Cutting tool

Abstract: A cutting tool having a positioning block (23) inserted between the cutting insert (22) and the insert-receiving seat (21) is disclosed. The disclosed cutting tool demonstrates excellent resistance to damage by severe vibration caused by the milling process. The cutting tool of the present invention comprises (a) a tool body (20) having a recess formed at a forward end thereof and defining an insert-receiving seat (21); (b) a cutting insert (22); (c) a positioning block (23) to be placed between the cutting insert and said insert-receiving seat, having a top and bottom faces and having a hardness thereof which is lower than that of a surface of insert-receiving seat; and (d) clamp means (24, 25) for securing the cutting insert and the positioning block on the insert-receiving seat. The above described positioning block (23) is able to absorb some extend of vibration of the cutting insert during the milling process. According to the present invention, there is also provided the cutting tool in which a positioning block (23) has two layers. A hardness of a surface of the insert-receiving seat is higher than that of the first layer but is lower than that of the second layer.

Description: The present invention relates to cutting tools having a releasible and disposable cutting insert secured to an insert-receiving seat, including milling cutters and the like. Particularly, the present invention relates to a cutting tool having a positioning block between the cutting insert and the insert-receiving seat. Prior Art There are two basic types of insert-clamped cutting tools provided with the disposable cutting inserts. For one type of conventional cutting tools, for example, a lever clamping type byte is depicted in FIG 9. In this figure, the cutting tool comprises a tool body 1 having an insert-receiving seat or recess 2 formed at its forward end. The tool body 1 also has a L-shaped lever 3 provided in a hole opening to the insert-receiving seat 2 and a bolt 4 provided in a hole adjoined to the first hole. In this example, a throwaway cutting insert 6 with a mounting bore 7 formed therethrough is received on the insert receiving seat 2, while the L-shaped lever 3 is received in the first hole so as to protrude its head portion 5 from the seat 2 to engage with the mounting bore 7 of the insert 6 when the end portion of the lever 3 is pushed downwardly by the bolt 4. In this example, a positioning block 8 is provided between the insert 6 and the seat 2. FIG 10 depicts another type of the conventional insert-clamped cutting tool which comprises a tool body 10 having an insert receiving seat or recess 11 formed at its forward end and a bolt-receiving hole opening on the insert-receiving seat 11. A positioning block 12 with a bore formed therethrough is provided on the insert receiving seat 11, and a bolt 13 is inserted through the bore to engage the bolt therewith. Furthermore, a throwaway cutting insert 14 is mounted on the positioning block 12 and pressed against the seat 11 by clamping means including a clamp 15 and a clamping bolt 16. In general, the positioning blocks 8 and 12 are made of materials such as cemented carbide, high speed steel or the like. Accordingly, these conventional blocks are characterized by their hardness which is lower than that of the cutting insert but higher than that of the surface of the seat to avoid wearing the insert down. However, the conventional positioning block is made of hard material and thus it is difficult to absorb severe vibration of the cutting insert during the milling process. Consequently, the conventional cutting tool using the above described positioning block has some problems i.e., slipping off of the insert from the insert-receiving seat, damaging the cutting edge of the insert, chipping the insert, or the like, caused by the vibration of the cutting insert. US 3,800,380 discloses a cutting tool wherein there is a gradual transition from the hard cutting exterior material to a relatively soft interior material to provide a viscous damped cutting tool having mechanical support for its cutting edge. GB-A-671,005 discloses a cutting tool as defined in the preamble of claim 1. SUMMARY OF THE INVENTION It is an object of the present invention to prevent chattering of the insert and damaging the cutting edge of the cutting insert while maintaining fine machining precision. This object is achieved by a cutting tool as claimed in claim 1. BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be readily carried into effect, it will now be described with reference to the accompanying drawings, wherein: FIG. 1 is a fragmentary cross sectional view of a cutting tool not embodying the present invention; FIG. 2 is a fragmentary cross sectional view of the cutting tool as shown in FIG. 1 except that embodying the present invention the positioning block comprises two layer; FIG. 3 is a fragmentary cross sectional view of the cutting tool as shown in FIG 2 except that the positioning block has a first layer with a thickness larger than that of a second layer; FIG. 4 is a fragmentary cross sectional view of the cutting tool as shown in FIGS. 2-3 except that the positioning block comprises a first layer on the side of the cutting insert; FIG. 5 is a plan view of a cutting insert having grooves on top and bottom faces thereof; FIG. 6 is a plan view of another cutting insert as shown in FIG. 5 except that the insert has a different pattern of grooves; FIG. 7 is a fragmentary cross sectional view of the cutting tool having a cutting insert of FIG. 5 or 6 embodying the present invention; FIG. 8 is a fragmentary