Cutting insert for a milling tool and milling tool

A cutting insert for a milling tool, having a first side, a second side which is identical to the first side and a circumferential surface which extends between the first and the second sides, with a bore which extends along a bore axis. The cutting insert is 120° rotationally symmetrical with respect to the bore axis and includes on each of the first side and the second side three identically formed cutting regions, respectively, which are situated at a transition between the first side and the circumferential surface or at a transition between the second side and the circumferential surface, respectively. Each of the in total six cutting regions includes a first rectilinear cutting edge, a second rectilinear cutting edge, and a third arcuate cutting edge, wherein a first end of the first cutting edge is connected to a first end of the third cutting edge, and a first end of the second cutting edge is connected to a second end of the third cutting edge, wherein the first and the second cutting edges are of same length. The cutting insert includes on the first side a first contact surface which extends orthogonally to the bore axis and lies in a first contact plane, and on the second side includes a second contact surface which extends orthogonally to the bore axis and lies in a second contact plane, and wherein each of the first cutting edges are connected at their second ends, which are located opposite the first ends, to one of a total of six arcuate edges, a vertex of which is located between the first and the second contact planes.

BACKGROUND OF THE INVENTION

This disclosure relates to a cutting insert for a milling tool. This disclosure furthermore relates to a milling tool having such a cutting insert, a tool holder and a fastening element for fastening the cutting insert to the tool holder.

The cutting insert according to the disclosure is a double-sided indexable cutting insert which is used, in particular, in milling tools. It has a first side, a second side which is identical to the first side and a circumferential surface which extends between the first and the second side. In addition, the cutting insert comprises a bore which extends along a bore axis, wherein the cutting insert is 120° rotationally symmetrical with respect to the bore axis. The cutting insert comprises on each of the first side and the second side three identically formed cutting regions, respectively, which are situated at a transition between the first side and the circumferential surface or at a transition between the second side and the circumferential surface, respectively. On account of the double-sided realization of the cutting insert (identical first side and second side), a total of six cutting regions are produced. Each of said six cutting regions comprises a rectilinear first cutting edge, a rectilinear second cutting edge and an arcuate third cutting edge, wherein a first end of the first cutting edge is connected directly to a first end of the third cutting edge, and a first end of the second cutting edge is connected directly to a second end of the third cutting edge. Each of the arcuate third cutting edges are arranged between a first and a second rectilinear cutting edge. The first and the second cutting edges are of same length. The cutting insert additionally comprises on the first side a first contact surface which extends orthogonally to the bore axis and lies in a first contact plane. On the second side, the cutting insert also comprises a second contact surface which extends orthogonally to the bore axis and lies in a second contact plane, which extends parallel to the first contact plane.

Although the cutting inserts already disclosed in the state of the art have proven to be advantageous in many kinds of aspects, they do nevertheless have some disadvantages, in particular with reference to the cutting properties.

SUMMARY OF THE INVENTION

It is an object to provide a cutting insert of the above-mentioned type which is advantageous compared to cutting inserts disclosed in the prior art, in particular with reference to the cutting properties.

According to a first aspect, a cutting insert for a milling tool is presented, having a first side, a second side which is identical to the first side, a circumferential surface which extends between the first and the second sides, and a bore which extends along a bore axis,wherein the cutting insert is 120° rotationally symmetrical with respect to the bore axis and comprises six identical cutting regions,wherein three of said six cutting regions are arranged at a transition between the first side and the circumferential surface, and wherein another three of said six cutting regions are arranged at a transition between the second side and the circumferential surface,wherein each of the six cutting regions comprises a first rectilinear cutting edge, a second rectilinear cutting edge, and a third arcuate cutting edge, wherein in each of the six cutting regions a first end of the first cutting edge is connected to a first end of the third cutting edge, and a first end of the second cutting edge is connected to a second end of the third cutting edge, and wherein the first and the second cutting edges are of same length,wherein the cutting insert further comprises on the first side a first contact surface which extends orthogonally to the bore axis and lies in a first contact plane, and on the second side comprises a second contact surface which extends orthogonally to the bore axis and lies in a second contact plane,wherein each of the first cutting edges has a second end located opposite the first end of the respective first cutting edge, wherein each of the second ends of the first cutting edges is connected to one of six arcuate edges, andwherein each of said six arcuate edges has a vertex which is located between the first and the second contact planes.

