End milling cutter
By setting a chamfer and a positive axial rake angle on the transition cutting edge of the end mill, the problems of corner wear and chipping of traditional end mills are solved, improving the durability of the tool and the cutting effect.
Patent Information
- Application Number
- CN202480032261.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-07-20
- Filing Date
- 2024-05-23
- Publication Date
- 2025-12-19
AI Technical Summary
Traditional end mills are prone to wear and damage at the corners, such as notch wear and chipping.
Design an end mill with a transition cutting edge of the cutting teeth extending along a chamfer to avoid sharp corners. The robustness of the cutting edge is enhanced by setting a positive axial rake angle and a convex flank face on the transition cutting edge.
It effectively reduces wear and chipping, improving the durability and cutting performance of end mills.
Smart Images
Figure CN121175138A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present invention relates to a solid end mill for metal cutting. BACKGROUND
[0002] A variety of components are machined from different types of materials, such as metals, composites or combinations thereof. As a result, a variety of different cutting tools, and in particular milling tools, such as end mills, have been developed. Traditionally, an end mill comprises a plurality of cutting edges extending axially along the tool and radially along the front end of the tool. The teeth have a front cutting edge which cuts the surface in an axial forward direction of feed and a side cutting edge which cuts the surface in a radial direction of feed. The front cutting edge typically extends radially outwards from a centre region at the longitudinal axis towards a corner portion. The corner portion connects the front cutting edge with the side cutting edge.
[0003] One problem with such known end mills is that the corner region is prone to wear and damage, such as notch wear and chipping. SUMMARY
[0004] It is an object of the present invention to at least partly eliminate the above-mentioned problems. According to the present invention, this object is achieved by an end mill according to claim 1.
[0005] The present invention relates to an end mill for metal cutting, the end mill comprising a body having a cutting head with a front end and a central longitudinal axis extending rearwardly from the front end, wherein the end mill is rotatable in a direction of rotation about the longitudinal axis, and wherein the cutting head comprises: - a plurality of cutting teeth, each cutting tooth of the plurality of cutting teeth having a cutting edge formed at an intersection of a respective rake face and a respective flank face, and - a plurality of chip flutes, each chip flute located in front of a respective one of the plurality of cutting teeth in the direction of rotation, each chip flute extending axially rearwardly from the front end, and each chip flute having a respective helix angle, wherein the cutting edge of each cutting tooth of the plurality of cutting teeth comprises: - a front cutting edge at the front end extending radially outwards from a central region at the longitudinal axis, - a side cutting edge extending axially rearwardly from a radially outer region of the front end, and - a transition cutting edge extending from the front cutting edge to the side cutting edge, wherein: - the relief of each of the cutting teeth is convex along the transition cutting edge in the direction of the extension of the transition cutting edge, and - the rake face of each of the plurality of cutting teeth has an axial rake angle, and wherein, along the transition cutting edge, the axial rake angle: - is positive, and - is equal to or smaller than the helix angle of the flute at the front end portion which is located in front of the transition cutting edge in the direction of rotation.
[0006] A milling end mill, or in other words an end milling tool, has both an axially forward cutting front cutting edge and a radially cutting side cutting edge, typically provided with a chamfer at the transition of the front cutting edge to the side cutting edge. The chamfer removes the sharp corner at the transition. Thereby, in prior art end milling tools, a new sharp corner is formed on the front cutting edge at a smaller distance radially inward from the periphery. In the end milling tool according to the invention, since the cutting edge has a rake face along the chamfer, and the axial rake angle of the rake face is smaller than or equal to the helix angle of the front end portion of the flute at the transition, any new sharp corner due to the convex relief is avoided. Thereby, the transition cutting edge with a positive axial rake angle is made more robust to better withstand wear and chipping.
[0007] The present invention relates to an end milling tool for metal cutting. The end milling tool comprises a body having a cutting head. Optionally, the end milling tool is of the type wherein the cutting head is a one-piece integral unit with a shaft, sometimes referred to as a "solid round tool". Alternatively, the end milling tool is a replaceable head and can be connected to a shaft. The shaft optionally has a coupling at a rear end portion. Thereby, the cutting head can be connected to a machine tool spindle, or to an adapter for a machine tool spindle. The machine tool spindle is typically part of a machine tool, for example a CNC machine tool. Preferably, the end milling tool comprises a wear resistant material, such as for example coated or uncoated cemented carbide, cermet, ceramic or cubic boron nitride (CBN).
