1. Field of the Invention
The present invention relates in general to a method of smoothing a diamond coating, and more particularly to such a method which makes it possible to efficiently and accurately smooth a diamond-coated body having a complicated, three-dimensional geometry.
2. Discussion of the Related Art
As one type of a cutting tool such as an end mill, a tap and a drill, there is proposed a diamond-coated cutting tool in which a tool substrate made of a cemented carbide or other material is coated with a diamond coating, as disclosed in JP-B2-2519037 (publication of Japanese Patent issued in 1996) by way of example. In the diamond-coated cutting tool disclosed in this Japanese Patent publication, the tool substrate is coated with the diamond coating in accordance with a CVD (chemical vapor deposition) method. The diamond coating of the disclosed tool consists of an aggregation of grown diamond crystals, each of which has a large grain size or diameter. The large diameter of each diamond crystal causes the outer surface of the diamond coating to have large pits and projections which are inevitably transferred onto a machined surface of a workpiece which is machined by the cutting tool, thereby making it difficult to obtain a required degree of smoothness of the machined surface. In the interest of improving the smoothness of the machine surface, there are proposed methods of smoothing the surface of the diamond coating, by using various techniques such as laser beam, ion beam, thermo-mechanical lapping and mechanical-chemical lapping, as described in an article entitled xe2x80x9cA preliminary investigation of the effect of post-deposition polishing of diamond films on the machining behavior of diamond-coated cutting toolsxe2x80x9d in pages 921-929 of xe2x80x9cDIAMOND AND RELATED MATERIALS Vol.4 (1995)xe2x80x9d.
However, the polishing method with the laser is not adequate for efficiently polishing a drill, end mill or other body having a three-dimensional geometry, although the method with the laser generally provides a high polishing rate. The polishing method with the ion beam requires a time as long as tens of hours for polishing a body, due to its low polishing rate. The polishing method with the thermo-mechanical or mechanical-chemical lapping cannot serve for polishing a body having a complicated, three-dimensional geometry with pits and projections on its surface.
It is therefore an object of the present invention to provide a method which makes it possible to smooth a surface of a diamond coating of a diamond-coated body with high efficiency and precision even where the diamond-coated body has a complicated three-dimensional geometry. This object may be achieved according to any one of first through nineteenth aspects of this invention which are described below.
The first aspect of the invention provides a method of smoothing a surface of a diamond coating of a diamond-coated body, by using an arc-type ion plating device in which at least one target is disposed, the method comprising: a step of causing arc discharge between an anode, and a cathode which is provided by each of the above-described at least one target, whereby positive ions are emitted from the above-described at least one target; and a step of applying a negative bias voltage to the diamond-coated body which is disposed in the arc-type ion plating device, whereby the surface of the diamond coating is bombarded with the positive ions, so as to be smoothed by the bombardment of the positive ions against the surface of the diamond coating.
According to the second aspect of the invention, in the method defined in the first aspect of the invention, each of the above-described at least one target includes, as a main component thereof, an element which belongs to one of groups IIIa through IVb of the periodic table.
According to the third aspect of the invention, in the method defined in the second aspect of the invention, each of the above-described at least one target includes at least one of Ti, TiAl, SiC, V, Y, Al and Cr.
According to the fourth aspect of the invention, in the method defined in any one of the first through third aspects of the invention, the negative bias voltage has a value of 500-1500 V.
The fifth aspect of the invention provides a method of smoothing a surface of a diamond coating of a diamond-coated body, by using an arc-type ion plating device in which at least one metallic target is disposed, the method comprising: a step of causing arc discharge between an anode, and a cathode which is provided by each of the above-described at least one metallic target, whereby metallic ions are emitted from the above-described at least one metallic target; and a step of applying a negative bias voltage to the diamond-coated body which is disposed in the arc-type ion plating device, whereby the surface of the diamond coating is bombarded with the metallic ions, so as to be smoothed by the bombardment of the metallic ions against the surface of the diamond coating.
According to the sixth aspect of the invention, in the method defined in the fifth aspect of the invention, each of the above-described at least one metallic target includes, as a main component thereof, a metal which belongs to one of groups IIIa through IIIb of the periodic table.
