SOLID END MILL

Abstract

A solid end mill is rotatable around a central rotational axis and includes a cutting portion having a plurality flutes with peripheral cutting edges formed between associated rake surfaces and clearance surfaces. The peripheral cutting edge forms a convexly curved lobe cutting edge portion disposed along an axial front part of the cutting portion. A neck cutting edge portion is connected to the lobe cutting edge portion and is disposed along an axial intermediate part of the cutting portion. A shoulder cutting edge portion is connected to the neck cutting edge portion and is disposed along an axial rear part of the cutting portion. The peripheral cutting edge extends at a linear and constant axial inclination angle θ within the range 5°≤θ≤15°. The rake surface forms positive radial rake angles α.sub.L,N,S along the entire extension of the peripheral cutting edge.

Claims

1. A solid end mill being rotatable around a central rotational axis, the solid end mill comprising: a cutting portion; and a shank portion, the cutting portion including a plurality flutes having peripheral cutting edges formed between associated rake surfaces and clearance surfaces, wherein each peripheral cutting edge, in a view perpendicular to the central rotational axis and toward the rake surface, forms: a single convexly curved lobe cutting edge portion disposed along an axial front part of the cutting portion, a single neck cutting edge portion connected to the convexly curved lobe cutting edge portion, wherein the neck cutting edge portion extends at a smaller radial distance to the central rotational axis compared to the convexly curved lobe cutting edge portion and is disposed along an axial intermediate part of the cutting portion, and a shoulder cutting edge portion connected to the neck cutting edge portion, wherein the shoulder cutting edge portion extends at a larger radial distance to the central rotational axis compared to the neck cutting edge portion and is disposed along an axial rear part of the cutting portion, characterized in that wherein each peripheral cutting edge, in the view perpendicular to the central rotational axis and toward the clearance surface, extends at a linear and constant axial inclination angle θ within the range 5°≤θ≤15° in relation to the central rotational axis, wherein the rake surface, as seen in cross-sections perpendicular to the central rotational axis, forma positive radial rake angles α.sub.L,N,S along an entire extension of the peripheral cutting edge.

2. The solid end mill of claim 1, wherein the positive radial rake angles α.sub.L, N, S are within the range 2°≤α.sub.L, N, S≤15° along the entire extension of the peripheral cutting edge.

3. The solid end mill of claim 1, wherein the positive radial rake angles α.sub.L, S on the rake surface along the convexly curved lobe cutting edge portion and the shoulder cutting edge portion are larger than the positive radial rake angle α.sub.N on the rake surface along the neck cutting edge portion.

4. The solid end mill according to claim 1, wherein the rake surface along the convexly curved lobe cutting edge portion, neck cutting edge portion and shoulder cutting edge portion is situated in a common plane.

5. The solid end mill according to claim 1, wherein each peripheral cutting edge, in the view perpendicular to the central rotational axis and toward the clearance surface, extends at an axial inclination angle θ within the range 8°≤θ≤12° in relation to the central rotational axis.

6. The solid end mill according to claim 1, wherein each flute includes a bottom surface, which is situated closest to the central rotational axis and extends at the axial inclination angle θ, wherein a radial distance between the bottom surface and the central rotational axis continuously increases in a direction from an axial front part of the cutting portion toward an axial rear part of the cutting portion.

7. The solid end mill according to claim 6, wherein the bottom surface, as seen in a view toward the rake surface, is axially extending in a curved manner, at a specific radius of curvature, from the axial front part of the cutting portion toward the axial rear part of the cutting portion.

8. The solid end mill according to claim 1, wherein the smaller radial distance between the neck cutting edge portion and the central rotational axis is 50%-70% of a largest radial distance between the convexly curved lobe cutting edge portion and the central rotational axis.

9. The solid end mill according to claim 8, wherein the smaller radial distance between the neck cutting edge portion and the central rotational axis is 50%-70% of the larger radial distance between the shoulder cutting edge portion and the central rotational axis.

10. The solid end mill according to claim 8, wherein the smaller radial distance between the neck cutting edge portion and the central rotational axis is within the range 1.5 mm≤D.sub.N≤8 mm.

11. The solid end mill according to claim 1, wherein the cutting portion has at least five flutes having identical peripheral cutting edges and associated rake surfaces.

12. The solid end mill according to claim 1, wherein one pair of adjacent peripheral cutting edges is spaced at a greater or smaller distance in a circumferential direction compared to another pair of adjacent peripheral cutting edges, so that a differential pitch is provided between the peripheral cutting edges.

13. The solid end mill according to claim 1, wherein each peripheral cutting edge further includes a concavely curved chamfer cutting edge portion connected to the shoulder cutting edge portion, the concavely curved chamfer cutting edge portion extending radially outwards at the end of the shoulder cutting edge portion.

