WO2010047428A1

WO2010047428A1 - An end mill and a cutting insert used for the same

Info

Publication number: WO2010047428A1
Application number: PCT/KR2008/006225
Authority: WO
Inventors: Myung Gi Kang; Jong Lim Hong
Original assignee: Taegutec Ltd.
Priority date: 2008-10-20
Filing date: 2008-10-21
Publication date: 2010-04-29
Also published as: KR20100043467A; KR101011053B1

Abstract

The present invention has a shank portion, a head portion extended from an end of the shank portion, a bottom cutting edge formed on a bottom surface of the head portion, a side cutting edge formed on a side surface of the head portion and connected to the bottom cutting edge, and a rake surface and a clearance surface extending from the bottom cutting edge. The bottom cutting edge has a first bottom cutting edge and a second bottom cutting edge. When viewed from the front of the end mill, the first bottom cutting edge extends from a central axis of the head portion to an intersection formed with the second bottom cutting edge in a direction away from the shank portion. The second bottom cutting edge extends straight at an angle from the intersection formed with the first bottom cutting edge to an intersection formed with the side cutting edge in a direction towards the shank portion. The rake surface forms a positive rake angle with respect to the central axis of the head portion.

Description

AN END MILLAND A CUTTING INSERT USED FOR THE SAME

TECHNICAL FIELD

The present invention generally relates to an end mill, and more particularly to a high-feed end mill capable of performing a cutting process at a high feed rate.

BACKGROUND ART

An end mill is a cutting tool, which is mounted and used on a holder of a milling machine. A typical end mill comprises a cylindrical shank portion, which is inserted and coupled to a bore formed in the holder of the milling machine, and a head portion at a lower of the cylindrical shank portion. The head portion has a side cutting edge at its side surface and a bottom cutting edge at its bottom end surface. The end mill can perform various cutting processes (e.g., bottom or side surface machining) or a hole- drilling along its relative motion to a workpiece. That is, the end mill can perform such cutting processes regardless of whether the rotating end mill itself is moved or the workpiece fixed on a table of the milling machine is moved while the end mill rotates in one place.

High-feed cutting processes are required in order to improve production efficiency. That is, it is desirable to shorten the cutting time by increasing the feed rate of the workpiece or the end mill. However, as the feed rate increases, the cutting resistance applied to a cutting edge during the cutting process will increase. Thus, the cutting edges of conventional end mills are easily deformed or destroyed and the tool's life cycle is very short when used at a high feed rate.

DISCLOSURE

TECHNICAL PROBLEM

The objective of the present invention is to solve the above problems of the prior art. The present invention is directed to providing an end mill, which can perform a cutting process at a high feed rate by significantly decreasing a cutting resistance applied to a cutting edge during the cutting process. Further, the present invention relates to providing an end mill, which can shorten a cutting time and improve production efficiency by performing the cutting process at a high feed rate, while the tool's life cycle is very long despite the high feed rate of the cutting process.

TECHNICAL SOLUTION

In order to achieve the above objectives, the end mill of the present invention comprises a bottom cutting edge that extends straight at an entering angle, thereby minimizing the contact length between a cutting edge and a workpiece during the cutting process. Further, a rake surface extending from the cutting edge has a positive rake angle. As such, the end mill of the present invention can significantly decrease the cutting resistance applied to the cutting edge during the cutting process.

According to one embodiment of the present invention, an end mill comprises a shank portion, a head portion extended from an end of the shank portion, a bottom cutting edge formed on a bottom surface of the head portion, a side cutting edge formed on a side surface of the head portion and connected to the bottom cutting edge, and a rake surface and a clearance surface extending from the bottom cutting edge. The bottom cutting edge comprises a first bottom cutting edge and a second bottom cutting edge. When viewed from the front of the end mill, the first bottom cutting edge extends from a central axis of the head portion to an intersection formed with the second bottom cutting edge in a direction away from the shank portion. The second bottom cutting edge extends straight at an angle from an intersection formed with the first bottom cutting edge to an intersection formed with the side cutting edge in a direction towards the shank portion. The rake surface forms a positive rake angle with respect to the central axis of the head portion.