[0008] The cutting head has a front end portion and a central longitudinal axis extending rearwardly from the front end portion, wherein the end mill is rotatable in a direction of rotation about the longitudinal axis. The cutting head defines a cutting circle having a cutting diameter. The cutting circle is to be understood as the circle formed by the radially outermost point of any of the cutting edges when the end mill is rotated one revolution about the longitudinal axis and the tool is not fed in any direction. The direction of rotation is the direction in which the end milling tool is rotated during normal cutting operation.
[0009] According to an embodiment, the cutting head is elongated in the longitudinal direction. Optionally, the axial length of the cutting head is equal to or smaller than, preferably larger than, the diameter of the cutting circle.
[0010] The cutting head comprises a plurality of cutting teeth, each having a cutting edge formed at the intersection of a respective rake face and a respective flank face. For example, the cutting head comprises at least 2, preferably at least 4, cutting teeth. For example, the cutting head comprises at most 10, preferably at most 6, cutting teeth.
[0011] The cutting teeth are arranged in a front end portion of the cutting head, each extending radially outwardly from a central region at the longitudinal axis, and each being provided with a front cutting edge that cuts mainly axially forwardly. Therein, optionally, the front cutting edge of a particular cutting tooth extends from the longitudinal axis, or from a point at a radial distance outwardly from the longitudinal axis. Optionally, the front cutting edge of a particular cutting tooth extends mainly along a radius or along a chord when seen in a front end view, wherein the cutting edge is optionally straight or curved. Optionally, all front cutting edges extend from the same radial distance from the longitudinal axis, or from different radial distances. For example, several cutting edges start at a first, same radial distance, and several cutting edges start at a second, same radial distance, the second radial distance being different from the first radial distance. The front end portion of the cutting head is preferably an axially forwardly facing end surface of an end mill.
[0012] The cutting teeth continue axially rearwardly from a radially outer region of the front end portion, and each is provided with a side cutting edge that cuts mainly radially. Preferably, the side cutting edge cuts only in the radial direction. The teeth generally extend along a peripheral surface of the body of the cutting head. The side cutting edge of each cutting tooth extends at an angle to the longitudinal axis, and preferably forms a helix. The axial extension of the side cutting edge rearwardly from the front end portion is for example less than, equal to, or greater than the cutting diameter, and is preferably 1-5 times the cutting diameter. According to a preferred embodiment, the side cutting edge is continuous. Alternatively, the side cutting edge is interrupted by a flute. In application, the flute is advantageous to reduce the width of the chip, or to form an additional minor cutting edge.
[0013] The cutting head comprises a plurality of chip flutes, each located in front of a respective one of the plurality of cutting teeth in the direction of rotation, each extending axially rearwardly from the front end portion. The chip flutes generally extend along a peripheral surface of the body of the cutting head.
[0014] Each chip flute extends at an angle to the longitudinal axis, and preferably forms a helix. The angle is referred to as the "helix angle", which also applies to chip flutes that are not helical but angled, and is understood to be the angle between the bottom of the chip flute and the longitudinal axis. Preferably, the helix angle of a particular side cutting edge is equal to the helix angle of the chip flute that is located in front of the side cutting edge in the direction of rotation. Optionally, the helix angle of the chip flutes varies or is constant, e.g. the helix angle decreases or increases axially from the leading end portion. According to an embodiment, the helix angle at the leading end portion of the chip flute that is located in front of the transition cutting edge in the direction of rotation is at least 10° and at most 60°, preferably at least 20° and at most 50°. Within this range, the chip flutes provide satisfactory chip evacuation and / or chip breakage for most applications.
[0015] Each cutting edge of the plurality of teeth further comprises a transition cutting edge extending from the leading cutting edge to the side cutting edge. Preferably, the transition cutting edge has a radially inner end portion connected to the leading cutting edge at the leading end portion, and the transition cutting edge has an axially rear end portion connected to the side cutting edge at an axially forward end portion of the side cutting edge.
[0016] For example, the transition cutting edge extends over a radially outer corner where the peripheral side surface meets the leading end surface of the main body of the cutting head. Each chip flute has a leading end portion which is a part of the chip flute at the corner portion having the transition cutting edge.
