Triangular double-sided milling insert and milling cutter therefor

Abstract

A milling cutter having a triangular double-sided milling insert and a tool body. The milling insert has three indexable portions. At each indexable portion the milling insert has a top main cutting edge, a top corner cutting edge, a bottom main cutting edge and a bottom corner cutting edge. On the top and bottom surfaces, a comer insert rake angle is greater than a main insert rake angle.

Description

TRIANGULAR DOUBLE-SIDED MILLING INSERT AND MILLING CUTTER THEREFORFIELD OF THE INVENTION

[0001] The subject matter of the present application relates to the field of metal milling machining operations in general. In particular, it relates to metal plunging machining operations using double-sided triangular milling inserts.BACKGROUND OF THE INVENTION

[0002] An example of a single-sided triangular milling insert fastened to a milling cutter used in milling operations is disclosed in CN207756980U.

[0003] It is an object of the present invention to provide an improved triangular plunging insert.SUMMARY OF THE INVENTION

[0004] In accordance with a first aspect of the subject matter of the present application there is provided a triangular double-sided milling insert comprising: a top surface, an opposite bottom surface and an insert peripheral surface connecting the top and bottom surfaces, with a first plane located between the top and bottom surfaces, and a central insert axis perpendicular to the first plane about which the milling insert is indexable; the insert peripheral surface comprising three main peripheral surfaces circumferentially alternating with three curved comer peripheral surfaces; three indexable portions, each indexable portion including one main peripheral surface and one corner peripheral surface; at each indexable portion: top and bottom main cutting edges are formed at the intersection of the main peripheral surface and the top and bottom surfaces, respectively; top and bottom comer cutting edges are formed at the intersection of the corner peripheral surface and the top and bottom surfaces, respectively; each of the top and bottom surfaces comprises a central main abutment surface, three main rake surfaces and three curved corner rake surfaces, each main rake surface located adjacent to one of the top and bottom main cutting edges, and each corner rake surface located adjacent to one of the top and bottom comer cutting edges; an acute main insert rake angle is defined between the main rake surface and the first plane, in a cross section perpendicular to, and intersecting, one of the top and bottom main cutting edges; and an acute comer insert rake angle is defined between the comerrake surface and the first plane, in a cross section perpendicular to, and intersecting, one of the top and bottom corner cutting edges; wherein: the corner insert rake angle is greater than the main insert rake angle.

[0005] Single-sided triangular inserts provide a consistent cut along the entire cutting edge with a simpler mounting arrangement due to the positive-type insert having a built-in relief angle. By contrast, a double-sided triangular milling insert provides more cutting edges, but a more complex mounting arrangement is needed, an inconsistent cut and an increased wear on the insert, especially near the corners. This is due to the rake angle at the corner and the rake angle at the main cutting edges being affected at differing rates by the mounting arrangement. To overcome these difficulties a special rake geometry was developed, where a corner insert rake angle is greater than a main insert rake angle. This rake angle arrangement compensates for the complex mounting arrangement, facilitating a more even plunge-cut than otherwise.

[0006] In accordance with a second aspect of the subject matter of the present application there is provided a milling cutter rotatable about a cutter rotational axis defining a rotation direction and opposing forward and rearward cutter directions, the milling cutter comprising: a tool body; a plurality of fasteners; and a plurality of milling inserts according to claim 1, each milling insert being releasably fastened to the tool body via a fastener.

[0007] It is understood that the above-said is a summary, and that features described hereinafter may be applicable in any combination to the subject matter of the present application, for example, any of the following features may be applicable to the milling insert and / or the milling cutter.

[0008] The main insert rake angle 9rm and the comer insert rake angle 9rcmay fulfil the following condition: 2°<9rc-9i-m< IO°.

[0009] The main insert rake angle 9rm and the comer insert rake angle 9rcmay fulfil the following condition: 10° < 9rm< 39° , 15° < 9rc< 35.

[0010] A main rake width Lm, defined as the width of the main rake surface in a cross section perpendicular to, and intersecting, the associated one of the top and bottom main cutting edges, and a corner rake width Lc, defined as the width of the corner rake surface in a cross section perpendicular to, and intersecting, the associated one of the top and bottom corner cutting edges, may fulfil the following condition: Lc>9.8*Lm.

[0011] Each of the top and bottom surfaces, at each indexable portion, may further comprise: a comer connection surface connecting the corner rake surface and the main abutment surface, the corner connection surface comprising: a first comer connection portion and a second comer connection portion located farther from the corner rake surface than the first comer connection portion; wherein: an acute first corner connection angle 0cci, defined between the first plane and the first comer connection portion in a cross section perpendicular to, and intersecting, one of the top and bottom corner cutting edges, and an acute second corner connection angle 0CC2, defined between the first plane and the second corner connection portion in a cross section perpendicular to, and intersecting, one of the top and bottom comer cutting edges, fulfil the following conditions: 9Cci<9rc, 9CCI<9CC2.

[0012] Each indexable portion may comprise exactly one insert comer.

[0013] A corner angle 9C, defined between two adjacent side abutment surfaces, may fulfil the following condition: 9C<69°.

[0014] A corner bisector plane contains the central insert axis and bisects a corner angle, defined between two adjacent side abutment surfaces; and the associated corner rake surface is asymmetrical about the corner bisector plane.

[0015] The tool body may comprise: a coupling portion and a cutting portion located forwardly of the coupling portion, the cutting portion comprising: a forward end surface facing in the forward cutter direction; a peripheral tool surface connecting the forward end surface to the coupling portion; and a plurality of insert seats circumferentially spaced about the cutter rotational axis, each insert seat opening out to the forward end surface and the peripheral tool surface, each insert seat comprising a main seat surface facing in the rotation direction and facing in the forward cutter direction at a seating angle, defined between the cutter rotational axis and a second plane parallel to the main seat surface; the bottom surface of each milling insert abuts the main seat surface of a respective insert seat; an operative main cutting edge, defined as the forwardmost top main cutting edge, extends transversely with respect to the cutter rotational axis; an operative corner cutting edge, defined as the radially outermost top comer cutting edge, extends from the operative main cutting edge; and the main rake surface associated with the operative main cutting edge and the corner rake surface associated with the operative comer cutting edge are oriented positively; wherein: an imaginary envelope is defined by the rotation of the operative main cutting edge and the operative cornercutting edge about the cutter rotational axis; an acute main tool rake angle 0tm is defined between the main rake surface adjacent the operative main cutting edge and a first normal, defined as perpendicular to the imaginary envelope and intersecting the operative main cutting edge, in a cross section taken in a plane perpendicular to, and intersecting, the operative main cutting edge; an acute comer tool rake angle 9tc is defined between the corner rake surface adjacent the operative corner cutting edge and a second normal, defined as perpendicular to the imaginary envelope and intersecting the operative comer cutting edge, in a cross section taken in a plane intersecting the operative comer cutting edge; and the main tool rake angle and the comer tool rake angle fulfil the following condition: 9tm, 0tc> 0°.