According to the seventh aspect of the invention, in the method defined in the sixth aspect of the invention, each of the above-described at least one metallic target includes at least one of Ti, TiAl, V, Y, Al and Cr.
According to the eighth aspect of the invention, in the method defined in any one of the fifth through seventh aspects of the invention, the negative bias voltage has a value of 500-1500 V.
The ninth aspect of the invention provides a method of manufacturing a diamond-coated body which includes a substrate and a diamond coating disposed on the substrate, the method comprising: a coating forming step of forming the diamond coating on the substrate; and a surface smoothing step of smoothing a surface of the diamond coating, by using an arc-type ion plating device in which at least one target is disposed, wherein the surface smoothing step including: a step of causing arc discharge between an anode, and a cathode which is provided by each of the above-described at least one target, whereby positive ions are emitted from the above-described at least one target; and a step of applying a negative bias voltage to the diamond-coated body which is disposed in the arc-type ion plating device, whereby the surface of the diamond coating is bombarded with the positive ions, so as to be smoothed by the bombardment of the positive ions against the surface of the diamond coating.
According to the tenth aspect of the invention, in the method defined in the ninth aspect of the invention, the diamond-coated body consists of a machining tool which is to be moved relative to a workpiece, for thereby machining the workpiece.
According to the eleventh aspect of the invention, in the method defined in the ninth or tenth aspect of the invention, the diamond-coated body consists of a rotary cutting tool which is to be rotated about an axis thereof-relative to a workpiece, for thereby cutting the workpiece, and which has a rake face, a flank face and a cutting edge that is defined by an intersection of the rake face and the flank face, and wherein the cutting edge is three-dimensional.
The twelfth aspect of the invention provides a method of manufacturing a diamond- coated body which includes a substrate and a diamond coating disposed on the substrate, the method comprising: a coating forming step of forming the diamond coating on the substrate; and a surface smoothing step of smoothing a surface of the diamond coating, by using an arc-type ion plating device in which at least one metallic target is disposed, wherein the surface smoothing step including: a step of causing arc discharge between an anode, and a cathode which is provided by each of the above-described at least one metallic target, whereby metallic ions are emitted from the above-described at least one metallic target; and a step of applying a negative bias voltage to the diamond-coated body which is disposed in the arc-type ion plating device, whereby the surface of the diamond coating is bombarded with the metallic ions, so as to be smoothed by the bombardment of the metallic ions against the surface of the diamond coating.
According to the thirteenth aspect of the invention, in the method defined in the twelfth aspect of the invention, each of the above-described at least one metallic target includes, as a main component thereof, a metal which belongs to one of groups IIIa through IIIb of the periodic table.
According to the fourteenth aspect of the invention, in the method defined in the thirteenth aspect of the invention, each of the above-described at least one metallic target includes at least one of Ti, TiAl, V, Y, Al and Cr.
According to the fifteenth aspect of the invention, in the method defined in any one of the twelfth through fourteenth aspects of the invention, the bias voltage has a value of 500-1500 V.
According to the sixteenth aspect of the invention, in the method defined in any one of the twelfth through fifteenth aspects of the invention, the diamond-coated body consists of a machining tool which is to be moved relative to a workpiece, for thereby machining the workpiece.
According to the seventeenth aspect of the invention, in the method defined in any one of the twelfth through sixteenth aspects of the invention, the diamond-coated body consists of a rotary cutting tool which is to be rotated about an axis thereof relative to a workpiece, for thereby cutting the workpiece, and which has a rake face, a flank face and a cutting edge that is defined by an intersection of the rake face and the flank face, and wherein the cutting edge is three-dimensional.
According to the eighteenth aspect of the invention, in the method defined in the seventeenth aspect of the invention, the rotary cutting tool has a flute which provides the rake face and which extends in a helical direction of the rotary cutting tool.
According to the nineteenth aspect of the invention, in the method defined in the eighteenth aspect of the invention, the rotary cutting tool consists of an end mill.
