END MILL HAVING A PERIPHERAL CUTTING EDGE WITH A VARIABLE ANGLE CONFIGURATION

Abstract

An end mill for shouldering and/or slotting applications includes at least one tooth including a cutting edge. The cutting edge includes a first sub-edge extending rearwardly from a cutting end face and a second sub-edge extending rearwardly from the first sub-edge. An angle transition intersection defines where the first sub-edge ends and the second sub-edge starts. The angle transition intersection is located generally between 20% to 75% of an effective cutting length from a cutting end face and more specifically at a location within the general location where there is an increase in the rake angle and/or a significant increase in the helix angle of the cutting edge.

Claims

1. An end mill having unitary one-piece construction and configured for configured for shouldering and/or slotting applications and rotating about a central rotation axis (A.sub.R) defining opposite axially forward and rearward directions (D.sub.F, D.sub.R), and opposite rotational preceding and succeeding directions (D.sub.P, D.sub.S), the preceding direction (D.sub.P) being the cutting direction, the end mill comprising: opposite rear and cutting end faces, and a peripheral surface extending therebetween; a shank portion extending forward from the rear end face; and a cutting portion extending forward from the shank portion to the cutting end face; the cutting portion comprising: a diameter (D.sub.E); an effective cutting length (L.sub.E); a plurality of integrally formed teeth; and a plurality of flutes alternating with the plurality of teeth; at least one tooth of the plurality of teeth comprising: a rake surface; a relief surface succeeding the rake surface and having a relief surface width which is measurable in a plane perpendicular to the rotation axis (A.sub.R); and a cutting edge formed at an intersection of the rake and relief surfaces; the cutting edge comprising: a first sub-edge extending rearwardly from the cutting end face; a second sub-edge extending rearwardly from the first sub-edge; and an angle transition intersection defining where the first sub-edge ends and the second sub-edge starts; the first sub-edge comprising: a first radial rake angle; a first helix angle; and a first relief angle; the second sub-edge comprising: a second radial rake angle; a second helix angle; and a second relief angle; the angle transition intersection comprising: an intersection rake angle; an intersection helix angle; and an intersection relief angle; wherein, for the cutting edge: the angle transition intersection is generally located in a general location GL which is an axial distance from the cutting end face defined by the condition: 0.20L.sub.EGL0.75L.sub.E; and the angle transition intersection is precisely located at a precise location PL within the general location GL, the precise location PL being defined as a closest axial location to the cutting end face, within the general location GL, which fulfills at least one of: a first condition wherein the intersection rake angle is greater than all of the rake angles which are closer to the cutting end face; and a second condition wherein the intersection helix angle is at least 5% greater than a first helix angle directly preceding the intersection helix angle.

2. The end mill according to claim 1, wherein the general location GL fulfills the condition 0.20L.sub.EGL0.50L.sub.E.

3. The end mill according to claim 1, wherein both the first and the second condition are fulfilled within an axial separation distance L.sub.P no greater than 0.15L.sub.E.

4. The end mill according to claim 3, wherein the axial separation distance L.sub.P is no greater than 0.05L.sub.E.

5. The end mill according to claim 4, wherein the axial separation distance L.sub.P is no greater than 0.02L.sub.E.

6. The end mill according to claim 1, wherein the intersection rake angle is at least 20% greater than the first rake angle directly adjacent thereto.

7. The end mill according to claim 6, wherein the intersection rake angle is at least 30% greater than the first rake angle directly adjacent thereto.

8. The end mill according to claim 1, wherein each first rake angle along the first sub-edge has a positive value.

9. The end mill according to claim 1, wherein each first rake angle of the first sub-edge has the same value.

10. The end mill according to claim 1, wherein the intersection helix angle is at least 10% greater than the first helix angle directly adjacent thereto.

11. The end mill according to claim 1, wherein either: the general location is located between 20% to 40% of the effective cutting length from the cutting end face, and each first helix angle along the first sub-edge has the same value; or the general location is located from 40% to 75% of the effective cutting length from the cutting end face and the first helix angle along the first sub-edge decreases in value with increasing proximity to the angle transition intersection.

12. The end mill according to claim 1, wherein the intersection rake angle is greater than the first rake angle directly adjacent thereto and the intersection relief angle is smaller than the first relief angle directly adjacent thereto.

13. The end mill according to claim 1, wherein a visible relief discontinuity is formed along the first sub-edge.

14. The end mill according to claim 1, wherein the first relief angle gradually increases from the cutting end face in a rearward direction toward the angle transition intersection.

15. The end mill according to claim 1, wherein each internal tooth angle measurable between the rake surface and the relief surface at each axial location along the first sub-edge has the same value.

