Endmill

Abstract

To suppress increase in cutting resistance caused by chip jamming by improving chip discharge performance.SOLUTION: Three cutting edges 10, 20, and 30 similar in a structure are formed on the tip side of a body 3 extending along a rotation axis O. The cutting edge 10 includes a projected circular-arc bottom blade 15 having a curvature larger than the radius of the body 3, an outer peripheral blade 13 positioned on the outer peripheral surface of the body 3 and twisted rearward around a center axis in a rotation axis, a corner blade 14 having a curvature smaller than that of the bottom plate 15 and connected to the bottom blade 15 and the outer peripheral blade 13, and a gash provided between front cutting blades 20 adjacent to each other front in the rotation direction. The gash includes a first gash groove which becomes a chip introduction space, and a second gash groove that is connected to the rear end side of the first gash groove in the axial direction and that extends the chip introduction space along the twisting of the outer peripheral space 13.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an end mill, which is an example of a rotary cutting tool. [Background technology]

[0002] As a rotary cutting tool that efficiently forms a bottom surface (surface shape) on a workpiece, an end mill having a curved convex arc portion on the bottom cutting edge is disclosed in Patent Document 1. This type of end mill is called a lens-type end mill or a barrel-type end mill, and is said to be able to increase the feed interval (pick feed) compared to a ball end mill, thereby reducing the processing time and improving the surface roughness. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-131397 A Summary of the Invention [Problem to be solved by the invention]

[0004] The end mill disclosed in Patent Document 1 tends to produce larger chips from the workpiece than a ball end mill with the same tool diameter. Therefore, when the cutting depth is increased (deepened) while rotating the end mill body at high speed, there is a problem that the chip discharge performance is impaired and cutting resistance increases. An excessive increase in cutting resistance causes chipping or breakage of the bottom cutting edge, shortening the tool life from the design time.

[0005] One object of the present invention is to provide a structure for an end mill having a convex arc-shaped bottom cutting edge with a curvature larger than the radius of the body, which improves chip discharge properties and suppresses an increase in cutting resistance caused by chip clogging. Other objects of the present invention will become apparent from the present disclosure. [Means for solving the problem]

[0006] One aspect of the present invention is an end mill having a plurality of cutting edge portions formed on the tip side of a body extending along a rotation axis, each of the cutting edge portions having a convex arc-shaped bottom blade with a curvature greater than the radius of the body, a peripheral blade located on the outer peripheral surface of the body and twisted rearward in the direction of rotation around a central axis, a corner blade connecting the bottom blade and the peripheral blade with a curvature smaller than that of the bottom blade, and a gash provided between adjacent front cutting edge portions at the front of the direction of rotation, the gash including a first gash groove that serves as a chip introduction space, and a second gash groove that continues to the axial rear end side of the first gash groove and expands the chip introduction space along the twist of the peripheral blade. Effect of the Invention

[0007] According to the above aspect, even in an end mill having a convex arc-shaped bottom cutting edge with a curvature larger than the radius of the body, it is possible to improve chip discharge properties and suppress an increase in cutting resistance caused by chip clogging. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is an external perspective view showing a structural example of the end mill according to the present embodiment. [Diagram 2] FIG. 2 is a front view of the end mill according to the embodiment. [Diagram 3] FIG. 2 is an external side view of the end mill according to the embodiment. [Figure 4] FIG. 2 is an enlarged view of a tip portion of the end mill according to the embodiment. [Diagram 5] 11A and 11B are front photographs for visually comparing the degree of wear of end mills, where (a) is an end mill serving as a comparative example, and (b) is an end mill according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described. The end mill of this embodiment is used for machining precision dies and parts, for example, by cutting alloy tool steel (SKD11) or powder high-speed tool steel (SKH55, etc.).

[0010] FIG. 1 is an external perspective view showing a structural example of an end mill according to this embodiment. FIG. 2 is a front view of this end mill. FIG. 3 is an external side view of this end mill. FIG. 4 is an enlarged view of the tip portion of FIG. 1. In the figure, a straight line is shown on one surface, but this indicates a continuous curved surface. Below, a structural example of the end mill 1 of this embodiment will be described with reference to these figures as appropriate.

