Cutting insert

A tangential cutting insert has three pairs of surfaces. A first pair has upper and lower surfaces, a second pair has front and rear surfaces, and a third pair has two side surfaces. The upper and lower surfaces and the side surfaces extend between the front and rear surfaces. A main cutting edge is formed at the intersection of the front surface with the upper surface. A front portion of the upper surface extends rearwardly from the main cutting edge and upwardly toward a central portion of the upper surface as seen in a side view of the cutting insert. The main cutting edge associated with the upper surface is curved and slopes downwardly toward each of the auxiliary cutting edges as seen in a front view of the cutting insert.

FIELD OF THE INVENTION

The present invention relates to tangential cutting inserts.

BACKGROUND OF THE INVENTION

Tangential cutting inserts are often used with milling cutters such as slotting cutters or extended flute cutters. Examples of such cutting inserts are found in U.S. Pat. No. 3,416,209, U.S. Pat. No. 3,490,117, U.S. Pat. No. 3,701,187 and U.S. Pat. No. 4,790,693.

U.S. Pat. No. 6,238,146 discloses an improved tangential cutting insert. The cutting insert has a body with an operative front surface associated with upper and lower main cutting edges. Each of the main cutting edges is connected, through corner edges, to side auxiliary cutting edges. The main cutting edges, side auxiliary cutting edges and corner edges have a rake surface associated therewith in the front surface of the cutting insert.

The two main cutting edges of the cutting insert of '146 each comprise two lateral component cutting edges giving rise to four right hand cutting edges and four left hand cutting edges. However, only one lateral component cutting edge of a given main cutting edge can be used at a time as a cutting edge to machine a 90° shoulder. If the cutting insert of '146 were to use the entire length of a main cutting edge to machine an extended shoulder, i.e., using two adjacent lateral component cutting edges, the result will not be a straight 90° shoulder.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a cutting insert having a front surface extending between an upper surface, a lower surface and two side surfaces that extend between the upper surface and the lower surface, the upper surface joins each of the side surfaces through a corner surface at each side of the upper surface;

a main cutting edge associated with the upper surface is formed at the intersection of the front surface with the upper surface, auxiliary cutting edges are formed at the intersection of the front surface with each of the side surfaces, and, corner cutting edges are formed at the intersection of the front surface with each of the corner surfaces;

the main cutting edge, the auxiliary cutting edges and the corner cutting edges have a rake surface associated therewith in the front surface; wherein

a front portion of the upper surface extends rearwardly from the main cutting edge and upwardly toward a central portion of the upper surface as seen in a side view of the cutting insert, and

the main cutting edge is curved and slopes downwardly toward each of the auxiliary cutting edges as seen in a front view of the cutting insert.

Typically, the main cutting edge slopes inwardly and rearwardly from the corner cutting edges as seen in a top view of the cutting insert, and, the entire length of the main cutting edge lies on a cylindrical surface.

If desired, the front surface has mirror symmetry with respect to a first symmetry plane that is located midway between the upper and lower surfaces, and

the rake surface extends along the entire circumference of the front surface.

Further if desired, the cutting insert has mirror symmetry with respect to a second symmetry plane that is perpendicular to the central portion of the upper surface and to the side surfaces, the second symmetry plane is located midway between the front surface and a rear surface.

Typically, the cutting insert further comprises a through bore that extends between the upper surface and the lower surface.

In some embodiments, the main cutting edge is continuously curved as seen in a top view of the cutting insert.

Still in some embodiments, the main cutting edge comprises two lateral cutting edge sections that slope inwardly and rearwardly from the corner cutting edges and a central cutting edge section between the two lateral cutting edge sections, as seen in a top view of the cutting insert.

If desired, the cutting insert further comprises a relief surface at one of the side surfaces, the relief surface joins one of the auxiliary cutting edges at a first edge of the relief surface and a corner surface at a second edge of the relief surface.

Further if desired, the cutting insert has rotational symmetry with respect to a symmetry axis that is located midway between the central portion of the upper and lower surfaces, parallel to the central portion of the upper and lower surfaces and parallel to the side surfaces.

Typically, the front portion of the upper surface extends upwardly toward the central portion of the upper surface at an upper slant angle as seen in a side view of the cutting insert, the upper slant angle is in the range of 1° to 15°.

According to a specific embodiment of the present invention, the upper slant angle is about 7°.

If desired, the cutting insert has a first land that extends from the main cutting edge toward the lower surface, the first land is slanted at a first land angle with respect to a second symmetry plane that is perpendicular to the central portion of the upper surface and to the side surfaces, the first land angle is in the range of −10° to 20° as seen in a side cross-section of the main cutting edge and measured upwardly from the main cutting edge.

