JP2019202395A - End mill - Google Patents

Abstract

To provide an end mill that is used in processing a contour line, which can enhance processing accuracy while setting a blade length as long as possible and reducing processing costs.SOLUTION: The end mill comprises a shaft part in a columnar shape extending along a center shaft and a blade part positioned at a tip side of the shaft part. In the blade part, eight outer peripheral blades with an outer diameter dimension larger than that of the shaft part are provided along a circumferential direction. The outer peripheral blades are helical teeth spirally extending around the center shaft, where upper ends of the outer peripheral blades are nearly identical to lower ends of the other outer peripheral blades adjacent to a rear side in a rotating direction of the end mill, in terms of positions in a circumferential direction.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an end mill.

  In the die machining, if an end mill with a long blade length is used when cutting a deep vertical wall (90 ° wall), the rigidity of the end mill is insufficient and the machining accuracy is lowered. For this reason, for the processing of standing walls, a contour process is proposed in which an end mill with a short blade length is used to perform cutting in a direction perpendicular to the axis while moving stepwise in the axial direction, and cutting in multiple steps. (For example, Patent Document 1).

JP 2000-334615 A

  In the contour processing of an upright wall, the processing accuracy tends to decrease due to vibration during cutting. Therefore, in order to obtain a highly accurate finished surface quality, it is necessary to repeat zero cutting many times, resulting in an increase in processing cost. Moreover, when the depth of cut is reduced, the end mill is moved while moving it in the axial direction many times, so that the processing time becomes longer and the processing cost also increases.

  The present invention has been made in view of such circumstances, and is an end mill used for contour processing, which aims to provide an end mill that can reduce zero cut in finishing and can increase processing accuracy. To do.

An end mill according to an aspect of the present invention includes a cylindrical shaft portion extending along a central axis, and a blade portion positioned on a tip side of the shaft portion, and the blade portion is larger than the shaft portion. Eight outer peripheral blades having an outer diameter are provided along the circumferential direction, and the outer peripheral blades are helical blades extending spirally around the central axis, and pay attention to one of the eight outer peripheral blades. , The blade length along the axial direction of the outer peripheral blade is L, the torsion angle of the outer peripheral blade is θ, the outer peripheral blade and the other outer peripheral blade adjacent to the rear of the outer peripheral blade in the tool rotation direction at the lower end of the outer peripheral blade An end mill in which n expressed by the following formula is substantially 1 for eight outer peripheral blades, where a is a circumferential distance.
n = (L × tan θ) / a

N represented by the above formula represents the number of outer peripheral blades that always come into contact with the work material during cutting of the work material by the end mill. According to the above-described configuration, the upper end of the outer peripheral blade substantially coincides with the lower end of the other outer peripheral blade adjacent to the rear in the tool rotation direction, so that approximately one outer peripheral blade is always covered during cutting. The cutting material comes into contact (the number of simultaneous contact blades is always about 1). If the number of simultaneous contact blades increases or decreases during cutting of the work material by the end mill, the cutting resistance that the end mill receives from the work material increases or decreases. Thereby, there is a problem that the end mill vibrates and the machining accuracy is lowered. Further, even when the number of simultaneous contact blades is always a natural number of 2 or more, the processing accuracy is reduced as compared with the case where the number of simultaneous contact blades is always approximately 1. According to the above-described configuration, the machining accuracy of the machined surface can be increased by always setting the number of simultaneous contact blades to approximately 1. As a result, the zero cut in the finishing process can be reduced.
In addition, the outer peripheral blade length can be secured long in the axial direction within a range that satisfies the above-described configuration, and a wider range can be processed in one step when performing contour line processing, resulting in a reduction in processing cost.
In addition, according to the above-described configuration, eight outer peripheral blades are provided. By increasing the number of outer peripheral blades while always setting the number of simultaneous contact blades to be approximately 1, the increase / decrease width of the cutting resistance when the outer peripheral blades contacting the work material are switched can be suppressed. By providing eight outer peripheral blades, it is possible to increase or decrease the cutting resistance, suppress the vibration of the end mill during cutting, and consequently increase the processing accuracy.

  In the above-described end mill, the n may be 0.9 or more and 1.1 or less.

  As described above, when the number of simultaneous contact blades is always about 1 (that is, n≈1), the processing accuracy of the processing surface can be increased. On the other hand, when n exceeds 1.1 or when n is less than 0.9, the vibration of the end mill during processing affects the processing accuracy, and it is difficult to form a processing surface with sufficient processing accuracy. It becomes. That is, according to the above-described configuration, the processing accuracy of the processed surface can be sufficiently increased. More preferably, n is 0.95 or more and 1.05 or less.

  Moreover, the above-mentioned end mill WHEREIN: The outer diameter D of the said outer periphery blade is good also as a structure which is 4 mm or more.

  When the outer diameter of the outer peripheral blade is reduced, it becomes difficult to form an eight-blade blade. Therefore, in the end mill of the present invention on the premise of 8 blades, the outer dimension of the outer peripheral blade is preferably 4 mm or more. Furthermore, the outer dimension of the outer peripheral blade is preferably 5 mm or more. Further, if the outer dimension becomes too large, it becomes difficult to manufacture as a solid end mill. Therefore, the outer dimension of the outer peripheral blade is preferably 30 mm or less.

  In the above-described end mill, the twist angle may be not less than 35 ° and not more than 40 °.

  According to the above configuration, in the end mill having eight outer peripheral blades in which the simultaneous contact blades of the outer peripheral blades are always approximately 1 by setting the twist angle of the outer peripheral blades to 35 ° or more and 40 ° or less, the blade length is long. Since the structure of the outer peripheral blade is not too small, the rigidity of the tool is increased, and the deflection of the tool is less likely to occur during machining. Thereby, the processing accuracy of the processing surface can be sufficiently increased without zero cut. Furthermore, it is preferable to set the twist angle of the outer peripheral blade to 37 ° or more and 39 ° or less.

  In the above-described end mill, the outer peripheral blade may have a positive rake face.

  According to the above-described configuration, since the outer peripheral blade has a positive rake face, the sharpness of the outer peripheral blade is improved as compared with the case of having a negative rake face. Thereby, the processing accuracy of the processing surface can be sufficiently increased without zero cut.

  In the above-described end mill, the outer peripheral blade may have a two-step flank.

  According to the above-described configuration, the accuracy of the processed surface can be improved even when the feed amount of the end mill is increased as compared with the case where the flank has one stage. Thereby, the processing accuracy of the processing surface can be sufficiently increased without zero cut.

