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 typically have a polygonal shape with a superhard material disclosed at the corners thereof. 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 2-4 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.
French Patent Publication No. 2,691,657 discloses a cutting insert made with a special autocentering shape made of polycrystalline diamond, CBN or other cutting material. The insert is clamped into the tip by a spring without brazing.
French Patent Publication No. 2,706,339, also an insert of similar materials of a shape (including securing lugs) such that the insert can be secured in the corresponding hole in the tip by a mechanical wedging without brazing.
Thus, a need exists in the art to address the problems discussed above and others.