[0011] [Example of end mill configuration] The end mill 1 of this embodiment is a rotary cutting tool that rotates around a central axis. The central axis is the rotation axis O of the end mill 1. In this specification, the direction extending along the rotation axis O is called the "axial direction", the direction perpendicular to the rotation axis O is called the "radial direction", and the direction around the axis of rotation O is called the "circumferential direction". The direction perpendicular to the rotation axis O is called the radial direction, the direction approaching the rotation axis O in the radial direction is called the radial inner side or center side, and the direction away from the rotation axis O is called the radial outer side or outer periphery side. The direction in which the end mill 1 rotates around the rotation axis O during cutting processing is called the tool rotation direction T. The direction in which cutting of the workpiece is started in the tool rotation direction T is called the front or tool rotation front, and the opposite direction is called the rear or tool rotation rear. The surface facing the workpiece is sometimes called the tip surface, the direction toward the workpiece is sometimes called the tip side, and the direction from the tip surface to the tool base end side is sometimes called the tool base end direction or tool base end side.

[0012] The end mill 1 has a shank 2 made of a hard material such as cemented carbide, and a body 3 at the end (effective cutting edge length) of the end mill body extending from the shank 2 toward the tip. The shank 2 is located on the rear end side of the end mill body, and the body 3 is located on the tip side of the end mill body. The shank 2 is, for example, cylindrical, and is held by a main shaft of a machine tool (not shown) and rotated in a rotation direction T around a central axis O. In the following explanation, the diameter of the body 3 (body diameter) is approximately φ6 mm, but it may be a small diameter less than φ6 mm, and as will be described in detail later, the effect is more pronounced as the diameter is smaller than φ6 mm.

[0013] As described above, the body 3 extends from the tip of the shank 2 toward the tip side along the rotation axis O. In this embodiment, the body 3 has a first cutting edge portion 10, a second cutting edge portion 20, and a third cutting edge portion 30. The cutting edges 10, 20, and 30 are provided symmetrically when viewed from the tip surface of the body 3 (when viewed from the front).

[0014] In one embodiment, the cutting edges 10, 20, and 30 are formed at intervals of 120° in the circumferential direction around the central axis O. However, the main feature of this embodiment is the structure of the individual cutting edges 10, 20, and 30, particularly the gash that forms the chip introduction space. Therefore, the formation intervals between the cutting edges do not necessarily have to be uniform.

[0015] [First cutting edge] The first cutting edge portion 10 will be described. The first cutting edge portion 10 has flute grooves 11 that serve as chip discharge grooves and an outer peripheral flank surface 12. The flute grooves 11 extend on the outer periphery of the body 3, twisting in the circumferential direction opposite the tool rotation direction T as they move from the axial tip side to the axial rear end side of the body 3. The end of the flute groove 11 on the rear side of the rotation axis merges with the outer peripheral surface of the end mill body extending from the shank 2. In other words, it is flush with the outer peripheral surface.

[0016] A peripheral blade 13 is formed at the intersection ridge between the flute groove 11 and the peripheral relief surface 12 on the forward side in the rotational direction. The peripheral blade 13 extends spirally from the axial tip to the rear end at a constant twist angle. A peripheral blade rake surface 131 is formed on the forward side in the rotational direction of the peripheral blade 13. The peripheral blade rake surface 131 is a concave twisted surface. A wall surface 132 facing the direction of the central axis O is formed on the tip side of the peripheral blade rake surface 131.

[0017] A bottom blade 15 is provided on the tip side of the peripheral blade 13 via a corner blade 14. The corner blade 14 and the bottom blade 15 extend from the tip of the peripheral blade 13 toward the inner periphery side (diametrically inward). The corner blade 14 is a so-called connecting blade that connects the peripheral blade 13 and the bottom blade 15 with a curvature (radius of curvature) smaller than that of the bottom blade 15. A bottom blade scooping surface 151 is formed in front of the corner blade 14 and the bottom blade 15 in the rotational direction. The bottom blade scooping surface 151 also serves as a gash wall that reaches the gash bottom 152. The gash bottom 152 is a surface that is formed by the shape of the grindstone during gash molding, and may not be formed depending on the molding process.