16. The end mill according to claim 1, wherein: at least one flute of the plurality of flutes comprises a sub-flute extending from the cutting end face in the rearward direction and having a sub-flute boundary; the sub-flute extending in the preceding direction from a cutting edge of one tooth towards an adjacent tooth.

17. The end mill according to claim 16, wherein the sub-flute boundary is spaced-apart from the second tooth's relief surface.

18. The end mill according to claim 1, wherein: the first helix angle of the cutting edge varies in value with increasing distance from the cutting end face to the angle transition intersection; and the second helix angle of the cutting edge has the same value with increasing distance from the angle transition intersection to the end of the effective cutting length.

19. The end mill according to claim 18, wherein: an additional cutting edge of the plurality of teeth, other than the previously defined cutting edge, has: a first helix angle which varies in value with increasing distance from the cutting end face to an angle transition intersection; and a second helix angle having the same value with increasing distance from the angle transition intersection of the second cutting edge to the end of the effective cutting length; and the second helix angle of the additional cutting edge being different from the second helix angle of said previously defined cutting edge.

20. The end mill according to claim 1, comprising at least five teeth, two non-adjacent teeth having cutting edges identical to said cutting edge of said at least one tooth.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0080] For a better understanding of the subject matter of the present application, and to show how the same may be carried out in practice, reference will now be made to the accompanying drawings, in which:

[0081] FIG. 1 is a side view of an end mill according to an example of the present invention;

[0082] FIG. 2 is an end view, along a rotation axis A.sub.R, of a cutting end face of the end mill in FIG. 1;

[0083] FIG. 3 is an enlarged view of the encircled portion designated III in FIG. 1;

[0084] FIG. 4 is an end view of the cutting end face, similar to FIG. 2, except before any facing operations have been carried out;

[0085] FIG. 5 is a schematic partial cross-section view of a tooth, along a rotation axis A.sub.R;

[0086] FIG. 6 is a cross-section view taken along line VI-VI in FIG. 1, corresponding to an axial location 12.5% of the effective cutting length from the cutting end face;

[0087] FIG. 7 is a cross-section view taken along line VII-VII in FIG. 1, corresponding to an axial location 25% of the effective cutting length from the cutting end face;

[0088] FIG. 8 is a cross-section view taken along line VIII-VIII in FIG. 1, corresponding to an axial location 37.5% of the effective cutting length from the cutting end face;

[0089] FIG. 9 is a cross-section view taken along line IX-IX in FIG. 1, corresponding to an axial location 50% of the effective cutting length from the cutting end face;

[0090] FIG. 10 is a cross-section view taken along line X-X in FIG. 1, corresponding to an axial location 75% of the effective cutting length from the cutting end face; and

[0091] FIG. 11 is a cross-section view taken along line XI-XI in FIG. 1, corresponding to an axial location 100% of the effective cutting length from the cutting end face.

DETAILED DESCRIPTION

[0092] FIGS. 1 and 2 illustrate an end mill 10, typically made of extremely hard and wear-resistant material such as cemented carbide, configured for rotating about a central rotation axis A.sub.R which extends longitudinally through the center thereof. The end mill 10 has unitary one-piece construction (i.e. it is devoid of replaceable cutting inserts).

[0093] The central rotation axis A.sub.R defines opposite axially forward and rearward directions D.sub.F, D.sub.R, and opposite rotational preceding and succeeding directions D.sub.P, D.sub.S, the preceding direction D.sub.P being the cutting direction.

[0094] The end mill 10 comprises a shank portion 12 and a cutting portion 14 extending in the forward direction D.sub.F therefrom.

[0095] The shank portion 12 extends in the forward direction D.sub.F from a rear end face 15 to a furthermost flute end 18.

[0096] The cutting portion 14 extends in the rearward direction D.sub.R from a cutting end face 16 to the furthermost flute end 18.

[0097] A peripheral surface 17 extends from the rear end face 15 to the cutting end face 16.

[0098] The cutting portion 14 is integrally formed with first, second, third, fourth and fifth teeth 20A, 20B, 20C, 20D, 20E (hereinafter generally referred to as tooth/teeth 20) alternated with helically shaped first, second, third, fourth and fifth flutes 22A, 22B, 22C, 22D, 22E (hereinafter generally referred to as flute(s) 22).

[0099] To explain relative terminology used herein, for example, the first flute 22A is adjacent to the first tooth 20A in the preceding direction D.sub.P, and could therefore be described as the flute which precedes the first tooth 20A.

[0100] An effective cutting length L.sub.E of the cutting portion 14 extends from the cutting end face 16 to an axial location where tooth relief surfaces are no longer effective, which is visible in this example at the axial location designated with the reference character 29 (in this example the axial location of the end of the effective cutting length L.sub.E coincides with section XI-XI).

[0101] The outer edge of the cutting portion 14 is substantially cylindrical, and a diameter D.sub.E (FIG. 2) of the end mill is measurable at the cutting end face 16 thereof.