According to another embodiment of the present invention, an end mill comprises a shank portion, a head portion extended from an end of the shank portion, and a cutting insert detachably mounted at an end of the head portion. The cutting insert comprises an upper surface contacting a seat surface formed at the end of the head portion, a lower surface positioned opposite to the upper surface and including a bottom cutting edge, a side surface connecting the upper surface and the lower surface and including a side cutting edge connected to the bottom cutting edge, and a rake surface and a clearance surface extending from the bottom cutting edge. The bottom cutting edge comprises a first bottom cutting edge and a second bottom cutting edge. When viewed from the front of the end mill, the first bottom cutting edge extends from a center of the lower surface to an intersection formed with the second bottom cutting edge in a direction away from the upper surface. The second bottom cutting edge extends straight at an angle from an intersection formed with the first bottom cutting edge to an intersection formed with the side cutting edge in a direction towards the upper surface. The rake surface forms a positive rake angle with respect to a central axis of the head portion. The end of the head portion comprises a slit for receiving the cutting insert. The cutting insert is fixed to the head portion by a screw, which passes through a through hole formed in the cutting insert and is fastened at the end of the head portion. ADVANTAGEOUS EFFECTS

According to the present invention, the end mill can perform a cutting process at a high feed rate by significantly decreasing a cutting resistance applied to a cutting edge during the cutting process. Since the cutting process can be performed at the high feed rate, the cutting time can be shortened and the production efficieny can be improved. Further, although the cutting process is performed at the high feed rate, the tool's life cycle is prolonged, not redcuced.

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of an end mill in accordance with a first embodiment of the present invention.

FIG. 2 is a front view of the end mill shown in FIG. 1. FIG. 3 is an enlarged view of a portion A shown in FIG. 2. FIG. 4 is a cross-sectional view taken along the line IV-IV of FIG. 3.

FIG. 5 is a cross-sectional view taken along the line V-V of FIG. 3. FIG. 6 is a cross-sectional view taken along the line VI-VI of FIG. 3. FIG. 7 is a view taken from the end (direction B) of the end mill of FIG. 2. FIG. 8 is an enlarged view of a portion C shown in FIG. 3. FIG. 9 is a schematic view of an end of a head portion having a bottom cutting edge extending straight at an entering angle according to the present invention.

FIG. 10 is a schematic view of an end of a head portion having a round bottom cutting edge.

FIG. 11 is a perspective view of an end mill in accordance with a second embodiment of the present invention.

FIG. 12 is a side view of the end mill shown in FIG. 11.

FIG. 13 is a perspective view of a cutting insert mounted within the head portion of the end mill shown in FIG. 11.

FIG. 14 is a front view of the cutting insert shown in FIG. 13.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a perspective view of an end mill in accordance with a first embodiment of the present invention. FIG. 2 is a front view of the end mill shown in FIG. 1. As used herein, the term "a front of an end mill" refers to a front view of the end mill standing upright with its two side cutting edges bilaterally symmetrically positioned with respect to a central axis of the end mill, as shown in FIG. 2. As shown in FIGS. 1 and 2, the end mill 10 comprises a cylindrical shank portion 12, which is inserted and coupled to a bore provided at a holder of a milling machine, and a head portion 14 extending from the shank portion 12. The head portion 14 has cutting edges 20, 26 for performing the cutting process. The shank portion 12 and the head portion 14 of the end mill 10 are integrally formed.

FIG. 3 is an enlarged view of a portion A of FIG. 2. As shown in FIG. 3, the head portion 14 has a bottom cutting edge 20 at its bottom surface and a side cutting edge 26 at its side surface. The bottom cutting edge 20 and the side cutting edge 26 are connected to each other to form a continuous cutting edge. The bottom cutting edge 20 includes a first bottom cutting edge 22 and a second bottom cutting edge 24.