[0017] The transition cutting edge extends at least partly along a chamfer in the form of a relief surface. The relief surface of the transition cutting edge is convex in the direction of extension of the transition cutting edge, i.e. in the radial direction along the leading end portion. The convex curvature of the relief surface can be observed in a plane that is perpendicular to the tangent of the circle that is cut through a point on the transition cutting edge when the tool is rotated without feed. Preferably, the relief surface extends with a constant clearance angle when observed in the direction of rotation behind the point on the transition cutting edge, i.e. along the part of the circle that is cut through the point when the tool is rotated without feed.
[0018] Each relief surface of the cutting edges has an axial rake angle. The axial rake angle is understood to be the inclination of the relief surface with respect to the longitudinal axis. The axial rake angle at a point on the cutting edge can be measured in a plane that is parallel to the longitudinal axis and that contains the tangent of the circle that is cut through the point when the tool is rotated without feed.
[0019] Preferably, the axial rake angle along the side cutting edge is 0°.
[0020] Along the transition cutting edge, the axial rake angle is positive and equal to or smaller than the helix angle at the front end of the chip flute located in front of the transition cutting edge in the direction of rotation. The axial rake angle is considered positive when the rake face is inclined backwards in the axial backwards direction in the direction of rotation. According to an embodiment, along the transition cutting edge, the axial rake angle is at most 10° smaller than the helix angle. Thereby, it is ensured that the transition cutting edge is sufficiently smooth for most applications. For example, any corner is obtuse with an angle of at least 170°. Preferably, the axial rake angle is chosen such that the transition cutting edge is continuously curved.
[0021] According to a preferred embodiment, the front cutting edge comprises a central portion extending radially outwards from a central region at the longitudinal axis and a peripheral portion extending radially outwards from an inner end at the central portion to an outer end at the transition cutting edge.
[0022] Over the length of the peripheral portion, the axial rake angle transitions from the axial rake angle of the transition cutting edge at the outer end to the axial rake angle of the central portion at the inner end. Thereby, the front cutting edge can be given any desired axial rake angle at the central portion without introducing sharp corners. Preferably, the axial rake angle β is constant along the transition cutting edge (1 1 ). Thereby, grinding of the axial rake angle is easier. Preferably, the transition of the axial rake angle of the peripheral portion is continuous. Thereby, the transition cutting edge and the peripheral portion of the front cutting edge are continuous, for example continuously curved or straight.
[0023] According to an embodiment, the axial rake angle of the central portion of the front cutting edge is constant. Thereby, grinding of the rake face is easier. Preferably, the axial rake angle of the central portion of the front cutting edge is positive. For example, the axial rake angle is at least 5° and at most 30°. A larger positive rake angle provides a sharper cutting edge, which reduces the cutting forces and the amount of heat. A smaller positive rake angle provides a duller cutting edge, which is stronger, which is advantageous when cutting harder materials.
[0024] Preferably, the cutting head further comprises a web, wherein the inner end of the peripheral portion of the front cutting edge is located at the intersection of the chip flute and the web when seen in a front end view. When grinding the rake face in embodiments where the axial rake angle transitions along the peripheral portion of the front cutting edge, the grinding wheel is inclined stepwise along the peripheral cutting edge. If the peripheral portion of the front cutting edge is located outside the web, this stepwise inclination is easier compared to grinding inside the web. The space cut out by the grinding wheel in the web is sometimes referred to as a "gash".
[0025] According to an embodiment, the outer end of the peripheral portion is located at a radial distance from the longitudinal axis of at least 37.5% and at most 42.5% of the cutting diameter when seen in a front view. Thereby, it is ensured that the transition cutting edge according to the present application with a constant axial rake is long enough to achieve a smooth transition and a front cutting edge. The position of the outer end of the peripheral portion also corresponds to the position of the inner end of the transition cutting edge.
[0026] According to an embodiment, the outer end of the peripheral portion is located at a radial distance from the longitudinal axis of at least 37.5% and at most 42.5% of the cutting diameter when seen in a front view. Thereby, it is ensured that the transition cutting edge according to the present application with a constant axial rake is long enough to achieve a smooth transition and a front cutting edge. The position of the outer end of the peripheral portion also corresponds to the position of the inner end of the transition cutting edge.
[0027] According to an embodiment, the end mill is a square end mill, a chamfer end mill, a taper end mill or a corner end mill. For example, the front end of the side cutting edge is located at a distance of at most 5% of the cutting diameter axially behind the most forward point of the cutting head. Optionally, the most forward point is the radially outer point of the cutting edge or the tool tip at the central longitudinal axis. The most forward point can also be any point on the front cutting edge without axial extension. For example, the corner radius of the transition cutting edge is less than 25% of the diameter of the cutting circle. The axial rake of the transition cutting edge of the present application is particularly advantageous for such tools. Since the corner region of such tools is relatively short in axial direction, a transition cutting edge with a smaller radius of curvature is more prone to wear and chipping, especially at the sharp corner introduced in the front cutting edge when grinding a chamfer / relief.