[0102] As shown from the unbroken appearance of the teeth 20 in FIG. 1, the teeth 20 are non-serrated.

[0103] In FIG. 2, for understanding, exemplary first, second, third, fourth and fifth index angles are shown I.sub.A, I.sub.B, I.sub.C, I.sub.D, I.sub.E extending between the cutting edges of the teeth 20.

[0104] Referring to FIG. 1, aside from the cutting end face 16 (i.e. the front axial position of the effective cutting length L.sub.E) and the axial position of section XI-XI (i.e. the rear axial position of the effective cutting length L.sub.E) intermediary axial locations or sections (or views of a plane perpendicular to the central rotation axis A.sub.R) have been chosen for explanatory purposes only.

[0105] Basic tooth geometry and angle definitions, as shown in FIGS. 4 and 5, are generally explained below.

[0106] Each tooth 20 comprises a rake surface 26, a relief surface 28 and a cutting edge 30 (i.e. a radial cutting edge).

[0107] Each relief surface 28 has a relief surface width W.sub.R.

[0108] As seen in the cross-section of FIG. 4, the cutting edge 30 comprises a relief angle . Relief angle is measurable between (a) a perpendicular line L.sub.P which passes through the cutting edge 30 and is perpendicular to a radial line L.sub.R extending from the central rotation axis A.sub.R to the cutting edge 30), and (b) the relief surface 28 associated with that cutting edge 30.

[0109] The cutting edge 30 further comprises a radial rake angle . An exemplary radial rake angle is shown in FIG. 5 and is measurable between a radial line L.sub.R extending from the central rotation axis A.sub.R to a cutting edge 24 and a tangent line L.sub.T extending tangentially from an associated rake surface 26.

[0110] An exemplary helix angle H is shown in FIG. 1 and is measurable relative to the central rotation axis A.sub.R at an axial position along the cutting edge 30 (according to some terminologies the helix angle is defined relative to the flute, however it will be understood here that the same physical parameter can be defined with relative to the cutting edge).

[0111] Referring to FIG. 2, the teeth 20 are each positioned front-of-center, as shown. To elaborate what is meant by front-of-center, a first radial line L.sub.R1 is drawn from the central rotation axis A.sub.R to intersect a start point 34 of an axial sub-edge 36, in this example of the second tooth 20B. Since every point of the entire cutting edge 36 is located rotationally behind the radial line L.sub.R1 (i.e. in the succeeding direction D.sub.S), when the material being machined (not shown) contacts any portion of the cutting edge 30 it is ejected outwardly from the end mill 10.

[0112] Referring to FIG. 1, a tooth designated 20 is shown. The tooth 20 comprises a first sub-edge 38 extending rearwardly from the cutting end face 16, a second sub-edge 40 extending rearwardly from the first sub-edge 38; and an angle transition intersection 42 defining where the first sub-edge 38 ends and the second sub-edge starts 40.

[0113] It is understood that the first and second sub-edges 38, 40 and the angle transition intersection 42 have radial rake angles, helix angles and relief angles at each axial location, of the type defined above.

[0114] As explained above, the angle transition intersection 42 is always located in a general location GL which is an axial distance from the cutting end face 16 defined by the condition: 0.20L.sub.EGL0.75L.sub.E. As the line VII-VII in FIG. 1 corresponds to an axial location 25% of the effective cutting length, the general location GL starts between the VI-VI line and the VII-VII line and ends at line X-X located exactly at an axial location 75% of the effective cutting length from the cutting end face 16.

[0115] For a given tooth, the precise location PL of the angle transition intersection 42 within the general location GL, is at the closest axial location to the cutting end face 16 where (a) the intersection rake angle is greater than all other rake angles closer to the cutting end face 16, and/or (b) the intersection helix angle is at least 5% greater than a first helix angle directly preceding the intersection helix angle.

[0116] In the example given, both of these conditions occur at the same axial location, which in this example is at 50% of the effective cutting length from the cutting end face 16, as shown in FIG. 1 and in more detail in FIGS. 3 and 9.

[0117] Regarding the first condition, the rake angles of an exemplary tooth are shown in FIGS. 6 to 11. In FIGS. 6 to 8 the rake angle .sub.1 of the first sub-edge 38 has a positive value of 8 and in FIGS. 9 to 11 the rake angle .sub.2 of the same tooth (FIG. 9 being at angle intersection 42 and FIGS. 10-11 being at the second sub-edge 40) has a positive value of 11. This is an abrupt increase of 38% (11/8=1.38=38%). For sake of completeness, even though the measurements shown were taken along selected axial positions, it will be understood that the entire first sub-edge 38 has a single/same rake angle (i.e. 8) and the entire second sub-edge 40 has a single/same rake angle (i.e. 11). For the sake of clarity, the rake angle .sub.1 of the first sub-edge is 8, the rake angle .sub.2 of the angle transition intersection is 11 and the rake angle of the second sub-edge is also 11. It will be understood that it is not essential for the rake angle of the second sub-edge to have the same value as the angle transition intersection, although it is advantageous that it has a greater value than the first sub-edge (for increased cutting efficiency).