  In the above-mentioned end mill, in addition to the eight outer peripheral blades, the blade portion includes eight bottom blades provided at the tip and extending radially outward from the central axis side, the outer peripheral blades, and the bottom blades. 8 radius blades that smoothly connect between each other, and the most advanced point of the blade portion is between the boundary of the radius blade and the outer peripheral blade, and the boundary of the radius blade and the bottom blade, It is good also as a structure located in a radius blade.

  According to the above-described configuration, when the bottom surface of the work material is machined using the bottom blade, it is possible to suppress the occurrence of a line-like scratch caused by the boundary between the radius blade and the bottom blade.

  Further, in the above-described end mill, the eight outer peripheral blades include a first outer peripheral blade and a second outer peripheral blade, and the torsion angle of the first outer peripheral blade and the second outer peripheral blade of the second outer peripheral blade. It is good also as a structure which is an angle from which a twist angle differs.

  The end mill having the above-described configuration is a so-called unequal lead end mill including outer peripheral blades having different helix angles. Even when the feed amount of the end mill is increased compared to the case where the outer peripheral blade is an equal lead by making the outer peripheral blade an unequal lead while the number of simultaneous contact blades is always approximately 1. Accuracy can be improved.

  In the above-described end mill, the eight outer peripheral blades include the four first outer peripheral blades, the two second outer peripheral blades having a twist angle larger than the twist angle of the first outer peripheral blade, Two third outer peripheral blades having a twist angle smaller than the twist angle of the first outer peripheral blade, and the four first outer peripheral blades are arranged at substantially equal intervals along the circumferential direction, The two outer peripheral blades and the third outer peripheral blade may be arranged alternately along the circumferential direction between a pair of different first outer peripheral blades.

  According to the above-described configuration, the eight outer peripheral blades serve as the first outer peripheral blade, the second outer peripheral blade, and the third outer peripheral blade, and the effect of improving the accuracy of the machining surface by making the twist angles different from each other. Is further increased.

  ADVANTAGE OF THE INVENTION According to this invention, it is an end mill used for contour processing, Comprising: The end mill which can set a blade length as long as possible and can raise processing precision, reducing processing cost can be provided.

FIG. 1 is a schematic diagram of an end mill according to the first embodiment. FIG. 2 is a front view of the blade portion of the end mill according to the first embodiment. FIG. 3 is a plan view of a blade portion of the end mill according to the first embodiment. FIG. 4 is an enlarged cross-sectional view of the outer peripheral blade of the end mill according to the first embodiment. FIG. 5 is a developed schematic view in which the outer peripheral blade of the first embodiment is developed along the circumferential direction. FIG. 6 is a schematic diagram showing a state of processing of the work material by the radius blade of the end mill according to the first embodiment. FIG. 7 is a schematic view schematically showing the bottom blade of the end mill according to the first embodiment. FIG. 8 is a developed schematic view in which the outer peripheral edge of the end mill according to the second embodiment is developed along the circumferential direction. FIG. 1-1, sample no. 1-2 and sample no. It is a graph which shows the relationship between the measurement result of the depth of a processed surface, and the amount of collapse of a processed surface in the process using the end mill of 1-3. FIG. It is a graph which shows the time-dependent change of the cutting resistance at the time of cutting using the 2-1 end mill. FIG. It is a graph which shows the time-dependent change of the cutting resistance at the time of cutting using the end mill of 2-2. FIG. 3-1, sample no. It is a graph which shows the relationship between the measurement result of the depth of a processed surface, and the amount of collapse of a processed surface in the process using a 3-2 end mill. FIG. 4-1, Sample No. 4-2 and Sample No. It is a graph which shows the relationship between the measurement result of the depth of a processed surface, and the amount of collapse of a processed surface in the process using a 4-3 end mill. FIG. 5-1, sample no. 5-2 and sample no. It is a graph which shows the relationship between the measurement result of the depth of a processed surface, and the amount of collapse of a processed surface in the process using a 5-3 end mill. FIG. 14A shows sample no. It is a graph which shows the relationship between the measurement result of the depth of a processed surface, and the amount of collapse of a processed surface in the process using a 4-1 end mill. FIG. 14B shows sample no. It is a graph which shows the relationship between the measurement result of the depth of a processed surface, and the amount of collapse of a processed surface in the process using a 4-2 end mill.

  Embodiments to which the present invention is applied will be described below in detail with reference to the drawings. Note that in the drawings used in the following description, in order to make the characteristic portions easy to understand, portions that do not become characteristic may be omitted for convenience.

(First embodiment)
Drawing 1 is a mimetic diagram of end mill 1 of a 1st embodiment. FIG. 2 is a front view of the blade portion 20 of the end mill 1. FIG. 3 is a plan view of the blade portion 20 of the end mill 1.

As shown in FIG. 1, the end mill 1 is a substantially cylindrical rod body that extends along an axial direction with an axis (center axis) O as a center. The end mill 1 is made of a hard material such as a cemented carbide.
In this specification, a direction parallel to the axis O of the end mill 1 is simply referred to as an axial direction. A direction orthogonal to the axis O is referred to as a radial direction. Further, a direction around the axis O is referred to as a circumferential direction. Of the circumferential directions, the direction in which the end mill 1 rotates during cutting is referred to as the tool rotation direction T. In the following description, a region on the tool rotation direction T side with respect to a specific part may be referred to as a rotation direction front side and a region opposite to the tool rotation direction T side may be referred to as a rotation direction rear side.

  The end mill 1 of this embodiment is a radius end mill. The end mill 1 processes the standing wall by contour line processing. The work material processed by the end mill 1 is, for example, a mold nesting for resin molding.

  The end mill 1 has a shank part 12, a neck part (shaft part) 11, and a blade part 20. The shank portion 12, the neck portion 11, and the blade portion 20 are arranged in this order along the axis O from the proximal end side toward the distal end side.

  The shank portion 12 has a cylindrical shape extending along the axis O. The shank portion 12 is gripped by the machine tool 9. The end mill 1 is held by the machine tool 9 in the shank portion 12 and is rotated in the tool rotation direction T around the axis O. The end mill 1 is used for cutting work (cutting work) of a work material such as a metal material. Further, the end mill 1 processes the workpiece by being fed by the machine tool 9 in the direction intersecting the axis O along with the rotation around the axis O.

  The neck portion 11 has a columnar shape extending along the axis O. The neck portion 11 is located on the tip side of the shank portion 12. In the present embodiment, the outer diameter of the neck portion 11 is smaller than the outer diameter of the shank portion 12. The neck portion 11 is a region facing a processed surface formed by contour processing using the end mill 1.

