WO2005084879A1

WO2005084879A1 - Diamond tool with separate tip attached and method for manufacturing the same

Info

Publication number: WO2005084879A1
Application number: PCT/KR2005/000590
Authority: WO
Inventors: Min Seok Song; Mun Seok Park; Kee Jeong Cheong; Shin Kyung Kim; Joon Won Suh; Hwan Chul Lee
Original assignee: Shinhan Diamond Industrial Co., Ltd.
Priority date: 2004-03-05
Filing date: 2005-03-03
Publication date: 2005-09-15
Also published as: KR100592711B1; KR20050089674A

Abstract

The present invention relates to a diamond tool manufactured through brazing or electroplating and a method for manufacturing the same. The object of the invention is to provide a diamond tool in which a shank and a tip member having abrasives attached thereto are manufactured separately and then bonded to each other to avoid heat-treatment unnecessary to the shank and thermal deformation resulting therefrom, a tip member thereof, and a method for manufacturing the diamond tool. The diamond tool of the invention for achieving the object comprises a shank and a tip member bonded to the shank. The tip member comprises a base material and a plurality of abrasives attached to at least a part of a surface of the base material except a bonding portion of the tip member that is to be bonded to the shank. The bonding portion of the tip member is bonded to the shank.

Description

Description DIAMOND TOOL WITH SEPARATE TIP ATTACHED AND METHOD FOR MANUFACTURING THE SAME Technical Field

[1] The present invention relates to a diamond tool manufactured through brazing and a method for manufacturing the same, and more particularly, to a diamond tool in which a shank and a cutting or grinding tip member are manufactured separately and then bonded to each other, a tip member thereof, and a method for manufacturing the diamond tool.

[2] The invention is also applied to building-stone tools such as a saw, a core drill, a cutter, a saw blade, a polishing cup, a profiler and an end mill, and industrial precision tools such as a straight wheel, an ID wheel, a rotary dresser and an edge grinding wheel. Background Art

[3] In general, a diamond tool comprises a shank and a diamond grinding stone portion (abrasive-impregnated section) attached to the shank to cut and grind a workpiece. Here, the abrasive-impregnated section comprises a plurality of diamond particles and a metallic bonding material. As used herein, the term "diamond" generally means a natural and synthetic diamond, cubic boron nitride (cBN), and additionally a super abrasive such as silicone carbide and alumina, and also a mixture of two or more thereof. Furthermore, the shank is commonly formed of a metallic material such as stainless steel and carbon steel.

[4] As a method for bonding the abrasive or diamond-impregnated section to a shank, it is well known a sintered-tip welding method (hereinafter, referred to as a "sintering method"), an electroplating method, a brazing method, or the like. In the sintering method, a metallic bonding material and abrasives are mixed, press-compacted, and sintered to form a cutting tip, and then the sintered cutting tip is bonded to a shank through silver brazing, laser welding, resistance welding or the like. In the electroplating method, abrasives are attached to a shank through a wet electroplating process using a bonding material such as nickel. In the brazing method, a liquid paste of a metallic bonding material and a binder is coated on the shank, abrasives are dispersed therein, and the dispersed abrasives are bonded to the shank at an elevated temperature. Fig. 1 is a sectional view of abrasives 130 bonded to a shank 110 via a bonding material 120 respectively through a sintering method (Fig. 1 (a)), an electroplating method (Fig. 1 (b)), and a brazing method (Fig. 1 (c)).

[5] Fig. 2 is a front view of a saw blade where abrasives 130 are attached to a shank 110 through a sintering method, and Fig. 3 is a sectional view taken along line II-II in Fig. 2. As described above, in the sintering method, a metallic bonding material 120 and abrasives 130 are mixed, press-formed, and sintered. Thus, as shown in Fig. 3, the cutting tip has a structure where 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 weldment 115 formed by laser welding, silver brazing, or resistance welding. Here, the cutting tip is provided with a blank 125 formed at the bonding area with the shank 110, as shown in Fig. 3. The blank 125 has no abrasive 130 so that subsequent laser welding with the shank 110 can be easily performed.

[6] Fig. 4 is a front view of a saw blade where abrasives 130 are bonded to a shank 110 through a brazing method or an electroplating method. Fig. 5 is a sectional view taken along line III-III in Fig. 4. As described above, in the brazing or electroplating method, the abrasives are directly attached to the shank 110, and thus the abrasives 130 are bonded to the surface of the shank 110 in a mono-layer, as shown in Fig. 5.

[7] Above about 80% of diamond tools are manufactured by the sintering method. In the diamond tools formed by the sintering method, abrasives are distributed in a multilayer and in a non-uniform fashion, and the sintering method cannot be readily applied to a very complicated shank. In contrast, the electroplating and brazing method can form a single non-uniform abrasive layer or a uniform abrasive layer, and thus suitable to manufacture a diamond tool having a complicated structure. In addition, the sintering and electroplating methods do not associate a chemical reaction between diamond particles and the metallic bonding material to thereby involve mechanical bonding having a relatively weak retention force. In the brazing method, strong chemical bonding is occurred in the interface between the abrasives and the metallic bonding material, and thus the abrasives are rarely released during the use of tools. In addition, it does not necessitate a time- and cost-consuming dressing process, and can be used in a bi-directional cutting and grinding process. Accordingly, diamond tools manufactured through a brazing method have good cutting performance, as compared with ones manufactured by a sintering or electroplating method, and in particular provides appropriate characteristics to a dry process or DIY (do-it-yourself) products. Furthermore, the brazing method can maximize exposure of the abrasives, precisely control the abrasive spacing, and form a chip pocket to thereby enable smooth flowability of slurry and grinding liquid. Moreover, in case where Ni-Cr alloy is used, the presence of Cr leads to good corrosion resistance.

