Indexable cutting inserts and methods for producing the same

Abstract

A related cutting insert includes a cutting insert body comprising sintering a layer of a superhard material, machining a hole through said sintered layer, brazing said machined layer onto a preformed cemented carbide substrate, and grinding a brazed product to form a cutting insert of predetermined shape.

Description

FIELD OF THE INVENTION

The present invention relates to cutting inserts having cutting edges formed from a superhard abrasive material, and methods of making the same.

BACKGROUND OF THE INVENTION

In the description of the background of the present invention that follows reference is made to certain structures and methods, however, such references should not necessarily be construed as an admission that these structures and methods qualify as prior art under the applicable statutory provisions. Applicants reserve the right to demonstrate that any of the referenced subject matter does not constitute prior art with regard to the present invention.

Indexable cutting inserts using a superhand material for cutting typically have a polygonal shape with the superhard material disposed at the corners of the polygon. The superhard material, often a cubic boron nitride or polycrystalline diamond material, aids in the cutting of hard workpiece materials such as metals. These cutting inserts are typically mounted in a fixed position to a cutting tool so as to present one of the corners or areas containing superhard material to the surface of a workpiece. After being used for a period of time, the area of superhard material becomes worn. The cutting insert can then be unfastened from the cutting tool and rotated so as to present a new fresh corner or area of superhard material to the surface of the workpiece.

There are two predominant ways of making such inserts. According to one technique, a stacked structure is formed comprising a first layer of hard backing material and a layer of superhard cutting material superimposed onto the backing layer. Cutting tips are then cut from this stacked structure and brazed to a cutting insert body, typically at a corner thereof. U.S. Pat. No. 5,183,362 to Kuroyama et al., the disclosure of which is incorporated herein by reference, in its entirety, describes such a technique.

However, several problems are associated with such techniques. The braze joint connecting the cutting tips to the body of the cutting insert creates an inherent weak point in the structure. This is particularly true due to the high temperatures that tend to exist during use of such cutting inserts, these high temperatures being in close proximity to the braze joint. Another problem posed by such techniques is that the extent of superhard material presented to the workpiece and available for wear is limited, thus limiting the useful operating period for that particular cutting edge.

A second technique for forming indexable cutting inserts involves providing a blank or substrate having pockets formed therein which are filled with superhard material, then subjecting the blank to a sintering operation which bonds the superhard material to the substrate. The blank is then subsequently machined to give the cutting insert its final shape, i.e.—a generally polygonal body with superhard material disposed at the corners thereof. U.S. Pat. No. 5,676,496, the disclosure of which is incorporated herein by reference, in its entirety, describes such a technique.

Such techniques also present certain difficulties. The process by which the superhard material is bonded to the blank or substrate is difficult and costly. In this regard, the cost of the superhard and substrate raw materials are relatively minor when compared with the costs associated with the process cycle necessary to join them. Thus, from a production efficiency point of view it would seem preferable to form an indexable insert with many corners containing superhard material. That way, the number of costly joining process cycles could be minimized while producing inserts that had many cutting corners. However, customers of such cutting inserts seem to strongly favor cutting inserts having relatively few cutting corners, which are more costly to make on a per unit basis using this technique. Most cutting inserts sold have only 24 cutting corners.

Another disadvantage associated with this second technique is that if a single pocket of superhard material is defective, the entire insert cannot be sold and may have to be scrapped. Yet another disadvantage or inefficiency is that only a single cutting insert is produced from each costly and difficult process cycle.

In general, such superhard material-containing inserts have been held in place by an external (e.g., top) clamp. See, for example, FIG. 25 of U.S. Pat. No. 5,183,362 which shows a top clamp with a preformed, separate chip breaker. Another type of clamping used with other types of cutting inserts involves the use of a screw which passes through a hole in the insert, often in the center of the insert. Such holes may be straight or involve an offset portion to assist in seaming the insert. See, for example, U.S. Pat. No. 5,147,158 which discloses in cross-section a “trumpet” style of central hole for securing purposes. Laser cutting or EDM (electro-discharge machining is used to cut the superhard material and it can be appreciated that machining of a “trumpet” style hole in the superhard material is quite difficult and expensive to do. In addition, the accuracy of such cuts is problematic.