  As shown in FIGS. 2 and 3, the blade portion 20 is located on the distal end side of the neck portion 11. The blade portion 20 includes eight outer peripheral blades 21, eight radius blades 23 that are continuous with the outer peripheral blade 21 on the distal end side of the outer peripheral blade 21, and eight radial blades 23 that are continuous with the radius blade 23 on the distal end side of the radius blade 23. A bottom blade 22 is provided.

  The eight outer peripheral blades 21 are arranged at equal intervals along the circumferential direction on the outer periphery of the blade portion 20. The eight radius blades 23 are arranged at equal intervals along the circumferential direction between the outer peripheral blade 21 and the bottom blade 22. Further, the eight bottom blades 22 are arranged at equal intervals along the circumferential direction at the tip of the blade portion 20.

  As shown in FIG. 2, the outer peripheral blade 21 is a twisted blade that extends spirally around the axis O. The outer peripheral blade 21 is spirally twisted at a constant twist angle θ toward the tool rotation direction T from the proximal end side of the end mill 1 toward the distal end side. In the present embodiment, the twist angles of the eight outer peripheral blades 21 are the same angle. That is, the outer peripheral blade 21 of this embodiment is an equal lead.

  The outer diameter D of the outer peripheral blade 21 is smaller than the outer diameter d of the neck 11. Thereby, it is suppressed that the neck part 11 interferes with the process surface formed by the contour process.

  A chip discharge groove 24 is formed between the outer peripheral blades 21. The plurality of chip discharge grooves 24 are formed at equal intervals in the circumferential direction. The chip discharge groove 24 is helically twisted at a constant twist angle along the axial direction. The twist angle of the chip discharge groove 24 coincides with the twist angle θ of the outer peripheral blade 21. The chip discharge groove 24 is rounded up to the outer periphery of the end mill 1 at the end portion on the proximal end side of the blade portion 20.

  An outer peripheral blade 21 is formed on the edge on the rear side in the rotational direction of the chip discharge groove 24. That is, the chip discharge groove 24 is located on the front side in the rotation direction of the outer peripheral blade 21. The wall surface of the chip discharge groove 24 includes a bottom surface 24a and a rake surface 24b. The bottom surface 24 a is a surface that faces radially outward with respect to the axis O in the chip discharge groove 24. Further, the rake face 24 b is a wall face facing the tool rotation direction T in the chip discharge groove 24.

  The outer peripheral blade 21 is formed at the intersecting ridge line between the rake face 24 b and the flank 25 on the outer peripheral surface of the blade portion 20. The flank 25 is a surface adjacent to the chip discharge groove 24 on the rear side in the rotation direction. The flank 25 extends in a row in the circumferential direction from the outer peripheral blade 21 toward the chip discharge groove 24 on the rear side in the rotational direction of the outer peripheral blade 21.

  FIG. 4 is a schematic cross-sectional view schematically showing an enlarged cross section perpendicular to the axis O of the outer peripheral blade 21. In FIG. 4, a work material to be cut by the outer peripheral blade 21 is shown.

  The outer peripheral blade 21 of this embodiment has a two-step flank. That is, the flank 25 of the outer peripheral blade 21 has a first region 25a and a second region 25b arranged in the circumferential direction. The first region 25a is located on the outer peripheral blade 21 side. Moreover, the 2nd area | region 25b is located in the chip discharge groove 24 side. The first region 25 a and the second region 25 b are each configured in a circular shape that is eccentric with respect to a virtual circle centered on the axis O in the cross section of the end mill 1. The first region 25a and the second region 25b are configured in different circular shapes that are different from each other. In the clearance surface 25 of the outer peripheral blade 21, the clearance angle β of the first region 25a is, for example, 4 °, and the clearance angle γ of the second region 25b is, for example, 11 °. That is, the clearance angle γ of the second region 25b is larger than the clearance angle β of the first region 25a.

  According to the present embodiment, since the outer peripheral blade 21 is configured with two flank surfaces, the outer peripheral blade 21 contacts the machining surface at the minute first flank surface (first region 25a) during cutting. Then rub the processed surface of the work material. Thereby, the damage | wound and unevenness | corrugation formed in the processing surface can be smoothed, and a processing surface precision can be improved. As a result, the zero cut in the finishing process can be reduced.

The clearance angle β of the first flank (first region 25a) is preferably 1 ° or more and 10 ° or less, and more preferably 4 ° ± 1 °. If the angle of the first-stage flank (first region 25a) is too small, the cutting resistance increases and the processed surface may become rough. On the other hand, if the angle of the first-stage flank (first region 25a) is too large, cutting resistance can be suppressed, but the effect of rubbing the processed surface on the first-stage flank and smoothing the unevenness is reduced. . By setting the clearance angle β of the first flank (first region 25a) within the above range, the machining surface can be smoothed while cutting resistance is suppressed, and the dimensional accuracy of the machining surface is increased. Can do.
In the present specification, the clearance angle of the flank is measured at a cut surface perpendicular to the axis O. At the time of measurement, first, a virtual circle connecting the tips of the outer peripheral blades is obtained, and the flank angle is obtained with respect to the tangent line of the virtual circle passing through the tip of the outer peripheral blade to be measured.

In addition, the width w of the first flank (first region 25a) is preferably 0.01 mm or more and 0.15 mm or less, and more preferably 0.03 ± 0.01. By setting the width w of the first flank (first region 25a) within the above range, the contact area of the flank 25 with the work material can be reduced, and the machining surface can be reduced while suppressing cutting resistance. Smoothness can be achieved, and the dimensional accuracy of the processed surface can be increased.
In the present specification, the width w of the first flank (the first region 25a) is measured at a cut surface perpendicular to the axis O. At the time of measurement, first, a virtual circle connecting the tips of the outer peripheral blades is obtained, and the length dimension of the first region 25a in the tangential direction of the virtual circle passing through the tips of the outer peripheral blades to be measured is defined as a width w.

  As shown in FIG. 4, the outer peripheral blade 21 of the present embodiment has a positive-type rake face 24b. That is, when viewed from the axial direction, the rake face 24b extends from the cutting edge of the outer peripheral blade 21 toward the opposite side of the tool rotation direction T with respect to the straight line connecting the cutting edge and the axis O. According to this embodiment, since the outer peripheral blade 21 has the positive type rake face 24b, the sharpness of the outer peripheral edge 21 is improved as compared with the case of having the negative type rake face. For this reason, the processing accuracy of the processed surface can be sufficiently increased. As a result, the zero cut in the finishing process can be reduced.