[8] As described above, the brazing method has various merits. Fig. 6 explains a process of bonding abrasives to a shank according to a brazing method. As shown in Fig. 6, a bonding material 120 containing brazing metal powder in the form of paste is coated on a shank 110 (Fig. 6 (a)), and then, a plurality of abrasives 130 are dispersed in the coated paste (Fig. 6 (b)). Here, the paste bonding material 120, which is used to bond the abrasives 130 to the shank 110, commonly contains metal powder and a binder providing flowability to the metal power. In addition, a drying process may be provided between the bonding material coating and the abrasive dispersion. The coated bonding material 120 and the abrasives 130 dispersed therein are dried at a certain temperature (Fig. 6 (c)). Thereafter, the resultant product is held in a vacuum furnace or a reduction/inert gas atmosphere furnace at a certain elevated temperature, where the metal power in the bonding material can flow in a liquid phase state and react chemically, such that the brazing metallic bonding material is melted and adhered to the shank 110 and the abrasives 110 (Fig. 6 (d)). At this time, the holding temperature depends on the type of the commercialized pastes, for example, about 600~1300°C.

[9] Fig. 7 shows an example in which abrasives 130 are attached to the shank 110 through a metallic bonding material as shown in Fig. 6 (d). A cutting tool such as a saw blade 100, for example having abrasives dispersed in a bonding paste, is placed in a furnace 300 maintained in a desired atmosphere required for brazing the saw blade 100. Then the furnace 300 is heated by means of a high frequency induction coil 310, for example, up to about 600-1300 °C, thereby bonding the abrasives to the shank.

[10] In addition, Fig. 8 shows a process of bonding abrasives to a shank through an electroplating method that can provide a non-uniform mono-layer of abrasives or a uniform abrasive layer and is suitable for manufacturing a diamond tool of complicated structure. As shown in Fig. 8 (a), a non-conductive film 115 is coated on a portion of a shank that abrasives are not to be attached, in order to prevent that portion from being electroplated. Abrasives 130 are uniformly disposed on the surface in the shank that the non-conductive film 115 is not coated (Fig. 8 (b)), and the resultant product is put in an electroplating bath to perform a wet electroplating process. Then, the area coated with the non-conductive film 115 and the non-conductive abrasives are not electroplated, and only the area in the shank that the abrasives 130 are disposed is electroplated. Thus, the abrasives 130 are bonded through a bonding material 120 formed by the electroplating (Fig. 8 (c)). Upon completion of the electroplating, the non- conductive film 115 is removed for subsequent procedures such as a coloring process (Fig. 8 (d)).

[11] However, contrary to the sintering method or electroplating method, in the brazing method, the shank and the abrasives are heat-treated together in a vacuum or gas atmosphere furnace of high temperature, so that thermal stress and thus thermal deformation is caused in the shank due to the high temperature. This thermal deformation leads to wobbling by unbalance of a tool when it rotates. In addition, the heat-treatment in the furnace may deteriorate significantly the mechanical property of the shank such as strength, hardness, toughness, and the like. Furthermore, in the sintering method, only the abrasive-impregnated section to be welded to a shank is heat-treated in a furnace. In the brazing method or the electroplating method, the entire tool including the shank is heat-treated inside a furnace, or immersed in an electroplating both. Accordingly, the brazing and electroplating methods necessitate a furnace or an electroplating both having an adequate size to accommodate the entire tool including the shank, contrary to the sintering method. In particular, in case of a large-sized saw blade having, for example, a diameter of l~2.5m, a large scaled furnace or electroplating bath is required for receiving the whole saw blade including the shank. In case of brazing method, the shank is unnecessarily heat-treated to thereby waste energy.

[12] Furthermore, in case of the electroplating method, all the area in the shank that abrasives are not to be provided must be coated with a non-conductive film, thus causing unnecessary consumption of non-conductive film, which leads to increase in the manufacturing cost of diamond tools. Disclosure of Invention Technical Problem

[13] The present invention is conceived to solve the above problems in the prior art, and an object of the invention is to provide a diamond tool in which a shank and a tip member having abrasives attached thereto are manufactured separately and then bonded to each other to avoid heat-treatment unnecessary to the shank and thermal deformation resulting therefrom, a tip member thereof, and a method for manufacturing the diamond tool.

[14] Another object of the invention is to provide a diamond tool that can be manufactured less expensively even in case of a large-scale diamond, a tip member thereof, and a method for manufacturing the diamond tool. Technical Solution

[15] According to the present invention for achieving these objects, there is provided a tip member to be attached to a shank of a diamond tool, comprising a base material; and a plurality of abrasives attached to at least a part of a surface of the base material except a bonding portion of the tip member that is to be bonded to the shank.

[16] In the tip member of the present invention, a plurality of depressed portions may be formed in the surface of the base material, and a plurality of abrasives may be attached to inner spaces of the depressed portions. Alternatively, each of the depressed portions may comprise a dimple type depressed portion, a groove type depressed portion, or a through-hole type depressed portion. A groove may be formed in a top surface of the tip member and a through-hole may be formed in a lateral face of the tip member.