[0018] The bottom cutting edge 15 is a convex arc shape with a curvature (radius of curvature) larger than the radius of the body 3, and the rotation trajectory is barrel-shaped (half of a convex lens). The bottom cutting edge 15 also has a convex arc shape that is convex toward the front in the direction of rotation when viewed from the front. In other words, the bottom cutting edge 15 has a barrel shape with a larger curvature than the bottom cutting edge of a three-blade ball end mill when viewed from the front. Adjacent to the bottom cutting edge 15, a tip flank 16, a third surface 17, and a gash bottom surface 18 are formed. The tip flank 16 has a constant width up to the tip surface portion of the third surface 17, but gradually becomes smaller as it approaches the tip surface portion toward the tip surface center, and is close to zero width at the tip surface center. Therefore, wear and the like at the portion where the rotation speed is the smallest can be suppressed.

[0019] An extended surface 19 is formed at the rear end of the gash bottom 152 and the rear end of the gash bottom surface 18. This extended surface 19 is a surface formed to extend the chip discharge space of the gash, which is a chip introduction space, and continues to the axial rear end side of the gash bottom surface 18. The extended surface 19 is a curved surface or a flat surface twisted in accordance with the twist of the peripheral blade 13, and its edge continues to the flute groove 11 on the rear end side. One side of the extended surface 19 extends along the peripheral blade rake face, and the opposite side gently continues to the flute groove 11.

[0020] In this embodiment, the rake angles of the peripheral cutting edge 13, the corner cutting edge 14 and the bottom cutting edge 15 are negative angles (negative shapes), but are not limited to negative angles and may be positive angles (positive shapes) or angles perpendicular to the rotation axis O.

[0021] [Other cutting edges] The second cutting edge portion 20 and the third cutting edge portion 30 have the same shape and structure as the first cutting edge portion 10. The correspondence with the first cutting edge portion 10 is as follows. Note that parts that are not visible in the figures, that is, parts that exist but are not shown, are distinguished by parentheses. <First cutting edge portion 10><Second cutting edge portion 20><Third cutting edge portion 30> Flute groove 11 ··· Flute groove 21 ··· Flute groove 31 Outer flank 12 (Outer flank 22) (Outer flank 32) Peripheral blade 13 (Peripheral blade 23) (Peripheral blade 33) Peripheral cutting edge rake face 131 (Peripheral cutting edge rake face 231) (Peripheral cutting edge rake face 331) Wall surface 132 (wall surface 232) (wall surface 332) Corner blade 14 ···· Corner blade 24 ···· Corner blade 34 Bottom blade 15 Bottom blade 25 Bottom blade 35 Bottom cutting edge rake face 151 ·· Bottom cutting edge rake face 251 ·· Bottom cutting edge rake face 351 Gash bottom 152 ·· Gash bottom 252 ·· Gash bottom 352 Tip flank 16 ··· Tip flank 26 ··· Tip flank 36 Third side 17 ... Third side 27 ... Third side 37 Gash bottom 18 Gash bottom 28 Gash bottom 38 Extension surface 19 ···· Extension surface 29 ···· Extension surface 39

[0022] [Gash] The end mill 1 of this embodiment has a gash with a characteristic structure provided between the cutting edges. The enlarged view of the tip portion in Fig. 4 shows an example of the structure of the gash provided between the first cutting edge portion 10 and the adjacent second cutting edge portion 20 at the front of the first cutting edge portion, i.e., at the front of the tool rotation direction. The gash has a first gash groove formed by a combination of multiple different surfaces, and a second gash groove on the rear end side.

[0023] The first gash groove is a chip introduction space including the bottom cutting edge rake face 151 and the third face 28 of the front cutting edge portion, i.e., the second cutting edge portion 20. The second gash groove is continuous with the axial rear end side of the first gash groove and expands the chip introduction space along the twist of the peripheral cutting edge 13.

[0024] Specifically, the second gash groove is formed including an expanded surface 29 of the second cutting edge portion 20 that is continuous with the third surface 28 of the first gash groove on the axial rear end side, and a wall surface 132 that faces toward the direction of the rotation axis O from the middle of the peripheral blade rake face 131. The chip introduction space formed by the rotation trajectory of the first gash groove and the second gash groove is about 1.15 to 2.0 times the chip introduction space formed by the rotation trajectory of only the first gash groove.

[0025] The wall surface 132 of the second gash groove is a twisted surface that follows the twist of the peripheral cutting edge 13, but may be a flat or curved surface. The second gash groove is significant in that it expands the chip introduction space formed by the rotation trajectory during tool rotation more than the first gash groove alone and enlarges the edge portion continuing to the flute groove 21 on the rear end side. Therefore, if the chip introduction space can be expanded by the third surface 28 alone, it is not necessarily necessary to provide the wall surface 132.