According to a second aspect, a milling tool is presented which comprises a cutting insert of the aforementioned type, a tool holder, and a fastening element for fastening the cutting insert to the tool holder.

On account of the fact that each of the vertices of the arcuate edges are arranged between the first and the second contact plane, the vertices, when viewed in a side view of the cutting insert, are each arranged “below” the first or second contact surface. Advantageous properties for the design of the chip shape geometry are produced as a result of the position of the vertices below the contact plane; like, for example, a certain chip break, a targeted chip form and chip control during machining.

Each of the second ends of the first cutting edges are preferably connected directly to a first end of the arcuate edges, wherein each of the second cutting edges are connected with their second ends, which are located opposite the first ends, to a second end of the arcuate edges. Thus, each of the arcuate edges (radii) preferably extends between a first cutting edge of a cutting region and a second cutting edge of another cutting region of the same cutting insert side. Thus, the arcuate edges separate, as it were, the cutting regions from one another. Three arcuate edges, which are offset by 120° with respect to one another, exist in total per cutting insert side.

The arcuate edges are not to be confused with the arcuate third cutting edges. The arcuate third cutting edges form the tips of the cutting regions. They are each arranged between a first cutting edge and a second cutting edge of the respectively same cutting region, and are connected directly to the first ends thereof.

According to a further refinement, the first cutting edges enclose an acute angle α with the second cutting edges of the respective same cutting regions.

In contrast to this, the majority of cutting inserts of the prior art comprise a right angle at this point. The structural realization as an acute angle produces improved “plunging” as correspondingly large freewheeling properties of the milling tool are produced. The fine cutting of the milling tool during the angled or circular “plunging” is also better with an acute angle.

“Plunging” of the milling tool refers, in particular, to processing where the milling tool rotates and is moved into the workpiece at an angle to the rotational axis. The feed direction, in this case, has both a movement component parallel to the rotational axis of the milling tool and a movement component perpendicular thereto. With reference to the cutting properties, angles α within the range of between 84° and 86° have proved to be advantageous. An angle α of 85° is particularly preferred.

According to a further refinement, an imaginary circle, the center of which lies on the bore axis, is at a total of six points tangent to the first and second cutting edges arranged on the first side. However, said circle is tangent to each of said cutting edges only at one point each. Corresponding to this, a second imaginary circle, the center of which also lies on the bore axis, is at a total of six points tangent to the first and second cutting edges arranged on the second side.

According to a further refinement, the cutting insert, at least except for the bore, is mirror-symmetrical to a center plane which extends orthogonally to the bore axis and is equidistant to the first and the second contact planes.

The restriction of the mirror symmetry “except for the bore” is based, in particular, on the fact that the bore, which is preferably designed as a through bore, is preferably not designed to be precisely mirror symmetrical with reference to the center plane due to the manufacturing process. This results, in particular, from the press molds which are used to press the cutting insert. Said non-precise mirror symmetry of the bore relative to the center plane, however, has no influence on how the cutting insert is arranged on the holder. The insert seat and the cutting properties, independently of whether the cutting insert rests on the tool holder with its first or its second side, are in each case the same, as the cutting insert is otherwise precisely symmetrical and the slight asymmetry of the bore with reference to the center plane has no influence on the fastening of the cutting insert on the tool holder.

It is obvious that it is possible, in principle, for the bore also to be precisely mirror-symmetrical to the center plane.

According to a further refinement, each of the arcuate third cutting edges comprises a vertex, wherein each of the vertices of the third cutting edges are at a greatest distance to the center plane compared to all remaining points of the cutting insert.