[17] In the tip member of the present invention, a plurality of abrasives may be attached to a surface of the shank and an upper side of the depressed portions to which the abrasives and a bonding material are attached. The portion of the base material to which the plurality of abrasives are attached may have a thickness larger than that of the bonding portion. The abrasives may comprise synthetic or natural diamond, cubic boron nitride (cBN), silicone carbide, alumina, and a mixture of two or more thereof.

[18] The present invention also provides a diamond tool, comprising a shank; and one or more tip members described above, wherein a bonding portion of each of the tip members is bonded to the shank.

[19] In the diamond tool of the present invention, positioning members may be provided in the bonding portion of the tip member and a bonding region of the shank to which the tip member is bonded. The positioning member may comprise a prominence and depression formed such that the bonding portion of the tip member is engaged with the bonding region of the shank. The shank and a base material for the tip member may be formed of an identical material. The thickness of the bonding portion of the tip member may be different from that of the shank. The diamond tool may include a saw, a core drill, a cutter, a saw blade, a polishing cup, a profiler, an end mill, a straight wheel, an ID wheel, a rotary dresser, or an edge grinding wheel.

[20] The present invention further provides a method for manufacturing a diamond tool, comprising the steps of manufacturing a tip member by attaching a plurality of abrasives to a part of a surface of a base material; preparing a shank of the diamond tool; and attaching the tip member to the shank.

[21] In the method of the present invention, the step of the manufacturing the tip member may comprise the step of attaching the plurality of abrasives to the base material through brazing. The step of the manufacturing the tip member may comprise the steps of coating a bonding material in the form of paste on the part of the surface of the base material of the tip member; dispersing the plurality of abrasives in the coated bonding material; drying the bonding material; and heating the base material to perform fusion-bonding. Alternatively, the step of the manufacturing the tip member may comprise the steps of preparing a mixture of a bonding material in the form of paste and the plurality of abrasives; coating the mixture on the part of the surface of the base material of the tip member; and performing fusion-bonding by heating the base material.

[22] The step of the manufacturing the tip member may comprise the step of attaching the plurality of abrasives to the base material through electroplating. The step of the manufacturing the tip member may comprise the steps of coating a non-conductive film on a part of the surface of the base material of the tip member except the portion thereof to which the abrasives are to be attached; dispersing the plurality of abrasives on another part of the surface of the base material except the part thereof on which the non-conductive film is coated; and electroplating the base material. The method may further comprise the step of removing the non-conductive film after the step of electroplating the base material. [23] The tip member may be bonded to the shank through silver brazing, resistance welding or laser welding. [24] The step of performing the fusion-bonding may be carried out using a batch-type vacuum furnace, a reduction/inert gas atmosphere furnace, or a continuous-type gas atmosphere furnace. The reduction/inert gas may comprise hydrogen gas. [25] That is, according to the invention, the tip member and the shank are separately manufactured and then bonded to each other, contrary to a conventional technique where a grinding/cutting tip and a shank are usually formed of an identical base material and abrasives are bonded to a part of the base material. Brief Description of the Drawings [26] Fig. 1 is a sectional view of abrasives bonded to a shank respectively through a sintering method (Fig. 1 (a)), an electroplating method (Fig. 1 (b)) and a brazing method (Fig. 1 (c). [27] Figs. 2 and 3 are a front view and a sectional view of a saw blade where abrasives are bonded to a shank through a sintering method. [28] Figs. 4 and 5 are a front view and a sectional view of a saw blade where abrasives are bonded to a shank through a brazing or electroplating method. [29] Fig. 6 shows a process of bonding abrasives to a shank through a conventional brazing method. [30] Fig. 7 is a schematic view illustrating the brazing method through heat treatment after abrasives are dispersed on the shank. [31] Fig. 8 shows a process of bonding abrasives to a shank through an electroplating method. [32] Fig. 9 is a schematic view explaining a diamond tool according to the present invention. [33] Fig. 10 is a schematic perspective view showing a tip member according to the present invention. [34] Figs. 11 and 12 are sectional views schematically showing a tip member according to the invention. [35] Figs. 13 and 14 show modified examples of a diamond tool according to the invention. [36] Figs. 15 and 16 shows other modified examples of a diamond tool according to the invention. [37] Fig. 17 shows a process of manufacturing a tip member having multiple abrasive layers through a brazing method according to the invention. [38] Fig. 18 shows a process of manufacturing a tip member having multiple abrasive layers through an electroplating method according to the invention.

[39] Figs. 19 and 20 are sectional views showing another examples of a depressed portion formed in the surface of a tip member.

[40] Figs. 21 to 23 are a perspective view, a font view and a sectional view showing another example of a depressed portion formed in the surface of a tip member.

[41] Figs. 24 to 26 are a perspective view, a font view and a sectional view showing yet another example of a depressed portion formed in the surface of a tip member.

[42] Figs. 27 to 29 are a perspective view, a front view and a sectional view showing a further example of a depressed portion formed in the surface of a tip member.

[43] Fig. 30 is a sectional view of a tip member having multiple abrasive layers according to the invention.

[44] Figs. 31 and 32 show core drills to which the present invention is applied. Best Mode for Carrying Out the Invention

[45] Hereinafter, a diamond tool and a tip member thereof, and a method for manufacturing the diamond tool will be described by way of example in connection with a saw blade with reference to the accompanying drawings. A typical saw blade has the shape of a circular disk and is provided with a plurality of cutting tips formed at regular intervals along the circumference thereof so as to protrude in radial directions. Abrasives are attached in these cutting tips, which participate in the cutting or grinding work.