Thus, a need exists in the art to address the problems discussed above and others.

SUMMARY OF THE INVENTION

The present invention provides devices and methods that address the above-mentioned problems, and others.

The present invention provides improved indexable cutting inserts and improved methods of producing the same.

According to one aspect, the present invention provides a method making a cutting insert comprising forming a layer of superhard material, forming a hole in said layer, attaching said layer onto a commented carbide substrate also having a hole corresponding to the hole in said superhard layer, and attaching a preformed annular body within said holes.

According to further aspect, the present invention provides a cutting insert a cutting insert comprising a base portion of a commented carbide, a layer of superhard material attached to said base and a hole through both said base portion and layer, said hole extending generally corrically from said layer through said base.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a top view of a blank or preform constructed according to the principles of the present invention.

FIG. 2 is a side view of the blank of FIG. 1.

FIG. 3 is a top view of another embodiment according to the principles of the present invention.

FIG. 4 is a side view of the blank of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary arrangements and techniques according to the present invention will now be described by reference to the drawing figures.

According to the present invention, a blank is formed from a superhard cutting material. The blank can also be formed from a hard material and a superhard cutting material. An illustrative embodiment of such a blank is shown in FIGS. 1 and 2. As shown therein, the blank 10 comprises a top layer or portion 11 of a superhard material and a bottom layer or portion 12 of a hard material. While the blank 10 is illustrated as having a polygonal-like shape, other geometries are clearly possible, such as a disk.

Generally, the superhard cutting material and the hard material are sintered together using conventional pressing and sintering techniques to form a solid shape. A central hole 13 may be formed during the pressing and sintering but is preferably machined after sintering. The hole 13 is designed so as to receive an appropriate mounting means, e.g., a screw, when the finally prepared insert is to be mounted in an appropriate holder.

In the embodiment of FIGS. 1 and 2, the shape of the central hole is defined by a preformed cemented carbide insert 14 which is brazed into place in the central hole 13. It will be appreciated that this cemented carbide insert 14 can be preformed into any particular shape necessary for the ultimate mounting. By performing the cemented carbide body 14 by pressing and sintering, various shapes of the central hole can be accurately and relatively easily made. Preferably, the cemented carbide of insert 14 is the same as that of layer 12. If desired, a chip breaking geometry may be formed (e.g., by EDM) on the appropriate surfaces of the superhard layer.

As shown in FIG. 2, the insert 14 is preferably preformed into a shape in which the inner walls 15 converge in a generally conical manner from the top of the superhard layer 11 towards the bottom of the hard material 12. Such a design assists in securing the screw (not shown) firmly within the central hole when attaching the insert to the holder.

In FIG. 1, there is indicated in dotted lines 14 a circle in which round inserts can be formed, if desired, of the superhard material and cemented carbide.

FIGS. 3 and 4 depicts another embodiment of the invention. In this aspect, the superhard cutting material 31 is first made with a shape such as described in Provisional Patent Application No. 60/474,956, herein incorporated by reference in its entirety, and cut into the particular shape as shown. The cemented carbide is either made in one piece or made as two pieces 32 and 34 as shown brazed together along braze lines 36 and 37. Again, the central hole 33 may be shaped by the perform 34 to the desired shape for ultimate mounting. In FIG. 4, line 38 depicts the final shape of a cutting insert to be formed from perform 32. Although the description has indicated that the center hole 13 is cut to a size sufficient to allow the cemented carbide insert 14 to be brazed into that hole, it should be understood, particularly if the initial blank is of sufficient size, that the material removed from the blank to form the center hole 13 may itself serve as a blank for the preparation of another, albeit smaller, cutting insert.

The substrate 12 is formed from any suitable hard material. Examples of suitable materials include cemented carbides, cermets, and hard metal alloys. One suitable composition is a WC-Co cemented carbide having 10 to 20 weight % Co, and preferably having 15 to 17 weight % Co. The superhard material 11 can comprise any suitable material chosen for its cutting characteristics.

