Cutters – for shaping – Rotary cutting tool – Face or end mill
Reexamination Certificate
2001-06-14
2003-04-15
Nguyen, Kien T. (Department: 3712)
Cutters, for shaping
Rotary cutting tool
Face or end mill
C407S119000
Reexamination Certificate
active
06547494
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a diamond-coated tool, and more particularly to such a diamond-coated tool which is capable of machining a workpiece with high degrees of surface smoothness and profile accuracy, and also to a method of manufacturing the same.
2. Discussion of the Related Art
As one type of a cutting tool such as an end mill, a drill, a tap and a disposable or throwaway insert, there is proposed a diamond-coated tool in which a tool substrate 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 tool disclosed in this Japanese Patent publication, the tool substrate is coated with the diamond coating in accordance with CVD (chemical vapor deposition) method.
The diamond coating of the disclosed tool consists of an aggregation of diamond crystals, each of which has grown or expanded from a nucleus disposed on the surface of the tool substrate so as to have a large columnar shape, so that each diamond crystal has a grain size or diameter as large as 5-10 &mgr;m as measured on or adjacent to an outer surface of the diamond coating, i.e., as measured on a plane perpendicular to a direction in which the diamond crystal has grown or expanded. The large diameter of each diamond crystal causes the outer surface of the diamond coating to have large pits and projections and a high degree of surface roughness (e.g. a large value in the maximum height Ry). The large pits and projection on the diamond coating surface 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 on the machined surface.
It is considered possible to somewhat smooth the diamond coating surface, for example, by grinding a portion of the diamond coating which portion covers the cutting edge, by attaining uniform crystal orientation of the diamond crystals, or by reducing the size of each crystal, namely, forming the diamond crystals in the form of crystallites. However, the grinding operation leads to an increase in a manufacturing cost of the tool, and provides a possibility that the diamond coating is damaged by a shock applied to the tool during the grinding operation, thereby possibly deteriorating a durability of the coating. The uniformity of the crystal orientation in (100) causes a large compressive stress to remain in the coating, thereby possibly causing easy removal of the coating from the substrate of the tool. Further, where the surface of the substrate is roughened to have pits and projections serving to increase an adhesion strength with which the diamond coating adheres to the substrate, the pits and projections, i.e., irregularities on the roughened surface of the substrate are not offset by the diamond crystallites, whereby the pits and projections formed on the substrate surface undesirably remain more or less on the coating surface, resulting in an unsatisfactory degree of smoothness of the coating surface. The cutting edge of the tool is rounded or chamfered in the roughening operation, whereby the cutting sharpness or performance of the tool is deteriorated. The deterioration of the cutting sharpness or performance also constitutes a factor causing the deterioration of the machined surface of the workpiece.
The above-described drawbacks or problems are encountered not only where the diamond-coated tool takes the form of a cutting tool but also where the diamond-coated tool takes the form of other machining tool such as a cold-forming tool which is designed to form the workpiece into a desired shape by plastically deforming the workpiece.
SUMMARY OF THE INVENTION
It is therefore a first object of the present invention to provide a diamond-coated tool which is capable of machining a workpiece with high degrees of surface smoothness and profile accuracy. This first object may be achieved according to any one of first, second, third, fourth and fifth aspects of this invention which are described below.
It is a second object of the present invention to provide a method of manufacturing a diamond-coated tool which is capable of machining a workpiece high degrees of surface smoothness and profile accuracy. This second object may be achieved according to any one of sixth, seventh, eighth, ninth and tenth aspects of this invention which are described below.
The first aspect of the invention provides a diamond-coated tool comprising: a substrate; and a diamond coating disposed on the substrate, the diamond coating being formed of diamond crystals grown on the substrate, each of the diamond crystals having a diameter not larger than 2 &mgr;m as measured on an outer surface of the diamond coating.
The term “diameter of each diamond crystal or each diamond crystallite” used in this specification is interpreted to mean the largest dimension of each diamond crystal or crystallite as measured in a direction substantially perpendicular to a direction in which the diamond crystal or crystallite has expanded or grown, namely, as measured in a direction substantially parallel to the surface of the substrate and the outer surface of the diamond coating. It is preferable that each of all the diamond crystals or crystallites which are exposed on the outer surface of the diamond coating has a diameter not larger than 2 &mgr;m. It is noted that the diameters of the diamond crystals or crystallites can be measured, for example, by using an electron microscope of about 1000-10000 magnification.
According to the second aspect of the invention, in the diamond-coated tool defined in the first aspect of the invention, the diameter of each of the diamond crystals is not larger than 2 &mgr;m as measured on any one of cross sections perpendicular to a direction in which each of the diamond crystals has expanded by growth thereof. It is preferable that each of all the diamond crystals which are exposed on the outer surface of the diamond coating has a diameter not larger than 2 &mgr;m as measured on any one of the cross sections perpendicular to the direction in which the diamond crystal has expanded in the growth.
According to the third aspect of the invention, in the diamond-coated tool defined in the first or second aspect of the invention, the grown diamond crystals consist of grown diamond crystallite, and the diamond coating consists of a plurality of layers.
The diamond-coated tool defined in any one of the first, second and third aspects of the invention provides a surface of a workpiece machined by the tool, with a high degree of surface smoothness, owing to reduced pits and projections, i.e., reduced irregularities on the outer surface of the diamond coating which is constituted by the diamond crystals each having the diameter not larger than 2 &mgr;m as measured on the outer surface of the diamond coating. The diamond-coated tool defined in the third aspect of the invention has an additional advantage that the diameter of each diamond crystal can be easily reduced owing to the multilayer diamond coating consisting of the plurality of layers superposed on each other. It is noted that the term “crystallites” used in this specification is interpreted to mean ones of the crystals each of which has the maximum diameter and length (the largest dimension as measured in the direction substantially perpendicular to the expanding direction of the diamond crystal and the largest dimension as measured in the expanding direction of the diamond crystal) not larger than about 3 &mgr;m.
The fourth aspect of the invention provides a diamond-coated tool comprising: a substrate; and a diamond coating consisting of a plurality of layers and disposed on the substrate, the diamond coating being formed of diamond crystals grown on the substrate, each of the diamond crystals having a length not larger than 2 &mgr;m as measured in a direction in which each of the diamond crystals has expanded by growth thereof. It is preferable that each of all the diamond crystals
Nguyen Kien T.
Oliff & Berridg,e PLC
OSG Corporation
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