[46] Fig. 9 shows a saw blade 200 as an example of a diamond tool according to the invention. The saw blade 200 comprises a shank 220 and plural tip members 210 having abrasives attached thereto, which cut or grind a workpiece. The tip members 210 are bonded to the shank 220 through silver brazing, laser welding, or resistance welding. As shown in Fig. 10, the tip member 210 includes a grinding/cutting portion 210a to which abrasives are attached, and a bonding portion 210b through which the tip member 210 is bonded to a shank 220. The tip member 210 is formed by providing a base material having the same shape as the cutting tip or part of the cutting tip of the saw blade 200 and bonding plural abrasives to the grinding/cutting portion 210a. The bonding portion 210b of the tip member 210 does not have abrasives so as to be bonded to the shank 220.

[47] In general, a diamond tool is constructed such that an abrasive containing portion has a thickness larger by about 10-45% than that of the shank to thereby provide a same appropriate clearance to both sides of the shank, thus preventing impact to the shank, degradation of the shank, and deterioration of cutting performance, which might be caused by contact and friction with a workpiece. That is, in the tip member 210, the thickness tl of the grinding/cutting portion 210a is preferred to be larger than the thickness t2 of the bonding portion 210b. In case of a small diamond tool, commonly, a shank having a uniform thickness is used and abrasives are bonded to the shank through a brazing or electroplating method to thereby form an abrasive portion. At this time, the abrasive portion can be made to have a desired thickness larger than the remaining shank portion. Thus, a clearance does not need to be formed, beforehand, in a base material for the tip member 210. In this case, the thickness of the shank 220 can be the same as that of the tip member 210. Alternatively, as shown in Fig. 11, the tip member 210 may be made to have a relatively higher height and then bonded to a shank 220 having a thickness larger than the tip member 210, considering the cutting depth of a workpiece by the diamond tool. In this case, the thickness of the cutting portion is relatively thin, but a thicker shank can be used, so that the strength of diamond tool can be improved.

[48] However, in case where the shank is thick to the extent that the attachment of abrasives thereto cannot provide a desired thickness larger than that of the shank, a clearance is preferred to be formed in the base material of the tip member 210. That is, in the base material, the thickness of the grinding/cutting portion 210a is preferred to be made larger than that of the bonding portion 210b. On the other hand, abrasives are bonded to all the surface of the tip member excepting the bottom face thereof or the bottom face and part of adjacent side face, so that the bottom face can serve as a bonding portion 210b or the height of the boding portion 210b in Fig. 10 can be made lower. In this case, as shown in Fig. 12, the tip member 210 can be attached to a shank 220 having a thickness smaller than that of the tip member 210, without forming beforehand a clearance in the base material for the tip member 210.

[49] The bonding of abrasives to the grinding/cutting portion 210a of the tip member 210 may be performed through a conventional brazing method shown in Fig. 6. That is, a bonding material 120 in the form of paste, which is composed of brazing metal powder and a binder, is coated on the surface of the grinding/cutting portion 210a of the tip member 210, and then plural abrasives 130 are dispersed in the coated paste. The coated paste may be pre-dried before dispersing the abrasives 130. The bonding material 120 with the abrasives 130 dispersed therein is dried at a desired temperature, and thereafter, heat-treated at a desired temperature of a reduction or inert atmosphere such that the brazing metal powder is melted and adhered to the grinding/cutting portion 210a and the abrasives 130 to thereby form a tip member 210. For the reduction or inert atmosphere, high purity hydrogen is used. The shank 220 is manufactured so as to have the same thickness as the bonding portion 210b of the tip member 210 or have a thickness smaller than that thereof. The finished tip member 210 is bonded to the shank 220 through silver brazing, laser welding, or resistance welding. Here, the shank 220 and the tip member 210 are formed, preferably, of materials that can be easily bonded to each other, more preferably, of a same material. On the other hand, the above procedures, where the paste bonding material 120 is coated and plural abrasives 130 are dispersed therein, may be replaced by a process, in which a mixture of bonding paste material 120 and plural abrasives 130 is coated on the surface of a base material for the tip member 210.

[50] Abrasives may be attached to the grinding/cutting portion 210a through a conventional electroplating method, as shown in Fig. 8. That is, in a base material for the tip member 210, a non-conductive film 115 is coated in the bonding portion thereof. The abrasives 130 are disposed uniformly in the grinding/cutting portion 210a, where the non-conductive film 115 is not coated, and the resultant product is put in an electroplating bath to perform a wet electroplating process, such that only the area not coated with the non-conductive film 115 is electroplated. Thus, the abrasives are bonded through a bonding material formed by the electroplating. Upon completion of the electroplating, the non-conductive film 120 is removed for subsequent procedures such as a coloring process.

[51] When the tip member 210 is bonded to a shank 220, it must be bonded at a correct position on the shank 220. For this purpose, the boding portion 210b of the tip member 210 and the shank 220 are provided with a positioning member 21 la, 21 lb, 221a, 221b in order for the tip member 210 to be bonded at the correct position on the shank 220, as shown in Figs. 13 and 14. In particular, the positioning member 21 la, 21 lb, 221a, 221b assists in bonding the tip member at the correct position on the shank. It also increases the resistant force against the circumferential external force exerted by a workpiece when the tool rotates (clockwise in Fig. 14), thereby preventing the tip member from being released from the shank. The positioning member is not limited to the prominence and depression shown in Figs. 13 and 14, which is designed such that the bonding portion of the tip member is tooth-engaged with the bonding area of the shank. It may employ other types of prominence and depression such as protrusions and grooves, as long as they conform and fit to each other. In addition, the positioning member may include a marking indicated in the tip member and the shank.