[0028] In an embodiment, the front cutting edges can have an inclination relative to the longitudinal axis so that they cut a short axial distance in addition to their main axial forward cutting direction. Optionally, two or more cutting edges meet in the point axially most forward so that a tool tip is formed. BRIEF DESCRIPTION OF DRAWINGS
[0029] In the following, example embodiments will be described in more detail with reference to the appended drawings, in which:
[0030] Figure 1 Perspective view of an embodiment of an end mill for metal cutting according to the present application;
[0031] Figure 2 Side view of an embodiment of the end mill;
[0032] Figure 3 is Figure 2 Enlarged view of the front end of the end mill shown;
[0033] Figure 4 Front view of an embodiment of the end mill;
[0034] Figures 5 to 8 is a cross-section over the leading cutting edge as indicated in Figure 4 Fig. 1, showing the axial rake angle.
[0035] All drawings are schematic and not necessarily to scale, and generally only show the parts that are necessary to illustrate the respective embodiments, while other parts can be omitted or only indicated schematically. Like reference numerals designate like parts throughout the different figures, unless otherwise stated. DETAILED DESCRIPTION
[0036] Reference is now made to Figures 1 to 8 Fig. 1, showing an embodiment of an end mill in the form of a square end mill. The square end mill comprises a body 1 provided with a cutting head 2. The cutting head 2 has a front end 3, which is also the front end of the square end mill, and a central longitudinal axis 4 extending rearwardly from the front end 3. The front end 3 of the cutting head 2 is an axially forwardly facing end surface of the square end mill.
[0037] The axis 4 is the central longitudinal axis of the square end mill. The square end mill has a rear end 5 at an end axially opposite the front end 3.
[0038] The cutting head comprises a plurality of cutting teeth 7, each having a cutting edge formed at the intersection of a respective rake face 8 and a respective flank face 9. The square end mill according to the present embodiment comprises four cutting teeth 7.
[0039] The cutting edges each have a radially outermost point at the same radial distance from the longitudinal axis 4. The cutting head 2 defines a cutting circle 12 formed by the radially outermost points of the cutting edges when the square end mill is rotated one revolution around the longitudinal axis 4 and without feed in any direction. The cutting circle 12 has a cutting diameter, which in the shown embodiment is 10 mm.
[0040] Each tooth 7 is provided with a primarily axially forwardly cutting leading cutting edge 10, wherein each leading cutting edge 10 extends radially outwardly from a central region at the longitudinal axis 4. Two of the leading cutting edges 10 start at the same first radial distance close to the longitudinal axis 4, and the other two of the four leading cutting edges 10 start at the same second radial distance from the longitudinal axis 4, wherein the second radial distance is greater than the first radial distance. Each of the four leading cutting edges 10 extends approximately along a chord of the cutting circle 12 sideways of the longitudinal axis 4. Each leading cutting edge 10 is a straight line when seen in both the front view and the side view, respectively, see Figure 4 and Figure 3 .
[0041] Each tooth 7 extends axially rearward from the radially outer region of the front end 2 and is provided with a side cutting edge 14 that mainly cuts radially only. This side cutting edge 14 extends axially rearward from the front end 3 along the peripheral surface of the main body of the cutting head 2. The side cutting edge 14 of each cutting tooth 7 extends at an angle to the longitudinal axis and forms a helix.
[0042] The cutting head 2 includes a plurality of chip grooves 13 that extend axially rearward from the front end portion 3 along the peripheral surface of the body of the cutting head 2. Each chip groove 13 extends in the rotational direction in front of a corresponding cutting tooth 7 among the plurality of cutting teeth 7.
[0043] Each chip groove 13 forms a helix and extends at an angle (in the form of a helix angle α) to the longitudinal axis 4. The helix angle α is measured as the angle between the bottom of the chip groove 13 and the longitudinal axis, see [reference needed]. Figure 3 The helix angle of the side cutting edge 14 is equal to the helix angle α of the chip groove located in front of the side cutting edge in the direction of rotation.