The first bottom cutting edge 22 extends from a central axis 16 of the head portion to an intersection formed with the second bottom cutting edge 24. When viewed from the front of the end mill 10, the first bottom cutting edge 22 extends from the central axis 16 of the head portion in a direction away from the shank portion 12 (i.e., in the lower direction in FIG. 3) at a dish angle b of 1° to 3° with respect to a line 18 perpendicular to the central axis 16 of the head portion. When the end mill 10 cuts the surface of a workpiece, the second bottom cutting edge 24 first cuts the workpiece along with a feed of a milling cutter or the workpiece, while the first bottom cutting edge 22 precisely cuts and smoothly polishes the portion of the workpiece cut by the second bottom cutting edge 24. A central portion of the bottom surface of the head portion 14 has a recessed shape, which is recessed toward the shank portion 12 (i.e., in the upper direction in FIG. 3), thereby preventing unnecessary contact between the first bottom cutting edge 22 and the workpiece as well as any undesirable increase of a cutting resistance during the cutting process. The dish angle b less than 1° may cause the unnecessary contact between the first bottom cutting edge 22 and the workpiece. On the other hand, the dish angle b more than 3° may excessively sharpen the intersection between the first bottom cutting edge 22 and the second bottom cutting edges 24, thereby causing a premature wear thereon.

The second bottom cutting edge 24 extends from the intersection formed with the first bottom cutting edge 22 to an intersection formed with the side cutting edge 26. When viewed from the front of the end mill 10, the second bottom cutting edge 24 extends straight from the intersection formed with the first bottom cutting edge 22 toward the shank portion 12 (i.e., in the upper direction in FIG. 3) at an entering angle a of 18° to 25° with respect to the line 18 perpendicular to the central axis 16 of the head portion 14. When the entering angle a is small under the same depth of cut, a contact length between the cutting edge and the workpiece becomes longer, and thus, a cutting resistance applied to the cutting edge increases during the cutting process. Thus, the entering angle a is preferably more than 18°. When the entering angle a is large, a feeding component force, which is a cutting resistance acting in a direction opposite to a feed direction, increases and vibrations may occur when performing the cutting process at a high feed rate. Thus, the entering angle a is preferably less than 25°. Further, a thickness and a length of a chip generated during the cutting process vary depending on the entering angle a of the second bottom cutting edge 24. When the entering angle a is small, the contact length between the cutting edge and the workpiece becomes longer, and thus, the length of the chip becomes longer. When the entering angle a is large, the contact length between the cutting edge and the workpiece becomes shorter and the thickness of the chip becomes thicker rather than the shorter chip length. Since the second bottom cutting edge 24 forms the entering angle a of 18° to 25°, the thickness and the length of the chip are optimized. As such, the chip can be smoothly discharged.

When the end mill 10 cuts the surface of a workpiece, the second bottom cutting edge 24 serves as a main cutting edge that cuts the workpiece along with the feed of the milling cutter or the workpiece. Most of the cutting resistance generated during the cutting process is applied to the second bottom cutting edge 24. However, since the second bottom cutting edge 24 is straight or linearly formed, the contact length between the cutting edge and the workpiece becomes shorter, the cutting resistance is minimized, and the chip is discharged with uniform thickness. Further, since the second bottom cutting edge 24 forms the entering angle a of 8° to 25°, the contact length between the cutting edge and the workpiece becomes shorter, the cutting resistance is minimized, and the thickness and the length of the chip are optimized. Thus, the chip can be smoothly discharged.

Further, in the end mill shown in FIG. 3, the intersection between the first bottom cutting edge 22 and the second bottom cutting edge 24 is away from the central axis 16 of the head portion by a distance equal to 0.15 to 0.25 times of a diameter of the head portion 14. This optimizes the length of the chip, which is generated by the second bottom cutting edge 24 during the cutting process. In the end mill shown in FIG. 3, the side cutting edge 26 extends straight inwardly at an angle from the intersection formed with the second bottom cutting edge 24 toward the central axis 16 of the shank portion. If the side cutting edge 26 goes beyond a certain depth of cut, then it is not involved in the cutting process any more. Alternatively, the side cutting edge 26 may extend parallel to the central axis 16 of the shank portion.