According to a specific embodiment of the present invention, the first land angle is about 10°.

Typically, the cutting insert has a second land that extends from the first land toward the lower surface, the second land is slanted at a second land angle with respect to the second symmetry plane, the second land angle is in the range of −10° to 25° as seen in a side cross-section of the main cutting edge and measured downwardly from the main cutting edge.

According to a specific embodiment of the present invention, the second land angle is about 5°.

Typically, the rake surface extends from the second land toward the lower surface, the rake surface is slanted at a rake angle with respect to the second symmetry plane, the rake angle is in the range of 0° to 60° as seen in a side cross-section of the main cutting edge and measured upwardly from the main cutting edge.

According to a specific embodiment of the present invention, the rake angle is about 44°.

If desired, the main cutting edge is curved and formed from various arc segments, each of the arc segments has a different radius, the radii of the various arc segments vary from 5 mm to infinity, as seen in a front view of the cutting insert.

Typically, the relief surface is slanted at a radial relief angle with respect to a third symmetry plane that is parallel to a central portion of the side surfaces, perpendicular to the central portion of the upper and lower surfaces and passes through a center of the front surface, the radial relief angle is in the range of 0° to 5° as seen in a front view of the cutting insert.

According to a specific embodiment of the present invention, the radial relief angle is about 2.8°.

Further typically, the relief surface is slanted at a peripheral relief angle with respect to the third symmetry plane, the peripheral relief angle is in the range of 0° to 8°.

According to a specific embodiment of the present invention, the peripheral relief angle is about 3°.

In some embodiments, the two lateral cutting edge sections form therebetween a lateral section angle that is in the range of 140° to 180°.

According to a specific embodiment of the present invention, the lateral section angle is about 160°.

If desired, the rake surface extends in an inward direction of the cutting insert.

DETAILED DESCRIPTION OF THE INVENTION

Attention is first drawn toFIGS. 1 to 7showing a cutting insert10in accordance with a first embodiment of the present invention. The cutting insert10comprises three pairs of surfaces, the surfaces of each pair being located on opposite sides of the cutting insert10. A first pair comprising an upper surface12and a lower surface14. A second pair comprising a front surface20and a rear surface22, and a third pair comprising two side surfaces24. The upper and lower surfaces12,14and the side surfaces24extend between the front and rear surfaces20,22.

The upper surface12joins each of the side surfaces24through a corner surface16at each side of the upper surface12. Likewise, the lower surface14joins each of the side surfaces24through a corner surface16at each side of the lower surface14.

The cutting insert10may have mirror symmetry with respect to a first symmetry plane P1. The first symmetry plane P1is located midway between the upper and lower surfaces12,14as seen inFIG. 3. A through bore18having an axis A extends between the upper surface12and the lower surface14. The axis A may be perpendicular to the first symmetry plane P1.

According to a specific embodiment of the present invention, the cutting insert10also has mirror symmetry with respect to a second symmetry plane P2. The second symmetry plane P2is perpendicular to a central portion48of the upper and lower surfaces12,14, perpendicular to the side surfaces24, and passes through the axis A of the through bore18as seen inFIGS. 2 and 4.

The cutting insert10also may have mirror symmetry with respect to a third symmetry plane P3that is perpendicular to the upper and lower surfaces12,14, includes the axis A of the through bore18and passes through a center26of the front surface20as seen inFIGS. 2 and 3.

The cutting insert10has 180° rotational symmetry with respect to a symmetry axis B that is formed by the intersection of the first and the third symmetry planes P1, P3.

Since the cutting insert10, according to the present invention, is symmetrical with respect to the second symmetry plane P2thus having a cutting insert front section28and an identical cutting insert rear section30, only the cutting insert front section28will be described. A main cutting edge32is formed at the intersection of the front surface20with the upper surface12. Likewise, another main cutting edge32is formed at the intersection of the front surface20with the lower surface14. Two auxiliary cutting edges34are formed at the intersection of the front surface20with each of the side surfaces24. Four corner cutting edges36are formed at the intersection of the front surface20with each of the corner surfaces16. The four corner cutting edges36join between each of the main cutting edges32and the auxiliary cutting edges34.

The main cutting edges32, auxiliary cutting edges34and corner cutting edges36have a rake surface38associated therewith in the front surface20. According to a specific embodiment of the present invention, the rake surface38extends along the entire circumference of the front surface20. Further according to a specific embodiment of the present invention, the rake surface38extends from an associated cutting edge to a base surface40of the front surface20in an inward direction of the cutting insert10. The inward direction means that the rake surface38extends from an associated cutting edge toward the center26of the front surface20, and, rearwardly with respect to the associated cutting edges, and toward the second symmetry plane P2.