FIG. 5 is a developed schematic view of the outer peripheral blade 21 of the blade portion 20 developed along the circumferential direction.
Here, paying attention to one of the eight outer peripheral blades 21, the blade length along the axial direction of the outer peripheral blade 21 is L, the twist angle of the outer peripheral blade 21 is θ, and the lower end 21b of the outer peripheral blade 21 is A circumferential distance between the outer peripheral blade 21 and the other outer peripheral blade 21 adjacent to the rear of the outer peripheral blade 21 in the tool rotation direction is defined as a. Here, the circumferential distance means an arc length extending in the circumferential direction around the axis O.

  The blade length L along the axial direction of the outer peripheral blade 21 is an effective blade length of the outer peripheral blade 21 that substantially cuts the work material. That is, the blade length L means a length along the axial direction of a region where the outer diameter dimension D is larger than the neck portion 11 in the outer peripheral blade 21 extending spirally along the axial direction.

  In the present embodiment, the circumferential distance a between all the peripheral blades 21 and the other peripheral blades 21 adjacent to the rear in the tool rotation direction is equal, and a = Dπ / 8. Similarly, in this embodiment, the blade length L along the axial direction and the twist angle θ of the outer peripheral blade 21 are equal for all the outer peripheral blades 21.

In the end mill 1 of the present embodiment, n expressed by the following (formula 1) is substantially 1 for the eight outer peripheral blades 21.
n = (L × tan θ) / a (Formula 1)

Here, attention is focused on a pair of outer peripheral blades 21 adjacent to each other in the circumferential direction. The end mill 1 in which n = 1 in (Expression 1) is the circumferential direction between the upper end 21a of one outer peripheral blade 21 in the front of the tool rotation direction and the lower end 21b of the other outer peripheral blade 21 adjacent to the rear in the tool rotation direction T. The positions are approximately the same. In (Equation 1), the end mill 1 where n = 1 is rotated around the axis O and cuts the work material at the blade portion 20, so that eight outer peripheral blades can be used regardless of the phase of the blade portion 20. Any one of the outer peripheral blades 21 is always in contact with the work material.
Note that the upper end 21 a of the outer peripheral blade 21 means the upper end of the region in which the outer diameter D is maintained in the outer peripheral blade 21. Similarly, the lower end 21b of the outer peripheral blade 21 means the lower end of the region in which the outer diameter D is maintained in the outer peripheral blade 21.

  N represented by the above formula represents the number of outer peripheral blades 21 that are always in contact with the work material during the cutting of the work material by the end mill 1. According to this embodiment, substantially one outer peripheral blade 21 always comes into contact with the work material during cutting (the number of simultaneous contact blades is always approximately 1).

  If the number of simultaneous contact blades increases or decreases during cutting of the work material by the end mill 1, the cutting resistance that the end mill 1 receives from the work material increases or decreases. More specifically, the cutting resistance rapidly decreases when the outer peripheral blade 21 moves away from the work material, and the cutting resistance increases rapidly when the outer peripheral blade 21 starts to contact the work material. Thereby, there is a problem that the end mill vibrates and the machining accuracy is lowered. Further, even when the number of simultaneous contact blades is always a natural number of 2 or more, the processing accuracy is reduced as compared with the case where the number of simultaneous contact blades is always approximately 1.

According to the present embodiment, since the number of simultaneous contact blades is always substantially 1, when one outer peripheral blade 21 is separated from the work material, the other outer peripheral blade 21 starts to contact the work material at the same time. The vibration of the end mill 1 during processing can be suppressed, and the processing accuracy of the processed surface can be increased. As a result, the zero cut in the finishing process can be reduced.
In addition, the blade length of the outer peripheral blade 21 can be secured long in the axial direction within the range satisfying the above-described configuration, and a wider range can be processed in one step when performing contour line processing, resulting in a reduction in processing cost. .

  In the end mill 1 of the present embodiment, n represented by the above (Formula 1) is preferably 0.9 or more and 1.1 or less. As described above, when the number of simultaneous contact blades is always about 1 (that is, n≈1), the processing accuracy of the processing surface can be maximized. On the other hand, when n exceeds 1.1 or when n is less than 0.9, the vibration of the end mill during processing affects the processing accuracy, and it is difficult to form a processing surface with sufficient processing accuracy. It becomes. That is, when n is 0.9 or more and 1.1 or less, the processing accuracy of the processed surface can be sufficiently increased.

  Further, according to the present embodiment, the blade portion 20 is provided with the eight outer peripheral blades 21. By increasing the number of outer peripheral blades 21 while the number of simultaneous contact blades is always substantially 1, it is possible to suppress the increase / decrease width of the cutting resistance when the outer peripheral blades 21 contacting the work material are switched. By providing eight outer peripheral blades 21, it is possible to increase or decrease the cutting resistance, suppress the vibration of the end mill during cutting, and consequently increase the processing accuracy.

  In the end mill 1, the outer diameter D of the outer peripheral blade 21 is preferably 4 mm or more. When the outer diameter D of the outer peripheral blade 21 is reduced, it becomes difficult to form an eight-blade. Therefore, in the end mill 1 according to the present embodiment on the premise of eight blades, the outer dimension D of the outer peripheral blade 21 is preferably 4 mm or more. Furthermore, the outer dimension D of the outer peripheral blade 21 is preferably 5 mm or more. Moreover, when the external dimension D becomes too large, manufacture as a solid end mill becomes difficult. Therefore, the outer dimension D of the outer peripheral blade 21 is preferably 30 mm or less.

  In the end mill 1, the twist angle θ is preferably 35 ° or more and 40 ° or less. By setting the twist angle θ of the outer peripheral blade 21 to 35 ° or more and 40 ° or less, in the end mill 1 having the eight outer peripheral blades 21 in which the simultaneous contact blade is always approximately 1, the outer peripheral blade whose length L is not excessively long. Therefore, the rigidity of the end mill 1 is increased, and the bending of the end mill 1 is less likely to occur during processing. Thereby, the processing accuracy of the processing surface can be sufficiently increased without zero cut. For the same reason, it is more preferable that the twist angle of the outer peripheral blade 21 is 37 ° or more and 39 ° or less.

  As shown in FIG. 2, in addition to the eight outer peripheral blades 21, the blade portion 20 smoothly connects the eight bottom blades 22 provided at the tip of the blade portion 20, and the outer peripheral blades 21 and the bottom blades 22. Eight radius blades 23 are provided. The bottom blade 22 extends radially outward from the axis O side.