FIG. 4 is a cross-sectional view taken along the line IV-IV of FIG. 3. FIG. 5 is a cross-sectional view taken along the line V-V of FIG. 3. As shown in FIGS. 4 and 5, a rake surface 28 and clearance surfaces 32, 34 extend from the second bottom cutting edge 24 and the first bottom cutting edge 22. The rake surface 28 forms a rake angle e with respect to an axis 16' parallel to the central axis 16 of the head portion. The rake angle e can have a positive value (+), 0 or a negative value (-). The positive value represents a case wherein the rake surface is inclined opposite the rotational direction. The negative value represents a case wherein the rake surface is inclined toward the rotational direction. The value of 0 represents a case wherein the rake surface is not inclined relative to the rotational axis. In the present invention, since the rake surface 28 has a positive rake angle e with respect to the axis 16', the chip is easily discharged and the cutting resistance is reduced. On the other hand, when the rake angle e of the rake surface 28 increases, the cutting edge becomes sharp and the cutting resistance is reduced. However, since the strength of a tool is reduced, vibration and chipping (i.e., fine breakage of the cutting edge) may occur when performing the cutting process at a high feed rate. Preferably, the rake angle e of the rake surface 28 is in a range of 8° to 12°. Further, the clearance surface is formed to avoid a surface contact between the end mill and the workpiece during the cutting process. The clearance surface comprises a first clearance surface 32 and a second clearance surface 34. The first clearance surface extends at a first clearance angle f from the first and second bottom cutting edges 22, 24. The second clearance surface 34 extends at a second clearance angle g from the first clearance surface 32. Preferably, the first clearance angle f is in a range of 10° to 12° and the second clearance angle g is in a range of 23° to 26°. FIG. 6 is a cross-sectional view taken along the line VI-VI of FIG. 3. As shown in FIG. 6, a rake surface 42 and clearance surfaces 44, 46 extend from the side cutting edge 26. The rake surface 42 extends at a positive rake angle h of 6° to 10° with respect to a line connecting the side cutting edge 26 and the central axis 16 of the head portion. The positive value represents that the rake surface 42 is inclined opposite the rotational direction with respect to the line connecting the side cutting edge 26 and the central axis 16 of the head portion. When the rake angle h is small, a cutting load increases. On the other hand, when the rake angle h is large, the strength of the cutting edge decreases. Thus, the cutting edge can be finely broken during the cutting process at a high feed rate. Preferably, the rake angle h is in a range of 6° to 10°. The clearance surface comprises a first clearance surface 44 and a second clearance surface 46. The first clearance surface 44 extends from the side cutting edge 26 at a first clearance angle i. The second clearance surface 46 extends from the first clearance surface at a second clearance angle j. Preferably, the first clearance angle i is in a range of 9° to 11° and the second clearance angle j is in a range of 18° to 22°.

FIG. 7 is a view taken from the end (direction B) of the end mill shown in FIG. 2. As shown in FIG. 7, the bottom surface of the head portion 14 has two bottom cutting edges 20 including the first bottom cutting edge 22 and the second bottom cutting edge 24. The two bottom cutting edges 20 are positioned at an interval of 180°. However, the number of cutting edges formed on the head portion 14 is not limited thereto. For example, the bottom surface of the head portion 14 may have four bottom cutting edges 20 positioned at an interval of 90°.

FIG. 8 is an enlarged view of a portion C of FIG. 3. As shown in FIG. 8, an intersection between the second bottom cutting edge 24 and the side cutting edge 26 is chamfered at an angle k of 40° to 50°. Chamfering the intersection between the bottom cutting edge 24 and the side cutting edge 26 can reinforce the strength of the cutting edge. Alternatively, the intersection between the second bottom cutting edge 24 and the side cutting edge 26 may be formed into a curve with a desired curvature.

Advantages of the above-described end mill according to the present invention will now be described in detail with reference to FIGS. 9 and 10. FIG. 9 is a schematic view of an end of a head portion having a bottom cutting edge extending straight at an entering angle according to the present invention. FIG. 10 is a schematic view of an end of a head portion having a round bottom cutting edge. Since the bottom cutting edge shown in FIG. 10 is round, the entering angle is not specified to a certain value. Hatched portions in FIG. 9 and FIG. 10 represent a processed amount, i.e., an amount of generated chip, when performing the cutting process with the same feed rate and depth of cut. The contact length between the cutting edge and the workpiece in FIG. 9 is shorter than that in FIG. 10. The cutting resistance is minimized by the shortened contact length. The thickness of the chip in FIG. 9 is constant, while the thickness of the chip in FIG. 10 increases in a lateral direction. In FIG. 9, the cutting resistance is generally uniformly applied to the cutting edge, whereas in FIG. 10, the cutting resistance applied to the cutting edge increases in the lateral direction. Due to such differences, the end mill 10 in FIG. 9 allows the cutting process with a high feed rate, thereby improving working efficiency and enabling a long-term use in a cutting process with a higher feed rate than the end mill in FIG. 10.

