1. Field of the Invention
The present invention relates to a diamond tool. More particularly, the invention relates to a diamond tool with a metal plate inserted therein, in which between abrasive layers containing diamond particles is inserted a ferrous or non-ferrous metal plate having a wear resistance lower than that of the abrasive layers so that a concave groove is spontaneously formed during a workpiece cutting process, thereby reducing the contact load with a workpiece to thereby avoid vibration (wobbling) of a shank and providing a discharge path through cutting chips and the cooling water are smoothly removed. In addition, the invention is applied to all the applicable tools such as a saw, a core drill, a cutter, a saw blade, a wire saw, and the like.
2. Background of the Related Art
In general, a diamond tool comprises a diamond grinding stone portion that is attached to a shank to cut and grind a workpiece, and a shank through which the grinding stone portion is mounted to a cutting or grinding machine. Here, the cutting tip comprises a plurality of diamond particles and a metallic bonding material. Diamond, abrasive or diamond particle generally means a natural or synthetic diamond, cubic boron nitride, and additionally a super abrasive such as silicone carbide and alumina and also a mixture of at least two of the aforementioned materials. Furthermore, the shank is commonly formed of a metallic material such as stainless steel and carbon steel.
As a method of bonding the abrasive or grinding stone portion to a shank, a sintered-tip welding method (hereinafter, referred to as a “sintering method”) has been known. In this sintering method, a metallic bonding material and abrasives are generally mixed, press-formed and sintered to form a cutting tip, and then the sintered cutting tip is bonded to a shank through a silver brazing, a laser welding, or a resistance welding.
FIG. 1a is a partial front view of a conventional saw blade where a cutting tip formed by a sintering method is attached to a shank. FIG. 1b is a cross-section taken along line I—I of FIG. 1a. 
A typical saw blade has the shape of a circular plate, and a plurality of cutting tips are formed at regular intervals along the circumference thereof in such a manner that they protrude in a radial direction. FIGS. 1a and 1b show a part of the cutting tips. As previously described, in the sintering method, a metallic bonding material 120 and abrasives 130 are beforehand mixed, press-formed, and sintered. Thus, as shown in FIG. 1b, the cutting tip has such a structure that a plurality of abrasives 130 are non-uniformly dispersed in the metallic bonding material 120. This cutting tip is bonded to a shank 110 through a welded portion 115 formed through a laser welding, a silver brazing, or a resistance welding. Here, the cutting tip is provided with a blank 125 formed at the bonding area with the shank 110. The blank 125 has only a bonding material without the abrasives 130 so that a subsequent laser welding with the shank 110 can be easily performed.
As another method of manufacturing a saw blade, it has been known a method of simultaneously compacting and sintering together with a shank, which is different from the aforementioned method. In this simultaneous compacting and sintering method, a shank 110 is positioned at the center of a mold, and a powder mixture of metallic bonding material 120 and diamond particles 130 is filled in the mold. Then, the metallic bonding material 120 and the abrasives 130 are powder-compacted and sintered, along with the shank 110, thereby fabricating a diamond tool. This method is commonly used in manufacturing general cutter products. Hereinafter, therefore, a sintering method means all the methods of fabricating diamond tools, including the method where a cutting tip is separately formed and bonded to a shank through a laser welding, a silver brazing, and a resistance welding, the simultaneous compacting and sintering method, and the like.
On the other hand, it should be noted that the size and shape of diamond particles shown in FIGS. 2a and 2b (including the other figures) are exaggerated relative to those of a shank 110 or the like, for the purpose of clear illustration therefor, and also the number of illustrated diamond particles may be more or less than the actual number thereof.
FIG. 2 shows a worn state of the cutting tip of a conventional saw blade formed by a sintering method when the conventional saw blade is used to cut a workpiece.