[52] According to the invention, the aforementioned tip member of a diamond tool is manufactured by attaching abrasives to a base material, which has the same shape as a common-type cutting tip or a part of the cutting tip. In this case, a number of tip members must be attached to a shank, and thus such a time-consuming procedure must be repeated many times. Figs. 15 and 16 show a modification according to the invention in order to solve the above disadvantages. First, as shown in Fig. 15, the base material for tip member is designed such that plural tip members 410a can be formed in a single piece of base material, thereby enabling easy bonding of the tip member 410a to a circular shank. In case of a large diamond tool, however, such a large-sized tip member 410a cannot be easily and readily heat-treated or electroplated, and thus the tip member 410a can be divided into several pieces, as shown in Fig. 16. As shown in Fig. 16, the tip member 410 of Fig. 15 is divided into four tip members 410b such that they can be easily brazed or electroplated in a small furnace or a small electroplating bath, but easily bonded to the shank, as compared with the tip member 210 shown in Fig. 9.

[53] On the other hand, the aforementioned tip member of the invention is formed through a brazing or electroplating method. In the brazing or electroplating method, typically a mono-layer of abrasive is formed, as shown in Figs. 1(b) and 1 (c), and thus the service life thereof is shortened, as compared with a diamond tool manufactured through a sintering method. In order to solve this problem, the present invention proposes a method for forming multiple abrasive layers using a brazing or electroplating method.

[54] Fig. 17 shows a process of forming a tip member with multiple abrasive layers according to the invention. Fig. 17 shows only a part of the tip member to which abrasives are to be attached. As shown in Fig. 17 (a), first, a plurality of depressed portion 520 are formed in a base material 510 for the tip member. The depth d, the width w and the spacing s of the depressed portion are to be determined, based on the size of abrasives. That is, considering the maximum diameter a of the abrasive, the depth d and the width w of the depressed portion 520 are predetermined, and these depressed portions are formed so as to be spaced apart from one another with certain desired spacing s provided between neighboring depressed portions.

[55] In Fig. 17 (a), the cross section of the depressed portion 520 is illustrated as a rectangular shape, but not limited thereto. Other shapes of the depressed portion 520 will be hereinafter explained. In order to form a lower abrasive layer, as shown in Fig. 17 (b), a bonding material 530a in the form of paste containing brazing metal powder and a binder is coated inside the depressed portions 520 of the base material in Fig. 17 (a). Then, a plurality of abrasives 540a are filled in the bonding paste coated in the depressed portion 520 and thereafter the bonding material 530a with the abrasives contained therein are primarily dried at a desired temperature (Fig. 17 (c)). The bonding paste 530a may be pre-dried before the abrasives 540a is dispersed in the coated paste. Next, in order to form an upper abrasive layer, a bonding paste 530b in the form of paste comprising brazing metal powder and a binder is coated again on the top of the depressed portion 520 filled with the bonding paste 530a and the abrasives 540a and on the surface of the base material 510 (i.e., the top surface of the wall) (Fig. 17 (d)). Then, a plurality of abrasives 540b are dispersed in the bonding paste 530b coated on the surface of the base material 510 and they are secondarily dried at a desired temperature (Fig. 17 (e)). Upon completion of drying, the resultant product is heat-treated in a vacuum or reduction/inert gas atmosphere brazing furnace at a certain desired temperature, such that the brazing metal powder can be melted and adhered to the abrasives 540a and 540b and the base material 510, as shown in Fig. 17 (f). Here, the vacuum furnace is mostly a batch type furnace so that a good productivity cannot be expected, but in the reduction/inert gas atmospheric furnace, a continuous brazing process using a conveyor can be utilized to thereby enhance the production efficiency significantly.

[56] On the other hand, as described above, the bonding paste 530a or 530b is first coated in the depressed portions and then the plural abrasives 540a or 540b are dispersed in the coated bonding paste 530a or 530b. Alternatively, the bonding paste 530a and the abrasives 540a may be first mixed and the mixture may be then coated in the depressed portion 520. Similarly, the bonding paste 530b and the abrasive 540b may be first mixed to form a mixture, which may be then coated above the previous coated mixture and the top surface of the wall 521 (the surface of the base material 510). In addition, the bonding material 530a filled in the depressed portion 520 and the bonding material 530b coated on the surface of the base material 510 may be the same as or different from each other. The upper abrasive layer comprises the bonding material 530b and the abrasive 540b, while the lower abrasive layer comprises the bonding material 530a, the abrasive 540a, and the wall 521 (part of the base material 510) between the depressed portions. Therefore, the composition of the bonding paste 530a and the bonding paste 530b may be made to become different from each other, and the metal powder contained in each bonding paste 530a, 530b may also be made different. In this way, the lower abrasive layer, which is to be exposed after the upper abrasive layer is released or fallen apart, can have a uniform and consistent cutting or grinding characteristic as in the upper abrasive layer.