Such effects have been verified through experiments using actual cutting tools. Table 1 below shows results of the experiments, wherein actual cutting processes are performed by using a tool according to an embodiment of the present invention and a tool of a comparison example for purposes of comparison with the present invention and their service life is then measured. The tool according to an embodiment of the present invention has a bottom cutting edge extending straight at an entering angel of 20°. On the other hand, the tool of the comparison example has a bottom cutting edge extending in a curve with a radius of curvature of about 9 mm. Except this, other geometrical conditions are substantially identical in the two tools. The cutting process was performed on the same workpiece under the same conditions by using the tool according to the embodiment and the tool of the comparison example. Specifically, in the cutting of both tools, a workpiece made of a SKD61 (HrC52) material was cut with a feed rate per cutting edge of 0.4 mm and a depth of cut of 0.1 mm. Further, a workpiece made of a KP4(HrC30) material was cut with a feed rate per cutting edge of 0.5 mm and a depth of cut of 0.4 mm. The service life of the tool was determined by the time when a breakage depth of a cutting edge reaches 0.1 mm. As shown in Table 1 below, it can be seen that the service life of the tool according to an embodiment the present invention is remarkably longer, i.e., about 5 to 6 times than that of the comparison example under the same cutting conditions. Table 1

Next, an end mill according to a second embodiment of the present invention will be described with reference to FIGS. 11 to 14. FIG. 11 is a perspective view of an end mill in accordance with the second embodiment of the present invention. FIG. 12 is a side view of the end mill shown in FIG. 11. FIG. 13 is a perspective view of a cutting insert mounted within the head portion of the end mill shown in FIG. 11. FIG. 14 is a front view of the cutting insert shown in FIG. 13.

The combination of a cutting insert 160 and an end mill 100 in accordance with the second embodiment has basically an identical configuration to the end mill 10 in accordance with the first embodiment. Thus, detailed descriptions on the same parts as the first embodiment will be omitted herein. A difference between the combination of the end mill 100 and the cutting insert 160 according to the second embodiment and the end mill 10 according to the first embodiment is that in the first embodiment, the shank portion 12 and the head portion 14 of the end mill 10 are integrally formed and the head portion 14 has the cutting edge. However, in the second embodiment, the cutting insert 160 is detachably mounted to an end of the head portion 140 and the cutting insert 160 has the cutting edge.

As shown in FIG. 12, the end of the head portion 140 of the end mill 100 includes a slit 142 for receiving the cutting insert 160 therein and a hole 146, to which a screw is fastened. When the cutting insert 160 is inserted into the slit 142, a through hole 184 of the cutting insert 160 is coaxially arranged with the hole 146 formed at the end of the head portion. The screw is fastened through the hole 146 of the end of the head portion and the through hole 184 of the cutting insert 160, thereby fixing the cutting insert 160 to the end of the head portion. The end mill of the second embodiment has advantages in that when the cutting edge is worn out, only the cutting insert can be replaced without replacing the entire tool, and thus, the tool can be used continuously. Further, the end mill has another advantage in that since only the cutting insert having the cutting edge can be manufactured with a material that has more strength than the shank portion and the head portion of the end mill, the material cost can be reduced.