[0044] Each of the plurality of teeth 7 further includes a transition cutting edge 11 that extends beyond a radial outer corner, where its peripheral surface merges with the front end surface of the cutting head 2. See also Figure 4 Specifically, the transition cutting edge 11 has a radially inner end portion connected to the front cutting edge 10, and the transition cutting edge 11 has an axially rear end portion connected to the side cutting edge 14.
[0045] Each chip groove 13 has a front end portion, which is part of the chip groove located at the corner portion with the transition cutting edge. In the illustrated embodiment, the helix angle α is the same for all chip grooves 13 and is constant along its axial length (including the front end portion). The helix angle α is 48°.
[0046] The transition cutting edge 11 extends at least partially along the chamfer 15 (in the form of the flank face 9). The flank face 15 of the transition cutting edge 11 is convex in the direction of extension of the transition cutting edge 11, see [reference needed]. Figure 3 .
[0047] Each rake face 8 of the cutting edge 10 has an axial rake angle β. The axial rake angle β should be understood as the angle of inclination of the rake face 8 relative to the longitudinal axis. The axial rake angle at a point on the cutting edge is measured in a plane parallel to the longitudinal axis and including the tangent to the circle cut from that point when the tool rotates without feed. See [reference needed]. Figures 5 to 8 The view.
[0048] As in Figure 5As can be seen, along the transition cutting edge 11, the axial rake angle β is positive and equal to or smaller than the helix angle at the front end of the chip flute which is located in the rotational direction in front of the transition cutting edge. In particular, in the shown embodiment, the axial rake angle β is 5° smaller than the helix angle and thus 43°. Preferably, the transition cutting edge 11 is continuously curved, see Figure 3 and Figure 4 .
[0049] Each front cutting edge 10 comprises a central portion 16 extending radially outwards from a central area at the longitudinal axis 4 and a peripheral portion 17 extending radially outwards from an inner end of the central portion 16 to an outer end at the transition cutting edge 11, see Figure 4 .
[0050] As can be seen in Figure 8 , the axial rake angle β of the central portion 16 of the front cutting edge 10 is constant and in the shown embodiment 10°.
[0051] As can be seen in Figure 6 and Figure 7 , over the length of the peripheral portion 17, the axial rake angle β transitions from the axial rake angle β of the transition cutting edge 11 at the outer end to the axial rake angle β of the central portion 16 of the front cutting edge 10 at the inner end. Thus, in the shown embodiment, the rake angle β transitions from 43° to 10° radially inwards along the peripheral cutting edge 17. The transition of the rake angle β is continuous along the peripheral portion 16 of the front cutting edge 10.
[0052] The cutting head further comprises a web 18, wherein the inner end of the peripheral portion 17 of the front cutting edge 10 is located at the intersection 19 of the chip flute 13 and the web 18 when seen in a front end view. The inner end of the peripheral portion 17 is located at a radial distance from the longitudinal axis 4 of 30% of the cutting diameter of the cutting circle 12. In the shown embodiment, this radial distance from the central longitudinal axis 4 to the inner end of the peripheral portion is 3 mm. The position of the inner end of the peripheral portion 17 also corresponds to the position of the outer end of the central portion 16 of the front cutting edge 10.
[0053] The outer end of the peripheral portion 17 is located at a radial distance from the longitudinal axis 4 of 42.5% of the cutting diameter of the cutting circle 12. In the shown embodiment, this radial distance from the central longitudinal axis 4 to the outer end of the peripheral portion is 4.25 mm. The position of the outer end of the peripheral portion 17 also corresponds to the position of the inner end of the transition cutting edge 11.
[0054] The radial length of the transition cutting edge 11 is equal for all four leading cutting edges 10. Likewise, the radial length of the peripheral portion 17 of the leading cutting edges 10 is equal for all four leading cutting edges 10. The central portion 16 of two of the leading cutting edges 10 is shorter than the central portion of the other two leading cutting edges.
[0055] The cutting head 2 is part of a square end mill which is rotatable about the longitudinal axis 4 in a rotational direction 6, which is the rotational direction of the square end mill when performing a normal cutting operation. Typically, the square end mill is operated to mill a surface which is at least partially defined by a wall extending approximately 90° to the surface. During operation, the square end mill is rotated in the rotational direction while feeding in a radial direction, and optionally, also in an axial forward direction.
[0056] The cutting head has an elongated extension along the longitudinal axis 4 and extends from the front end rearwardly for about 2 times the cutting diameter of the cutting circle 12. The rear end of the cutting head is the rear end of the side cutting edge 14. The front end of the side cutting edge 14 is located at an axial distance rearward from the front most point of the cutting head 2 equal to 3% of the cutting diameter. In the shown embodiment, the axial distance from the front most tip to the front end of the side cutting edge 14 is 0.3 mm. In the shown embodiment, the front most point is an arbitrary location on the leading cutting edge 10.