[0016] The main and corner tool rake angles 0tm, 0tc may further fulfil the following condition: 0 <9tm -9tc < 5°.

[0017] The operative main cutting edge may extend substantially perpendicular to the cutter rotational axis.

[0018] Each of the top and bottom surfaces, at each indexable portion, may further comprise a main connection surface connecting the main rake surface and the central main abutment surface, the main connection surface being inclined at a steeper angle relative to the first plane than the main rake surface.

[0019] The central main abutment surface may be planar and oriented perpendicular to the central insert axis.BRIEF DESCRIPTION OF THE FIGURES

[0020] For a better understanding 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:Fig- 1 is a perspective view of a milling cutter in accordance with an aspect of the present application;Fig- 2 is a perspective view of a tool body of the milling cutter of Fig. 1;Fig. 3a is a perspective view of a milling insert of the milling cutter of Fig. 1;Fig. 3b is a bottom view of the milling insert of Fig. 3a;Fig. 3c is a first side view of the milling insert of Fig. 3a;Fig. 3d is a second side view of the milling insert of Fig. 3a;Fig. 3e is a top view of the milling insert of Fig. 3a;Fig. 3f is a corner-side view of the milling insert of Fig. 3a;Fig. 4a is a first cross-sectional view of the milling insert along line A-A in Fig- 3e;Fig. 4b is a second cross-sectional view of the milling insert along line B-B in Fig. 3e;Fig. 4c is a third cross-sectional view of the milling insert along line C-C in Fig. 3e;Fig. 4d is a detailed view of the second cross-sectional view of Fig. 4b;Fig. 5 is a perspective view of the milling cutter of Fig. 1 with an imaginary envelope;Fig. 6 is a detailed view of the milling cutter of Fig. 5;Fig. 7 is a side view of the milling cutter of Fig. 1;Fig. 8 is a detailed view of the milling cutter of Fig. 7;Fig. 9a is a first cross-sectional view of the milling cutter along line I-I in Fig.8;Fig. 9b is a second cross-sectional view of the milling cutter along line II-II in Fig. 8;Fig. 9c is a third cross-sectional view of the milling cutter along line III-III in Fig. 8;Fig. 9d is a fourth cross-sectional view of the milling cutter along line IV-IV in Fig. 8;Fig. 10a is a detailed view of the first cross-sectional view of Fig. 9a;Fig. 10b is a detailed view of the second cross-sectional view of Fig. 9b;Fig. 10c is a detailed view of the third cross-sectional view of Fig. 9c; and Fig. lOd is a detailed view of the fourth cross-sectional view of Fig. 9d.

[0021] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity, or several physical components may be included in one functional block or element. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.DETAILED DESCRIPTION OF THE INVENTION

[0022] The present disclosure will now be described more fully hereinafter with reference to example embodiments thereof with reference to the drawings in which like reference numerals designate identical or corresponding elements in each of the several views. These example embodiments are described so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. However, it will also be apparent to one skilled in the art that the subject matter of the present application can be practiced without the specific configurations and details presented herein. Features from one embodiment or aspect can be combined with features from any other embodiment or aspect in any appropriate combination. The disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. As used in the specification and the appended claims, the singular forms “a,” “an,” “the,” and the like include plural referents unless the context clearly dictates otherwise. As used herein, the phrase “configured such” describes a related element that must be made, suited by nature, character, or designed for a particular use, purpose, or situation.

[0023] First drawing attention to Figs. 1 & 7, a milling cutter 1 is shown. The milling cutter 1 is rotatable about a cutter rotational axis Cl in a rotation direction DR, and has a plurality of triangular milling inserts 20, a tool body 100 and a plurality of fasteners 10. The cutter rotational axis Cl defines a forward cutter direction Fc and an opposing rearward cutter direction Rc. The opposing forward and rearward cutter directions Fc, Rc are parallel to the cutter rotational axis Cl. Specifically, the milling cutter 1 may be referred to as a plunging cutter. Similarly, the milling insert 20 may be referred to, more specifically, as a plunging insert.

[0024] Each milling insert 20 is releasably fastened to the tool body 100 with one of the fasteners 10. Differently worded, the plurality of milling inserts 20 are releasably attached to the tool body 100 via a plurality of fasteners 10. For example, the fastener 10 may be a threaded screw. The tool body 100 is typically made of metal. The milling insert 20 is typically made of materials harder than metal, for example tungsten and cemented carbide.

[0025] Now drawing attention to Figs. 3a to 4c, each milling insert 20 is doublesided (i.e. reversible). The milling insert 20 has a central insert axis C2 about which itis indexable. Specifically, the milling insert 20 is three-way indexable about the central insert axis C2 on each side, meaning the milling insert 20 is six-way indexable in total. The central insert axis C2 defines a top insert direction Ti and an opposite bottom insert direction Bi. The opposing top and bottom insert directions Ti, Bi are parallel to the central insert axis C2.

[0026] The milling insert 20 includes a top surface 24, an opposite bottom surface 26 and an insert peripheral surface 50. The milling insert 20 further includes three insert corners 29. The top surface 24 is located farther in the top insert direction Ti relative to the bottom surface 26 (i.e. the top surface 24 is forward of the bottom surface 26, in the top insert direction Ti). Generally speaking, the top surface 24 faces in the top insert direction Ti. The bottom surface 26 is located farther in the bottom insert direction Bi relative to the top surface 24 (i.e. the bottom surface 26 is forward of the top surface 24, in the bottom insert direction Bi). The insert peripheral surface 50 connects the top and bottom surfaces 24, 26. The insert peripheral surface 50 extends about the central insert axis C2. Optionally, the insert peripheral surface 50 is centered about the central insert axis C2.