In the smoothing method defined in any one of the first through eighth aspects of the invention, the arc discharge is caused between the anode and the cathode that is provided by the suitable target (e.g., a metallic target), whereby the positive ions (e.g., metallic ions) are emitted from the target. Meanwhile, the negative bias voltage is applied to the diamond-coated body, whereby the surface of the diamond coating is bombarded with the positive ions at high velocity. Thus, the surface of the diamond coating is polished or smoothed by the bombardment of the positive ions to the diamond coating surface at high speed, making it possible to smooth the diamond coating surface of the diamond-coated body even where the diamond-coated body has a complicated three-dimensional geometry. In addition, it is possible to smooth the surfaces of the diamond coatings of a larger number of diamond-coated bodies in a short time owing to the use of the arc-type ion plating device, leading to an improved production efficiency of the diamond-coated body.
The manufacturing method defined in any one of the ninth through nineteenth aspects of the invention includes the surface smoothing step which is implemented in substantially the same manner as in the smoothing method defined in any one of the first through eighth aspects of the invention. Thus, the manufacturing method provides substantially the same technical advantages as the smoothing method. In addition, the manufacturing method makes it possible to efficiently manufacture the diamond-coated body having a high degree of surface smoothness. Particularly, the method defined in any one of the seventeenth through nineteenth aspects of the invention, in which the diamond-coated body consists of the rotary cutting tool, makes it possible to provide the diamond coating with a high degree of surface smoothness, while maintaining an accuracy of the complicated three-dimensional geometry of the cutting edge which does not lie on a plane, thereby enabling the rotary cutting tool to machine a workpiece with high degrees of surface smoothness and profile accuracy.
The smoothing method of the present invention is advantageously applicable in manufacturing of a diamond-coated cutting tool having a cutting tooth or teeth. However, the smoothing method is also applicable in manufacturing of any one of the other diamond-coated bodies such as a diamond-coated machining tool other than a diamond-coated cutting.tool.
The target preferably consists of the metallic target including at least one of Ti, TiAl, V, Y, Al and Cr. However, the target may consist of the non-metallic target including, for example, SiC, as long as the target makes it possible to cause the arc discharge in the arc-type ion plating device so that the surface of the diamond coating is smoothed by the arc discharge. It is noted that the above-described TiAl is interpreted to mean an alloy consisting of Ti and Al, and that the above-described SiC is interpreted to mean an alloy consisting of Si and C.
The optimum value of the negative bias voltage varies depending upon the type of the target. However, the value of the negative bias voltage is preferably 500-1500 V, more preferably 800-1200 V. If the negative bias voltage value is smaller than 500 V, the surface of the diamond coating is not bombarded with the positive ions at sufficiently high velocity, namely, the velocity at which the positive ions collide against the diamond coating surface is reduced to be too small to satisfactorily smooth the diamond coating surface. If the negative bias voltage value is larger than 1500 V, on the other hand, the diamond coating surface is bombarded with the positive ions at excessively high velocity, namely, the velocity at which the positive ions collide against the diamond coating surface is increased to be so large that the diamond coating is likely to be easily removed from the substrate.
The diamond-coated body defined in each of the ninth and twelfth aspects of the invention may be a rotary cutting tool such as an end mil, a drill, a tap and a threading die each of which is to be rotated about its axis relative to a workpiece; a non-rotary cutting tool such as a replaceable insert which is fixed to a tool holder used for a lathe cutting operation; a cold-forming tool which is designed to form a workpiece into a desired shape by plastically deforming the workpiece; and any other machining tools each of which is to be moved relative to a workpiece for thereby machining the workpiece. In addition, the diamond-coated body of the invention may be other than such machining tools. The cutting tool provided by the diamond-coated body of the invention is advantageously used to cut, particularly, an aluminum casting, an aluminum alloy, a copper, a copper alloy or other non-ferrous metal, although the cutting tool may be used to cut a material other than the non-ferrous metal.
Since the negative bias voltage is applied to the diamond-coated body in the manufacturing or smoothing method of the invention, the substrate of the diamond-coated body defined in each of the ninth and twelfth aspects of the invention is preferably made of a cemented carbide or other material having a certain degree of conductivity. Similarly, the diamond-coated body defined in each of the first and fifth aspects of the invention is formed by applying the diamond coating onto a substrate which is preferably made of a cemented carbide or other material having a certain degree of conductivity.
The coating forming step, in which the substrate is covered at its surface with the diamond coating, is implemented by using preferably a CVD method such as a microwave plasma CVD method and a hot filament CVD method. However, the coating forming step may be implemented by using the other method such as an ion-beam method.