Single-crystalline diamond tip for dresser and dresser employing the same

Abstract: In relation to a diamond dresser having a long life and excellent wear resistance, provided are a diamond tip having an end surface which is perpendicular to its longitudinal direction formed by a {211} plane in crystal orientation and two opposite side surfaces along the longitudinal direction which are formed by {111} planes in crystal orientation and a diamond dresser employing the same.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a diamond dresser which is employed for adjusting a grindstone, and more particularly, it provides a single-crystalline diamond tip for a dresser and a diamond dresser which are of high performance and economic. Description of the Background Art Diamond which is excellent in hardness and wear resistance is widely employed in the industrial field of wear-resistant tools, cutting tools and the like. In particular, the so-called blade dresser which is mainly formed by embedding a single or a number of diamond tips 1 in a holding member (shank portion) 2 as shown in Figs. 1A and 1B is generally employed as a dresser for dressing a rotary grindstone for grinding which is formed by a base material of Al 2 O 3 , SiC or the like. Particularly in relation to such a blade dresser or a rotary dresser, it is known that the performance of the dresser is stabilized and a long life is attained by working each single-crystalline diamond tip into a bar shape, as described in Japanese Patent Laying-Open No. 59-30668 (1984) or 5-185373 (1993). It is known that the wear resistance of single-crystalline diamond remarkably varies with the plane orientation of the crystal. In case of applying single-crystalline diamond to a tool material, selection of the plane orientation is extremely important in consideration of the tool life. As described in Japanese Patent Laying-Open No. 59-30668 (1984) or 5-185373 (1993), for example, a conventional single-crystalline diamond dresser employs a bar-shaped single-crystalline diamond tip having an end surface which is formed by a {110}, {100} or {111} plane for dressing a grindstone. However, a diamond dresser having a working end surface of a {110} or {100} plane orientation is disadvantageously inferior in wear resistance. On the other hand, a diamond dresser having a working end surface of a {111} plane orientation has a short tool life and the tool must be frequently exchanged since the end surface acting on a grindstone is easy to cleave/separate or break during employment due to the property of the single-crystalline diamond which is easy to cleave along the {111} plane. In relation to a single-crystalline diamond dresser, it is obviously advantageous that its diamond tip is so embedded that the maximum wear-resistant direction of the diamond is in parallel with the dressing direction, i.e., the frictional direction with the adjusted grindstone. Fig. 2A shows the maximum wear-resistant direction, i.e., a <110> direction, in case of forming an end surface and opposite side surfaces by a {110} plane and {111} planes respectively, and Fig. 2B shows the maximum wear-resistant direction, i.e., a 〈110〉 direction, in case of forming both of an end surface and opposite side surfaces by {100} planes respectively by arrows. In general, a method of identifying crystal planes by X-ray diffraction or the like, determining the maximum wear-resistant direction and embedding the diamond tip, or a method of indexing crystal planes by the technique of a skilled operator and embedding the diamond tip has been employed in order to correctly find the maximum wear-resistant direction. As to general steps of manufacturing a bar-shaped tip for a dresser, on the other hand, it is the most economical tip manufacturing method to prepare a thin plate by cleaving rough diamond and work the same into a prismatic form by cutting with a laser beam or the like, as described in Japanese Patent Laying-Open No. 3-138106 (1991). When an end surface of the tip prepared in such a manner is formed by a {110} plane, it is necessary to position the wear-resistant direction of the end surface, i.e., the 〈110〉 direction, not to be in parallel with each side surface but to be inclined by 55° as shown in Fig. 2A, as described in Japanese Patent Laying-Open No. 5-185373 (1993). This comes into question particularly in case of preparing a multi-stone dresser such that it is difficult to correctly arrange all tips along the maximum wear-resistant directions for embedding the same in a holding member. Thus, working efficiency is deteriorated to result in an economic problem, while this leads to dispersion in performance of the dresser as a product. It is well known that diamond is the hardest substance among those present on earth. In case of applying diamond to a dresser, however, its wear resistance remarkably varies with the orientation of single-crystalline diamond. The conventional single-crystalline diamond tip shown in Fig. 2A or 2B has the minimum abrasion loss along substantially diagonal directions, and hence the diamond dresser must inevitably be in the mode shown in Figs. 1A and 1B. In this case, the substantially diagonal lines of the single-crystalline tips must be parallel to the directions of the dresser rubbed by the grindstone, i.e., the side surfaces