[0027] The milling insert 20 further includes a plurality of top main cutting edges 70, curved top comer cutting edges 72, bottom main cutting edges 74 and curved bottom corner cutting edges 76. Each of the top main cutting edges 70 and the top corner cutting edges 72 are formed at the intersection of the top surface 24 and the insert peripheral surface 50. Each of the bottom main cutting edges 74 and the bottom corner cutting edges 76 are formed at the intersection of the bottom surface 26 and the insert peripheral surface 50.

[0028] A first plane Pl is located between the top and bottom surfaces 24, 26. The central insert axis C2 is perpendicular to the first plane Pl. Optionally, the first plane Pl may be located mid-way between the top and bottom surfaces 24, 26.

[0029] Each of the top and bottom surfaces 24, 26 includes a central main abutment surface 28, a plurality of main rake surfaces 30 and a plurality of corner rake surfaces 32. Specifically, each of the top and bottom surfaces 24, 26 includes three main rake surfaces 30 and three corner rake surfaces 32. Optionally, each main abutment surface 28 may be planar. Each main abutment surface 28 may further be oriented perpendicular to the central insert axis C2 (i.e. extend parallel to the first plane Pl).Optionally, each main abutment surface 28 may be sunken into the milling insert 20relative to its respective main and corner rake surfaces 30, 32. Differently worded, the main abutment surface 28 may be located closer to the first plane Pl than its respective main and comer rake surfaces 30, 32.

[0030] In some embodiments, an insert bore 42 may extend along the central insert axis C2 and open out to the top and bottom surfaces 24, 26 of the milling insert 20. Optionally, the insert bore 42 may be coaxial with the central insert axis C2. Further optionally, the insert bore 42 may open out to the main abutment surface 28 of the top and bottom surfaces 24, 26 of the milling insert 20.

[0031] The main abutment surface 28 is encircled by circumferentially alternating main rake surfaces 30 and comer rake surfaces 32. Each main rake surface 30 connects two corner rake surfaces 32 which are adjacent to one another. Each comer rake surface 32 is curved (i.e. non-planar). Optionally, each main rake surface 30 may be planar.

[0032] As seen in Fig. 3b, the milling insert 20 comprises three indexable portions 22. The three indexable portions 22 are circumferentially adjacent to one another and may be separately referred to as a first indexable portion 23a, a second indexable portion 23b and a third indexable portion 23c. Each indexable portion 22 encompasses a portion of the top surface 24, a portion of the bottom surface 26 and a portion of the insert peripheral surface 50. That is to say, the three indexable portions 22 divide up the top surface 24, the bottom surface 26 and the insert peripheral surface 50. Optionally, the indexable portions 22 may circumferentially partition the milling insert 20.

[0033] Each indexable portion 22 includes one main rake surface 30 and one corner rake surface 32 at each of the top and bottom surfaces 24, 26. Differently worded, each indexable portion 22 includes two main rake surfaces 30 and two corner rake surfaces 32. One main rake surface 30 and one corner rake surface 32 are part of the top surface 24. The other main rake surface 30 and the other comer rake surface 32 are part of the bottom surface 26.

[0034] The milling insert 20 is triangular. Thus, the number of indexable portions 22 is exactly three. In milling operations, and specifically in plunging operations, it is desirable to provide indexable milling inserts with more operable cutting edges. Due to the nature of plunging operations the cutting edge in operation can be split into two portions, one directed along, and cutting, the floor of the workpiece being machined. The other portion extends along, and cuts, the shoulder of the workpiece. To avoiddamaging other comers of the milling insert, for example, the insert must be configured such that the portion of the cutting edge that extends along, and cuts the shoulder of the workpiece is the radially outermost element, with other elements (such as the comers of the insert not participating in the cutting operation directly) being recessed relative thereto. In rectangular cutting inserts this is achieved by having only two comers operable out of the four corners (the other two being recessed relatively), thus each side of the insert is only two-way indexable.

[0035] The three indexable portions 22 may equally divide the milling insert 20. For example, in Fig. 3b, the milling insert 20 is shown to be triangular with exactly three indexable portions 22 equally dividing the milling insert 20. Having an insert divided into equal portions ensures indexability of the insert in a milling cutter, allowing for a plurality of replaceable cutting edges on the same insert. Optionally, the indexable portions 22 may be identical.

[0036] The insert peripheral surface 50 includes three main peripheral surfaces 52 circumferentially alternating with three curved comer peripheral surfaces 60. Each corner peripheral surface 60 is located at a respective insert corner 29. Specifically, at each indexable portion 22, the insert peripheral surface 50 includes one main peripheral surface 52 and one comer peripheral surface 60 extending from the main peripheral surface 52. The comer peripheral surface 60 is located adjacent to the corner rake surface 32. Each corner peripheral surface 60 connects two adjacent main peripheral surfaces 52. Optionally, each indexable portion 22 includes exactly one main peripheral surface 52 and exactly one corner peripheral surface 60. Optionally, the insert peripheral surface 50 includes exactly three main peripheral surfaces 52 and exactly three corner peripheral surfaces 60.

[0037] The three indexable portions 22 divide the milling insert 20 such that each indexable portion 22 includes one main peripheral surface 52 and a respective comer peripheral surface 60 extending therefrom. At each indexable portion 22 the milling insert 20 includes one insert corner 29. The insert comer 29 includes the comer peripheral surface 60 and two comer rake surfaces 32, each corner rake surface 32 belonging to one of the top and bottom surfaces 24, 26.

[0038] The main peripheral surface 52 of each indexable portion 22 includes a top main relief surface 54, a bottom main relief surface 56 and a side abutment surface 58 located between the top and bottom main relief surfaces 54, 56. The top main reliefsurface 54 intersects the top surface 24. The bottom main relief surface 56 intersects the bottom surface 26. The side abutment surface 58 connects the top main relief surface 54 and the bottom main relief surface 56.