FIG. 6 is a schematic diagram showing how the workpiece is machined by the radius blade 23.
The radius blade 23 has a circular arc shape with a uniform curvature radius R centering on the curvature center O1. The blade portion 20 is positioned at the radius blade 23 at the most distal point TP located at the tip in the axial direction. The most advanced point TP is located between the boundary P1 between the radius blade 23 and the outer peripheral blade 21 and the boundary P2 between the radius blade 23 and the bottom blade 22. That is, the radius blade 23 protrudes from the outer peripheral blade 21 and the bottom blade 22 toward the front end in the axial direction.

  By providing the cutting edge TP on the radius blade 23, it is possible to prevent the boundary P2 between the bottom blade 22 and the radius blade 23 from coming into contact with the workpiece in the bottom machining of the workpiece. The boundary P2 between the radius blade 23 and the bottom blade 22 can be a discontinuous point on the cutting edge. According to the present embodiment, it is possible to suppress the formation of streak-like flaws (cutting flaws) on the work surface by avoiding discontinuous points on the cutting edge from coming into contact with the work material. In addition, since it is avoided that cutting flaws due to discontinuous points are given to the work material, even when the cutting speed is increased for the purpose of improving the work efficiency, chatter vibration of the end mill 1 is suppressed and the work material is reduced. A highly accurate machined surface roughness can be obtained.

  The radius of curvature R of the radius blade 23 is preferably uniform from the boundary P1 between the radius blade 23 and the outer peripheral blade 21 to the boundary P2 between the radius blade 23 and the bottom blade 22. If the radius of curvature R of the radius blade 23 is constant, the distance from the center of curvature O1 to the radius blade 23 is always constant in the section from the boundary P1 to the boundary P2. For this reason, even if the inclination angle of the axis O of the end mill 1 with respect to the bottom surface of the work material changes and the region in contact with the work material on the radius blade 23 changes, the radius blade can be a discontinuous point on the cutting blade. It can suppress that boundary P2 of 23 and the bottom blade 22 contacts a work material. For this reason, it is possible to suppress the formation of streak-like flaws (cutting flaws) on the work surface, to suppress chatter vibration of the end mill 1, and to obtain a highly accurate work surface roughness on the work material. be able to.

(Second Embodiment)
FIG. 7 is a schematic diagram schematically illustrating the bottom blades 122A, 122B, and 122C of the end mill 101 according to the second embodiment. FIG. 8 is a developed schematic view in which the outer peripheral blades 121A, 121B, and 121C of the blade portion 120 of the end mill 101 of the second embodiment are developed along the circumferential direction.
The end mill 101 of the second embodiment is mainly different from the above-described embodiment in that the outer peripheral blades 121A, 121B, 121C are unequal leads.
In addition, about the component of the same aspect as the above-mentioned embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  The end mill 101 of this embodiment has a blade part 120 located on the tip side. The blade portion 120 is provided with eight outer peripheral blades 121A, 121B, 121C, eight radius blades (not shown), and eight bottom blades 122A, 122B, 122C.

  As shown in FIG. 7, the eight bottom blades 122A, 122B, 122C include four first bottom blades 122A, two second bottom blades 122B, and two third bottom blades 122C. . The first bottom blade 122A, the second bottom blade 122B, and the third bottom blade 122C extend linearly outward from the axis O in the radial direction when viewed from the axial direction.

  The four first bottom blades 122A, the two second bottom blades 122B, and the two third bottom blades 122C are arranged along the tool rotation direction T with the first bottom blade 122A, the second bottom blade 122B, The first bottom blade 122A, the third bottom blade 122C, the first bottom blade 122A, the second bottom blade 122B, the first bottom blade 122A, and the third bottom blade 122C are arranged in this order. The four first bottom blades 122A are arranged at substantially equal intervals along the circumferential direction. Further, the second bottom blade 122B and the third bottom blade 122C are alternately arranged along the circumferential direction between a pair of different first bottom blades 122A.

The first bottom blade 122A is adjacent to the circumferential direction at a first boundary angle φ1 with a bottom blade (second bottom blade 122B or third bottom blade 122C) behind the tool rotation direction T. The second bottom blade 122B is adjacent to the first bottom blade 122A behind the tool rotation direction T and the second boundary angle φ2 in the circumferential direction. The third bottom blade 122C is adjacent to the first bottom blade 122A behind the tool rotation direction T and the third boundary angle φ3 in the circumferential direction. The second boundary angle φ2 is larger than the first boundary angle φ1. The third boundary angle φ3 is smaller than the first boundary angle φ1. That is, the magnitude relationship between the first boundary angle φ1, the second boundary angle φ2, and the third boundary angle φ3 is as follows.
φ2>φ1> φ3

  In the present embodiment, the four first boundary angles φ1 are all 44.8 °, for example. The two second boundary angles φ2 are both 48.1 °, for example. One of the two third boundary angles φ3 is 42.2 °, and the other is, for example, 42.4 °. In the present embodiment, the two third boundary angles φ3 are slightly different from each other. However, the two third boundary angles φ3 may be the same.

  As shown in FIG. 8, the eight outer peripheral blades 121A, 121B, 121C include four first outer peripheral blades 121A, two second outer peripheral blades 121B, and two third outer peripheral blades 121C. . The first outer peripheral blade 121 </ b> A, the second outer peripheral blade 121 </ b> B, and the third outer peripheral blade 121 </ b> C are helical blades that extend spirally around the axis O.

  The first outer peripheral blade 121A is connected to the first bottom blade 122A via a radial blade (not shown). The second outer peripheral blade 121B is connected to the second bottom blade 122B via a radial blade. The third outer peripheral blade 121C is connected to the third bottom blade 122C through a radial blade.

  The four first outer peripheral blades 121A, the two second outer peripheral blades 121B, and the two third outer peripheral blades 121C are arranged along the tool rotation direction T with the first outer peripheral blade 121A, the second outer peripheral blade 121B, The first outer peripheral blade 121A, the third outer peripheral blade 121C, the first outer peripheral blade 121A, the second outer peripheral blade 121B, the first outer peripheral blade 121A, and the third outer peripheral blade 121C are arranged in this order. The four first outer peripheral blades 121A are arranged at substantially equal intervals along the circumferential direction. In addition, the second outer peripheral blade 121B and the third outer peripheral blade 121C are alternately arranged along the circumferential direction between a pair of different first outer peripheral blades 121A.