[57] Here, the metal powders contained in the bonding materials of the upper and lower abrasive layers are melted at the same time. However, since the metal powder of the bonding material 530a is filled in the depressed portion 520, the melted metal powder is held in place, along with the abrasives 540a, due to the surface tension thereof, and thus cannot easily flow with the melted metal powder of the bonding material of the upper abrasive layer. Accordingly, the abrasives dispersed in the upper and lower abrasive layers are retained in their places without being scattered or disturbed, thereby enabling avoidance of a deviation with the thickness thereof. Consequently, the abrasives 540a filled in the plural depressed portions 520, which are formed in the surface of the base material 510, constitute a lower abrasive layer, and the abrasives 540b disposed on the above abrasive 540a and the surface of the base material 510 constitute an upper abrasive layer, i.e., multiple abrasive layers are formed on the base material. [58] With the tip member having the above construction, when in use, the upper abrasives 540b of the upper abrasive layer are fallen apart therefrom, the lower abrasive layer is subsequently exposed and the lower abrasives 540a contained therein come to participate in the grinding and cutting work, thereby extending the service life of the tool. That is, although the lower abrasives 540a of the lower abrasive layer are retained inside the depressed portion 520, the wall 521 between the depressed portions 520 (in Fig. 17(a)) is easily abraded during a cutting or grinding process such that the abrasives 540a inside the depressed portion 520 come to protrude above the surface of the tool and participate in the cutting or grinding work. Therefore, the width w, the depth d, and the spacing s of the depressed portions 520 can be optimized, preferably, such that the wall 521 can be appropriately abraded.

[59] On the other hand, considering the abrasive size a, the minimum width and depth of the depressed portion are preferred to be designed so as to be larger than the abrasive size, so that some of the abrasives can be held, in its entirety, inside the depressed portion, as shown in Fig. 17. At this time, the spacing s between the neighboring depressed portions is designed preferably such that the upper and lower abrasive layers can have a same abrasive concentration and thus exhibit a uniform and consistent cutting or grinding speed or performance.

[60] The tip member having multiple abrasive layers of the invention may be manufactured through an electroplating method, instead of the above brazing method. Referring to Fig. 18, a process of manufacturing a tip member with multiple abrasive layers using an electroplating method will be described. In Fig. 18, only a part of the tip member to which abrasives are to be attached is partially illustrated. Similarly to the brazing method, as shown in Fig. 18 (a), a plurality of depressed portions 520 are first formed in a base material 510. As shown in Fig. 18 (b), the top surface of the wall 521 is coated with a non-conductive film 526 in order to prevent the top surface of the wall from being electroplated. Abrasives 540a are filled inside the depressed portion 520 (Fig. 18 (c)) and then a wet electroplating process is performed in an electroplating bath. Thus, the electroplating is not processed on the non-conductive abrasives, but processed from the base material and gradually forms a bonding material 530a simultaneously while embedding the abrasives into the bonding material 530a being formed by the electroplating (Fig. 18 (d)). When the bonding material 530a is formed adequately inside the depressed portion 520, the base material 510 is removed from the electroplating bath, thereby completing a primary electroplating to form a lower abrasive layer. Thereafter, the non-conductive film 526 coated on top of the wall 521 is removed (Fig. 18 (e)), and abrasives 540b are then uniformly disposed on the lower abrasive layer and on the top of the wall 521 (Fig. 18 (f)). In this case, both the depressed portion 520 and the wall 521 become conductive and thus a secondary electroplating can be performed thereon to thereby form an upper abrasive layer (Fig. 18 (g)). In this way, a diamond tool with two or more abrasive layers can be manufactured. In the brazing method, a bonding paste is preferably filled in the depressed portion 520 and the abrasives are then dispersed. In contrast, in the electroplating method, the abrasives 540a are filled inside the depressed portion 520 and a bonding material is then electroplated inside the depressed portion 520, and at the same time the abrasives 540a are fixed into the bonding material and the base material.

[61] On the other hand, the upper and lower abrasive layers may be formed through a combination of the brazing method and the electroplating method. That is, the upper and lower abrasive layers may be formed using either one of the brazing method and the electroplating method. Alternatively, the lower abrasive layer may be formed by the brazing method and the upper abrasive layer may be formed through the electroplating method, and vice versa. In a case where the lower and upper abrasive layers are formed respectively through a brazing method and an electroplating method, just after the step of Fig. 17 (c), the base material is to be heat-treated to bond the abrasives to the base material before performing next steps for electroplating.

[62] The diamond tools manufactured through the above brazing and electroplating methods according to the invention can be modified in various ways. For example, in case of a brazing method, just after the step of Fig. 17 (c), the base material can be heat-treated to perform fusion-bonding (brazing), thereby providing a diamond tool to be used without an upper abrasive layer. Similarly, in case of an electroplating method, after finishing the step of Fig. 18 (d) or 18 (e), the resultant product without an upper abrasive layer, in which the abrasive 540a and the bonding material 530a are provided in the depressed portion 520, can be used as a diamond tool. In another modification, if the width w of and spacing s between the depressed portions 520 are not changed and the depth d of the depressed portion is made to be almost the same as the abrasive size a, two-layered abrasives can be formed, thereby providing an identical cutting and grinding characteristic to the upper and lower abrasive layers when in use. In addition, contrary to Figs. 17 and 18, the size of the depressed portion 520 can made to be smaller than those of the abrasives such that the abrasives are partially inserted into the depressed portion 520 and thus only the inserted portions of the abrasives are bonded to the base material through brazing or electroplating. In a case where an upper abrasive layer is formed on top of this lower abrasive layer, just after the abrasives of the upper layer are released therefrom, the abrasives of the lower layer can be exposed to thereby achieve a continuity of cutting or grinding work between the upper and lower abrasive layers.

