Tangential cutting insert
This application claims the benefit of the filing date of Korean Patent Application No. 10-2008-0027864 filed on March 26, 2008 in the Korean intellectual Property Office, the disclosure of which is incorporated herein its entirety by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a tangential cutting insert, more particularly, to a tangential cutting insert which is suitable for machining right angled wall surface with a minimized cutting resistance from the machined planar surface of a workpiece.
2. Description of the Related Art
In general, the plurality of cutting inserts are mounted to a milling cutter to machine a surface of a workpiece.
Fig- 1 and Fig. 2 are perspective view and front view of a conventional tangential cutting insert, the tangential cutting insert 10 comprises a front end surface 13, a rear end surface 14, an upper side surface 12, a lower side surface 11 and first and second mounting side surfaces 15 and 16.
Cutting edges are formed at intersection between the end surfaces 13 and 14 and each of side surfaces 11, 12, 15, and 16. On the other hand, both ends of a through bore 17 passing through the member are located on the first and second mounting side surfaces 15 and 16.
Fig. 3 is a view illustrating a state where the cutting inserts shown in Fig. 1 are mounted to a milling cutter.

A plurality of pockets 2 are formed on a milling cutter 1, the cutting insert 10 shown in Fig. 1 and Fig. 2 is received and secured in each pocket 2 by a clamping screw 3. A border portion between the lower side surface 11 and the front end surface 13 of the cutting insert 10 secured in the pocket 2 is exposed out of the lower end of the milling cutter 1,
Here, in the cutting insert 10 mounted in the pocket 2, the second mounting side surface 16 is in contact with a main surface of the pocket 2, and the first mounting side surface 15 opposite to the second mounting side surface is exposed out of the pocket 2. Accordingly, an comer edge 18-1 between the first mounting side surface 15 and the lower side surface 11 of the cutting insert 10 mounted in the pocket 2 acts as a main cutting edge.
As shown in Fig, 1 and Fig. 2, to decrease a planar contacting area between the cutting insert 10 and the workpiece, that is, the cutting resistance, the upper and lower side surfaces 12 and 11 of the cutting insert 10 are formed in a convex surface or two inclined sub-surfaces, not a plane surfaces. For the sake of convenience, only the lower side surface 11 shown in Fig. 1 is illustrated below.
That is, the lower side surface 11 consists of first and second inclined sub¬surfaces 11-1 and 11-2, each of which is inclined upward from a vertical center plane V of the cutting insert 10 toward the corresponding side surface 15 (or 16) at a certain angle (al ; for example, 2°). Accordingly, the first inclined surface 11-1 and the second inclined surface 11-2 make an angle of 184°.
In the meantime, due to the this shape of the cutting insert 10, the first inclined sub-surface 11-1 of the lower side surface 11 and the first mounting side surface 15 forming a main comer cutting edge 18-1 make an obtuse angle of 92°.
The cutting insert 10 having the configuration as described above is mounted to in

the pocket 2 of the milling cutter 1 in a state where the main comer cutting edge 18-1 between the first inclined surface 11-1 of the lower side surface 11 and the first mounting side surface 15 is in contact with a planar surface of the workpiece to be machined.
As describe above, in a case where the workpiece is machined by the milling cutter 1 to which the cutting inserts 10 are mounted, the following problems are caused.
Fig, 4 is a sectional view of a working piece machined by the milling cutter shown in Fig. 3. Fig. 4 schematically illustrates that a machined planar surface Wl and a wall surface W2 adjacent to the machined planar surface make an angle A which correspond to the angle of (92°) made by the first inclined sub-surface 11-1 of the lower side surface 11 and the first mounting side surface 15.
As describe above, the first inclined sub-surface 11-1 of the lower side surface 11 and the first mounting side surface 15 forming the main comer cutting edge 18-1 make an obtuse angle (92°), and so the side wall surface W2 and the machined planar surface Wl of the workpiece W machined by the cutting inserts 10 are not perpendicular each other, but make an obtuse angle.
Therefore, by using the milling cutter 1 to which the cutting inserts 10 having the structure shown Fig, 1 are mounted, it is difficult to machine the workpiece W to make a shape in which the machined planar surface Wl is perpendicular to the side wall W2 adjacent to thereof
In addition, in the machining process, the machined planar surface Wl of the workpiece W is contacted not only with the comer cutting edge 18-1 of the insert 10 but also with a portion of the lower side surface 11 adjacent to the comer cutting edge 18-1 (that is, the first inclined sub-surface 11-1) so that an excessive cutting resistance is generated between the cutting insert 10 and the workpiece W,