[0039] The comer peripheral surface 60 includes a top comer relief surface 62 and a bottom comer relief surface 64. A comer side surface 66 connects the top and bottom corner relief surfaces 62, 64. The top corner relief surface 62 intersects the top surface 24. The bottom corner relief surface 64 intersects the bottom surface 26. Optionally, the top comer relief surface 62 extends from the top main relief surface 54 and the bottom corner relief surface 64 extends from the bottom main relief surface 56.

[0040] In some embodiments the side abutment surface 58 is at least partially planar, and optionally completely planar. The top and bottom main relief surfaces 54, 56 may be planar, and may further be coplanar with the side abutment surface 58. That is to say, the main peripheral surface 52 may be planar. Each main peripheral surface 52 may be parallel to the central insert axis C2. The corner peripheral surface 60 may curve continuously. Each comer peripheral surface 60 may be parallel to the central insert axis C2. The aforementioned configuration of each main peripheral surface 52 and each corner peripheral surface 60 parallel to the central insert axis C2 is commonly seen in so-called negative inserts, such as the embodiment shown in the figures. In such cases a relief angle with respect to the workpiece is created by tilting the negative insert in the cutter, as will be discussed below.

[0041] Each indexable portion 22 further includes one top main cutting edge 70, one top corner cutting edge 72, one bottom main cutting edge 74 and one bottom corner cutting edge 76. The top main cutting edge 70 is formed at the intersection of the top surface 24 and the main peripheral surface 52 (specifically the top main relief surface 54). Optionally, the top main cutting edge 70 may be formed at an intersection of a land surface 44 of the top surface 24 and the top main relief surface 54. The land surface 44 is typically used to maintain cutting edge strength and extends from a respective rake surface to a respective cutting edge. Optionally, the land surface 44 is of constant width along the entire circumference of the milling insert 20.

[0042] Similarly, the bottom main cutting edge 74 is formed at an intersection of the bottom surface 26 and the main peripheral surface 52 (specifically the bottom main relief surface 56). Each main rake surface 30 is elongated along one of the top and bottom main cutting edges 70, 74 (i.e. in a direction transverse to the central insert axisC2). The top corner cutting edge 72 extends from the top main cutting edge 70. The top corner cutting edge 72 is formed at an intersection of the top surface 24 and the corner peripheral surface 60 (specifically the top corner relief surface 62). The bottom corner cutting edge 76 extends from the bottom main cutting edge 74. The bottom corner cutting edge 76 is formed at an intersection of the bottom surface 26 and the corner peripheral surface 60 (specifically the bottom corner relief surface 64). Each corner rake surface 32 extends along one of the top and bottom comer cutting edges 72, 76 (i.e. in a direction transverse to the central insert axis C2). The insert corner 29 further includes the top and bottom corner cutting edges 72, 76 and their respective corner rake surfaces 32.

[0043] In some embodiments, each indexable portion 22 includes exactly one insert corner 29. Similarly, each indexable portion 22 includes exactly one top main cutting edge 70 and exactly one bottom main cutting edge 74. Each top main cutting edge 70 connects two circumferentially adjacent top corner cutting edges 72. Each bottom main cutting edge 74 connects two circumferentially adjacent bottom comer cutting edges 76. Optionally, the top and bottom main cutting edges 70, 74 are straight. Additionally, the top and bottom main cutting edges 70, 74 may be parallel to the first plane Pl and thus perpendicular to the central insert axis C2.

[0044] As shown in Fig. 4a, a main insert rake angle 0rm is defined between the main rake surface 30 and the first plane Pl. The main insert rake angle 0rm is an acute angle. Specifically, the main insert rake angle 0rm is defined in a cross section perpendicular to, and intersecting, one of the top and bottom main cutting edges 70, 74. The cross section may be defined as taken in a plane perpendicular to, and intersecting, one of the top and bottom main cutting edges 70, 74.

[0045] As shown in Fig. 4d, a corner insert rake angle Orc is defined between the corner rake surface 32 and the first plane Pl. The corner insert rake angle Orc is an acute angle. Further, the corner insert rake angle Orc is defined in a cross section perpendicular to, and intersecting, one of the top and bottom corner cutting edges 72, 76. Specifically, the cross section is perpendicular to a tangent line Tg. The tangent line Tg is defined as being tangent, at the cross section, to a respective corner cutting edge. In this case, the tangent line is tangent to one of the top and bottom corner cutting edges 72, 76. Differently worded, the comer insert rake angle Orc is defined, in a cross sectionperpendicular to a tangent line Tg, between the comer rake surface 32 and the first plane Pl.

[0046] For example, cross-section lines A-A, B-B, C-C in Fig. 3e (with their respective views in Figs. 4a to 4c) are each perpendicular to a line which is tangent to the cutting edge at the intersection of the cross-section line and the cutting edge (i.e. tangent line Tg). Similarly, cross-section lines I-I, II-II, III-III, IV-IV in Fig. 8 (with their respective views in Figs. 9a to lOd) are each perpendicular to a line which is tangent to the cutting edge at their intersection (i.e. tangent line Tg). Note that the cross sections in Figs. 4a, 9b and 10b do not show the main abutment surface 28.

[0047] The main insert rake angle 0rm and the comer insert rake angle Orc fulfil the following condition: 9rm<9rc. Differently worded, the corner insert rake angle Orc is greater than the main insert rake angle 0rm. When such a double-sided negative milling insert is placed (at a tilt, as will be discussed below) as part of a milling cutter, the rake surface at the corner of the milling insert is inclined more steeply than the rake surface along the main cutting edge. The condition mentioned above ensures that chips flow smoothly without interacting with the rake surface at the comer of the insert. This may, for example, extend the longevity of the milling insert.

[0048] In some embodiments the main insert rake angle 0rm and the corner insert rake angle Orc further fulfil the following condition: 2°<9rc-9rm<10°. Specifically, the main insert rake angle 0rm and the corner insert rake angle Orc may additionally fulfil the following condition: 3°<9rc-9rm<8°. In choosing the angle difference between the main insert rake angle 0rm and the corner insert rake angle Orc there are a few considerations which need to be taken into account.