[0026] The boundaries between the third surface 28 and the extended surface 29, and between the bottom blade rake surface 151 and the wall surface 132 that constitute the second gash groove may be non-seamless structures with a certain angle difference, or may be seamless structures in which the boundaries are continuous. The angle difference θg between the tip side part of the gash bottom surface 28 and the rear end side part of the extended surface 29 in the direction from the central axis O toward the outer periphery is preferably in the range of about 2 to 50 degrees, as shown in FIG. 3. It is preferably the same angle as the twist angle of the peripheral blade 13. In addition, the angle between the tip side part of the gash bottom surface 28 and the rear end side part of the extended surface 29 with respect to the central axis O is preferably less than the twist angle of the peripheral blade 13 from the viewpoint of preventing interference of chips with the peripheral blade rake surface 131.

[0027] The end mill 1 constructed as above has a barrel-shaped (convex lens-shaped) bottom blade 15, so the efficiency of bottom cutting of the workpiece is significantly improved compared to a ball end mill of the same body diameter used for the same purpose. In addition, because it is a so-called three-blade end mill, the effect is improved by about three times, and the rigidity and efficiency of the structure sandwiching the bottom blade rake faces 151, 251, 351 of each cutting blade portion 10, 20, 30 and the gash bottom faces 18, 28, 38 can be balanced. In addition, vibrations generated during cutting can be suppressed.

[0028] The end mill 1 of this embodiment also has a gash including a second gash groove that is continuous with the rear end side of the first gash groove and expands the chip introduction space along the twist of the peripheral cutting edge 13. Therefore, during cutting, when the chips introduced into the first gash groove are guided to the second gash groove, centrifugal force caused by the tool rotation is applied to the chips, and the chips are discharged toward the flute grooves 11, 21, 31 at an increased speed without coming into contact with unexpected locations, and are dissipated from the outer periphery of the end mill body into the external space.

[0029] The arrows in FIG. 4 indicate the direction of chip discharge. With this gash structure, the chips move smoothly from the first gash groove to the second gash groove, so they retain the shape they had immediately after cutting without being deformed, and become a shape that is more suitable for discharge. This prevents even chips that are relatively large compared to the body diameter from staying in the first gash groove, and prevents an increase in cutting resistance. This reduces wear on the corner blade 14, bottom blade 15, and bottom blade rake faces 151, 251, and 351. At least, abnormal wear caused by chip retention is prevented.

[0030] In order to visually demonstrate the above-mentioned effects, the applicant created a comparative end mill with the same body diameter and material as end mill 1, and compared the same workpiece under the same cutting conditions (same cutting depth, same cutting time, etc.). The comparative end mill is an end mill of end mill 1 that only has the first gash groove.

[0031] FIG. 5 is a front view photograph for comparing the degree of wear of the end mill 1, where (a) is that of the comparative end mill 5 and (b) is that of the end mill 1 according to this embodiment. In the vicinity of the cutting edge 51 in FIG. 5(a), abnormal wear occurs due to the obstruction of chip discharge. In contrast, in the vicinity of the cutting edge 52 in FIG. 5(b), the retention of chips is suppressed, so only scraping wear occurs, and the end mill 1 can be used continuously for cutting after that. In other words, the end mill 1 according to this embodiment has a longer tool life than the comparative end mill 5.

[0032] In this embodiment, the body diameter of the end mill 1 is approximately 6 mm, but the body diameter of the end mill 1 may be smaller than 6 mm. Small diameter end mills can produce relatively large chips, but the structure of the end mill of this embodiment allows even such large chips to be smoothly dispersed to the outside via the outer periphery of the end mill body, suppressing an increase in cutting resistance. In other words, the smaller the diameter, the more effective the structure of this embodiment.

[0033] In this embodiment, the end mill 1 has a so-called three-blade configuration, but the number of cutting edges may be two, or four or more.

[0034] In this embodiment, the bottom cutting edges 15, 25, 35 are barrel-shaped in which the cutting edge action is concentrated near the rotation axis O and the width of the tip flank 16, 26, 36 is almost zero, but a configuration in which a recess is provided near the rotation axis O is also possible. This configuration makes it easy to suppress heat generation and cool with a coolant, and also reduces burrs and chipping that occur near the rotation axis O.