As seen inFIG. 2, the main cutting edge32slopes inwardly and rearwardly from the corner cutting edges36. The main cutting edge32comprises two lateral cutting edge sections42. Each of the lateral cutting edge sections42slopes inwardly and rearwardly from its associated corner cutting edge36, as seen in a top view of the cutting insert10. The lateral cutting edge sections42join a central cutting edge section44that is generally parallel to the second symmetry plane P2. The two lateral cutting edge sections42form therebetween a lateral section angle α that is typically in the range of 140° to 180°. According to a specific embodiment of the present invention, the lateral section angle α is about 160°, the term “about” meaning that the value is within a degree or so of the given figure. If desired, the two lateral cutting edge sections42and the central cutting edge section44therebetween may form a continuously curved cutting edge32as seen in a top view of the cutting insert10.

As seen inFIG. 2, the two lateral cutting edge sections42of the main cutting edge32are slanted at opposite directions with respect to the second symmetry plane P2. There can be advantages to retaining the cutting insert10in a pocket of an associated tool holder (not shown) in a “tangential” manner as known in the art, and using the entire length of the main cutting edge32to cut a workpiece.

First, the axial forces acting on the oppositely directed lateral cutting edge sections42more or less cancel each other out. As a consequence, almost no net axial force acts on the cutting insert10during machining. This reduces chatter of the cutting insert10, thus potentially increasing the quality of the surface finish and increasing the tool life of the cutting insert10.

A second advantage may be realized by the oppositely directed lateral cutting edge sections42when the entire main cutting edge32is used to cut a workpiece. The chip produced by the cutting edge32is formed in a shape of two truncated cones connected at their base. Thus, since each portion of the chip, i.e., a portion having the shape of a single truncated cone, is formed by a single lateral cutting edge portion42, the chip portion tends to roll around its axis, toward the center of the chip, and toward the other chip portion. Hence, the chip tends to shrink from its peripheral ends toward its center. In this manner, the total length of the chip is somewhat smaller then the length of cut. This introduces a meaningful advantage when machining parts that have limited space for chip removal, such as crankshafts.

The upper surface12of the cutting insert10comprises a front portion46and a central portion48rearward of the front portion46. The central portion48of the upper surface12may be flat and is parallel to the first symmetry plane P1. The front portion46of the upper surface12extends rearwardly from the main cutting edge32and upwardly toward the central portion48of the upper surface12. As seen inFIG. 5, the front portion46of the upper surface12extends upwardly toward the central portion48of the upper surface12at an upper slant angle β. Typically, the upper slant angle β is in the range of 1° to 15°. According to a specific embodiment of the present invention, the upper slant angle β is about 7°.

As seen in a front view of the cutting insert10(seeFIG. 3), each main cutting edge32is curved and slopes in a direction of the first symmetry plane P1(and thus in the direction of the other main cutting edge32), from the central cutting edge section44toward each of the auxiliary cutting edges34. Thus, the main cutting edge32associated with the upper surface12slopes downwardly while the main cutting edge32associated with the lower surface14slopes upwardly. The main cutting edge32is curved and is formed from various arc segments50. According to some embodiments, each of the arc segments50has a different radius. Typically, the radii of the various arc segments vary from 5 mm to infinity (i.e., straight line segments).

As seen inFIG. 5, the cutting insert10has a first land52that extends from the main cutting edge32toward the first symmetry plane P1. The first land52is slanted at a first land angle γ with respect to the second symmetry plane P2. Typically, the first land angle γ is in the range of −10° to 20° as seen in a side cross-section of the main cutting edge32and measured upwardly from the main cutting edge32. According to a specific embodiment of the present invention, the first land angle γ is about 10°.

As seen inFIG. 5, the cutting insert10has a second land54that extends from the first land52toward the first symmetry plane P1. The second land54is slanted at a second land angle δ with respect to the second symmetry plane P2. Typically, the second land angle δ is in the range of −10° to 25° as seen in a side cross-section of the main cutting edge32and measured downwardly from the main cutting edge32. According to a specific embodiment of the present invention, the second land angle δ is about 5°.