Both the first and the second cutting edges extend with reference to the center plane, that is to say at an angle. The corners of the cutting regions in which the arcuate third cutting edges are arranged, form the respectively highest points (measured parallel to the bore axis) of the first or second side of the cutting insert.

According to a further refinement, the first contact surface comprises three first part surfaces which are separated from one another and lie in the first contact plane. The second contact surface also preferably comprises three part surfaces with are separated from one another and lie in the second contact plane. The three first part surfaces are preferably separated from one another by three first indentations which are arranged offset to one another by 120°. The three second part surfaces are also separated from one another by three second indentations which are offset to one another by 120°. A mechanically defined three-point support, which provides a mechanically stable seat for the indexable cutting insert in the insert seat, is generated by said separation of the contact surfaces.

According to a refinement of the herein presented milling tool, the fastening element is designed as a screw and the tool holder comprises a thread which extends along a thread axis, in which thread engages the screw by way of which the cutting insert is fastened on the tool holder, wherein the tool holder comprises a first, a second and a third holder-contact surface. The first holder contact surface extends orthogonally to the thread axis. The second and the third holder contact surfaces extend transversely to one another and substantially parallel to the thread axis. The cutting insert, in a mounted state of the tool, abuts against the tool holder only at the first, the second and the third holder contact surfaces.

In contrast to the majority of milling tools of this type disclosed in the prior art, the cutting insert abuts against the tool holder therefore “only” at a total of three surfaces and not, as otherwise usual, at four surfaces.

The second and the third holder contact surfaces enclose an obtuse angle between one another, wherein the cutting insert abuts against the second holder contact surface with a first region of the circumferential surface and abuts against the third holder contact surface with a second region of the circumferential surface.

According to a further refinement of the herein presented milling tool, a distance between the thread axis and the second holder contact surface is as large as a distance between the thread axis and the third holder contact surface but smaller than a distance between the bore axis and the first or second regions of the circumferential surface. This results in a kind of pull-down action such that the screw automatically presses the cutting insert against the second and third holder contact surfaces during tightening. This increases the stability of the indexable cutting insert in the insert seat.

It is obvious that the features named above and the features yet to be explained below can be used not only in the respectively provided combinations but also in other combinations or standing alone without departing from the spirit and scope of the present disclosure.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1-7show two different embodiments of the cutting insert.FIGS. 8 and 9show an embodiment of a tool holder of the milling tool.FIGS. 10-12show an embodiment of the milling tool including cutting insert and tool holder.

The milling tool is designated in its entirety by way of the reference numeral10in the figures. The cutting insert is designated in its entirety by way of the reference numeral12in the figures. The tool holder is designated in its entirety by way of the reference numeral14in the figures.

The cutting insert12is a double-sided indexable cutting insert. It has a top side16which is designated as a first side of the cutting insert12and a bottom side18which is designated in the present case as a second side of the cutting insert12. The first side16of the cutting insert12is shown in top view inFIG. 2. The second side18is designed identically to said first side. The cutting insert12is designed to be mirror-symmetrical to a center plane20which divides the cutting insert12into two halves of the same size (seeFIG. 4) at least except for minor details which are to be explained further below. Said center plane20extends orthogonally to a symmetry axis22(seeFIG. 3). The symmetry axis22coincides with a center axis of a bore24which penetrates the cutting insert12completely. The symmetry axis or center axis22of the bore24is consequently designated below as bore axis22.

As can be seen in particular fromFIG. 2, the cutting insert12is also 120° rotationally symmetrical with respect to the bore axis22in addition to the mentioned mirror symmetry. Each cutting insert12is therefore projected onto itself again with a rotation of 120° about the bore axis22.

A circumferential surface26, which surrounds the cutting insert12completely on the circumferential side, extends between the first side16and the second side18of the cutting insert12. Three identically formed cutting regions28,28′,28″ are situated at the transition between said circumferential surface26and the first side16and at the transition between the circumferential surface26and the second side18, respectively.

