Interference fit type cutting tool

Abstract: An interference fit type cutting tool (100,120) has a tool (112) and a tool holding section (113) detachably fitted together. A presser section (114) is provided to separate one of said tool (111) and said tool holding section (113) from the other. Said presser section is a stepped portion (114) formed by making the diameter of at least a part of a base end portion of said tool (111) larger than that of a leading end portion of said tool holding section (113).

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an interference fit type cutting tool having a tool holding section and a tool mounted therein. This specification is based on patent applications filed in Japan (Japanese Patent Applications Nos. 10-350404 and 11-123211), and the descriptions in the Japanese applications are incorporated as a part of this specification. Background Art Conventionally, a cutting tool is known as an example of this type of cutting tool, in which a projection is formed in one of an edge section and a shank section, a recess is formed in the other section, and the projection and the recess are fitted by shrinkage fitting. In a case in which the cutting tool is, for example, a milling tool such as an endmill, the shank section is made of, for example, steel, and the edge section is made of cemented carbide or the like and is detachably and replaceably fitted by shrinkage fitting. By making the edge section replaceable, edge sections having different types of cutting edges can be mounted. When producing such a cutting tool using shrinkage fitting, while the shank section with a recess having a substantially high coefficient of thermal expansion is heated, the recess and a projection of the edge section are fitted together. In this case, when the shank section having the recess is heated to, for example, approximately 200°C, the recess is thereby expanded so that the inner diameter exceeds the interference for fitting to the projection, and is allowed to be fitted. When the edge section is detached from the shank section in the fitted cutting tool, however, if the shank section having the recess is heated, the edge section having the projection is simultaneously heated and is thermally expanded. Therefore, the shank section must be heated above approximately 300°C to detach the edge section, and this is inefficient. Furthermore, when there is a small difference in coefficient of thermal expansion between the materials of the edge section and the shank section, it is more difficult to detach the edge section. As a method of overcoming such problems, a technique has been disclosed and proposed in Japanese Unexamined Patent Publication No. 10-34408. In this method, a space is formed over the entire periphery of a fitting section between a projection and a recess of an edge section and a tool holder that are fitted together, the edge section is pushed by supplying hydraulic pressure into the space during heating, and is thereby detached from the tool holder. Another means has also been proposed in which a tool holder is provided with a communication hole that extends to a fitting section, and a rod is inserted in the communication hole in a heated state and is struck with a hammer to apply impact, thereby detaching the edge section. In the above-described detaching method using hydraulic pressure, however, a high-temperature state is established by heating when detaching the edge section, and there is a danger that oil will ignite, and waste oil disposal is necessary. In the method using the rod for striking, since the communication hole forms a space during cutting, stiffness and strength of the tool are deteriorated, rotation balance may be upset, and whirling may be caused by vibration. Furthermore, there is a danger that the edge section will be chipped due to impact resulting from being struck by the hammer, that the service life will be shortened, and that an operator will suffer burns. DE 32 30 688 A discloses a tool which is detachably fitted into a tool holding section. At normal temperature, the outer diameter of the tool or of an inserting section of the tool, respectively, is larger than the inner diameter of the tool holding section. A pin is provided for restricting a rotational movement between the tool and the tool holding section. An interference fit type cutting tool according to the preamble of claim 1 is described in DE 36 07 938 A1. SUMMARY OF THE INVENTION An object of the present invention is to provide a safe interference fit type cutting tool that does not affect the environment and does not shorten tool life. Another object of the present invention is to improve workability in replacing a tool, a tool holding section, or the like in a cutting tool. An interference fit type cutting tool according to the present invention includes a tool according to claim 1. When detaching the tool after interference fitting, the fitting strength is weakened by heating or cooling the interference-fitted section, the tool and/or the tool holding section is directly or indirectly pushed by operating the presser section, and one of the tool and the tool holding section is