Milling insert and a milling tool

Abstract

A milling insert for shoulder milling having s a positive basic shape and includes an upper side having a rake surface, a lower side including a planar bottom surface, a side surface extending around the periphery of the milling insert, and a cutting edge formed between the side surface and the rake surface. The cutting edge has at least a major cutting edge portion, a corner radius cutting edge portion, a ramping cutting edge portion, and a surface wiping cutting edge portion. The side surface includes an upper set of primary clearance surfaces and a lower set of secondary clearance surfaces having a plurality of planar secondary clearance surfaces, wherein the upper set of primary clearance surfaces forms an overhang protruding with respect to the secondary clearance surfaces and extending around the entire upper periphery of the milling insert.

Claims

1. A milling insert for mounting in a shoulder milling tool, the milling insert having a positive basic shape and comprising: an upper side having a rake surface; a lower side opposite the upper side, the lower side including a planar bottom surface; a side surface extending between the upper side and the lower side and around a periphery of the milling insert; and a cutting edge formed between the side surface and the rake surface, the cutting edge including at least a major cutting edge portion, a corner radius cutting edge portion, a ramping cutting edge portion, and a surface wiping cutting edge portion positioned between the corner radius cutting edge portion and the ramping cutting edge portion and forming an angle with the ramping cutting edge portion, the side surface including an upper set of primary clearance surfaces and a lower set of secondary clearance surfaces including a plurality of planar support surfaces, wherein the upper set of primary clearance surfaces forms an overhang protruding with respect to an entirety of the secondary clearance surfaces, so that extension planes in which the planar secondary clearance surfaces extend are located inside the associated primary clearance surfaces with respect to a central axis of the milling insert, and wherein the protruding overhang extends around the entire upper periphery of the milling insert.

2. The milling insert according to claim 1, wherein the cutting edge extends in parallel with the bottom surface.

3. The milling insert according to claim 1, wherein the upper side includes a planar central region extending in parallel with the bottom surface, wherein the planar central region is recessed with respect to the cutting edge.

4. The milling insert according to claim 1, wherein the major cutting edge portion is convex as seen in a plane parallel with the bottom surface.

5. The milling insert according to claim 1, wherein the milling insert has a thickness t.sub.tot in a direction perpendicular to the bottom surface, and wherein the lower set of secondary clearance surfaces extends along at least 50% of the thickness.

6. The milling insert according to claim 1, wherein the overhang has a thickness t.sub.oh within the range 0.20 mmt.sub.oh0.5 mm in a direction perpendicular to the bottom surface.

7. The milling insert according to claim 1, wherein, when the milling insert is mounted in a tool body, at least one of the planar support surfaces is configured to form an axial support surface and at least another one of the planar support surfaces is configured to form a radial support surface, the radial support surface and the axial support surface forming an acute angle with each other as seen in a plane parallel with the bottom surface.

8. The milling insert according to claim 1, wherein the secondary clearance surfaces are formed at acute seating angles with respect to an upper extension plane parallel with the bottom surface and extending at the level of the cutting edge.

9. The milling insert according to claim 1, wherein the cutting edge includes an additional cutting edge portion positioned between, and forming an angle with, the surface wiping cutting edge portion and the ramping cutting edge portion.

10. The milling insert according to claim 1, wherein the primary clearance surface below the major cutting edge is formed at an overhang angle .sub.major with respect to an upper extension plane parallel with the bottom surface and extending at the level of the cutting edge, the overhang angle .sub.major decreasing from the corner radius cutting edge portion and along the major cutting edge portion, so that an effective clearance angle along the major cutting edge portion is constant when the milling insert is mounted in a tool body.

11. The milling insert according to claim 10, wherein the secondary clearance surface below the major cutting edge portion is formed at a seating angle .sub.major with respect to the upper extension plane, the seating angle .sub.major being constant along the major cutting edge portion.

12. The milling insert according to claim 1, wherein the primary clearance surface below the ramping cutting edge portion is formed at an acute overhang angle .sub.ramp with respect to an upper extension plane parallel with the bottom surface and extending at the level of the cutting edge, the secondary clearance surface below the ramping cutting edge portion being formed at an acute seating angle .sub.ramp with respect to said upper extension plane, and wherein .sub.ramp<.sub.ramp.

13. The milling insert according to claim 1, wherein below each of the major cutting edge portion, the corner radius cutting edge portion, and the surface wiping cutting edge portion, the secondary clearance surface associated with the respective cutting edge portion is formed at an acute seating angle with respect to an upper extension plane parallel with the bottom surface and extending at the level of the cutting edge, and the primary clearance surface associated with the respective cutting edge portion is formed at an acute overhang angle with respect to said upper extension plane, wherein the seating angle is smaller than the overhang angle.