As shown in FIGS. 13 and 14, the cutting insert 160 comprises an upper surface 162, a lower surface 164 positioned opposite the upper surface 162, and a side surface 166 connecting the upper surface 162 and the lower surface 164. The upper surface 162 contacts a seat surface 144 within the slit 142 formed at the end of the head portion. The lower surface 164 includes a bottom cutting edge 170. The side surface 166 includes a side cutting edge 176. The bottom cutting edge 170 and the side cutting edge 176 have the same shapes as the cutting edges formed on the end of the head portion of the end mill according to the first embodiment. A front of the cutting insert refers to a front view of the cutting insert as its two side cutting edges are bilaterally symmetrically positioned with respect to a line connecting centers of the upper and lower surfaces, as shown in FIG. 14. When viewed from the front of the cutting insert, the first bottom cutting edge 172 forms a dish angle b' of 1° to 3° with respect to a line 182 perpendicular to a line 180 connecting centers of the upper surface 162 and the lower surface 164. Further, the first bottom cutting edge 172 extends from the line 180 connecting centers of the upper surface 162 and the lower surface 164 in a direction away from the upper surface 162. The second bottom cutting edge 174 forms an entering angle a' of 18° to 25° with respect to the line 182 perpendicular to the line 180 connecting centers of the upper surface 162 and the lower surface 164. Further, the second bottom cutting edge 174 extends straight from an intersection formed with the first bottom cutting edge 172 toward the upper surface 162.

A rake surface 190 and clearance surfaces 192, 194 extend from the bottom cutting edge 170. The rake surface 190 and the clearance surfaces 192, 194 have the same cross-sectional shapes as those of the first embodiment shown in FIG. 4 and 5. The rake surface 190 and clearance surfaces 196, 198 extend from the side cutting edge 176. The rake surface 190 and clearance surfaces 196, 198 have the same cross- sectional shapes as those of the first embodiment shown in FIG. 6. The rake surface 190 and clearance surfaces 192, 194 extending from the bottom cutting edge 170 and the rake surface 190 and clearance surfaces 196, 198 extending from the side cutting edge 176 have the same rake angle or clearance angles as the first embodiment. Other configurations of the second embodiment not specifically described herein are the same as the first embodiment.

While the present invention has been described by way of preferred embodiments thereof, those embodiments are for illustrative purposes only. It will be understood by those of ordinary skill in the art that various modifications and variations may be made without departing from the scope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention provides an end mill, which can perform a cutting process at a high feed rate by significantly decreasing a cutting resistance applied to a cutting edge during the cutting process.

Claims

1. An end mill, comprising: a shank portion; a head portion extended from an end of the shank portion; a bottom cutting edge formed on a bottom surface of the head portion; a side cutting edge formed on a side surface of the head portion and connected to the bottom cutting edge; and a rake surface and a clearance surface extending from the bottom cutting edge; wherein the bottom cutting edge includes a first bottom cutting edge and a second bottom cutting edge, wherein when viewed from the front of the end mill, the first bottom cutting edge extends from a central axis of the head portion to an intersection formed with the second bottom cutting edge in a direction away from the shank portion, and wherein the second bottom cutting edge extends straight at an angle from the intersection formed with the first bottom cutting edge to an intersection formed with the side cutting edge in a direction towards the shank portion.

2. An end mill, comprising: a shank portion; a head portion extended from an end of the shank portion; and a cutting insert detachably mounted at an end of the head portion; wherein the cutting insert includes an upper surface contacting a seat surface formed at the end of the head portion, a lower surface positioned opposite to the upper surface and including a bottom cutting edge, a side surface connecting the upper surface and the lower surface and including a side cutting edge connected to the bottom cutting edge, and a rake surface and a clearance surface extending from the bottom cutting edge, wherein the bottom cutting edge includes a first bottom cutting edge and a second bottom cutting edge, wherein when viewed from the front of the end mill, the first bottom cutting edge extends from a center of the lower surface to an intersection formed with the second bottom cutting edge in a direction away from the upper surface, and wherein the second bottom cutting edge extends straight at an angle from the intersection formed with the first bottom cutting edge to an intersection formed with the side cutting edge in a direction towards the upper surface.

3. The end mill according to Claim 2, wherein the end of the head portion comprises a slit for receiving the cutting insert, and wherein a screw passes through a hole formed in the cutting insert and is fastened at the end of the head portion to thereby fix the cutting insert within the head portion.

4. The end mill according to any one of Claims 1 to 3, wherein the second bottom cutting edge forms an angle of 18° to 25° with respect to a line perpendicular to the central axis of the head portion.

5. The end mill according to any one of Claims 1 to 3, wherein the rake surface forms a positive rake angle of 8° to 12° with respect to the central axis of the head portion.

6. The end mill according to any one of Claims 1 to 3, wherein the first bottom cutting edge forms an angle of 1° to 3° with respect to a line perpendicular to the central axis of the head portion.