FIG. 2(a) is a partial sectionals view showing a cutting tip 140 comprised of a metallic bonding material 120 and abrasives 130, and a shank 110 with the cutting tip 140 attached thereto in the saw blade of FIG. 1b. That is, FIG. 2(a) shows a state before the cutting tip 140 is used. When the above saw blade is used for cutting a workpiece, the cutting process is carried out initially while the leading edge portion 140a of the cutting tip 140 contacts the workpiece. Then, the side portion 140b of the cutting tip 140 is also participated in the cutting process, along with the leading edge portion 140a thereof.
In the above conventional saw blade, the leading edge portion 140a of the cutting tip 140 is flat and thus its initial cutting force is lowered due to an increased load in the initial cutting process. In addition, as the saw blade is used over time, the cutting tip 140 is worn gradually. At this time, the height and width of the cutting tip 140 are reduced and also the leading edge portion 140a thereof becomes rounded, as shown in FIG. 2(b). This rounded shape of the leading edge portion 140a results from the fact that the cutting work is performed most actively at an area where the leading edge and the side portion of the cutting tip join with each other. In this way, during the cutting process, the leading edge portion 140a is worn to a rounded shape, and thus, the friction area thereof is increased to thereby cause a wobbling phenomenon, which leads to degradation in the cutting performance thereof. Furthermore, when machining a workpiece, an appropriate discharge path for the release of cutting chips and the cooling water is not provided, thereby failing to provide an excellent cutting performance.
FIG. 2a shows a worn state of the cutting tip of a conventional saw blade when the conventional saw blade spontaneously forming a convex groove during the cutting process is used to cut a workpiece.
In order to solve the above problems, various approaches for fabricating a diamond tip have been proposed. One of them is presented in FIG. 3a (a). The cutting tip of FIG. 3a (a) is configured in such a manner that the content of abrasives 130 is uniform throughout an entire cutting tip, but the side metallic bonding material 120b has a higher wear resistance than that of the central metallic bonding material 120a. Thus, as shown in FIG. 3a (b), during the cutting process, a concave groove 154 is formed spontaneously, due to friction with the workpiece 160. Alternatively, as shown in FIG. 3b (a), in order for the wear resistance of the bonding material to be uniform throughout an entire cutting tip, the content of abrasives 130 may be made to be higher at the side portion of the cutting tip, as compared with the central portion thereof. Therefore, as shown in FIG. 3b (b), due to friction with a workpiece 160 during a cutting or grinding work, a concave groove 154 can be formed spontaneously. As another alternative, the cutting tip shown in FIG. 3c (a) is configured in such a way that the wear resistance of the side bonding material 120b is higher than that of the central bonding material 120a and also the abrasive content of the side portion is higher than that of the central portion. Therefore, as shown in FIG. 3c (b), a concave groove 154 is formed spontaneously due to friction with a workpiece 160.
In the conventional cutting tip manufacturing methods having the aforementioned construction, however, both side portions and the central portion of the cutting tip must be made to be different from each other in terms of their abrasive contents and their wear resistance. Therefore, the procedures for mixing the abrasives and the bonding materials and their powder-compaction become complicated. In addition, since the cutting tip has a three-layered structure of both side portions and the central portion, the press-forming process must require considering the properties of each layer appropriately, and thus becomes more complicated, as compared with the case having a uniform structure. Consequently, this complicated process will result in an increase in the manufacturing cost and a decrease in the productivity, and will be likely to cause errors of workers.
Furthermore, in the sintering process for the above cutting tip structure, since the abrasive contents and the wear resistances of bonding material in both side portions and the central portion are different, the shrinkage rates of the respective portions become different from each other. Thus, it is difficult to manufacture a sintered cutting tip having good mechanical properties. Also, in the design process therefor, there is a disadvantage in that the content of diamond particles must be adjusted and the wear resistance of bonding material must be determined, depending on the working conditions of tool, the workpiece to be machined, or the like after selecting one of the cutting tips shown in FIGS. 3a, 3b, and 3c. 