14. The milling insert according to claim 1, wherein the milling insert is indexable with two index positions.

15. A milling tool comprising: a tool body; and at least one milling insert detachably mounted in an insert seat of the tool body, the at least one milling insert including an upper side having a rake surface; a lower side opposite the upper side, the lower side including a planar bottom surface; a side surface extending between the upper side and the lower side and around a periphery of the milling insert; and a cutting edge formed between the side surface and the rake surface, the cutting edge including at least a major cutting edge portion a corner radius cutting edge portion, a ramping cutting edge portion, and a surface wiping cutting edge portion positioned between the corner radius cutting edge portion and the ramping cutting edge portion and forming an angle with the ramping cutting edge, the side surface including an upper set of primary clearance surfaces, and a lower set of secondary clearance surfaces including a plurality of planar support surfaces, wherein the upper set of primary clearance surfaces forms an overhang protruding with respect to an entirety of the secondary clearance surfaces, so that extension planes in which the planar secondary clearance surfaces extend are located inside the associated primary clearance surfaces with respect to a central axis of the milling insert, and wherein the protruding overhang extends around the entire upper periphery of the milling insert.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A detailed description of embodiments of the invention with reference to the appended drawings follows below. In the drawings:

(2) FIG. 1 shows a perspective view of a milling insert according to an embodiment of the invention;

(3) FIG. 2 shows a perspective view of the milling insert in FIG. 1;

(4) FIG. 3 shows a top view of the milling insert in FIG. 1;

(5) FIG. 4 shows a side view of the milling insert in FIG. 1;

(6) FIG. 5 shows a side view of the milling insert in FIG. 1;

(7) FIG. 6 shows a bottom view of the milling insert in FIG. 1;

(8) FIG. 7 shows a cross section of the milling insert along the line VII-VII in FIG. 3;

(9) FIG. 8 shows a partial cross section of the milling insert along the line VIII-VIII in FIG. 3;

(10) FIG. 9 shows a partial cross section of the milling insert along the line IX-IX in FIG. 3;

(11) FIG. 10 shows a partial cross section of the milling insert along the line X-X in FIG. 3;

(12) FIG. 11 shows a partly exploded perspective view of a milling tool according to an embodiment of the invention;

(13) FIG. 12 shows a side view of the milling tool in FIG. 11; and

(14) FIG. 13 shows a top view of the milling tool in FIG. 11.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(15) FIG. 1-10 show different views of a milling insert 100 intended for shoulder milling, i.e. milling at an entering angle of 90 according to an embodiment of the invention. The milling insert 100 is indexable with two index positions and has a positive basic shape. It comprises an upper side 101 and a lower side 102 opposite the upper side 101. A central axis C1 extends between the upper side 101 and the lower side 102. A central hole is provided for mounting the milling insert in a tool body. The upper side 101 comprises a rake surface 103 having a planar central region 120 extending around the central hole. The lower side 102 comprises a planar bottom surface 105. Around the periphery of the milling insert, a side surface 104 extends. A cutting edge 106 is formed between the rake surface 103 and the side surface 104. An upper extension plane P.sub.U is defined, extending in parallel with the bottom surface 105 at the level of the cutting edge 106. The cutting edge 106 extends in parallel, or essentially in parallel, with the upper extension plane P.sub.U. The planar central region 120 of the rake surface 103 is recessed with respect to the cutting edge 106, wherein an inclined surface 121 of the rake surface 103 extends from the planar central region 120 toward the cutting edge 106. A reinforcement land 122 is formed between the inclined surface 121 and the cutting edge 106.

(16) Since the milling insert 100 has two index positions, the cutting edge 106 comprises two major cutting edge portions 107a, 107b formed to be active one at a time. The cutting edge 106 further comprises two corner radius cutting edge portions 108a, 108b, two surface wiping cutting edge portions 109a, 109b, and two ramping cutting edge portions 110a, 110b. Each surface wiping cutting edge portion 109a, 109b is positioned between its associated corner radius cutting edge portion 108a, 108b and its associated ramping cutting edge portion 110a, 110b and forms a right angle or an essentially right angle with its associated major cutting edge portion 107a, 107b. The angle between the surface wiping cutting edge 109a, 109b and the major cutting edge portion 107a, 107b is designed to generate a 90 shoulder in the workpiece during a milling operation. However, this angle may vary depending on the radial and the axial tipping-in angle on the mounted insert 100 in the insert seat of the tool body. In this specific embodiment the surface wiping cutting edge portions 109a, 109b form a 92 angle with the major cutting edge portions 107a, 107b due to its intended mounting at a negative radial and positive axial tipping-in angle (further described below) in order to generate the 90 shoulder in the workpiece. Each ramping cutting edge portion 110a, 110b is formed at sharp angle with respect to the associated major cutting edge portion 107a, 107b to allow ramping of a workpiece. In the shown embodiment, the ramping cutting edge portion 110a, 110b is formed at an angle of approximately 70 with respect to the major cutting edge portion 107a, 107b.