cross sectional view of the cutting tool as shown in FIG. 7 except that the cutting insert is clamped directly against the second layer. FIG. 9 is a fragmentary cross sectional view of a conventional cutting tool, a lever clamping type bite; and FIG. 10 is a fragmentary cross sectional view of another type of the conventional cutting tool. DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION Referring to FIG. 1, a cutting tool comprises a tool body 20 having recess formed at its forward end and defining an insert-receiving seat 21, a throwaway cutting insert 23 which can be fixed on the seat and replaced regularly, a positioning block 22 which is interposed between the insert-receiving seat 21 and the cutting insert 23, and clamp means including a clamp 24 and a bolt 25. In this embodiment, the cutting insert 23 and top and bottom faces of the positioning block 22 have the same shape to each other. In addition, a hardness of the positioning block is lower than that of a surface of the insert-receiving seat for absorbing some extent of vibration of the cutting insert during the milling process. In the above described cutting tool as illustrated in FIG.1, the cutting insert 23 is fixed on the insert-receiving seat 21 by clamp means 24 and 25. The clamp 24 is disposed at a position shifted rearward of the tool body 20 relative to the insert-receiving seat 21 and is connected with the tool body 20 via a bolt 25. In the cutting tool described above, when the clamp bolt 25 is tightened, the insert 23 and the positioning block are pressed by the clamp 24 against the insert-receiving seat 23. FIG. 2 shows a cutting tool of FIG 1 except that embodying the present invention the positioning block 22 comprises two layers i.e., a first layer 22a which is on the side of the insert-receiving seat 21 and a second layer 22b which is on the side of the cutting insert 23. In this first embodiment, the first layer 22a is characterized by having a thickness lower than that of the second layer 22b and is made of a soft metal such as copper, aluminum or the like. This first layer 22a is not only responsible for absorbing undesirable vibrations and shocks which act on the cutting insert 23 during the milling operation by its elastic property but also for preventing the wear of the insert-receiving seat 21. On the other hand, the second layer 22b is made of a high-hardness material such as cemented carbide, high speed steel or the like, and is responsible for preventing the wear of the positioning block. It is noted that a hardness of a surface of the insert-receiving seat 21 is higher than that of the first layer 22a but lower than that of the second layer 22b. FIG. 3 shows a second preferred embodiment of the same invention as illustrated in FIG. 2 except that the positioning block 30 has a first layer 30a with a thickness larger than that of a second layer 30b. Therefore, comparing with the first embodiment of the present invention, severe vibration of the insert 23 can be absorbed more effectively by the positioning block 22 having a thickness of the soft layer 30a which is thicker than that of the hard layer 30b. In the case of the first embodiment of the present invention, on the other hand, in spite of the fact that a shape of the first layer 22a is elastically changed by the vibration during the milling process, a size change of the block 22 is hardly occurred, because a thickness of the soft layer 22a is smaller than that of the hard layer 22b and thus milling operation can be performed with accuracy. FIG. 4 shows a third preferred embodiment of the same invention as illustrated in FIGS. 2 and 3 except that the positioning block 40 comprises a first layer 40a which is on the side of the cutting insert 23 and a second layer 40b which is on the side of the insert-receiving seat 21. The first layer 40a is characterized by having a thickness smaller than that of the second layer 40b and is made of a soft metal such as copper, aluminum or the like. On the other hand, the second layer 40b is made of a high-hardness material such as cemented carbide, high speed steel or the like. It is noted that the first layer 40a of the block is easily formed into various shapes by means of press and thus this layer 40 also responsible to fit to the shape of the insert to be attached. In the cutting tool according to the present invention, the throwaway cutting insert 23 having top and bottom faces in the form of square. As shown in FIGS. 5 and 6, these faces are provided as rake faces where cutting edges 26 are formed on ridge lines thereof. For holding the cutting insert 23 on the insert-receiving seat 21, there are several grooves or notches 27 formed along the cutting edges 26 on the surface. As shown in FIG. 7, the insert 23 can be attached on a surface of the first layer 40a by an attaching portion thereof which is surrounded by the above mentioned grooves 27. When the insert 23 of FIG. 5 or 6 is pressed by the clamp against the first layer 40a of the positioning block 40, the surface of the first layer 40a can be deformed so as to be fitted to the shape of the bottom face of the insert 23. Consequently, the substantial improvement of securing the insert 23 on the seat 21 can be achieved. Referring to FIG.8, on the other hand, when the insert 23 of FIG. 5 or 6 is pressed by the clamp directly against the second layer 40b, there are some spaced portion between the insert 23 and the second layer 40b remains. Therefore the distance L1 between a ridge of the top face and a portion coming into contact with a surface of the layer 40b becomes larger than the distance L2 of FIG. 7.