In total, the cutting insert12consequently therefore has six identical cutting regions28,28′,28″. Each of said cutting regions28,28′,28″ comprises two rectilinear cutting edges30,32as well as one arcuate cutting edge34which extends between said two cutting edges30,32. The first and second cutting edges30,32are non-curved, non-angled, continuous cutting edges which extend along a straight line. The first and second cutting edges30,32preferably have an identical form and length. The third cutting edges34are curved, preferably also continuous cutting edges. The third cutting edges34directly adjoin the first cutting edges30and the second cutting edges32. More precisely, a first end36of the third cutting edge34of the first cutting region28is connected to a first end38of the first cutting edge30of the first cutting region28(seeFIGS. 1, 2 and 4). A second end40of the third cutting edge34of the first cutting region28is connected to a first end42of the second cutting edge32of the first cutting region28. The same applies correspondingly to the two other cutting regions28′,28″ of the same cutting insert side16or also to the three other cutting regions which are arranged in an identical manner on the second cutting insert side18.

The first and second cutting edges30,32of the respective cutting region28,28′,28″ each enclose between on another an acute angle α which is preferably chosen within the range of between 84° and 86°. According to an embodiment, the size of the angle α is 85°.

A first cutting edge30of a cutting region28,28′,28″ encloses in each case an obtuse angle β with a second cutting edge32of another, adjacent cutting region28,28′,28″.

Each cutting insert12comprises, at the transition between the circumferential surface26and the first side16or at the transition between the circumferential surface26and the second side18, additionally per side16,18, three arcuate edges44which are preferably designed as radii. Similarly to the arcuate cutting edges34, said radii44are also arranged in each case between a first cutting edge30and a second cutting edge32. Each first end46of the radii44adjoins a second end48of one of the first cutting edges30. Each second end50of the radii44adjoins a second end52of one of the second cutting edges32(seeFIGS. 5A and 5B). In contrast to the third, arcuate cutting edges34, the radii44are, however, arranged between the three cutting regions28,28′,28″ of each cutting insert side16,18(seeFIGS. 1 and 2). They therefore adjoin a second end48of the cutting edge30of a cutting region28,28′ or28″ as well as a second end52of the second cutting edge32of another cutting region28,28′,28″.

The cutting insert12additionally comprises on the first side16a first contact surface54which is divided into three part surfaces54.1,54,2,54.3. The first contact surface54or the three first part surfaces54.1,54.2,54.3all lie in a plane which is designated in the present case as a first contact plane56(seeFIG. 5A). Said first contact plane56extends orthogonally to the bore axis22. The three first part surfaces54.1,54.2,54.3are separated from one another by three first indentations58. Said first indentations extend, with reference to the bore axis22, substantially radially outward. They are offset to one another by 120°. The first contact surface54, as is explained in more detail further below, serves to abut against the tool holder14. As a result of dividing the first contact surface54into three part surfaces54.1,54.2,54.3, a defined three-point or three-surface support is created which contributes to the indexable cutting insert having a sturdy seat in the insert seat.

On account of the already named mirror symmetry to the center plane20, the cutting insert12comprises on its second side18an equivalent contact surface60which is designated in the present case as a second contact surface60and is also divided into three second part surfaces. The second contact surface60or the three part surfaces of the second contact surface60also lie in a common plane which is designated in the present case as a second contact plane62(seeFIG. 5B). Said second contact plane62extends parallel to the first contact plane56and perpendicularly to the bore axis22.

From the views of details shown inFIGS. 5A and 5B, it is additionally evident that the arcuate edges44each comprise a vertex64, which vertices lie below the named contact planes56or62. More precisely, the vertices64of the arcuate edges44arranged on the first side16lie below the first contact plane56and the vertices64of the arcuate edges44arranged on the second side18lie below the second contact plane62. The total of six vertices64of the total of six arcuate edges44all lie therefore spatially between the first contact plane56and the second contact plane62. The vertices64are therefore at a shorter distance from the center plane20than the contact planes56,58.