[0035] In the end mill 1 of this embodiment, the material of the end mill body (tool material) may be a cBN sintered body or a diamond sintered body, or may be coated with a hard film. This can further extend the tool life. In addition, the end mill may be honed after coating. This can suppress unevenness on the cutting surface.

[0036] The disclosure according to this embodiment includes the following aspects of the invention. [Aspect 1] The invention of aspect 1 is an end mill having a plurality of cutting edge portions formed on the tip side of a body extending along a rotation axis, each of the cutting edge portions having a convex arc-shaped bottom blade with a curvature greater than the radius of the body, a peripheral blade located on the outer peripheral surface of the body and twisted rearward in the direction of rotation around the central axis, a corner blade connecting the bottom blade and the peripheral blade with a curvature smaller than that of the bottom blade, and a gash provided between adjacent front cutting edge portions at the front of the direction of rotation, the gash including a first gash groove that serves as a chip introduction space, and a second gash groove that continues to the axial rear end side of the first gash groove and expands the chip introduction space along the twist of the peripheral blade.

[0037] According to the first aspect of the invention, the chips generated by the bottom cutting edge and the corner cutting edge are introduced into the first gash groove, and then guided to the second gash groove and dispersed. Therefore, the flow of the chips toward the axial rear end side becomes smoother than when there is only the first gash groove, and further, since the discharge speed and direction of the chips change when they move from the first gash groove to the second gash groove, the retention of the chips in the gash is suppressed even when the chips are large. Therefore, it becomes easier to handle high-speed machining and deep cuts.

[0038] [Aspect 2] A second aspect of the invention is an end mill according to the first aspect of the invention, wherein the bottom cutting edge has a convex arc shape that is convex toward the front in the direction of rotation when viewed from the front. According to the invention of aspect 2, a barrel-shaped bottom cutting edge is formed, so that the cutting efficiency is remarkably improved compared to a ball end mill with the same body diameter.

[0039] [Aspect 3] A third aspect of the invention is an end mill according to the first aspect of the invention, wherein the second gash groove is formed by a flat or curved surface extending along the twist of the peripheral cutting edge. According to the invention of the third aspect, the chips are discharged in the same direction as the air current generated by the tool rotation, which acts to further prevent the chips from accumulating.

[0040] [Aspect 4] A fourth aspect of the invention is the end mill according to any one of the first to third aspects, wherein a plurality of the cutting edges are provided symmetrically as viewed from the tip end face of the body. According to the sixth aspect of the invention, the cutting efficiency can be further improved.

[0041] [Aspect 5] A fifth aspect of the invention is the end mill of the fourth aspect of the invention, wherein the diameter of the body is a small diameter of approximately 6 mm or less than 6 mm. According to the invention of aspect 5, the chips tend to be relatively larger than those of end mills with a body diameter exceeding 6 mm, but since the chips can be effectively discharged to the outside, wear of the cutting edge portion can be suppressed. [Explanation of symbols]

[0042] 1···End mill, 2···Shank, 3···Body, 13, 23, 33···Peripheral cutting edge, 131, 231, 331···Peripheral cutting edge rake face, 132, 232, 332···Wall surface, 14, 24, 34···Corner cutting edge, 14, 24, 34···Bottom cutting edge, 151, 251, 351···Bottom cutting edge rake face, 19, 29, 39···Extended surface.

Claims

1. A plurality of cutting edge portions are formed on the tip side of a body extending along the rotation axis, and each of the cutting edge portions has a bottom blade having a convex arc shape with a curvature larger than the radius of the body, a peripheral blade located on the outer circumferential surface of the body and twisted backward in the direction of rotation around the central axis, a corner blade connecting the bottom blade and the peripheral blade with a curvature smaller than that of the bottom blade, and a gash provided between adjacent front cutting edge portions at the front of the direction of rotation, The end mill includes a first gash groove, which serves as a chip introduction space, and a second gash groove, which is continuous with the axial rear end side of the first gash groove and expands the chip introduction space along the twist of the peripheral cutting edge.

2. The end cutting edge has a convex arc shape that is convex toward the front in the direction of rotation when viewed from the front. The end mill according to claim 1 .

3. The end mill according to claim 1 , wherein the second gash groove is formed by a flat or curved surface extending along the twist of the peripheral cutting edge.

4. The cutting edge portion is provided symmetrically as viewed from the tip end surface of the body. An end mill according to any one of claims 1 to 3.

5. The diameter of the body is approximately 6 mm or less than 6 mm. The end mill according to claim 4.

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