separated from the other, whereby the tool or the tool holding section can be detached. According to the present invention, the presser section is a stepped portion formed by making the diameter of at least a part of the base end portion of the tool larger than that of the leading end portion of the tool holding section. When the tool is drawn out of the tool holding section, the interference-fitted section is heated or cooled, and a jig can be pulled out while being caught by the stepped portion of the tool, which allows the tool to be easily separated. Moreover, this stepped portion ensures a clearance between the tool holding section and a workpiece, which smoothes the movement of the cutting tool and the discharge of chips. According to the present invention, the tool and the tool holding section have projections, and both the projections are fitted and connected by the connecting member. Both of the projections and the connecting member has an interference. The presser section is a stepped portion formed by making the diameter of at least a part of the base end portion of the tool larger than that of the leading end portion of the tool holding section. According to a preferred embodiment of the present invention, a cutting edge is provided in the stepped portion. According to this structure, cutting can also be performed with the cutting edge provided in the stepped portion even when the cutting tool is pulled back, which facilitates finishing and lifting of the cutting tool. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a longitudinal sectional view of a ball endmill according to a first embodiment. Fig. 2 is a longitudinal sectional view of a ball endmill according to a second embodiment. Fig. 3 is a longitudinal sectional view showing a state in which lift cutting is being performed by the ball endmill shown in Fig. 2. Fig. 4 is a longitudinal sectional view showing a modification of the ball endmill according to the second embodiment (not part of the invention). DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 is a longitudinal sectional view of a ball endmill according to a first embodiment of the present invention. A ball endmill 100 is mainly composed of an edge section 111, a shank section 113, and a connecting member 112 for connecting these sections along the axis O. The edge section 111 is made of, for example, cemented carbide, and is composed of a substantially hemispherical leading end portion 111a, a base end portion 111b shaped like a cylindrical shaft, and a projection 111c having a smaller diameter than that of the base end portion 111b and shaped like a cylindrical shaft. In the leading end portion 111a, one or more cutting edges (not shown) are provided that are of substantially a 1/4-arc shape. The projection 112c is a portion that serves to make connection with the connecting member 112, extends coaxially with the base end portion 111b, and has a slightly larger diameter than the inner diameter of the connecting member 112. The connecting member 112 is made of a material having a higher coefficient of thermal expansion than those of the edge section 111 and the shank section 113, for example, steel. The connecting member 112 is shaped like a hollow cylinder. The outer diameter d thereof is smaller than the outer diameter D of the base end portion 111b, and the inner diameter is slightly smaller than the outer diameter of the projection 111c. The shank section 113 is made of, for example, cemented carbide, and the outer diameter d thereof is equal to that of the connecting member 112. At the leading end of the shank section 113, a projection 113a is coaxially formed so as to make connection with the connecting member 112, and the outer diameter thereof is slightly larger than the inner diameter of the connecting member 112. Next, description will be given of the procedure for connecting the edge section 111, the connecting member 112, and the shank section 113 together. First, the connecting member 112 is heated to thermally expand an opening end portion 112a until the projection 113a can be inserted therein, and then the projection 113a is inserted into the opening end portion 112a. Subsequently, when the connecting member 112 is air-cooled or forcibly cooled to decrease its diameter, and the connecting member 112 and the shank section 113 are shrinkage-fitted by the pressure of interference caused by the difference between the outer diameter of the projection 113a and the inner diameter of the opening end portion 112a. Similarly, when connecting the shank section 113 and the edge section 111, the connecting member 112 is heated to thermally expand an opening end portion 112b until the projection 111c can be inserted therein, and the projection 111c is inserted into the opening end portion 112b. Then, the diameter of the opening end portion 112b is reduced, and the connecting member 112 and the edge section 111 are shrinkage-fitted by the pressure of interference caused by the difference between the outer diameter of the projection 111c and the inner diameter of the opening end portion 112b. In the ball endmill 100 configured as described above, since the outer diameter