of the dresser. In general, this type of dresser is obtained by inclinedly embedding the single-crystalline diamond tips in metal powder and sintering the same. The inclination must ideally be 55° in this case. However, the single-crystalline diamond tips are so instable that it is extremely difficult to attain the set inclination. Particularly in case of employing a number of single-crystalline diamond tips, it is further difficult to manufacture a diamond dresser having stable wear resistance, due to inclination of each single-crystalline diamond tip. The present invention is adapted to solve such problems. SUMMARY OF THE INVENTION An object of the present invention is to provide a single-crystalline diamond tip for a dresser allowing easy determination of a wear-resistant direction and embedding. Another object of the present invention is to provide a single-crystalline diamond tip for a dresser which can simplify an embedding operation and improve accuracy of the embedded position. Still another object of the present invention is to provide a diamond dresser which is excellent in wear resistance and has a long tool life. A further object of the present invention is to provide a diamond dresser having small dispersion of wear resistance. In the inventive diamond tip made of single-crystalline diamond which is worked into a bar shape, an end surface perpendicular to its longitudinal direction has a crystal orientation along a {211} plane, and two opposite side surfaces along the longitudinal direction have crystal orientations along {111} planes. The single-crystalline diamond employed for the tip is preferably prepared from artificially synthesized diamond containing nitrogen by 5 to 300 ppm. A diamond dresser is manufactured by embedding a single or a plurality of such diamond tips in a holder so that an end surface of each tip defines a working surface for a grindstone serving as a workpiece and a pair of opposite sides of a polygon forming this end surface is substantially parallel to a frictional direction of the grindstone serving as a workpiece to be worked. In order to solve the aforementioned problems, the present invention provides a single-crystalline diamond tip for a dresser which is at a low cost, has high wear resistance, allows easy determination of a wear-resistant direction and embedding, and is excellent in economy, and a dresser by forming an end surface, which is perpendicular to a longitudinal direction, of single-crystalline diamond for adjusting a grindstone surface by a {211} plane while forming opposite side surfaces by {111} planes. According to the present invention, the crystal plane orientation of the working surface for adjusting the grindstone surface is formed by a {211} plane which has higher wear resistance than {110} and {100} planes and higher chipping resistance and breaking resistance than a {111} plane due to the property of the crystal plane, whereby the tool life is improved. In case of manufacturing a diamond tool, a {100} or {110} plane is generally employed for a working surface. This is mainly because the {100} or {110} plane can be readily ground. In other words, the {100} or {110} plane is easy to wear, and hence this plane is not preferable as a working surface of a dresser. While a {111} plane is known as a plane having the highest wear resistance, diamond is easy to cleave along this plane, leading to breakage of the tool. Thus, the {111} plane is not utilized as a tool working surface in general. The inventors have made various studies on the aforementioned points, and discovered that a working surface for a grindstone which is formed by a {211} plane is excellent in wear resistance and has no cleavability. A working surface of a general diamond tool must be formed by grinding in a step of manufacturing the same as described above, and hence the {211} plane which is hard to grind is not used as a working surface. In a dresser to which the present invention is applied, however, an end surface of each tip thereof is already worked into a flat surface by a laser beam or the like, and hence the end surface may not be ground in a manufacturing step while the tip can be employed to the end with no requirement for re-grinding even if the same is worn during employment. Thus, remarkable improvement of performance for serving as a dresser has been discovered through employment of the {211} plane, which is hard to grind and has not been employed for general tools. Such a diamond tip can be obtained by cutting a plate-type diamond member, which is prepared by cleaving single-crystalline diamond along its {111} plane, into the form of a strip. This diamond tip is manufactured through steps similar to those for the conventional diamond tip shown in Fig. 2A or 2B. The difference between the inventive and conventional diamond tips resides in angles for cutting plate-shaped diamond members having {111} planes into the form of strips. The diamond tip shown in Fig. 2A or 2B has such advantages that the cutting angle can be readily set and the product yield is high due to employment of a simple plane orientation. However, this diamond tip is inferior in practicalness for application to a diamond dresser, as described above. It has been possible to attain the present invention only by ignoring difficulty in manufacturing of a diamond