  The first outer peripheral blade 121A is spirally twisted at a first twist angle θ1 that is a constant twist angle toward the tool rotation direction T as it goes from the proximal end side to the distal end side of the end mill 101. The second outer peripheral blade 121B is spirally twisted at a second twist angle θ2 that is a constant twist angle toward the tool rotation direction T as it goes from the proximal end side to the distal end side of the end mill 101. The third outer peripheral blade 121 </ b> C is spirally twisted at a third twist angle θ <b> 3 that is a constant twist angle toward the tool rotation direction T from the proximal end side to the distal end side of the end mill 101. The twist angle of the first outer peripheral blade 121A (first twist angle θ1), the twist angle of the second outer peripheral blade 121B (second twist angle θ2), and the twist angle of the third outer peripheral blade 121C (third Is a different angle from the twist angle θ3). That is, that is, the outer peripheral blades 121A, 121B, 121C of the present embodiment are unequal leads.

The twist angle (second twist angle θ2) of the second outer peripheral blade 121B is larger than the twist angle (first twist angle θ1) of the first outer peripheral blade 121A. Further, the twist angle (third twist angle θ3) of the third outer peripheral blade 121C is smaller than the twist angle (first twist angle θ1) of the first outer peripheral blade 121A. That is, the first torsion angle θ1, the second torsion angle θ2, and the third torsion angle θ3 have the following magnitude relationship.
θ2>θ1> θ3

  In the present embodiment, the four first twist angles θ1 are all 38 °, for example. The two second twist angles θ2 are both 40 °, for example. One of the two third twist angles θ3 is 36 °, and the other is, for example, 36.5 °. In the present embodiment, the two third twist angles θ3 are slightly different from each other. However, the two third twist angles θ3 may be the same.

  The outer peripheral blades 121A, 121B, and 121C of this embodiment are set so that the number of simultaneous contact blades is always one as in the above-described embodiment. That is, the upper end of one outer peripheral blade substantially coincides with the lower end of another outer peripheral blade adjacent to the rear in the tool rotation direction in the circumferential direction. For this reason, the processing accuracy of the processing surface can be increased.

The configuration in which the number of simultaneous contact blades is always about 1 in the configuration of the present embodiment will be described more specifically. As shown in FIG. 8, attention is paid to one outer peripheral blade (the outer peripheral blade 121X in FIG. 8) among the eight outer peripheral blades 121A, 121B, 121C. The blade length along the axial direction of the outer peripheral blade 121X is L, the twist angle of the outer peripheral blade 121X is θ, and the lower end 121Xb of the outer peripheral blade 121X is adjacent to the rear in the tool rotation direction of the outer peripheral blade 121X and the outer peripheral blade 121X. The circumferential distance from the outer peripheral blade 121Y is a.
At this time, n represented by the following (Formula 2) is substantially 1 for the eight outer peripheral blades 121A, 121B, and 121C.
n = (L × tan θ2) / a (Expression 2)
In addition, like the above-mentioned embodiment, the processing precision of a processing surface can fully be raised by making n into 0.9 or more and 1.1 or less.

  The end mill 101 according to this embodiment is a so-called unequal lead end mill including outer peripheral blades 121A, 121B, and 121C having different twist angles. By making the outer peripheral blades 121A, 121B, and 121C unequal leads while the number of simultaneous contact blades is always approximately 1, the timing from when the outer peripheral blades arranged in the circumferential direction start to contact with the work material until they are separated is different. . For this reason, the vibration of the end mill 101 is difficult to be amplified. According to the present embodiment, even if the outer milling blades 121A, 121B, and 121C are unequal leads, even when the feed amount of the end mill 101 is increased as compared with the case where the outer circumferential blades are equal leads. Amplification of vibration of the end mill 101 can be suppressed, and the accuracy of the processed surface can be improved.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated further in detail, this invention is not limited to these Examples.

(Test 1)
First, Test 1 showing the superiority of the number of simultaneous contact blades being one will be described.
Under the following conditions, sample no. 1-1, sample no. 1-2 and sample no. The work material is cut by the end mill of 1-3.
・ Cover cut material: DAC (H) 48HRC
・ End mill: Outer diameter of outer peripheral edge Φ6mm
・ Machine: MAKINO V33 (HSK-F63)
Cutting conditions: Rotational speed n = 2650 revolutions / minute
Feeding speed Vf = 636mm / min
Allow 0.1mm
Down cut
Dry-air blow processing

  Sample No. 1-1, sample no. 1-2 and sample no. The 1-3 end mills each have eight peripheral blades with equal leads. Sample No. 1-1, sample no. 1-2 and sample no. The outer peripheral blade of the 1-3 end mill has a positive type rake face.

  Sample No. The end mill of 1-1 is set so that the number of simultaneous contact blades is 1 (that is, n = 1 in the above-described (Expression 1)). Sample No. The end mill of 1-2 is set so that the number of simultaneous contact blades is less than 1 (that is, n <1 in the above-described (Expression 1)) of 0.17. Sample No. The end mill of 1-3 is set so that the number of simultaneous contact blades is 2 (that is, n = 2 in the above (Expression 1)).

  FIG. 1-1, sample no. 1-2 and sample no. It is a graph which shows the relationship between the measurement result of the depth of a processed surface, and the amount of collapse of a processed surface in the process using the end mill of 1-3. As shown in FIG. The end mill of 1-1 was sample No. 1-2 and sample no. It can be confirmed that the amount of collapse is sufficiently small compared to the end mill of 1-3.

(Test 2)
Next, Test 2 showing the advantage of setting the number of outer peripheral blades to 8 will be described.
Under the following conditions, sample no. 2-1, sample no. The work material is cut by the end mill 2-2.
・ Cover cut material: DAC (H) 48HRC
・ End mill: Outer diameter of outer peripheral edge Φ6mm
・ Machine: MAKINO V33 (HSK-F63)
Cutting conditions: Rotational speed n = 2650 revolutions / minute
Feeding speed Vf = 636mm / min
Allow 0.1mm
Down cut
Dry-air blow processing

  Sample No. 2-1, sample no. The outer peripheral blade of the 2-2 end mill has a positive type rake face. Sample No. 2-1, sample no. 2-2 is set so that the number of simultaneous contact blades is one.

  Sample No. 2-1 has eight outer peripheral blades of equal leads, and the twist angle of the outer peripheral blade is 38 °. On the other hand, sample no. 2-2 has two outer peripheral blades of equal leads, and the twist angle of the outer peripheral blade is 72 °.

  FIG. It is a graph which shows the time-dependent change of the cutting resistance at the time of cutting using the 2-1 end mill. FIG. It is a graph which shows the time-dependent change of the cutting resistance at the time of cutting using the end mill of 2-2. That is, the horizontal axis in FIGS. 10A and 10B is time. Moreover, in FIG. 10A and FIG. 10B, the scale of a horizontal axis corresponds. In the graphs of FIG. 10A and FIG. 10B, numerals are shown at points where the outer peripheral blades arranged in the circumferential direction start to contact each other.