The following further features of the cutting insert12can be seen, in particular, inFIGS. 2-4: An imaginary circle66, the center of which lies on the bore axis22, touches the first and second cutting edges30,32of the first side16at a total of six places, each cutting edge30,32only being touched in each case by the imaginary circle66at one place. As can be seen in particular fromFIG. 4, the cutting edges30,32do not lie, however, in a common plane but extend transversely (that is to say not parallel) to one another. They all also extend transversely to the center plane20or to the contact planes56,58. The highest places of the cutting insert12or the places of the cutting insert12which are at the greatest distance to the center plane20compared to all remaining points of the cutting insert12, are located at the vertices of the arcuate third cutting edges34. Each of the first and second cutting edges30,32, accordingly proceeding from their respective first end38,42, extend at an angle toward the center plane20in the direction of their respective second end48,52. Each of the second ends48of the first cutting edges30and of the second ends52of the second cutting edges32are therefore at a shorter distance from the center plane20than the first ends38of the first cutting edges30and the first ends42of the second cutting edges32.

As can additionally be seen fromFIG. 2, each cutting region28,28′,28″ comprises a curved cutting surface68. Each of said cutting surfaces68extend in each cutting region28,28′,28″ between the part contact surface54.1,54.2,54.3of the respective cutting region28,28′,28″ and the respective cutting edges30,32,34. A transition surface70extends in each case at the transition between the cutting surfaces68and the part contact surfaces54,1,54.2and54.3. Both the cutting surfaces68and the transition surfaces70lie “below” the vertices of the third cutting edges34. The cutting surfaces68or the transition surfaces70are therefore at a smaller distance from the center plane20than the vertices of the third cutting edges34. It is obvious that the same also applies to the second side18of the cutting insert12.

FIGS. 6 and 7show a second exemplary embodiment of the cutting insert12. Said second exemplary embodiment corresponds substantially to the first exemplary embodiment shown inFIGS. 1-5. The radius of curvature of the third arcuate cutting edge34is simply a little smaller. So that there is no discontinuity at the respective transitions between the third cutting edges34and the first cutting edges30or the second cutting edges32, the third cutting edge34according to said exemplary embodiment is curved in particular in the region of its ends36,40about an axis which extends perpendicularly to the bore axis22. The third cutting edges34are therefore not only curved about an axis which extends parallel to the bore axis22but also orthogonally thereto. This enables a constant transition from the third cutting edges34to the first or second cutting edges30,32.

The tool holder14comprises a shank72, by way of which the tool holder14may be clamped in a suitable clamping means in a power tool. In the region of its front end74, the shank72, in the present exemplary embodiment, comprises two cutting insert receiving means76which serve for receiving one cutting insert12each. However, it is obvious that the tool holder14, in alternative exemplary embodiments, is also able to comprise more than two cutting insert receiving means76.

Each of the cutting insert receiving means76comprises a thread78which is provided in a bore and extends along a thread axis80and in which a screw82, which serves for fastening the cutting insert12to the tool holder14, is able to engage. Each cutting insert receiving means76additionally comprises three holder contact surfaces84,86,88. The first holder contact surface84extends orthogonally to the thread axis80. The second and the third holder contact surfaces86,88extend parallel to the thread axis80, that is to say orthogonally to the first holder contact surface84. The second holder contact surface86and the third holder contact surface88enclose an obtuse angle together.

The cutting insert12, in the mounted state of the tool10, abuts exclusively against the three aforementioned holder contact surfaces84,86,88on the tool holder14. The cutting insert12abuts against the first holder contact surface84with the first contact surface54or the second contact surface60. In addition, it abuts against the holder contact surface86,88with its circumferential surface26.

The thread axis80is intentionally somewhat offset compared to the arrangement of the bore axis22of the cutting insert12. More precisely, a distance between the thread axis80and the second holder contact surface86is the same size as a distance between the thread axis80and the third holder contact surface88but is smaller than a distance between the bore axis22and the two regions of the circumferential surface26by way of which the cutting insert12abuts against the holder contact surfaces86or88. A pull-down action, which presses the cutting insert12against the holder contact surfaces86,88, is generated as a result when the screw82is tightened.