tip and regarding handiness and performance of a diamond dresser as important. The maximum wear-resistant direction of the inventive diamond tip is parallel to the {111} plane, whereby angle displacement in embedding can be extremely reduced and a diamond dresser having small dispersion in wear resistance can be provided. In order to effectively carry out the present invention, accuracy of the crystal orientation is preferably as high as possible, and it is preferable that an error of the crystal orientation of the end surface is within 5° from the {211} plane in the inventive single-crystalline diamond tip for a dresser. When the end surface is formed by the {211} plane, it is possible to employ a working method utilizing cleavage as described in Japanese Patent Laying-Open No. 3-138106 (1991) for manufacturing the tip by forming a pair of opposite surfaces thereof by {111} planes since the {111} plane is one of plane orientations perpendicular to the {211} plane. Due to employment of this working method, high-priced rough diamond having a small working margin can be worked into a thin plate in a high yield and the working time for cutting the rough diamond can be remarkably shortened as compared with cutting with a laser beam or a diamond blade. The thin plate obtained in this manner has flat upper and lower surfaces which are formed by {111} planes, and a tip can be readily manufactured at a low cost by cutting the same into the form of a strip with a laser beam machine or the like. While the tip typically has a rectangular or square section, the same may have a parallelogrammic or trapezoidal section. The maximum wear resistance is attained along the 〈110〉 direction on the {211} plane which is the plane orientation of the end surface of the tip and the {211} plane forming the end surface and the {111} planes forming the side surfaces intersect with each other on ridge lines which are matched with the maximum wear-resistant <110> direction, whereby this wear-resistant direction can be readily identified in case of embedding the tip. It is a well-known fact that the maximum wear-resistant direction on a working surface of a diamond tip which is embedded in a dresser is preferably matched with the rotational direction of a grindstone, i.e., the direction for dressing the grindstone, in an operation for adjusting the grindstone. Therefore, it is an important factor deciding the performance of the tool itself in case of manufacturing a dresser, to reliably perform a tip embedding operation in high accuracy so that the dressing direction is matched with the maximum wear-resistant direction of each tip, particularly in relation to a dresser having a plurality of tips. In general, a diamond tip for a dresser is embedded in a holder by a method of embedding the tip in metal powder, thereafter pressurizing the same and sintering/contracting the metal powder at a high temperature, so that the tip is not displaced or loosened by high stress during the operation. When it is necessary to remarkably incline the tip with respect to the shank portion for embedding the same as described in Japanese Patent Laying-Open No. 5-185373 (1993), it is not easy to arrange the tip in the metal powder while maintaining a correct angle in operation, and it is extremely difficult to correctly hold the crystal orientations through pressurizing and heating steps. According to the present invention, however, the wear-resistant directions of the tips are matched with a direction for using the dresser when the tips are simply arranged on metal powder which is brought into a flat state, whereby the operation can be extremely readily carried out. Therefore, effects of the present invention in easiness of the operation and accuracy of embedding are effectively exhibited as the number of the embedded tips is increased. It is obvious that the present invention is remarkably effective in a rotary dresser having several 10 or several 100 tips embedded in its outer peripheral portion, in particular. When each tip has a rectangular or square sectional shape, plane orientations of another pair of side surfaces which are different from the opposite {111} planes are {110} planes, and the end surface of the {211} plane intersects with the side surfaces of the {110} planes on ridge lines in the 〈111〉 direction having wear resistance close to that of the aforementioned 〈110〉 direction. Therefore, the dresser can also be used in this direction, in response to the shape or application of the tool. According to the inventors' knowledge obtained as a result of their studies, it has been clarified that a 〈111〉 direction on a {211} plane exhibits wear resistance which is remarkably superior to that in the maximum wear-resistant direction on a {100} or {110} plane, i.e., a 〈110〉 direction. Thus, the present invention can also provide a dresser which is usable not only in one direction but in two perpendicular directions. The volume of the single-crystalline diamond employed in the present invention is relatively reduced with respect to the area of the working surface as compared with the so-called single-stone dresser prepared by embedding natural rough diamond in a holder in a rough state, which is widely employed in general, due to the bar shape of the tip. In order to solve this problem, it is preferable that