Coated cutting tool

Details Coated cutting tool Coated cutting tool

2001-03-30

2003-05-20

Turner, Archene (Department: 1775)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

C051S307000, C051S309000, C428S336000, C428S697000, C428S698000, C428S699000, C428S701000

Reexamination Certificate

active

06565957

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATION
This application claims priority under 35 U.S.C. §119 from Japanese Patent Application Nos. 2000-390 038, 390 039 and 390 040, all filed on Dec. 22, 2000, and 2001-054 097 and 054 098, both filed on Feb. 28, 2001, which are incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a coated cutting tool in which a hard coating layer has excellent strength and hardness at high temperature. Therefore, it has high wear resistance even when it is applied to a high-speed cutting operation of ferrous materials such as steel and cast iron.
2. Discussion of the Background
Many kinds of conventional cutting tools are known. Throw-away inserts are used in various cutting operations such as turning or milling of steels and cast irons by flexibly attaching on bite holders, face milling cutter bodies and end-milling cutter bodies. Twist drills that are used for a drilling of the above-mentioned work materials are also well known. Recently, micro drills are extensively used in a drilling process of printed circuit boards. Furthermore, solid end-milling cutters, used in various operations such as face milling, groove milling and shoulder milling, are also widely used, for example, in mold machining processes.
Furthermore, in general, as a material constituting the above-mentioned putting tools, a coated cutting tool which comprises a hard coating, such as titanium nitride (hereinafter referred to as TiN), and/or titanium carbonitride (hereinafter referred to as TiCN), having 0.5-10 &mgr;m for the average layer thickness, on the surface of a hard material substrate, such as tungsten carbide-based cemented carbide (hereinafter referred to as cemented carbide), titanium carbonitride-based cermet (hereinafter referred to as cermet) and a high speed steel, is well known, and it is also known that said coated cutting tool is used for continuous cutting and to interrupt cutting of steels and cast irons.
As one of the hard coating layers of the above-mentioned coated cutting tool, according to Japanese Patent Laid Open Application No. 62-56565, it is known that a titanium-aluminum nitride [(Ti, Al) N] layer is coated under the following conditions, that is, for example, at first, in a condition of about 3 Pa and 500° C. inside the chamber, an arc discharge is generated between an anode electrode and a cathode electrode (an evaporation source) in which an Ti—Al alloy having predetermined composition is set, by loading electrical potential of 35V and electrical current of 90A, and after that, nitrogen gas is introduced as a reaction gas into the chamber, and the bias potential of, for example 200V, is applied to the substrate, by using an arc ion plating system which is one of the physical vapor deposition processes having equipment shown in FIG.
1
.
Moreover, it is known that the residual compressive stress is given to the hard coating deposited by the physical vapor deposition process in this way, and the value of said compressive stress can be changed by selecting the coating conditions, such as the above-mentioned bias potential. It is also well known that the resistance against breakage, in other words, toughness, of said coated cutting tool can be raised by controlling this compressive stress suitably.
In addition, according to Japanese Patent Laid Open Application No. 1-240215, it is also known that other composite hard coatings, such as a composite nitride of titanium and zirconium [hereinafter referred to as (Ti, Zr)N] can be formed by utilizing another metal alloy target such as a Ti—Zr alloy as the evaporation source instead of above-mentioned Ti—Al alloy. These hard coatings can also raise the resistance against breakage of the coated cutting tool by suitably controlling the residual compressive stress of the coating like said (Ti, Al)N layer.
In recent years, there has been an increasing demand for labor-saving, less time-consuming cutting operations. Accordingly, there is a tendency that the condition of the cutting operation has changed to the severe side, such as high speed, along with the improvement of the performance of a cutting machine. With regard to various kinds of coated cutting tools conventionally proposed, as far as they are used in cutting operations of steel or cast iron using the usual cutting conditions, it has almost no problem. However, when they are used in high speed cutting operations, the hardness of these tools, especially at cutting edges, falls remarkably due to the extremely high heat generated. Therefore, thermal plastic deformation along the edge line occurs, and it promotes the severe wear of the cutting edge. As a result, the tool life becomes comparatively short.
SUMMARY OF THE INVENTION
Accordingly, the object of this invention provides for a coated cutting tool which has excellent strength and hardness at high temperatures and resists thermal plastic deformation at its cutting edge for a long period of time even when the machining process is performed under the severe conditions such as high speed cutting operations of, for example, steels and cast irons which conditions are accompanied by a high heat evolution.
The object of the present invention has been satisfied by the discovery of a coated cutting tool whose hard sintered substrate is coated with a hard coating layer preferably comprising an inner hard layer deposited by physical vapor deposition and has residual compressive stress, and an outer Al
2
O
3
layer deposited by chemical vapor deposition at a middle temperature, for example, 700-850° C. This coated cutting tool gives excellent wear resistance even at the high speed cutting operations and enables the prolongation of tool life. Thus, they can respond sufficiently satisfactorily to the labor-saving and energy-saving of the cutting operations.


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