In the meantime, the above problem also arises when one of the other comer cutting edge 18-2 , 18-3 and 18-4 is used as the main comer cutting edge.
SUMMARY OF THE INVENTION
The present invention is conceived to solve the above problems. An objective of the present invention is to provide a tangential cutting insert which allows to minimize a cutting resistance by a machined planar surface of a workpiece and to machine a vertical wall surface right-angled to the machined planar surface of the workpiece.
To achieve the above object, a tangential cutting insert according to the present invention has a generally hexahedral shape with a front end surface, a rear end surface, an upper side surface, a lower side surface, a first mounting side surface and a second mounting side surface, provided with a through bore passing through the centers of the mounting side surfaces, cutting edges are formed at the intersection of each end surface and the side surfaces; wherein the lower side surface has four comers and comprises two inclined sub-surfaces which have a border ridge therebetween extending between two diagonally opposing comers and are inclined toward one of the other two diagonally opposing comers. Therefore, the angle in the view of the front end surface made by the intersection of the front end surface and the first mounting side surface and the intersection of the front end surface and the lower side surface, and the angle in the view of the rear end surface made by the intersection of the rear end surface and the second mounting side surface and the intersection of the rear end surface and the lower side surface are a substantially identical acute angle.
Here, the upper side surface is preferred to have a shape which is substantially rotationally symmetric to that of the lower side surface with respect to the axis of the through bore.
The end surfaces are also preferred to have shapes which are substantially rotationally symmetric with respect to a line axis passing through the centers of the

upper and lower side surfaces,
The cutting insert according to the present invention can decrease the friction area between the cutting edge and a machined planar surface of the workpiece during a maching process.
In addition, the cutting insert according to the present invention can machine a vertical side wall surface right-angled to the machined planar surface of a workpiece.
The cutting insert according to the present invention has four acute-angled comer cutting edges in total and has no orientational preference when mounted to a pocket of the milling cutten Accordingly, it is possible to extend the service life time of the cutting insert through four times of indexing.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 and Fig. 2 are perspective view and front view of a conventional tangential cutting insert;
Fig, 3 is a view illustrating a state where the cutting inserts shown in Fig. 1 are mounted to a milling cutter;
Fig. 4 is a sectional view of a working piece machined by the milling cutter shown in Fig. 3;
Fig. 5 and Fig. 6 are perspective view and front view of a cutting insert according to the present invention; and
Fig. 7 is a partial sectional view of a working piece machined by a milling cutter to which the cutting inserts shown in Fig. 5 and 6 are mounted.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Hereinafter, a cutting insert according to the present invention is described in detail with reference to the accompanying drawings. Below, as an example of the cutting Inserts of the present invention, a tangential cutting insert mounted to a milling cutter is illustrated.

Fig. 5 and Fig. 6 are perspective view and front view of a cutting insert according to the present invention,
A cutting insert 100 according to the present invention comprises a front end surface 130, a rear end surface 140, an upper side surface 120, a lower side surface 110 and right and left mounting side surfaces 150 and 160. Both ends of a through bore 170 passing through a member are located on the right and left mounting side surfaces 150 and 160. However, right and left may be interchangeable depending on the revolving direction of the milling cutter, the right and the left mounting side surfaces are called a first and a second mounting surfaces 150 and 160, hereinafter, to be applicable for both cases.
The upper side surface 120 and the lower side surface 110 have the shapes which are substantially rotational symmetric about the axis S passing through the center of the through bore 170. For the sake of convenience, only the shape of the lower side surface 110 shown Fig. 5 is illustrated as an example below.
The lower side surface 110 of the cutting insert 100 according to the present invention consists of two inclined sub-surfaces. That is, the lower side surface 110 consists of first and second inclined sub-surfaces 111 and 112 inclined from a ridge border therebetween extending between the diagonally opposing first and second comers 100-1 and 100-3 toward the second and fourth comers 100-2 and 100-4, respectively.
Due to the above configuration, a ridge 113 with a certain height is formed at the border between the first inclined sub-surface 111 and the second inclined sub-surface 112 of the lower side surface 110 of the cutting insert 100.
On the other hand, the comer cutting edges on the end surfaces corresponding to the first and third comers 100-land 100-3 of the lower side surface 110, where the