[0049] For example, the overall geometry of the milling insert must be considered. On the one hand, it would be desirable to ensure the rake angle difference is minimal after the milling insert is seated in the milling cutter. However, when changing the rake angle at the corner, the surfaces adjacent to the rake surface at the comer will be warped to compensate. For example, “dimples” (i.e. sunken portions) may appear at the comers of the milling insert to provide the angle difference. Such “warped” surfaces may hamper chip evacuation (during machining operations), create challenges in the manufacturing process (of the cutting insert) or weaken the cutting edge at the comer of the insert, to name a few possibilities.

[0050] In some embodiments, the main insert rake angle Orm and the corner insert rake angle Orc fulfil the following conditions: 10°< Orm < 30°, 15°< 9rc< 35°. The main insert rake angle Orm and the comer insert rake angle Orc may further fulfil the following conditions: 15°< Orm < 25°, 20°< 9rc< 30°. Specifically, the main insert rake angle Orm and the corner insert rake angle Orc may further fulfil the following conditions: 18°< 6rm < 23°, 21°< 6rc< 28°. These angle ranges may, for example, ensure that the insert will perform well during plunging operations while the angle difference between the main insert rake angle Orm and the corner insert rake angle Orc is in a desirable range.

[0051] Now referring to Fig. 4b, a main rake width Lm is defined as the width of the main rake surface 30 in a cross section perpendicular to, and intersecting, the associated (i.e. respective) one of the top and bottom main cutting edges 70, 74.Specifically, the main rake width Lm is defined in a direction from a respective one of the top and bottom main cutting edges 70, 74 towards a respective main abutment surface 28 (i.e. the main abutment surface 28 on the same surface of the top and bottom surfaces 24, 26 as the main rake surface 30).

[0052] A corner rake width Lc is defined as the width of the corner rake surface 32 in a cross section perpendicular to, and intersecting, the associated one of the top and bottom comer cutting edges 72, 76. Specifically, the corner rake width Lc is defined in a direction from a respective one of the top and bottom corner cutting edges 72, 76 towards a respective main abutment surface 28.

[0053] In some embodiments, the main rake width Lm and the comer rake width Lc fulfil the following condition: Lc>0.8*Lm. Specifically, the main rake width Lm and the corner rake width Lc may further fulfil the following condition: Lc>0.9*Lm. Generally, the width of a rake surface in a milling insert in metal cutting operations has to be maintained at a minimal value. This ensures the chips, which curl about themselves, flow smoothly. Otherwise other surfaces (which are not designed with the formation of chips in mind) may, if too close to the cutting edge, interact with the chips during machining operations.

[0054] The width of the corner rake surface 32 (i.e. the comer rake width Lc) is impacted due to the higher values of the corner insert rake angle Orc. Note that in most cases the comer rake width Lc is greater than the main rake width Lm. This is not the case in the embodiment shown due to the changes made to the comer rake angle Orc.

[0055] If the corner rake width Lc is too small then, as discussed above, chips may interact with other surfaces of the milling insert 20, resulting in reduced lifespan. It is desired that any interaction between materials being machined and the milling insert 20 is limited to cutting edges and lands (such as the land surface 44), as otherwise cracks may form on the milling insert 20, for example.

[0056] On the other hand, if the comer rake width Lc is too large, then the cutting edge at the insert comer 29 (i.e. one of the top and bottom corner cutting edges 72, 76) may, for example, become fragile (due to the region having a reduced thickness). Other examples may be that, if the region around the insert comer 29 is thickened (as will be discussed below), a larger comer rake width Lc may cause problems with the chip flow or with complications in manufacture of the milling insert 20.

[0057] In some embodiments, each of the top and bottom surfaces 24, 26, at each indexable portion 22, may include a main connection surface 34. Each main connection surface 34 connects a respective main rake surface 30 and the main abutment surface 28. The main connection surface 34 is at a different incline relative to its respective main rake surface 30. Specifically, the main connection surface 34 slopes towards the main abutment surface 28 at a steeper incline, relative to the main rake surface 30. A main connection surface 34 may help maintain a main abutment surface 28 at a certain minimal size while also allowing a main abutment depth Dm of the main abutment surface 28 to be increased. The main abutment depth Dm is defined as the maximum height parallel to the central insert axis C2 from the main abutment surface 28 to a respective one of the top and bottom main cutting edges 70, 74. The main abutment depth Dm being large may, for example, facilitate chip flow during machining operations.

[0058] In some embodiments, the top and bottom corner cutting edges 72, 76 are not raised. That is to say, the top and bottom comer cutting edges 72, 76 are level with their respective top and bottom main cutting edges 70, 74 (i.e. they all lie in a common plane). Differently worded, if the main abutment depth Dm was measured from the main abutment surface 28 to a respective one of the top and bottom corner cutting edges 72, 76 instead, the main abutment depth Dm would be constant (i.e. not change). Optionally, the top main cutting edges 70 and the top corner cutting edges 72 may all be parallel to the first plane Pl. Similarly, the bottom main cutting edges 74 and the bottom corner cutting edges 76 may all be parallel to the first plane Pl.

[0059] Referring back to Fig. 4d, in some embodiments, each of the top and bottom surfaces 24, 26, at each indexable portion 22, may include a corner connection surface 36. Each corner connection surface 36 connects the corner rake surface 32 and the main abutment surface 28. The corner connection surface 36 is at a different incline, relative to its respective corner rake surface 32. The corner connection surface 36 may include a first corner connection portion 38 and a second corner connection portion 40. The second comer connection portion 40 is located farther from the comer rake surface 32 than the first corner connection portion 38. The first corner connection portion 38 is located closer to its respective corner rake surface 32 relative to the second corner connection portion 40.

[0060] A first corner connection angle Occi is defined between the first plane Pl and the first corner connection portion 38 in a cross section perpendicular to, and intersecting, one of the top and bottom comer cutting edges 72, 76. The first corner connection angle Occi is an acute angle. A second corner connection angle 0cc2 is defined between the first plane Pl and the second corner connection portion 40 in a cross section perpendicular to, and intersecting, one of the top and bottom comer cutting edges 72, 76. The second corner connection angle 0cc2 is an acute angle.