[0118] Referring to FIG. 3, while the change in rake angle cannot be seen in this view, a change in relief angle was designed to coincide with the change in rake angle and is visible via a relief discontinuity 44. While a change in relief angle at the location of the change in rake angle is not essential, it is a preferred option since it maintains a constant internal tooth angle. To elaborate, in this example the relief angle along the first sub-edge is equal to 12 and along the second sub-edge is equal to 9, corresponding to the 3 change of the rake angle. For the sake of clarity, the relief angle of the first sub-edge is 12, and the relief angle of the angle transition intersection and, optionally, the second sub-edge is 9 (it will be understood that maintaining a relatively constant internal tooth angle, schematically shown in FIG. 4 as .sub.I, is advantageous, in the present example .sub.I=70 which is calculated as 90relief anglerake angle; this equaling 90128=70 along the first sub-edge and 90911=70 along the second sub-edge).

[0119] Regarding the second condition, the helix angle H of cutting edges at the cutting end face 16 for the cutting edges of the first and third teeth (20A, 20C) is 42 and this value progressively decreases to 35 at a portion of the first edge 38 directly adjacent to the transition intersection. At the transition intersection, however, the helix angle abruptly becomes 40. This is an abrupt increase of 36% (40/35=1.14=14%). For the sake of clarity, the helix angle of the first sub-edge directly adjacent to the angle transition intersection is 35, the helix angle of the angle transition intersection is 40 and the helix angle of the second sub-edge stays at 40, although it will be understood that it is not essential for the helix angle of the second sub-edge to have the same value.

[0120] The helix angle H for the second. fourth and fifth teeth (20B, 20D, 20E) is 40 and this value progressively decreases to 33 at a portion of the first edge 38 directly adjacent to the transition intersection. At the transition intersection, the helix angle abruptly becomes 38. This is an abrupt increase of 40% (38/33=1.15=15%). For the sake of clarity, the helix angle of the first sub-edge directly adjacent to the angle transition intersection is 33, the helix angle of the angle transition intersection is 38 and the helix angle of the second sub-edge stays at 38, although it will be understood that it is not essential for the helix angle of the second sub-edge to have the same value.

[0121] Nonetheless, to reduce vibrations it is preferred that the helix angles values of the different second sub-edges have some difference. In the present example, some are 38 and some are 40.

[0122] The abrupt change in helix angle is most easily achieved by first producing a flute 22 with a helix angle and then producing a sub-flute 32 adjacent thereto. For example, the first and third teeth 20A, 20C can be ground with a helix angle of 40. A second flute (the sub-flute) is then ground along a similar path (having the above mentioned 42 which decreases to 35 and ends directly adjacent to the transition intersection. As best shown in enlarged FIG. 3, the sub-flute 32 extends from the cutting end face in a rearward direction therefrom and the sub-flute 32 comprises a sub-flute boundary 46.

[0123] In FIG. 6 the sub-flute boundary 46 is further shown ending before reaching the adjacent tooth's relief surface 28 in the preceding direction D.sub.P. Notably the sub-flute boundary 46 is shown in FIGS. 6 to 8 but is no longer visible in FIGS. 9 to 11 since the sub-flute ends at an axial position closer to the cutting end face 16.

[0124] As shown in FIG. 3, the change in helix angles from the first sub-edge 38 to the second sub-edge 40 causes the cutting edge to have a non-linear shape (i.e. forming an internal cutting edge angle which is less than 180), which provides, in theory, a bump to an adjacent chip. The internal cutting edge angle in this example is 176, although even an internal cutting edge angle of 179 is thought to be able to provide a desired bump (for initiating wear at this axial location). However, it is believed a larger angle, such as the exemplified angle having a value 176, is preferred.

[0125] Notably, this exemplary end mill 10 has a general location GL located between 40% to 75% of the effective cutting length from the cutting end face, and the first helix angle along the first sub-edge decreases in value with increasing proximity to the angle transition intersection, which is advantageous for shouldering applications.

[0126] Further, as seen by the dashed circles in FIGS. 6 to 11, the end mill's core is tapered (i.e. enlarging with increased distance from the cutting end face). To give an example, the core designated C1 in FIG. 9 is visibly larger than the core designated C2 in FIG. 6.

[0127] The description above includes an exemplary embodiment which does not exclude non-exemplified embodiments from the claim scope of the present application.