ridge 113 ends, act as main comer cutting edges. The angle of the main comer cutting edge is the angle made by the intersections of the end surfaces 130 and 140 and the mounting side surfaces 130 and 140 and the intersections of the end surfaces and the lower side sub-surfaces 112 and 111(See angle B in Fig. 6). This angle of the main comer cutting edge is an acute angle in the view of both end surfaces.
In a case where the cutting insert 100 having the structure as described above is mounted to a pocket (2 in Fig. 3) of the milling cutter, the second mounting side surface 106 is in contact with the main supporting surface of the pocket, and the first mounting side surface 150 opposite to the second mounting side surface is exposed out of the pocket. Accordingly, the comer cutting edge of the front end surface being a rake surface, corresponding to the first comer 100-1 of the lower side surface, functions as the main cutting edge.
When the cutting insert 100 is mounted to the pocket of the milling cutter in a state with a negative axial rake angle as shown in Fig. 3, the lower side surface 110 of the cutting insert 100 faces the workpiece to be machined, and only the first comer 100-1 becomes in contact with the workpiece. In other words, when the cutting insert 100 is mounted with a negative axial rake angle, the first and second inclined sub-surfaces 111 and 112 and the ridge 113 of the lower side surface 110 are not in surface or line contact with the planar surface of the workpiece.
Under this cutting conditions as described above, when the cutting insert machines the workpiece by rotational and up-and-down linear movement of the milling cutter, the contact areas between the workpiece and the lower side surface 110 can be minimized, and so the cutting resistance between the workpiece and the cutting insert 100 can be decreased.
In any cases where the cutting insert 100 is mounted to the milling cutter to place either one of the four acute angled comer cutting edge as the main comer cutting edge, the above same cutting condition can be achieved.

Fig. 7 is a partial sectional view of a workpiece machined by a milling cutter mounted with the cutting inserts according to the present invention, and shows that the machined planar surface W1 and the side wall surface make a strict right angle (90°).
The angle of the main cutting edge of the cutting insert 100 in accordance to the present invention is an acute angle as illustrated as angle B in Fig 6. Therefore, even though the insert is mounted with a negative axial rake angle, it is allowed with ease to machine a right-angled comer structure having a strictly vertical wall surface W2 with a minimized frictional contact area with the machined planar surface Wl. Here, for the purpose of securing a straightness of the machined vertical wall surface, the axial cutting edge facing the wall surface may take a tangentially curved line, an equivalent of which can be found in Fig. 1.
On the other hand, the Insert according to the present invention is substantially rotationally symmetric with respect to both the axis S of the through bore 170 and a line axis passing through the centers of the upper and lower side surfaces. Therefore, upper side surface 120 has a shape which is substantially rotationally symmetric to that of the lower side surface 110 with respect to the axis of the through bore. And the rear end surface 140 has a shape which is substantially rotationally symmetric to that of the front end surface 130 with respect to the line axis passing through the centers of the upper and lower side surfaces.
Due to the above structural features, the cutting insert according to the present invention has four acute-angled comer cutting edges in total and has no orientational preference when mounted to a pocket of the milling cutter. Accordingly, it is possible to extend the service life time of the cutting insert through four times of indexing.
The scope of the present invention is not limited to the embodiments described above and the scope of the present invention is determined and defined only by the appended claims. Further, those skilled in the art can make various changes and

modifications thereto without departing from its true spirit. Therefore, various changes and modifications obvious to those skilled in the art will fall within the scope of the present invention.

We claim:
1. A tangential cutting insert, having a generally hexahedral shape with a
front end surface, a rear end surface, an upper side surface, a lower side surface, a first
mounting side surface and a second mounting side surface, provided with a through
bore passing through the centers of the mounting side surfaces, cutting edges are formed
at the intersection of each end surface and the side surfaces; wherein:
the lower side surface has four corners and comprises two inclined sub-surfaces which have a border ridge therebetween extending between two diagonally opposing corners and are inclined toward one of the other two diagonally opposing corners,
whereby the angle in the view of the front end surface made by the intersection of the front end surface and the first mounting side surface and the intersection of the front end surface and the lower side surface, and the angle in the view of the rear end surface made by the intersection of the rear end surface and the second mounting side surface and the intersection of the rear end surface and the lower side surface are a substantially identical acute angle.
2. The cutting insert according to claim 1, wherein the upper side surface
has a shape which is substantially rotationally symmetric to that of the lower side
surface with respect to the axis of the through bore .
3. The cutting insert according to claim 1 or 2, wherein the end surfaces
have shapes which are substantially rotationally symmetric with respect to a line axis
passing through the centers of the upper and lower side surfaces.