(17) Below each of the cutting edge portions 107a-110b, the side surface 104 comprises an upper set of primary clearance surfaces 111a, 111b, 112a, 112b, 113a, 113b, 114a, 114b, formed immediately below the cutting edge 106, and a lower set of secondary clearance surfaces 115a, 115b, 116a, 116b, 117a, 117b, 118a, 118b, formed below the primary clearance surfaces 111a-114b as shown in FIG. 6. Each of the secondary clearance surfaces 115a-118b is associated with a primary clearance surface 111a-114b below which it extends. The secondary clearance surfaces 115a, 115b located below the major cutting edge portions 107a, 107b form radial support surfaces for supporting the milling insert 100 in the insert seat of a tool body, wherein the secondary clearance surface 115b below the inactive major cutting edge portion 107b forms the radial support surface when the major cutting edge portion 107a is active and vice versa. The secondary clearance surfaces 118a, 118b located below the ramping cutting edge portions 110a, 110b, respectively, form axial support surfaces, wherein the secondary clearance surface 118b is an active support surface when the major cutting edge portion 107a is active and vice versa. The secondary clearance surfaces 115a, 115b, 118a, 118b formed as support surfaces are planar surfaces, as well as the secondary clearance surfaces 117a, 117b located below the surface wiping cutting edge portions 109a, 109b. Each of the secondary clearance surfaces is formed at a sharp seating angle with respect to the upper extension plane P.sub.U. The seating angle varies around the milling insert. Each of the secondary clearance surfaces 118a, 118b, acting as an axial support surface, is formed at a sharp angle of approximately 70 with respect to the associated secondary clearance surface 115a, 115b acting as a radial support surface.

(18) The primary clearance surfaces 111a, 111b, 112a, 112b, 113a, 113b, 114a, 114b form an overhang 119 extending around the entire upper periphery of the milling insert 100 just below the cutting edge 106. The overhang 119 protrudes with respect to the lower part of the milling insert 100. This means that extension planes in which the planar secondary clearance surfaces 115a, 115b, 117a, 117b, 118a, 118b extend are located inside the associated primary clearance surfaces with respect to the central axis C1.

(19) As shown in FIG. 5, the milling insert 100 has a thickness t.sub.tot in a direction perpendicular to the bottom surface 105. Here, the thickness t.sub.tot is approximately 2.4 mm, but t.sub.tot may be up to 6 mm for larger milling inserts according to the invention. The lower set of secondary clearance surfaces 115a-118b extends over at least 50% of the thickness t.sub.tot, preferably over at least 60% of the thickness t.sub.tot, more preferably over at least 70% of the thickness t.sub.tot. For large milling inserts, with a larger thickness t.sub.tot, the lower set of clearance surfaces may extend over more than 85% of the total thickness t.sub.tot. The overhang has a thickness t.sub.oh which is here 0.3 mm and which should preferably be within the range 0.20 mmt.sub.oh0.5 mm, and more preferably within the range 0.25 mmt.sub.oh0.5 mm. The thickness t.sub.oh of the overhang 119 is chosen to allow an acceptable amount of wear on the cutting edge 106, and is therefore independent of the total thickness t.sub.tot of the milling insert 100. The lower set of secondary clearance surfaces 115a-118b in the shown embodiment extends over approximately 75% of the thickness t.sub.tot of the milling insert 100.

(20) The primary clearance surfaces 111a-114b are formed at a sharp overhang angle with respect to the upper extension plane P.sub.U as shown in FIG. 7-10. Below the ramping cutting edge portion 110a, 110b, the overhang angle .sub.ramp is smaller than the seating angle .sub.ramp that the secondary clearance surface 118a, 118b makes with the upper extension plane P.sub.U. In the shown embodiment, the overhang angle .sub.ramp decreases along the ramping cutting edge portion 110a, 110b, from approximately 63 closest to the surface wiping cutting edge portion 109a, 109b to approximately 57. The seating angle .sub.ramp is approximately 70. Below the corner radius cutting edge portion 108a, 108b and the surface wiping cutting edge portion 109a, 109b, the seating angle is smaller than the overhang angle . The overhang angle is here above 70, while the seating angle is below 70.