[63] As described above, in order for the abrasives to be continually exposed and protrude, the ratio d/a of the depth of depressed portion to the abrasive size is to be at least 1/4, and the ratio w/a of the width of depressed portion to the abrasive size is also preferred to be at least 1/4. In addition, in order to obtain uniform cutting and grinding characteristics, the ratio s/w of the spacing to the width of the depressed portion is preferred to be within a range of 0.2 to 0.8, in a case where the abrasive concentration is substantially the same in the upper and lower layers.

[64] In Figs. 17 and 18, the depressed portion 520 is illustrated to have a rectangular cross section, but not limited thereto. As illustrated in Figs. 19 and 20, the depressed portion may have a semi-elliptic cross section 520a or a V-shaped cross section 520b. In addition, the depressed portion may have a semi-circular cross section, a U-shaped cross section, a wavy cross section, or the like. On the other hand, in Figs. 17 and 18, the upper end portion of the wall 521 is illustrated to have a right-angled edge, but it may be formed so as to have a round shape 521R, as shown in Figs. 19 and 20, thereby facilitating the flowability of paste and improving the adhesiveness of abrasives near the edge. This round shape 521R can be applied to the rectangular cross section shown in Figs. 17 and 18.

[65] In the foregoing, the present invention has been described in connection with the only illustrated cross section of the depressed portion 520. Hereafter, the entire configuration of the depressed portion formed in the base material will be explained. In the description, the term "depressed portion" includes all the shapes, which are sunken under the surface of the base material. For example, the shape of the depressed portion includes a dimple type such as a semi-sphere, a semi-ellipsoid, an inverse cone, a rectangular block, a cylinder or the like. In addition, it may include an elongated groove type having a cross section such as a semi-circle, a semi-oval, a U-shape, a V- shape, or a rectangular shape, and furthermore a through-hole type passing through the opposing sides of the base material and having various shapes in cross section. Also, this depressed portion includes a space between projected portions, which may be formed on the surface of the base material through a coating process, an electroplating process, a bonding process or the like. Figs. 21, 24 and 27 are perspective views showing tip members, where in the surface of the tip member is formed respectively a dimple type depressed portion 520c, an elongated groove type depressed portion 520d, and a through-hole type depressed portion 520e. Figs. 22, 25 and 28 are front views of the tip members shown in Figs. 21, 24 and 27, respectively. Figs. 23, 26 and 29 are sectional views taken along line M-M, N-N, and O-O in Figs. 22, 25 and 28, respectively.

[66] On the other hand, in Figs. 21 to 29, the size of the depressed portions 520c to 520e is exaggerated, relative to the tip member of the saw blade, for the purpose of clear illustration of the shape thereof. The number of the depressed portions is illustrated more or less than the actual number thereof. The shape, the size and the number of depressed portions are to be designed appropriately, depending on the strength and ductility of a workpiece, etc.

[67] It will be apparent that the aforementioned depressed portions with various shapes may be combined with each other in various ways. For example, preferably, the top surface of the tip member, i.e., a main cutting face, is provided with a depressed portion 520d of a concave groove type formed along the thickness direction, and the side surface of the tip member, i.e., a sub-cutting face, is provided with a depressed portion 520e of a through-hole type formed in such a way to pass through in the thickness direction. Fig. 30 shows a cross section of a diamond tool according to the invention, wherein abrasives are bonded to a base material 510 with a depressed portion 520d of a groove type and a depressed portion 520e of a through-hole type using the methods illustrated in Figs. 17 and 18.

[68] In the depressed portion 520d of a groove type formed in the top surface of the tip member 500, abrasives 540al are bonded through a bonding material 530a. In the depression portion 520e2, 520e3, and 520e4 of a through-hole type, abrasives 540a2, 540a3, 540a4 are bonded through a bonding material 530a. In the surface of the base material, abrasives 540bl and 540b2 are bonded through a bonding material 530b.

[69] When a common diamond tool is used for cutting or grinding, its main cutting face, i.e., the top surface of the tool tip, is involved mostly in the cutting or grinding process, and thus the abrasives 540b 1 bonded to the top surface of the tool tip are first released or fallen apart. As the cutting or grinding proceeds, along with continuous release of the abrasives 520b2 in the sub-cutting face, release of the abrasives 540a2, wear of the base material between the abrasives 540a2 and 540a3, release of the abrasives 540a3, wear of the base material between the abrasives 540a3 and 540a4, and release of the abrasives 540a4 occur sequentially in a direction designated by an arrow A, thereby extending significantly the service life of the tool.

[70] Although the present invention has been explained by way of example in connection with the saw blade, it may be applied to a chemi-mechanical grinding pad conditioner, a straight wheel, an ID wheel, a core drill, a cutter, an end mill, or a polishing cup. By way of an example, Fig. 31 shows a core drill 500a comprising plural tip members 510a and a shank 520a, and Fig. 32 shows another core drill 500b comprising a single piece of tip member 510b and a shank 520b. In these examples, their basic constitutions are the same as the previous embodiments, except for the shapes of the tip member and the shank. Industrial Applicability

[71] As described above, according to the present invention, since a tip member of a diamond tool for cutting and grinding a workpiece and a shank of the diamond tool for supporting the tip member are separately manufactured, only a part of the diamond tool, i.e., the tip member, is required to be heat-treated without heat treatment of the entire diamond tool. Accordingly, the diamond tool does not suffer thermal deformation, which may be caused by unnecessary heat treatment, thereby avoiding degradation in its mechanical properties and reducing the wobbling caused by unbalance of a tool.