14. The solid end mill according to claim 1, wherein an internal axial coolant channel is provided in the solid end mill, the internal axial coolant channel having an outlet opening in a front end of the solid end mill.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] An embodiment is hereby described with references to the drawings, in which:

[0021] FIG. 1. shows a perspective view of a solid end mill according to an embodiment of the invention,

[0022] FIG. 2 shows a side view of the solid end mill of the embodiment including three different cross-sectional lines IV-IV, V-V and VI-VI perpendicular to a central rotational axis of the solid end mill,

[0023] FIG. 3 shows an axial front view of the solid end mill of the embodiment,

[0024] FIGS. 4-6 show cross-sections IV-IV, V-V and VI-VI respectively in FIG. 2,

[0025] FIG. 7 shows an enlarged side view perpendicular to the central rotational axis and toward a clearance surface of one of the peripheral cutting edges, and

[0026] FIG. 8 shows an enlarged axial front view of the solid end mill.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

[0027] FIGS. 1-8 discloses a solid end mill according to an embodiment of the present invention. The solid end mill 1 is rotatable around a central rotational axis R, wherein the solid end mill has a cutting portion 2 and a shank portion 3. The cutting portion 2 includes a plurality flutes 4 with peripheral cutting edges 5 formed between associated rake surfaces 6 and clearance surfaces 7. Each peripheral cutting edge 5, in a view perpendicular to the central rotational axis and toward the rake surface 6, is forming a single convexly curved lobe cutting edge portion 8 disposed along an axial front part of the cutting portion 2. A single neck cutting edge portion 9 is connected to the convexly curved lobe cutting edge portion 8, wherein the neck cutting edge portion 9 extends at a smaller radial distance D.sub.N to the central rotational axis R compared to the convexly curved lobe cutting edge portion 8 and is disposed along an axial intermediate part of the cutting portion 2. A shoulder cutting edge portion 10 is connected to the neck cutting edge portion 9, wherein the shoulder cutting edge portion 10 extends at a larger radial distance D.sub.S to the central rotational axis R compared to the neck cutting edge portion 9 and is disposed along an axial rear part of the cutting portion 2. The shoulder cutting edge portion 10 is extending essentially in parallel with the central rotational axis R to machine a shoulder surface at the top end portion of the dovetail slot for mounting the root portion of the turbine blade.

[0028] Each peripheral cutting edge 5 further comprises a concavely curved chamfer cutting edge portion 11 connected to the shoulder cutting edge portion 10, wherein the concavely curved chamfer cutting edge portion 11 is extending radially outwards at the end of the shoulder cutting edge portion 10. This produces a rounded chamfer at the top end of the dovetail slot. Hence, the concavely curved chamfer cutting portion 11 produces a rounded corner and defines the depth of the single tang dovetail slot being milled or, in other words, a maximum depth of cut used when milling with the solid end mill.

[0029] The peripheral cutting edge 5, as seen in FIG. 7, in a view perpendicular to the central rotational axis R and toward the clearance surface 7, extends at a linear and constant axial inclination angle θ within the range 5°≤θ≤15°, and preferably within the range 8°≤θ≤12°, in relation to the central rotational axis R. In the shown embodiment the axial inclination angle θ is 10° in relation to the central rotational axis R. Furthermore, as seen in FIGS. 4-6, the rake surface 6, as seen in cross-sections IV-IV, V-V and VI-VI perpendicular to the central rotational axis R as also shown in FIG. 2, is forming positive radial rake angles α.sub.L, N, S along the entire extension of the peripheral cutting edge 5. The positive radial rake angles α.sub.L, N, S are within the range 2°≤α.sub.L, N, S≤15°, and preferably within the range 4°≤α.sub.L, N, S≤15°, along the entire extension of the peripheral cutting edge 5. Moreover, the positive radial rake angles α.sub.L, S on the rake surface 6 along the convexly curved lobe cutting edge portion 8 and the shoulder cutting edge portion 10 are larger than the positive radial rake angle α.sub.N on the rake surface along the neck cutting edge portion 9. In the embodiment shown the radial rake angle α.sub.L on the convexly curved lobe cutting edge portion 8 is approximately 10° and the radial rake angle α.sub.N on the neck cutting edge portion 9 is approximately 7°. Additionally, the radial rake angle α.sub.S on the shoulder cutting edge portion 10 in the shown embodiment is approximately 12°.

[0030] The rake surface 6 along the convexly curved lobe cutting edge portion 8, neck cutting edge portion 9 and shoulder cutting edge portion 10 is situated in a common plane. Hence, the radial rake angle is achieved by grinding the rake surface in a single flat grinding operation. The difference in radial rake angles α.sub.L, N, S is due to the axial inclination angle θ and the different radial distances D.sub.L, N, S on the lobe, neck and shoulder cutting edge portions in relation to the central rotational axis R.