Claims: A cutting tool comprising: (a) a tool body (20) having a recess formed at a forward end thereof and defining an insert-receiving seat (21); (b) a disposable cutting insert (23) (c) a positioning block (22, 30, 40) to be placed between said cutting insert (23) and said insert-receiving seat (21); and (d) clamp means (24, 25) for securing said cutting insert (23) and said positioning block (22, 30, 40) on said insert-receiving seat (21); characterized in that said positioning block (22; 30; 40) comprises two layers (22a, 22b; 30a, 30b; 40a, 40b), wherein a hardness of a first layer (22a; 30a; 40a) is lower than a hardness of a surface of said insert-receiving seat (21) and a hardness of a second layer (22b; 30b; 40b) is higher than said hardness of said surface of said insert-receiving seat (21). A cutting tool claimed in claim 1, wherein said first layer (22a; 30a; 40a) is made of a soft metal selected from the group consisting of copper and aluminum, said second layer (22b; 30b; 40b) is made of a high-hardness material selected from the group consisting of cemented carbide and high speed steel. A cutting tool claimed in claim 1 or 2, wherein said first layer (22a; 30a; 40a) is on the side of the insert-receiving seat (21), while said second layer (22b; 30b; 40b) is on the side of the cutting insert (23). A cutting tool claimed in claim 1 or 2, wherein said first layer (22a; 30a; 40a) is on the side of the cutting insert (23), while said second layer (22b; 30b; 40b) is on the side of the insert-receiving seat (21). A cutting tool claimed in one of claims 1, 2 and 4, wherein a surface of said cutting insert (23) contacting with first layer (22a; 30a; 40a) has at least one groove (27). A cutting tool claimed in one of claims 1 to 5, wherein said first layer (22a; 30a; 40a) is thicker than said second layer (22b; 30b; 40b). A cutting tool claimed in one of claims 1 to 5, wherein said second layer (22b; 30b; 40b) is thicker than said first layer (22a; 30a; 40a). A cutting tool claimed in one of the above claims, wherein said cutting insert (23) having top and bottom faces in the form of square, and said faces are provided as rake faces where cutting edges (26) are formed on ridge lines thereof. A cutting tool claimed in claim 1, wherein said top and bottom faces of said cutting insert (23) and said top and bottom faces of said positioning block (22; 30; 40) have the same shape to each other.

Inventors: NAKAYAMA MASAAKI C O TSUKUBA-S, OKAWA MASAYUKI C O TSUKUBA-SEI, SAITO JUNICHI C O TSUKUBA-SEIS, NAKAYAMA, MASAAKI, C/O TSUKUBA-SEISAKUSHO, OKAWA, MASAYUKI, C/O TSUKUBA-SEISAKUSHO, SAITO, JUNICHI, C/O TSUKUBA-SEISAKUSHO
Applicants: MITSUBISHI MATERIALS CORP, MITSUBISHI MATERIALS CORPORATION
Application year: 1992
Main classification: B23B27
IPC codes: B23B27, B23C5