During machining, the cutting insert10is securely clamped by a clamping screw within a pocket of a cutting tool (not shown). The design of the first land angle γ and the second land angle δ is such that it considerably reduces the torque applied on the cutting insert10during machining, a torque that tends to move the cutting insert10out of its pocket. Consequently, the torque applied on the clamping screw is also considerably reduced. Hence, the stresses on the clamping screw are reduced, a fact that increases the screw's life and allows the cutting insert10to work at high feed rates without worrying that the clamping screw may shear.

Furthermore, the design of the first land angle γ and the second land angle δ may be such that the forces applied on the cutting insert10during machining will tend to further retain the cutting insert10within its pocket, thus, the clamping will be more stable and the screw's life will be increased.

As seen inFIG. 5, the rake surface38extends from the second land54towards the first symmetry plane P1. The rake surface38is slanted at a rake angle θ with respect to the second symmetry plane P2. Typically, the rake angle θ is in the range of 0° to 60° as seen in a side cross-section of the main cutting edge32and measured upwardly from the main cutting edge32. According to a specific embodiment of the present invention, the rake angle θ is about 44°.

When machining a workpiece, the cutting insert10cuts up to a depth of cut that is approximately equal to the length L of the cutting insert10. Therefore, the cutting insert10is provided with four full length main cutting edges32. Two of the main cutting edges32are located at the front surface20and can be used for a specific hand machining, i.e., either for right hand machining or for left hand machining. The other two main cutting edges32are located at the rear surface22, and can be used for the opposite specific hand machining used by the main cutting edges32of the front surface20. The cutting insert10according to the present invention may be used to cut a perfect 90° extended shoulder due to the fact that the entire length of the main cutting edge32lies on a cylindrical surface.

In order to enable the use of the cutting insert10for machining in different directions, the cutting insert has two pairs of side relief surfaces56. A first pair of identical side relief surfaces56is located in the cutting insert front section28, and a second pair of identical side relief surfaces56is located in the cutting insert rear section30.

A given side relief surface56is formed on a given side surface24. According to a specific embodiment of the present invention, the side relief surface56is provided with two edges. A first edge58of the side relief surface56is formed at the intersection of the side relief surface56with the adjacent auxiliary cutting edge34. A second edge62of the side relief surface56is formed at the intersection of the side relief surface56with the adjacent corner surface16. The side relief surface may be flat or curved.

As seen inFIG. 6, the side relief surface56is slanted at a radial relief angle λ with respect to the third symmetry plane P3. Typically, the radial relief angle λ is in the range of 0° to 5° as seen in a front view of the cutting insert10. According to a specific embodiment of the present invention, a central portion60of the side surface24is planar and parallel to the third symmetry plane P3. Therefore, in such a case, the side relief surface56is slanted at the radial relief angle λ also with respect to the central portion60of the side surface24.

As seen inFIG. 7, the side relief surface56is slanted at a peripheral relief angle φ with respect to the third symmetry plane P3. Typically, the peripheral relief angle φ is in the range of 0° to 8°. Since the central portion60of the side surface24is planar and parallel to the third symmetry plane P3, the side relief surface56is also slanted at the peripheral relief angle φ with respect to the central portion60of the side surface24.

Although the present invention has been described to a certain degree of particularity, it should be understood that various alterations and modifications could be made without departing from the spirit or scope of the invention as hereinafter claimed.

For example, as seen inFIG. 3, the corner cutting edges36associated with a given main cutting edge32are identical. Thus, cutting insert10has mirror symmetry with respect to the third symmetry plane P3except for the corner surfaces16and the side relief surfaces56. However, in other embodiments, depending on the design needs, the four corner cutting edges36may differ from one another in different ways, such as by having different radii or shapes.

For instance, in the front view of a second embodiment of a cutting insert110, seen inFIG. 8, the corner cutting edges associated with a given main cutting edge have a different shape or radius while diagonally opposite corner cutting edges have an identical shape or radius. As a consequence, in a front view of cutting insert110, there is no general mirror symmetry with respect to the first and third symmetry planes P1, P3, but, only a 180° rotational symmetry with respect to the symmetry axis B.

The design needs may be such that the shape or radius of the corner cutting edges36will eliminate the option of having a first symmetry plane P1between the upper surface12and the lower surface14. In such a case, as shown schematically inFIG. 9, the cutting insert210according to a third embodiment of the present invention will not be indexable between the upper surface12and the lower surface14. Rather, only a main cutting edge232associated with the upper surface12, and one of the associated corner cutting edges236may be used.

In other embodiments, the cutting insert rear section30may be different from the cutting insert front section28, so that the cutting insert rear section30or the rear surface32may be received into a different type of insert pocket and/or abutted in a different manner when the cutting insert is retained in a pocket of an associated tool holder.