[0031] Each flute 4 comprises a bottom surface 12, which is situated closest to the central rotational axis R and extends at the axial inclination angle θ, wherein a radial distance DB between the bottom surface 12 and the central rotational axis R continuously increases in a direction from the axial front part of the cutting portion 2 toward the axial rear part of the cutting portion 2. More precisely, the bottom surface 12, as seen in a view toward the rake surface 6, is axially extending in a slightly curved manner, at a radius of curvature, from the axial front part of the cutting portion 2 toward the axial rear part of the cutting portion 2. This facilitates the grinding operation with a grinding wheel having a corresponding radius as the bottom surface, as the grinding wheel is inserted into the flute and a flat grinding surface of the grinding wheel is used for grinding the rake surface.

[0032] The smaller radial distance D.sub.N between the neck cutting edge portion 9 and the central rotational axis R may be 50%-70% of a largest radial distance D.sub.L between the convexly curved lobe cutting edge portion 8 and the central rotational axis R. More precisely, the shown embodiment exhibits a radial distance D.sub.N between the neck cutting edge portion 9 and the central rotational axis R, which is approximately 58% of the largest radial distance D.sub.L between the convexly curved lobe cutting edge portion 8 and the central rotational axis R. Moreover, the smaller radial distance D.sub.N between the neck cutting edge portion 9 and the central rotational axis R may also be 50%-70% of the larger radial distance D.sub.S between the shoulder cutting edge portion 10 and the central rotational axis R. More precisely, the shown embodiment exhibits a smaller radial distance D.sub.N between the neck cutting edge portion 9 and the central rotational axis R, which is 62% of the larger radial distance D.sub.L between the shoulder cutting edge portion 10 and the central rotational axis R. The smaller radial distance D.sub.N between the neck cutting edge portion 8 and the central rotational axis R may be within the range 1.5 mm≤D.sub.N≤8 mm. In other words, the single neck cutting edge portion is relatively slender. In this embodiment, the smaller radial distance D.sub.N on the neck cutting edge portion is approximately 3.11 mm and the largest radial distance D.sub.L between the convexly curved lobe cutting edge portion 8 and the central rotational axis R is 5.4 mm. Additionally, the radial distance D.sub.S between the shoulder cutting edge portion 10 and the central rotational axis R is 5 mm in the shown embodiment.

[0033] As can be seen in FIGS. 3 and 8, the cutting portion 2 is provided with five flutes 4 having identical peripheral cutting edges 5 and associated rake surfaces 6. Furthermore, one pair of adjacent peripheral cutting edges 5 is spaced at a greater or smaller distance ε, γ in a circumferential direction compared to another pair of adjacent peripheral cutting edges 5, so that a differential pitch is provided between the peripheral cutting edges 5.

[0034] Furthermore, the solid end mill includes an internal axial coolant channel 13 extending along the central rotational axis R, wherein the internal axial coolant channel 13 has an outlet opening 14 in a front end of the solid end mill. Hence, liquid coolant is supplied via an inlet opening in a rear end of the shank portion 3 and conducted through the internal axial coolant channel 13 to the outlet opening 14 in the front end of the solid end mill. The coolant thereby enters at the bottom of the dovetail slot during a milling operation and flushes the chips out of the slot via the flutes of the solid end mill. Moreover, the solid end mill is used for milling slots in components made of super alloys, which are extremely heat resistant, so that most of the heat produced during milling is absorbed by the peripheral cutting edges 5. Accordingly, in this embodiment the liquid coolant supplied via the internal axial coolant channel 13 and discharged through the outlet opening 14 cools the peripheral cutting edges 5.

[0035] The invention is of course not limited to the embodiment disclosed but may be varied and modified within the scope of the appended claims. The solid end mill may for instance include four flutes, instead of five, having identical peripheral cutting edges and associated rake surfaces. Furthermore, it's not necessary that the cutting portion is provided with a concavely curved chamfer cutting edge portion. The rounded or chamfered edges at the top end of the dovetail slot may instead be produced in a different machining operation. The solid end mill may also be formed without the internal axial coolant channel and the outlet opening at the front end. The internal axial coolant channel, depending on the size of the solid end mill and the internal axial coolant channel, can hereby weaken the core of the solid end mill to such a degree that the tool life decreases instead of increases. Additionally, the peripheral cutting edges may be subjected to so called micro-geometrical edge treatment, wherein the peripheral cutting edge in a cross-section is provided with an edge rounding (ER) or reinforcement land/bevel to increase the strength of the peripheral cutting edges.