7. The end mill according to any one of Claims 1 to 3, wherein the clearance surface comprises a first clearance surface extending from the bottom cutting edge at a first clearance angle and a second clearance surface extending from the first clearance surface at a second clearance angle, and wherein the first clearance angle is in a range of 10° to 12° and the second clearance angle is in a range of 23° to 26°.

8. The end mill according to any one of Claims 1 to 3, further comprising a rake surface and a clearance surface extending from the side cutting edges, wherein the rake surface extending from the side cutting edge forms a positive rake angle of 6° to 10° with respect to a line connecting the central axis of the head portion to the side cutting edge, wherein the clearance surface extending from the side cutting includes a first clearance surface extending from the side cutting edge at a first clearance angle and a second clearance surface extending from the first clearance surface at a second clearance angle, and wherein the first clearance angle is in a range of 9° to 11° and the second clearance angle is in a range of 18° to 22°.

9. The end mill according to any one of Claims 1 to 3, wherein the intersection of the first and second bottom cutting edges is located at a distance of 0.15 to 0.25 times the diameter of the head portion from the central axis of the head portion.

10. The end mill according to any one of Claims 1 to 3, wherein the intersection of the second bottom cutting edge and the side cutting edge is chamfered at an angle of 40° to 50°.

11. The end mill according to any one of Claims 1 to 3, comprising two cutting edges formed by the bottom cutting edge connecting to the side cutting edge, wherein the two cutting edges are positioned at an interval of 180° when viewed from the end of the end mill.

12. The end mill according to any one of Claims 1 to 3, comprising four cutting edges formed by the bottom cutting edge connecting to the side cutting edge, wherein the four cutting edges are positioned at an interval of 90° when viewed from the end of the end mill.

13. A cutting insert used for an end mill and mounted at an end of the end mill, comprising: an upper surface contacting a seat surface formed at the end of the end mill; a lower surface positioned opposite to the upper surface and including a bottom cutting edge; a side surface connecting the upper surface and the lower surface and including a side cutting edge connected to the bottom cutting edge; and a rake surface and a clearance surface extending from the bottom cutting edge; wherein the bottom cutting edge comprises a first bottom cutting edge and a second bottom cutting edge, wherein when viewed from the front of the cutting insert, the first bottom cutting edge extends from a center of the lower surface to an intersection formed with the second bottom cutting edge in a direction away from the upper surface, and wherein the second bottom cutting edge extends straight at an angle from the intersection formed with the first bottom cutting edge to an intersection formed with the side cutting edge in a direction towards the upper surface.

14. The cutting insert according to Claim 13, wherein the second bottom cutting edge forms an angle of 18° to 25° with respect to a line perpendicular to a line connecting the centers of the upper and lower surfaces.

15. The cutting insert according to Claim 13 or 14, wherein the rake surface forms a positive rake angle of 8° to 12° with respect to a line connecting the centers of the upper and lower surfaces.

16. The cutting insert according to Claim 13 or 14, wherein the first bottom cutting edge forms an angle of 1° to 3° with respect to a line perpendicular to a line connecting the centers of the upper and lower surfaces.

17. The cutting insert according to Claim 13 or 14, wherein the clearance surface comprises a first clearance surface extending from the bottom cutting edge at a first clearance angle and a second clearance surface extending from the first clearance surface at a second clearance angle, and wherein the first clearance angle is in a range of 10° to 12° and the second clearance angle is in a range of 23° to 26°.

18. The cutting insert according to Claim 13 or 14, further comprising a rake surface and a clearance surface extending from the side cutting edge, wherein the rake surface extending from the side cutting edge forms a positive rake angle of 6° to 10° with respect to a line connecting the side cutting edge and the line connecting the centers of the upper and lower surfaces, wherein the clearance surface extending from the side cutting comprises a first clearance surface extending from the side cutting edge at a first clearance angle and a second clearance surface extending from the first clearance surface at a second clearance angle, and wherein the first clearance angle is in a range of 9° to 11° and the second clearance angle is in a range of 18° to 22°.

19. The cutting insert according to Claim 13 or 14, wherein the intersection of the second bottom cutting edge and the side cutting edge is chamfered at an angle of 40° to

50°.