[0061] In some embodiments the first and second corner connection angles 0cci ,0cc2 fulfil the following conditions: 9Cci<9rc, 9Cd<9Cc2. Differently worded, each of the main rake surface 30 and the second corner connection portion 40 slope towards the main abutment surface 28 at a steeper incline, relative to the first comer connection portion 38. Such geometry at the insert comer 29 may ensure a more robust cutting edge at the insert corner 29 (i.e. the top and bottom comer cutting edges 72, 76).

[0062] As shown in Fig. 3b, a corner angle 0Cis defined between two adjacent side abutment surfaces 58. Differently worded, the corner angle 0Cis defined between the side abutment surface 58 of one of the indexable portions 22 and the side abutment surface 58 of an adjacent indexable portion 22. For example, in the embodiment shown in the figures, the first and second indexable portions 23a, 23b are adjacent to one another and thus the corner angle may be formed therebetween. Similarly, the first and third indexable portions 23a, 23c are adjacent to one another in the present embodiment as well as the second and third indexable portions 23b, 23c.

[0063] In some embodiments, the corner angle 0c fulfils the following condition: 9c<60°. Although the axial extent (i.e. the extent in the direction of the cutter rotationalaxis Cl) of the operative cutting edge of triangular milling inserts with such a condition is significantly shorter (as it only includes a portion of the comer cutting edge), relative to rectangular milling inserts or trigonal inserts (which may, for example, have an additional straight axial extent of the cutting edge), it was found desirable to provide triangular milling inserts with an additional operable corner which is also compact, which may be preferred in some operations.

[0064] Referring to Fig. 3e, in some embodiments, a corner bisector plane Be is defined. The comer bisector plane Be contains the central insert axis C2 and bisects the corner angle 0C. The associated corner rake surface 32 may be asymmetrical about the corner bisector plane Be. Specifically, the corner rake surface 32 lacks mirror symmetry about the comer bisector plane Be. In such cases the same milling insert 20 will not work in a similar manner in both left-hand and right-hand milling cutters. However, although a short portion of the comer cutting edge located on one side of the comer bisector plane Be does not participate in the cutting operation (as will be discussed below), this asymmetry allows further adjustment of the comer insert rake angle Orc to a more desirable angle range.

[0065] The corner bisector plane Be may further bisect the side abutment surface 58 opposite to the corner angle 0Cwhich it bisects. The associated main rake surface 30 may be symmetrical about the corner bisector plane Be.

[0066] Referring now to Figs. 1, 2 and 5 to lOd, the tool body 100 includes a coupling portion 102 and a cutting portion 110. The cutting portion 110 is located forwardly of the coupling portion 102 (i.e. located farther in the forward cutter direction Fc) and includes a forward end surface 114, a peripheral tool surface 120 and a plurality of insert seats 130. The plurality of insert seats 130 are circumferentially spaced about the cutter rotational axis Cl. Optionally, the cutting portion 110 may further include a plurality of flutes 124.

[0067] The forward end surface 114 faces in the forward cutter direction Fc. The peripheral tool surface 120 connects the forward end surface 114 to the coupling portion 102. Each insert seat 130 opens out to the forward end surface 114 and to the peripheral tool surface 120. Each flute 124 opens out to the forward end surface 114 and to the peripheral tool surface 120. Each insert seat 130 may further open out to a respective one of the flutes 124.

[0068] Each insert seat 130 includes a main seat surface 132 and a first side seat surface 136. The main seat surface 132 faces in the rotation direction DR and also in the forward cutter direction Fc. Specifically, as shown in Fig. 7, the main seat surface 132 is tilted (i.e. inclined) in the forward cutter direction Fc at a seating angle 0S. The seating angle 0Sis defined between the cutter rotational axis Cl and a second plane P2.The second plane P2 is parallel to the main seat surface 132. If the main seat surface 132 is not planar the second plane P2 may then be defined as perpendicular to an average direction summed from normals to (i.e. lines perpendicular to) portions of the main seat surface 132 facing in different directions.

[0069] In some embodiments, the seating angle 0Sfulfils the following condition: 3°< 9s < 15°. The seating angle 0Smay further fulfil the following condition: 5°< 9S< 10°. The seating angle 0Sensures that any cutting edges located rotationally behind the respective insert's operative cutting edge (i.e. located in a direction opposite to the rotation direction DR) are relieved from the workpiece during machining.

[0070] Referring to Fig. 7, the first side seat surface 136 is facing away from the cutter rotational axis Cl (i.e. facing radially outwards). Optionally, each insert seat 130 may further include a second side seat surface 138. The second side seat surface 138 is facing towards the cutter rotational axis Cl (i.e. facing radially inwards). The second side seat surface 138 may further brace the milling insert 20 against cutting forces arising during machining operations.

[0071] Each milling insert 20 is seated within an insert seat 130. The bottom surface 26 of each milling insert 20 abuts the main seat surface 132 of a respective insert seat 130. The fastener 10 releasably fastens the milling insert 20 to the insert seat 130.Optionally, on assembly of the milling cutter 1, the fastener 10 may pass through the insert bore 42 and engage with a fastener bore 134 formed in the tool body 100. The fastener bore 134 is located at the insert seat 130 and opens out to the main seat surface 132. The fastener bore 134 may be threaded and the fastener 10 may be a threaded screw which threadingly engage with one another.

[0072] An operative main cutting edge 70’ is defined as the forwardmost top main cutting edge 70 (i.e. located axially forwardly relative to the other top main cutting edges 70). The operative main cutting edge 70’ extends transversely to the cutter rotational axis Cl. That is to say, in some views (not shown) the operative main cutting edge 70’ intersects the cutter rotational axis Cl. In other words, the operative maincutting edge 70’ is not parallel to the cutter rotational axis Cl. Specifically, the operative main cutting edge 70’ may extend substantially perpendicular to the cutter rotational axis Cl. Optionally, the operative main cutting edge 70’ may be exactly perpendicular to the cutter rotational axis Cl.

[0073] An operative corner cutting edge 72’ is defined as the radially outermost top corner cutting edge 72 (i.e. located radially farthest from the cutter rotational axis Cl relative to the other top corner cutting edges 72). The operative corner cutting edge 72’ extends from the operative main cutting edge 70’ and curves along its respective insert corner 29.