the diamond itself has high heat conductivity for dissipating heat generated in dressing. It is known that artificially synthesized single-crystalline diamond has higher heat conductivity than natural diamond due to differences in amounts and modes of nitrogen contained in the crystals, and that a crystal having a lower nitrogen content has higher heat conductivity. With respect to the present invention, therefore, it is preferable to use synthetic diamond having a nitrogen content of not more than 300 ppm. On the other hand, it is known that the growth rate must be reduced in order to grow a crystal having a nitrogen content of less than 5 ppm in a preparation process for synthetic diamond, and the cost for synthetic rough diamond itself is uneconomically increased in this case. Also in a step utilizing cleavage which is the most economically effective means for manufacturing the inventive diamond tip, {111} cleavage planes can be readily indexed by employing synthetic diamond having a polygonal rough shape formed by flat planes, and this can be regarded as preferable as compared with the case of employing natural rough diamond formed by curved surfaces. As hereinabove described in detail, the present invention provides a dresser having smaller abrasion loss and a longer tool life as compared with the prior art, while stability in dresser manufacturing steps and economy are improved due to simplification of operations and improvement of accuracy resulting from easiness of determination of the wear-resistant direction and embedding. Thus, laborsaving and simplification in grinding steps are enabled by employing the low-priced dresser having a long life and stable performance manufactured according to the present invention. The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A and 1B are a perspective view and a sectional view showing a conventional blade dresser respectively; Figs. 2A and 2B are perspective views showing wear-resistant directions of conventional single-crystalline diamond tips by arrows respectively; Fig. 3A is a perspective view showing a blade dresser according to the present invention, and Fig. 3B is a front elevational view showing a working surface thereof; and Figs. 4A to 4G illustrate working surfaces of dressers employed in Examples and crystal orientations of diamond tips embedded therein, with arrows showing maximum wear-resistant directions on end surfaces of the diamond tips. DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention is now described with reference to the drawings. As shown in Figs. 3A and 3B, a blade dresser according to the embodiment of the present invention is formed by embedding a plurality of single-crystalline diamond tips 1, which are worked into bar shapes, in a shank portion 2 so that end surfaces of the tips 1 acting in dressing are exposed. The tips 1 are held by a sintered metal. Figs. 4A to 4G illustrate working surfaces of such blade dressers. Square prismatic artificial single-crystalline diamond tips of 4.0 mm in longitudinal length having square sectional shapes of 0.8 by 0.8 mm were prepared from inventive samples having end surfaces of {211} plane orientations and side surfaces of {111} and {110} plane orientations as shown in Figs. 4D and 4E, conventional samples having end surfaces of {110} plane orientations and side surfaces of {111} and {211} plane orientations as shown in Figs. 4B and 4G, conventional samples having end surfaces of {100} plane orientations and side surfaces of {100} plane orientations as shown in Figs. 4A and 4F, and a sample having a working end surface of a {111} plane orientation having the maximum wear resistance and side surfaces of {110} and {211} plane orientations as shown in Fig. 4C. Dressers each having five such single-crystalline diamond tips were manufactured and subjected to dressing tests. The aforementioned blade dressers were reciprocated in directions parallel to rotation axes of grindstones at a constant speed for 10 minutes under the following wet conditions: grindstone peripheral speed: 1500 rpm grindstone: SN80N8V51S depth of cut: 0.1 mm/pass feed rate: 0.5 mm/rev. for dressing grindstone surfaces and measuring amounts of abrasion loss. Embedding accuracy of each dresser was evaluated by an average value of displacement of the five diamond tips from a set angle. (Example 1) The aforementioned diamond tips were arranged substantially in parallel with respective sides of the end surfaces as shown in Figs. 4A, 4B, 4C, 4D and 4E for dressing grindstone surfaces along the horizontal directions in the figures, and amounts of abrasion loss were compared with each other. Further, working times required for embedding the respective tips and plane orientation accuracy after embedding were also compared with each other. Table 1 shows the results. The forward end surface of the sample (3) having the working end surface of the {111} plane orientation was cloven/separated in an initial stage of dressing, and it was impossible to continue the operation. As to the samples (1), (2), (4) and (5), it was possible to continuously and stably dress grindstone surfaces. The embedding times and embedding accuracy of these samples were hardly different from each other. In particular, every sample exhibited embedding accuracy of within 1.2 degrees, and it is conceivable that