The superhard material 11 can comprise a boron nitride, such as cubic boron nitride (CBN), or a diamond material such as polycrystalline diamond (PCD). The CBN or PCD material may have additions of other materials, such as carbides, nitrides, carbonitrides, oxides, and/or borides of metals chosen from groups IVa to Vla of the periodic table. The superhard material 16 can be in the form of a composite of CBN or PCD particles forming a first phase, and at least a second phase of a semiconductor (e.g.—Si), metal (e.g.—Cu, Ti, Al), metalloid, or alloys thereof.

The sintering type treatment can be performed at elevated temperatures and pressures as described, for example, in U.S. Pat. No. 5,676,496. Examples of suitable processes are described, for example, in U.S. Pat. Nos. 4,991,467 and 5,115,697, the disclosures of which are incorporated herein by reference, in their entirety.

The cutting tips 31 can be formed from a disk by any suitable cutting or material removal/separation procedure. Once such procedure is wire cutting, such as EDM wire cutting.

The cutting tips can be provided with any suitable geometry. According to one advantageous aspect of the present invention, the cutting tips 31 are provided with a geometry that will provide a mechanical retention or lock when placed within the body of an indexable cutting insert in addition to the brazed joints, as will be described in more detail. Acording to the illustrated embodiment of FIG. 3, a cutting tip 31 which is removed from the blank 10 has a geometry or shape that can generally be characterized as a dovetail shape or geometry.

A specific illustrative example of this type of cutting tip geometry comprehended by the present invention is illustrated in FIG. 3. The geometry or shape of the cutting tip 31 illustrated in FIG. 3 can be described as follows. A pair of converging forward surfaces 42a and 42b meet at a forward nose 44, which is preferably rounded. The nose 44 is presented to the workpiece during use of the cutting tip. As illustrated in FIG. 3, a portion of the surfaces 42a and 42b, and the nose 44 comprise superhard cutting material 31. The extent of superhard cutting material 31 extending from the apex of the nose 44 and back along surfaces 42a and 42b corresponds to dimension “L”, and can be termed the leg length. According to one embodiment of the present invention, the dimension L is at least 2 mm. According to another embodiment, the dimension L can be at least 3 mm.

Moving in the direction away from the forward nose 44, subsequent to the converging surfaces 42a and 42b is an area of reduced width or a waisted section 45. The waisted section is defined by a first pair of angled surfaces 46a and 46b, as well as a second set of surfaces 48a and 48b. Surfaces 46a and 48a, as well as 46b and 48b meet at the area of reduced width and define a trough-like formation. The cutting tip may also comprise a planar rear surface 49.

Numerous modifications to the above-described geometry are contemplated, so long as the insert geometry provides a self-locating, self-retention property when placed in a cutting insert body.

Additional advantages will be evident to those of ordinary skill in the art.

The described embodiments of the present invention are intended to be illustrative rather than restrictive, and are not intended to represent every possible embodiment of the present invention. Various modifications can be made to the disclosed embodiments without departing form the spirit or scope of the invention as set forth in the following claims, both literally and in equivalents recognized by law.

Claims

1-10. (canceled)

11. A cutting insert comprising a base portion of a superhard material or a cemented carbide, a layer of superhard material attached to said base and a hole through both said base portion and layer, said hole extending generally conically from said layer through said base, wherein said hole is in a cemented carbide body attached to said base portion and said superhard layer.

12. The cutting insert of claim 1 wherein said base portion is a cemented carbide and said layer of superhard material is attached to said base by sintering.

13. The cutting insert of claim 2 wherein said cemented carbide body is attached to said base portion and said superhard layer by brazing.

14. The cutting insert of claim 1 wherein said superhard material is cubic boron nitride or polycrystalline diamond.

15. The cutting insert of claim 1 wherein said superhard layer includes a chip breaker portion.

16. A method for making a cutting insert comprising:

forming a layer of superhard material;

attaching said layer onto a superhard material or a cemented carbide substrate;

forming a hole through said layers; and

attaching a preformed annular body within said hole.

17. The method of claim 6 wherein the preformed annular body has a through hole of conical shape.

18. The method of claim 6 wherein said substrate is a cemented carbide and said layer is attached to said substrate by sintering.

19. The method of claim 6 wherein said preformed annular body is attached by brazing.

20. The method of claim 6 wherein said layer and said substrate are both made of a superhard material.