d of the connecting member 112 is smaller than the outer diameter D of the base end portion 111b, a height difference is formed between the outer peripheral surface of the edge section 111 and the outer peripheral surface of the connecting member 112, which forms a stepped portion 114 between the edge section 111 and the connecting member 112. In order to replace the edge section 111 of the ball endmill 100, the connecting member 112 is heated to thermally expand the opening end portion 112b until the projection 111c can be drawn out thereof, the stepped portion 114 of the edge section 111 is retained and gripped by a jig, and then, the edge section 111 is drawn out of the connecting member 112. Accordingly, in the ball endmill 100 of this embodiment, workability in replacing the edge section is greatly enhanced. Since a clearance corresponding to the stepped portion 114 is ensured between the shank section 113 and a workpiece, it is possible to effectively prevent the shank section 113 and the workpiece from interfering with each other during cutting. Fig. 2 shows a ball endmill 120 according to a second embodiment of the present invention. The same elements and components as those in Fig. 1 are denoted by the same numerals, and description thereof is omitted. This ball endmill 120 is characterized in that at least one or more cutting edges 121 are provided in a stepped portion 114 formed between an edge section 111 and a connecting member 112. The cutting edge 121 extends so that the outer diameter gradually increases toward the leading end along the axis O, as shown in Fig. 2. The length t along the axis O and the crossing angle with respect to the axis O of the cutting edge 121 may be appropriately set according to cutting conditions or the like. In this way, the ball endmill having the cutting edge 121 in the stepped portion 114 allows lift cutting to be performed with the cutting edge 121 while the tool is being lifted, as shown in Fig. 3. For this reason, it is possible to effectively prevent smooth lifting from being hindered by the stepped portion 114 caught by a workpiece W when the ball endmill 120 is being raised from a hole, a groove, or the like. Fig. 4 shows a modification of the second embodiment which modification is not part of the invention. In this ball endmill 130, the connecting member 112 is not provided, a hole portion 132 is formed in a leading end face of a shank section 131, and a projection 133 is formed at the base end of an edge section 132. One of the projection 133 and the hole portion 132 has an interference so as to establish shrinkage fitting therebetween. According to the ball endmill 130, in a state in which the edge section 132 is interference-fitted in the shank section 131, the outer diameter of the edge section 132 at the base end is larger than the outer diameter of the leading end face of the shank section 131. Therefore, a stepped portion 114 is formed, and a cutting edge 121 is provided in a part of or the overall stepped portion 114. The present invention is not limited to the ball endmill, and is also applicable to various types of cutting tools, for example, a drill and other milling tools and a single-point tool and other turning tools.

Claims: An interference fit type cutting tool (100, 120) having a tool (111) and a tool holding section (113) detachably fitted together, wherein a presser section (114) is provided to separate one of said tool (111) and said tool holding section (113) from the other, wherein said presser section is a stepped portion (114) formed by making the diameter of at least a part of a base end portion of said tool (111) larger than that of a leading end portion of said tool holding section (113), characterized in that said tool (111) and said tool holding section (113) have projections (111c, 113a) and both said projections (111c, 113a) are fitted and connected by a connecting member (112), wherein both projections (111c, 113a) have an interference fit with said connecting member (112). An interference fit type cutting tool (100, 120) according to claim 1, characterized in that a cutting edge (121) is provided in said stepped portion. An interference fit type cutting tool (100, 120) according to any one of claims 1 or 2, characterized in that said tool is an edge section having a cutting edge (111), and said holding section (113) is a shank section. An interference fit type cutting tool (100, 120) according to any one of claims 1 to 3, characterized in that one of said tool (111) and said tool holding said section (113) has a higher coefficient of thermal expansion than the other. An interference fit type cutting tool (100, 120) according to claim 1, characterized in that said connecting member (112) has a higher coefficient of thermal expansion than those of said tool (111) and said tool holding section (113).

Inventors: NAGAYA HIDEHIKO, SHIMOMURA HIROSHI, NAGAYA, HIDEHIKO, SHIMOMURA, HIROSHI, Nagaya, Hidehiko, Mitsubishi Materials Corp., Shimomura, Hiroshi, Mitsubishi Materials Corp.
Applicants: MITSUBISHI MATERIALS CORP, MITSUBISHI MATERIALS CORPORATION
Application year: 1999
Main classification: B23C5
IPC codes: B23C5, B23B31