  As shown in FIG. 10A and FIG. 2-1, sample no. In the cutting process using the 2-2 end mill, the cutting resistance increases at the moment when one outer peripheral blade is separated from the work material and the other outer peripheral blade starts to contact the work material. Paying attention to the absolute value of cutting resistance, sample No. The cutting resistance of the end mill of 2-1 is the sample No. It is larger than the cutting resistance of the 2-2 end mill. This is sample no. The end mill of No. 2-1, sample No. This is considered to be due to a small twist angle as compared with the 2-2 end mill. However, paying attention to the range of increase / decrease in cutting resistance, sample No. The increase / decrease width of the cutting resistance of the end mill of 2-1 is sample No. It is smaller than the increase / decrease width of the cutting resistance of the 2-2 end mill. When the increase / decrease width of the cutting force increases, the end mill vibrates due to the increase / decrease of the cutting resistance, and the machining accuracy decreases. That is, sample No. By using the end mill of 2-1, sample no. Compared with the case of using the 2-2 end mill, the accuracy of the processed surface can be increased.

(Test 3)
Next, Test 3 showing the superiority of having a positive-type rake face will be described.
Under the following conditions, sample no. 3-1, sample no. The work material is cut by a 3-2 end mill.
・ Cover cut material: DAC (H) 48HRC
・ End mill: Outer diameter of outer peripheral edge Φ6mm
・ Machine: MAKINO V33 (HSK-F63)
Cutting conditions: Rotational speed n = 2650 revolutions / minute
Feeding speed Vf = 636mm / min
Allow 0.1mm
Down cut
Dry-air blow

  Sample No. 3-1, sample no. Each of the 3-2 end mills has eight outer peripheral blades with equal leads. Sample No. 3-1, sample no. 3-2 is set so that the number of simultaneous contact blades is one.

  Sample No. The outer peripheral blade of the 3-1 end mill has a positive type rake face. On the other hand, sample no. The outer peripheral edge of the 3-2 end mill has a negative rake face.

  FIG. 3-1, sample no. It is a graph which shows the relationship between the measurement result of the depth of a processed surface, and the amount of collapse of a processed surface in the process using a 3-2 end mill. As shown in FIG. 11, sample No. 1 provided with an outer peripheral blade having a positive type rake face. The end mill of 3-1 is a sample No. 1 provided with an outer peripheral blade having a negative type rake face. It can be confirmed that the amount of collapse is sufficiently small compared to the end mill of 3-2.

(Test 4)
Next, the test 4 for confirming the optimum width of the flank on the first step surface (width w in FIG. 4) in the outer peripheral blade having the two flank surfaces will be described.
Under the following conditions, sample no. 4-1, Sample No. 4-2 and Sample No. Work material is cut by a 4-3 end mill.
・ Cover cut material: DAC (H) 48HRC
・ End mill: Outer diameter of outer peripheral edge Φ6mm
・ Machine: YASDA YBM640V (BT40)
Cutting conditions: Rotational speed n = 2650 revolutions / minute
Feeding speed Vf = 636mm / min
Allow 0.1mm
Down cut
Dry-air blow processing

  Sample No. 4-1, Sample No. 4-2 and Sample No. Both 4-3 end mills have eight outer peripheral edges. Sample No. 4-1, Sample No. 4-2 and Sample No. 4-3 is set so that the number of simultaneous contact blades is one. Sample No. 4-1, Sample No. 4-2 and Sample No. The outer peripheral edge of the 4-32 end mill has a positive type rake face.

Sample No. The width w of the first-stage flank 4-1 is 0.03 mm. Sample No. The width w of the first-stage flank 4-2 is 0.06 mm. Sample No. The width w of the first flank 4-3 is 0.1 mm.
Sample No. 4-1, Sample No. 4-2 and Sample No. The clearance angle of the flank on the first step surface 4-3 (the clearance angle β in FIG. 4) is 4 °. Sample No. 4-1, Sample No. 4-2 and Sample No. The clearance angle of the flank of the two-step surface 4-3 (the clearance angle γ in FIG. 4) is 15 °.

FIG. 4-1, Sample No. 4-2 and Sample No. It is a graph which shows the relationship between the measurement result of the depth of a processed surface, and the amount of collapse of a processed surface in the process using a 4-3 end mill.
Sample No. 4-1, Sample No. 4-2 and Sample No. Table 1 shows the evaluation results of the processed surface by processing using the 4-3 end mill.

  In Table 1 and Table 2 below, “Ra” is the arithmetic average roughness of the machined surface, and “Rz” is the maximum height of the machined surface. Further, “roughness / appearance” is an evaluation result of the processed surface visually. “Falling accuracy” is an evaluation result based on a graph. Cutting resistance is the evaluation result evaluated based on the measurement result of cutting resistance. In each item, A is the best, B is the next best, C is the next best, and D is not preferable.

  As shown in FIG. 12 and Table 1, sample No. 1 in which the width w of the first flank is 0.03 mm. The end mill of 4-1 is sample No. 4-2 and Sample No. It can be confirmed that the formed processed surface is superior to the 4-3 end mill.

(Test 5)
Next, Test 5 for confirming the optimum relief angle of the relief surface of the first step surface (the relief angle β in FIG. 4) in the outer peripheral blade having the two steps of the relief surface will be described.
Under the following conditions, sample no. 5-1, sample no. 5-2 and sample no. Work material is cut with an end mill of 5-3.
・ Cover cut material: DAC (H) 48HRC
・ End mill: Outer diameter of outer peripheral edge Φ6mm
・ Machine: YASDA YBM640V (BT40)
Cutting conditions: Rotational speed n = 2650 revolutions / minute
Feeding speed Vf = 636mm / min
Allow 0.1mm
Down cut
Dry-air blow processing

  Sample No. 5-1, sample no. 5-2 and sample no. Both 5-3 end mills have eight peripheral edges. Sample No. 5-1, sample no. 5-2 and sample no. 5-3 is set so that the number of simultaneous contact blades is one. Sample No. 5-1, sample no. 5-2 and sample no. The outer peripheral edge of the 5-32 end mill has a positive rake face.