the results of execution correctly reflect wear properties of the plane orientations. It has been verified that the inventive samples (4) and (5) have extremely smaller amounts of abrasion loss and superior wear resistance as compared with the conventional samples. Sample No. Plane Orientation Dressing Direction Abrasion Loss (10 -3 mm 3 ) Embedding Time (min.) Embedding Accuracy (deg.) Tip Arrangement Comparative Sample (1) {100} 〈100〉 77.0 3.0 1.2 Fig. 4A (2) {110} 〈211〉 31.2 3.0 0.9 Fig. 4B (3) {111} 〈110〉 x 3.0 1.1 Fig. 4C Inventive Sample (4) {211} 〈110〉 7.0 3.0 0.95 Fig. 4D (5) {211} 〈111〉 9.0 3.0 1.1 Fig. 4E (Example 2) As to tips similar to those of Example 1, maximum wear-resistant directions of respective surfaces were arranged in the same directions as dressing directions as shown in Figs. 4F, 4G, 4C and 4D for dressing grindstone surfaces, and amounts of abrasion loss, embedding times and embedding accuracy were compared with each other. In a sample (8), chipping was caused by cleavage in an initial stage of dressing similarly to the sample (3) in Example 1, and it was impossible to continuously execute the test. Samples (6) and (7) required long embedding times since the maximum wear-resistant directions of the diamond tips had constant inclinations with respect to ridge lines of the tips, and it was difficult to improve the embedding accuracy. In an inventive sample (9), on the other hand, it was possible to extremely reduce the working time as compared with the conventional samples since the maximum wear-resistant direction was parallel to ridge lines and it was possible to readily position the maximum wear-resistant direction in the same direction as a working direction, while the embedding accuracy was excellent. As to samples (6) and (7), wear resistance was remarkably improved since it was possible to match the wear-resistant directions substantially with working directions as compared with Example 1, while the amounts of abrasion loss thereof were in excess of twice as compared with the inventive sample (9). Thus, it has been clarified that wear resistance of the inventive sample is extremely high as compared with the conventional samples. Sample No. Plane Orientation Dressing Direction Abrasion Loss (10 -3 mm 3 ) Embedding Time (min.) Embedding Accuracy (deg.) Tip Arrangement Comparative Sample (6) {100} 〈110〉 27.6 11.0 3.5 Fig. 4F (7) {110} 〈110〉 14.8 10.5 5.9 Fig. 4G (8) {111} 〈110〉 x 3.5 1.1 Fig. 4C Inventive Sample (9) {211} 〈110〉 7.0 3.0 0.95 Fig. 4D Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being limited only by the terms of the appended claims.

Claims: A single-crystalline diamond tip for a dresser being prepared from single-crystalline diamond being worked into a bar shape and having an end surface being perpendicular to its longitudinal direction and side surfaces along said longitudinal direction, wherein said end surface includes a {211} plane as a crystal plane orientation and a first opposite pair of said side surfaces include {111} planes as crystal plane orientations. The single-crystalline diamond tip for a dresser in accordance with claim 1, wherein said single-crystalline diamond is artificially synthesized diamond, and the concentration of nitrogen being contained in said single-crystalline diamond is at least 5 ppm and not more than 300 ppm. The single-crystalline diamond tip for a dresser in accordance with claim 1, wherein a second opposite pair of said side surfaces include {110} planes as crystal plane orientations. A diamond dresser comprising: one or at least two single-crystalline diamond tips (1) each being prepared from single-crystalline diamond being worked into a bar shape and having an end surface being perpendicular to its longitudinal direction and side surfaces along said longitudinal direction; and a holder (2) having said single-crystalline diamond tip(s) being so embedded that said end surface of each said single-crystalline diamond tip defines a working surface for a workpiece, wherein said end surface of each said single-crystalline diamond tip includes a {211} plane as a crystal plane orientation and a first opposite pair of said side surfaces of each said single-crystalline diamond tip include {111} planes as crystal plane orientations, and each said single-crystalline diamond tip is so arranged that two opposite sides of a polygon forming said end surface of each said single-crystalline diamond tip is substantially parallel to a frictional direction of said workpiece. The diamond dresser in accordance with claim 4, wherein each said single-crystalline diamond is artificially synthesized diamond, and the concentration of nitrogen being contained in said single-crystalline diamond is at least 5 ppm and not more than 300 ppm. The diamond dresser in accordance with claim 4, wherein a second opposite pair of said side surfaces include {110} planes as crystal plane orientations. The diamond dresser in accordance with claim 4, wherein each said single-crystalline diamond tip is so arranged that said first opposite pair of said side surfaces are substantially parallel to said frictional direction of said workpiece.

Inventors: KOBAYASHI YUTAKA, YOSHIDA AKITO, KOBAYASHI, YUTAKA, YOSHIDA, AKITO
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1996
Main classification: B24B53
IPC codes: B24B53