[0074] Note that the operative main cutting edge 70’ and the operative comer cutting edge 72’ do not necessarily belong to the same indexable portion 22 as defined. For example, to make full use of the milling insert 20, it may be flipped, allowing the operative main cutting edge 70’, as well as the operative corner cutting edge 72’, to be on any of the top and bottom surfaces 24, 26. An indexable portion 22 may encompass the operative main cutting edge 70’ as well as the operative corner cutting edge 72’ at the top surface 24. However, when the milling insert 20 is flipped, the same indexable portion 22 may encompass the new operative main cutting edge 70’, but at the same time this same indexable portion may exclude, the new operative corner cutting edge 72’.

[0075] Now referring to Figs. 5 & 6, an imaginary envelope Ieis shown, marked by hatched lines. The imaginary envelope Ieis defined by the operative main cutting edge 70’ and the operative corner cutting edge 72’ as they rotate about the cutter rotational axis Cl in the rotation direction DR. Note that the imaginary envelope Ie shown is a segment, and on further rotation of the milling cutter 1 (in the rotation direction DR) said envelope would, eventually, become an annularly extending ring-shaped envelope encircling the cutter rotational axis Cl.

[0076] The main rake surface 30 associated with the operative main cutting edge 70’ and the comer rake surface 32 associated with the operative corner cutting edge 72’ are oriented positively. In some embodiments, it may be desirable to accommodate positively oriented inserts in milling cutters (and specifically plunging tools) with tilted insert seats 130. Positively oriented inserts are defined by the angle between the rake surface and the workpiece (not shown) being machined, which is emulated by the imaginary envelope Ie. If the angle is greater than 90° the insert is considered to have apositive rake orientation. Otherwise, the insert is considered to have a negative rake orientation.

[0077] As shown in Figs. 10a & 10b, a main tool rake angle Otm is defined between the main rake surface 30 adjacent the operative main cutting edge 70’ and a first normal Nl, in a cross section perpendicular to, and intersecting, the operative main cutting edge 70’. The main tool rake angle Otm is an acute angle. The first normal Nl is defined as perpendicular to the imaginary envelope Ieand intersecting the operative main cutting edge 70’.

[0078] As shown in Figs. 10c & lOd, corner tool rake angle Otc is defined between the corner rake surface 32 adjacent the operative comer cutting edge 72’ and a second normal N2, in a cross section intersecting the operative corner cutting edge 72’ and perpendicular to the tangent line Tg. The corner tool rake angle Otc is an acute angle. The second normal N2 is defined as perpendicular to the imaginary envelope Ieand intersecting the operative corner cutting edge 72’.

[0079] The main tool rake angle Otm and the comer tool rake angle Otc fulfil the following condition: Otm, Otc > 0°. This condition ensures that, during machining operations, chips can flow smoothly without contacting the milling insert 20.

[0080] In some embodiments, the main tool rake angle Otm and the comer tool rake angle Otc fulfils the following condition: 0° < 9tm-9tc< 5°. The main tool rake angle Otm and the comer tool rake angle Otc may further fulfil the following condition: 0° < 9tm-9tc < 3°. Additionally, the main tool rake angle Otm and the comer tool rake angle Otc may further fulfil the following condition: 0° < 9tm-9tc < 2°.

[0081] As explained above, when the milling insert 20 is seated in its respective insert seat 130 in which the main seat surface 132 is tilted at a seating angle 0S, the tilt causes an angle difference between the rake angles at the corner edge and the rake angles along the main edge. It is desirable to ensure that the main and corner tool rake angles Otm, Otc are equal (i.e. 9tm-9tc = 0°), however due to different considerations, as specified above, that is not always possible. As such, defining the maximal difference between the rake angles may ensure optimal angle differences. The different ranges may, for example, correspond for machining different types of materials - some materials may be more brittle, some may be more elastic etc., all of which require different designs for inserts to cut optimally.

[0082] Now referring to Fig. 8, a radially outermost end-cut point Ep is shown. The end-cut point Ep is defined as a point, on the operative corner cutting edge 72’, located farthest from the cutter rotation axis Cl. Optionally, another definition may be that the end-cut point Ep is defined as a point, on the operative comer cutting edge 72’, where the tangent line Tg to said point is parallel to the cutter rotation axis Cl. Note that the operative comer cutting edge 72’ is located radially outwards relative to the operative main cutting edge 70’.

[0083] Any portion of the operative corner cutting edge 72’ located after the end-cut point Ep, in a direction away from the operative main cutting edge 70’ (in this case this direction coincides partially with the rearward cutter direction Rc), does not participate in the machining operation. The depth of cut of the milling cutter may be defined by the distance between the operative main cutting edge 70’ and the end-cut point Ep.

[0084] While several embodiments of the disclosure have been shown in the drawings, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Any combination of the above embodiments is also envisioned and is within the scope of the appended claims. Therefore, the above description should not be constmed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope of the claims appended hereto.

Claims

CLAIMSWhat is claimed is:

1. A triangular double-sided milling insert (20) comprising:a top surface (24), an opposite bottom surface (26), and an insert peripheral surface (50) connecting the top and bottom surfaces (24, 26), with a first plane Pl located between the top and bottom surfaces (24, 26), and a central insert axis C2 perpendicular to the first plane Pl about which the milling insert (20) is indexable;the insert peripheral surface (50) comprising three main peripheral surfaces (52) circumferentially alternating with three curved corner peripheral surfaces (60);three indexable portions (22), each indexable portion (22) including one main peripheral surface (52) and one corner peripheral surface (60);at each indexable portion (22):top and bottom main cutting edges (70, 74) are formed at the intersection of the main peripheral surface (52) and the top and bottom surfaces (24, 26), respectively;top and bottom corner cutting edges (72, 76) are formed at the intersection of the comer peripheral surface (60) and the top and bottom surfaces (24, 26), respectively;each of the top and bottom surfaces (24, 26) comprises a central main abutment surface (28), three main rake surfaces (30), and three curved corner rake surfaces (32), each main rake surface (30) located adjacent to one of the top or bottom main cutting edges (70, 74), and each corner rake surface (32) located adjacent to one of the top or bottom comer cutting edges (72, 76);an acute main insert rake angle Orm is defined between the main rake surface (30) and the first plane Pl, in a cross section perpendicular to, and intersecting, one of the top or bottom main cutting edges (70, 74); andan acute corner insert rake angle 0rcis defined between the corner rake surface (32) and the first plane Pl, in a cross sectionperpendicular to, and intersecting, one of the top or bottom comer cutting edges (72, 76);wherein:the corner insert rake angle 9rcis greater than the main insert rake angle 0mi.