Sample No. The clearance angle β of the first-stage flank of 5-1 is 0 °. Sample No. The clearance angle β of the first flank of 5-2 is 4 °. Sample No. The clearance angle β of the flank of the first stage 5-3 is 8 °.
Sample No. 5-1, sample no. 5-2 and sample no. The width of the flank of the first step surface 5-3 (width w in FIG. 4) is 0.06 mm. Sample No. 5-1, sample no. 5-2 and sample no. The clearance angle of the flank of the two-step surface 5-3 (the clearance angle γ in FIG. 4) is 15 °.

FIG. 5-1, sample no. 5-2 and sample no. It is a graph which shows the relationship between the measurement result of the depth of a processed surface, and the amount of collapse of a processed surface in the process using a 5-3 end mill.
Sample No. 5-1, sample no. 5-2 and sample no. Table 2 shows the evaluation results of the processed surface by processing using the 5-3 end mill.

  As shown in FIG. 13 and Table 2, sample No. 1 in which the relief angle β of the first flank is 4 °. The end mill of 5-2 is sample No. 5-1 and Sample No. It can be confirmed that the formed processed surface is superior to the 5-3 end mill.

(Test 6)
Next, test 6 showing the superiority of an end mill having an outer peripheral blade with unequal leads will be described.
Under the following conditions, sample no. 6-1 and Sample No. The work material is cut by an end mill of 6-2.
・ Cover cut material: DAC (H) 48HRC
・ End mill: Outer diameter of outer peripheral edge Φ6mm
・ Machine: MAKINO V33 (HSK-F63)
Cutting conditions: Rotational speed n = 2650 revolutions / minute
Feeding speed Vf = 636mm / min
Allow 0.1mm
Down cut
Dry-air blow processing

  Sample No. 6-1 and Sample No. Both of the 6-2 end mills have eight peripheral blades. Sample No. 6-1 and Sample No. 6-2 is set so that the number of simultaneous contact blades is one. Sample No. 6-1 and Sample No. The outer peripheral blade of the 6-2 end mill has a positive type rake face.

  Sample No. The outer peripheral blade of the 6-1 end mill is an equal lead. Sample No. The twist angle of the outer peripheral edge of the 6-1 end mill is 38 °. On the other hand, sample no. The outer peripheral blade of the 6-2 end mill is an unequal lead. Sample No. In the 6-2 end mill, outer peripheral blades having helix angles of 38 °, 40 °, 38 °, 36 °, 38 °, 40 °, 38 °, and 36.5 ° are arranged in the tool rotation direction.

  FIG. 14A shows sample no. It is a graph which shows the relationship between the measurement result of the depth of a process surface, and the amount of collapse of a process surface in the process using a 6-1 end mill. FIG. 14B shows sample no. It is a graph which shows the relationship between the measurement result of the depth of a processed surface, and the amount of collapse of a processed surface in the process using a 6-2 end mill. Sample No. 6-1 and Sample No. In the processing using the 6-2 end mill, the end mill feed rates were measured at 50 m / min, 70 m / min, and 100 m / min, respectively.

  As shown in FIG. 14A and FIG. In the processing with the 6-1 end mill, a good machined surface can be formed when the feed speed of the end mill is 50 m / min and 70 m / min. However, when the feed speed of the end mill is 100 m / min, the amount of tilting is reduced. growing. On the other hand, sample no. In the machining by the end mill of 6-2, even when the feed speed of the end mill is changed, a certain amount of collapse can be maintained. That is, it was confirmed that the accuracy of the machined surface can be improved even when the feed amount of the end mill is increased by making the outer peripheral blade an unequal lead.

  Although the embodiments of the present invention have been described above, the configurations and combinations thereof in the embodiments are examples, and additions, omissions, substitutions, and other modifications of the configurations are within the scope that does not depart from the spirit of the present invention. Is possible. Further, the present invention is not limited by the embodiment.

  DESCRIPTION OF SYMBOLS 1,101 ... End mill, 11 ... Neck part (shaft part), 20, 120 ... Blade part, 21, 121A ... Outer peripheral blade, 21a ... Upper end, 21b ... Lower end, 22, 122A ... Bottom blade, 23 ... Radius blade, 24b ... Rake face, 25 ... flank, 121A ... first outer peripheral edge, 121B ... second outer peripheral edge, 121C ... third outer peripheral edge, d, D ... outer diameter, L ... blade length, O ... axis (center) Axis), P1, P2 ... boundary, T ... tool rotation direction, TP ... most advanced point, [theta], [theta] 1, [theta] 2, [theta] 3 ... twist angle

Claims (9)

A cylindrical shaft extending along the central axis;
A blade portion located on the tip side of the shaft portion,
The blade portion is provided with eight outer peripheral blades having a larger outer diameter than the shaft portion along the circumferential direction.
The outer peripheral blade is a twisted blade extending spirally around the central axis,
Paying attention to one of the eight peripheral blades, the blade length along the axial direction of the peripheral blade is L, the twist angle of the peripheral blade is θ, and the peripheral blade and the peripheral blade at the lower end of the peripheral blade When the circumferential distance between the other peripheral blades adjacent to the rear of the tool rotation direction is a, n represented by the following formula is approximately 1 for all eight peripheral blades.
End mill.
n = (L × tan θ) / a N is 0.9 or more and 1.1 or less,
The end mill according to claim 1. The outer diameter dimension is 4 mm or more.
The end mill according to claim 1 or 2. The twist angle is 35 ° or more and 40 ° or less.
The end mill as described in any one of Claims 1-3. The outer peripheral blade has a positive type rake face,
The end mill as described in any one of Claims 1-4. The outer peripheral edge has two flank faces;
The end mill as described in any one of Claims 1-5. In the blade portion, in addition to the eight outer peripheral blades, eight bottom blades provided at the tip and extending radially outward from the central axis side, and smoothly connecting between the outer peripheral blade and the bottom blade 8 And two radius blades,
The cutting edge of the blade portion is located on the radius blade between the radius blade and the boundary between the outer peripheral blade and the boundary between the radius blade and the bottom blade.
The end mill as described in any one of Claims 1-6. The eight outer peripheral blades include a first outer peripheral blade and a second outer peripheral blade,
The twist angle of the first outer peripheral blade and the twist angle of the second outer peripheral blade are different angles.
The end mill as described in any one of Claims 1-7. The eight peripheral blades are
Four first outer peripheral blades;
Two second outer peripheral blades having a twist angle larger than the twist angle of the first outer peripheral blade;
Two third outer peripheral blades having a twist angle smaller than the twist angle of the first outer peripheral blade,
The four first outer peripheral blades are arranged at substantially equal intervals along the circumferential direction,
The second outer peripheral blades and the third outer peripheral blades are alternately arranged along the circumferential direction between a pair of different first outer peripheral blades.
The end mill according to claim 8.

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