[0057] The square end mill is of the type wherein the cutting head 2 is a monolithic unit with a shank 19 which is connectable to a spindle of a CNC machine tool.
Claims
1. A milling tool for metal cutting, the milling tool comprising a main body (1) having a cutting head (2) with a front end (3) and a central longitudinal axis (4) extending rearwardly from the front end (3), wherein the milling tool is rotatable about the longitudinal axis (4) in a direction of rotation (6), and wherein the cutting head (2) comprises: - a plurality of cutting teeth (7), each cutting tooth (7) having a cutting edge formed at the intersection of a respective rake face (8) and a respective flank face (9), and - a plurality of chip flutes (13), each chip flute being located in front of a respective one of the plurality of cutting teeth (7) in the direction of rotation, each chip flute extending axially rearwardly from the front end (3), and each chip flute having a respective helix angle a, wherein the cutting edge of each of the plurality of cutting teeth (7) comprises: - a front cutting edge (10) located at the front end (3), the front cutting edge extending radially outwardly from a central region located at the longitudinal axis (4), - a side cutting edge (14) extending axially rearwardly from a radially outer region of the front end (3), and - a transition cutting edge (11) extending from the front cutting edge (10) to the side cutting edge (14), wherein: - the flank face (9) of each of the cutting teeth (7) is convex along the transition cutting edge (11) in the direction of extension of the transition cutting edge (11), and - the rake face (8) of each of the plurality of cutting teeth (7) has an axial rake angle β, characterized in that: along the transition cutting edge (11), the axial rake angle β: - is positive, and - is equal to or smaller than the helix angle a at the front end of the chip flute (13) located in front of the transition cutting edge (11) in the direction of rotation.
2. The end mill according to claim 1, wherein, Along the transition cutting edge (11), the axial rake angle β is at most 10° smaller than the helix angle a.
3. The end mill according to claim 1 or 2, wherein Along the transition cutting edge (11), the axial rake angle β is constant.
4. The milling tool according to any preceding claim, wherein the transition cutting edge (11) is continuously curved.
5. The milling tool according to any preceding claim, wherein the helix angle a at the front end of the chip flute (13) located in front of the transition cutting edge (11) in the direction of rotation is at least 10° and at most 60°.
6. The milling tool according to any preceding claim, wherein: - the front cutting edge (10) comprises a central portion (16) extending radially outwardly from the central region located at the longitudinal axis (4), and a peripheral portion (17) extending radially outwardly from an inner end at the central portion (16) to an outer end at the transition cutting edge (11), and - the cutting head (2) defines a cutting circle (12) having a cutting diameter.
7. The end mill according to claim 6, wherein, The axial rake angle β of the peripheral portion (17) transitions from the axial rake angle β of the transition cutting edge (11) at the outer end to the axial rake angle β of the central portion (16) at the inner end over the length of the peripheral portion (17).
8. The end mill according to claim 6 or 7, wherein the transition of the axial rake angle β of the peripheral portion (17) is continuous.
9. The end mill according to any one of claims 6 to 8, wherein the axial rake angle β of the central portion (16) is constant.
10. The end mill according to claim 9, wherein the axial rake angle β of the central portion (16) is positive and at least 5° and at most 30°.
11. The end mill according to any one of claims 6 to 10, wherein the cutting head (2) further comprises a web (18), wherein, The inner end of the peripheral portion (17) is located at the intersection of the chip flute (13) and the web (18) when seen in a front end view.
12. The end mill according to any one of claims 6 to 11, wherein, The inner end of the peripheral portion (17) is located at a radial distance from the longitudinal axis (4) of at least 25% and at most 30% of the cutting diameter of the cutting circle when seen in a front end view.
13. The end mill according to any one of claims 6 to 12, wherein, The outer end of the peripheral portion (17) is located at a radial distance from the longitudinal axis (4) of at least 37.5% and at most 42.5% of the cutting diameter when seen in a front end view.
14. The end mill according to any preceding claim, wherein the end mill is a square end mill.
15. The end mill according to any one of claims 6 to 14, wherein a front end of the side cutting edge (14) is located at a distance axially rearward from a forwardmost nose of the cutting head (2) of at most 5% of the cutting diameter.