2. The milling insert (20) according to claim 1, wherein:the main insert rake angle Orm and the corner insert rake angle 9rcfulfil the following condition:2°<9rc -9rm<10°.

3. The milling insert (20) as claimed in claims 1-2, wherein:the main insert rake angle 9rm and the corner insert rake angle 9rcfulfil the following conditions:10° < 9nn< 30° , 15° < 9rc< 35° .

4. The milling insert (20) as claimed in claims 1-3, wherein:a main rake width Lm, defined as the width of the main rake surface (30) in a cross section perpendicular to, and intersecting, the associated one of the top or bottom main cutting edges (70, 74), and a corner rake width Lc, defined as the width of the comer rake surface (32) in a cross section perpendicular to, and intersecting, the associated one of the top or bottom corner cutting edges (72, 76), fulfil the following condition: Lc>0.8*Lm.

5. The milling insert (20) as claimed in claims 1-4, wherein:each of the top and bottom surfaces (24, 26), at each indexable portion (22), further comprises:a corner connection surface (36) connecting the comer rake surface (32) and the main abutment surface (28), the corner connection surface (36) comprising:a first corner connection portion (38) and a second corner connection portion (49) located farther from the cornerrake surface (32) than the first comer connection portion (38);wherein:an acute first corner connection angle 0cci, defined between the first plane Pl and the first corner connection portion (38) in a cross section perpendicular to, and intersecting, one of the top or bottom corner cutting edges (72, 76), and an acute second corner connection angle 0Cc2, defined between the first plane Pl and the second corner connection portion (40) in a cross section perpendicular to, and intersecting, one of the top or bottom corner cutting edges (72, 76), fulfil the following conditions:Occl Oic, 0ccl 0cc2.

6. The milling insert (20) as claimed in claim 5, wherein:each indexable portion (22) comprises exactly one insert corner (29).

7. The milling insert (20) as claimed in claim 6, wherein:a comer angle 0C, defined between two adjacent side abutment surfaces (58), fulfils the following condition:9c<60°.

8. The milling insert (20) as claimed in claims 1-7, wherein:a comer bisector plane Be contains the central insert axis C2 and bisects a comer angle 9c, defined between two adjacent side abutment surfaces (58); and the associated corner rake surface (32) is asymmetrical about the comer bisector plane Be.

9. The milling insert (20) as claimed in claims 1-8, wherein each of the top and bottom surfaces (24, 26), at each indexable portion (22), further comprises a main connection surface (34) connecting the main rake surface (30) and the central main abutment surface (28), the main connection surface (34) being inclined at a steeper angle relative to the first plane Pl than the main rake surface (30).

10. The milling insert (20) as claimed in claims 1-9, wherein:the central main abutment surface (28) is planar and oriented perpendicular to the central insert axis C2.

11. A milling cutter (1) rotatable about a cutter rotational axis Cl defining a rotation direction DR and opposing forward and rearward cutter directions Fc, Rc, the milling cutter (1) comprising:a tool body (100);a plurality of fasteners (10); anda plurality of milling inserts (20) as claimed in claims 1-10, each milling insert (20) being releasably fastened to the tool body (100) via a fastener (10).

12. The milling cutter (1) as claimed in claim 11, wherein the tool body (100) comprises:a coupling portion (102) and a cutting portion (110) located forwardly of the coupling portion (102), the cutting portion (110) comprising:a forward end surface (114) facing in the forward cutter direction Fc; a peripheral tool surface (120) connecting the forward end surface (11 ) to the coupling portion (102); anda plurality of insert seats (130) circumferentially spaced about the cutter rotational axis Cl, each insert seat (130) opening out to the forward end surface (114) and the peripheral tool surface (120), each insert seat (130) comprising a main seat surface (132) facing in the rotation direction DR and facing in the forward cutter direction Fc at a seating angle 0S, defined between the cutter rotational axis Cl and a second plane P2 parallel to the main seat surface (132);the bottom surface (26) of each milling insert (20) abuts the main seat surface (132) of a respective insert seat (130);an operative main cutting edge (70’), defined as the forwardmost top main cutting edge, extends transversely with respect to the cutter rotational axis Cl;an operative corner cutting edge (72’), defined as the radially outermost top comer cutting edge (72), extends from the operative main cutting edge (70’); andthe main rake surface (30) associated with the operative main cutting edge (70’) and the corner rake surface (32) associated with the operative corner cutting edge (72’) are oriented positively;wherein:an imaginary envelope Ieis defined by the rotation of the operative main cutting edge (70’) and the operative comer cutting edge (72’) about the cutter rotational axis Cl;an acute main tool rake angle Otm is defined between the main rake surface (30) adjacent the operative main cutting edge (70’) and a first normal Nl, defined as perpendicular to the imaginary envelope Ieand intersecting the operative main cutting edge (70’), in a cross section taken in a plane perpendicular to, and intersecting, the operative main cutting edge (70’); an acute comer tool rake angle Otc is defined between the corner rake surface (32) adjacent the operative corner cutting edge (72’) and a second normal N2, defined as perpendicular to the imaginary envelope Ieand intersecting the operative corner cutting edge (72’), in a cross section taken in a plane intersecting the operative comer cutting edge (72’); and the main tool rake angle Otm and the comer tool rake angle Otc fulfil the following condition:Otm, Otc — 0°.

13. The milling cutter (1) as claimed in claim 12, wherein:the main and corner tool rake angles Otm, Otc further fulfil the following condition:0 <0tm -Otc < 5°.

14. The milling cutter (1) as claimed in claims 12-13, wherein:the operative main cutting edge (70’) extends substantially perpendicular to the cutter rotational axis (Cl).

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