(21) Below and along the major cutting edge portion 107a, 107b, the seating angle .sub.major (see FIG. 7) is constant and approximately 82. The overhang angle .sub.major here varies along the major cutting edge portion 107a, 107b, from approximately 89 close to the corner cutting edge portion 108a, 108b to approximately 83 at the maximum cutting depth. Functionally, when mounted in a milling tool with a radial tipping-in angle of between 11 to 18 and an axial tipping-in angle of 8 to 10 (see further explanation below), this gives a constant effective primary clearance angle of between 10-15 just behind the major cutting edge portion 107a, 107b, while an effective secondary clearance angle behind the overhang 119 decreases along the major cutting edge portion 107a, 107b, and is approximately 10 at the maximum cutting depth.

(22) The major cutting edge portion 107a, 107b is in the shown embodiment convex as seen in the upper extension plane PU. A chord of the major cutting edge portion 107a, 107b forms a chord angle of 24 with the secondary clearance surface 115a, 115b. The chord angle should preferably be within the interval 0<<1.

(23) The milling insert 100 in the shown embodiment further comprises two additional cutting edge portions 124a, 124b, each formed between one of the surface wiping cutting edge portions 109a, 109b and one of the ramping cutting edge portions 110a, 110b. Each additional cutting edge portion 124a, 124b is formed at an angle with respect to the adjacent surface wiping cutting edge portion, which angle may be approximately 2-4. Here, each primary clearance surface 113a, 113b below the surface wiping cutting edge portions 109a, 109b, is shown as a single surface extending also below the additional cutting edge portion 124a, 124b.

(24) The lower side 102 of the milling insert 100, apart from the bottom surface 105, also comprises a circumferential surface 123, which is raised with respect to the bottom surface 105, meaning that it is closer to the upper side 101 than the bottom surface 105. This circumferential surface 123 is formed for manufacturing purposes. Since the milling insert 100 according to the invention is preferably manufactured using a pressing process with as little machining as possible needed after pressing, it is important that no parts of the milling insert protrude below the bottom surface 105, serving as a bottom support for the milling insert in the tool body, after pressing. The circumferential surface 123 ensures that no residuals from the pressing process protrude below the bottom surface 105 after pressing.

(25) Reference is now made to FIG. 11-13, showing a milling tool 200 for shoulder milling according to the invention. The milling tool 200 comprises a tool body 201 with a cylindrical base shape. The tool body includes a front end 202 and a rear end 203, between which a central rotation axis C2 extends. The tool 200 is rotatable in a direction of rotation R around the central rotation axis C2. Two insert seats 204 are formed in a transition between the front end 202 and a peripheral surface 205 extending between the front end 202 and the rear end 203. A chip pocket 206 is provided rotationally ahead of the at least one insert seat 204. In each insert seat 204, a milling insert 100 as described above is securely mounted by means of a fastening member 300 in the form of a screw, with the bottom surface 105 abutting the insert seat 204 and with the major cutting edge portion 107a being active. An axial contact surface 207 is provided for supporting the axial support surface of the milling insert 100, in this case the secondary clearance surface 118b. A radial contact surface 208 is provided for radially supporting the milling insert 100 along the secondary clearance surface 115b.

(26) The milling insert 100 is mounted in the tool body 101 at a radial tipping-in angle .sub.f and an axial tipping-in angle .sub.m. The radial tipping-in angle .sub.f, shown in FIG. 13, is the angle between the upper extension plane P.sub.U of the milling insert 100 and a line along the radial vector r of the tool as seen in planar view. The radial tipping-in angle .sub.f is in this case negative and approximately 15, i.e. the upper extension plane P.sub.U is inclined outward/forward. The radial tipping in-angle may vary between 11 to 18 depending on milling tool diameter. The axial tipping-in angle .sub.m, shown in FIG. 12, is the angle between the upper extension plane P.sub.U of the milling insert 100 and the central rotation axis C2 of the tool. The milling insert 100 is here mounted at a positive axial tipping-in angle .sub.m of approximately 10, i.e. the upper extension plane P.sub.U leans in the upward/rearward direction. For milling tools with a diameter of less than 12 mm, the axial tipping-in angle .sub.m may be set to 8. Together with an overhang angle .sub.major of approximately 89 close to the corner and 83 at the maximum cutting depth, the axial and radial tipping-in angles should result in an effective clearance of 10-15 during a milling operation.

(27) The tool body 201 of the milling tool 200 is usually manufactured from steel, while the milling inserts 100 are manufactured from a harder material, in particular cemented carbide.

(28) The invention is of course not limited to the embodiments disclosed but may be varied and modified within the scope of the appended claims. For example, the milling insert may be formed as a non-indexable milling insert with a single major cutting edge portion. The milling insert may be designed for left hand rotation of the tool as well as for right hand rotation of the tool.