[72] In addition, since only a part of a diamond tool, i.e., the tip member, is brazed or electroplated, even in case of a large-sized diamond tool, a large-scaled furnace or electroplating bath is not required, contrary to a conventional technique. In this way, a large-sized diamond tool can be manufactured using small-scale facilities, thereby avoiding the occurrence of costs for preparing separate large-scale equipment when manufacturing a large-sized diamond tool.

[73] In case of a brazing method, only the tip member to be brazed is heat-treated, thereby reducing energy consumption. In case of an electroplating method, only a part of the tip member is coated with a non-conductive film, thereby reducing unnecessary consumption of the non-conductive film. Therefore, the manufacturing cost therefor can be reduced significantly.

[74] Furthermore, in a sintering method, the sintered tip has a blank, through which the tip is bonded to a shank, for an easy bonding between them. However, the blank of the sintered tip and the shank are formed of different materials, thus failing to achieve a maximum bonding force through welding. In the present invention, the tip member and the shank can be formed of an identical material, thus maximizing the bonding force between the tip member and the shank.

[75] As described above, in case where the tip members are manufactured through a brazing or electroplating method, the tip members only, excepting the shank, can be sold or purchased in the country or abroad. Thus, users themselves can manufacture various diamond tools by bonding the tip member to an appropriate shank, for example, using silver brazing or laser welding. Therefore, the transportation cost for the entire tool including a shank can be saved.

Claims

[I] A tip member to be attached to a shank of a diamond tool, comprising: a base material; and a plurality of abrasives attached to at least a part of a surface of the base material except a bonding portion of the tip member that is to be bonded to the shank. [2] The tip member as claimed in claim 1, wherein a plurality of depressed portions are formed in the surface of the base material, and a plurality of abrasives are attached to inner spaces of the depressed portions. [3] The tip member as claimed in claim 2, wherein each of the depressed portions comprises a dimple type depressed portion, a groove type depressed portion, or a through-hole type depressed portion. [4] The tip member as claimed in claim 2, wherein a groove is formed in a top surface of the tip member and a through-hole is formed in a lateral face of the tip member. [5] The tip member as claimed in any one of claims 2 to 4, wherein a plurality of abrasives are attached to a surface of the shank and an upper side of the depressed portions to which the abrasives and a bonding material are attached. [6] The tip member as claimed in any one of claims 1 to 4, wherein the portion of the base material to which the plurality of abrasives are attached has a thickness larger than that of the bonding portion. [7] The tip member as claimed in any one of claims 1 to 4, wherein the abrasives comprise synthetic or natural diamond, cubic boron nitride (cBN), silicone carbide, alumina, and a mixture of two or more thereof. [8] A diamond tool, comprising: a shank; and one or more tip members according to any one of claims 1 to 4, wherein a bonding portion of each of the tip members is bonded to the shank. [9] The diamond tool as claimed in claim 8, wherein positioning members are provided in the bonding portion of the tip member and a bonding region of the shank to which the tip member is bonded. [10] The diamond tool as claimed in claim 9, wherein the positioning member comprises a prominence and depression formed such that the bonding portion of the tip member is engaged with the bonding region of the shank.

[II] The diamond tool as claimed in claim 8, wherein the shank and a base material for the tip member are formed of an identical material.

[12] The diamond tool as claimed in claim 8, wherein the thickness of the bonding portion of the tip member is different from that of the shank. [13] The diamond tool as claimed in claim 8, wherein the diamond tool includes a saw, a core drill, a cutter, a saw blade, a polishing cup, a profiler, an end mill, a straight wheel, an ID wheel, a rotary dresser, or an edge grinding wheel. [14] A method for manufacturing a diamond tool, comprising the steps of: manufacturing a tip member by attaching a plurality of abrasives to a part of a surface of a base material; preparing a shank of the diamond tool; and attaching the tip member to the shank. [15] The method as claimed in claim 14, wherein the step of the manufacturing the tip member comprises the step of attaching the plurality of abrasives to the base material through brazing. [16] The method as claimed in claim 15, wherein the step of the manufacturing the tip member comprises the steps of: coating a bonding material in the form of paste on the part of the surface of the base material of the tip member; dispersing the plurality of abrasives in the coated bonding material; drying the bonding material; and heating the base material to perform fusion-bonding. [17] The method as claimed in claim 15, wherein the step of the manufacturing the tip member comprises the steps of: preparing a mixture of a bonding material in the form of paste and the plurality of abrasives; coating the mixture on the part of the surface of the base material of the tip member; and performing fusion-bonding by heating the base material. [18] The method as claimed in claim 14, wherein the step of the manufacturing the tip member comprises the step of attaching the plurality of abrasives to the base material through electroplating. [19] The method as claimed in claim 18, wherein the step of the manufacturing the tip member comprises the steps of: coating a non-conductive film on a part of the surface of the base material of the tip member except the portion thereof to which the abrasives are to be attached; dispersing the plurality of abrasives on another part of the surface of the base material except the part thereof on which the non-conductive film is coated; and electroplating the base material. [20] The method as claimed in claim 19, further comprising the step of removing the non-conductive film after the step of electroplating the base material. [21] The method as claimed in any one of claims 14 to 20, wherein the tip member is bonded to the shank through silver brazing, resistance welding or laser welding. [22] The method as claimed in claim 16 or 17, wherein the step of performing the fusion-bonding is carried out using a batch-type vacuum furnace, a reduction/ inert gas atmosphere furnace, or a continuous-type gas atmosphere furnace. [23] The method as claimed in claim 22, wherein the reduction/inert gas comprises hydrogen gas.