurement results are summarized in Figure 4. In Figure 4, Test 1 uses an end mill 1 filled with spherical powder, Test 2 uses an end mill 1 filled with irregularly shaped powder, and Test 3 uses a solid end mill 2 without powder. In Figure 4, a good result is indicated by ○ and a bad result by ×.

A negative result (×) 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). Otherwise (measured surface roughness less than twice the theoretical value and one impact force during one rotation), a good result (〇) was given.

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 should have been pre-cut and not contribute to machining, unintentionally contacts (collides with) the workpiece. This phenomenon can occur when the amplitude of chatter vibration is large.

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/chatter resistance).

"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.

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

[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.

《Test powder》
As test powders, four types of zirconia powders with different particle sizes (YTZ balls manufactured by Tosoh Corporation / true density: 6.09 g/ ^cm³ ) were prepared, as shown in Figure 6. The average particle size (Dv50) obtained by image processing of observation images of approximately 100 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.

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.

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

The reason for selecting the six levels above as vibration frequencies is as follows: In cutting processes, chatter vibration caused by the tool often occurs when L/D ≥ 6. Furthermore, from the perspective of the tool's static rigidity and strength, 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 subjected to a hammering test, 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 within the range of 300 to 800 Hz, the six levels mentioned above were selected.

(2) In a cutting test separate from 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 typically performed in normal cutting operations, 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.

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 between 2 and 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).

"evaluation"
As can be seen from Figure 8, under normal cutting conditions (acceleration of 5 Grms 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.

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.

1. End mill (cutting tool)
10 Shank (main body)
11 Holder 12 Cap 101 Enclosed space p Powder

Claims (5)

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. The cutting tool according to claim 1, wherein the powder comprises particles having a circularity of 0.75 to 1.00. The cutting tool according to claim 2, wherein the powder comprises spherical particles. 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%. The cutting tool according to any one of claims 1 to 4, wherein the enclosed space is biased towards the cutting tool side that cuts the workpiece rather than the gripping side by the machine tool.